4 * Copyright (C) 2002, Linus Torvalds.
5 * Copyright (C) 2007 Red Hat, Inc., Peter Zijlstra <pzijlstr@redhat.com>
7 * Contains functions related to writing back dirty pages at the
10 * 10Apr2002 Andrew Morton
14 #include <linux/kernel.h>
15 #include <linux/module.h>
16 #include <linux/spinlock.h>
19 #include <linux/swap.h>
20 #include <linux/slab.h>
21 #include <linux/pagemap.h>
22 #include <linux/writeback.h>
23 #include <linux/init.h>
24 #include <linux/backing-dev.h>
25 #include <linux/task_io_accounting_ops.h>
26 #include <linux/blkdev.h>
27 #include <linux/mpage.h>
28 #include <linux/rmap.h>
29 #include <linux/percpu.h>
30 #include <linux/notifier.h>
31 #include <linux/smp.h>
32 #include <linux/sysctl.h>
33 #include <linux/cpu.h>
34 #include <linux/syscalls.h>
35 #include <linux/buffer_head.h>
36 #include <linux/pagevec.h>
39 * The maximum number of pages to writeout in a single bdflush/kupdate
40 * operation. We do this so we don't hold I_SYNC against an inode for
41 * enormous amounts of time, which would block a userspace task which has
42 * been forced to throttle against that inode. Also, the code reevaluates
43 * the dirty each time it has written this many pages.
45 #define MAX_WRITEBACK_PAGES 1024
48 * After a CPU has dirtied this many pages, balance_dirty_pages_ratelimited
49 * will look to see if it needs to force writeback or throttling.
51 static long ratelimit_pages
= 32;
54 * When balance_dirty_pages decides that the caller needs to perform some
55 * non-background writeback, this is how many pages it will attempt to write.
56 * It should be somewhat larger than RATELIMIT_PAGES to ensure that reasonably
57 * large amounts of I/O are submitted.
59 static inline long sync_writeback_pages(void)
61 return ratelimit_pages
+ ratelimit_pages
/ 2;
64 /* The following parameters are exported via /proc/sys/vm */
67 * Start background writeback (via pdflush) at this percentage
69 int dirty_background_ratio
= 10;
72 * dirty_background_bytes starts at 0 (disabled) so that it is a function of
73 * dirty_background_ratio * the amount of dirtyable memory
75 unsigned long dirty_background_bytes
;
78 * free highmem will not be subtracted from the total free memory
79 * for calculating free ratios if vm_highmem_is_dirtyable is true
81 int vm_highmem_is_dirtyable
;
84 * The generator of dirty data starts writeback at this percentage
86 int vm_dirty_ratio
= 20;
89 * vm_dirty_bytes starts at 0 (disabled) so that it is a function of
90 * vm_dirty_ratio * the amount of dirtyable memory
92 unsigned long vm_dirty_bytes
;
95 * The interval between `kupdate'-style writebacks
97 unsigned int dirty_writeback_interval
= 5 * 100; /* centiseconds */
100 * The longest time for which data is allowed to remain dirty
102 unsigned int dirty_expire_interval
= 30 * 100; /* centiseconds */
105 * Flag that makes the machine dump writes/reads and block dirtyings.
110 * Flag that puts the machine in "laptop mode". Doubles as a timeout in jiffies:
111 * a full sync is triggered after this time elapses without any disk activity.
115 EXPORT_SYMBOL(laptop_mode
);
117 /* End of sysctl-exported parameters */
120 static void background_writeout(unsigned long _min_pages
);
123 * Scale the writeback cache size proportional to the relative writeout speeds.
125 * We do this by keeping a floating proportion between BDIs, based on page
126 * writeback completions [end_page_writeback()]. Those devices that write out
127 * pages fastest will get the larger share, while the slower will get a smaller
130 * We use page writeout completions because we are interested in getting rid of
131 * dirty pages. Having them written out is the primary goal.
133 * We introduce a concept of time, a period over which we measure these events,
134 * because demand can/will vary over time. The length of this period itself is
135 * measured in page writeback completions.
138 static struct prop_descriptor vm_completions
;
139 static struct prop_descriptor vm_dirties
;
142 * couple the period to the dirty_ratio:
144 * period/2 ~ roundup_pow_of_two(dirty limit)
146 static int calc_period_shift(void)
148 unsigned long dirty_total
;
151 dirty_total
= vm_dirty_bytes
/ PAGE_SIZE
;
153 dirty_total
= (vm_dirty_ratio
* determine_dirtyable_memory()) /
155 return 2 + ilog2(dirty_total
- 1);
159 * update the period when the dirty threshold changes.
161 static void update_completion_period(void)
163 int shift
= calc_period_shift();
164 prop_change_shift(&vm_completions
, shift
);
165 prop_change_shift(&vm_dirties
, shift
);
168 int dirty_background_ratio_handler(struct ctl_table
*table
, int write
,
169 struct file
*filp
, void __user
*buffer
, size_t *lenp
,
174 ret
= proc_dointvec_minmax(table
, write
, filp
, buffer
, lenp
, ppos
);
175 if (ret
== 0 && write
)
176 dirty_background_bytes
= 0;
180 int dirty_background_bytes_handler(struct ctl_table
*table
, int write
,
181 struct file
*filp
, void __user
*buffer
, size_t *lenp
,
186 ret
= proc_doulongvec_minmax(table
, write
, filp
, buffer
, lenp
, ppos
);
187 if (ret
== 0 && write
)
188 dirty_background_ratio
= 0;
192 int dirty_ratio_handler(struct ctl_table
*table
, int write
,
193 struct file
*filp
, void __user
*buffer
, size_t *lenp
,
196 int old_ratio
= vm_dirty_ratio
;
199 ret
= proc_dointvec_minmax(table
, write
, filp
, buffer
, lenp
, ppos
);
200 if (ret
== 0 && write
&& vm_dirty_ratio
!= old_ratio
) {
201 update_completion_period();
208 int dirty_bytes_handler(struct ctl_table
*table
, int write
,
209 struct file
*filp
, void __user
*buffer
, size_t *lenp
,
212 unsigned long old_bytes
= vm_dirty_bytes
;
215 ret
= proc_doulongvec_minmax(table
, write
, filp
, buffer
, lenp
, ppos
);
216 if (ret
== 0 && write
&& vm_dirty_bytes
!= old_bytes
) {
217 update_completion_period();
224 * Increment the BDI's writeout completion count and the global writeout
225 * completion count. Called from test_clear_page_writeback().
