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 "internal.h"
#define CREATE_TRACE_POINTS
#include <trace/events/compaction.h>
/*
* compact_control is used to track pages being migrated and the free pages
* they are being migrated to during memory compaction. The free_pfn starts
* at the end of a zone and migrate_pfn begins at the start. Movable pages
* are moved to the end of a zone during a compaction run and the run
* completes when free_pfn <= migrate_pfn
*/
struct compact_control {
struct list_head freepages; /* List of free pages to migrate to */
struct list_head migratepages; /* List of pages being migrated */
unsigned long nr_freepages; /* Number of isolated free pages */
unsigned long nr_migratepages; /* Number of pages to migrate */
unsigned long free_pfn; /* isolate_freepages search base */
unsigned long migrate_pfn; /* isolate_migratepages search base */
bool sync; /* Synchronous migration */
unsigned int order; /* order a direct compactor needs */
int migratetype; /* MOVABLE, RECLAIMABLE etc */
struct zone *zone;
};
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;
}
/* Isolate free pages onto a private freelist. Must hold zone->lock */
static unsigned long isolate_freepages_block(struct zone *zone,
unsigned long blockpfn,
struct list_head *freelist)
{
unsigned long zone_end_pfn, end_pfn;
int nr_scanned = 0, total_isolated = 0;
struct page *cursor;
/* Get the last PFN we should scan for free pages at */
zone_end_pfn = zone->zone_start_pfn + zone->spanned_pages;
end_pfn = min(blockpfn + pageblock_nr_pages, zone_end_pfn);
/* Find the first usable PFN in the block to initialse page cursor */
for (; blockpfn < end_pfn; blockpfn++) {
if (pfn_valid_within(blockpfn))
break;
}
cursor = pfn_to_page(blockpfn);
/* Isolate free pages. This assumes the block is valid */
for (; blockpfn < end_pfn; blockpfn++, cursor++) {
int isolated, i;
struct page *page = cursor;
if (!pfn_valid_within(blockpfn))
continue;
nr_scanned++;
if (!PageBuddy(page))
continue;
/* Found a free page, break it into order-0 pages */
isolated = split_free_page(page);
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);
return total_isolated;
}
/* 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, allow migration */
if (migratetype == MIGRATE_MOVABLE)
return true;
/* Otherwise skip the block */
return false;
}
/*
* 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;
unsigned long flags;
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);
/*
* 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: minimise the time IRQs are disabled while isolating free pages compaction_alloc() isolates free pages to be used as migration targets. While its scanning, IRQs are disabled on the mistaken assumption the scanning should be short. Analysis showed that IRQs were in fact being disabled for substantial time. A simple test was run using large anonymous mappings with transparent hugepage support enabled to trigger frequent compactions. A monitor sampled what the worst IRQ-off latencies were and a post-processing tool found the following; Total sampled time IRQs off (not real total time): 22355 Event compaction_alloc..compaction_alloc 8409 us count 1 Event compaction_alloc..compaction_alloc 7341 us count 1 Event compaction_alloc..compaction_alloc 2463 us count 1 Event compaction_alloc..compaction_alloc 2054 us count 1 Event shrink_inactive_list..shrink_zone 1864 us count 1 Event shrink_inactive_list..shrink_zone 88 us count 1 Event save_args..call_softirq 36 us count 1 Event save_args..call_softirq 35 us count 2 Event __make_request..__blk_run_queue 24 us count 1 Event __alloc_pages_nodemask..