linux/mm/page-writeback.c

817 lines
23 KiB
C

/*
* mm/page-writeback.c.
*
* Copyright (C) 2002, Linus Torvalds.
*
* Contains functions related to writing back dirty pages at the
* address_space level.
*
* 10Apr2002 akpm@zip.com.au
* Initial version
*/
#include <linux/kernel.h>
#include <linux/module.h>
#include <linux/spinlock.h>
#include <linux/fs.h>
#include <linux/mm.h>
#include <linux/swap.h>
#include <linux/slab.h>
#include <linux/pagemap.h>
#include <linux/writeback.h>
#include <linux/init.h>
#include <linux/backing-dev.h>
#include <linux/blkdev.h>
#include <linux/mpage.h>
#include <linux/percpu.h>
#include <linux/notifier.h>
#include <linux/smp.h>
#include <linux/sysctl.h>
#include <linux/cpu.h>
#include <linux/syscalls.h>
/*
* The maximum number of pages to writeout in a single bdflush/kupdate
* operation. We do this so we don't hold I_LOCK against an inode for
* enormous amounts of time, which would block a userspace task which has
* been forced to throttle against that inode. Also, the code reevaluates
* the dirty each time it has written this many pages.
*/
#define MAX_WRITEBACK_PAGES 1024
/*
* After a CPU has dirtied this many pages, balance_dirty_pages_ratelimited
* will look to see if it needs to force writeback or throttling.
*/
static long ratelimit_pages = 32;
static long total_pages; /* The total number of pages in the machine. */
static int dirty_exceeded; /* Dirty mem may be over limit */
/*
* When balance_dirty_pages decides that the caller needs to perform some
* non-background writeback, this is how many pages it will attempt to write.
* It should be somewhat larger than RATELIMIT_PAGES to ensure that reasonably
* large amounts of I/O are submitted.
*/
static inline long sync_writeback_pages(void)
{
return ratelimit_pages + ratelimit_pages / 2;
}
/* The following parameters are exported via /proc/sys/vm */
/*
* Start background writeback (via pdflush) at this percentage
*/
int dirty_background_ratio = 10;
/*
* The generator of dirty data starts writeback at this percentage
*/
int vm_dirty_ratio = 40;
/*
* The interval between `kupdate'-style writebacks, in centiseconds
* (hundredths of a second)
*/
int dirty_writeback_centisecs = 5 * 100;
/*
* The longest number of centiseconds for which data is allowed to remain dirty
*/
int dirty_expire_centisecs = 30 * 100;
/*
* Flag that makes the machine dump writes/reads and block dirtyings.
*/
int block_dump;
/*
* Flag that puts the machine in "laptop mode".
*/
int laptop_mode;
EXPORT_SYMBOL(laptop_mode);
/* End of sysctl-exported parameters */
static void background_writeout(unsigned long _min_pages);
struct writeback_state
{
unsigned long nr_dirty;
unsigned long nr_unstable;
unsigned long nr_mapped;
unsigned long nr_writeback;
};
static void get_writeback_state(struct writeback_state *wbs)
{
wbs->nr_dirty = read_page_state(nr_dirty);
wbs->nr_unstable = read_page_state(nr_unstable);
wbs->nr_mapped = read_page_state(nr_mapped);
wbs->nr_writeback = read_page_state(nr_writeback);
}
/*
* Work out the current dirty-memory clamping and background writeout
* thresholds.
*
* The main aim here is to lower them aggressively if there is a lot of mapped
* memory around. To avoid stressing page reclaim with lots of unreclaimable
* pages. It is better to clamp down on writers than to start swapping, and
* performing lots of scanning.
*
* We only allow 1/2 of the currently-unmapped memory to be dirtied.
*
* We don't permit the clamping level to fall below 5% - that is getting rather
* excessive.
*
* We make sure that the background writeout level is below the adjusted
* clamping level.
*/
static void
get_dirty_limits(struct writeback_state *wbs, long *pbackground, long *pdirty,
struct address_space *mapping)
{
int background_ratio; /* Percentages */
int dirty_ratio;
int unmapped_ratio;
long background;
long dirty;
unsigned long available_memory = total_pages;
struct task_struct *tsk;
get_writeback_state(wbs);
#ifdef CONFIG_HIGHMEM
/*
* If this mapping can only allocate from low memory,
* we exclude high memory from our count.
