linux/mm/compaction.c

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/*
* linux/mm/compaction.c
*
* Memory compaction for the reduction of external fragmentation. Note that
* this heavily depends upon page migration to do all the real heavy
* lifting
*
* Copyright IBM Corp. 2007-2010 Mel Gorman <mel@csn.ul.ie>
*/
#include <linux/swap.h>
#include <linux/migrate.h>
#include <linux/compaction.h>
#include <linux/mm_inline.h>
#include <linux/backing-dev.h>
#include <linux/sysctl.h>
#include <linux/sysfs.h>
#include <linux/balloon_compaction.h>
#include "internal.h"
#ifdef CONFIG_COMPACTION
static inline void count_compact_event(enum vm_event_item item)
{
count_vm_event(item);
}
static inline void count_compact_events(enum vm_event_item item, long delta)
{
count_vm_events(item, delta);
}
#else
#define count_compact_event(item) do { } while (0)
#define count_compact_events(item, delta) do { } while (0)
#endif
#if defined CONFIG_COMPACTION || defined CONFIG_CMA
#define CREATE_TRACE_POINTS
#include <trace/events/compaction.h>
static unsigned long release_freepages(struct list_head *freelist)
{
struct page *page, *next;
unsigned long count = 0;
list_for_each_entry_safe(page, next, freelist, lru) {
list_del(&page->lru);
__free_page(page);
count++;
}
return count;
}
static void map_pages(struct list_head *list)
{
struct page *page;
list_for_each_entry(page, list, lru) {
arch_alloc_page(page, 0);
kernel_map_pages(page, 1, 1);
}
}
static inline bool migrate_async_suitable(int migratetype)
{
return is_migrate_cma(migratetype) || migratetype == MIGRATE_MOVABLE;
}
mm: compaction: cache if a pageblock was scanned and no pages were isolated When compaction was implemented it was known that scanning could potentially be excessive. The ideal was that a counter be maintained for each pageblock but maintaining this information would incur a severe penalty due to a shared writable cache line. It has reached the point where the scanning costs are a serious problem, particularly on long-lived systems where a large process starts and allocates a large number of THPs at the same time. Instead of using a shared counter, this patch adds another bit to the pageblock flags called PG_migrate_skip. If a pageblock is scanned by either migrate or free scanner and 0 pages were isolated, the pageblock is marked to be skipped in the future. When scanning, this bit is checked before any scanning takes place and the block skipped if set. The main difficulty with a patch like this is "when to ignore the cached information?" If it's ignored too often, the scanning rates will still be excessive. If the information is too stale then allocations will fail that might have otherwise succeeded. In this patch o CMA always ignores the information o If the migrate and free scanner meet then the cached information will be discarded if it's at least 5 seconds since the last time the cache was discarded o If there are a large number of allocation failures, discard the cache. The time-based heuristic is very clumsy but there are few choices for a better event. Depending solely on multiple allocation failures still allows excessive scanning when THP allocations are failing in quick succession due to memory pressure. Waiting until memory pressure is relieved would cause compaction to continually fail instead of using reclaim/compaction to try allocate the page. The time-based mechanism is clumsy but a better option is not obvious. Signed-off-by: Mel Gorman <mgorman@suse.de> Acked-by: Rik van Riel <riel@redhat.com> Cc: Richard Davies <richard@arachsys.com> Cc: Shaohua Li <shli@kernel.org> Cc: Avi Kivity <avi@redhat.com> Acked-by: Rafael Aquini <aquini@redhat.com> Cc: Fengguang Wu <fengguang.wu@intel.com> Cc: Michal Nazarewicz <mina86@mina86.com> Cc: Bartlomiej Zolnierkiewicz <b.zolnierkie@samsung.com> Cc: Kyungmin Park <kyungmin.park@samsung.com> Cc: Mark Brown <broonie@opensource.wolfsonmicro.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2012-10-08 23:32:41 +00:00
#ifdef CONFIG_COMPACTION
/* Returns true if the pageblock should be scanned for pages to isolate. */
static inline bool isolation_suitable(struct compact_control *cc,
struct page *page)
{
if (cc->ignore_skip_hint)
return true;
return !get_pageblock_skip(page);
}
/*
* This function is called to clear all cached information on pageblocks that
* should be skipped for page isolation when the migrate and free page scanner
* meet.
*/
mm: compaction: clear PG_migrate_skip based on compaction and reclaim activity Compaction caches if a pageblock was scanned and no pages were isolated so that the pageblocks can be skipped in the future to reduce scanning. This information is not cleared by the page allocator based on activity due to the impact it would have to the page allocator fast paths. Hence there is a requirement that something clear the cache or pageblocks will be skipped forever. Currently the cache is cleared if there were a number of recent allocation failures and it has not been cleared within the last 5 seconds. Time-based decisions like this are terrible as they have no relationship to VM activity and is basically a big hammer. Unfortunately, accurate heuristics would add cost to some hot paths so this patch implements a rough heuristic. There are two cases where the cache is cleared. 1. If a !kswapd process completes a compaction cycle (migrate and free scanner meet), the zone is marked compact_blockskip_flush. When kswapd goes to sleep, it will clear the cache. This is expected to be the common case where the cache is cleared. It does not really matter if kswapd happens to be asleep or going to sleep when the flag is set as it will be woken on the next allocation request. 2. If there have been multiple failures recently and compaction just finished being deferred then a process will clear the cache and start a full scan. This situation happens if there are multiple high-order allocation requests under heavy memory pressure. The clearing of the PG_migrate_skip bits and other scans is inherently racy but the race is harmless. For allocations that can fail such as THP, they will simply fail. For requests that cannot fail, they will retry the allocation. Tests indicated that scanning rates were roughly similar to when the time-based heuristic was used and the allocation success rates were similar. Signed-off-by: Mel Gorman <mgorman@suse.de> Cc: Rik van Riel <riel@redhat.com> Cc: Richard Davies <richard@arachsys.com> Cc: Shaohua Li <shli@kernel.org> Cc: Avi Kivity <avi@redhat.com> Cc: Rafael Aquini <aquini@redhat.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2012-10-08 23:32:47 +00:00
static void __reset_isolation_suitable(struct zone *zone)
mm: compaction: cache if a pageblock was scanned and no pages were isolated When compaction was implemented it was known that scanning could potentially be excessive. The ideal was that a counter be maintained for each pageblock but maintaining this information would incur a severe penalty due to a shared writable cache line. It has reached the point where the scanning costs are a serious problem, particularly on long-lived systems where a large process starts and allocates a large number of THPs at the same time. Instead of using a shared counter, this patch adds another bit to the pageblock flags called PG_migrate_skip. If a pageblock is scanned by either migrate or free scanner and 0 pages were isolated, the pageblock is marked to be skipped in the future. When scanning, this bit is checked before any scanning takes place and the block skipped if set. The main difficulty with a patch like this is "when to ignore the cached information?" If it's ignored too often, the scanning rates will still be excessive. If the information is too stale then allocations will fail that might have otherwise succeeded. In this patch o CMA always ignores the information o If the migrate and free scanner meet then the cached information will be discarded if it's at least 5 seconds since the last time the cache was discarded o If there are a large number of allocation failures, discard the cache. The time-based heuristic is very clumsy but there are few choices for a better event. Depending solely on multiple allocation failures still allows excessive scanning when THP allocations are failing in quick succession due to memory pressure. Waiting until memory pressure is relieved would cause compaction to continually fail instead of using reclaim/compaction to try allocate the page. The time-based mechanism is clumsy but a better option is not obvious. Signed-off-by: Mel Gorman <mgorman@suse.de> Acked-by: Rik van Riel <riel@redhat.com> Cc: Richard Davies <richard@arachsys.com> Cc: Shaohua Li <shli@kernel.org> Cc: Avi Kivity <avi@redhat.com> Acked-by: Rafael Aquini <aquini@redhat.com> Cc: Fengguang Wu <fengguang.wu@intel.com> Cc: Michal Nazarewicz <mina86@mina86.com> Cc: Bartlomiej Zolnierkiewicz <b.zolnierkie@samsung.com> Cc: Kyungmin Park <kyungmin.park@samsung.com> Cc: Mark Brown <broonie@opensource.wolfsonmicro.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2012-10-08 23:32:41 +00:00
{
unsigned long start_pfn = zone->zone_start_pfn;
unsigned long end_pfn = zone->zone_start_pfn + zone->spanned_pages;
unsigned long pfn;
mm: compaction: Restart compaction from near where it left off This is almost entirely based on Rik's previous patches and discussions with him about how this might be implemented. Order > 0 compaction stops when enough free pages of the correct page order have been coalesced. When doing subsequent higher order allocations, it is possible for compaction to be invoked many times. However, the compaction code always starts out looking for things to compact at the start of the zone, and for free pages to compact things to at the end of the zone. This can cause quadratic behaviour, with isolate_freepages starting at the end of the zone each time, even though previous invocations of the compaction code already filled up all free memory on that end of the zone. This can cause isolate_freepages to take enormous amounts of CPU with certain workloads on larger memory systems. This patch caches where the migration and free scanner should start from on subsequent compaction invocations using the pageblock-skip information. When compaction starts it begins from the cached restart points and will update the cached restart points until a page is isolated or a pageblock is skipped that would have been scanned by synchronous compaction. Signed-off-by: Mel Gorman <mgorman@suse.de> Acked-by: Rik van Riel <riel@redhat.com> Cc: Richard Davies <richard@arachsys.com> Cc: Shaohua Li <shli@kernel.org> Cc: Avi Kivity <avi@redhat.com> Acked-by: Rafael Aquini <aquini@redhat.com> Cc: Fengguang Wu <fengguang.wu@intel.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2012-10-08 23:32:45 +00:00
zone->compact_cached_migrate_pfn = start_pfn;
zone->compact_cached_free_pfn = end_pfn;
mm: compaction: clear PG_migrate_skip based on compaction and reclaim activity Compaction caches if a pageblock was scanned and no pages were isolated so that the pageblocks can be skipped in the future to reduce scanning. This information is not cleared by the page allocator based on activity due to the impact it would have to the page allocator fast paths. Hence there is a requirement that something clear the cache or pageblocks will be skipped forever. Currently the cache is cleared if there were a number of recent allocation failures and it has not been cleared within the last 5 seconds. Time-based decisions like this are terrible as they have no relationship to VM activity and is basically a big hammer. Unfortunately, accurate heuristics would add cost to some hot paths so this patch implements a rough heuristic. There are two cases where the cache is cleared. 1. If a !kswapd process completes a compaction cycle (migrate and free scanner meet), the zone is marked compact_blockskip_flush. When kswapd goes to sleep, it will clear the cache. This is expected to be the common case where the cache is cleared. It does not really matter if kswapd happens to be asleep or going to sleep when the flag is set as it will be woken on the next allocation request. 2. If there have been multiple failures recently and compaction just finished being deferred then a process will clear the cache and start a full scan. This situation happens if there are multiple high-order allocation requests under heavy memory pressure. The clearing of the PG_migrate_skip bits and other scans is inherently racy but the race is harmless. For allocations that can fail such as THP, they will simply fail. For requests that cannot fail, they will retry the allocation. Tests indicated that scanning rates were roughly similar to when the time-based heuristic was used and the allocation success rates were similar. Signed-off-by: Mel Gorman <mgorman@suse.de> Cc: Rik van Riel <riel@redhat.com> Cc: Richard Davies <richard@arachsys.com> Cc: Shaohua Li <shli@kernel.org> Cc: Avi Kivity <avi@redhat.com> Cc: Rafael Aquini <aquini@redhat.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2012-10-08 23:32:47 +00:00
zone->compact_blockskip_flush = false;
mm: compaction: cache if a pageblock was scanned and no pages were isolated When compaction was implemented it was known that scanning could potentially be excessive. The ideal was that a counter be maintained for each pageblock but maintaining this information would incur a severe penalty due to a shared writable cache line. It has reached the point where the scanning costs are a serious problem, particularly on long-lived systems where a large process starts and allocates a large number of THPs at the same time. Instead of using a shared counter, this patch adds another bit to the pageblock flags called PG_migrate_skip. If a pageblock is scanned by either migrate or free scanner and 0 pages were isolated, the pageblock is marked to be skipped in the future. When scanning, this bit is checked before any scanning takes place and the block skipped if set. The main difficulty with a patch like this is "when to ignore the cached information?" If it's ignored too often, the scanning rates will still be excessive. If the information is too stale then allocations will fail that might have otherwise succeeded. In this patch o CMA always ignores the information o If the migrate and free scanner meet then the cached information will be discarded if it's at least 5 seconds since the last time the cache was discarded o If there are a large number of allocation failures, discard the cache. The time-based heuristic is very clumsy but there are few choices for a better event. Depending solely on multiple allocation failures still allows excessive scanning when THP allocations are failing in quick succession due to memory pressure. Waiting until memory pressure is relieved would cause compaction to continually fail instead of using reclaim/compaction to try allocate the page. The time-based mechanism is clumsy but a better option is not obvious. Signed-off-by: Mel Gorman <mgorman@suse.de> Acked-by: Rik van Riel <riel@redhat.com> Cc: Richard Davies <richard@arachsys.com> Cc: Shaohua Li <shli@kernel.org> Cc: Avi Kivity <avi@redhat.com> Acked-by: Rafael Aquini <aquini@redhat.com> Cc: Fengguang Wu <fengguang.wu@intel.com> Cc: Michal Nazarewicz <mina86@mina86.com> Cc: Bartlomiej Zolnierkiewicz <b.zolnierkie@samsung.com> Cc: Kyungmin Park <kyungmin.park@samsung.com> Cc: Mark Brown <broonie@opensource.wolfsonmicro.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2012-10-08 23:32:41 +00:00
/* Walk the zone and mark every pageblock as suitable for isolation */
for (pfn = start_pfn; pfn < end_pfn; pfn += pageblock_nr_pages) {
struct page *page;
cond_resched();
if (!pfn_valid(pfn))
continue;
page = pfn_to_page(pfn);
if (zone != page_zone(page))
continue;
clear_pageblock_skip(page);
}
}
mm: compaction: clear PG_migrate_skip based on compaction and reclaim activity Compaction caches if a pageblock was scanned and no pages were isolated so that the pageblocks can be skipped in the future to reduce scanning. This information is not cleared by the page allocator based on activity due to the impact it would have to the page allocator fast paths. Hence there is a requirement that something clear the cache or pageblocks will be skipped forever. Currently the cache is cleared if there were a number of recent allocation failures and it has not been cleared within the last 5 seconds. Time-based decisions like this are terrible as they have no relationship to VM activity and is basically a big hammer. Unfortunately, accurate heuristics would add cost to some hot paths so this patch implements a rough heuristic. There are two cases where the cache is cleared. 1. If a !kswapd process completes a compaction cycle (migrate and free scanner meet), the zone is marked compact_blockskip_flush. When kswapd goes to sleep, it will clear the cache. This is expected to be the common case where the cache is cleared. It does not really matter if kswapd happens to be asleep or going to sleep when the flag is set as it will be woken on the next allocation request. 2. If there have been multiple failures recently and compaction just finished being deferred then a process will clear the cache and start a full scan. This situation happens if there are multiple high-order allocation requests under heavy memory pressure. The clearing of the PG_migrate_skip bits and other scans is inherently racy but the race is harmless. For allocations that can fail such as THP, they will simply fail. For requests that cannot fail, they will retry the allocation. Tests indicated that scanning rates were roughly similar to when the time-based heuristic was used and the allocation success rates were similar. Signed-off-by: Mel Gorman <mgorman@suse.de> Cc: Rik van Riel <riel@redhat.com> Cc: Richard Davies <richard@arachsys.com> Cc: Shaohua Li <shli@kernel.org> Cc: Avi Kivity <avi@redhat.com> Cc: Rafael Aquini <aquini@redhat.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2012-10-08 23:32:47 +00:00
void reset_isolation_suitable(pg_data_t *pgdat)
{
int zoneid;
for (zoneid = 0; zoneid < MAX_NR_ZONES; zoneid++) {
struct zone *zone = &pgdat->node_zones[zoneid];
if (!populated_zone(zone))
continue;
/* Only flush if a full compaction finished recently */
if (zone->compact_blockskip_flush)
__reset_isolation_suitable(zone);
}
}
mm: compaction: cache if a pageblock was scanned and no pages were isolated When compaction was implemented it was known that scanning could potentially be excessive. The ideal was that a counter be maintained for each pageblock but maintaining this information would incur a severe penalty due to a shared writable cache line. It has reached the point where the scanning costs are a serious problem, particularly on long-lived systems where a large process starts and allocates a large number of THPs at the same time. Instead of using a shared counter, this patch adds another bit to the pageblock flags called PG_migrate_skip. If a pageblock is scanned by either migrate or free scanner and 0 pages were isolated, the pageblock is marked to be skipped in the future. When scanning, this bit is checked before any scanning takes place and the block skipped if set. The main difficulty with a patch like this is "when to ignore the cached information?" If it's ignored too often, the scanning rates will still be excessive. If the information is too stale then allocations will fail that might have otherwise succeeded. In this patch o CMA always ignores the information o If the migrate and free scanner meet then the cached information will be discarded if it's at least 5 seconds since the last time the cache was discarded o If there are a large number of allocation failures, discard the cache. The time-based heuristic is very clumsy but there are few choices for a better event. Depending solely on multiple allocation failures still allows excessive scanning when THP allocations are failing in quick succession due to memory pressure. Waiting until memory pressure is relieved would cause compaction to continually fail instead of using reclaim/compaction to try allocate the page. The time-based mechanism is clumsy but a better option is not obvious. Signed-off-by: Mel Gorman <mgorman@suse.de> Acked-by: Rik van Riel <riel@redhat.com> Cc: Richard Davies <richard@arachsys.com> Cc: Shaohua Li <shli@kernel.org> Cc: Avi Kivity <avi@redhat.com> Acked-by: Rafael Aquini <aquini@redhat.com> Cc: Fengguang Wu <fengguang.wu@intel.com> Cc: Michal Nazarewicz <mina86@mina86.com> Cc: Bartlomiej Zolnierkiewicz <b.zolnierkie@samsung.com> Cc: Kyungmin Park <kyungmin.park@samsung.com> Cc: Mark Brown <broonie@opensource.wolfsonmicro.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2012-10-08 23:32:41 +00:00
/*
* If no pages were isolated then mark this pageblock to be skipped in the
mm: compaction: clear PG_migrate_skip based on compaction and reclaim activity Compaction caches if a pageblock was scanned and no pages were isolated so that the pageblocks can be skipped in the future to reduce scanning. This information is not cleared by the page allocator based on activity due to the impact it would have to the page allocator fast paths. Hence there is a requirement that something clear the cache or pageblocks will be skipped forever. Currently the cache is cleared if there were a number of recent allocation failures and it has not been cleared within the last 5 seconds. Time-based decisions like this are terrible as they have no relationship to VM activity and is basically a big hammer. Unfortunately, accurate heuristics would add cost to some hot paths so this patch implements a rough heuristic. There are two cases where the cache is cleared. 1. If a !kswapd process completes a compaction cycle (migrate and free scanner meet), the zone is marked compact_blockskip_flush. When kswapd goes to sleep, it will clear the cache. This is expected to be the common case where the cache is cleared. It does not really matter if kswapd happens to be asleep or going to sleep when the flag is set as it will be woken on the next allocation request. 2. If there have been multiple failures recently and compaction just finished being deferred then a process will clear the cache and start a full scan. This situation happens if there are multiple high-order allocation requests under heavy memory pressure. The clearing of the PG_migrate_skip bits and other scans is inherently racy but the race is harmless. For allocations that can fail such as THP, they will simply fail. For requests that cannot fail, they will retry the allocation. Tests indicated that scanning rates were roughly similar to when the time-based heuristic was used and the allocation success rates were similar. Signed-off-by: Mel Gorman <mgorman@suse.de> Cc: Rik van Riel <riel@redhat.com> Cc: Richard Davies <richard@arachsys.com> Cc: Shaohua Li <shli@kernel.org> Cc: Avi Kivity <avi@redhat.com> Cc: Rafael Aquini <aquini@redhat.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2012-10-08 23:32:47 +00:00
* future. The information is later cleared by __reset_isolation_suitable().
mm: compaction: cache if a pageblock was scanned and no pages were isolated When compaction was implemented it was known that scanning could potentially be excessive. The ideal was that a counter be maintained for each pageblock but maintaining this information would incur a severe penalty due to a shared writable cache line. It has reached the point where the scanning costs are a serious problem, particularly on long-lived systems where a large process starts and allocates a large number of THPs at the same time. Instead of using a shared counter, this patch adds another bit to the pageblock flags called PG_migrate_skip. If a pageblock is scanned by either migrate or free scanner and 0 pages were isolated, the pageblock is marked to be skipped in the future. When scanning, this bit is checked before any scanning takes place and the block skipped if set. The main difficulty with a patch like this is "when to ignore the cached information?" If it's ignored too often, the scanning rates will still be excessive. If the information is too stale then allocations will fail that might have otherwise succeeded. In this patch o CMA always ignores the information o If the migrate and free scanner meet then the cached information will be discarded if it's at least 5 seconds since the last time the cache was discarded o If there are a large number of allocation failures, discard the cache. The time-based heuristic is very clumsy but there are few choices for a better event. Depending solely on multiple allocation failures still allows excessive scanning when THP allocations are failing in quick succession due to memory pressure. Waiting until memory pressure is relieved would cause compaction to continually fail instead of using reclaim/compaction to try allocate the page. The time-based mechanism is clumsy but a better option is not obvious. Signed-off-by: Mel Gorman <mgorman@suse.de> Acked-by: Rik van Riel <riel@redhat.com> Cc: Richard Davies <richard@arachsys.com> Cc: Shaohua Li <shli@kernel.org> Cc: Avi Kivity <avi@redhat.com> Acked-by: Rafael Aquini <aquini@redhat.com> Cc: Fengguang Wu <fengguang.wu@intel.com> Cc: Michal Nazarewicz <mina86@mina86.com> Cc: Bartlomiej Zolnierkiewicz <b.zolnierkie@samsung.com> Cc: Kyungmin Park <kyungmin.park@samsung.com> Cc: Mark Brown <broonie@opensource.wolfsonmicro.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2012-10-08 23:32:41 +00:00
*/
mm: compaction: Restart compaction from near where it left off This is almost entirely based on Rik's previous patches and discussions with him about how this might be implemented. Order > 0 compaction stops when enough free pages of the correct page order have been coalesced. When doing subsequent higher order allocations, it is possible for compaction to be invoked many times. However, the compaction code always starts out looking for things to compact at the start of the zone, and for free pages to compact things to at the end of the zone. This can cause quadratic behaviour, with isolate_freepages starting at the end of the zone each time, even though previous invocations of the compaction code already filled up all free memory on that end of the zone. This can cause isolate_freepages to take enormous amounts of CPU with certain workloads on larger memory systems. This patch caches where the migration and free scanner should start from on subsequent compaction invocations using the pageblock-skip information. When compaction starts it begins from the cached restart points and will update the cached restart points until a page is isolated or a pageblock is skipped that would have been scanned by synchronous compaction. Signed-off-by: Mel Gorman <mgorman@suse.de> Acked-by: Rik van Riel <riel@redhat.com> Cc: Richard Davies <richard@arachsys.com> Cc: Shaohua Li <shli@kernel.org> Cc: Avi Kivity <avi@redhat.com> Acked-by: Rafael Aquini <aquini@redhat.com> Cc: Fengguang Wu <fengguang.wu@intel.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2012-10-08 23:32:45 +00:00
static void update_pageblock_skip(struct compact_control *cc,
struct page *page, unsigned long nr_isolated,
bool migrate_scanner)
mm: compaction: cache if a pageblock was scanned and no pages were isolated When compaction was implemented it was known that scanning could potentially be excessive. The ideal was that a counter be maintained for each pageblock but maintaining this information would incur a severe penalty due to a shared writable cache line. It has reached the point where the scanning costs are a serious problem, particularly on long-lived systems where a large process starts and allocates a large number of THPs at the same time. Instead of using a shared counter, this patch adds another bit to the pageblock flags called PG_migrate_skip. If a pageblock is scanned by either migrate or free scanner and 0 pages were isolated, the pageblock is marked to be skipped in the future. When scanning, this bit is checked before any scanning takes place and the block skipped if set. The main difficulty with a patch like this is "when to ignore the cached information?" If it's ignored too often, the scanning rates will still be excessive. If the information is too stale then allocations will fail that might have otherwise succeeded. In this patch o CMA always ignores the information o If the migrate and free scanner meet then the cached information will be discarded if it's at least 5 seconds since the last time the cache was discarded o If there are a large number of allocation failures, discard the cache. The time-based heuristic is very clumsy but there are few choices for a better event. Depending solely on multiple allocation failures still allows excessive scanning when THP allocations are failing in quick succession due to memory pressure. Waiting until memory pressure is relieved would cause compaction to continually fail instead of using reclaim/compaction to try allocate the page. The time-based mechanism is clumsy but a better option is not obvious. Signed-off-by: Mel Gorman <mgorman@suse.de> Acked-by: Rik van Riel <riel@redhat.com> Cc: Richard Davies <richard@arachsys.com> Cc: Shaohua Li <shli@kernel.org> Cc: Avi Kivity <avi@redhat.com> Acked-by: Rafael Aquini <aquini@redhat.com> Cc: Fengguang Wu <fengguang.wu@intel.com> Cc: Michal Nazarewicz <mina86@mina86.com> Cc: Bartlomiej Zolnierkiewicz <b.zolnierkie@samsung.com> Cc: Kyungmin Park <kyungmin.park@samsung.com> Cc: Mark Brown <broonie@opensource.wolfsonmicro.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2012-10-08 23:32:41 +00:00
{
mm: compaction: Restart compaction from near where it left off This is almost entirely based on Rik's previous patches and discussions with him about how this might be implemented. Order > 0 compaction stops when enough free pages of the correct page order have been coalesced. When doing subsequent higher order allocations, it is possible for compaction to be invoked many times. However, the compaction code always starts out looking for things to compact at the start of the zone, and for free pages to compact things to at the end of the zone. This can cause quadratic behaviour, with isolate_freepages starting at the end of the zone each time, even though previous invocations of the compaction code already filled up all free memory on that end of the zone. This can cause isolate_freepages to take enormous amounts of CPU with certain workloads on larger memory systems. This patch caches where the migration and free scanner should start from on subsequent compaction invocations using the pageblock-skip information. When compaction starts it begins from the cached restart points and will update the cached restart points until a page is isolated or a pageblock is skipped that would have been scanned by synchronous compaction. Signed-off-by: Mel Gorman <mgorman@suse.de> Acked-by: Rik van Riel <riel@redhat.com> Cc: Richard Davies <richard@arachsys.com> Cc: Shaohua Li <shli@kernel.org> Cc: Avi Kivity <avi@redhat.com> Acked-by: Rafael Aquini <aquini@redhat.com> Cc: Fengguang Wu <fengguang.wu@intel.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2012-10-08 23:32:45 +00:00
struct zone *zone = cc->zone;
mm: compaction: cache if a pageblock was scanned and no pages were isolated When compaction was implemented it was known that scanning could potentially be excessive. The ideal was that a counter be maintained for each pageblock but maintaining this information would incur a severe penalty due to a shared writable cache line. It has reached the point where the scanning costs are a serious problem, particularly on long-lived systems where a large process starts and allocates a large number of THPs at the same time. Instead of using a shared counter, this patch adds another bit to the pageblock flags called PG_migrate_skip. If a pageblock is scanned by either migrate or free scanner and 0 pages were isolated, the pageblock is marked to be skipped in the future. When scanning, this bit is checked before any scanning takes place and the block skipped if set. The main difficulty with a patch like this is "when to ignore the cached information?" If it's ignored too often, the scanning rates will still be excessive. If the information is too stale then allocations will fail that might have otherwise succeeded. In this patch o CMA always ignores the information o If the migrate and free scanner meet then the cached information will be discarded if it's at least 5 seconds since the last time the cache was discarded o If there are a large number of allocation failures, discard the cache. The time-based heuristic is very clumsy but there are few choices for a better event. Depending solely on multiple allocation failures still allows excessive scanning when THP allocations are failing in quick succession due to memory pressure. Waiting until memory pressure is relieved would cause compaction to continually fail instead of using reclaim/compaction to try allocate the page. The time-based mechanism is clumsy but a better option is not obvious. Signed-off-by: Mel Gorman <mgorman@suse.de> Acked-by: Rik van Riel <riel@redhat.com> Cc: Richard Davies <richard@arachsys.com> Cc: Shaohua Li <shli@kernel.org> Cc: Avi Kivity <avi@redhat.com> Acked-by: Rafael Aquini <aquini@redhat.com> Cc: Fengguang Wu <fengguang.wu@intel.com> Cc: Michal Nazarewicz <mina86@mina86.com> Cc: Bartlomiej Zolnierkiewicz <b.zolnierkie@samsung.com> Cc: Kyungmin Park <kyungmin.park@samsung.com> Cc: Mark Brown <broonie@opensource.wolfsonmicro.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2012-10-08 23:32:41 +00:00
if (!page)
return;