227 static inline void __bdi_writeout_inc(struct backing_dev_info
*bdi
)
229 __prop_inc_percpu_max(&vm_completions
, &bdi
->completions
,
233 void bdi_writeout_inc(struct backing_dev_info
*bdi
)
237 local_irq_save(flags
);
238 __bdi_writeout_inc(bdi
);
239 local_irq_restore(flags
);
241 EXPORT_SYMBOL_GPL(bdi_writeout_inc
);
243 void task_dirty_inc(struct task_struct
*tsk
)
245 prop_inc_single(&vm_dirties
, &tsk
->dirties
);
249 * Obtain an accurate fraction of the BDI's portion.
251 static void bdi_writeout_fraction(struct backing_dev_info
*bdi
,
252 long *numerator
, long *denominator
)
254 if (bdi_cap_writeback_dirty(bdi
)) {
255 prop_fraction_percpu(&vm_completions
, &bdi
->completions
,
256 numerator
, denominator
);
264 * Clip the earned share of dirty pages to that which is actually available.
265 * This avoids exceeding the total dirty_limit when the floating averages
266 * fluctuate too quickly.
268 static void clip_bdi_dirty_limit(struct backing_dev_info
*bdi
,
269 unsigned long dirty
, unsigned long *pbdi_dirty
)
271 unsigned long avail_dirty
;
273 avail_dirty
= global_page_state(NR_FILE_DIRTY
) +
274 global_page_state(NR_WRITEBACK
) +
275 global_page_state(NR_UNSTABLE_NFS
) +
276 global_page_state(NR_WRITEBACK_TEMP
);
278 if (avail_dirty
< dirty
)
279 avail_dirty
= dirty
- avail_dirty
;
283 avail_dirty
+= bdi_stat(bdi
, BDI_RECLAIMABLE
) +
284 bdi_stat(bdi
, BDI_WRITEBACK
);
286 *pbdi_dirty
= min(*pbdi_dirty
, avail_dirty
);
289 static inline void task_dirties_fraction(struct task_struct
*tsk
,
290 long *numerator
, long *denominator
)
292 prop_fraction_single(&vm_dirties
, &tsk
->dirties
,
293 numerator
, denominator
);
297 * scale the dirty limit
299 * task specific dirty limit:
301 * dirty -= (dirty/8) * p_{t}
303 static void task_dirty_limit(struct task_struct
*tsk
, unsigned long *pdirty
)
305 long numerator
, denominator
;
306 unsigned long dirty
= *pdirty
;
307 u64 inv
= dirty
>> 3;
309 task_dirties_fraction(tsk
, &numerator
, &denominator
);
311 do_div(inv
, denominator
);
314 if (dirty
< *pdirty
/2)
323 static DEFINE_SPINLOCK(bdi_lock
);
324 static unsigned int bdi_min_ratio
;
326 int bdi_set_min_ratio(struct backing_dev_info
*bdi
, unsigned int min_ratio
)
331 spin_lock_irqsave(&bdi_lock
, flags
);
332 if (min_ratio
> bdi
->max_ratio
) {
335 min_ratio
-= bdi
->min_ratio
;
336 if (bdi_min_ratio
+ min_ratio
< 100) {
337 bdi_min_ratio
+= min_ratio
;
338 bdi
->min_ratio
+= min_ratio
;
343 spin_unlock_irqrestore(&bdi_lock
, flags
);
348 int bdi_set_max_ratio(struct backing_dev_info
*bdi
, unsigned max_ratio
)
356 spin_lock_irqsave(&bdi_lock
, flags
);
357 if (bdi
->min_ratio
> max_ratio
) {
360 bdi
->max_ratio
= max_ratio
;
361 bdi
->max_prop_frac
= (PROP_FRAC_BASE
* max_ratio
) / 100;
363 spin_unlock_irqrestore(&bdi_lock
, flags
);
367 EXPORT_SYMBOL(bdi_set_max_ratio
);
370 * Work out the current dirty-memory clamping and background writeout
373 * The main aim here is to lower them aggressively if there is a lot of mapped
374 * memory around. To avoid stressing page reclaim with lots of unreclaimable
375 * pages. It is better to clamp down on writers than to start swapping, and
376 * performing lots of scanning.
378 * We only allow 1/2 of the currently-unmapped memory to be dirtied.
380 * We don't permit the clamping level to fall below 5% - that is getting rather
383 * We make sure that the background writeout level is below the adjusted
387 static unsigned long highmem_dirtyable_memory(unsigned long total
)
389 #ifdef CONFIG_HIGHMEM
393 for_each_node_state(node
, N_HIGH_MEMORY
) {
395 &NODE_DATA(node
)->node_zones
[ZONE_HIGHMEM
];
397 x
+= zone_page_state(z
, NR_FREE_PAGES
) + zone_lru_pages(z
);
400 * Make sure that the number of highmem pages is never larger
401 * than the number of the total dirtyable memory. This can only
402 * occur in very strange VM situations but we want to make sure
403 * that this does not occur.