*/
if (mapping && !(mapping_gfp_mask(mapping) & __GFP_HIGHMEM))
available_memory -= totalhigh_pages;
#endif
unmapped_ratio = 100 - (wbs->nr_mapped * 100) / total_pages;
dirty_ratio = vm_dirty_ratio;
if (dirty_ratio > unmapped_ratio / 2)
dirty_ratio = unmapped_ratio / 2;
if (dirty_ratio < 5)
dirty_ratio = 5;
background_ratio = dirty_background_ratio;
if (background_ratio >= dirty_ratio)
background_ratio = dirty_ratio / 2;
background = (background_ratio * available_memory) / 100;
dirty = (dirty_ratio * available_memory) / 100;
tsk = current;
if (tsk->flags & PF_LESS_THROTTLE || rt_task(tsk)) {
background += background / 4;
dirty += dirty / 4;
}
*pbackground = background;
*pdirty = dirty;
}
/*
* balance_dirty_pages() must be called by processes which are generating dirty
* data. It looks at the number of dirty pages in the machine and will force
* the caller to perform writeback if the system is over `vm_dirty_ratio'.
* If we're over `background_thresh' then pdflush is woken to perform some
* writeout.
*/
static void balance_dirty_pages(struct address_space *mapping)
{
struct writeback_state wbs;
long nr_reclaimable;
long background_thresh;
long dirty_thresh;
unsigned long pages_written = 0;
unsigned long write_chunk = sync_writeback_pages();
struct backing_dev_info *bdi = mapping->backing_dev_info;
for (;;) {
struct writeback_control wbc = {
.bdi = bdi,
.sync_mode = WB_SYNC_NONE,
.older_than_this = NULL,
.nr_to_write = write_chunk,
};
get_dirty_limits(&wbs, &background_thresh,
&dirty_thresh, mapping);
nr_reclaimable = wbs.nr_dirty + wbs.nr_unstable;
if (nr_reclaimable + wbs.nr_writeback <= dirty_thresh)
break;
dirty_exceeded = 1;
/* Note: nr_reclaimable denotes nr_dirty + nr_unstable.
* Unstable writes are a feature of certain networked
* filesystems (i.e. NFS) in which data may have been
* written to the server's write cache, but has not yet
* been flushed to permanent storage.
*/
if (nr_reclaimable) {
writeback_inodes(&wbc);
get_dirty_limits(&wbs, &background_thresh,
&dirty_thresh, mapping);
nr_reclaimable = wbs.nr_dirty + wbs.nr_unstable;
if (nr_reclaimable + wbs.nr_writeback <= dirty_thresh)
break;
pages_written += write_chunk - wbc.nr_to_write;
if (pages_written >= write_chunk)
break; /* We've done our duty */
}
blk_congestion_wait(WRITE, HZ/10);
}
if (nr_reclaimable + wbs.nr_writeback <= dirty_thresh)
dirty_exceeded = 0;
if (writeback_in_progress(bdi))
return; /* pdflush is already working this queue */
/*
* In laptop mode, we wait until hitting the higher threshold before
* starting background writeout, and then write out all the way down
* to the lower threshold. So slow writers cause minimal disk activity.
*
* In normal mode, we start background writeout at the lower
* background_thresh, to keep the amount of dirty memory low.
*/
if ((laptop_mode && pages_written) ||
(!laptop_mode && (nr_reclaimable > background_thresh)))
pdflush_operation(background_writeout, 0);
}
/**
* balance_dirty_pages_ratelimited - balance dirty memory state
* @mapping: address_space which was dirtied
*
* Processes which are dirtying memory should call in here once for each page
* which was newly dirtied. The function will periodically check the system's
* dirty state and will initiate writeback if needed.
*
* On really big machines, get_writeback_state is expensive, so try to avoid
* calling it too often (ratelimiting). But once we're over the dirty memory
* limit we decrease the ratelimiting by a lot, to prevent individual processes
* from overshooting the limit by (ratelimit_pages) each.