__alloc_pages_nodemask 6 us count 1 i.e. compaction is disabled IRQs for a prolonged period of time - 8ms in one instance. The full report generated by the tool can be found at http://www.csn.ul.ie/~mel/postings/minfree-20110225/irqsoff-vanilla-micro.report This patch reduces the time IRQs are disabled by simply disabling IRQs at the last possible minute. An updated IRQs-off summary report then looks 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 A full report is again available at http://www.csn.ul.ie/~mel/postings/minfree-20110225/irqsoff-minimiseirq-free-v1r4-micro.report As should be obvious, IRQ disabled latencies due to compaction are almost elimimnated for this particular test. [aarcange@redhat.com: Fix initialisation of isolated] Signed-off-by: Mel Gorman <mel@csn.ul.ie> Acked-by: Johannes Weiner <hannes@cmpxchg.org> Reviewed-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujisu.com> Reviewed-by: Minchan Kim <minchan.kim@gmail.com> Acked-by: Andrea Arcangeli <aarcange@redhat.com> Cc: Arthur Marsh <arthur.marsh@internode.on.net> Cc: Clemens Ladisch <cladisch@googlemail.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2011-03-22 23:33:08 +00:00
/*
* Found a block suitable for isolating free pages from. Now
* we disabled interrupts, double check things are ok and
* isolate the pages. This is to minimise the time IRQs
* are disabled
*/
isolated = 0;
spin_lock_irqsave(&zone->lock, flags);
if (suitable_migration_target(page)) {
isolated = isolate_freepages_block(zone, pfn, freelist);
nr_freepages += isolated;
}
spin_unlock_irqrestore(&zone->lock, flags);
/*
* 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
*/
if (isolated)
high_pfn = max(high_pfn, pfn);
}
/* split_free_page does not map the pages */
list_for_each_entry(page, freelist, lru) {
arch_alloc_page(page, 0);
kernel_map_pages(page, 1, 1);
}
cc->free_pfn = high_pfn;
cc->nr_freepages = nr_freepages;
}
/* Update the number of anon and file isolated pages in the zone */
static void acct_isolated(struct zone *zone, 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)]++;
__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;
}
/* 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;
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 = ISOLATE_ACTIVE|ISOLATE_INACTIVE;
/* 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;
}
/*
* 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 ISOLATE_ABORT;
congestion_wait(BLK_RW_ASYNC, HZ/10);
if (fatal_signal_pending(current))
return ISOLATE_ABORT;
}
/* 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();
spin_lock_irq(&zone->lru_lock);
for (; low_pfn < end_pfn; low_pfn++) {
struct page *page;
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
bool locked = true;
/* give a chance to irqs before checking need_resched() */
if (!((low_pfn+1) % SWAP_CLUSTER_MAX)) {
spin_unlock_irq(&zone->lru_lock);
locked = false;
}
if (need_resched() || spin_is_contended(&zone->lru_lock)) {
if (locked)
spin_unlock_irq(&zone->lru_lock);
cond_resched();
spin_lock_irq(&zone->lru_lock);
if (fatal_signal_pending(current))
break;
} else if (!locked)
spin_lock_irq(&zone->lru_lock);
if (!pfn_valid_within(low_pfn))
continue;
nr_scanned++;
/* Get the page and skip if free */
page = pfn_to_page(low_pfn);
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
*/
pageblock_nr = low_pfn >> pageblock_order;
if (!cc->sync && last_pageblock_nr != pageblock_nr &&
get_pageblock_migratetype(page) != MIGRATE_MOVABLE) {
low_pfn += pageblock_nr_pages;
low_pfn = ALIGN(low_pfn, pageblock_nr_pages) - 1;
last_pageblock_nr = pageblock_nr;
continue;
}
if (!PageLRU(page))
continue;
/*
* PageLRU is set, and lru_lock excludes isolation,
* splitting and collapsing (collapsing has already
* happened if PageLRU is set).