405 return min(x
, total
);
412 * determine_dirtyable_memory - amount of memory that may be used
414 * Returns the numebr of pages that can currently be freed and used
415 * by the kernel for direct mappings.
417 unsigned long determine_dirtyable_memory(void)
421 x
= global_page_state(NR_FREE_PAGES
) + global_lru_pages();
423 if (!vm_highmem_is_dirtyable
)
424 x
-= highmem_dirtyable_memory(x
);
426 return x
+ 1; /* Ensure that we never return 0 */
430 get_dirty_limits(unsigned long *pbackground
, unsigned long *pdirty
,
431 unsigned long *pbdi_dirty
, struct backing_dev_info
*bdi
)
433 unsigned long background
;
435 unsigned long available_memory
= determine_dirtyable_memory();
436 struct task_struct
*tsk
;
439 dirty
= DIV_ROUND_UP(vm_dirty_bytes
, PAGE_SIZE
);
443 dirty_ratio
= vm_dirty_ratio
;
446 dirty
= (dirty_ratio
* available_memory
) / 100;
449 if (dirty_background_bytes
)
450 background
= DIV_ROUND_UP(dirty_background_bytes
, PAGE_SIZE
);
452 background
= (dirty_background_ratio
* available_memory
) / 100;
454 if (background
>= dirty
)
455 background
= dirty
/ 2;
457 if (tsk
->flags
& PF_LESS_THROTTLE
|| rt_task(tsk
)) {
458 background
+= background
/ 4;
461 *pbackground
= background
;
466 long numerator
, denominator
;
469 * Calculate this BDI's share of the dirty ratio.
471 bdi_writeout_fraction(bdi
, &numerator
, &denominator
);
473 bdi_dirty
= (dirty
* (100 - bdi_min_ratio
)) / 100;
474 bdi_dirty
*= numerator
;
475 do_div(bdi_dirty
, denominator
);
476 bdi_dirty
+= (dirty
* bdi
->min_ratio
) / 100;
477 if (bdi_dirty
> (dirty
* bdi
->max_ratio
) / 100)
478 bdi_dirty
= dirty
* bdi
->max_ratio
/ 100;
480 *pbdi_dirty
= bdi_dirty
;
481 clip_bdi_dirty_limit(bdi
, dirty
, pbdi_dirty
);
482 task_dirty_limit(current
, pbdi_dirty
);
487 * balance_dirty_pages() must be called by processes which are generating dirty
488 * data. It looks at the number of dirty pages in the machine and will force
489 * the caller to perform writeback if the system is over `vm_dirty_ratio'.
490 * If we're over `background_thresh' then pdflush is woken to perform some
493 static void balance_dirty_pages(struct address_space
*mapping
)
495 long nr_reclaimable
, bdi_nr_reclaimable
;
496 long nr_writeback
, bdi_nr_writeback
;
497 unsigned long background_thresh
;
498 unsigned long dirty_thresh
;
499 unsigned long bdi_thresh
;
500 unsigned long pages_written
= 0;
501 unsigned long write_chunk
= sync_writeback_pages();
503 struct backing_dev_info
*bdi
= mapping
->backing_dev_info
;
506 struct writeback_control wbc
= {
508 .sync_mode
= WB_SYNC_NONE
,
509 .older_than_this
= NULL
,
510 .nr_to_write
= write_chunk
,
514 get_dirty_limits(&background_thresh
, &dirty_thresh
,
517 nr_reclaimable
= global_page_state(NR_FILE_DIRTY
) +
518 global_page_state(NR_UNSTABLE_NFS
);
519 nr_writeback
= global_page_state(NR_WRITEBACK
);
521 bdi_nr_reclaimable
= bdi_stat(bdi
, BDI_RECLAIMABLE
);
522 bdi_nr_writeback
= bdi_stat(bdi
, BDI_WRITEBACK
);
524 if (bdi_nr_reclaimable
+ bdi_nr_writeback
<= bdi_thresh
)
528 * Throttle it only when the background writeback cannot
529 * catch-up. This avoids (excessively) small writeouts
530 * when the bdi limits are ramping up.
532 if (nr_reclaimable
+ nr_writeback
<
533 (background_thresh
+ dirty_thresh
) / 2)
536 if (!bdi
->dirty_exceeded
)
537 bdi
->dirty_exceeded
= 1;
539 /* Note: nr_reclaimable denotes nr_dirty + nr_unstable.
540 * Unstable writes are a feature of certain networked
541 * filesystems (i.e. NFS) in which data may have been
542 * written to the server's write cache, but has not yet
543 * been flushed to permanent storage.
544 * Only move pages to writeback if this bdi is over its
545 * threshold otherwise wait until the disk writes catch
548 if (bdi_nr_reclaimable
> bdi_thresh
) {
549 writeback_inodes(&wbc
);
550 pages_written
+= write_chunk
- wbc
.nr_to_write
;
551 get_dirty_limits(&background_thresh
, &dirty_thresh
,
556 * In order to avoid the stacked BDI deadlock we need
557 * to ensure we accurately count the 'dirty' pages when
558 * the threshold is low.