*/
void balance_dirty_pages_ratelimited(struct address_space *mapping)
{
static DEFINE_PER_CPU(int, ratelimits) = 0;
long ratelimit;
ratelimit = ratelimit_pages;
if (dirty_exceeded)
ratelimit = 8;
/*
* Check the rate limiting. Also, we do not want to throttle real-time
* tasks in balance_dirty_pages(). Period.
*/
if (get_cpu_var(ratelimits)++ >= ratelimit) {
__get_cpu_var(ratelimits) = 0;
put_cpu_var(ratelimits);
balance_dirty_pages(mapping);
return;
}
put_cpu_var(ratelimits);
}
EXPORT_SYMBOL(balance_dirty_pages_ratelimited);
void throttle_vm_writeout(void)
{
struct writeback_state wbs;
long background_thresh;
long dirty_thresh;
for ( ; ; ) {
get_dirty_limits(&wbs, &background_thresh, &dirty_thresh, NULL);
/*
* Boost the allowable dirty threshold a bit for page
* allocators so they don't get DoS'ed by heavy writers
*/
dirty_thresh += dirty_thresh / 10; /* wheeee... */
if (wbs.nr_unstable + wbs.nr_writeback <= dirty_thresh)
break;
blk_congestion_wait(WRITE, HZ/10);
}
}
/*
* writeback at least _min_pages, and keep writing until the amount of dirty
* memory is less than the background threshold, or until we're all clean.
*/
static void background_writeout(unsigned long _min_pages)
{
long min_pages = _min_pages;
struct writeback_control wbc = {
.bdi = NULL,
.sync_mode = WB_SYNC_NONE,
.older_than_this = NULL,
.nr_to_write = 0,
.nonblocking = 1,
};
for ( ; ; ) {
struct writeback_state wbs;
long background_thresh;
long dirty_thresh;
get_dirty_limits(&wbs, &background_thresh, &dirty_thresh, NULL);
if (wbs.nr_dirty + wbs.nr_unstable < background_thresh
&& min_pages <= 0)
break;
wbc.encountered_congestion = 0;
wbc.nr_to_write = MAX_WRITEBACK_PAGES;
wbc.pages_skipped = 0;
writeback_inodes(&wbc);
min_pages -= MAX_WRITEBACK_PAGES - wbc.nr_to_write;
if (wbc.nr_to_write > 0 || wbc.pages_skipped > 0) {
/* Wrote less than expected */
blk_congestion_wait(WRITE, HZ/10);
if (!wbc.encountered_congestion)
break;
}
}
}
/*
* Start writeback of `nr_pages' pages. If `nr_pages' is zero, write back
* the whole world. Returns 0 if a pdflush thread was dispatched. Returns
* -1 if all pdflush threads were busy.
*/
int wakeup_pdflush(long nr_pages)
{
if (nr_pages == 0) {
struct writeback_state wbs;
get_writeback_state(&wbs);
nr_pages = wbs.nr_dirty + wbs.nr_unstable;
}
return pdflush_operation(background_writeout, nr_pages);
}
static void wb_timer_fn(unsigned long unused);
static void laptop_timer_fn(unsigned long unused);
static DEFINE_TIMER(wb_timer, wb_timer_fn, 0, 0);
static DEFINE_TIMER(laptop_mode_wb_timer, laptop_timer_fn, 0, 0);
/*
* Periodic writeback of "old" data.
*
* Define "old": the first time one of an inode's pages is dirtied, we mark the
* dirtying-time in the inode's address_space. So this periodic writeback code
* just walks the superblock inode list, writing back any inodes which are
* older than a specific point in time.
*
* Try to run once per dirty_writeback_centisecs. But if a writeback event
* takes longer than a dirty_writeback_centisecs interval, then leave a
* one-second gap.
*
* older_than_this takes precedence over nr_to_write. So we'll only write back
* all dirty pages if they are all attached to "old" mappings.