mm: compaction: Restart compaction from near where it left off This is almost entirely based on Rik's previous patches and discussions with him about how this might be implemented. Order > 0 compaction stops when enough free pages of the correct page order have been coalesced. When doing subsequent higher order allocations, it is possible for compaction to be invoked many times. However, the compaction code always starts out looking for things to compact at the start of the zone, and for free pages to compact things to at the end of the zone. This can cause quadratic behaviour, with isolate_freepages starting at the end of the zone each time, even though previous invocations of the compaction code already filled up all free memory on that end of the zone. This can cause isolate_freepages to take enormous amounts of CPU with certain workloads on larger memory systems. This patch caches where the migration and free scanner should start from on subsequent compaction invocations using the pageblock-skip information. When compaction starts it begins from the cached restart points and will update the cached restart points until a page is isolated or a pageblock is skipped that would have been scanned by synchronous compaction. Signed-off-by: Mel Gorman <mgorman@suse.de> Acked-by: Rik van Riel <riel@redhat.com> Cc: Richard Davies <richard@arachsys.com> Cc: Shaohua Li <shli@kernel.org> Cc: Avi Kivity <avi@redhat.com> Acked-by: Rafael Aquini <aquini@redhat.com> Cc: Fengguang Wu <fengguang.wu@intel.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2012-10-08 23:32:45 +00:00
if (!nr_isolated) {
unsigned long pfn = page_to_pfn(page);
mm: compaction: cache if a pageblock was scanned and no pages were isolated When compaction was implemented it was known that scanning could potentially be excessive. The ideal was that a counter be maintained for each pageblock but maintaining this information would incur a severe penalty due to a shared writable cache line. It has reached the point where the scanning costs are a serious problem, particularly on long-lived systems where a large process starts and allocates a large number of THPs at the same time. Instead of using a shared counter, this patch adds another bit to the pageblock flags called PG_migrate_skip. If a pageblock is scanned by either migrate or free scanner and 0 pages were isolated, the pageblock is marked to be skipped in the future. When scanning, this bit is checked before any scanning takes place and the block skipped if set. The main difficulty with a patch like this is "when to ignore the cached information?" If it's ignored too often, the scanning rates will still be excessive. If the information is too stale then allocations will fail that might have otherwise succeeded. In this patch o CMA always ignores the information o If the migrate and free scanner meet then the cached information will be discarded if it's at least 5 seconds since the last time the cache was discarded o If there are a large number of allocation failures, discard the cache. The time-based heuristic is very clumsy but there are few choices for a better event. Depending solely on multiple allocation failures still allows excessive scanning when THP allocations are failing in quick succession due to memory pressure. Waiting until memory pressure is relieved would cause compaction to continually fail instead of using reclaim/compaction to try allocate the page. The time-based mechanism is clumsy but a better option is not obvious. Signed-off-by: Mel Gorman <mgorman@suse.de> Acked-by: Rik van Riel <riel@redhat.com> Cc: Richard Davies <richard@arachsys.com> Cc: Shaohua Li <shli@kernel.org> Cc: Avi Kivity <avi@redhat.com> Acked-by: Rafael Aquini <aquini@redhat.com> Cc: Fengguang Wu <fengguang.wu@intel.com> Cc: Michal Nazarewicz <mina86@mina86.com> Cc: Bartlomiej Zolnierkiewicz <b.zolnierkie@samsung.com> Cc: Kyungmin Park <kyungmin.park@samsung.com> Cc: Mark Brown <broonie@opensource.wolfsonmicro.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2012-10-08 23:32:41 +00:00
set_pageblock_skip(page);
mm: compaction: Restart compaction from near where it left off This is almost entirely based on Rik's previous patches and discussions with him about how this might be implemented. Order > 0 compaction stops when enough free pages of the correct page order have been coalesced. When doing subsequent higher order allocations, it is possible for compaction to be invoked many times. However, the compaction code always starts out looking for things to compact at the start of the zone, and for free pages to compact things to at the end of the zone. This can cause quadratic behaviour, with isolate_freepages starting at the end of the zone each time, even though previous invocations of the compaction code already filled up all free memory on that end of the zone. This can cause isolate_freepages to take enormous amounts of CPU with certain workloads on larger memory systems. This patch caches where the migration and free scanner should start from on subsequent compaction invocations using the pageblock-skip information. When compaction starts it begins from the cached restart points and will update the cached restart points until a page is isolated or a pageblock is skipped that would have been scanned by synchronous compaction. Signed-off-by: Mel Gorman <mgorman@suse.de> Acked-by: Rik van Riel <riel@redhat.com> Cc: Richard Davies <richard@arachsys.com> Cc: Shaohua Li <shli@kernel.org> Cc: Avi Kivity <avi@redhat.com> Acked-by: Rafael Aquini <aquini@redhat.com> Cc: Fengguang Wu <fengguang.wu@intel.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2012-10-08 23:32:45 +00:00
/* Update where compaction should restart */
if (migrate_scanner) {
if (!cc->finished_update_migrate &&
pfn > zone->compact_cached_migrate_pfn)
zone->compact_cached_migrate_pfn = pfn;
} else {
if (!cc->finished_update_free &&
pfn < zone->compact_cached_free_pfn)
zone->compact_cached_free_pfn = pfn;
}
}
mm: compaction: cache if a pageblock was scanned and no pages were isolated When compaction was implemented it was known that scanning could potentially be excessive. The ideal was that a counter be maintained for each pageblock but maintaining this information would incur a severe penalty due to a shared writable cache line. It has reached the point where the scanning costs are a serious problem, particularly on long-lived systems where a large process starts and allocates a large number of THPs at the same time. Instead of using a shared counter, this patch adds another bit to the pageblock flags called PG_migrate_skip. If a pageblock is scanned by either migrate or free scanner and 0 pages were isolated, the pageblock is marked to be skipped in the future. When scanning, this bit is checked before any scanning takes place and the block skipped if set. The main difficulty with a patch like this is "when to ignore the cached information?" If it's ignored too often, the scanning rates will still be excessive. If the information is too stale then allocations will fail that might have otherwise succeeded. In this patch o CMA always ignores the information o If the migrate and free scanner meet then the cached information will be discarded if it's at least 5 seconds since the last time the cache was discarded o If there are a large number of allocation failures, discard the cache. The time-based heuristic is very clumsy but there are few choices for a better event. Depending solely on multiple allocation failures still allows excessive scanning when THP allocations are failing in quick succession due to memory pressure. Waiting until memory pressure is relieved would cause compaction to continually fail instead of using reclaim/compaction to try allocate the page. The time-based mechanism is clumsy but a better option is not obvious. Signed-off-by: Mel Gorman <mgorman@suse.de> Acked-by: Rik van Riel <riel@redhat.com> Cc: Richard Davies <richard@arachsys.com> Cc: Shaohua Li <shli@kernel.org> Cc: Avi Kivity <avi@redhat.com> Acked-by: Rafael Aquini <aquini@redhat.com> Cc: Fengguang Wu <fengguang.wu@intel.com> Cc: Michal Nazarewicz <mina86@mina86.com> Cc: Bartlomiej Zolnierkiewicz <b.zolnierkie@samsung.com> Cc: Kyungmin Park <kyungmin.park@samsung.com> Cc: Mark Brown <broonie@opensource.wolfsonmicro.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2012-10-08 23:32:41 +00:00
}
#else
static inline bool isolation_suitable(struct compact_control *cc,
struct page *page)
{
return true;
}
mm: compaction: Restart compaction from near where it left off This is almost entirely based on Rik's previous patches and discussions with him about how this might be implemented. Order > 0 compaction stops when enough free pages of the correct page order have been coalesced. When doing subsequent higher order allocations, it is possible for compaction to be invoked many times. However, the compaction code always starts out looking for things to compact at the start of the zone, and for free pages to compact things to at the end of the zone. This can cause quadratic behaviour, with isolate_freepages starting at the end of the zone each time, even though previous invocations of the compaction code already filled up all free memory on that end of the zone. This can cause isolate_freepages to take enormous amounts of CPU with certain workloads on larger memory systems. This patch caches where the migration and free scanner should start from on subsequent compaction invocations using the pageblock-skip information. When compaction starts it begins from the cached restart points and will update the cached restart points until a page is isolated or a pageblock is skipped that would have been scanned by synchronous compaction. Signed-off-by: Mel Gorman <mgorman@suse.de> Acked-by: Rik van Riel <riel@redhat.com> Cc: Richard Davies <richard@arachsys.com> Cc: Shaohua Li <shli@kernel.org> Cc: Avi Kivity <avi@redhat.com> Acked-by: Rafael Aquini <aquini@redhat.com> Cc: Fengguang Wu <fengguang.wu@intel.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2012-10-08 23:32:45 +00:00
static void update_pageblock_skip(struct compact_control *cc,
struct page *page, unsigned long nr_isolated,
bool migrate_scanner)
mm: compaction: cache if a pageblock was scanned and no pages were isolated When compaction was implemented it was known that scanning could potentially be excessive. The ideal was that a counter be maintained for each pageblock but maintaining this information would incur a severe penalty due to a shared writable cache line. It has reached the point where the scanning costs are a serious problem, particularly on long-lived systems where a large process starts and allocates a large number of THPs at the same time. Instead of using a shared counter, this patch adds another bit to the pageblock flags called PG_migrate_skip. If a pageblock is scanned by either migrate or free scanner and 0 pages were isolated, the pageblock is marked to be skipped in the future. When scanning, this bit is checked before any scanning takes place and the block skipped if set. The main difficulty with a patch like this is "when to ignore the cached information?" If it's ignored too often, the scanning rates will still be excessive. If the information is too stale then allocations will fail that might have otherwise succeeded. In this patch o CMA always ignores the information o If the migrate and free scanner meet then the cached information will be discarded if it's at least 5 seconds since the last time the cache was discarded o If there are a large number of allocation failures, discard the cache. The time-based heuristic is very clumsy but there are few choices for a better event. Depending solely on multiple allocation failures still allows excessive scanning when THP allocations are failing in quick succession due to memory pressure. Waiting until memory pressure is relieved would cause compaction to continually fail instead of using reclaim/compaction to try allocate the page. The time-based mechanism is clumsy but a better option is not obvious. Signed-off-by: Mel Gorman <mgorman@suse.de> Acked-by: Rik van Riel <riel@redhat.com> Cc: Richard Davies <richard@arachsys.com> Cc: Shaohua Li <shli@kernel.org> Cc: Avi Kivity <avi@redhat.com> Acked-by: Rafael Aquini <aquini@redhat.com> Cc: Fengguang Wu <fengguang.wu@intel.com> Cc: Michal Nazarewicz <mina86@mina86.com> Cc: Bartlomiej Zolnierkiewicz <b.zolnierkie@samsung.com> Cc: Kyungmin Park <kyungmin.park@samsung.com> Cc: Mark Brown <broonie@opensource.wolfsonmicro.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2012-10-08 23:32:41 +00:00
{
}
#endif /* CONFIG_COMPACTION */
mm: compaction: acquire the zone->lru_lock as late as possible Richard Davies and Shaohua Li have both reported lock contention problems in compaction on the zone and LRU locks as well as significant amounts of time being spent in compaction. This series aims to reduce lock contention and scanning rates to reduce that CPU usage. Richard reported at https://lkml.org/lkml/2012/9/21/91 that this series made a big different to a problem he reported in August: http://marc.info/?l=kvm&m=134511507015614&w=2 Patch 1 defers acquiring the zone->lru_lock as long as possible. Patch 2 defers acquiring the zone->lock as lock as possible. Patch 3 reverts Rik's "skip-free" patches as the core concept gets reimplemented later and the remaining patches are easier to understand if this is reverted first. Patch 4 adds a pageblock-skip bit to the pageblock flags to cache what pageblocks should be skipped by the migrate and free scanners. This drastically reduces the amount of scanning compaction has to do. Patch 5 reimplements something similar to Rik's idea except it uses the pageblock-skip information to decide where the scanners should restart from and does not need to wrap around. I tested this on 3.6-rc6 + linux-next/akpm. Kernels tested were akpm-20120920 3.6-rc6 + linux-next/akpm as of Septeber 20th, 2012 lesslock Patches 1-6 revert Patches 1-7 cachefail Patches 1-8 skipuseless Patches 1-9 Stress high-order allocation tests looked ok. Success rates are more or less the same with the full series applied but there is an expectation that there is less opportunity to race with other allocation requests if there is less scanning. The time to complete the tests did not vary that much and are uninteresting as were the vmstat statistics so I will not present them here. Using ftrace I recorded how much scanning was done by compaction and got this 3.6.0-rc6 3.6.0-rc6 3.6.0-rc6 3.6.0-rc6 3.6.0-rc6 akpm-20120920 lockless revert-v2r2 cachefail skipuseless Total free scanned 360753976 515414028 565479007 17103281 18916589 Total free isolated 2852429 3597369 4048601 670493 727840 Total free efficiency 0.0079% 0.0070% 0.0072% 0.0392% 0.0385% Total migrate scanned 247728664 822729112 1004645830 17946827 14118903 Total migrate isolated 2555324 3245937 3437501 616359 658616 Total migrate efficiency 0.0103% 0.0039% 0.0034% 0.0343% 0.0466% The efficiency is worthless because of the nature of the test and the number of failures. The really interesting point as far as this patch series is concerned is the number of pages scanned. Note that reverting Rik's patches massively increases the number of pages scanned indicating that those patches really did make a difference to CPU usage. However, caching what pageblocks should be skipped has a much higher impact. With patches 1-8 applied, free page and migrate page scanning are both reduced by 95% in comparison to the akpm kernel. If the basic concept of Rik's patches are implemened on top then scanning then the free scanner barely changed but migrate scanning was further reduced. That said, tests on 3.6-rc5 indicated that the last patch had greater impact than what was measured here so it is a bit variable. One way or the other, this series has a large impact on the amount of scanning compaction does when there is a storm of THP allocations. This patch: Compaction's migrate scanner acquires the zone->lru_lock when scanning a range of pages looking for LRU pages to acquire. It does this even if there are no LRU pages in the range. If multiple processes are compacting then this can cause severe locking contention. To make matters worse commit b2eef8c0 ("mm: compaction: minimise the time IRQs are disabled while isolating pages for migration") releases the lru_lock every SWAP_CLUSTER_MAX pages that are scanned. This patch makes two changes to how the migrate scanner acquires the LRU lock. First, it only releases the LRU lock every SWAP_CLUSTER_MAX pages if the lock is contended. This reduces the number of times it unnecessarily disables and re-enables IRQs. The second is that it defers acquiring the LRU lock for as long as possible. If there are no LRU pages or the only LRU pages are transhuge then the LRU lock will not be acquired at all which reduces contention on zone->lru_lock. [minchan@kernel.org: augment comment] [akpm@linux-foundation.org: tweak comment text] Signed-off-by: Mel Gorman <mgorman@suse.de> Acked-by: Rik van Riel <riel@redhat.com> Cc: Richard Davies <richard@arachsys.com> Cc: Shaohua Li <shli@kernel.org> Cc: Avi Kivity <avi@redhat.com> Acked-by: Rafael Aquini <aquini@redhat.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2012-10-08 23:32:33 +00:00
static inline bool should_release_lock(spinlock_t *lock)
{
return need_resched() || spin_is_contended(lock);
}
mm: compaction: Abort async compaction if locks are contended or taking too long Jim Schutt reported a problem that pointed at compaction contending heavily on locks. The workload is straight-forward and in his own words; The systems in question have 24 SAS drives spread across 3 HBAs, running 24 Ceph OSD instances, one per drive. FWIW these servers are dual-socket Intel 5675 Xeons w/48 GB memory. I've got ~160 Ceph Linux clients doing dd simultaneously to a Ceph file system backed by 12 of these servers. Early in the test everything looks fine procs -------------------memory------------------ ---swap-- -----io---- --system-- -----cpu------- r b swpd free buff cache si so bi bo in cs us sy id wa st 31 15 0 287216 576 38606628 0 0 2 1158 2 14 1 3 95 0 0 27 15 0 225288 576 38583384 0 0 18 2222016 203357 134876 11 56 17 15 0 28 17 0 219256 576 38544736 0 0 11 2305932 203141 146296 11 49 23 17 0 6 18 0 215596 576 38552872 0 0 7 2363207 215264 166502 12 45 22 20 0 22 18 0 226984 576 38596404 0 0 3 2445741 223114 179527 12 43 23 22 0 and then it goes to pot procs -------------------memory------------------ ---swap-- -----io---- --system-- -----cpu------- r b swpd free buff cache si so bi bo in cs us sy id wa st 163 8 0 464308 576 36791368 0 0 11 22210 866 536 3 13 79 4 0 207 14 0 917752 576 36181928 0 0 712 1345376 134598 47367 7 90 1 2 0 123 12 0 685516 576 36296148 0 0 429 1386615 158494 60077 8 84 5 3 0 123 12 0 598572 576 36333728 0 0 1107 1233281 147542 62351 7 84 5 4 0 622 7 0 660768 576 36118264 0 0 557 1345548 151394 59353 7 85 4 3 0 223 11 0 283960 576 36463868 0 0 46 1107160 121846 33006 6 93 1 1 0 Note that system CPU usage is very high blocks being written out has dropped by 42%. He analysed this with perf and found perf record -g -a sleep 10 perf report --sort symbol --call-graph fractal,5 34.63% [k] _raw_spin_lock_irqsave | |--97.30%-- isolate_freepages | compaction_alloc | unmap_and_move | migrate_pages | compact_zone | compact_zone_order | try_to_compact_pages | __alloc_pages_direct_compact | __alloc_pages_slowpath | __alloc_pages_nodemask | alloc_pages_vma | do_huge_pmd_anonymous_page | handle_mm_fault | do_page_fault | page_fault | | | |--87.39%-- skb_copy_datagram_iovec | | tcp_recvmsg | | inet_recvmsg | | sock_recvmsg | | sys_recvfrom | | system_call | | __recv | | | | | --100.00%-- (nil) | | | --12.61%-- memcpy --2.70%-- [...] There was other data but primarily it is all showing that compaction is contended heavily on the zone->lock and zone->lru_lock. commit [b2eef8c0: mm: compaction: minimise the time IRQs are disabled while isolating pages for migration] noted that it was possible for migration to hold the lru_lock for an excessive amount of time. Very broadly speaking this patch expands the concept. This patch introduces compact_checklock_irqsave() to check if a lock is contended or the process needs to be scheduled. If either condition is true then async compaction is aborted and the caller is informed. The page allocator will fail a THP allocation if compaction failed due to contention. This patch also introduces compact_trylock_irqsave() which will acquire the lock only if it is not contended and the process does not need to schedule. Reported-by: Jim Schutt <jaschut@sandia.gov> Tested-by: Jim Schutt <jaschut@sandia.gov> Signed-off-by: Mel Gorman <mgorman@suse.de> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2012-08-21 23:16:17 +00:00
/*
* Compaction requires the taking of some coarse locks that are potentially
* very heavily contended. Check if the process needs to be scheduled or
* if the lock is contended. For async compaction, back out in the event
* if contention is severe. For sync compaction, schedule.
*
* Returns true if the lock is held.
* Returns false if the lock is released and compaction should abort
*/
static bool compact_checklock_irqsave(spinlock_t *lock, unsigned long *flags,
bool locked, struct compact_control *cc)
{
mm: compaction: acquire the zone->lru_lock as late as possible Richard Davies and Shaohua Li have both reported lock contention problems in compaction on the zone and LRU locks as well as significant amounts of time being spent in compaction. This series aims to reduce lock contention and scanning rates to reduce that CPU usage. Richard reported at https://lkml.org/lkml/2012/9/21/91 that this series made a big different to a problem he reported in August: http://marc.info/?l=kvm&m=134511507015614&w=2 Patch 1 defers acquiring the zone->lru_lock as long as possible. Patch 2 defers acquiring the zone->lock as lock as possible. Patch 3 reverts Rik's "skip-free" patches as the core concept gets reimplemented later and the remaining patches are easier to understand if this is reverted first. Patch 4 adds a pageblock-skip bit to the pageblock flags to cache what pageblocks should be skipped by the migrate and free scanners. This drastically reduces the amount of scanning compaction has to do. Patch 5 reimplements something similar to Rik's idea except it uses the pageblock-skip information to decide where the scanners should restart from and does not need to wrap around. I tested this on 3.6-rc6 + linux-next/akpm. Kernels tested were akpm-20120920 3.6-rc6 + linux-next/akpm as of Septeber 20th, 2012 lesslock Patches 1-6 revert Patches 1-7 cachefail Patches 1-8 skipuseless Patches 1-9 Stress high-order allocation tests looked ok. Success rates are more or less the same with the full series applied but there is an expectation that there is less opportunity to race with other allocation requests if there is less scanning. The time to complete the tests did not vary that much and are uninteresting as were the vmstat statistics so I will not present them here. Using ftrace I recorded how much scanning was done by compaction and got this 3.6.0-rc6 3.6.0-rc6 3.6.0-rc6 3.6.0-rc6 3.6.0-rc6 akpm-20120920 lockless revert-v2r2 cachefail skipuseless Total free scanned 360753976 515414028 565479007 17103281 18916589 Total free isolated 2852429 3597369 4048601 670493 727840 Total free efficiency 0.0079% 0.0070% 0.0072% 0.0392% 0.0385% Total migrate scanned 247728664 822729112 1004645830 17946827 14118903 Total migrate isolated 2555324 3245937 3437501 616359 658616 Total migrate efficiency 0.0103% 0.0039% 0.0034% 0.0343% 0.0466% The efficiency is worthless because of the nature of the test and the number of failures. The really interesting point as far as this patch series is concerned is the number of pages scanned. Note that reverting Rik's patches massively increases the number of pages scanned indicating that those patches really did make a difference to CPU usage. However, caching what pageblocks should be skipped has a much higher impact. With patches 1-8 applied, free page and migrate page scanning are both reduced by 95% in comparison to the akpm kernel. If the basic concept of Rik's patches are implemened on top then scanning then the free scanner barely changed but migrate scanning was further reduced. That said, tests on 3.6-rc5 indicated that the last patch had greater impact than what was measured here so it is a bit variable. One way or the other, this series has a large impact on the amount of scanning compaction does when there is a storm of THP allocations. This patch: Compaction's migrate scanner acquires the zone->lru_lock when scanning a range of pages looking for LRU pages to acquire. It does this even if there are no LRU pages in the range. If multiple processes are compacting then this can cause severe locking contention. To make matters worse commit b2eef8c0 ("mm: compaction: minimise the time IRQs are disabled while isolating pages for migration") releases the lru_lock every SWAP_CLUSTER_MAX pages that are scanned. This patch makes two changes to how the migrate scanner acquires the LRU lock. First, it only releases the LRU lock every SWAP_CLUSTER_MAX pages if the lock is contended. This reduces the number of times it unnecessarily disables and re-enables IRQs. The second is that it defers acquiring the LRU lock for as long as possible. If there are no LRU pages or the only LRU pages are transhuge then the LRU lock will not be acquired at all which reduces contention on zone->lru_lock. [minchan@kernel.org: augment comment] [akpm@linux-foundation.org: tweak comment text] Signed-off-by: Mel Gorman <mgorman@suse.de> Acked-by: Rik van Riel <riel@redhat.com> Cc: Richard Davies <richard@arachsys.com> Cc: Shaohua Li <shli@kernel.org> Cc: Avi Kivity <avi@redhat.com> Acked-by: Rafael Aquini <aquini@redhat.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2012-10-08 23:32:33 +00:00
if (should_release_lock(lock)) {
mm: compaction: Abort async compaction if locks are contended or taking too long Jim Schutt reported a problem that pointed at compaction contending heavily on locks. The workload is straight-forward and in his own words; The systems in question have 24 SAS drives spread across 3 HBAs, running 24 Ceph OSD instances, one per drive. FWIW these servers are dual-socket Intel 5675 Xeons w/48 GB memory. I've got ~160 Ceph Linux clients doing dd simultaneously to a Ceph file system backed by 12 of these servers. Early in the test everything looks fine procs -------------------memory------------------ ---swap-- -----io---- --system-- -----cpu------- r b swpd free buff cache si so bi bo in cs us sy id wa st 31 15 0 287216 576 38606628 0 0 2 1158 2 14 1 3 95 0 0 27 15 0 225288 576 38583384 0 0 18 2222016 203357 134876 11 56 17 15 0 28 17 0 219256 576 38544736 0 0 11 2305932 203141 146296 11 49 23 17 0 6 18 0 215596 576 38552872 0 0 7 2363207 215264 166502 12 45 22 20 0 22 18 0 226984 576 38596404 0 0 3 2445741 223114 179527 12 43 23 22 0 and then it goes to pot procs -------------------memory------------------ ---swap-- -----io---- --system-- -----cpu------- r b swpd free buff cache si so bi bo in cs us sy id wa st 163 8 0 464308 576 36791368 0 0 11 22210 866 536 3 13 79 4 0 207 14 0 917752 576 36181928 0 0 712 1345376 134598 47367 7 90 1 2 0 123 12 0 685516 576 36296148 0 0 429 1386615 158494 60077 8 84 5 3 0 123 12 0 598572 576 36333728 0 0 1107 1233281 147542 62351 7 84 5 4 0 622 7 0 660768 576 36118264 0 0 557 1345548 151394 59353 7 85 4 3 0 223 11 0 283960 576 36463868 0 0 46 1107160 121846 33006 6 93 1 1 0 Note that system CPU usage is very high blocks being written out has dropped by 42%. He analysed this with perf and found perf record -g -a sleep 10 perf report --sort symbol --call-graph fractal,5 34.63% [k] _raw_spin_lock_irqsave | |--97.30%-- isolate_freepages | compaction_alloc | unmap_and_move | migrate_pages | compact_zone | compact_zone_order | try_to_compact_pages | __alloc_pages_direct_compact | __alloc_pages_slowpath | __alloc_pages_nodemask | alloc_pages_vma | do_huge_pmd_anonymous_page | handle_mm_fault | do_page_fault | page_fault | | | |--87.39%-- skb_copy_datagram_iovec | | tcp_recvmsg | | inet_recvmsg | | sock_recvmsg | | sys_recvfrom | | system_call | | __recv | | | | | --100.00%-- (nil) | | | --12.61%-- memcpy --2.70%-- [...] There was other data but primarily it is all showing that compaction is contended heavily on the zone->lock and zone->lru_lock. commit [b2eef8c0: mm: compaction: minimise the time IRQs are disabled while isolating pages for migration] noted that it was possible for migration to hold the lru_lock for an excessive amount of time. Very broadly speaking this patch expands the concept. This patch introduces compact_checklock_irqsave() to check if a lock is contended or the process needs to be scheduled. If either condition is true then async compaction is aborted and the caller is informed. The page allocator will fail a THP allocation if compaction failed due to contention. This patch also introduces compact_trylock_irqsave() which will acquire the lock only if it is not contended and the process does not need to schedule. Reported-by: Jim Schutt <jaschut@sandia.gov> Tested-by: Jim Schutt <jaschut@sandia.gov> Signed-off-by: Mel Gorman <mgorman@suse.de> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2012-08-21 23:16:17 +00:00
if (locked) {
spin_unlock_irqrestore(lock, *flags);
locked = false;
}
/* async aborts if taking too long or contended */
if (!cc->sync) {
cc->contended = true;
mm: compaction: Abort async compaction if locks are contended or taking too long Jim Schutt reported a problem that pointed at compaction contending heavily on locks. The workload is straight-forward and in his own words; The systems in question have 24 SAS drives spread across 3 HBAs, running 24 Ceph OSD instances, one per drive. FWIW these servers are dual-socket Intel 5675 Xeons w/48 GB memory. I've got ~160 Ceph Linux clients doing dd simultaneously to a Ceph file system backed by 12 of these servers. Early in the test everything looks fine procs -------------------memory------------------ ---swap-- -----io---- --system-- -----cpu------- r b swpd free buff cache si so bi bo in cs us sy id wa st 31 15 0 287216 576 38606628 0 0 2 1158 2 14 1 3 95 0 0 27 15 0 225288 576 38583384 0 0 18 2222016 203357 134876 11 56 17 15 0 28 17 0 219256 576 38544736 0 0 11 2305932 203141 146296 11 49 23 17 0 6 18 0 215596 576 38552872 0 0 7 2363207 215264 166502 12 45 22 20 0 22 18 0 226984 576 38596404 0 0 3 2445741 223114 179527 12 43 23 22 0 and then it goes to pot procs -------------------memory------------------ ---swap-- -----io---- --system-- -----cpu------- r b swpd free buff cache si so bi bo in cs us sy id wa st 163 8 0 464308 576 36791368 0 0 11 22210 866 536 3 13 79 4 0 207 14 0 917752 576 36181928 0 0 712 1345376 134598 47367 7 90 1 2 0 123 12 0 685516 576 36296148 0 0 429 1386615 158494 60077 8 84 5 3 0 123 12 0 598572 576 36333728 0 0 1107 1233281 147542 62351 7 84 5 4 0 622 7 0 660768 576 36118264 0 0 557 1345548 151394 59353 7 85 4 3 0 223 11 0 283960 576 36463868 0 0 46 1107160 121846 33006 6 93 1 1 0 Note that system CPU usage is very high blocks being written out has dropped by 42%. He analysed this with perf and found perf record -g -a sleep 10 perf report --sort symbol --call-graph fractal,5 34.63% [k] _raw_spin_lock_irqsave | |--97.30%-- isolate_freepages | compaction_alloc | unmap_and_move | migrate_pages | compact_zone | compact_zone_order | try_to_compact_pages | __alloc_pages_direct_compact | __alloc_pages_slowpath | __alloc_pages_nodemask | alloc_pages_vma | do_huge_pmd_anonymous_page | handle_mm_fault | do_page_fault | page_fault | | | |--87.39%-- skb_copy_datagram_iovec | | tcp_recvmsg | | inet_recvmsg | | sock_recvmsg | | sys_recvfrom | | system_call | | __recv | | | | | --100.00%-- (nil) | | | --12.61%-- memcpy --2.70%-- [...] There was other data but primarily it is all showing that compaction is contended heavily on the zone->lock and zone->lru_lock. commit [b2eef8c0: mm: compaction: minimise the time IRQs are disabled while isolating pages for migration] noted that it was possible for migration to hold the lru_lock for an excessive amount of time. Very broadly speaking this patch expands the concept. This patch introduces compact_checklock_irqsave() to check if a lock is contended or the process needs to be scheduled. If either condition is true then async compaction is aborted and the caller is informed. The page allocator will fail a THP allocation if compaction failed due to contention. This patch also introduces compact_trylock_irqsave() which will acquire the lock only if it is not contended and the process does not need to schedule. Reported-by: Jim Schutt <jaschut@sandia.gov> Tested-by: Jim Schutt <jaschut@sandia.gov> Signed-off-by: Mel Gorman <mgorman@suse.de> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2012-08-21 23:16:17 +00:00
return false;
}
cond_resched();
}
if (!locked)
spin_lock_irqsave(lock, *flags);
return true;
}
static inline bool compact_trylock_irqsave(spinlock_t *lock,
unsigned long *flags, struct compact_control *cc)
{
return compact_checklock_irqsave(lock, flags, false, cc);
}
/* Returns true if the page is within a block suitable for migration to */
static bool suitable_migration_target(struct page *page)
{
int migratetype = get_pageblock_migratetype(page);
/* Don't interfere with memory hot-remove or the min_free_kbytes blocks */
if (migratetype == MIGRATE_ISOLATE || migratetype == MIGRATE_RESERVE)
return false;
/* If the page is a large free page, then allow migration */
if (PageBuddy(page) && page_order(page) >= pageblock_order)
return true;
/* If the block is MIGRATE_MOVABLE or MIGRATE_CMA, allow migration */
if (migrate_async_suitable(migratetype))
return true;
/* Otherwise skip the block */
return false;
}
/*
* Isolate free pages onto a private freelist. Caller must hold zone->lock.