*/
if (PageTransHuge(page)) {
low_pfn += (1 << compound_order(page)) - 1;
continue;
}
if (!cc->sync)
mode |= ISOLATE_CLEAN;
/* Try isolate the page */
if (__isolate_lru_page(page, mode, 0) != 0)
continue;
VM_BUG_ON(PageTransCompound(page));
/* Successfully isolated */
del_page_from_lru_list(zone, page, page_lru(page));
list_add(&page->lru, migratelist);
cc->nr_migratepages++;
nr_isolated++;
/* Avoid isolating too much */
if (cc->nr_migratepages == COMPACT_CLUSTER_MAX)
break;
}
acct_isolated(zone, cc);
spin_unlock_irq(&zone->lru_lock);
cc->migrate_pfn = low_pfn;
trace_mm_compaction_isolate_migratepages(nr_scanned, nr_isolated);
return ISOLATE_SUCCESS;
}
/*
* 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;
}
static int compact_finished(struct zone *zone,
struct compact_control *cc)
{
unsigned int order;
unsigned long watermark;
if (fatal_signal_pending(current))
return COMPACT_PARTIAL;
/* Compaction run completes if the migrate and free scanner meet */
if (cc->free_pfn <= cc->migrate_pfn)
return COMPACT_COMPLETE;
/*
* 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? */
for (order = cc->order; order < MAX_ORDER; order++) {
/* Job done if page is free of the right migratetype */
if (!list_empty(&zone->free_area[order].free_list[cc->migratetype]))
return COMPACT_PARTIAL;
/* Job done if allocation would set block type */
if (order >= pageblock_order && zone->free_area[order].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 int compact_zone(struct zone *zone, struct compact_control *cc)
{
int ret;
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 */
;
}
/* Setup to move all movable pages to the end of the zone */
cc->migrate_pfn = zone->zone_start_pfn;
cc->free_pfn = cc->migrate_pfn + zone->spanned_pages;
cc->free_pfn &= ~(pageblock_nr_pages-1);
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;
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);
update_nr_listpages(cc);
nr_remaining = cc->nr_migratepages;
count_vm_event(COMPACTBLOCKS);
count_vm_events(COMPACTPAGES, nr_migrate - nr_remaining);
if (nr_remaining)
count_vm_events(COMPACTPAGEFAILED, nr_remaining);
trace_mm_compaction_migratepages(nr_migrate - nr_remaining,
nr_remaining);
/* Release LRU pages not migrated */
if (err) {
putback_lru_pages(&cc->migratepages);
cc->nr_migratepages = 0;
}
}
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,
mm: compaction: prevent kswapd compacting memory to reduce CPU usage This patch reverts 5a03b051 ("thp: use compaction in kswapd for GFP_ATOMIC order > 0") due to reports stating that kswapd CPU usage was higher and IRQs were being disabled more frequently. This was reported at http://www.spinics.net/linux/fedora/alsa-user/msg09885.html. Without this patch applied, CPU usage by kswapd hovers around the 20% mark according to the tester (Arthur Marsh: http://www.spinics.net/linux/fedora/alsa-user/msg09899.html). With this patch applied, it's around 2%. The problem is not related to THP which specifies __GFP_NO_KSWAPD but is triggered by high-order allocations hitting the low watermark for their order and waking kswapd on kernels with CONFIG_COMPACTION set. The most common trigger for this is network cards configured for jumbo frames but it's also possible it'll be triggered by fork-heavy workloads (order-1) and some wireless cards which depend on order-1 allocations. The symptoms for the user will be high CPU usage by kswapd in low-memory situations which could be confused with another writeback problem. While a patch like 5a03b051 may be reintroduced in the future, this patch plays it safe for now and reverts it. [mel@csn.ul.ie: Beefed up the changelog] Signed-off-by: Andrea Arcangeli <aarcange@redhat.com> Signed-off-by: Mel Gorman <mel@csn.ul.ie> Reported-by: Arthur Marsh <arthur.marsh@internode.on.net> Tested-by: Arthur Marsh <arthur.marsh@internode.on.net> Cc: <stable@kernel.org> [2.6.38.1] Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2011-03-22 23:30:38 +00:00
bool sync)
{
struct compact_control cc = {
.nr_freepages = 0,