*/
static void wb_kupdate(unsigned long arg)
{
unsigned long oldest_jif;
unsigned long start_jif;
unsigned long next_jif;
long nr_to_write;
struct writeback_state wbs;
struct writeback_control wbc = {
.bdi = NULL,
.sync_mode = WB_SYNC_NONE,
.older_than_this = &oldest_jif,
.nr_to_write = 0,
.nonblocking = 1,
.for_kupdate = 1,
};
sync_supers();
get_writeback_state(&wbs);
oldest_jif = jiffies - (dirty_expire_centisecs * HZ) / 100;
start_jif = jiffies;
next_jif = start_jif + (dirty_writeback_centisecs * HZ) / 100;
nr_to_write = wbs.nr_dirty + wbs.nr_unstable +
(inodes_stat.nr_inodes - inodes_stat.nr_unused);
while (nr_to_write > 0) {
wbc.encountered_congestion = 0;
wbc.nr_to_write = MAX_WRITEBACK_PAGES;
writeback_inodes(&wbc);
if (wbc.nr_to_write > 0) {
if (wbc.encountered_congestion)
blk_congestion_wait(WRITE, HZ/10);
else
break; /* All the old data is written */
}
nr_to_write -= MAX_WRITEBACK_PAGES - wbc.nr_to_write;
}
if (time_before(next_jif, jiffies + HZ))
next_jif = jiffies + HZ;
if (dirty_writeback_centisecs)
mod_timer(&wb_timer, next_jif);
}
/*
* sysctl handler for /proc/sys/vm/dirty_writeback_centisecs
*/
int dirty_writeback_centisecs_handler(ctl_table *table, int write,
struct file *file, void __user *buffer, size_t *length, loff_t *ppos)
{
proc_dointvec(table, write, file, buffer, length, ppos);
if (dirty_writeback_centisecs) {
mod_timer(&wb_timer,
jiffies + (dirty_writeback_centisecs * HZ) / 100);
} else {
del_timer(&wb_timer);
}
return 0;
}
static void wb_timer_fn(unsigned long unused)
{
if (pdflush_operation(wb_kupdate, 0) < 0)
mod_timer(&wb_timer, jiffies + HZ); /* delay 1 second */
}
static void laptop_flush(unsigned long unused)
{
sys_sync();
}
static void laptop_timer_fn(unsigned long unused)
{
pdflush_operation(laptop_flush, 0);
}
/*
* We've spun up the disk and we're in laptop mode: schedule writeback
* of all dirty data a few seconds from now. If the flush is already scheduled
* then push it back - the user is still using the disk.
*/
void laptop_io_completion(void)
{
mod_timer(&laptop_mode_wb_timer, jiffies + laptop_mode * HZ);
}
/*
* We're in laptop mode and we've just synced. The sync's writes will have
* caused another writeback to be scheduled by laptop_io_completion.
* Nothing needs to be written back anymore, so we unschedule the writeback.
*/
void laptop_sync_completion(void)
{
del_timer(&laptop_mode_wb_timer);
}
/*
* If ratelimit_pages is too high then we can get into dirty-data overload
* if a large number of processes all perform writes at the same time.
* If it is too low then SMP machines will call the (expensive)
* get_writeback_state too often.
*
* Here we set ratelimit_pages to a level which ensures that when all CPUs are
* dirtying in parallel, we cannot go more than 3% (1/32) over the dirty memory
* thresholds before writeback cuts in.
*
* But the limit should not be set too high. Because it also controls the
* amount of memory which the balance_dirty_pages() caller has to write back.
* If this is too large then the caller will block on the IO queue all the
* time. So limit it to four megabytes - the balance_dirty_pages() caller
* will write six megabyte chunks, max.
*/
static void set_ratelimit(void)
{
ratelimit_pages = total_pages / (num_online_cpus() * 32);
if (ratelimit_pages < 16)
ratelimit_pages = 16;
if (ratelimit_pages * PAGE_CACHE_SIZE > 4096 * 1024)
ratelimit_pages = (4096 * 1024) / PAGE_CACHE_SIZE;
}
static int
ratelimit_handler(struct notifier_block *self, unsigned long u, void *v)
{
set_ratelimit();
return 0;
}
static struct notifier_block ratelimit_nb = {
.notifier_call = ratelimit_handler,
.next = NULL,
};
/*
* If the machine has a large highmem:lowmem ratio then scale back the default
* dirty memory thresholds: allowing too much dirty highmem pins an excessive
* number of buffer_heads.