* If @strict is true, will abort returning 0 on any invalid PFNs or non-free
* pages inside of the pageblock (even though it may still end up isolating
* some pages).
*/
static unsigned long isolate_freepages_block(struct compact_control *cc,
unsigned long blockpfn,
unsigned long end_pfn,
struct list_head *freelist,
bool strict)
{
int nr_scanned = 0, total_isolated = 0;
mm: compaction: cache if a pageblock was scanned and no pages were isolated When compaction was implemented it was known that scanning could potentially be excessive. The ideal was that a counter be maintained for each pageblock but maintaining this information would incur a severe penalty due to a shared writable cache line. It has reached the point where the scanning costs are a serious problem, particularly on long-lived systems where a large process starts and allocates a large number of THPs at the same time. Instead of using a shared counter, this patch adds another bit to the pageblock flags called PG_migrate_skip. If a pageblock is scanned by either migrate or free scanner and 0 pages were isolated, the pageblock is marked to be skipped in the future. When scanning, this bit is checked before any scanning takes place and the block skipped if set. The main difficulty with a patch like this is "when to ignore the cached information?" If it's ignored too often, the scanning rates will still be excessive. If the information is too stale then allocations will fail that might have otherwise succeeded. In this patch o CMA always ignores the information o If the migrate and free scanner meet then the cached information will be discarded if it's at least 5 seconds since the last time the cache was discarded o If there are a large number of allocation failures, discard the cache. The time-based heuristic is very clumsy but there are few choices for a better event. Depending solely on multiple allocation failures still allows excessive scanning when THP allocations are failing in quick succession due to memory pressure. Waiting until memory pressure is relieved would cause compaction to continually fail instead of using reclaim/compaction to try allocate the page. The time-based mechanism is clumsy but a better option is not obvious. Signed-off-by: Mel Gorman <mgorman@suse.de> Acked-by: Rik van Riel <riel@redhat.com> Cc: Richard Davies <richard@arachsys.com> Cc: Shaohua Li <shli@kernel.org> Cc: Avi Kivity <avi@redhat.com> Acked-by: Rafael Aquini <aquini@redhat.com> Cc: Fengguang Wu <fengguang.wu@intel.com> Cc: Michal Nazarewicz <mina86@mina86.com> Cc: Bartlomiej Zolnierkiewicz <b.zolnierkie@samsung.com> Cc: Kyungmin Park <kyungmin.park@samsung.com> Cc: Mark Brown <broonie@opensource.wolfsonmicro.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2012-10-08 23:32:41 +00:00
struct page *cursor, *valid_page = NULL;
unsigned long nr_strict_required = end_pfn - blockpfn;
unsigned long flags;
bool locked = false;
cursor = pfn_to_page(blockpfn);
/* Isolate free pages. */
for (; blockpfn < end_pfn; blockpfn++, cursor++) {
int isolated, i;
struct page *page = cursor;
nr_scanned++;
if (!pfn_valid_within(blockpfn))
continue;
mm: compaction: cache if a pageblock was scanned and no pages were isolated When compaction was implemented it was known that scanning could potentially be excessive. The ideal was that a counter be maintained for each pageblock but maintaining this information would incur a severe penalty due to a shared writable cache line. It has reached the point where the scanning costs are a serious problem, particularly on long-lived systems where a large process starts and allocates a large number of THPs at the same time. Instead of using a shared counter, this patch adds another bit to the pageblock flags called PG_migrate_skip. If a pageblock is scanned by either migrate or free scanner and 0 pages were isolated, the pageblock is marked to be skipped in the future. When scanning, this bit is checked before any scanning takes place and the block skipped if set. The main difficulty with a patch like this is "when to ignore the cached information?" If it's ignored too often, the scanning rates will still be excessive. If the information is too stale then allocations will fail that might have otherwise succeeded. In this patch o CMA always ignores the information o If the migrate and free scanner meet then the cached information will be discarded if it's at least 5 seconds since the last time the cache was discarded o If there are a large number of allocation failures, discard the cache. The time-based heuristic is very clumsy but there are few choices for a better event. Depending solely on multiple allocation failures still allows excessive scanning when THP allocations are failing in quick succession due to memory pressure. Waiting until memory pressure is relieved would cause compaction to continually fail instead of using reclaim/compaction to try allocate the page. The time-based mechanism is clumsy but a better option is not obvious. Signed-off-by: Mel Gorman <mgorman@suse.de> Acked-by: Rik van Riel <riel@redhat.com> Cc: Richard Davies <richard@arachsys.com> Cc: Shaohua Li <shli@kernel.org> Cc: Avi Kivity <avi@redhat.com> Acked-by: Rafael Aquini <aquini@redhat.com> Cc: Fengguang Wu <fengguang.wu@intel.com> Cc: Michal Nazarewicz <mina86@mina86.com> Cc: Bartlomiej Zolnierkiewicz <b.zolnierkie@samsung.com> Cc: Kyungmin Park <kyungmin.park@samsung.com> Cc: Mark Brown <broonie@opensource.wolfsonmicro.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2012-10-08 23:32:41 +00:00
if (!valid_page)
valid_page = page;
if (!PageBuddy(page))
continue;
/*
* The zone lock must be held to isolate freepages.
* Unfortunately this is a very coarse lock and can be
* heavily contended if there are parallel allocations
* or parallel compactions. For async compaction do not
* spin on the lock and we acquire the lock as late as
* possible.
*/
locked = compact_checklock_irqsave(&cc->zone->lock, &flags,
locked, cc);
if (!locked)
break;
/* Recheck this is a suitable migration target under lock */
if (!strict && !suitable_migration_target(page))
break;
/* Recheck this is a buddy page under lock */
if (!PageBuddy(page))
continue;
/* Found a free page, break it into order-0 pages */
isolated = split_free_page(page);
if (!isolated && strict)
break;
total_isolated += isolated;
for (i = 0; i < isolated; i++) {
list_add(&page->lru, freelist);
page++;
}
/* If a page was split, advance to the end of it */
if (isolated) {
blockpfn += isolated - 1;
cursor += isolated - 1;
}
}
trace_mm_compaction_isolate_freepages(nr_scanned, total_isolated);
/*
* If strict isolation is requested by CMA then check that all the
* pages requested were isolated. If there were any failures, 0 is
* returned and CMA will fail.
*/
if (strict && nr_strict_required > total_isolated)
total_isolated = 0;
if (locked)
spin_unlock_irqrestore(&cc->zone->lock, flags);
mm: compaction: cache if a pageblock was scanned and no pages were isolated When compaction was implemented it was known that scanning could potentially be excessive. The ideal was that a counter be maintained for each pageblock but maintaining this information would incur a severe penalty due to a shared writable cache line. It has reached the point where the scanning costs are a serious problem, particularly on long-lived systems where a large process starts and allocates a large number of THPs at the same time. Instead of using a shared counter, this patch adds another bit to the pageblock flags called PG_migrate_skip. If a pageblock is scanned by either migrate or free scanner and 0 pages were isolated, the pageblock is marked to be skipped in the future. When scanning, this bit is checked before any scanning takes place and the block skipped if set. The main difficulty with a patch like this is "when to ignore the cached information?" If it's ignored too often, the scanning rates will still be excessive. If the information is too stale then allocations will fail that might have otherwise succeeded. In this patch o CMA always ignores the information o If the migrate and free scanner meet then the cached information will be discarded if it's at least 5 seconds since the last time the cache was discarded o If there are a large number of allocation failures, discard the cache. The time-based heuristic is very clumsy but there are few choices for a better event. Depending solely on multiple allocation failures still allows excessive scanning when THP allocations are failing in quick succession due to memory pressure. Waiting until memory pressure is relieved would cause compaction to continually fail instead of using reclaim/compaction to try allocate the page. The time-based mechanism is clumsy but a better option is not obvious. Signed-off-by: Mel Gorman <mgorman@suse.de> Acked-by: Rik van Riel <riel@redhat.com> Cc: Richard Davies <richard@arachsys.com> Cc: Shaohua Li <shli@kernel.org> Cc: Avi Kivity <avi@redhat.com> Acked-by: Rafael Aquini <aquini@redhat.com> Cc: Fengguang Wu <fengguang.wu@intel.com> Cc: Michal Nazarewicz <mina86@mina86.com> Cc: Bartlomiej Zolnierkiewicz <b.zolnierkie@samsung.com> Cc: Kyungmin Park <kyungmin.park@samsung.com> Cc: Mark Brown <broonie@opensource.wolfsonmicro.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2012-10-08 23:32:41 +00:00
/* Update the pageblock-skip if the whole pageblock was scanned */
if (blockpfn == end_pfn)
mm: compaction: Restart compaction from near where it left off This is almost entirely based on Rik's previous patches and discussions with him about how this might be implemented. Order > 0 compaction stops when enough free pages of the correct page order have been coalesced. When doing subsequent higher order allocations, it is possible for compaction to be invoked many times. However, the compaction code always starts out looking for things to compact at the start of the zone, and for free pages to compact things to at the end of the zone. This can cause quadratic behaviour, with isolate_freepages starting at the end of the zone each time, even though previous invocations of the compaction code already filled up all free memory on that end of the zone. This can cause isolate_freepages to take enormous amounts of CPU with certain workloads on larger memory systems. This patch caches where the migration and free scanner should start from on subsequent compaction invocations using the pageblock-skip information. When compaction starts it begins from the cached restart points and will update the cached restart points until a page is isolated or a pageblock is skipped that would have been scanned by synchronous compaction. Signed-off-by: Mel Gorman <mgorman@suse.de> Acked-by: Rik van Riel <riel@redhat.com> Cc: Richard Davies <richard@arachsys.com> Cc: Shaohua Li <shli@kernel.org> Cc: Avi Kivity <avi@redhat.com> Acked-by: Rafael Aquini <aquini@redhat.com> Cc: Fengguang Wu <fengguang.wu@intel.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2012-10-08 23:32:45 +00:00
update_pageblock_skip(cc, valid_page, total_isolated, false);
mm: compaction: cache if a pageblock was scanned and no pages were isolated When compaction was implemented it was known that scanning could potentially be excessive. The ideal was that a counter be maintained for each pageblock but maintaining this information would incur a severe penalty due to a shared writable cache line. It has reached the point where the scanning costs are a serious problem, particularly on long-lived systems where a large process starts and allocates a large number of THPs at the same time. Instead of using a shared counter, this patch adds another bit to the pageblock flags called PG_migrate_skip. If a pageblock is scanned by either migrate or free scanner and 0 pages were isolated, the pageblock is marked to be skipped in the future. When scanning, this bit is checked before any scanning takes place and the block skipped if set. The main difficulty with a patch like this is "when to ignore the cached information?" If it's ignored too often, the scanning rates will still be excessive. If the information is too stale then allocations will fail that might have otherwise succeeded. In this patch o CMA always ignores the information o If the migrate and free scanner meet then the cached information will be discarded if it's at least 5 seconds since the last time the cache was discarded o If there are a large number of allocation failures, discard the cache. The time-based heuristic is very clumsy but there are few choices for a better event. Depending solely on multiple allocation failures still allows excessive scanning when THP allocations are failing in quick succession due to memory pressure. Waiting until memory pressure is relieved would cause compaction to continually fail instead of using reclaim/compaction to try allocate the page. The time-based mechanism is clumsy but a better option is not obvious. Signed-off-by: Mel Gorman <mgorman@suse.de> Acked-by: Rik van Riel <riel@redhat.com> Cc: Richard Davies <richard@arachsys.com> Cc: Shaohua Li <shli@kernel.org> Cc: Avi Kivity <avi@redhat.com> Acked-by: Rafael Aquini <aquini@redhat.com> Cc: Fengguang Wu <fengguang.wu@intel.com> Cc: Michal Nazarewicz <mina86@mina86.com> Cc: Bartlomiej Zolnierkiewicz <b.zolnierkie@samsung.com> Cc: Kyungmin Park <kyungmin.park@samsung.com> Cc: Mark Brown <broonie@opensource.wolfsonmicro.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2012-10-08 23:32:41 +00:00
count_compact_events(COMPACTFREE_SCANNED, nr_scanned);
mm: compaction: Add scanned and isolated counters for compaction Compaction already has tracepoints to count scanned and isolated pages but it requires that ftrace be enabled and if that information has to be written to disk then it can be disruptive. This patch adds vmstat counters for compaction called compact_migrate_scanned, compact_free_scanned and compact_isolated. With these counters, it is possible to define a basic cost model for compaction. This approximates of how much work compaction is doing and can be compared that with an oprofile showing TLB misses and see if the cost of compaction is being offset by THP for example. Minimally a compaction patch can be evaluated in terms of whether it increases or decreases cost. The basic cost model looks like this Fundamental unit u: a word sizeof(void *) Ca = cost of struct page access = sizeof(struct page) / u Cmc = Cost migrate page copy = (Ca + PAGE_SIZE/u) * 2 Cmf = Cost migrate failure = Ca * 2 Ci = Cost page isolation = (Ca + Wi) where Wi is a constant that should reflect the approximate cost of the locking operation. Csm = Cost migrate scanning = Ca Csf = Cost free scanning = Ca Overall cost = (Csm * compact_migrate_scanned) + (Csf * compact_free_scanned) + (Ci * compact_isolated) + (Cmc * pgmigrate_success) + (Cmf * pgmigrate_failed) Where the values are read from /proc/vmstat. This is very basic and ignores certain costs such as the allocation cost to do a migrate page copy but any improvement to the model would still use the same vmstat counters. Signed-off-by: Mel Gorman <mgorman@suse.de> Reviewed-by: Rik van Riel <riel@redhat.com>
2012-10-19 11:00:10 +00:00
if (total_isolated)
count_compact_events(COMPACTISOLATED, total_isolated);
return total_isolated;
}
/**
* isolate_freepages_range() - isolate free pages.
* @start_pfn: The first PFN to start isolating.
* @end_pfn: The one-past-last PFN.
*
* Non-free pages, invalid PFNs, or zone boundaries within the
* [start_pfn, end_pfn) range are considered errors, cause function to
* undo its actions and return zero.
*
* Otherwise, function returns one-past-the-last PFN of isolated page
* (which may be greater then end_pfn if end fell in a middle of
* a free page).
*/
unsigned long
mm: compaction: cache if a pageblock was scanned and no pages were isolated When compaction was implemented it was known that scanning could potentially be excessive. The ideal was that a counter be maintained for each pageblock but maintaining this information would incur a severe penalty due to a shared writable cache line. It has reached the point where the scanning costs are a serious problem, particularly on long-lived systems where a large process starts and allocates a large number of THPs at the same time. Instead of using a shared counter, this patch adds another bit to the pageblock flags called PG_migrate_skip. If a pageblock is scanned by either migrate or free scanner and 0 pages were isolated, the pageblock is marked to be skipped in the future. When scanning, this bit is checked before any scanning takes place and the block skipped if set. The main difficulty with a patch like this is "when to ignore the cached information?" If it's ignored too often, the scanning rates will still be excessive. If the information is too stale then allocations will fail that might have otherwise succeeded. In this patch o CMA always ignores the information o If the migrate and free scanner meet then the cached information will be discarded if it's at least 5 seconds since the last time the cache was discarded o If there are a large number of allocation failures, discard the cache. The time-based heuristic is very clumsy but there are few choices for a better event. Depending solely on multiple allocation failures still allows excessive scanning when THP allocations are failing in quick succession due to memory pressure. Waiting until memory pressure is relieved would cause compaction to continually fail instead of using reclaim/compaction to try allocate the page. The time-based mechanism is clumsy but a better option is not obvious. Signed-off-by: Mel Gorman <mgorman@suse.de> Acked-by: Rik van Riel <riel@redhat.com> Cc: Richard Davies <richard@arachsys.com> Cc: Shaohua Li <shli@kernel.org> Cc: Avi Kivity <avi@redhat.com> Acked-by: Rafael Aquini <aquini@redhat.com> Cc: Fengguang Wu <fengguang.wu@intel.com> Cc: Michal Nazarewicz <mina86@mina86.com> Cc: Bartlomiej Zolnierkiewicz <b.zolnierkie@samsung.com> Cc: Kyungmin Park <kyungmin.park@samsung.com> Cc: Mark Brown <broonie@opensource.wolfsonmicro.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2012-10-08 23:32:41 +00:00
isolate_freepages_range(struct compact_control *cc,
unsigned long start_pfn, unsigned long end_pfn)
{
unsigned long isolated, pfn, block_end_pfn;
LIST_HEAD(freelist);
for (pfn = start_pfn; pfn < end_pfn; pfn += isolated) {
mm: compaction: cache if a pageblock was scanned and no pages were isolated When compaction was implemented it was known that scanning could potentially be excessive. The ideal was that a counter be maintained for each pageblock but maintaining this information would incur a severe penalty due to a shared writable cache line. It has reached the point where the scanning costs are a serious problem, particularly on long-lived systems where a large process starts and allocates a large number of THPs at the same time. Instead of using a shared counter, this patch adds another bit to the pageblock flags called PG_migrate_skip. If a pageblock is scanned by either migrate or free scanner and 0 pages were isolated, the pageblock is marked to be skipped in the future. When scanning, this bit is checked before any scanning takes place and the block skipped if set. The main difficulty with a patch like this is "when to ignore the cached information?" If it's ignored too often, the scanning rates will still be excessive. If the information is too stale then allocations will fail that might have otherwise succeeded. In this patch o CMA always ignores the information o If the migrate and free scanner meet then the cached information will be discarded if it's at least 5 seconds since the last time the cache was discarded o If there are a large number of allocation failures, discard the cache. The time-based heuristic is very clumsy but there are few choices for a better event. Depending solely on multiple allocation failures still allows excessive scanning when THP allocations are failing in quick succession due to memory pressure. Waiting until memory pressure is relieved would cause compaction to continually fail instead of using reclaim/compaction to try allocate the page. The time-based mechanism is clumsy but a better option is not obvious. Signed-off-by: Mel Gorman <mgorman@suse.de> Acked-by: Rik van Riel <riel@redhat.com> Cc: Richard Davies <richard@arachsys.com> Cc: Shaohua Li <shli@kernel.org> Cc: Avi Kivity <avi@redhat.com> Acked-by: Rafael Aquini <aquini@redhat.com> Cc: Fengguang Wu <fengguang.wu@intel.com> Cc: Michal Nazarewicz <mina86@mina86.com> Cc: Bartlomiej Zolnierkiewicz <b.zolnierkie@samsung.com> Cc: Kyungmin Park <kyungmin.park@samsung.com> Cc: Mark Brown <broonie@opensource.wolfsonmicro.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2012-10-08 23:32:41 +00:00
if (!pfn_valid(pfn) || cc->zone != page_zone(pfn_to_page(pfn)))
break;
/*
* On subsequent iterations ALIGN() is actually not needed,
* but we keep it that we not to complicate the code.
*/
block_end_pfn = ALIGN(pfn + 1, pageblock_nr_pages);
block_end_pfn = min(block_end_pfn, end_pfn);
mm: compaction: cache if a pageblock was scanned and no pages were isolated When compaction was implemented it was known that scanning could potentially be excessive. The ideal was that a counter be maintained for each pageblock but maintaining this information would incur a severe penalty due to a shared writable cache line. It has reached the point where the scanning costs are a serious problem, particularly on long-lived systems where a large process starts and allocates a large number of THPs at the same time. Instead of using a shared counter, this patch adds another bit to the pageblock flags called PG_migrate_skip. If a pageblock is scanned by either migrate or free scanner and 0 pages were isolated, the pageblock is marked to be skipped in the future. When scanning, this bit is checked before any scanning takes place and the block skipped if set. The main difficulty with a patch like this is "when to ignore the cached information?" If it's ignored too often, the scanning rates will still be excessive. If the information is too stale then allocations will fail that might have otherwise succeeded. In this patch o CMA always ignores the information o If the migrate and free scanner meet then the cached information will be discarded if it's at least 5 seconds since the last time the cache was discarded o If there are a large number of allocation failures, discard the cache. The time-based heuristic is very clumsy but there are few choices for a better event. Depending solely on multiple allocation failures still allows excessive scanning when THP allocations are failing in quick succession due to memory pressure. Waiting until memory pressure is relieved would cause compaction to continually fail instead of using reclaim/compaction to try allocate the page. The time-based mechanism is clumsy but a better option is not obvious. Signed-off-by: Mel Gorman <mgorman@suse.de> Acked-by: Rik van Riel <riel@redhat.com> Cc: Richard Davies <richard@arachsys.com> Cc: Shaohua Li <shli@kernel.org> Cc: Avi Kivity <avi@redhat.com> Acked-by: Rafael Aquini <aquini@redhat.com> Cc: Fengguang Wu <fengguang.wu@intel.com> Cc: Michal Nazarewicz <mina86@mina86.com> Cc: Bartlomiej Zolnierkiewicz <b.zolnierkie@samsung.com> Cc: Kyungmin Park <kyungmin.park@samsung.com> Cc: Mark Brown <broonie@opensource.wolfsonmicro.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2012-10-08 23:32:41 +00:00
isolated = isolate_freepages_block(cc, pfn, block_end_pfn,
&freelist, true);
/*
* In strict mode, isolate_freepages_block() returns 0 if
* there are any holes in the block (ie. invalid PFNs or
* non-free pages).
*/
if (!isolated)
break;
/*
* If we managed to isolate pages, it is always (1 << n) *
* pageblock_nr_pages for some non-negative n. (Max order
* page may span two pageblocks).
*/
}
/* split_free_page does not map the pages */
map_pages(&freelist);
if (pfn < end_pfn) {
/* Loop terminated early, cleanup. */
release_freepages(&freelist);
return 0;
}
/* We don't use freelists for anything. */
return pfn;
}
/* Update the number of anon and file isolated pages in the zone */
mm: compaction: Abort async compaction if locks are contended or taking too long Jim Schutt reported a problem that pointed at compaction contending heavily on locks. The workload is straight-forward and in his own words; The systems in question have 24 SAS drives spread across 3 HBAs, running 24 Ceph OSD instances, one per drive. FWIW these servers are dual-socket Intel 5675 Xeons w/48 GB memory. I've got ~160 Ceph Linux clients doing dd simultaneously to a Ceph file system backed by 12 of these servers. Early in the test everything looks fine procs -------------------memory------------------ ---swap-- -----io---- --system-- -----cpu------- r b swpd free buff cache si so bi bo in cs us sy id wa st 31 15 0 287216 576 38606628 0 0 2 1158 2 14 1 3 95 0 0 27 15 0 225288 576 38583384 0 0 18 2222016 203357 134876 11 56 17 15 0 28 17 0 219256 576 38544736 0 0 11 2305932 203141 146296 11 49 23 17 0 6 18 0 215596 576 38552872 0 0 7 2363207 215264 166502 12 45 22 20 0 22 18 0 226984 576 38596404 0 0 3 2445741 223114 179527 12 43 23 22 0 and then it goes to pot procs -------------------memory------------------ ---swap-- -----io---- --system-- -----cpu------- r b swpd free buff cache si so bi bo in cs us sy id wa st 163 8 0 464308 576 36791368 0 0 11 22210 866 536 3 13 79 4 0 207 14 0 917752 576 36181928 0 0 712 1345376 134598 47367 7 90 1 2 0 123 12 0 685516 576 36296148 0 0 429 1386615 158494 60077 8 84 5 3 0 123 12 0 598572 576 36333728 0 0 1107 1233281 147542 62351 7 84 5 4 0 622 7 0 660768 576 36118264 0 0 557 1345548 151394 59353 7 85 4 3 0 223 11 0 283960 576 36463868 0 0 46 1107160 121846 33006 6 93 1 1 0 Note that system CPU usage is very high blocks being written out has dropped by 42%. He analysed this with perf and found perf record -g -a sleep 10 perf report --sort symbol --call-graph fractal,5 34.63% [k] _raw_spin_lock_irqsave | |--97.30%-- isolate_freepages | compaction_alloc | unmap_and_move | migrate_pages | compact_zone | compact_zone_order | try_to_compact_pages | __alloc_pages_direct_compact | __alloc_pages_slowpath | __alloc_pages_nodemask | alloc_pages_vma | do_huge_pmd_anonymous_page | handle_mm_fault | do_page_fault | page_fault | | | |--87.39%-- skb_copy_datagram_iovec | | tcp_recvmsg | | inet_recvmsg | | sock_recvmsg | | sys_recvfrom | | system_call | | __recv | | | | | --100.00%-- (nil) | | | --12.61%-- memcpy --2.70%-- [...] There was other data but primarily it is all showing that compaction is contended heavily on the zone->lock and zone->lru_lock. commit [b2eef8c0: mm: compaction: minimise the time IRQs are disabled while isolating pages for migration] noted that it was possible for migration to hold the lru_lock for an excessive amount of time. Very broadly speaking this patch expands the concept. This patch introduces compact_checklock_irqsave() to check if a lock is contended or the process needs to be scheduled. If either condition is true then async compaction is aborted and the caller is informed. The page allocator will fail a THP allocation if compaction failed due to contention. This patch also introduces compact_trylock_irqsave() which will acquire the lock only if it is not contended and the process does not need to schedule. Reported-by: Jim Schutt <jaschut@sandia.gov> Tested-by: Jim Schutt <jaschut@sandia.gov> Signed-off-by: Mel Gorman <mgorman@suse.de> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2012-08-21 23:16:17 +00:00
static void acct_isolated(struct zone *zone, bool locked, struct compact_control *cc)
{
struct page *page;
unsigned int count[2] = { 0, };
list_for_each_entry(page, &cc->migratepages, lru)
count[!!page_is_file_cache(page)]++;
mm: compaction: Abort async compaction if locks are contended or taking too long Jim Schutt reported a problem that pointed at compaction contending heavily on locks. The workload is straight-forward and in his own words; The systems in question have 24 SAS drives spread across 3 HBAs, running 24 Ceph OSD instances, one per drive. FWIW these servers are dual-socket Intel 5675 Xeons w/48 GB memory. I've got ~160 Ceph Linux clients doing dd simultaneously to a Ceph file system backed by 12 of these servers. Early in the test everything looks fine procs -------------------memory------------------ ---swap-- -----io---- --system-- -----cpu------- r b swpd free buff cache si so bi bo in cs us sy id wa st 31 15 0 287216 576 38606628 0 0 2 1158 2 14 1 3 95 0 0 27 15 0 225288 576 38583384 0 0 18 2222016 203357 134876 11 56 17 15 0 28 17 0 219256 576 38544736 0 0 11 2305932 203141 146296 11 49 23 17 0 6 18 0 215596 576 38552872 0 0 7 2363207 215264 166502 12 45 22 20 0 22 18 0 226984 576 38596404 0 0 3 2445741 223114 179527 12 43 23 22 0 and then it goes to pot procs -------------------memory------------------ ---swap-- -----io---- --system-- -----cpu------- r b swpd free buff cache si so bi bo in cs us sy id wa st 163 8 0 464308 576 36791368 0 0 11 22210 866 536 3 13 79 4 0 207 14 0 917752 576 36181928 0 0 712 1345376 134598 47367 7 90 1 2 0 123 12 0 685516 576 36296148 0 0 429 1386615 158494 60077 8 84 5 3 0 123 12 0 598572 576 36333728 0 0 1107 1233281 147542 62351 7 84 5 4 0 622 7 0 660768 576 36118264 0 0 557 1345548 151394 59353 7 85 4 3 0 223 11 0 283960 576 36463868 0 0 46 1107160 121846 33006 6 93 1 1 0 Note that system CPU usage is very high blocks being written out has dropped by 42%. He analysed this with perf and found perf record -g -a sleep 10 perf report --sort symbol --call-graph fractal,5 34.63% [k] _raw_spin_lock_irqsave | |--97.30%-- isolate_freepages | compaction_alloc | unmap_and_move | migrate_pages | compact_zone | compact_zone_order | try_to_compact_pages | __alloc_pages_direct_compact | __alloc_pages_slowpath | __alloc_pages_nodemask | alloc_pages_vma | do_huge_pmd_anonymous_page | handle_mm_fault | do_page_fault | page_fault | | | |--87.39%-- skb_copy_datagram_iovec | | tcp_recvmsg | | inet_recvmsg | | sock_recvmsg | | sys_recvfrom | | system_call | | __recv | | | | | --100.00%-- (nil) | | | --12.61%-- memcpy --2.70%-- [...] There was other data but primarily it is all showing that compaction is contended heavily on the zone->lock and zone->lru_lock. commit [b2eef8c0: mm: compaction: minimise the time IRQs are disabled while isolating pages for migration] noted that it was possible for migration to hold the lru_lock for an excessive amount of time. Very broadly speaking this patch expands the concept. This patch introduces compact_checklock_irqsave() to check if a lock is contended or the process needs to be scheduled. If either condition is true then async compaction is aborted and the caller is informed. The page allocator will fail a THP allocation if compaction failed due to contention. This patch also introduces compact_trylock_irqsave() which will acquire the lock only if it is not contended and the process does not need to schedule. Reported-by: Jim Schutt <jaschut@sandia.gov> Tested-by: Jim Schutt <jaschut@sandia.gov> Signed-off-by: Mel Gorman <mgorman@suse.de> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2012-08-21 23:16:17 +00:00
/* If locked we can use the interrupt unsafe versions */
if (locked) {
__mod_zone_page_state(zone, NR_ISOLATED_ANON, count[0]);
__mod_zone_page_state(zone, NR_ISOLATED_FILE, count[1]);
} else {
mod_zone_page_state(zone, NR_ISOLATED_ANON, count[0]);
mod_zone_page_state(zone, NR_ISOLATED_FILE, count[1]);
}
}
/* Similar to reclaim, but different enough that they don't share logic */
static bool too_many_isolated(struct zone *zone)
{
unsigned long active, inactive, isolated;
inactive = zone_page_state(zone, NR_INACTIVE_FILE) +
zone_page_state(zone, NR_INACTIVE_ANON);
active = zone_page_state(zone, NR_ACTIVE_FILE) +
zone_page_state(zone, NR_ACTIVE_ANON);
isolated = zone_page_state(zone, NR_ISOLATED_FILE) +
zone_page_state(zone, NR_ISOLATED_ANON);
return isolated > (inactive + active) / 2;
}
/**
* isolate_migratepages_range() - isolate all migrate-able pages in range.