560 * Otherwise it would be possible to get thresh+n pages
561 * reported dirty, even though there are thresh-m pages
562 * actually dirty; with m+n sitting in the percpu
565 if (bdi_thresh
< 2*bdi_stat_error(bdi
)) {
566 bdi_nr_reclaimable
= bdi_stat_sum(bdi
, BDI_RECLAIMABLE
);
567 bdi_nr_writeback
= bdi_stat_sum(bdi
, BDI_WRITEBACK
);
568 } else if (bdi_nr_reclaimable
) {
569 bdi_nr_reclaimable
= bdi_stat(bdi
, BDI_RECLAIMABLE
);
570 bdi_nr_writeback
= bdi_stat(bdi
, BDI_WRITEBACK
);
573 if (bdi_nr_reclaimable
+ bdi_nr_writeback
<= bdi_thresh
)
575 if (pages_written
>= write_chunk
)
576 break; /* We've done our duty */
578 congestion_wait(WRITE
, HZ
/10);
581 if (bdi_nr_reclaimable
+ bdi_nr_writeback
< bdi_thresh
&&
583 bdi
->dirty_exceeded
= 0;
585 if (writeback_in_progress(bdi
))
586 return; /* pdflush is already working this queue */
589 * In laptop mode, we wait until hitting the higher threshold before
590 * starting background writeout, and then write out all the way down
591 * to the lower threshold. So slow writers cause minimal disk activity.
593 * In normal mode, we start background writeout at the lower
594 * background_thresh, to keep the amount of dirty memory low.
596 if ((laptop_mode
&& pages_written
) ||
597 (!laptop_mode
&& (global_page_state(NR_FILE_DIRTY
)
598 + global_page_state(NR_UNSTABLE_NFS
)
599 > background_thresh
)))
600 pdflush_operation(background_writeout
, 0);
603 void set_page_dirty_balance(struct page
*page
, int page_mkwrite
)
605 if (set_page_dirty(page
) || page_mkwrite
) {
606 struct address_space
*mapping
= page_mapping(page
);
609 balance_dirty_pages_ratelimited(mapping
);
614 * balance_dirty_pages_ratelimited_nr - balance dirty memory state
615 * @mapping: address_space which was dirtied
616 * @nr_pages_dirtied: number of pages which the caller has just dirtied
618 * Processes which are dirtying memory should call in here once for each page
619 * which was newly dirtied. The function will periodically check the system's
620 * dirty state and will initiate writeback if needed.
622 * On really big machines, get_writeback_state is expensive, so try to avoid
623 * calling it too often (ratelimiting). But once we're over the dirty memory
624 * limit we decrease the ratelimiting by a lot, to prevent individual processes
625 * from overshooting the limit by (ratelimit_pages) each.
627 void balance_dirty_pages_ratelimited_nr(struct address_space
*mapping
,
628 unsigned long nr_pages_dirtied
)
630 static DEFINE_PER_CPU(unsigned long, ratelimits
) = 0;
631 unsigned long ratelimit
;
634 ratelimit
= ratelimit_pages
;
635 if (mapping
->backing_dev_info
->dirty_exceeded
)
639 * Check the rate limiting. Also, we do not want to throttle real-time
640 * tasks in balance_dirty_pages(). Period.
643 p
= &__get_cpu_var(ratelimits
);
644 *p
+= nr_pages_dirtied
;
645 if (unlikely(*p
>= ratelimit
)) {
648 balance_dirty_pages(mapping
);
653 EXPORT_SYMBOL(balance_dirty_pages_ratelimited_nr
);
655 void throttle_vm_writeout(gfp_t gfp_mask
)
657 unsigned long background_thresh
;
658 unsigned long dirty_thresh
;
661 get_dirty_limits(&background_thresh
, &dirty_thresh
, NULL
, NULL
);
664 * Boost the allowable dirty threshold a bit for page
665 * allocators so they don't get DoS'ed by heavy writers
667 dirty_thresh
+= dirty_thresh
/ 10; /* wheeee... */
669 if (global_page_state(NR_UNSTABLE_NFS
) +
670 global_page_state(NR_WRITEBACK
) <= dirty_thresh
)
672 congestion_wait(WRITE
, HZ
/10);
675 * The caller might hold locks which can prevent IO completion
676 * or progress in the filesystem. So we cannot just sit here
677 * waiting for IO to complete.
679 if ((gfp_mask
& (__GFP_FS
|__GFP_IO
)) != (__GFP_FS
|__GFP_IO
))
685 * writeback at least _min_pages, and keep writing until the amount of dirty
686 * memory is less than the background threshold, or until we're all clean.
688 static void background_writeout(unsigned long _min_pages
)
690 long min_pages
= _min_pages
;
691 struct writeback_control wbc
= {
693 .sync_mode
= WB_SYNC_NONE
,
694 .older_than_this
= NULL
,
701 unsigned long background_thresh
;
702 unsigned long dirty_thresh
;
704 get_dirty_limits(&background_thresh
, &dirty_thresh
, NULL
, NULL
);
705 if (global_page_state(NR_FILE_DIRTY
) +
706 global_page_state(NR_UNSTABLE_NFS
) < background_thresh
710 wbc
.encountered_congestion
= 0;
711 wbc
.nr_to_write
= MAX_WRITEBACK_PAGES
;
712 wbc
.pages_skipped
= 0;
713 writeback_inodes(&wbc
);
714 min_pages
-= MAX_WRITEBACK_PAGES
- wbc
.nr_to_write
;
715 if (wbc
.nr_to_write
> 0 || wbc
.pages_skipped
> 0) {
716 /* Wrote less than expected */
717 if (wbc
.encountered_congestion
|| wbc
.more_io
)
718 congestion_wait(WRITE
, HZ
/10);
726 * Start writeback of `nr_pages' pages. If `nr_pages' is zero, write back
727 * the whole world. Returns 0 if a pdflush thread was dispatched. Returns
728 * -1 if all pdflush threads were busy.