*/
void __init page_writeback_init(void)
{
long buffer_pages = nr_free_buffer_pages();
long correction;
total_pages = nr_free_pagecache_pages();
correction = (100 * 4 * buffer_pages) / total_pages;
if (correction < 100) {
dirty_background_ratio *= correction;
dirty_background_ratio /= 100;
vm_dirty_ratio *= correction;
vm_dirty_ratio /= 100;
if (dirty_background_ratio <= 0)
dirty_background_ratio = 1;
if (vm_dirty_ratio <= 0)
vm_dirty_ratio = 1;
}
mod_timer(&wb_timer, jiffies + (dirty_writeback_centisecs * HZ) / 100);
set_ratelimit();
register_cpu_notifier(&ratelimit_nb);
}
int do_writepages(struct address_space *mapping, struct writeback_control *wbc)
{
if (wbc->nr_to_write <= 0)
return 0;
if (mapping->a_ops->writepages)
return mapping->a_ops->writepages(mapping, wbc);
return generic_writepages(mapping, wbc);
}
/**
* write_one_page - write out a single page and optionally wait on I/O
*
* @page: the page to write
* @wait: if true, wait on writeout
*
* The page must be locked by the caller and will be unlocked upon return.
*
* write_one_page() returns a negative error code if I/O failed.
*/
int write_one_page(struct page *page, int wait)
{
struct address_space *mapping = page->mapping;
int ret = 0;
struct writeback_control wbc = {
.sync_mode = WB_SYNC_ALL,
.nr_to_write = 1,
};
BUG_ON(!PageLocked(page));
if (wait)
wait_on_page_writeback(page);
if (clear_page_dirty_for_io(page)) {
page_cache_get(page);
ret = mapping->a_ops->writepage(page, &wbc);
if (ret == 0 && wait) {
wait_on_page_writeback(page);
if (PageError(page))
ret = -EIO;
}
page_cache_release(page);
} else {
unlock_page(page);
}
return ret;
}
EXPORT_SYMBOL(write_one_page);
/*
* For address_spaces which do not use buffers. Just tag the page as dirty in
* its radix tree.
*
* This is also used when a single buffer is being dirtied: we want to set the
* page dirty in that case, but not all the buffers. This is a "bottom-up"
* dirtying, whereas __set_page_dirty_buffers() is a "top-down" dirtying.
*
* Most callers have locked the page, which pins the address_space in memory.
* But zap_pte_range() does not lock the page, however in that case the
* mapping is pinned by the vma's ->vm_file reference.
*
* We take care to handle the case where the page was truncated from the
* mapping by re-checking page_mapping() insode tree_lock.
*/
int __set_page_dirty_nobuffers(struct page *page)
{
int ret = 0;
if (!TestSetPageDirty(page)) {
struct address_space *mapping = page_mapping(page);
struct address_space *mapping2;
if (mapping) {
write_lock_irq(&mapping->tree_lock);
mapping2 = page_mapping(page);
if (mapping2) { /* Race with truncate? */
BUG_ON(mapping2 != mapping);
if (mapping_cap_account_dirty(mapping))
inc_page_state(nr_dirty);
radix_tree_tag_set(&mapping->page_tree,
page_index(page), PAGECACHE_TAG_DIRTY);
}
write_unlock_irq(&mapping->tree_lock);
if (mapping->host) {
/* !PageAnon && !swapper_space */
__mark_inode_dirty(mapping->host,
I_DIRTY_PAGES);
}
}
}
return ret;
}
EXPORT_SYMBOL(__set_page_dirty_nobuffers);
/*
* When a writepage implementation decides that it doesn't want to write this
* page for some reason, it should redirty the locked page via
* redirty_page_for_writepage() and it should then unlock the page and return 0
*/
int redirty_page_for_writepage(struct writeback_control *wbc, struct page *page)
{
wbc->pages_skipped++;
return __set_page_dirty_nobuffers(page);
}
EXPORT_SYMBOL(redirty_page_for_writepage);
/*
* If the mapping doesn't provide a set_page_dirty a_op, then
* just fall through and assume that it wants buffer_heads.
*/
int fastcall set_page_dirty(struct page *page)
{
struct address_space *mapping = page_mapping(page);
if (likely(mapping)) {
int (*spd)(struct page *) = mapping->a_ops->set_page_dirty;
if (spd)
return (*spd)(page);
return __set_page_dirty_buffers(page);
}
if (!PageDirty(page))
SetPageDirty(page);
return 0;
}
EXPORT_SYMBOL(set_page_dirty);
/*
* set_page_dirty() is racy if the caller has no reference against
* page->mapping->host, and if the page is unlocked. This is because another
* CPU could truncate the page off the mapping and then free the mapping.