* @zone: Zone pages are in.
* @cc: Compaction control structure.
* @low_pfn: The first PFN of the range.
* @end_pfn: The one-past-the-last PFN of the range.
* @unevictable: true if it allows to isolate unevictable pages
*
* Isolate all pages that can be migrated from the range specified by
* [low_pfn, end_pfn). Returns zero if there is a fatal signal
* pending), otherwise PFN of the first page that was not scanned
* (which may be both less, equal to or more then end_pfn).
*
* Assumes that cc->migratepages is empty and cc->nr_migratepages is
* zero.
*
* Apart from cc->migratepages and cc->nr_migratetypes this function
* does not modify any cc's fields, in particular it does not modify
* (or read for that matter) cc->migrate_pfn.
*/
unsigned long
isolate_migratepages_range(struct zone *zone, struct compact_control *cc,
unsigned long low_pfn, unsigned long end_pfn, bool unevictable)
{
unsigned long last_pageblock_nr = 0, pageblock_nr;
unsigned long nr_scanned = 0, nr_isolated = 0;
struct list_head *migratelist = &cc->migratepages;
isolate_mode_t mode = 0;
struct lruvec *lruvec;
mm: compaction: Abort async compaction if locks are contended or taking too long Jim Schutt reported a problem that pointed at compaction contending heavily on locks. The workload is straight-forward and in his own words; The systems in question have 24 SAS drives spread across 3 HBAs, running 24 Ceph OSD instances, one per drive. FWIW these servers are dual-socket Intel 5675 Xeons w/48 GB memory. I've got ~160 Ceph Linux clients doing dd simultaneously to a Ceph file system backed by 12 of these servers. Early in the test everything looks fine procs -------------------memory------------------ ---swap-- -----io---- --system-- -----cpu------- r b swpd free buff cache si so bi bo in cs us sy id wa st 31 15 0 287216 576 38606628 0 0 2 1158 2 14 1 3 95 0 0 27 15 0 225288 576 38583384 0 0 18 2222016 203357 134876 11 56 17 15 0 28 17 0 219256 576 38544736 0 0 11 2305932 203141 146296 11 49 23 17 0 6 18 0 215596 576 38552872 0 0 7 2363207 215264 166502 12 45 22 20 0 22 18 0 226984 576 38596404 0 0 3 2445741 223114 179527 12 43 23 22 0 and then it goes to pot procs -------------------memory------------------ ---swap-- -----io---- --system-- -----cpu------- r b swpd free buff cache si so bi bo in cs us sy id wa st 163 8 0 464308 576 36791368 0 0 11 22210 866 536 3 13 79 4 0 207 14 0 917752 576 36181928 0 0 712 1345376 134598 47367 7 90 1 2 0 123 12 0 685516 576 36296148 0 0 429 1386615 158494 60077 8 84 5 3 0 123 12 0 598572 576 36333728 0 0 1107 1233281 147542 62351 7 84 5 4 0 622 7 0 660768 576 36118264 0 0 557 1345548 151394 59353 7 85 4 3 0 223 11 0 283960 576 36463868 0 0 46 1107160 121846 33006 6 93 1 1 0 Note that system CPU usage is very high blocks being written out has dropped by 42%. He analysed this with perf and found perf record -g -a sleep 10 perf report --sort symbol --call-graph fractal,5 34.63% [k] _raw_spin_lock_irqsave | |--97.30%-- isolate_freepages | compaction_alloc | unmap_and_move | migrate_pages | compact_zone | compact_zone_order | try_to_compact_pages | __alloc_pages_direct_compact | __alloc_pages_slowpath | __alloc_pages_nodemask | alloc_pages_vma | do_huge_pmd_anonymous_page | handle_mm_fault | do_page_fault | page_fault | | | |--87.39%-- skb_copy_datagram_iovec | | tcp_recvmsg | | inet_recvmsg | | sock_recvmsg | | sys_recvfrom | | system_call | | __recv | | | | | --100.00%-- (nil) | | | --12.61%-- memcpy --2.70%-- [...] There was other data but primarily it is all showing that compaction is contended heavily on the zone->lock and zone->lru_lock. commit [b2eef8c0: mm: compaction: minimise the time IRQs are disabled while isolating pages for migration] noted that it was possible for migration to hold the lru_lock for an excessive amount of time. Very broadly speaking this patch expands the concept. This patch introduces compact_checklock_irqsave() to check if a lock is contended or the process needs to be scheduled. If either condition is true then async compaction is aborted and the caller is informed. The page allocator will fail a THP allocation if compaction failed due to contention. This patch also introduces compact_trylock_irqsave() which will acquire the lock only if it is not contended and the process does not need to schedule. Reported-by: Jim Schutt <jaschut@sandia.gov> Tested-by: Jim Schutt <jaschut@sandia.gov> Signed-off-by: Mel Gorman <mgorman@suse.de> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2012-08-21 23:16:17 +00:00
unsigned long flags;
mm: compaction: acquire the zone->lru_lock as late as possible Richard Davies and Shaohua Li have both reported lock contention problems in compaction on the zone and LRU locks as well as significant amounts of time being spent in compaction. This series aims to reduce lock contention and scanning rates to reduce that CPU usage. Richard reported at https://lkml.org/lkml/2012/9/21/91 that this series made a big different to a problem he reported in August: http://marc.info/?l=kvm&m=134511507015614&w=2 Patch 1 defers acquiring the zone->lru_lock as long as possible. Patch 2 defers acquiring the zone->lock as lock as possible. Patch 3 reverts Rik's "skip-free" patches as the core concept gets reimplemented later and the remaining patches are easier to understand if this is reverted first. Patch 4 adds a pageblock-skip bit to the pageblock flags to cache what pageblocks should be skipped by the migrate and free scanners. This drastically reduces the amount of scanning compaction has to do. Patch 5 reimplements something similar to Rik's idea except it uses the pageblock-skip information to decide where the scanners should restart from and does not need to wrap around. I tested this on 3.6-rc6 + linux-next/akpm. Kernels tested were akpm-20120920 3.6-rc6 + linux-next/akpm as of Septeber 20th, 2012 lesslock Patches 1-6 revert Patches 1-7 cachefail Patches 1-8 skipuseless Patches 1-9 Stress high-order allocation tests looked ok. Success rates are more or less the same with the full series applied but there is an expectation that there is less opportunity to race with other allocation requests if there is less scanning. The time to complete the tests did not vary that much and are uninteresting as were the vmstat statistics so I will not present them here. Using ftrace I recorded how much scanning was done by compaction and got this 3.6.0-rc6 3.6.0-rc6 3.6.0-rc6 3.6.0-rc6 3.6.0-rc6 akpm-20120920 lockless revert-v2r2 cachefail skipuseless Total free scanned 360753976 515414028 565479007 17103281 18916589 Total free isolated 2852429 3597369 4048601 670493 727840 Total free efficiency 0.0079% 0.0070% 0.0072% 0.0392% 0.0385% Total migrate scanned 247728664 822729112 1004645830 17946827 14118903 Total migrate isolated 2555324 3245937 3437501 616359 658616 Total migrate efficiency 0.0103% 0.0039% 0.0034% 0.0343% 0.0466% The efficiency is worthless because of the nature of the test and the number of failures. The really interesting point as far as this patch series is concerned is the number of pages scanned. Note that reverting Rik's patches massively increases the number of pages scanned indicating that those patches really did make a difference to CPU usage. However, caching what pageblocks should be skipped has a much higher impact. With patches 1-8 applied, free page and migrate page scanning are both reduced by 95% in comparison to the akpm kernel. If the basic concept of Rik's patches are implemened on top then scanning then the free scanner barely changed but migrate scanning was further reduced. That said, tests on 3.6-rc5 indicated that the last patch had greater impact than what was measured here so it is a bit variable. One way or the other, this series has a large impact on the amount of scanning compaction does when there is a storm of THP allocations. This patch: Compaction's migrate scanner acquires the zone->lru_lock when scanning a range of pages looking for LRU pages to acquire. It does this even if there are no LRU pages in the range. If multiple processes are compacting then this can cause severe locking contention. To make matters worse commit b2eef8c0 ("mm: compaction: minimise the time IRQs are disabled while isolating pages for migration") releases the lru_lock every SWAP_CLUSTER_MAX pages that are scanned. This patch makes two changes to how the migrate scanner acquires the LRU lock. First, it only releases the LRU lock every SWAP_CLUSTER_MAX pages if the lock is contended. This reduces the number of times it unnecessarily disables and re-enables IRQs. The second is that it defers acquiring the LRU lock for as long as possible. If there are no LRU pages or the only LRU pages are transhuge then the LRU lock will not be acquired at all which reduces contention on zone->lru_lock. [minchan@kernel.org: augment comment] [akpm@linux-foundation.org: tweak comment text] Signed-off-by: Mel Gorman <mgorman@suse.de> Acked-by: Rik van Riel <riel@redhat.com> Cc: Richard Davies <richard@arachsys.com> Cc: Shaohua Li <shli@kernel.org> Cc: Avi Kivity <avi@redhat.com> Acked-by: Rafael Aquini <aquini@redhat.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2012-10-08 23:32:33 +00:00
bool locked = false;
mm: compaction: cache if a pageblock was scanned and no pages were isolated When compaction was implemented it was known that scanning could potentially be excessive. The ideal was that a counter be maintained for each pageblock but maintaining this information would incur a severe penalty due to a shared writable cache line. It has reached the point where the scanning costs are a serious problem, particularly on long-lived systems where a large process starts and allocates a large number of THPs at the same time. Instead of using a shared counter, this patch adds another bit to the pageblock flags called PG_migrate_skip. If a pageblock is scanned by either migrate or free scanner and 0 pages were isolated, the pageblock is marked to be skipped in the future. When scanning, this bit is checked before any scanning takes place and the block skipped if set. The main difficulty with a patch like this is "when to ignore the cached information?" If it's ignored too often, the scanning rates will still be excessive. If the information is too stale then allocations will fail that might have otherwise succeeded. In this patch o CMA always ignores the information o If the migrate and free scanner meet then the cached information will be discarded if it's at least 5 seconds since the last time the cache was discarded o If there are a large number of allocation failures, discard the cache. The time-based heuristic is very clumsy but there are few choices for a better event. Depending solely on multiple allocation failures still allows excessive scanning when THP allocations are failing in quick succession due to memory pressure. Waiting until memory pressure is relieved would cause compaction to continually fail instead of using reclaim/compaction to try allocate the page. The time-based mechanism is clumsy but a better option is not obvious. Signed-off-by: Mel Gorman <mgorman@suse.de> Acked-by: Rik van Riel <riel@redhat.com> Cc: Richard Davies <richard@arachsys.com> Cc: Shaohua Li <shli@kernel.org> Cc: Avi Kivity <avi@redhat.com> Acked-by: Rafael Aquini <aquini@redhat.com> Cc: Fengguang Wu <fengguang.wu@intel.com> Cc: Michal Nazarewicz <mina86@mina86.com> Cc: Bartlomiej Zolnierkiewicz <b.zolnierkie@samsung.com> Cc: Kyungmin Park <kyungmin.park@samsung.com> Cc: Mark Brown <broonie@opensource.wolfsonmicro.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2012-10-08 23:32:41 +00:00
struct page *page = NULL, *valid_page = NULL;
/*
* Ensure that there are not too many pages isolated from the LRU
* list by either parallel reclaimers or compaction. If there are,
* delay for some time until fewer pages are isolated
*/
while (unlikely(too_many_isolated(zone))) {
/* async migration should just abort */
if (!cc->sync)
return 0;
congestion_wait(BLK_RW_ASYNC, HZ/10);
if (fatal_signal_pending(current))
return 0;
}
/* Time to isolate some pages for migration */
mm: compaction: minimise the time IRQs are disabled while isolating pages for migration compaction_alloc() isolates pages for migration in isolate_migratepages. While it's scanning, IRQs are disabled on the mistaken assumption the scanning should be short. Tests show this to be true for the most part but contention times on the LRU lock can be increased. Before this patch, the IRQ disabled times for a simple test looked like Total sampled time IRQs off (not real total time): 5493 Event shrink_inactive_list..shrink_zone 1596 us count 1 Event shrink_inactive_list..shrink_zone 1530 us count 1 Event shrink_inactive_list..shrink_zone 956 us count 1 Event shrink_inactive_list..shrink_zone 541 us count 1 Event shrink_inactive_list..shrink_zone 531 us count 1 Event split_huge_page..add_to_swap 232 us count 1 Event save_args..call_softirq 36 us count 1 Event save_args..call_softirq 35 us count 2 Event __wake_up..__wake_up 1 us count 1 This patch reduces the worst-case IRQs-disabled latencies by releasing the lock every SWAP_CLUSTER_MAX pages that are scanned and releasing the CPU if necessary. The cost of this is that the processing performing compaction will be slower but IRQs being disabled for too long a time has worse consequences as the following report shows; Total sampled time IRQs off (not real total time): 4367 Event shrink_inactive_list..shrink_zone 881 us count 1 Event shrink_inactive_list..shrink_zone 875 us count 1 Event shrink_inactive_list..shrink_zone 868 us count 1 Event shrink_inactive_list..shrink_zone 555 us count 1 Event split_huge_page..add_to_swap 495 us count 1 Event compact_zone..compact_zone_order 269 us count 1 Event split_huge_page..add_to_swap 266 us count 1 Event shrink_inactive_list..shrink_zone 85 us count 1 Event save_args..call_softirq 36 us count 2 Event __wake_up..__wake_up 1 us count 1 [akpm@linux-foundation.org: simplify with s/unlocked/locked/] Signed-off-by: Andrea Arcangeli <aarcange@redhat.com> Signed-off-by: Mel Gorman <mel@csn.ul.ie> Cc: Johannes Weiner <hannes@cmpxchg.org> Cc: Arthur Marsh <arthur.marsh@internode.on.net> Cc: Clemens Ladisch <cladisch@googlemail.com> Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com> Cc: Minchan Kim <minchan.kim@gmail.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2011-03-22 23:33:10 +00:00
cond_resched();
for (; low_pfn < end_pfn; low_pfn++) {
mm: compaction: minimise the time IRQs are disabled while isolating pages for migration compaction_alloc() isolates pages for migration in isolate_migratepages. While it's scanning, IRQs are disabled on the mistaken assumption the scanning should be short. Tests show this to be true for the most part but contention times on the LRU lock can be increased. Before this patch, the IRQ disabled times for a simple test looked like Total sampled time IRQs off (not real total time): 5493 Event shrink_inactive_list..shrink_zone 1596 us count 1 Event shrink_inactive_list..shrink_zone 1530 us count 1 Event shrink_inactive_list..shrink_zone 956 us count 1 Event shrink_inactive_list..shrink_zone 541 us count 1 Event shrink_inactive_list..shrink_zone 531 us count 1 Event split_huge_page..add_to_swap 232 us count 1 Event save_args..call_softirq 36 us count 1 Event save_args..call_softirq 35 us count 2 Event __wake_up..__wake_up 1 us count 1 This patch reduces the worst-case IRQs-disabled latencies by releasing the lock every SWAP_CLUSTER_MAX pages that are scanned and releasing the CPU if necessary. The cost of this is that the processing performing compaction will be slower but IRQs being disabled for too long a time has worse consequences as the following report shows; Total sampled time IRQs off (not real total time): 4367 Event shrink_inactive_list..shrink_zone 881 us count 1 Event shrink_inactive_list..shrink_zone 875 us count 1 Event shrink_inactive_list..shrink_zone 868 us count 1 Event shrink_inactive_list..shrink_zone 555 us count 1 Event split_huge_page..add_to_swap 495 us count 1 Event compact_zone..compact_zone_order 269 us count 1 Event split_huge_page..add_to_swap 266 us count 1 Event shrink_inactive_list..shrink_zone 85 us count 1 Event save_args..call_softirq 36 us count 2 Event __wake_up..__wake_up 1 us count 1 [akpm@linux-foundation.org: simplify with s/unlocked/locked/] Signed-off-by: Andrea Arcangeli <aarcange@redhat.com> Signed-off-by: Mel Gorman <mel@csn.ul.ie> Cc: Johannes Weiner <hannes@cmpxchg.org> Cc: Arthur Marsh <arthur.marsh@internode.on.net> Cc: Clemens Ladisch <cladisch@googlemail.com> Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com> Cc: Minchan Kim <minchan.kim@gmail.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2011-03-22 23:33:10 +00:00
/* give a chance to irqs before checking need_resched() */
mm: compaction: acquire the zone->lru_lock as late as possible Richard Davies and Shaohua Li have both reported lock contention problems in compaction on the zone and LRU locks as well as significant amounts of time being spent in compaction. This series aims to reduce lock contention and scanning rates to reduce that CPU usage. Richard reported at https://lkml.org/lkml/2012/9/21/91 that this series made a big different to a problem he reported in August: http://marc.info/?l=kvm&m=134511507015614&w=2 Patch 1 defers acquiring the zone->lru_lock as long as possible. Patch 2 defers acquiring the zone->lock as lock as possible. Patch 3 reverts Rik's "skip-free" patches as the core concept gets reimplemented later and the remaining patches are easier to understand if this is reverted first. Patch 4 adds a pageblock-skip bit to the pageblock flags to cache what pageblocks should be skipped by the migrate and free scanners. This drastically reduces the amount of scanning compaction has to do. Patch 5 reimplements something similar to Rik's idea except it uses the pageblock-skip information to decide where the scanners should restart from and does not need to wrap around. I tested this on 3.6-rc6 + linux-next/akpm. Kernels tested were akpm-20120920 3.6-rc6 + linux-next/akpm as of Septeber 20th, 2012 lesslock Patches 1-6 revert Patches 1-7 cachefail Patches 1-8 skipuseless Patches 1-9 Stress high-order allocation tests looked ok. Success rates are more or less the same with the full series applied but there is an expectation that there is less opportunity to race with other allocation requests if there is less scanning. The time to complete the tests did not vary that much and are uninteresting as were the vmstat statistics so I will not present them here. Using ftrace I recorded how much scanning was done by compaction and got this 3.6.0-rc6 3.6.0-rc6 3.6.0-rc6 3.6.0-rc6 3.6.0-rc6 akpm-20120920 lockless revert-v2r2 cachefail skipuseless Total free scanned 360753976 515414028 565479007 17103281 18916589 Total free isolated 2852429 3597369 4048601 670493 727840 Total free efficiency 0.0079% 0.0070% 0.0072% 0.0392% 0.0385% Total migrate scanned 247728664 822729112 1004645830 17946827 14118903 Total migrate isolated 2555324 3245937 3437501 616359 658616 Total migrate efficiency 0.0103% 0.0039% 0.0034% 0.0343% 0.0466% The efficiency is worthless because of the nature of the test and the number of failures. The really interesting point as far as this patch series is concerned is the number of pages scanned. Note that reverting Rik's patches massively increases the number of pages scanned indicating that those patches really did make a difference to CPU usage. However, caching what pageblocks should be skipped has a much higher impact. With patches 1-8 applied, free page and migrate page scanning are both reduced by 95% in comparison to the akpm kernel. If the basic concept of Rik's patches are implemened on top then scanning then the free scanner barely changed but migrate scanning was further reduced. That said, tests on 3.6-rc5 indicated that the last patch had greater impact than what was measured here so it is a bit variable. One way or the other, this series has a large impact on the amount of scanning compaction does when there is a storm of THP allocations. This patch: Compaction's migrate scanner acquires the zone->lru_lock when scanning a range of pages looking for LRU pages to acquire. It does this even if there are no LRU pages in the range. If multiple processes are compacting then this can cause severe locking contention. To make matters worse commit b2eef8c0 ("mm: compaction: minimise the time IRQs are disabled while isolating pages for migration") releases the lru_lock every SWAP_CLUSTER_MAX pages that are scanned. This patch makes two changes to how the migrate scanner acquires the LRU lock. First, it only releases the LRU lock every SWAP_CLUSTER_MAX pages if the lock is contended. This reduces the number of times it unnecessarily disables and re-enables IRQs. The second is that it defers acquiring the LRU lock for as long as possible. If there are no LRU pages or the only LRU pages are transhuge then the LRU lock will not be acquired at all which reduces contention on zone->lru_lock. [minchan@kernel.org: augment comment] [akpm@linux-foundation.org: tweak comment text] Signed-off-by: Mel Gorman <mgorman@suse.de> Acked-by: Rik van Riel <riel@redhat.com> Cc: Richard Davies <richard@arachsys.com> Cc: Shaohua Li <shli@kernel.org> Cc: Avi Kivity <avi@redhat.com> Acked-by: Rafael Aquini <aquini@redhat.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2012-10-08 23:32:33 +00:00
if (locked && !((low_pfn+1) % SWAP_CLUSTER_MAX)) {
if (should_release_lock(&zone->lru_lock)) {
spin_unlock_irqrestore(&zone->lru_lock, flags);
locked = false;
}
mm: compaction: minimise the time IRQs are disabled while isolating pages for migration compaction_alloc() isolates pages for migration in isolate_migratepages. While it's scanning, IRQs are disabled on the mistaken assumption the scanning should be short. Tests show this to be true for the most part but contention times on the LRU lock can be increased. Before this patch, the IRQ disabled times for a simple test looked like Total sampled time IRQs off (not real total time): 5493 Event shrink_inactive_list..shrink_zone 1596 us count 1 Event shrink_inactive_list..shrink_zone 1530 us count 1 Event shrink_inactive_list..shrink_zone 956 us count 1 Event shrink_inactive_list..shrink_zone 541 us count 1 Event shrink_inactive_list..shrink_zone 531 us count 1 Event split_huge_page..add_to_swap 232 us count 1 Event save_args..call_softirq 36 us count 1 Event save_args..call_softirq 35 us count 2 Event __wake_up..__wake_up 1 us count 1 This patch reduces the worst-case IRQs-disabled latencies by releasing the lock every SWAP_CLUSTER_MAX pages that are scanned and releasing the CPU if necessary. The cost of this is that the processing performing compaction will be slower but IRQs being disabled for too long a time has worse consequences as the following report shows; Total sampled time IRQs off (not real total time): 4367 Event shrink_inactive_list..shrink_zone 881 us count 1 Event shrink_inactive_list..shrink_zone 875 us count 1 Event shrink_inactive_list..shrink_zone 868 us count 1 Event shrink_inactive_list..shrink_zone 555 us count 1 Event split_huge_page..add_to_swap 495 us count 1 Event compact_zone..compact_zone_order 269 us count 1 Event split_huge_page..add_to_swap 266 us count 1 Event shrink_inactive_list..shrink_zone 85 us count 1 Event save_args..call_softirq 36 us count 2 Event __wake_up..__wake_up 1 us count 1 [akpm@linux-foundation.org: simplify with s/unlocked/locked/] Signed-off-by: Andrea Arcangeli <aarcange@redhat.com> Signed-off-by: Mel Gorman <mel@csn.ul.ie> Cc: Johannes Weiner <hannes@cmpxchg.org> Cc: Arthur Marsh <arthur.marsh@internode.on.net> Cc: Clemens Ladisch <cladisch@googlemail.com> Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com> Cc: Minchan Kim <minchan.kim@gmail.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2011-03-22 23:33:10 +00:00
}
mm: compaction: Abort async compaction if locks are contended or taking too long Jim Schutt reported a problem that pointed at compaction contending heavily on locks. The workload is straight-forward and in his own words; The systems in question have 24 SAS drives spread across 3 HBAs, running 24 Ceph OSD instances, one per drive. FWIW these servers are dual-socket Intel 5675 Xeons w/48 GB memory. I've got ~160 Ceph Linux clients doing dd simultaneously to a Ceph file system backed by 12 of these servers. Early in the test everything looks fine procs -------------------memory------------------ ---swap-- -----io---- --system-- -----cpu------- r b swpd free buff cache si so bi bo in cs us sy id wa st 31 15 0 287216 576 38606628 0 0 2 1158 2 14 1 3 95 0 0 27 15 0 225288 576 38583384 0 0 18 2222016 203357 134876 11 56 17 15 0 28 17 0 219256 576 38544736 0 0 11 2305932 203141 146296 11 49 23 17 0 6 18 0 215596 576 38552872 0 0 7 2363207 215264 166502 12 45 22 20 0 22 18 0 226984 576 38596404 0 0 3 2445741 223114 179527 12 43 23 22 0 and then it goes to pot procs -------------------memory------------------ ---swap-- -----io---- --system-- -----cpu------- r b swpd free buff cache si so bi bo in cs us sy id wa st 163 8 0 464308 576 36791368 0 0 11 22210 866 536 3 13 79 4 0 207 14 0 917752 576 36181928 0 0 712 1345376 134598 47367 7 90 1 2 0 123 12 0 685516 576 36296148 0 0 429 1386615 158494 60077 8 84 5 3 0 123 12 0 598572 576 36333728 0 0 1107 1233281 147542 62351 7 84 5 4 0 622 7 0 660768 576 36118264 0 0 557 1345548 151394 59353 7 85 4 3 0 223 11 0 283960 576 36463868 0 0 46 1107160 121846 33006 6 93 1 1 0 Note that system CPU usage is very high blocks being written out has dropped by 42%. He analysed this with perf and found perf record -g -a sleep 10 perf report --sort symbol --call-graph fractal,5 34.63% [k] _raw_spin_lock_irqsave | |--97.30%-- isolate_freepages | compaction_alloc | unmap_and_move | migrate_pages | compact_zone | compact_zone_order | try_to_compact_pages | __alloc_pages_direct_compact | __alloc_pages_slowpath | __alloc_pages_nodemask | alloc_pages_vma | do_huge_pmd_anonymous_page | handle_mm_fault | do_page_fault | page_fault | | | |--87.39%-- skb_copy_datagram_iovec | | tcp_recvmsg | | inet_recvmsg | | sock_recvmsg | | sys_recvfrom | | system_call | | __recv | | | | | --100.00%-- (nil) | | | --12.61%-- memcpy --2.70%-- [...] There was other data but primarily it is all showing that compaction is contended heavily on the zone->lock and zone->lru_lock. commit [b2eef8c0: mm: compaction: minimise the time IRQs are disabled while isolating pages for migration] noted that it was possible for migration to hold the lru_lock for an excessive amount of time. Very broadly speaking this patch expands the concept. This patch introduces compact_checklock_irqsave() to check if a lock is contended or the process needs to be scheduled. If either condition is true then async compaction is aborted and the caller is informed. The page allocator will fail a THP allocation if compaction failed due to contention. This patch also introduces compact_trylock_irqsave() which will acquire the lock only if it is not contended and the process does not need to schedule. Reported-by: Jim Schutt <jaschut@sandia.gov> Tested-by: Jim Schutt <jaschut@sandia.gov> Signed-off-by: Mel Gorman <mgorman@suse.de> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2012-08-21 23:16:17 +00:00
mm: compaction: check pfn_valid when entering a new MAX_ORDER_NR_PAGES block during isolation for migration When isolating for migration, migration starts at the start of a zone which is not necessarily pageblock aligned. Further, it stops isolating when COMPACT_CLUSTER_MAX pages are isolated so migrate_pfn is generally not aligned. This allows isolate_migratepages() to call pfn_to_page() on an invalid PFN which can result in a crash. This was originally reported against a 3.0-based kernel with the following trace in a crash dump. PID: 9902 TASK: d47aecd0 CPU: 0 COMMAND: "memcg_process_s" #0 [d72d3ad0] crash_kexec at c028cfdb #1 [d72d3b24] oops_end at c05c5322 #2 [d72d3b38] __bad_area_nosemaphore at c0227e60 #3 [d72d3bec] bad_area at c0227fb6 #4 [d72d3c00] do_page_fault at c05c72ec #5 [d72d3c80] error_code (via page_fault) at c05c47a4 EAX: 00000000 EBX: 000c0000 ECX: 00000001 EDX: 00000807 EBP: 000c0000 DS: 007b ESI: 00000001 ES: 007b EDI: f3000a80 GS: 6f50 CS: 0060 EIP: c030b15a ERR: ffffffff EFLAGS: 00010002 #6 [d72d3cb4] isolate_migratepages at c030b15a #7 [d72d3d14] zone_watermark_ok at c02d26cb #8 [d72d3d2c] compact_zone at c030b8de #9 [d72d3d68] compact_zone_order at c030bba1 #10 [d72d3db4] try_to_compact_pages at c030bc84 #11 [d72d3ddc] __alloc_pages_direct_compact at c02d61e7 #12 [d72d3e08] __alloc_pages_slowpath at c02d66c7 #13 [d72d3e78] __alloc_pages_nodemask at c02d6a97 #14 [d72d3eb8] alloc_pages_vma at c030a845 #15 [d72d3ed4] do_huge_pmd_anonymous_page at c03178eb #16 [d72d3f00] handle_mm_fault at c02f36c6 #17 [d72d3f30] do_page_fault at c05c70ed #18 [d72d3fb0] error_code (via page_fault) at c05c47a4 EAX: b71ff000 EBX: 00000001 ECX: 00001600 EDX: 00000431 DS: 007b ESI: 08048950 ES: 007b EDI: bfaa3788 SS: 007b ESP: bfaa36e0 EBP: bfaa3828 GS: 6f50 CS: 0073 EIP: 080487c8 ERR: ffffffff EFLAGS: 00010202 It was also reported by Herbert van den Bergh against 3.1-based kernel with the following snippet from the console log. BUG: unable to handle kernel paging request at 01c00008 IP: [<c0522399>] isolate_migratepages+0x119/0x390 *pdpt = 000000002f7ce001 *pde = 0000000000000000 It is expected that it also affects 3.2.x and current mainline. The problem is that pfn_valid is only called on the first PFN being checked and that PFN is not necessarily aligned. Lets say we have a case like this H = MAX_ORDER_NR_PAGES boundary | = pageblock boundary m = cc->migrate_pfn f = cc->free_pfn o = memory hole H------|------H------|----m-Hoooooo|ooooooH-f----|------H The migrate_pfn is just below a memory hole and the free scanner is beyond the hole. When isolate_migratepages started, it scans from migrate_pfn to migrate_pfn+pageblock_nr_pages which is now in a memory hole. It checks pfn_valid() on the first PFN but then scans into the hole where there are not necessarily valid struct pages. This patch ensures that isolate_migratepages calls pfn_valid when necessary. Reported-by: Herbert van den Bergh <herbert.van.den.bergh@oracle.com> Tested-by: Herbert van den Bergh <herbert.van.den.bergh@oracle.com> Signed-off-by: Mel Gorman <mgorman@suse.de> Acked-by: Michal Nazarewicz <mina86@mina86.com> Cc: <stable@vger.kernel.org> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2012-02-03 23:37:18 +00:00
/*
* migrate_pfn does not necessarily start aligned to a
* pageblock. Ensure that pfn_valid is called when moving
* into a new MAX_ORDER_NR_PAGES range in case of large
* memory holes within the zone
*/
if ((low_pfn & (MAX_ORDER_NR_PAGES - 1)) == 0) {
if (!pfn_valid(low_pfn)) {
low_pfn += MAX_ORDER_NR_PAGES - 1;
continue;
}
}
if (!pfn_valid_within(low_pfn))
continue;
nr_scanned++;
mm: compaction: check for overlapping nodes during isolation for migration When isolating pages for migration, migration starts at the start of a zone while the free scanner starts at the end of the zone. Migration avoids entering a new zone by never going beyond the free scanned. Unfortunately, in very rare cases nodes can overlap. When this happens, migration isolates pages without the LRU lock held, corrupting lists which will trigger errors in reclaim or during page free such as in the following oops BUG: unable to handle kernel NULL pointer dereference at 0000000000000008 IP: [<ffffffff810f795c>] free_pcppages_bulk+0xcc/0x450 PGD 1dda554067 PUD 1e1cb58067 PMD 0 Oops: 0000 [#1] SMP CPU 37 Pid: 17088, comm: memcg_process_s Tainted: G X RIP: free_pcppages_bulk+0xcc/0x450 Process memcg_process_s (pid: 17088, threadinfo ffff881c2926e000, task ffff881c2926c0c0) Call Trace: free_hot_cold_page+0x17e/0x1f0 __pagevec_free+0x90/0xb0 release_pages+0x22a/0x260 pagevec_lru_move_fn+0xf3/0x110 putback_lru_page+0x66/0xe0 unmap_and_move+0x156/0x180 migrate_pages+0x9e/0x1b0 compact_zone+0x1f3/0x2f0 compact_zone_order+0xa2/0xe0 try_to_compact_pages+0xdf/0x110 __alloc_pages_direct_compact+0xee/0x1c0 __alloc_pages_slowpath+0x370/0x830 __alloc_pages_nodemask+0x1b1/0x1c0 alloc_pages_vma+0x9b/0x160 do_huge_pmd_anonymous_page+0x160/0x270 do_page_fault+0x207/0x4c0 page_fault+0x25/0x30 The "X" in the taint flag means that external modules were loaded but but is unrelated to the bug triggering. The real problem was because the PFN layout looks like this Zone PFN ranges: DMA 0x00000010 -> 0x00001000 DMA32 0x00001000 -> 0x00100000 Normal 0x00100000 -> 0x01e80000 Movable zone start PFN for each node early_node_map[14] active PFN ranges 0: 0x00000010 -> 0x0000009b 0: 0x00000100 -> 0x0007a1ec 0: 0x0007a354 -> 0x0007a379 0: 0x0007f7ff -> 0x0007f800 0: 0x00100000 -> 0x00680000 1: 0x00680000 -> 0x00e80000 0: 0x00e80000 -> 0x01080000 1: 0x01080000 -> 0x01280000 0: 0x01280000 -> 0x01480000 1: 0x01480000 -> 0x01680000 0: 0x01680000 -> 0x01880000 1: 0x01880000 -> 0x01a80000 0: 0x01a80000 -> 0x01c80000 1: 0x01c80000 -> 0x01e80000 The fix is straight-forward. isolate_migratepages() has to make a similar check to isolate_freepage to ensure that it never isolates pages from a zone it does not hold the LRU lock for. This was discovered in a 3.0-based kernel but it affects 3.1.x, 3.2.x and current mainline. Signed-off-by: Mel Gorman <mgorman@suse.de> Acked-by: Michal Nazarewicz <mina86@mina86.com> Cc: <stable@vger.kernel.org> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2012-02-09 01:13:38 +00:00
/*
* Get the page and ensure the page is within the same zone.