730 int wakeup_pdflush(long nr_pages
)
733 nr_pages
= global_page_state(NR_FILE_DIRTY
) +
734 global_page_state(NR_UNSTABLE_NFS
);
735 return pdflush_operation(background_writeout
, nr_pages
);
738 static void wb_timer_fn(unsigned long unused
);
739 static void laptop_timer_fn(unsigned long unused
);
741 static DEFINE_TIMER(wb_timer
, wb_timer_fn
, 0, 0);
742 static DEFINE_TIMER(laptop_mode_wb_timer
, laptop_timer_fn
, 0, 0);
745 * Periodic writeback of "old" data.
747 * Define "old": the first time one of an inode's pages is dirtied, we mark the
748 * dirtying-time in the inode's address_space. So this periodic writeback code
749 * just walks the superblock inode list, writing back any inodes which are
750 * older than a specific point in time.
752 * Try to run once per dirty_writeback_interval. But if a writeback event
753 * takes longer than a dirty_writeback_interval interval, then leave a
756 * older_than_this takes precedence over nr_to_write. So we'll only write back
757 * all dirty pages if they are all attached to "old" mappings.
759 static void wb_kupdate(unsigned long arg
)
761 unsigned long oldest_jif
;
762 unsigned long start_jif
;
763 unsigned long next_jif
;
765 struct writeback_control wbc
= {
767 .sync_mode
= WB_SYNC_NONE
,
768 .older_than_this
= &oldest_jif
,
777 oldest_jif
= jiffies
- msecs_to_jiffies(dirty_expire_interval
* 10);
779 next_jif
= start_jif
+ msecs_to_jiffies(dirty_writeback_interval
* 10);
780 nr_to_write
= global_page_state(NR_FILE_DIRTY
) +
781 global_page_state(NR_UNSTABLE_NFS
) +
782 (inodes_stat
.nr_inodes
- inodes_stat
.nr_unused
);
783 while (nr_to_write
> 0) {
785 wbc
.encountered_congestion
= 0;
786 wbc
.nr_to_write
= MAX_WRITEBACK_PAGES
;
787 writeback_inodes(&wbc
);
788 if (wbc
.nr_to_write
> 0) {
789 if (wbc
.encountered_congestion
|| wbc
.more_io
)
790 congestion_wait(WRITE
, HZ
/10);
792 break; /* All the old data is written */
794 nr_to_write
-= MAX_WRITEBACK_PAGES
- wbc
.nr_to_write
;
796 if (time_before(next_jif
, jiffies
+ HZ
))
797 next_jif
= jiffies
+ HZ
;
798 if (dirty_writeback_interval
)
799 mod_timer(&wb_timer
, next_jif
);
803 * sysctl handler for /proc/sys/vm/dirty_writeback_centisecs
805 int dirty_writeback_centisecs_handler(ctl_table
*table
, int write
,
806 struct file
*file
, void __user
*buffer
, size_t *length
, loff_t
*ppos
)
808 proc_dointvec(table
, write
, file
, buffer
, length
, ppos
);
809 if (dirty_writeback_interval
)
810 mod_timer(&wb_timer
, jiffies
+
811 msecs_to_jiffies(dirty_writeback_interval
* 10));
813 del_timer(&wb_timer
);
817 static void wb_timer_fn(unsigned long unused
)
819 if (pdflush_operation(wb_kupdate
, 0) < 0)
820 mod_timer(&wb_timer
, jiffies
+ HZ
); /* delay 1 second */
823 static void laptop_flush(unsigned long unused
)
828 static void laptop_timer_fn(unsigned long unused
)
830 pdflush_operation(laptop_flush
, 0);
834 * We've spun up the disk and we're in laptop mode: schedule writeback
835 * of all dirty data a few seconds from now. If the flush is already scheduled
836 * then push it back - the user is still using the disk.
838 void laptop_io_completion(void)
840 mod_timer(&laptop_mode_wb_timer
, jiffies
+ laptop_mode
);
844 * We're in laptop mode and we've just synced. The sync's writes will have
845 * caused another writeback to be scheduled by laptop_io_completion.
846 * Nothing needs to be written back anymore, so we unschedule the writeback.
848 void laptop_sync_completion(void)
850 del_timer(&laptop_mode_wb_timer
);
854 * If ratelimit_pages is too high then we can get into dirty-data overload
855 * if a large number of processes all perform writes at the same time.
856 * If it is too low then SMP machines will call the (expensive)
857 * get_writeback_state too often.
859 * Here we set ratelimit_pages to a level which ensures that when all CPUs are
860 * dirtying in parallel, we cannot go more than 3% (1/32) over the dirty memory
861 * thresholds before writeback cuts in.
863 * But the limit should not be set too high. Because it also controls the
864 * amount of memory which the balance_dirty_pages() caller has to write back.
865 * If this is too large then the caller will block on the IO queue all the
866 * time. So limit it to four megabytes - the balance_dirty_pages() caller
867 * will write six megabyte chunks, max.
870 void writeback_set_ratelimit(void)
872 ratelimit_pages
= vm_total_pages
/ (num_online_cpus() * 32);
873 if (ratelimit_pages
< 16)
874 ratelimit_pages
= 16;
875 if (ratelimit_pages
* PAGE_CACHE_SIZE
> 4096 * 1024)
876 ratelimit_pages
= (4096 * 1024) / PAGE_CACHE_SIZE
;
880 ratelimit_handler(struct notifier_block
*self
, unsigned long u
, void *v
)
882 writeback_set_ratelimit();
886 static struct notifier_block __cpuinitdata ratelimit_nb
= {
887 .notifier_call
= ratelimit_handler
,
892 * Called early on to tune the page writeback dirty limits.