.nr_migratepages = 0,
.order = order,
.migratetype = allocflags_to_migratetype(gfp_mask),
.zone = zone,
.sync = sync,
};
INIT_LIST_HEAD(&cc.freepages);
INIT_LIST_HEAD(&cc.migratepages);
return compact_zone(zone, &cc);
}
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
*
* 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)
{
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;
/*
* Check whether it is worth even starting compaction. The order check is
* made because an assumption is made that the page allocator can satisfy
* the "cheaper" orders without taking special steps
*/
if (!order || !may_enter_fs || !may_perform_io)
return rc;
count_vm_event(COMPACTSTALL);
/* Compact each zone in the list */
for_each_zone_zonelist_nodemask(zone, z, zonelist, high_zoneidx,
nodemask) {
int status;
mm: compaction: prevent kswapd compacting memory to reduce CPU usage This patch reverts 5a03b051 ("thp: use compaction in kswapd for GFP_ATOMIC order > 0") due to reports stating that kswapd CPU usage was higher and IRQs were being disabled more frequently. This was reported at http://www.spinics.net/linux/fedora/alsa-user/msg09885.html. Without this patch applied, CPU usage by kswapd hovers around the 20% mark according to the tester (Arthur Marsh: http://www.spinics.net/linux/fedora/alsa-user/msg09899.html). With this patch applied, it's around 2%. The problem is not related to THP which specifies __GFP_NO_KSWAPD but is triggered by high-order allocations hitting the low watermark for their order and waking kswapd on kernels with CONFIG_COMPACTION set. The most common trigger for this is network cards configured for jumbo frames but it's also possible it'll be triggered by fork-heavy workloads (order-1) and some wireless cards which depend on order-1 allocations. The symptoms for the user will be high CPU usage by kswapd in low-memory situations which could be confused with another writeback problem. While a patch like 5a03b051 may be reintroduced in the future, this patch plays it safe for now and reverts it. [mel@csn.ul.ie: Beefed up the changelog] Signed-off-by: Andrea Arcangeli <aarcange@redhat.com> Signed-off-by: Mel Gorman <mel@csn.ul.ie> Reported-by: Arthur Marsh <arthur.marsh@internode.on.net> Tested-by: Arthur Marsh <arthur.marsh@internode.on.net> Cc: <stable@kernel.org> [2.6.38.1] Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2011-03-22 23:30:38 +00:00
status = compact_zone_order(zone, order, gfp_mask, sync);
rc = max(status, rc);
/* If a normal allocation would succeed, stop compacting */
if (zone_watermark_ok(zone, order, low_wmark_pages(zone), 0, 0))
break;
}
return rc;
}
/* Compact all zones within a node */
static int compact_node(int nid)
{
int zoneid;
pg_data_t *pgdat;
struct zone *zone;
if (nid < 0 || nid >= nr_node_ids || !node_online(nid))
return -EINVAL;
pgdat = NODE_DATA(nid);
/* Flush pending updates to the LRU lists */
lru_add_drain_all();
for (zoneid = 0; zoneid < MAX_NR_ZONES; zoneid++) {
struct compact_control cc = {
.nr_freepages = 0,
.nr_migratepages = 0,
.order = -1,
};
zone = &pgdat->node_zones[zoneid];
if (!populated_zone(zone))
continue;
cc.zone = zone;
INIT_LIST_HEAD(&cc.freepages);
INIT_LIST_HEAD(&cc.migratepages);
compact_zone(zone, &cc);
VM_BUG_ON(!list_empty(&cc.freepages));
VM_BUG_ON(!list_empty(&cc.migratepages));
}
return 0;
}
/* Compact all nodes in the system */
static int compact_nodes(void)
{
int nid;
for_each_online_node(nid)
compact_node(nid);
return COMPACT_COMPLETE;
}
/* 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)
return 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 sys_device *dev,
struct sysdev_attribute *attr,
const char *buf, size_t count)
{
compact_node(dev->id);
return count;
}
static SYSDEV_ATTR(compact, S_IWUSR, NULL, sysfs_compact_node);
int compaction_register_node(struct node *node)
{
return sysdev_create_file(&node->sysdev, &attr_compact);
}
void compaction_unregister_node(struct node *node)
{
return sysdev_remove_file(&node->sysdev, &attr_compact);
}
#endif /* CONFIG_SYSFS && CONFIG_NUMA */