* See the comment in isolate_freepages about overlapping
* nodes. It is deliberate that the new zone lock is not taken
* as memory compaction should not move pages between nodes.
*/
page = pfn_to_page(low_pfn);
mm: compaction: check for overlapping nodes during isolation for migration When isolating pages for migration, migration starts at the start of a zone while the free scanner starts at the end of the zone. Migration avoids entering a new zone by never going beyond the free scanned. Unfortunately, in very rare cases nodes can overlap. When this happens, migration isolates pages without the LRU lock held, corrupting lists which will trigger errors in reclaim or during page free such as in the following oops BUG: unable to handle kernel NULL pointer dereference at 0000000000000008 IP: [<ffffffff810f795c>] free_pcppages_bulk+0xcc/0x450 PGD 1dda554067 PUD 1e1cb58067 PMD 0 Oops: 0000 [#1] SMP CPU 37 Pid: 17088, comm: memcg_process_s Tainted: G X RIP: free_pcppages_bulk+0xcc/0x450 Process memcg_process_s (pid: 17088, threadinfo ffff881c2926e000, task ffff881c2926c0c0) Call Trace: free_hot_cold_page+0x17e/0x1f0 __pagevec_free+0x90/0xb0 release_pages+0x22a/0x260 pagevec_lru_move_fn+0xf3/0x110 putback_lru_page+0x66/0xe0 unmap_and_move+0x156/0x180 migrate_pages+0x9e/0x1b0 compact_zone+0x1f3/0x2f0 compact_zone_order+0xa2/0xe0 try_to_compact_pages+0xdf/0x110 __alloc_pages_direct_compact+0xee/0x1c0 __alloc_pages_slowpath+0x370/0x830 __alloc_pages_nodemask+0x1b1/0x1c0 alloc_pages_vma+0x9b/0x160 do_huge_pmd_anonymous_page+0x160/0x270 do_page_fault+0x207/0x4c0 page_fault+0x25/0x30 The "X" in the taint flag means that external modules were loaded but but is unrelated to the bug triggering. The real problem was because the PFN layout looks like this Zone PFN ranges: DMA 0x00000010 -> 0x00001000 DMA32 0x00001000 -> 0x00100000 Normal 0x00100000 -> 0x01e80000 Movable zone start PFN for each node early_node_map[14] active PFN ranges 0: 0x00000010 -> 0x0000009b 0: 0x00000100 -> 0x0007a1ec 0: 0x0007a354 -> 0x0007a379 0: 0x0007f7ff -> 0x0007f800 0: 0x00100000 -> 0x00680000 1: 0x00680000 -> 0x00e80000 0: 0x00e80000 -> 0x01080000 1: 0x01080000 -> 0x01280000 0: 0x01280000 -> 0x01480000 1: 0x01480000 -> 0x01680000 0: 0x01680000 -> 0x01880000 1: 0x01880000 -> 0x01a80000 0: 0x01a80000 -> 0x01c80000 1: 0x01c80000 -> 0x01e80000 The fix is straight-forward. isolate_migratepages() has to make a similar check to isolate_freepage to ensure that it never isolates pages from a zone it does not hold the LRU lock for. This was discovered in a 3.0-based kernel but it affects 3.1.x, 3.2.x and current mainline. Signed-off-by: Mel Gorman <mgorman@suse.de> Acked-by: Michal Nazarewicz <mina86@mina86.com> Cc: <stable@vger.kernel.org> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2012-02-09 01:13:38 +00:00
if (page_zone(page) != zone)
continue;
mm: compaction: cache if a pageblock was scanned and no pages were isolated When compaction was implemented it was known that scanning could potentially be excessive. The ideal was that a counter be maintained for each pageblock but maintaining this information would incur a severe penalty due to a shared writable cache line. It has reached the point where the scanning costs are a serious problem, particularly on long-lived systems where a large process starts and allocates a large number of THPs at the same time. Instead of using a shared counter, this patch adds another bit to the pageblock flags called PG_migrate_skip. If a pageblock is scanned by either migrate or free scanner and 0 pages were isolated, the pageblock is marked to be skipped in the future. When scanning, this bit is checked before any scanning takes place and the block skipped if set. The main difficulty with a patch like this is "when to ignore the cached information?" If it's ignored too often, the scanning rates will still be excessive. If the information is too stale then allocations will fail that might have otherwise succeeded. In this patch o CMA always ignores the information o If the migrate and free scanner meet then the cached information will be discarded if it's at least 5 seconds since the last time the cache was discarded o If there are a large number of allocation failures, discard the cache. The time-based heuristic is very clumsy but there are few choices for a better event. Depending solely on multiple allocation failures still allows excessive scanning when THP allocations are failing in quick succession due to memory pressure. Waiting until memory pressure is relieved would cause compaction to continually fail instead of using reclaim/compaction to try allocate the page. The time-based mechanism is clumsy but a better option is not obvious. Signed-off-by: Mel Gorman <mgorman@suse.de> Acked-by: Rik van Riel <riel@redhat.com> Cc: Richard Davies <richard@arachsys.com> Cc: Shaohua Li <shli@kernel.org> Cc: Avi Kivity <avi@redhat.com> Acked-by: Rafael Aquini <aquini@redhat.com> Cc: Fengguang Wu <fengguang.wu@intel.com> Cc: Michal Nazarewicz <mina86@mina86.com> Cc: Bartlomiej Zolnierkiewicz <b.zolnierkie@samsung.com> Cc: Kyungmin Park <kyungmin.park@samsung.com> Cc: Mark Brown <broonie@opensource.wolfsonmicro.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2012-10-08 23:32:41 +00:00
if (!valid_page)
valid_page = page;
/* If isolation recently failed, do not retry */
pageblock_nr = low_pfn >> pageblock_order;
if (!isolation_suitable(cc, page))
goto next_pageblock;
mm: compaction: check for overlapping nodes during isolation for migration When isolating pages for migration, migration starts at the start of a zone while the free scanner starts at the end of the zone. Migration avoids entering a new zone by never going beyond the free scanned. Unfortunately, in very rare cases nodes can overlap. When this happens, migration isolates pages without the LRU lock held, corrupting lists which will trigger errors in reclaim or during page free such as in the following oops BUG: unable to handle kernel NULL pointer dereference at 0000000000000008 IP: [<ffffffff810f795c>] free_pcppages_bulk+0xcc/0x450 PGD 1dda554067 PUD 1e1cb58067 PMD 0 Oops: 0000 [#1] SMP CPU 37 Pid: 17088, comm: memcg_process_s Tainted: G X RIP: free_pcppages_bulk+0xcc/0x450 Process memcg_process_s (pid: 17088, threadinfo ffff881c2926e000, task ffff881c2926c0c0) Call Trace: free_hot_cold_page+0x17e/0x1f0 __pagevec_free+0x90/0xb0 release_pages+0x22a/0x260 pagevec_lru_move_fn+0xf3/0x110 putback_lru_page+0x66/0xe0 unmap_and_move+0x156/0x180 migrate_pages+0x9e/0x1b0 compact_zone+0x1f3/0x2f0 compact_zone_order+0xa2/0xe0 try_to_compact_pages+0xdf/0x110 __alloc_pages_direct_compact+0xee/0x1c0 __alloc_pages_slowpath+0x370/0x830 __alloc_pages_nodemask+0x1b1/0x1c0 alloc_pages_vma+0x9b/0x160 do_huge_pmd_anonymous_page+0x160/0x270 do_page_fault+0x207/0x4c0 page_fault+0x25/0x30 The "X" in the taint flag means that external modules were loaded but but is unrelated to the bug triggering. The real problem was because the PFN layout looks like this Zone PFN ranges: DMA 0x00000010 -> 0x00001000 DMA32 0x00001000 -> 0x00100000 Normal 0x00100000 -> 0x01e80000 Movable zone start PFN for each node early_node_map[14] active PFN ranges 0: 0x00000010 -> 0x0000009b 0: 0x00000100 -> 0x0007a1ec 0: 0x0007a354 -> 0x0007a379 0: 0x0007f7ff -> 0x0007f800 0: 0x00100000 -> 0x00680000 1: 0x00680000 -> 0x00e80000 0: 0x00e80000 -> 0x01080000 1: 0x01080000 -> 0x01280000 0: 0x01280000 -> 0x01480000 1: 0x01480000 -> 0x01680000 0: 0x01680000 -> 0x01880000 1: 0x01880000 -> 0x01a80000 0: 0x01a80000 -> 0x01c80000 1: 0x01c80000 -> 0x01e80000 The fix is straight-forward. isolate_migratepages() has to make a similar check to isolate_freepage to ensure that it never isolates pages from a zone it does not hold the LRU lock for. This was discovered in a 3.0-based kernel but it affects 3.1.x, 3.2.x and current mainline. Signed-off-by: Mel Gorman <mgorman@suse.de> Acked-by: Michal Nazarewicz <mina86@mina86.com> Cc: <stable@vger.kernel.org> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2012-02-09 01:13:38 +00:00
/* Skip if free */
if (PageBuddy(page))
continue;
/*
* For async migration, also only scan in MOVABLE blocks. Async
* migration is optimistic to see if the minimum amount of work
* satisfies the allocation
*/
if (!cc->sync && last_pageblock_nr != pageblock_nr &&
!migrate_async_suitable(get_pageblock_migratetype(page))) {
mm: compaction: Restart compaction from near where it left off This is almost entirely based on Rik's previous patches and discussions with him about how this might be implemented. Order > 0 compaction stops when enough free pages of the correct page order have been coalesced. When doing subsequent higher order allocations, it is possible for compaction to be invoked many times. However, the compaction code always starts out looking for things to compact at the start of the zone, and for free pages to compact things to at the end of the zone. This can cause quadratic behaviour, with isolate_freepages starting at the end of the zone each time, even though previous invocations of the compaction code already filled up all free memory on that end of the zone. This can cause isolate_freepages to take enormous amounts of CPU with certain workloads on larger memory systems. This patch caches where the migration and free scanner should start from on subsequent compaction invocations using the pageblock-skip information. When compaction starts it begins from the cached restart points and will update the cached restart points until a page is isolated or a pageblock is skipped that would have been scanned by synchronous compaction. Signed-off-by: Mel Gorman <mgorman@suse.de> Acked-by: Rik van Riel <riel@redhat.com> Cc: Richard Davies <richard@arachsys.com> Cc: Shaohua Li <shli@kernel.org> Cc: Avi Kivity <avi@redhat.com> Acked-by: Rafael Aquini <aquini@redhat.com> Cc: Fengguang Wu <fengguang.wu@intel.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2012-10-08 23:32:45 +00:00
cc->finished_update_migrate = true;
mm: compaction: acquire the zone->lru_lock as late as possible Richard Davies and Shaohua Li have both reported lock contention problems in compaction on the zone and LRU locks as well as significant amounts of time being spent in compaction. This series aims to reduce lock contention and scanning rates to reduce that CPU usage. Richard reported at https://lkml.org/lkml/2012/9/21/91 that this series made a big different to a problem he reported in August: http://marc.info/?l=kvm&m=134511507015614&w=2 Patch 1 defers acquiring the zone->lru_lock as long as possible. Patch 2 defers acquiring the zone->lock as lock as possible. Patch 3 reverts Rik's "skip-free" patches as the core concept gets reimplemented later and the remaining patches are easier to understand if this is reverted first. Patch 4 adds a pageblock-skip bit to the pageblock flags to cache what pageblocks should be skipped by the migrate and free scanners. This drastically reduces the amount of scanning compaction has to do. Patch 5 reimplements something similar to Rik's idea except it uses the pageblock-skip information to decide where the scanners should restart from and does not need to wrap around. I tested this on 3.6-rc6 + linux-next/akpm. Kernels tested were akpm-20120920 3.6-rc6 + linux-next/akpm as of Septeber 20th, 2012 lesslock Patches 1-6 revert Patches 1-7 cachefail Patches 1-8 skipuseless Patches 1-9 Stress high-order allocation tests looked ok. Success rates are more or less the same with the full series applied but there is an expectation that there is less opportunity to race with other allocation requests if there is less scanning. The time to complete the tests did not vary that much and are uninteresting as were the vmstat statistics so I will not present them here. Using ftrace I recorded how much scanning was done by compaction and got this 3.6.0-rc6 3.6.0-rc6 3.6.0-rc6 3.6.0-rc6 3.6.0-rc6 akpm-20120920 lockless revert-v2r2 cachefail skipuseless Total free scanned 360753976 515414028 565479007 17103281 18916589 Total free isolated 2852429 3597369 4048601 670493 727840 Total free efficiency 0.0079% 0.0070% 0.0072% 0.0392% 0.0385% Total migrate scanned 247728664 822729112 1004645830 17946827 14118903 Total migrate isolated 2555324 3245937 3437501 616359 658616 Total migrate efficiency 0.0103% 0.0039% 0.0034% 0.0343% 0.0466% The efficiency is worthless because of the nature of the test and the number of failures. The really interesting point as far as this patch series is concerned is the number of pages scanned. Note that reverting Rik's patches massively increases the number of pages scanned indicating that those patches really did make a difference to CPU usage. However, caching what pageblocks should be skipped has a much higher impact. With patches 1-8 applied, free page and migrate page scanning are both reduced by 95% in comparison to the akpm kernel. If the basic concept of Rik's patches are implemened on top then scanning then the free scanner barely changed but migrate scanning was further reduced. That said, tests on 3.6-rc5 indicated that the last patch had greater impact than what was measured here so it is a bit variable. One way or the other, this series has a large impact on the amount of scanning compaction does when there is a storm of THP allocations. This patch: Compaction's migrate scanner acquires the zone->lru_lock when scanning a range of pages looking for LRU pages to acquire. It does this even if there are no LRU pages in the range. If multiple processes are compacting then this can cause severe locking contention. To make matters worse commit b2eef8c0 ("mm: compaction: minimise the time IRQs are disabled while isolating pages for migration") releases the lru_lock every SWAP_CLUSTER_MAX pages that are scanned. This patch makes two changes to how the migrate scanner acquires the LRU lock. First, it only releases the LRU lock every SWAP_CLUSTER_MAX pages if the lock is contended. This reduces the number of times it unnecessarily disables and re-enables IRQs. The second is that it defers acquiring the LRU lock for as long as possible. If there are no LRU pages or the only LRU pages are transhuge then the LRU lock will not be acquired at all which reduces contention on zone->lru_lock. [minchan@kernel.org: augment comment] [akpm@linux-foundation.org: tweak comment text] Signed-off-by: Mel Gorman <mgorman@suse.de> Acked-by: Rik van Riel <riel@redhat.com> Cc: Richard Davies <richard@arachsys.com> Cc: Shaohua Li <shli@kernel.org> Cc: Avi Kivity <avi@redhat.com> Acked-by: Rafael Aquini <aquini@redhat.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2012-10-08 23:32:33 +00:00
goto next_pageblock;
}
/*
* Check may be lockless but that's ok as we recheck later.
* It's possible to migrate LRU pages and balloon pages
* Skip any other type of page
*/
if (!PageLRU(page)) {
if (unlikely(balloon_page_movable(page))) {
if (locked && balloon_page_isolate(page)) {
/* Successfully isolated */
cc->finished_update_migrate = true;
list_add(&page->lru, migratelist);
cc->nr_migratepages++;
nr_isolated++;
goto check_compact_cluster;
}
}
continue;
}
/*
mm: compaction: acquire the zone->lru_lock as late as possible Richard Davies and Shaohua Li have both reported lock contention problems in compaction on the zone and LRU locks as well as significant amounts of time being spent in compaction. This series aims to reduce lock contention and scanning rates to reduce that CPU usage. Richard reported at https://lkml.org/lkml/2012/9/21/91 that this series made a big different to a problem he reported in August: http://marc.info/?l=kvm&m=134511507015614&w=2 Patch 1 defers acquiring the zone->lru_lock as long as possible. Patch 2 defers acquiring the zone->lock as lock as possible. Patch 3 reverts Rik's "skip-free" patches as the core concept gets reimplemented later and the remaining patches are easier to understand if this is reverted first. Patch 4 adds a pageblock-skip bit to the pageblock flags to cache what pageblocks should be skipped by the migrate and free scanners. This drastically reduces the amount of scanning compaction has to do. Patch 5 reimplements something similar to Rik's idea except it uses the pageblock-skip information to decide where the scanners should restart from and does not need to wrap around. I tested this on 3.6-rc6 + linux-next/akpm. Kernels tested were akpm-20120920 3.6-rc6 + linux-next/akpm as of Septeber 20th, 2012 lesslock Patches 1-6 revert Patches 1-7 cachefail Patches 1-8 skipuseless Patches 1-9 Stress high-order allocation tests looked ok. Success rates are more or less the same with the full series applied but there is an expectation that there is less opportunity to race with other allocation requests if there is less scanning. The time to complete the tests did not vary that much and are uninteresting as were the vmstat statistics so I will not present them here. Using ftrace I recorded how much scanning was done by compaction and got this 3.6.0-rc6 3.6.0-rc6 3.6.0-rc6 3.6.0-rc6 3.6.0-rc6 akpm-20120920 lockless revert-v2r2 cachefail skipuseless Total free scanned 360753976 515414028 565479007 17103281 18916589 Total free isolated 2852429 3597369 4048601 670493 727840 Total free efficiency 0.0079% 0.0070% 0.0072% 0.0392% 0.0385% Total migrate scanned 247728664 822729112 1004645830 17946827 14118903 Total migrate isolated 2555324 3245937 3437501 616359 658616 Total migrate efficiency 0.0103% 0.0039% 0.0034% 0.0343% 0.0466% The efficiency is worthless because of the nature of the test and the number of failures. The really interesting point as far as this patch series is concerned is the number of pages scanned. Note that reverting Rik's patches massively increases the number of pages scanned indicating that those patches really did make a difference to CPU usage. However, caching what pageblocks should be skipped has a much higher impact. With patches 1-8 applied, free page and migrate page scanning are both reduced by 95% in comparison to the akpm kernel. If the basic concept of Rik's patches are implemened on top then scanning then the free scanner barely changed but migrate scanning was further reduced. That said, tests on 3.6-rc5 indicated that the last patch had greater impact than what was measured here so it is a bit variable. One way or the other, this series has a large impact on the amount of scanning compaction does when there is a storm of THP allocations. This patch: Compaction's migrate scanner acquires the zone->lru_lock when scanning a range of pages looking for LRU pages to acquire. It does this even if there are no LRU pages in the range. If multiple processes are compacting then this can cause severe locking contention. To make matters worse commit b2eef8c0 ("mm: compaction: minimise the time IRQs are disabled while isolating pages for migration") releases the lru_lock every SWAP_CLUSTER_MAX pages that are scanned. This patch makes two changes to how the migrate scanner acquires the LRU lock. First, it only releases the LRU lock every SWAP_CLUSTER_MAX pages if the lock is contended. This reduces the number of times it unnecessarily disables and re-enables IRQs. The second is that it defers acquiring the LRU lock for as long as possible. If there are no LRU pages or the only LRU pages are transhuge then the LRU lock will not be acquired at all which reduces contention on zone->lru_lock. [minchan@kernel.org: augment comment] [akpm@linux-foundation.org: tweak comment text] Signed-off-by: Mel Gorman <mgorman@suse.de> Acked-by: Rik van Riel <riel@redhat.com> Cc: Richard Davies <richard@arachsys.com> Cc: Shaohua Li <shli@kernel.org> Cc: Avi Kivity <avi@redhat.com> Acked-by: Rafael Aquini <aquini@redhat.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2012-10-08 23:32:33 +00:00
* PageLRU is set. lru_lock normally excludes isolation
* splitting and collapsing (collapsing has already happened
* if PageLRU is set) but the lock is not necessarily taken
* here and it is wasteful to take it just to check transhuge.
* Check TransHuge without lock and skip the whole pageblock if
* it's either a transhuge or hugetlbfs page, as calling
* compound_order() without preventing THP from splitting the
* page underneath us may return surprising results.