894 * We used to scale dirty pages according to how total memory
895 * related to pages that could be allocated for buffers (by
896 * comparing nr_free_buffer_pages() to vm_total_pages.
898 * However, that was when we used "dirty_ratio" to scale with
899 * all memory, and we don't do that any more. "dirty_ratio"
900 * is now applied to total non-HIGHPAGE memory (by subtracting
901 * totalhigh_pages from vm_total_pages), and as such we can't
902 * get into the old insane situation any more where we had
903 * large amounts of dirty pages compared to a small amount of
904 * non-HIGHMEM memory.
906 * But we might still want to scale the dirty_ratio by how
907 * much memory the box has..
909 void __init
page_writeback_init(void)
914 jiffies
+ msecs_to_jiffies(dirty_writeback_interval
* 10));
915 writeback_set_ratelimit();
916 register_cpu_notifier(&ratelimit_nb
);
918 shift
= calc_period_shift();
919 prop_descriptor_init(&vm_completions
, shift
);
920 prop_descriptor_init(&vm_dirties
, shift
);
924 * write_cache_pages - walk the list of dirty pages of the given address space and write all of them.
925 * @mapping: address space structure to write
926 * @wbc: subtract the number of written pages from *@wbc->nr_to_write
927 * @writepage: function called for each page
928 * @data: data passed to writepage function
930 * If a page is already under I/O, write_cache_pages() skips it, even
931 * if it's dirty. This is desirable behaviour for memory-cleaning writeback,
932 * but it is INCORRECT for data-integrity system calls such as fsync(). fsync()
933 * and msync() need to guarantee that all the data which was dirty at the time
934 * the call was made get new I/O started against them. If wbc->sync_mode is
935 * WB_SYNC_ALL then we were called for data integrity and we must wait for
936 * existing IO to complete.
938 int write_cache_pages(struct address_space
*mapping
,
939 struct writeback_control
*wbc
, writepage_t writepage
,
942 struct backing_dev_info
*bdi
= mapping
->backing_dev_info
;
947 pgoff_t
uninitialized_var(writeback_index
);
949 pgoff_t end
; /* Inclusive */
953 long nr_to_write
= wbc
->nr_to_write
;
955 if (wbc
->nonblocking
&& bdi_write_congested(bdi
)) {
956 wbc
->encountered_congestion
= 1;
960 pagevec_init(&pvec
, 0);
961 if (wbc
->range_cyclic
) {
962 writeback_index
= mapping
->writeback_index
; /* prev offset */
963 index
= writeback_index
;
970 index
= wbc
->range_start
>> PAGE_CACHE_SHIFT
;
971 end
= wbc
->range_end
>> PAGE_CACHE_SHIFT
;
972 if (wbc
->range_start
== 0 && wbc
->range_end
== LLONG_MAX
)
974 cycled
= 1; /* ignore range_cyclic tests */
978 while (!done
&& (index
<= end
)) {
981 nr_pages
= pagevec_lookup_tag(&pvec
, mapping
, &index
,
983 min(end
- index
, (pgoff_t
)PAGEVEC_SIZE
-1) + 1);
987 for (i
= 0; i
< nr_pages
; i
++) {
988 struct page
*page
= pvec
.pages
[i
];
991 * At this point, the page may be truncated or
992 * invalidated (changing page->mapping to NULL), or
993 * even swizzled back from swapper_space to tmpfs file
994 * mapping. However, page->index will not change
995 * because we have a reference on the page.
997 if (page
->index
> end
) {
999 * can't be range_cyclic (1st pass) because
1000 * end == -1 in that case.
1006 done_index
= page
->index
+ 1;
1011 * Page truncated or invalidated. We can freely skip it
1012 * then, even for data integrity operations: the page
1013 * has disappeared concurrently, so there could be no
1014 * real expectation of this data interity operation
1015 * even if there is now a new, dirty page at the same
1016 * pagecache address.
1018 if (unlikely(page
->mapping
!= mapping
)) {
1024 if (!PageDirty(page
)) {
1025 /* someone wrote it for us */
1026 goto continue_unlock
;
1029 if (PageWriteback(page
)) {
1030 if (wbc
->sync_mode
!= WB_SYNC_NONE
)
1031 wait_on_page_writeback(page
);
1033 goto continue_unlock
;
1036 BUG_ON(PageWriteback(page
));
1037 if (!clear_page_dirty_for_io(page
))
1038 goto continue_unlock
;
1040 ret
= (*writepage
)(page
, wbc
, data
);
1041 if (unlikely(ret
)) {
1042 if (ret
== AOP_WRITEPAGE_ACTIVATE
) {
1047 * done_index is set past this page,
1048 * so media errors will not choke
1049 * background writeout for the entire
1050 * file. This has consequences for
1051 * range_cyclic semantics (ie. it may
1052 * not be suitable for data integrity
1060 if (nr_to_write
> 0) {
1062 if (nr_to_write
== 0 &&
1063 wbc
->sync_mode
== WB_SYNC_NONE
) {
1065 * We stop writing back only if we are
1066 * not doing integrity sync. In case of
1067 * integrity sync we have to keep going
1068 * because someone may be concurrently
1069 * dirtying pages, and we might have
1070 * synced a lot of newly appeared dirty
1071 * pages, but have not synced all of the
1079 if (wbc
->nonblocking
&& bdi_write_congested(bdi
)) {
1080 wbc
->encountered_congestion
= 1;
1085 pagevec_release(&pvec
);
1088 if (!cycled
&& !done
) {
1091 * We hit the last page and there is more work to be done: wrap
1092 * back to the start of the file
1096 end
= writeback_index
- 1;
1099 if (!wbc
->no_nrwrite_index_update
) {
1100 if (wbc
->range_cyclic
|| (range_whole
&& nr_to_write
> 0))
1101 mapping
->writeback_index
= done_index
;
1102 wbc
->nr_to_write
= nr_to_write
;
1107 EXPORT_SYMBOL(write_cache_pages
);
1110 * Function used by generic_writepages to call the real writepage
1111 * function and set the mapping flags on error
1113 static int __writepage(struct page
*page
, struct writeback_control
*wbc
,
1116 struct address_space
*mapping
= data
;
1117 int ret
= mapping
->a_ops
->writepage(page
, wbc
);
1118 mapping_set_error(mapping
, ret
);
1123 * generic_writepages - walk the list of dirty pages of the given address space and writepage() all of them.