*
* Usually, the page _is_ locked, or the caller is a user-space process which
* holds a reference on the inode by having an open file.
*
* In other cases, the page should be locked before running set_page_dirty().
*/
int set_page_dirty_lock(struct page *page)
{
int ret;
lock_page(page);
ret = set_page_dirty(page);
unlock_page(page);
return ret;
}
EXPORT_SYMBOL(set_page_dirty_lock);
/*
* Clear a page's dirty flag, while caring for dirty memory accounting.
* Returns true if the page was previously dirty.
*/
int test_clear_page_dirty(struct page *page)
{
struct address_space *mapping = page_mapping(page);
unsigned long flags;
if (mapping) {
write_lock_irqsave(&mapping->tree_lock, flags);
if (TestClearPageDirty(page)) {
radix_tree_tag_clear(&mapping->page_tree,
page_index(page),
PAGECACHE_TAG_DIRTY);
write_unlock_irqrestore(&mapping->tree_lock, flags);
if (mapping_cap_account_dirty(mapping))
dec_page_state(nr_dirty);
return 1;
}
write_unlock_irqrestore(&mapping->tree_lock, flags);
return 0;
}
return TestClearPageDirty(page);
}
EXPORT_SYMBOL(test_clear_page_dirty);
/*
* Clear a page's dirty flag, while caring for dirty memory accounting.
* Returns true if the page was previously dirty.
*
* This is for preparing to put the page under writeout. We leave the page
* tagged as dirty in the radix tree so that a concurrent write-for-sync
* can discover it via a PAGECACHE_TAG_DIRTY walk. The ->writepage
* implementation will run either set_page_writeback() or set_page_dirty(),
* at which stage we bring the page's dirty flag and radix-tree dirty tag
* back into sync.
*
* This incoherency between the page's dirty flag and radix-tree tag is
* unfortunate, but it only exists while the page is locked.
*/
int clear_page_dirty_for_io(struct page *page)
{
struct address_space *mapping = page_mapping(page);
if (mapping) {
if (TestClearPageDirty(page)) {
if (mapping_cap_account_dirty(mapping))
dec_page_state(nr_dirty);
return 1;
}
return 0;
}
return TestClearPageDirty(page);
}
int test_clear_page_writeback(struct page *page)
{
struct address_space *mapping = page_mapping(page);
int ret;
if (mapping) {
unsigned long flags;
write_lock_irqsave(&mapping->tree_lock, flags);
ret = TestClearPageWriteback(page);
if (ret)
radix_tree_tag_clear(&mapping->page_tree,
page_index(page),
PAGECACHE_TAG_WRITEBACK);
write_unlock_irqrestore(&mapping->tree_lock, flags);
} else {
ret = TestClearPageWriteback(page);
}
return ret;
}
int test_set_page_writeback(struct page *page)
{
struct address_space *mapping = page_mapping(page);
int ret;
if (mapping) {
unsigned long flags;
write_lock_irqsave(&mapping->tree_lock, flags);
ret = TestSetPageWriteback(page);
if (!ret)
radix_tree_tag_set(&mapping->page_tree,
page_index(page),
PAGECACHE_TAG_WRITEBACK);
if (!PageDirty(page))
radix_tree_tag_clear(&mapping->page_tree,
page_index(page),
PAGECACHE_TAG_DIRTY);
write_unlock_irqrestore(&mapping->tree_lock, flags);
} else {
ret = TestSetPageWriteback(page);
}
return ret;
}
EXPORT_SYMBOL(test_set_page_writeback);
/*
* Return true if any of the pages in the mapping are marged with the
* passed tag.
*/
int mapping_tagged(struct address_space *mapping, int tag)
{
unsigned long flags;
int ret;
read_lock_irqsave(&mapping->tree_lock, flags);
ret = radix_tree_tagged(&mapping->page_tree, tag);
read_unlock_irqrestore(&mapping->tree_lock, flags);
return ret;
}
EXPORT_SYMBOL(mapping_tagged);