*/
mm: compaction: acquire the zone->lru_lock as late as possible Richard Davies and Shaohua Li have both reported lock contention problems in compaction on the zone and LRU locks as well as significant amounts of time being spent in compaction. This series aims to reduce lock contention and scanning rates to reduce that CPU usage. Richard reported at https://lkml.org/lkml/2012/9/21/91 that this series made a big different to a problem he reported in August: http://marc.info/?l=kvm&m=134511507015614&w=2 Patch 1 defers acquiring the zone->lru_lock as long as possible. Patch 2 defers acquiring the zone->lock as lock as possible. Patch 3 reverts Rik's "skip-free" patches as the core concept gets reimplemented later and the remaining patches are easier to understand if this is reverted first. Patch 4 adds a pageblock-skip bit to the pageblock flags to cache what pageblocks should be skipped by the migrate and free scanners. This drastically reduces the amount of scanning compaction has to do. Patch 5 reimplements something similar to Rik's idea except it uses the pageblock-skip information to decide where the scanners should restart from and does not need to wrap around. I tested this on 3.6-rc6 + linux-next/akpm. Kernels tested were akpm-20120920 3.6-rc6 + linux-next/akpm as of Septeber 20th, 2012 lesslock Patches 1-6 revert Patches 1-7 cachefail Patches 1-8 skipuseless Patches 1-9 Stress high-order allocation tests looked ok. Success rates are more or less the same with the full series applied but there is an expectation that there is less opportunity to race with other allocation requests if there is less scanning. The time to complete the tests did not vary that much and are uninteresting as were the vmstat statistics so I will not present them here. Using ftrace I recorded how much scanning was done by compaction and got this 3.6.0-rc6 3.6.0-rc6 3.6.0-rc6 3.6.0-rc6 3.6.0-rc6 akpm-20120920 lockless revert-v2r2 cachefail skipuseless Total free scanned 360753976 515414028 565479007 17103281 18916589 Total free isolated 2852429 3597369 4048601 670493 727840 Total free efficiency 0.0079% 0.0070% 0.0072% 0.0392% 0.0385% Total migrate scanned 247728664 822729112 1004645830 17946827 14118903 Total migrate isolated 2555324 3245937 3437501 616359 658616 Total migrate efficiency 0.0103% 0.0039% 0.0034% 0.0343% 0.0466% The efficiency is worthless because of the nature of the test and the number of failures. The really interesting point as far as this patch series is concerned is the number of pages scanned. Note that reverting Rik's patches massively increases the number of pages scanned indicating that those patches really did make a difference to CPU usage. However, caching what pageblocks should be skipped has a much higher impact. With patches 1-8 applied, free page and migrate page scanning are both reduced by 95% in comparison to the akpm kernel. If the basic concept of Rik's patches are implemened on top then scanning then the free scanner barely changed but migrate scanning was further reduced. That said, tests on 3.6-rc5 indicated that the last patch had greater impact than what was measured here so it is a bit variable. One way or the other, this series has a large impact on the amount of scanning compaction does when there is a storm of THP allocations. This patch: Compaction's migrate scanner acquires the zone->lru_lock when scanning a range of pages looking for LRU pages to acquire. It does this even if there are no LRU pages in the range. If multiple processes are compacting then this can cause severe locking contention. To make matters worse commit b2eef8c0 ("mm: compaction: minimise the time IRQs are disabled while isolating pages for migration") releases the lru_lock every SWAP_CLUSTER_MAX pages that are scanned. This patch makes two changes to how the migrate scanner acquires the LRU lock. First, it only releases the LRU lock every SWAP_CLUSTER_MAX pages if the lock is contended. This reduces the number of times it unnecessarily disables and re-enables IRQs. The second is that it defers acquiring the LRU lock for as long as possible. If there are no LRU pages or the only LRU pages are transhuge then the LRU lock will not be acquired at all which reduces contention on zone->lru_lock. [minchan@kernel.org: augment comment] [akpm@linux-foundation.org: tweak comment text] Signed-off-by: Mel Gorman <mgorman@suse.de> Acked-by: Rik van Riel <riel@redhat.com> Cc: Richard Davies <richard@arachsys.com> Cc: Shaohua Li <shli@kernel.org> Cc: Avi Kivity <avi@redhat.com> Acked-by: Rafael Aquini <aquini@redhat.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2012-10-08 23:32:33 +00:00
if (PageTransHuge(page)) {
if (!locked)
goto next_pageblock;
low_pfn += (1 << compound_order(page)) - 1;
continue;
}
/* Check if it is ok to still hold the lock */
locked = compact_checklock_irqsave(&zone->lru_lock, &flags,
locked, cc);
if (!locked || fatal_signal_pending(current))
break;
/* Recheck PageLRU and PageTransHuge under lock */
if (!PageLRU(page))
continue;
if (PageTransHuge(page)) {
low_pfn += (1 << compound_order(page)) - 1;
continue;
}
if (!cc->sync)
mode |= ISOLATE_ASYNC_MIGRATE;
if (unevictable)
mode |= ISOLATE_UNEVICTABLE;
lruvec = mem_cgroup_page_lruvec(page, zone);
/* Try isolate the page */
if (__isolate_lru_page(page, mode) != 0)
continue;
VM_BUG_ON(PageTransCompound(page));
/* Successfully isolated */
mm: compaction: Restart compaction from near where it left off This is almost entirely based on Rik's previous patches and discussions with him about how this might be implemented. Order > 0 compaction stops when enough free pages of the correct page order have been coalesced. When doing subsequent higher order allocations, it is possible for compaction to be invoked many times. However, the compaction code always starts out looking for things to compact at the start of the zone, and for free pages to compact things to at the end of the zone. This can cause quadratic behaviour, with isolate_freepages starting at the end of the zone each time, even though previous invocations of the compaction code already filled up all free memory on that end of the zone. This can cause isolate_freepages to take enormous amounts of CPU with certain workloads on larger memory systems. This patch caches where the migration and free scanner should start from on subsequent compaction invocations using the pageblock-skip information. When compaction starts it begins from the cached restart points and will update the cached restart points until a page is isolated or a pageblock is skipped that would have been scanned by synchronous compaction. Signed-off-by: Mel Gorman <mgorman@suse.de> Acked-by: Rik van Riel <riel@redhat.com> Cc: Richard Davies <richard@arachsys.com> Cc: Shaohua Li <shli@kernel.org> Cc: Avi Kivity <avi@redhat.com> Acked-by: Rafael Aquini <aquini@redhat.com> Cc: Fengguang Wu <fengguang.wu@intel.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2012-10-08 23:32:45 +00:00
cc->finished_update_migrate = true;
del_page_from_lru_list(page, lruvec, page_lru(page));
list_add(&page->lru, migratelist);
cc->nr_migratepages++;
nr_isolated++;
check_compact_cluster:
/* Avoid isolating too much */
if (cc->nr_migratepages == COMPACT_CLUSTER_MAX) {
++low_pfn;
break;
}
mm: compaction: acquire the zone->lru_lock as late as possible Richard Davies and Shaohua Li have both reported lock contention problems in compaction on the zone and LRU locks as well as significant amounts of time being spent in compaction. This series aims to reduce lock contention and scanning rates to reduce that CPU usage. Richard reported at https://lkml.org/lkml/2012/9/21/91 that this series made a big different to a problem he reported in August: http://marc.info/?l=kvm&m=134511507015614&w=2 Patch 1 defers acquiring the zone->lru_lock as long as possible. Patch 2 defers acquiring the zone->lock as lock as possible. Patch 3 reverts Rik's "skip-free" patches as the core concept gets reimplemented later and the remaining patches are easier to understand if this is reverted first. Patch 4 adds a pageblock-skip bit to the pageblock flags to cache what pageblocks should be skipped by the migrate and free scanners. This drastically reduces the amount of scanning compaction has to do. Patch 5 reimplements something similar to Rik's idea except it uses the pageblock-skip information to decide where the scanners should restart from and does not need to wrap around. I tested this on 3.6-rc6 + linux-next/akpm. Kernels tested were akpm-20120920 3.6-rc6 + linux-next/akpm as of Septeber 20th, 2012 lesslock Patches 1-6 revert Patches 1-7 cachefail Patches 1-8 skipuseless Patches 1-9 Stress high-order allocation tests looked ok. Success rates are more or less the same with the full series applied but there is an expectation that there is less opportunity to race with other allocation requests if there is less scanning. The time to complete the tests did not vary that much and are uninteresting as were the vmstat statistics so I will not present them here. Using ftrace I recorded how much scanning was done by compaction and got this 3.6.0-rc6 3.6.0-rc6 3.6.0-rc6 3.6.0-rc6 3.6.0-rc6 akpm-20120920 lockless revert-v2r2 cachefail skipuseless Total free scanned 360753976 515414028 565479007 17103281 18916589 Total free isolated 2852429 3597369 4048601 670493 727840 Total free efficiency 0.0079% 0.0070% 0.0072% 0.0392% 0.0385% Total migrate scanned 247728664 822729112 1004645830 17946827 14118903 Total migrate isolated 2555324 3245937 3437501 616359 658616 Total migrate efficiency 0.0103% 0.0039% 0.0034% 0.0343% 0.0466% The efficiency is worthless because of the nature of the test and the number of failures. The really interesting point as far as this patch series is concerned is the number of pages scanned. Note that reverting Rik's patches massively increases the number of pages scanned indicating that those patches really did make a difference to CPU usage. However, caching what pageblocks should be skipped has a much higher impact. With patches 1-8 applied, free page and migrate page scanning are both reduced by 95% in comparison to the akpm kernel. If the basic concept of Rik's patches are implemened on top then scanning then the free scanner barely changed but migrate scanning was further reduced. That said, tests on 3.6-rc5 indicated that the last patch had greater impact than what was measured here so it is a bit variable. One way or the other, this series has a large impact on the amount of scanning compaction does when there is a storm of THP allocations. This patch: Compaction's migrate scanner acquires the zone->lru_lock when scanning a range of pages looking for LRU pages to acquire. It does this even if there are no LRU pages in the range. If multiple processes are compacting then this can cause severe locking contention. To make matters worse commit b2eef8c0 ("mm: compaction: minimise the time IRQs are disabled while isolating pages for migration") releases the lru_lock every SWAP_CLUSTER_MAX pages that are scanned. This patch makes two changes to how the migrate scanner acquires the LRU lock. First, it only releases the LRU lock every SWAP_CLUSTER_MAX pages if the lock is contended. This reduces the number of times it unnecessarily disables and re-enables IRQs. The second is that it defers acquiring the LRU lock for as long as possible. If there are no LRU pages or the only LRU pages are transhuge then the LRU lock will not be acquired at all which reduces contention on zone->lru_lock. [minchan@kernel.org: augment comment] [akpm@linux-foundation.org: tweak comment text] Signed-off-by: Mel Gorman <mgorman@suse.de> Acked-by: Rik van Riel <riel@redhat.com> Cc: Richard Davies <richard@arachsys.com> Cc: Shaohua Li <shli@kernel.org> Cc: Avi Kivity <avi@redhat.com> Acked-by: Rafael Aquini <aquini@redhat.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2012-10-08 23:32:33 +00:00
continue;
next_pageblock:
low_pfn += pageblock_nr_pages;
low_pfn = ALIGN(low_pfn, pageblock_nr_pages) - 1;
last_pageblock_nr = pageblock_nr;
}
mm: compaction: Abort async compaction if locks are contended or taking too long Jim Schutt reported a problem that pointed at compaction contending heavily on locks. The workload is straight-forward and in his own words; The systems in question have 24 SAS drives spread across 3 HBAs, running 24 Ceph OSD instances, one per drive. FWIW these servers are dual-socket Intel 5675 Xeons w/48 GB memory. I've got ~160 Ceph Linux clients doing dd simultaneously to a Ceph file system backed by 12 of these servers. Early in the test everything looks fine procs -------------------memory------------------ ---swap-- -----io---- --system-- -----cpu------- r b swpd free buff cache si so bi bo in cs us sy id wa st 31 15 0 287216 576 38606628 0 0 2 1158 2 14 1 3 95 0 0 27 15 0 225288 576 38583384 0 0 18 2222016 203357 134876 11 56 17 15 0 28 17 0 219256 576 38544736 0 0 11 2305932 203141 146296 11 49 23 17 0 6 18 0 215596 576 38552872 0 0 7 2363207 215264 166502 12 45 22 20 0 22 18 0 226984 576 38596404 0 0 3 2445741 223114 179527 12 43 23 22 0 and then it goes to pot procs -------------------memory------------------ ---swap-- -----io---- --system-- -----cpu------- r b swpd free buff cache si so bi bo in cs us sy id wa st 163 8 0 464308 576 36791368 0 0 11 22210 866 536 3 13 79 4 0 207 14 0 917752 576 36181928 0 0 712 1345376 134598 47367 7 90 1 2 0 123 12 0 685516 576 36296148 0 0 429 1386615 158494 60077 8 84 5 3 0 123 12 0 598572 576 36333728 0 0 1107 1233281 147542 62351 7 84 5 4 0 622 7 0 660768 576 36118264 0 0 557 1345548 151394 59353 7 85 4 3 0 223 11 0 283960 576 36463868 0 0 46 1107160 121846 33006 6 93 1 1 0 Note that system CPU usage is very high blocks being written out has dropped by 42%. He analysed this with perf and found perf record -g -a sleep 10 perf report --sort symbol --call-graph fractal,5 34.63% [k] _raw_spin_lock_irqsave | |--97.30%-- isolate_freepages | compaction_alloc | unmap_and_move | migrate_pages | compact_zone | compact_zone_order | try_to_compact_pages | __alloc_pages_direct_compact | __alloc_pages_slowpath | __alloc_pages_nodemask | alloc_pages_vma | do_huge_pmd_anonymous_page | handle_mm_fault | do_page_fault | page_fault | | | |--87.39%-- skb_copy_datagram_iovec | | tcp_recvmsg | | inet_recvmsg | | sock_recvmsg | | sys_recvfrom | | system_call | | __recv | | | | | --100.00%-- (nil) | | | --12.61%-- memcpy --2.70%-- [...] There was other data but primarily it is all showing that compaction is contended heavily on the zone->lock and zone->lru_lock. commit [b2eef8c0: mm: compaction: minimise the time IRQs are disabled while isolating pages for migration] noted that it was possible for migration to hold the lru_lock for an excessive amount of time. Very broadly speaking this patch expands the concept. This patch introduces compact_checklock_irqsave() to check if a lock is contended or the process needs to be scheduled. If either condition is true then async compaction is aborted and the caller is informed. The page allocator will fail a THP allocation if compaction failed due to contention. This patch also introduces compact_trylock_irqsave() which will acquire the lock only if it is not contended and the process does not need to schedule. Reported-by: Jim Schutt <jaschut@sandia.gov> Tested-by: Jim Schutt <jaschut@sandia.gov> Signed-off-by: Mel Gorman <mgorman@suse.de> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2012-08-21 23:16:17 +00:00
acct_isolated(zone, locked, cc);
mm: compaction: Abort async compaction if locks are contended or taking too long Jim Schutt reported a problem that pointed at compaction contending heavily on locks. The workload is straight-forward and in his own words; The systems in question have 24 SAS drives spread across 3 HBAs, running 24 Ceph OSD instances, one per drive. FWIW these servers are dual-socket Intel 5675 Xeons w/48 GB memory. I've got ~160 Ceph Linux clients doing dd simultaneously to a Ceph file system backed by 12 of these servers. Early in the test everything looks fine procs -------------------memory------------------ ---swap-- -----io---- --system-- -----cpu------- r b swpd free buff cache si so bi bo in cs us sy id wa st 31 15 0 287216 576 38606628 0 0 2 1158 2 14 1 3 95 0 0 27 15 0 225288 576 38583384 0 0 18 2222016 203357 134876 11 56 17 15 0 28 17 0 219256 576 38544736 0 0 11 2305932 203141 146296 11 49 23 17 0 6 18 0 215596 576 38552872 0 0 7 2363207 215264 166502 12 45 22 20 0 22 18 0 226984 576 38596404 0 0 3 2445741 223114 179527 12 43 23 22 0 and then it goes to pot procs -------------------memory------------------ ---swap-- -----io---- --system-- -----cpu------- r b swpd free buff cache si so bi bo in cs us sy id wa st 163 8 0 464308 576 36791368 0 0 11 22210 866 536 3 13 79 4 0 207 14 0 917752 576 36181928 0 0 712 1345376 134598 47367 7 90 1 2 0 123 12 0 685516 576 36296148 0 0 429 1386615 158494 60077 8 84 5 3 0 123 12 0 598572 576 36333728 0 0 1107 1233281 147542 62351 7 84 5 4 0 622 7 0 660768 576 36118264 0 0 557 1345548 151394 59353 7 85 4 3 0 223 11 0 283960 576 36463868 0 0 46 1107160 121846 33006 6 93 1 1 0 Note that system CPU usage is very high blocks being written out has dropped by 42%. He analysed this with perf and found perf record -g -a sleep 10 perf report --sort symbol --call-graph fractal,5 34.63% [k] _raw_spin_lock_irqsave | |--97.30%-- isolate_freepages | compaction_alloc | unmap_and_move | migrate_pages | compact_zone | compact_zone_order | try_to_compact_pages | __alloc_pages_direct_compact | __alloc_pages_slowpath | __alloc_pages_nodemask | alloc_pages_vma | do_huge_pmd_anonymous_page | handle_mm_fault | do_page_fault | page_fault | | | |--87.39%-- skb_copy_datagram_iovec | | tcp_recvmsg | | inet_recvmsg | | sock_recvmsg | | sys_recvfrom | | system_call | | __recv | | | | | --100.00%-- (nil) | | | --12.61%-- memcpy --2.70%-- [...] There was other data but primarily it is all showing that compaction is contended heavily on the zone->lock and zone->lru_lock. commit [b2eef8c0: mm: compaction: minimise the time IRQs are disabled while isolating pages for migration] noted that it was possible for migration to hold the lru_lock for an excessive amount of time. Very broadly speaking this patch expands the concept. This patch introduces compact_checklock_irqsave() to check if a lock is contended or the process needs to be scheduled. If either condition is true then async compaction is aborted and the caller is informed. The page allocator will fail a THP allocation if compaction failed due to contention. This patch also introduces compact_trylock_irqsave() which will acquire the lock only if it is not contended and the process does not need to schedule. Reported-by: Jim Schutt <jaschut@sandia.gov> Tested-by: Jim Schutt <jaschut@sandia.gov> Signed-off-by: Mel Gorman <mgorman@suse.de> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2012-08-21 23:16:17 +00:00
if (locked)
spin_unlock_irqrestore(&zone->lru_lock, flags);
mm: compaction: cache if a pageblock was scanned and no pages were isolated When compaction was implemented it was known that scanning could potentially be excessive. The ideal was that a counter be maintained for each pageblock but maintaining this information would incur a severe penalty due to a shared writable cache line. It has reached the point where the scanning costs are a serious problem, particularly on long-lived systems where a large process starts and allocates a large number of THPs at the same time. Instead of using a shared counter, this patch adds another bit to the pageblock flags called PG_migrate_skip. If a pageblock is scanned by either migrate or free scanner and 0 pages were isolated, the pageblock is marked to be skipped in the future. When scanning, this bit is checked before any scanning takes place and the block skipped if set. The main difficulty with a patch like this is "when to ignore the cached information?" If it's ignored too often, the scanning rates will still be excessive. If the information is too stale then allocations will fail that might have otherwise succeeded. In this patch o CMA always ignores the information o If the migrate and free scanner meet then the cached information will be discarded if it's at least 5 seconds since the last time the cache was discarded o If there are a large number of allocation failures, discard the cache. The time-based heuristic is very clumsy but there are few choices for a better event. Depending solely on multiple allocation failures still allows excessive scanning when THP allocations are failing in quick succession due to memory pressure. Waiting until memory pressure is relieved would cause compaction to continually fail instead of using reclaim/compaction to try allocate the page. The time-based mechanism is clumsy but a better option is not obvious. Signed-off-by: Mel Gorman <mgorman@suse.de> Acked-by: Rik van Riel <riel@redhat.com> Cc: Richard Davies <richard@arachsys.com> Cc: Shaohua Li <shli@kernel.org> Cc: Avi Kivity <avi@redhat.com> Acked-by: Rafael Aquini <aquini@redhat.com> Cc: Fengguang Wu <fengguang.wu@intel.com> Cc: Michal Nazarewicz <mina86@mina86.com> Cc: Bartlomiej Zolnierkiewicz <b.zolnierkie@samsung.com> Cc: Kyungmin Park <kyungmin.park@samsung.com> Cc: Mark Brown <broonie@opensource.wolfsonmicro.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2012-10-08 23:32:41 +00:00
/* Update the pageblock-skip if the whole pageblock was scanned */
if (low_pfn == end_pfn)
mm: compaction: Restart compaction from near where it left off This is almost entirely based on Rik's previous patches and discussions with him about how this might be implemented. Order > 0 compaction stops when enough free pages of the correct page order have been coalesced. When doing subsequent higher order allocations, it is possible for compaction to be invoked many times. However, the compaction code always starts out looking for things to compact at the start of the zone, and for free pages to compact things to at the end of the zone. This can cause quadratic behaviour, with isolate_freepages starting at the end of the zone each time, even though previous invocations of the compaction code already filled up all free memory on that end of the zone. This can cause isolate_freepages to take enormous amounts of CPU with certain workloads on larger memory systems. This patch caches where the migration and free scanner should start from on subsequent compaction invocations using the pageblock-skip information. When compaction starts it begins from the cached restart points and will update the cached restart points until a page is isolated or a pageblock is skipped that would have been scanned by synchronous compaction. Signed-off-by: Mel Gorman <mgorman@suse.de> Acked-by: Rik van Riel <riel@redhat.com> Cc: Richard Davies <richard@arachsys.com> Cc: Shaohua Li <shli@kernel.org> Cc: Avi Kivity <avi@redhat.com> Acked-by: Rafael Aquini <aquini@redhat.com> Cc: Fengguang Wu <fengguang.wu@intel.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2012-10-08 23:32:45 +00:00
update_pageblock_skip(cc, valid_page, nr_isolated, true);
mm: compaction: cache if a pageblock was scanned and no pages were isolated When compaction was implemented it was known that scanning could potentially be excessive. The ideal was that a counter be maintained for each pageblock but maintaining this information would incur a severe penalty due to a shared writable cache line. It has reached the point where the scanning costs are a serious problem, particularly on long-lived systems where a large process starts and allocates a large number of THPs at the same time. Instead of using a shared counter, this patch adds another bit to the pageblock flags called PG_migrate_skip. If a pageblock is scanned by either migrate or free scanner and 0 pages were isolated, the pageblock is marked to be skipped in the future. When scanning, this bit is checked before any scanning takes place and the block skipped if set. The main difficulty with a patch like this is "when to ignore the cached information?" If it's ignored too often, the scanning rates will still be excessive. If the information is too stale then allocations will fail that might have otherwise succeeded. In this patch o CMA always ignores the information o If the migrate and free scanner meet then the cached information will be discarded if it's at least 5 seconds since the last time the cache was discarded o If there are a large number of allocation failures, discard the cache. The time-based heuristic is very clumsy but there are few choices for a better event. Depending solely on multiple allocation failures still allows excessive scanning when THP allocations are failing in quick succession due to memory pressure. Waiting until memory pressure is relieved would cause compaction to continually fail instead of using reclaim/compaction to try allocate the page. The time-based mechanism is clumsy but a better option is not obvious. Signed-off-by: Mel Gorman <mgorman@suse.de> Acked-by: Rik van Riel <riel@redhat.com> Cc: Richard Davies <richard@arachsys.com> Cc: Shaohua Li <shli@kernel.org> Cc: Avi Kivity <avi@redhat.com> Acked-by: Rafael Aquini <aquini@redhat.com> Cc: Fengguang Wu <fengguang.wu@intel.com> Cc: Michal Nazarewicz <mina86@mina86.com> Cc: Bartlomiej Zolnierkiewicz <b.zolnierkie@samsung.com> Cc: Kyungmin Park <kyungmin.park@samsung.com> Cc: Mark Brown <broonie@opensource.wolfsonmicro.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2012-10-08 23:32:41 +00:00
trace_mm_compaction_isolate_migratepages(nr_scanned, nr_isolated);
count_compact_events(COMPACTMIGRATE_SCANNED, nr_scanned);
mm: compaction: Add scanned and isolated counters for compaction Compaction already has tracepoints to count scanned and isolated pages but it requires that ftrace be enabled and if that information has to be written to disk then it can be disruptive. This patch adds vmstat counters for compaction called compact_migrate_scanned, compact_free_scanned and compact_isolated. With these counters, it is possible to define a basic cost model for compaction. This approximates of how much work compaction is doing and can be compared that with an oprofile showing TLB misses and see if the cost of compaction is being offset by THP for example. Minimally a compaction patch can be evaluated in terms of whether it increases or decreases cost. The basic cost model looks like this Fundamental unit u: a word sizeof(void *) Ca = cost of struct page access = sizeof(struct page) / u Cmc = Cost migrate page copy = (Ca + PAGE_SIZE/u) * 2 Cmf = Cost migrate failure = Ca * 2 Ci = Cost page isolation = (Ca + Wi) where Wi is a constant that should reflect the approximate cost of the locking operation. Csm = Cost migrate scanning = Ca Csf = Cost free scanning = Ca Overall cost = (Csm * compact_migrate_scanned) + (Csf * compact_free_scanned) + (Ci * compact_isolated) + (Cmc * pgmigrate_success) + (Cmf * pgmigrate_failed) Where the values are read from /proc/vmstat. This is very basic and ignores certain costs such as the allocation cost to do a migrate page copy but any improvement to the model would still use the same vmstat counters. Signed-off-by: Mel Gorman <mgorman@suse.de> Reviewed-by: Rik van Riel <riel@redhat.com>
2012-10-19 11:00:10 +00:00
if (nr_isolated)
count_compact_events(COMPACTISOLATED, nr_isolated);
mm: compaction: Add scanned and isolated counters for compaction Compaction already has tracepoints to count scanned and isolated pages but it requires that ftrace be enabled and if that information has to be written to disk then it can be disruptive. This patch adds vmstat counters for compaction called compact_migrate_scanned, compact_free_scanned and compact_isolated. With these counters, it is possible to define a basic cost model for compaction. This approximates of how much work compaction is doing and can be compared that with an oprofile showing TLB misses and see if the cost of compaction is being offset by THP for example. Minimally a compaction patch can be evaluated in terms of whether it increases or decreases cost. The basic cost model looks like this Fundamental unit u: a word sizeof(void *) Ca = cost of struct page access = sizeof(struct page) / u Cmc = Cost migrate page copy = (Ca + PAGE_SIZE/u) * 2 Cmf = Cost migrate failure = Ca * 2 Ci = Cost page isolation = (Ca + Wi) where Wi is a constant that should reflect the approximate cost of the locking operation. Csm = Cost migrate scanning = Ca Csf = Cost free scanning = Ca Overall cost = (Csm * compact_migrate_scanned) + (Csf * compact_free_scanned) + (Ci * compact_isolated) + (Cmc * pgmigrate_success) + (Cmf * pgmigrate_failed) Where the values are read from /proc/vmstat. This is very basic and ignores certain costs such as the allocation cost to do a migrate page copy but any improvement to the model would still use the same vmstat counters. Signed-off-by: Mel Gorman <mgorman@suse.de> Reviewed-by: Rik van Riel <riel@redhat.com>
2012-10-19 11:00:10 +00:00
return low_pfn;
}
#endif /* CONFIG_COMPACTION || CONFIG_CMA */
#ifdef CONFIG_COMPACTION
/*
* Based on information in the current compact_control, find blocks
* suitable for isolating free pages from and then isolate them.
*/
static void isolate_freepages(struct zone *zone,
struct compact_control *cc)
{
struct page *page;
unsigned long high_pfn, low_pfn, pfn, zone_end_pfn, end_pfn;
int nr_freepages = cc->nr_freepages;
struct list_head *freelist = &cc->freepages;
/*
* Initialise the free scanner. The starting point is where we last
* scanned from (or the end of the zone if starting). The low point
* is the end of the pageblock the migration scanner is using.
*/
pfn = cc->free_pfn;
low_pfn = cc->migrate_pfn + pageblock_nr_pages;
/*
* Take care that if the migration scanner is at the end of the zone
* that the free scanner does not accidentally move to the next zone
* in the next isolation cycle.
*/
high_pfn = min(low_pfn, pfn);
zone_end_pfn = zone->zone_start_pfn + zone->spanned_pages;
/*
* Isolate free pages until enough are available to migrate the
* pages on cc->migratepages. We stop searching if the migrate
* and free page scanners meet or enough free pages are isolated.
*/
for (; pfn > low_pfn && cc->nr_migratepages > nr_freepages;
pfn -= pageblock_nr_pages) {
unsigned long isolated;
if (!pfn_valid(pfn))
continue;
/*
* Check for overlapping nodes/zones. It's possible on some
* configurations to have a setup like
* node0 node1 node0
* i.e. it's possible that all pages within a zones range of
* pages do not belong to a single zone.