1124 * @mapping: address space structure to write
1125 * @wbc: subtract the number of written pages from *@wbc->nr_to_write
1127 * This is a library function, which implements the writepages()
1128 * address_space_operation.
1130 int generic_writepages(struct address_space
*mapping
,
1131 struct writeback_control
*wbc
)
1133 /* deal with chardevs and other special file */
1134 if (!mapping
->a_ops
->writepage
)
1137 return write_cache_pages(mapping
, wbc
, __writepage
, mapping
);
1140 EXPORT_SYMBOL(generic_writepages
);
1142 int do_writepages(struct address_space
*mapping
, struct writeback_control
*wbc
)
1146 if (wbc
->nr_to_write
<= 0)
1148 wbc
->for_writepages
= 1;
1149 if (mapping
->a_ops
->writepages
)
1150 ret
= mapping
->a_ops
->writepages(mapping
, wbc
);
1152 ret
= generic_writepages(mapping
, wbc
);
1153 wbc
->for_writepages
= 0;
1158 * write_one_page - write out a single page and optionally wait on I/O
1159 * @page: the page to write
1160 * @wait: if true, wait on writeout
1162 * The page must be locked by the caller and will be unlocked upon return.
1164 * write_one_page() returns a negative error code if I/O failed.
1166 int write_one_page(struct page
*page
, int wait
)
1168 struct address_space
*mapping
= page
->mapping
;
1170 struct writeback_control wbc
= {
1171 .sync_mode
= WB_SYNC_ALL
,
1175 BUG_ON(!PageLocked(page
));
1178 wait_on_page_writeback(page
);
1180 if (clear_page_dirty_for_io(page
)) {
1181 page_cache_get(page
);
1182 ret
= mapping
->a_ops
->writepage(page
, &wbc
);
1183 if (ret
== 0 && wait
) {
1184 wait_on_page_writeback(page
);
1185 if (PageError(page
))
1188 page_cache_release(page
);
1194 EXPORT_SYMBOL(write_one_page
);
1197 * For address_spaces which do not use buffers nor write back.
1199 int __set_page_dirty_no_writeback(struct page
*page
)
1201 if (!PageDirty(page
))
1207 * Helper function for set_page_dirty family.
1208 * NOTE: This relies on being atomic wrt interrupts.
1210 void account_page_dirtied(struct page
*page
, struct address_space
*mapping
)
1212 if (mapping_cap_account_dirty(mapping
)) {
1213 __inc_zone_page_state(page
, NR_FILE_DIRTY
);
1214 __inc_bdi_stat(mapping
->backing_dev_info
, BDI_RECLAIMABLE
);
1215 task_dirty_inc(current
);
1216 task_io_account_write(PAGE_CACHE_SIZE
);
1221 * For address_spaces which do not use buffers. Just tag the page as dirty in
1224 * This is also used when a single buffer is being dirtied: we want to set the
1225 * page dirty in that case, but not all the buffers. This is a "bottom-up"
1226 * dirtying, whereas __set_page_dirty_buffers() is a "top-down" dirtying.
1228 * Most callers have locked the page, which pins the address_space in memory.
1229 * But zap_pte_range() does not lock the page, however in that case the
1230 * mapping is pinned by the vma's ->vm_file reference.
1232 * We take care to handle the case where the page was truncated from the
1233 * mapping by re-checking page_mapping() inside tree_lock.
1235 int __set_page_dirty_nobuffers(struct page
*page
)
1237 if (!TestSetPageDirty(page
)) {
1238 struct address_space
*mapping
= page_mapping(page
);
1239 struct address_space
*mapping2
;
1244 spin_lock_irq(&mapping
->tree_lock
);
1245 mapping2
= page_mapping(page
);
1246 if (mapping2
) { /* Race with truncate? */
1247 BUG_ON(mapping2
!= mapping
);
1248 WARN_ON_ONCE(!PagePrivate(page
) && !PageUptodate(page
));
1249 account_page_dirtied(page
, mapping
);
1250 radix_tree_tag_set(&mapping
->page_tree
,
1251 page_index(page
), PAGECACHE_TAG_DIRTY
);
1253 spin_unlock_irq(&mapping
->tree_lock
);
1254 if (mapping
->host
) {
1255 /* !PageAnon && !swapper_space */
1256 __mark_inode_dirty(mapping
->host
, I_DIRTY_PAGES
);
1262 EXPORT_SYMBOL(__set_page_dirty_nobuffers
);
1265 * When a writepage implementation decides that it doesn't want to write this
1266 * page for some reason, it should redirty the locked page via
1267 * redirty_page_for_writepage() and it should then unlock the page and return 0
1269 int redirty_page_for_writepage(struct writeback_control
*wbc
, struct page
*page
)
1271 wbc
->pages_skipped
++;
1272 return __set_page_dirty_nobuffers(page
);
1274 EXPORT_SYMBOL(redirty_page_for_writepage
);
1277 * If the mapping doesn't provide a set_page_dirty a_op, then
1278 * just fall through and assume that it wants buffer_heads.