*/
page = pfn_to_page(pfn);
if (page_zone(page) != zone)
continue;
/* Check the block is suitable for migration */
if (!suitable_migration_target(page))
continue;
mm: compaction: cache if a pageblock was scanned and no pages were isolated When compaction was implemented it was known that scanning could potentially be excessive. The ideal was that a counter be maintained for each pageblock but maintaining this information would incur a severe penalty due to a shared writable cache line. It has reached the point where the scanning costs are a serious problem, particularly on long-lived systems where a large process starts and allocates a large number of THPs at the same time. Instead of using a shared counter, this patch adds another bit to the pageblock flags called PG_migrate_skip. If a pageblock is scanned by either migrate or free scanner and 0 pages were isolated, the pageblock is marked to be skipped in the future. When scanning, this bit is checked before any scanning takes place and the block skipped if set. The main difficulty with a patch like this is "when to ignore the cached information?" If it's ignored too often, the scanning rates will still be excessive. If the information is too stale then allocations will fail that might have otherwise succeeded. In this patch o CMA always ignores the information o If the migrate and free scanner meet then the cached information will be discarded if it's at least 5 seconds since the last time the cache was discarded o If there are a large number of allocation failures, discard the cache. The time-based heuristic is very clumsy but there are few choices for a better event. Depending solely on multiple allocation failures still allows excessive scanning when THP allocations are failing in quick succession due to memory pressure. Waiting until memory pressure is relieved would cause compaction to continually fail instead of using reclaim/compaction to try allocate the page. The time-based mechanism is clumsy but a better option is not obvious. Signed-off-by: Mel Gorman <mgorman@suse.de> Acked-by: Rik van Riel <riel@redhat.com> Cc: Richard Davies <richard@arachsys.com> Cc: Shaohua Li <shli@kernel.org> Cc: Avi Kivity <avi@redhat.com> Acked-by: Rafael Aquini <aquini@redhat.com> Cc: Fengguang Wu <fengguang.wu@intel.com> Cc: Michal Nazarewicz <mina86@mina86.com> Cc: Bartlomiej Zolnierkiewicz <b.zolnierkie@samsung.com> Cc: Kyungmin Park <kyungmin.park@samsung.com> Cc: Mark Brown <broonie@opensource.wolfsonmicro.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2012-10-08 23:32:41 +00:00
/* If isolation recently failed, do not retry */
if (!isolation_suitable(cc, page))
continue;
/* Found a block suitable for isolating free pages from */
isolated = 0;
/*
* As pfn may not start aligned, pfn+pageblock_nr_page
* may cross a MAX_ORDER_NR_PAGES boundary and miss
* a pfn_valid check. Ensure isolate_freepages_block()
* only scans within a pageblock
*/
end_pfn = ALIGN(pfn + 1, pageblock_nr_pages);
end_pfn = min(end_pfn, zone_end_pfn);
isolated = isolate_freepages_block(cc, pfn, end_pfn,
freelist, false);
nr_freepages += isolated;
/*
* Record the highest PFN we isolated pages from. When next
* looking for free pages, the search will restart here as
* page migration may have returned some pages to the allocator
*/
mm: compaction: Restart compaction from near where it left off This is almost entirely based on Rik's previous patches and discussions with him about how this might be implemented. Order > 0 compaction stops when enough free pages of the correct page order have been coalesced. When doing subsequent higher order allocations, it is possible for compaction to be invoked many times. However, the compaction code always starts out looking for things to compact at the start of the zone, and for free pages to compact things to at the end of the zone. This can cause quadratic behaviour, with isolate_freepages starting at the end of the zone each time, even though previous invocations of the compaction code already filled up all free memory on that end of the zone. This can cause isolate_freepages to take enormous amounts of CPU with certain workloads on larger memory systems. This patch caches where the migration and free scanner should start from on subsequent compaction invocations using the pageblock-skip information. When compaction starts it begins from the cached restart points and will update the cached restart points until a page is isolated or a pageblock is skipped that would have been scanned by synchronous compaction. Signed-off-by: Mel Gorman <mgorman@suse.de> Acked-by: Rik van Riel <riel@redhat.com> Cc: Richard Davies <richard@arachsys.com> Cc: Shaohua Li <shli@kernel.org> Cc: Avi Kivity <avi@redhat.com> Acked-by: Rafael Aquini <aquini@redhat.com> Cc: Fengguang Wu <fengguang.wu@intel.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2012-10-08 23:32:45 +00:00
if (isolated) {
cc->finished_update_free = true;
high_pfn = max(high_pfn, pfn);
mm: compaction: Restart compaction from near where it left off This is almost entirely based on Rik's previous patches and discussions with him about how this might be implemented. Order > 0 compaction stops when enough free pages of the correct page order have been coalesced. When doing subsequent higher order allocations, it is possible for compaction to be invoked many times. However, the compaction code always starts out looking for things to compact at the start of the zone, and for free pages to compact things to at the end of the zone. This can cause quadratic behaviour, with isolate_freepages starting at the end of the zone each time, even though previous invocations of the compaction code already filled up all free memory on that end of the zone. This can cause isolate_freepages to take enormous amounts of CPU with certain workloads on larger memory systems. This patch caches where the migration and free scanner should start from on subsequent compaction invocations using the pageblock-skip information. When compaction starts it begins from the cached restart points and will update the cached restart points until a page is isolated or a pageblock is skipped that would have been scanned by synchronous compaction. Signed-off-by: Mel Gorman <mgorman@suse.de> Acked-by: Rik van Riel <riel@redhat.com> Cc: Richard Davies <richard@arachsys.com> Cc: Shaohua Li <shli@kernel.org> Cc: Avi Kivity <avi@redhat.com> Acked-by: Rafael Aquini <aquini@redhat.com> Cc: Fengguang Wu <fengguang.wu@intel.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2012-10-08 23:32:45 +00:00
}
}
/* split_free_page does not map the pages */
map_pages(freelist);
cc->free_pfn = high_pfn;
cc->nr_freepages = nr_freepages;
}
/*
* This is a migrate-callback that "allocates" freepages by taking pages
* from the isolated freelists in the block we are migrating to.
*/
static struct page *compaction_alloc(struct page *migratepage,
unsigned long data,
int **result)
{
struct compact_control *cc = (struct compact_control *)data;
struct page *freepage;
/* Isolate free pages if necessary */
if (list_empty(&cc->freepages)) {
isolate_freepages(cc->zone, cc);
if (list_empty(&cc->freepages))
return NULL;
}
freepage = list_entry(cc->freepages.next, struct page, lru);
list_del(&freepage->lru);
cc->nr_freepages--;
return freepage;
}
/*
* We cannot control nr_migratepages and nr_freepages fully when migration is
* running as migrate_pages() has no knowledge of compact_control. When
* migration is complete, we count the number of pages on the lists by hand.
*/
static void update_nr_listpages(struct compact_control *cc)
{
int nr_migratepages = 0;
int nr_freepages = 0;
struct page *page;
list_for_each_entry(page, &cc->migratepages, lru)
nr_migratepages++;
list_for_each_entry(page, &cc->freepages, lru)
nr_freepages++;
cc->nr_migratepages = nr_migratepages;
cc->nr_freepages = nr_freepages;
}
/* possible outcome of isolate_migratepages */
typedef enum {
ISOLATE_ABORT, /* Abort compaction now */
ISOLATE_NONE, /* No pages isolated, continue scanning */
ISOLATE_SUCCESS, /* Pages isolated, migrate */
} isolate_migrate_t;
/*
* Isolate all pages that can be migrated from the block pointed to by
* the migrate scanner within compact_control.
*/
static isolate_migrate_t isolate_migratepages(struct zone *zone,
struct compact_control *cc)
{
unsigned long low_pfn, end_pfn;
/* Do not scan outside zone boundaries */
low_pfn = max(cc->migrate_pfn, zone->zone_start_pfn);
/* Only scan within a pageblock boundary */
end_pfn = ALIGN(low_pfn + pageblock_nr_pages, pageblock_nr_pages);
/* Do not cross the free scanner or scan within a memory hole */
if (end_pfn > cc->free_pfn || !pfn_valid(low_pfn)) {
cc->migrate_pfn = end_pfn;
return ISOLATE_NONE;
}
/* Perform the isolation */
low_pfn = isolate_migratepages_range(zone, cc, low_pfn, end_pfn, false);
if (!low_pfn || cc->contended)
return ISOLATE_ABORT;
cc->migrate_pfn = low_pfn;
return ISOLATE_SUCCESS;
}
static int compact_finished(struct zone *zone,
struct compact_control *cc)
{
unsigned long watermark;
if (fatal_signal_pending(current))
return COMPACT_PARTIAL;
/* Compaction run completes if the migrate and free scanner meet */
mm: compaction: cache if a pageblock was scanned and no pages were isolated When compaction was implemented it was known that scanning could potentially be excessive. The ideal was that a counter be maintained for each pageblock but maintaining this information would incur a severe penalty due to a shared writable cache line. It has reached the point where the scanning costs are a serious problem, particularly on long-lived systems where a large process starts and allocates a large number of THPs at the same time. Instead of using a shared counter, this patch adds another bit to the pageblock flags called PG_migrate_skip. If a pageblock is scanned by either migrate or free scanner and 0 pages were isolated, the pageblock is marked to be skipped in the future. When scanning, this bit is checked before any scanning takes place and the block skipped if set. The main difficulty with a patch like this is "when to ignore the cached information?" If it's ignored too often, the scanning rates will still be excessive. If the information is too stale then allocations will fail that might have otherwise succeeded. In this patch o CMA always ignores the information o If the migrate and free scanner meet then the cached information will be discarded if it's at least 5 seconds since the last time the cache was discarded o If there are a large number of allocation failures, discard the cache. The time-based heuristic is very clumsy but there are few choices for a better event. Depending solely on multiple allocation failures still allows excessive scanning when THP allocations are failing in quick succession due to memory pressure. Waiting until memory pressure is relieved would cause compaction to continually fail instead of using reclaim/compaction to try allocate the page. The time-based mechanism is clumsy but a better option is not obvious. Signed-off-by: Mel Gorman <mgorman@suse.de> Acked-by: Rik van Riel <riel@redhat.com> Cc: Richard Davies <richard@arachsys.com> Cc: Shaohua Li <shli@kernel.org> Cc: Avi Kivity <avi@redhat.com> Acked-by: Rafael Aquini <aquini@redhat.com> Cc: Fengguang Wu <fengguang.wu@intel.com> Cc: Michal Nazarewicz <mina86@mina86.com> Cc: Bartlomiej Zolnierkiewicz <b.zolnierkie@samsung.com> Cc: Kyungmin Park <kyungmin.park@samsung.com> Cc: Mark Brown <broonie@opensource.wolfsonmicro.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2012-10-08 23:32:41 +00:00
if (cc->free_pfn <= cc->migrate_pfn) {
mm: compaction: clear PG_migrate_skip based on compaction and reclaim activity Compaction caches if a pageblock was scanned and no pages were isolated so that the pageblocks can be skipped in the future to reduce scanning. This information is not cleared by the page allocator based on activity due to the impact it would have to the page allocator fast paths. Hence there is a requirement that something clear the cache or pageblocks will be skipped forever. Currently the cache is cleared if there were a number of recent allocation failures and it has not been cleared within the last 5 seconds. Time-based decisions like this are terrible as they have no relationship to VM activity and is basically a big hammer. Unfortunately, accurate heuristics would add cost to some hot paths so this patch implements a rough heuristic. There are two cases where the cache is cleared. 1. If a !kswapd process completes a compaction cycle (migrate and free scanner meet), the zone is marked compact_blockskip_flush. When kswapd goes to sleep, it will clear the cache. This is expected to be the common case where the cache is cleared. It does not really matter if kswapd happens to be asleep or going to sleep when the flag is set as it will be woken on the next allocation request. 2. If there have been multiple failures recently and compaction just finished being deferred then a process will clear the cache and start a full scan. This situation happens if there are multiple high-order allocation requests under heavy memory pressure. The clearing of the PG_migrate_skip bits and other scans is inherently racy but the race is harmless. For allocations that can fail such as THP, they will simply fail. For requests that cannot fail, they will retry the allocation. Tests indicated that scanning rates were roughly similar to when the time-based heuristic was used and the allocation success rates were similar. Signed-off-by: Mel Gorman <mgorman@suse.de> Cc: Rik van Riel <riel@redhat.com> Cc: Richard Davies <richard@arachsys.com> Cc: Shaohua Li <shli@kernel.org> Cc: Avi Kivity <avi@redhat.com> Cc: Rafael Aquini <aquini@redhat.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2012-10-08 23:32:47 +00:00
/*
* Mark that the PG_migrate_skip information should be cleared
* by kswapd when it goes to sleep. kswapd does not set the
* flag itself as the decision to be clear should be directly
* based on an allocation request.
*/
if (!current_is_kswapd())
zone->compact_blockskip_flush = true;
return COMPACT_COMPLETE;
mm: compaction: cache if a pageblock was scanned and no pages were isolated When compaction was implemented it was known that scanning could potentially be excessive. The ideal was that a counter be maintained for each pageblock but maintaining this information would incur a severe penalty due to a shared writable cache line. It has reached the point where the scanning costs are a serious problem, particularly on long-lived systems where a large process starts and allocates a large number of THPs at the same time. Instead of using a shared counter, this patch adds another bit to the pageblock flags called PG_migrate_skip. If a pageblock is scanned by either migrate or free scanner and 0 pages were isolated, the pageblock is marked to be skipped in the future. When scanning, this bit is checked before any scanning takes place and the block skipped if set. The main difficulty with a patch like this is "when to ignore the cached information?" If it's ignored too often, the scanning rates will still be excessive. If the information is too stale then allocations will fail that might have otherwise succeeded. In this patch o CMA always ignores the information o If the migrate and free scanner meet then the cached information will be discarded if it's at least 5 seconds since the last time the cache was discarded o If there are a large number of allocation failures, discard the cache. The time-based heuristic is very clumsy but there are few choices for a better event. Depending solely on multiple allocation failures still allows excessive scanning when THP allocations are failing in quick succession due to memory pressure. Waiting until memory pressure is relieved would cause compaction to continually fail instead of using reclaim/compaction to try allocate the page. The time-based mechanism is clumsy but a better option is not obvious. Signed-off-by: Mel Gorman <mgorman@suse.de> Acked-by: Rik van Riel <riel@redhat.com> Cc: Richard Davies <richard@arachsys.com> Cc: Shaohua Li <shli@kernel.org> Cc: Avi Kivity <avi@redhat.com> Acked-by: Rafael Aquini <aquini@redhat.com> Cc: Fengguang Wu <fengguang.wu@intel.com> Cc: Michal Nazarewicz <mina86@mina86.com> Cc: Bartlomiej Zolnierkiewicz <b.zolnierkie@samsung.com> Cc: Kyungmin Park <kyungmin.park@samsung.com> Cc: Mark Brown <broonie@opensource.wolfsonmicro.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2012-10-08 23:32:41 +00:00
}
/*
* order == -1 is expected when compacting via
* /proc/sys/vm/compact_memory
*/
if (cc->order == -1)
return COMPACT_CONTINUE;
/* Compaction run is not finished if the watermark is not met */
watermark = low_wmark_pages(zone);
watermark += (1 << cc->order);
if (!zone_watermark_ok(zone, cc->order, watermark, 0, 0))
return COMPACT_CONTINUE;
/* Direct compactor: Is a suitable page free? */
if (cc->page) {
/* Was a suitable page captured? */
if (*cc->page)
return COMPACT_PARTIAL;
} else {
unsigned int order;
for (order = cc->order; order < MAX_ORDER; order++) {
struct free_area *area = &zone->free_area[cc->order];
/* Job done if page is free of the right migratetype */
if (!list_empty(&area->free_list[cc->migratetype]))
return COMPACT_PARTIAL;
/* Job done if allocation would set block type */
if (cc->order >= pageblock_order && area->nr_free)
return COMPACT_PARTIAL;
}
}
return COMPACT_CONTINUE;
}
/*
* compaction_suitable: Is this suitable to run compaction on this zone now?
* Returns
* COMPACT_SKIPPED - If there are too few free pages for compaction
* COMPACT_PARTIAL - If the allocation would succeed without compaction
* COMPACT_CONTINUE - If compaction should run now
*/
unsigned long compaction_suitable(struct zone *zone, int order)
{
int fragindex;
unsigned long watermark;
/*
* order == -1 is expected when compacting via
* /proc/sys/vm/compact_memory
*/
if (order == -1)
return COMPACT_CONTINUE;
/*
* Watermarks for order-0 must be met for compaction. Note the 2UL.
* This is because during migration, copies of pages need to be
* allocated and for a short time, the footprint is higher
*/
watermark = low_wmark_pages(zone) + (2UL << order);
if (!zone_watermark_ok(zone, 0, watermark, 0, 0))
return COMPACT_SKIPPED;
/*
* fragmentation index determines if allocation failures are due to
* low memory or external fragmentation
*
* index of -1000 implies allocations might succeed depending on
* watermarks
* index towards 0 implies failure is due to lack of memory
* index towards 1000 implies failure is due to fragmentation
*
* Only compact if a failure would be due to fragmentation.
*/
fragindex = fragmentation_index(zone, order);
if (fragindex >= 0 && fragindex <= sysctl_extfrag_threshold)
return COMPACT_SKIPPED;
if (fragindex == -1000 && zone_watermark_ok(zone, order, watermark,
0, 0))
return COMPACT_PARTIAL;
return COMPACT_CONTINUE;
}
static void compact_capture_page(struct compact_control *cc)
{
unsigned long flags;
int mtype, mtype_low, mtype_high;
if (!cc->page || *cc->page)
return;
/*
* For MIGRATE_MOVABLE allocations we capture a suitable page ASAP
* regardless of the migratetype of the freelist is is captured from.
* This is fine because the order for a high-order MIGRATE_MOVABLE
* allocation is typically at least a pageblock size and overall
* fragmentation is not impaired. Other allocation types must
* capture pages from their own migratelist because otherwise they
* could pollute other pageblocks like MIGRATE_MOVABLE with
* difficult to move pages and making fragmentation worse overall.
*/
if (cc->migratetype == MIGRATE_MOVABLE) {
mtype_low = 0;
mtype_high = MIGRATE_PCPTYPES;
} else {
mtype_low = cc->migratetype;
mtype_high = cc->migratetype + 1;
}
/* Speculatively examine the free lists without zone lock */
for (mtype = mtype_low; mtype < mtype_high; mtype++) {
int order;
for (order = cc->order; order < MAX_ORDER; order++) {
struct page *page;
struct free_area *area;
area = &(cc->zone->free_area[order]);
if (list_empty(&area->free_list[mtype]))
continue;
/* Take the lock and attempt capture of the page */
if (!compact_trylock_irqsave(&cc->zone->lock, &flags, cc))
return;
if (!list_empty(&area->free_list[mtype])) {
page = list_entry(area->free_list[mtype].next,
struct page, lru);
if (capture_free_page(page, cc->order, mtype)) {
spin_unlock_irqrestore(&cc->zone->lock,
flags);
*cc->page = page;
return;
}
}
spin_unlock_irqrestore(&cc->zone->lock, flags);
}
}
}
static int compact_zone(struct zone *zone, struct compact_control *cc)
{
int ret;
mm: compaction: Restart compaction from near where it left off This is almost entirely based on Rik's previous patches and discussions with him about how this might be implemented. Order > 0 compaction stops when enough free pages of the correct page order have been coalesced. When doing subsequent higher order allocations, it is possible for compaction to be invoked many times. However, the compaction code always starts out looking for things to compact at the start of the zone, and for free pages to compact things to at the end of the zone. This can cause quadratic behaviour, with isolate_freepages starting at the end of the zone each time, even though previous invocations of the compaction code already filled up all free memory on that end of the zone. This can cause isolate_freepages to take enormous amounts of CPU with certain workloads on larger memory systems. This patch caches where the migration and free scanner should start from on subsequent compaction invocations using the pageblock-skip information. When compaction starts it begins from the cached restart points and will update the cached restart points until a page is isolated or a pageblock is skipped that would have been scanned by synchronous compaction. Signed-off-by: Mel Gorman <mgorman@suse.de> Acked-by: Rik van Riel <riel@redhat.com> Cc: Richard Davies <richard@arachsys.com> Cc: Shaohua Li <shli@kernel.org> Cc: Avi Kivity <avi@redhat.com> Acked-by: Rafael Aquini <aquini@redhat.com> Cc: Fengguang Wu <fengguang.wu@intel.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2012-10-08 23:32:45 +00:00
unsigned long start_pfn = zone->zone_start_pfn;
unsigned long end_pfn = zone->zone_start_pfn + zone->spanned_pages;
ret = compaction_suitable(zone, cc->order);
switch (ret) {
case COMPACT_PARTIAL:
case COMPACT_SKIPPED:
/* Compaction is likely to fail */
return ret;
case COMPACT_CONTINUE:
/* Fall through to compaction */
;
}
mm: compaction: Restart compaction from near where it left off This is almost entirely based on Rik's previous patches and discussions with him about how this might be implemented. Order > 0 compaction stops when enough free pages of the correct page order have been coalesced. When doing subsequent higher order allocations, it is possible for compaction to be invoked many times. However, the compaction code always starts out looking for things to compact at the start of the zone, and for free pages to compact things to at the end of the zone. This can cause quadratic behaviour, with isolate_freepages starting at the end of the zone each time, even though previous invocations of the compaction code already filled up all free memory on that end of the zone. This can cause isolate_freepages to take enormous amounts of CPU with certain workloads on larger memory systems. This patch caches where the migration and free scanner should start from on subsequent compaction invocations using the pageblock-skip information. When compaction starts it begins from the cached restart points and will update the cached restart points until a page is isolated or a pageblock is skipped that would have been scanned by synchronous compaction. Signed-off-by: Mel Gorman <mgorman@suse.de> Acked-by: Rik van Riel <riel@redhat.com> Cc: Richard Davies <richard@arachsys.com> Cc: Shaohua Li <shli@kernel.org> Cc: Avi Kivity <avi@redhat.com> Acked-by: Rafael Aquini <aquini@redhat.com> Cc: Fengguang Wu <fengguang.wu@intel.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2012-10-08 23:32:45 +00:00
/*
* Setup to move all movable pages to the end of the zone. Used cached
* information on where the scanners should start but check that it
* is initialised by ensuring the values are within zone boundaries.
*/
cc->migrate_pfn = zone->compact_cached_migrate_pfn;
cc->free_pfn = zone->compact_cached_free_pfn;
if (cc->free_pfn < start_pfn || cc->free_pfn > end_pfn) {
cc->free_pfn = end_pfn & ~(pageblock_nr_pages-1);
zone->compact_cached_free_pfn = cc->free_pfn;
}
if (cc->migrate_pfn < start_pfn || cc->migrate_pfn > end_pfn) {
cc->migrate_pfn = start_pfn;
zone->compact_cached_migrate_pfn = cc->migrate_pfn;
}
mm: compaction: clear PG_migrate_skip based on compaction and reclaim activity Compaction caches if a pageblock was scanned and no pages were isolated so that the pageblocks can be skipped in the future to reduce scanning. This information is not cleared by the page allocator based on activity due to the impact it would have to the page allocator fast paths. Hence there is a requirement that something clear the cache or pageblocks will be skipped forever. Currently the cache is cleared if there were a number of recent allocation failures and it has not been cleared within the last 5 seconds. Time-based decisions like this are terrible as they have no relationship to VM activity and is basically a big hammer. Unfortunately, accurate heuristics would add cost to some hot paths so this patch implements a rough heuristic. There are two cases where the cache is cleared. 1. If a !kswapd process completes a compaction cycle (migrate and free scanner meet), the zone is marked compact_blockskip_flush. When kswapd goes to sleep, it will clear the cache. This is expected to be the common case where the cache is cleared. It does not really matter if kswapd happens to be asleep or going to sleep when the flag is set as it will be woken on the next allocation request. 2. If there have been multiple failures recently and compaction just finished being deferred then a process will clear the cache and start a full scan. This situation happens if there are multiple high-order allocation requests under heavy memory pressure. The clearing of the PG_migrate_skip bits and other scans is inherently racy but the race is harmless. For allocations that can fail such as THP, they will simply fail. For requests that cannot fail, they will retry the allocation. Tests indicated that scanning rates were roughly similar to when the time-based heuristic was used and the allocation success rates were similar. Signed-off-by: Mel Gorman <mgorman@suse.de> Cc: Rik van Riel <riel@redhat.com> Cc: Richard Davies <richard@arachsys.com> Cc: Shaohua Li <shli@kernel.org> Cc: Avi Kivity <avi@redhat.com> Cc: Rafael Aquini <aquini@redhat.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2012-10-08 23:32:47 +00:00
/*
* Clear pageblock skip if there were failures recently and compaction
* is about to be retried after being deferred. kswapd does not do
* this reset as it'll reset the cached information when going to sleep.
*/
if (compaction_restarting(zone, cc->order) && !current_is_kswapd())
__reset_isolation_suitable(zone);
mm: compaction: cache if a pageblock was scanned and no pages were isolated When compaction was implemented it was known that scanning could potentially be excessive. The ideal was that a counter be maintained for each pageblock but maintaining this information would incur a severe penalty due to a shared writable cache line. It has reached the point where the scanning costs are a serious problem, particularly on long-lived systems where a large process starts and allocates a large number of THPs at the same time. Instead of using a shared counter, this patch adds another bit to the pageblock flags called PG_migrate_skip. If a pageblock is scanned by either migrate or free scanner and 0 pages were isolated, the pageblock is marked to be skipped in the future. When scanning, this bit is checked before any scanning takes place and the block skipped if set. The main difficulty with a patch like this is "when to ignore the cached information?" If it's ignored too often, the scanning rates will still be excessive. If the information is too stale then allocations will fail that might have otherwise succeeded. In this patch o CMA always ignores the information o If the migrate and free scanner meet then the cached information will be discarded if it's at least 5 seconds since the last time the cache was discarded o If there are a large number of allocation failures, discard the cache. The time-based heuristic is very clumsy but there are few choices for a better event. Depending solely on multiple allocation failures still allows excessive scanning when THP allocations are failing in quick succession due to memory pressure. Waiting until memory pressure is relieved would cause compaction to continually fail instead of using reclaim/compaction to try allocate the page. The time-based mechanism is clumsy but a better option is not obvious. Signed-off-by: Mel Gorman <mgorman@suse.de> Acked-by: Rik van Riel <riel@redhat.com> Cc: Richard Davies <richard@arachsys.com> Cc: Shaohua Li <shli@kernel.org> Cc: Avi Kivity <avi@redhat.com> Acked-by: Rafael Aquini <aquini@redhat.com> Cc: Fengguang Wu <fengguang.wu@intel.com> Cc: Michal Nazarewicz <mina86@mina86.com> Cc: Bartlomiej Zolnierkiewicz <b.zolnierkie@samsung.com> Cc: Kyungmin Park <kyungmin.park@samsung.com> Cc: Mark Brown <broonie@opensource.wolfsonmicro.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2012-10-08 23:32:41 +00:00
migrate_prep_local();
while ((ret = compact_finished(zone, cc)) == COMPACT_CONTINUE) {
unsigned long nr_migrate, nr_remaining;
int err;
switch (isolate_migratepages(zone, cc)) {
case ISOLATE_ABORT:
ret = COMPACT_PARTIAL;
putback_movable_pages(&cc->migratepages);
cc->nr_migratepages = 0;
goto out;
case ISOLATE_NONE:
continue;
case ISOLATE_SUCCESS:
;
}
nr_migrate = cc->nr_migratepages;
err = migrate_pages(&cc->migratepages, compaction_alloc,
(unsigned long)cc, false,
cc->sync ? MIGRATE_SYNC_LIGHT : MIGRATE_ASYNC,
MR_COMPACTION);
update_nr_listpages(cc);
nr_remaining = cc->nr_migratepages;
trace_mm_compaction_migratepages(nr_migrate - nr_remaining,
nr_remaining);
/* Release isolated pages not migrated */
if (err) {
putback_movable_pages(&cc->migratepages);
cc->nr_migratepages = 0;
if (err == -ENOMEM) {
ret = COMPACT_PARTIAL;
goto out;
}
}
/* Capture a page now if it is a suitable size */
compact_capture_page(cc);
}
out:
/* Release free pages and check accounting */
cc->nr_freepages -= release_freepages(&cc->freepages);
VM_BUG_ON(cc->nr_freepages != 0);
return ret;
}
static unsigned long compact_zone_order(struct zone *zone,
int order, gfp_t gfp_mask,
bool sync, bool *contended,
struct page **page)
{
unsigned long ret;
struct compact_control cc = {
.nr_freepages = 0,
.nr_migratepages = 0,
.order = order,
.migratetype = allocflags_to_migratetype(gfp_mask),
.zone = zone,
.sync = sync,
.page = page,
};
INIT_LIST_HEAD(&cc.freepages);
INIT_LIST_HEAD(&cc.migratepages);
ret = compact_zone(zone, &cc);
VM_BUG_ON(!list_empty(&cc.freepages));
VM_BUG_ON(!list_empty(&cc.migratepages));
*contended = cc.contended;
return ret;
}
int sysctl_extfrag_threshold = 500;
/**
* try_to_compact_pages - Direct compact to satisfy a high-order allocation
* @zonelist: The zonelist used for the current allocation
* @order: The order of the current allocation
* @gfp_mask: The GFP mask of the current allocation
* @nodemask: The allowed nodes to allocate from
* @sync: Whether migration is synchronous or not
* @contended: Return value that is true if compaction was aborted due to lock contention
* @page: Optionally capture a free page of the requested order during compaction
*
* This is the main entry point for direct page compaction.
*/
unsigned long try_to_compact_pages(struct zonelist *zonelist,
int order, gfp_t gfp_mask, nodemask_t *nodemask,
bool sync, bool *contended, struct page **page)
{
enum zone_type high_zoneidx = gfp_zone(gfp_mask);
int may_enter_fs = gfp_mask & __GFP_FS;
int may_perform_io = gfp_mask & __GFP_IO;
struct zoneref *z;
struct zone *zone;
int rc = COMPACT_SKIPPED;
int alloc_flags = 0;
mm: compaction: update comment in try_to_compact_pages Allocation success rates have been far lower since 3.4 due to commit fe2c2a106663 ("vmscan: reclaim at order 0 when compaction is enabled"). This commit was introduced for good reasons and it was known in advance that the success rates would suffer but it was justified on the grounds that the high allocation success rates were achieved by aggressive reclaim. Success rates are expected to suffer even more in 3.6 due to commit 7db8889ab05b ("mm: have order > 0 compaction start off where it left") which testing has shown to severely reduce allocation success rates under load - to 0% in one case. This series aims to improve the allocation success rates without regressing the benefits of commit fe2c2a106663. The series is based on latest mmotm and takes into account the __GFP_NO_KSWAPD flag is going away. Patch 1 updates a stale comment seeing as I was in the general area. Patch 2 updates reclaim/compaction to reclaim pages scaled on the number of recent failures. Patch 3 captures suitable high-order pages freed by compaction to reduce races with parallel allocation requests. Patch 4 fixes the upstream commit [7db8889a: mm: have order > 0 compaction start off where it left] to enable compaction again Patch 5 identifies when compacion is taking too long due to contention and aborts. STRESS-HIGHALLOC 3.6-rc1-akpm full-series Pass 1 36.00 ( 0.00%) 51.00 (15.00%) Pass 2 42.00 ( 0.00%) 63.00 (21.00%) while Rested 86.00 ( 0.00%) 86.00 ( 0.00%) From http://www.csn.ul.ie/~mel/postings/mmtests-20120424/global-dhp__stress-highalloc-performance-ext3/hydra/comparison.html I know that the allocation success rates in 3.3.6 was 78% in comparison to 36% in in the current akpm tree. With the full series applied, the success rates are up to around 51% with some variability in the results. This is not as high a success rate but it does not reclaim excessively which is a key point. MMTests Statistics: vmstat Page Ins 3050912 3078892 Page Outs 8033528 8039096 Swap Ins 0 0 Swap Outs 0 0 Note that swap in/out rates remain at 0. In 3.3.6 with 78% success rates there were 71881 pages swapped out. Direct pages scanned 70942 122976 Kswapd pages scanned 1366300 1520122 Kswapd pages reclaimed 1366214 1484629 Direct pages reclaimed 70936 105716 Kswapd efficiency 99% 97% Kswapd velocity 1072.550 1182.615 Direct efficiency 99% 85% Direct velocity 55.690 95.672 The kswapd velocity changes very little as expected. kswapd velocity is around the 1000 pages/sec mark where as in kernel 3.3.6 with the high allocation success rates it was 8140 pages/second. Direct velocity is higher as a result of patch 2 of the series but this is expected and is acceptable. The direct reclaim and kswapd velocities change very little. If these get accepted for merging then there is a difficulty in how they should be handled. 7db8889a ("mm: have order > 0 compaction start off where it left") is broken but it is already in 3.6-rc1 and needs to be fixed. However, if just patch 4 from this series is applied then Jim Schutt's workload is known to break again as his workload also requires patch 5. While it would be preferred to have all these patches in 3.6 to improve compaction in general, it would at least be acceptable if just patches 4 and 5 were merged to 3.6 to fix a known problem without breaking compaction completely. On the face of it, that would force __GFP_NO_KSWAPD patches to be merged at the same time but I can do a version of this series with __GFP_NO_KSWAPD change reverted and then rebase it on top of this series. That might be best overall because I note that the __GFP_NO_KSWAPD patch should have removed deferred_compaction from page_alloc.c but it didn't but fixing that causes collisions with this series. This patch: The comment about order applied when the check was order > PAGE_ALLOC_COSTLY_ORDER which has not been the case since c5a73c3d ("thp: use compaction for all allocation orders"). Fixing the comment while I'm in the general area. Signed-off-by: Mel Gorman <mgorman@suse.de> Reviewed-by: Rik van Riel <riel@redhat.com> Reviewed-by: Minchan Kim <minchan@kernel.org> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2012-10-08 23:29:09 +00:00
/* Check if the GFP flags allow compaction */
if (!order || !may_enter_fs || !may_perform_io)
return rc;
count_compact_event(COMPACTSTALL);
#ifdef CONFIG_CMA
if (allocflags_to_migratetype(gfp_mask) == MIGRATE_MOVABLE)
alloc_flags |= ALLOC_CMA;
#endif
/* Compact each zone in the list */
for_each_zone_zonelist_nodemask(zone, z, zonelist, high_zoneidx,
nodemask) {
int status;
mm: compaction: Abort async compaction if locks are contended or taking too long Jim Schutt reported a problem that pointed at compaction contending heavily on locks. The workload is straight-forward and in his own words; The systems in question have 24 SAS drives spread across 3 HBAs, running 24 Ceph OSD instances, one per drive. FWIW these servers are dual-socket Intel 5675 Xeons w/48 GB memory. I've got ~160 Ceph Linux clients doing dd simultaneously to a Ceph file system backed by 12 of these servers. Early in the test everything looks fine procs -------------------memory------------------ ---swap-- -----io---- --system-- -----cpu------- r b swpd free buff cache si so bi bo in cs us sy id wa st 31 15 0 287216 576 38606628 0 0 2 1158 2 14 1 3 95 0 0 27 15 0 225288 576 38583384 0 0 18 2222016 203357 134876 11 56 17 15 0 28 17 0 219256 576 38544736 0 0 11 2305932 203141 146296 11 49 23 17 0 6 18 0 215596 576 38552872 0 0 7 2363207 215264 166502 12 45 22 20 0 22 18 0 226984 576 38596404 0 0 3 2445741 223114 179527 12 43 23 22 0 and then it goes to pot procs -------------------memory------------------ ---swap-- -----io---- --system-- -----cpu------- r b swpd free buff cache si so bi bo in cs us sy id wa st 163 8 0 464308 576 36791368 0 0 11 22210 866 536 3 13 79 4 0 207 14 0 917752 576 36181928 0 0 712 1345376 134598 47367 7 90 1 2 0 123 12 0 685516 576 36296148 0 0 429 1386615 158494 60077 8 84 5 3 0 123 12 0 598572 576 36333728 0 0 1107 1233281 147542 62351 7 84 5 4 0 622 7 0 660768 576 36118264 0 0 557 1345548 151394 59353 7 85 4 3 0 223 11 0 283960 576 36463868 0 0 46 1107160 121846 33006 6 93 1 1 0 Note that system CPU usage is very high blocks being written out has dropped by 42%. He analysed this with perf and found perf record -g -a sleep 10 perf report --sort symbol --call-graph fractal,5 34.63% [k] _raw_spin_lock_irqsave | |--97.30%-- isolate_freepages | compaction_alloc | unmap_and_move | migrate_pages | compact_zone | compact_zone_order | try_to_compact_pages | __alloc_pages_direct_compact | __alloc_pages_slowpath | __alloc_pages_nodemask | alloc_pages_vma | do_huge_pmd_anonymous_page | handle_mm_fault | do_page_fault | page_fault | | | |--87.39%-- skb_copy_datagram_iovec | | tcp_recvmsg | | inet_recvmsg | | sock_recvmsg | | sys_recvfrom | | system_call | | __recv | | | | | --100.00%-- (nil) | | | --12.61%-- memcpy --2.70%-- [...] There was other data but primarily it is all showing that compaction is contended heavily on the zone->lock and zone->lru_lock. commit [b2eef8c0: mm: compaction: minimise the time IRQs are disabled while isolating pages for migration] noted that it was possible for migration to hold the lru_lock for an excessive amount of time. Very broadly speaking this patch expands the concept. This patch introduces compact_checklock_irqsave() to check if a lock is contended or the process needs to be scheduled. If either condition is true then async compaction is aborted and the caller is informed. The page allocator will fail a THP allocation if compaction failed due to contention. This patch also introduces compact_trylock_irqsave() which will acquire the lock only if it is not contended and the process does not need to schedule. Reported-by: Jim Schutt <jaschut@sandia.gov> Tested-by: Jim Schutt <jaschut@sandia.gov> Signed-off-by: Mel Gorman <mgorman@suse.de> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2012-08-21 23:16:17 +00:00
status = compact_zone_order(zone, order, gfp_mask, sync,
contended, page);
rc = max(status, rc);
/* If a normal allocation would succeed, stop compacting */
if (zone_watermark_ok(zone, order, low_wmark_pages(zone), 0,
alloc_flags))
break;
}
return rc;
}
/* Compact all zones within a node */
static int __compact_pgdat(pg_data_t *pgdat, struct compact_control *cc)
{
int zoneid;
struct zone *zone;
for (zoneid = 0; zoneid < MAX_NR_ZONES; zoneid++) {
zone = &pgdat->node_zones[zoneid];
if (!populated_zone(zone))
continue;
cc->nr_freepages = 0;
cc->nr_migratepages = 0;
cc->zone = zone;
INIT_LIST_HEAD(&cc->freepages);
INIT_LIST_HEAD(&cc->migratepages);
if (cc->order == -1 || !compaction_deferred(zone, cc->order))
compact_zone(zone, cc);
if (cc->order > 0) {
int ok = zone_watermark_ok(zone, cc->order,
low_wmark_pages(zone), 0, 0);
if (ok && cc->order >= zone->compact_order_failed)
zone->compact_order_failed = cc->order + 1;
/* Currently async compaction is never deferred. */
else if (!ok && cc->sync)
defer_compaction(zone, cc->order);
}
VM_BUG_ON(!list_empty(&cc->freepages));
VM_BUG_ON(!list_empty(&cc->migratepages));
}
return 0;
}
int compact_pgdat(pg_data_t *pgdat, int order)
{
struct compact_control cc = {
.order = order,
.sync = false,
.page = NULL,
};
return __compact_pgdat(pgdat, &cc);
}
static int compact_node(int nid)
{
struct compact_control cc = {
.order = -1,
.sync = true,
.page = NULL,
};
compact_pgdat: workaround lockdep warning in kswapd I get this lockdep warning from swapping load on linux-next, due to "vmscan: kswapd carefully call compaction". ================================= [ INFO: inconsistent lock state ] 3.3.0-rc2-next-20120201 #5 Not tainted --------------------------------- inconsistent {RECLAIM_FS-ON-W} -> {IN-RECLAIM_FS-W} usage. kswapd0/28 [HC0[0]:SC0[0]:HE1:SE1] takes: (pcpu_alloc_mutex){+.+.?.}, at: [<ffffffff810d6684>] pcpu_alloc+0x67/0x325 {RECLAIM_FS-ON-W} state was registered at: [<ffffffff81099b75>] mark_held_locks+0xd7/0x103 [<ffffffff8109a13c>] lockdep_trace_alloc+0x85/0x9e [<ffffffff810f6bdc>] __kmalloc+0x6c/0x14b [<ffffffff810d57fd>] pcpu_mem_zalloc+0x59/0x62 [<ffffffff810d5d16>] pcpu_extend_area_map+0x26/0xb1 [<ffffffff810d679f>] pcpu_alloc+0x182/0x325 [<ffffffff810d694d>] __alloc_percpu+0xb/0xd [<ffffffff8142ebfd>] snmp_mib_init+0x1e/0x2e [<ffffffff8185cd8d>] ipv4_mib_init_net+0x7a/0x184 [<ffffffff813dc963>] ops_init.clone.0+0x6b/0x73 [<ffffffff813dc9cc>] register_pernet_operations+0x61/0xa0 [<ffffffff813dca8e>] register_pernet_subsys+0x29/0x42 [<ffffffff8185d044>] inet_init+0x1ad/0x252 [<ffffffff810002e3>] do_one_initcall+0x7a/0x12f [<ffffffff81832bc5>] kernel_init+0x9d/0x11e [<ffffffff814e51e4>] kernel_thread_helper+0x4/0x10 irq event stamp: 656613 hardirqs last enabled at (656613): [<ffffffff814e0ddc>] __mutex_unlock_slowpath+0x104/0x128 hardirqs last disabled at (656612): [<ffffffff814e0d34>] __mutex_unlock_slowpath+0x5c/0x128 softirqs last enabled at (655568): [<ffffffff8105b4a5>] __do_softirq+0x120/0x136 softirqs last disabled at (654757): [<ffffffff814e52dc>] call_softirq+0x1c/0x30 other info that might help us debug this: Possible unsafe locking scenario: CPU0 ---- lock(pcpu_alloc_mutex); <Interrupt> lock(pcpu_alloc_mutex); *** DEADLOCK *** no locks held by kswapd0/28. stack backtrace: Pid: 28, comm: kswapd0 Not tainted 3.3.0-rc2-next-20120201 #5 Call Trace: [<ffffffff810981f4>] print_usage_bug+0x1bf/0x1d0 [<ffffffff81096c3e>] ? print_irq_inversion_bug+0x1d9/0x1d9 [<ffffffff810982c0>] mark_lock_irq+0xbb/0x22e [<ffffffff810c5399>] ? free_hot_cold_page+0x13d/0x14f [<ffffffff81098684>] mark_lock+0x251/0x331 [<ffffffff81098893>] mark_irqflags+0x12f/0x141 [<ffffffff81098e32>] __lock_acquire+0x58d/0x753 [<ffffffff810d6684>] ? pcpu_alloc+0x67/0x325 [<ffffffff81099433>] lock_acquire+0x54/0x6a [<ffffffff810d6684>] ? pcpu_alloc+0x67/0x325 [<ffffffff8107a5b8>] ? add_preempt_count+0xa9/0xae [<ffffffff814e0a21>] mutex_lock_nested+0x5e/0x315 [<ffffffff810d6684>] ? pcpu_alloc+0x67/0x325 [<ffffffff81098f81>] ? __lock_acquire+0x6dc/0x753 [<ffffffff810c9fb0>] ? __pagevec_release+0x2c/0x2c [<ffffffff810d6684>] pcpu_alloc+0x67/0x325 [<ffffffff810c9fb0>] ? __pagevec_release+0x2c/0x2c [<ffffffff810d694d>] __alloc_percpu+0xb/0xd [<ffffffff8106c35e>] schedule_on_each_cpu+0x23/0x110 [<ffffffff810c9fcb>] lru_add_drain_all+0x10/0x12 [<ffffffff810f126f>] __compact_pgdat+0x20/0x182 [<ffffffff810f15c2>] compact_pgdat+0x27/0x29 [<ffffffff810c306b>] ? zone_watermark_ok+0x1a/0x1c [<ffffffff810cdf6f>] balance_pgdat+0x732/0x751 [<ffffffff810ce0ed>] kswapd+0x15f/0x178 [<ffffffff810cdf8e>] ? balance_pgdat+0x751/0x751 [<ffffffff8106fd11>] kthread+0x84/0x8c [<ffffffff814e51e4>] kernel_thread_helper+0x4/0x10 [<ffffffff810787ed>] ? finish_task_switch+0x85/0xea [<ffffffff814e3861>] ? retint_restore_args+0xe/0xe [<ffffffff8106fc8d>] ? __init_kthread_worker+0x56/0x56 [<ffffffff814e51e0>] ? gs_change+0xb/0xb The RECLAIM_FS notations indicate that it's doing the GFP_FS checking that Nick hacked into lockdep a while back: I think we're intended to read that "<Interrupt>" in the DEADLOCK scenario as "<Direct reclaim>". I'm hazy, I have not reached any conclusion as to whether it's right to complain or not; but I believe it's uneasy about kswapd now doing the mutex_lock(&pcpu_alloc_mutex) which lru_add_drain_all() entails. Nor have I reached any conclusion as to whether it's important for kswapd to do that draining or not. But so as not to get blocked on this, with lockdep disabled from giving further reports, here's a patch which removes the lru_add_drain_all() from kswapd's callpath (and calls it only once from compact_nodes(), instead of once per node). Signed-off-by: Hugh Dickins <hughd@google.com> Cc: Rik van Riel <riel@redhat.com> Acked-by: Mel Gorman <mel@csn.ul.ie> Cc: Tejun Heo <tj@kernel.org> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2012-03-21 23:33:53 +00:00
return __compact_pgdat(NODE_DATA(nid), &cc);
}
/* Compact all nodes in the system */
static void compact_nodes(void)
{
int nid;
compact_pgdat: workaround lockdep warning in kswapd I get this lockdep warning from swapping load on linux-next, due to "vmscan: kswapd carefully call compaction". ================================= [ INFO: inconsistent lock state ] 3.3.0-rc2-next-20120201 #5 Not tainted --------------------------------- inconsistent {RECLAIM_FS-ON-W} -> {IN-RECLAIM_FS-W} usage. kswapd0/28 [HC0[0]:SC0[0]:HE1:SE1] takes: (pcpu_alloc_mutex){+.+.?.}, at: [<ffffffff810d6684>] pcpu_alloc+0x67/0x325 {RECLAIM_FS-ON-W} state was registered at: [<ffffffff81099b75>] mark_held_locks+0xd7/0x103 [<ffffffff8109a13c>] lockdep_trace_alloc+0x85/0x9e [<ffffffff810f6bdc>] __kmalloc+0x6c/0x14b [<ffffffff810d57fd>] pcpu_mem_zalloc+0x59/0x62 [<ffffffff810d5d16>] pcpu_extend_area_map+0x26/0xb1 [<ffffffff810d679f>] pcpu_alloc+0x182/0x325 [<ffffffff810d694d>] __alloc_percpu+0xb/0xd [<ffffffff8142ebfd>] snmp_mib_init+0x1e/0x2e [<ffffffff8185cd8d>] ipv4_mib_init_net+0x7a/0x184 [<ffffffff813dc963>] ops_init.clone.0+0x6b/0x73 [<ffffffff813dc9cc>] register_pernet_operations+0x61/0xa0 [<ffffffff813dca8e>] register_pernet_subsys+0x29/0x42 [<ffffffff8185d044>] inet_init+0x1ad/0x252 [<ffffffff810002e3>] do_one_initcall+0x7a/0x12f [<ffffffff81832bc5>] kernel_init+0x9d/0x11e [<ffffffff814e51e4>] kernel_thread_helper+0x4/0x10 irq event stamp: 656613 hardirqs last enabled at (656613): [<ffffffff814e0ddc>] __mutex_unlock_slowpath+0x104/0x128 hardirqs last disabled at (656612): [<ffffffff814e0d34>] __mutex_unlock_slowpath+0x5c/0x128 softirqs last enabled at (655568): [<ffffffff8105b4a5>] __do_softirq+0x120/0x136 softirqs last disabled at (654757): [<ffffffff814e52dc>] call_softirq+0x1c/0x30 other info that might help us debug this: Possible unsafe locking scenario: CPU0 ---- lock(pcpu_alloc_mutex); <Interrupt> lock(pcpu_alloc_mutex); *** DEADLOCK *** no locks held by kswapd0/28. stack backtrace: Pid: 28, comm: kswapd0 Not tainted 3.3.0-rc2-next-20120201 #5 Call Trace: [<ffffffff810981f4>] print_usage_bug+0x1bf/0x1d0 [<ffffffff81096c3e>] ? print_irq_inversion_bug+0x1d9/0x1d9 [<ffffffff810982c0>] mark_lock_irq+0xbb/0x22e [<ffffffff810c5399>] ? free_hot_cold_page+0x13d/0x14f [<ffffffff81098684>] mark_lock+0x251/0x331 [<ffffffff81098893>] mark_irqflags+0x12f/0x141 [<ffffffff81098e32>] __lock_acquire+0x58d/0x753 [<ffffffff810d6684>] ? pcpu_alloc+0x67/0x325 [<ffffffff81099433>] lock_acquire+0x54/0x6a [<ffffffff810d6684>] ? pcpu_alloc+0x67/0x325 [<ffffffff8107a5b8>] ? add_preempt_count+0xa9/0xae [<ffffffff814e0a21>] mutex_lock_nested+0x5e/0x315 [<ffffffff810d6684>] ? pcpu_alloc+0x67/0x325 [<ffffffff81098f81>] ? __lock_acquire+0x6dc/0x753 [<ffffffff810c9fb0>] ? __pagevec_release+0x2c/0x2c [<ffffffff810d6684>] pcpu_alloc+0x67/0x325 [<ffffffff810c9fb0>] ? __pagevec_release+0x2c/0x2c [<ffffffff810d694d>] __alloc_percpu+0xb/0xd [<ffffffff8106c35e>] schedule_on_each_cpu+0x23/0x110 [<ffffffff810c9fcb>] lru_add_drain_all+0x10/0x12 [<ffffffff810f126f>] __compact_pgdat+0x20/0x182 [<ffffffff810f15c2>] compact_pgdat+0x27/0x29 [<ffffffff810c306b>] ? zone_watermark_ok+0x1a/0x1c [<ffffffff810cdf6f>] balance_pgdat+0x732/0x751 [<ffffffff810ce0ed>] kswapd+0x15f/0x178 [<ffffffff810cdf8e>] ? balance_pgdat+0x751/0x751 [<ffffffff8106fd11>] kthread+0x84/0x8c [<ffffffff814e51e4>] kernel_thread_helper+0x4/0x10 [<ffffffff810787ed>] ? finish_task_switch+0x85/0xea [<ffffffff814e3861>] ? retint_restore_args+0xe/0xe [<ffffffff8106fc8d>] ? __init_kthread_worker+0x56/0x56 [<ffffffff814e51e0>] ? gs_change+0xb/0xb The RECLAIM_FS notations indicate that it's doing the GFP_FS checking that Nick hacked into lockdep a while back: I think we're intended to read that "<Interrupt>" in the DEADLOCK scenario as "<Direct reclaim>". I'm hazy, I have not reached any conclusion as to whether it's right to complain or not; but I believe it's uneasy about kswapd now doing the mutex_lock(&pcpu_alloc_mutex) which lru_add_drain_all() entails. Nor have I reached any conclusion as to whether it's important for kswapd to do that draining or not. But so as not to get blocked on this, with lockdep disabled from giving further reports, here's a patch which removes the lru_add_drain_all() from kswapd's callpath (and calls it only once from compact_nodes(), instead of once per node). Signed-off-by: Hugh Dickins <hughd@google.com> Cc: Rik van Riel <riel@redhat.com> Acked-by: Mel Gorman <mel@csn.ul.ie> Cc: Tejun Heo <tj@kernel.org> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2012-03-21 23:33:53 +00:00
/* Flush pending updates to the LRU lists */
lru_add_drain_all();
for_each_online_node(nid)
compact_node(nid);
}
/* The written value is actually unused, all memory is compacted */
int sysctl_compact_memory;
/* This is the entry point for compacting all nodes via /proc/sys/vm */
int sysctl_compaction_handler(struct ctl_table *table, int write,
void __user *buffer, size_t *length, loff_t *ppos)
{
if (write)
compact_nodes();
return 0;
}
int sysctl_extfrag_handler(struct ctl_table *table, int write,
void __user *buffer, size_t *length, loff_t *ppos)
{
proc_dointvec_minmax(table, write, buffer, length, ppos);
return 0;
}
#if defined(CONFIG_SYSFS) && defined(CONFIG_NUMA)
ssize_t sysfs_compact_node(struct device *dev,
struct device_attribute *attr,
const char *buf, size_t count)
{
compact_pgdat: workaround lockdep warning in kswapd I get this lockdep warning from swapping load on linux-next, due to "vmscan: kswapd carefully call compaction". ================================= [ INFO: inconsistent lock state ] 3.3.0-rc2-next-20120201 #5 Not tainted --------------------------------- inconsistent {RECLAIM_FS-ON-W} -> {IN-RECLAIM_FS-W} usage. kswapd0/28 [HC0[0]:SC0[0]:HE1:SE1] takes: (pcpu_alloc_mutex){+.+.?.}, at: [<ffffffff810d6684>] pcpu_alloc+0x67/0x325 {RECLAIM_FS-ON-W} state was registered at: [<ffffffff81099b75>] mark_held_locks+0xd7/0x103 [<ffffffff8109a13c>] lockdep_trace_alloc+0x85/0x9e [<ffffffff810f6bdc>] __kmalloc+0x6c/0x14b [<ffffffff810d57fd>] pcpu_mem_zalloc+0x59/0x62 [<ffffffff810d5d16>] pcpu_extend_area_map+0x26/0xb1 [<ffffffff810d679f>] pcpu_alloc+0x182/0x325 [<ffffffff810d694d>] __alloc_percpu+0xb/0xd [<ffffffff8142ebfd>] snmp_mib_init+0x1e/0x2e [<ffffffff8185cd8d>] ipv4_mib_init_net+0x7a/0x184 [<ffffffff813dc963>] ops_init.clone.0+0x6b/0x73 [<ffffffff813dc9cc>] register_pernet_operations+0x61/0xa0 [<ffffffff813dca8e>] register_pernet_subsys+0x29/0x42 [<ffffffff8185d044>] inet_init+0x1ad/0x252 [<ffffffff810002e3>] do_one_initcall+0x7a/0x12f [<ffffffff81832bc5>] kernel_init+0x9d/0x11e [<ffffffff814e51e4>] kernel_thread_helper+0x4/0x10 irq event stamp: 656613 hardirqs last enabled at (656613): [<ffffffff814e0ddc>] __mutex_unlock_slowpath+0x104/0x128 hardirqs last disabled at (656612): [<ffffffff814e0d34>] __mutex_unlock_slowpath+0x5c/0x128 softirqs last enabled at (655568): [<ffffffff8105b4a5>] __do_softirq+0x120/0x136 softirqs last disabled at (654757): [<ffffffff814e52dc>] call_softirq+0x1c/0x30 other info that might help us debug this: Possible unsafe locking scenario: CPU0 ---- lock(pcpu_alloc_mutex); <Interrupt> lock(pcpu_alloc_mutex); *** DEADLOCK *** no locks held by kswapd0/28. stack backtrace: Pid: 28, comm: kswapd0 Not tainted 3.3.0-rc2-next-20120201 #5 Call Trace: [<ffffffff810981f4>] print_usage_bug+0x1bf/0x1d0 [<ffffffff81096c3e>] ? print_irq_inversion_bug+0x1d9/0x1d9 [<ffffffff810982c0>] mark_lock_irq+0xbb/0x22e [<ffffffff810c5399>] ? free_hot_cold_page+0x13d/0x14f [<ffffffff81098684>] mark_lock+0x251/0x331 [<ffffffff81098893>] mark_irqflags+0x12f/0x141 [<ffffffff81098e32>] __lock_acquire+0x58d/0x753 [<ffffffff810d6684>] ? pcpu_alloc+0x67/0x325 [<ffffffff81099433>] lock_acquire+0x54/0x6a [<ffffffff810d6684>] ? pcpu_alloc+0x67/0x325 [<ffffffff8107a5b8>] ? add_preempt_count+0xa9/0xae [<ffffffff814e0a21>] mutex_lock_nested+0x5e/0x315 [<ffffffff810d6684>] ? pcpu_alloc+0x67/0x325 [<ffffffff81098f81>] ? __lock_acquire+0x6dc/0x753 [<ffffffff810c9fb0>] ? __pagevec_release+0x2c/0x2c [<ffffffff810d6684>] pcpu_alloc+0x67/0x325 [<ffffffff810c9fb0>] ? __pagevec_release+0x2c/0x2c [<ffffffff810d694d>] __alloc_percpu+0xb/0xd [<ffffffff8106c35e>] schedule_on_each_cpu+0x23/0x110 [<ffffffff810c9fcb>] lru_add_drain_all+0x10/0x12 [<ffffffff810f126f>] __compact_pgdat+0x20/0x182 [<ffffffff810f15c2>] compact_pgdat+0x27/0x29 [<ffffffff810c306b>] ? zone_watermark_ok+0x1a/0x1c [<ffffffff810cdf6f>] balance_pgdat+0x732/0x751 [<ffffffff810ce0ed>] kswapd+0x15f/0x178 [<ffffffff810cdf8e>] ? balance_pgdat+0x751/0x751 [<ffffffff8106fd11>] kthread+0x84/0x8c [<ffffffff814e51e4>] kernel_thread_helper+0x4/0x10 [<ffffffff810787ed>] ? finish_task_switch+0x85/0xea [<ffffffff814e3861>] ? retint_restore_args+0xe/0xe [<ffffffff8106fc8d>] ? __init_kthread_worker+0x56/0x56 [<ffffffff814e51e0>] ? gs_change+0xb/0xb The RECLAIM_FS notations indicate that it's doing the GFP_FS checking that Nick hacked into lockdep a while back: I think we're intended to read that "<Interrupt>" in the DEADLOCK scenario as "<Direct reclaim>". I'm hazy, I have not reached any conclusion as to whether it's right to complain or not; but I believe it's uneasy about kswapd now doing the mutex_lock(&pcpu_alloc_mutex) which lru_add_drain_all() entails. Nor have I reached any conclusion as to whether it's important for kswapd to do that draining or not. But so as not to get blocked on this, with lockdep disabled from giving further reports, here's a patch which removes the lru_add_drain_all() from kswapd's callpath (and calls it only once from compact_nodes(), instead of once per node). Signed-off-by: Hugh Dickins <hughd@google.com> Cc: Rik van Riel <riel@redhat.com> Acked-by: Mel Gorman <mel@csn.ul.ie> Cc: Tejun Heo <tj@kernel.org> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2012-03-21 23:33:53 +00:00
int nid = dev->id;
if (nid >= 0 && nid < nr_node_ids && node_online(nid)) {
/* Flush pending updates to the LRU lists */
lru_add_drain_all();
compact_node(nid);
}
return count;
}
static DEVICE_ATTR(compact, S_IWUSR, NULL, sysfs_compact_node);
int compaction_register_node(struct node *node)
{
return device_create_file(&node->dev, &dev_attr_compact);
}
void compaction_unregister_node(struct node *node)
{
return device_remove_file(&node->dev, &dev_attr_compact);
}
#endif /* CONFIG_SYSFS && CONFIG_NUMA */
#endif /* CONFIG_COMPACTION */