1280 int set_page_dirty(struct page
*page
)
1282 struct address_space
*mapping
= page_mapping(page
);
1284 if (likely(mapping
)) {
1285 int (*spd
)(struct page
*) = mapping
->a_ops
->set_page_dirty
;
1288 spd
= __set_page_dirty_buffers
;
1290 return (*spd
)(page
);
1292 if (!PageDirty(page
)) {
1293 if (!TestSetPageDirty(page
))
1298 EXPORT_SYMBOL(set_page_dirty
);
1301 * set_page_dirty() is racy if the caller has no reference against
1302 * page->mapping->host, and if the page is unlocked. This is because another
1303 * CPU could truncate the page off the mapping and then free the mapping.
1305 * Usually, the page _is_ locked, or the caller is a user-space process which
1306 * holds a reference on the inode by having an open file.
1308 * In other cases, the page should be locked before running set_page_dirty().
1310 int set_page_dirty_lock(struct page
*page
)
1314 lock_page_nosync(page
);
1315 ret
= set_page_dirty(page
);
1319 EXPORT_SYMBOL(set_page_dirty_lock
);
1322 * Clear a page's dirty flag, while caring for dirty memory accounting.
1323 * Returns true if the page was previously dirty.
1325 * This is for preparing to put the page under writeout. We leave the page
1326 * tagged as dirty in the radix tree so that a concurrent write-for-sync
1327 * can discover it via a PAGECACHE_TAG_DIRTY walk. The ->writepage
1328 * implementation will run either set_page_writeback() or set_page_dirty(),
1329 * at which stage we bring the page's dirty flag and radix-tree dirty tag
1332 * This incoherency between the page's dirty flag and radix-tree tag is
1333 * unfortunate, but it only exists while the page is locked.
1335 int clear_page_dirty_for_io(struct page
*page
)
1337 struct address_space
*mapping
= page_mapping(page
);
1339 BUG_ON(!PageLocked(page
));
1341 ClearPageReclaim(page
);
1342 if (mapping
&& mapping_cap_account_dirty(mapping
)) {
1344 * Yes, Virginia, this is indeed insane.
1346 * We use this sequence to make sure that
1347 * (a) we account for dirty stats properly
1348 * (b) we tell the low-level filesystem to
1349 * mark the whole page dirty if it was
1350 * dirty in a pagetable. Only to then
1351 * (c) clean the page again and return 1 to
1352 * cause the writeback.
1354 * This way we avoid all nasty races with the
1355 * dirty bit in multiple places and clearing
1356 * them concurrently from different threads.
1358 * Note! Normally the "set_page_dirty(page)"
1359 * has no effect on the actual dirty bit - since
1360 * that will already usually be set. But we
1361 * need the side effects, and it can help us
1364 * We basically use the page "master dirty bit"
1365 * as a serialization point for all the different
1366 * threads doing their things.
1368 if (page_mkclean(page
))
1369 set_page_dirty(page
);
1371 * We carefully synchronise fault handlers against
1372 * installing a dirty pte and marking the page dirty
1373 * at this point. We do this by having them hold the
1374 * page lock at some point after installing their
1375 * pte, but before marking the page dirty.
1376 * Pages are always locked coming in here, so we get
1377 * the desired exclusion. See mm/memory.c:do_wp_page()
1378 * for more comments.
1380 if (TestClearPageDirty(page
)) {
1381 dec_zone_page_state(page
, NR_FILE_DIRTY
);
1382 dec_bdi_stat(mapping
->backing_dev_info
,
1388 return TestClearPageDirty(page
);
1390 EXPORT_SYMBOL(clear_page_dirty_for_io
);
1392 int test_clear_page_writeback(struct page
*page
)
1394 struct address_space
*mapping
= page_mapping(page
);
1398 struct backing_dev_info
*bdi
= mapping
->backing_dev_info
;
1399 unsigned long flags
;
1401 spin_lock_irqsave(&mapping
->tree_lock
, flags
);
1402 ret
= TestClearPageWriteback(page
);
1404 radix_tree_tag_clear(&mapping
->page_tree
,
1406 PAGECACHE_TAG_WRITEBACK
);
1407 if (bdi_cap_account_writeback(bdi
)) {
1408 __dec_bdi_stat(bdi
, BDI_WRITEBACK
);
1409 __bdi_writeout_inc(bdi
);
1412 spin_unlock_irqrestore(&mapping
->tree_lock
, flags
);
1414 ret
= TestClearPageWriteback(page
);
1417 dec_zone_page_state(page
, NR_WRITEBACK
);
1421 int test_set_page_writeback(struct page
*page
)
1423 struct address_space
*mapping
= page_mapping(page
);
1427 struct backing_dev_info
*bdi
= mapping
->backing_dev_info
;
1428 unsigned long flags
;
1430 spin_lock_irqsave(&mapping
->tree_lock
, flags
);
1431 ret
= TestSetPageWriteback(page
);
1433 radix_tree_tag_set(&mapping
->page_tree
,
1435 PAGECACHE_TAG_WRITEBACK
);
1436 if (bdi_cap_account_writeback(bdi
))
1437 __inc_bdi_stat(bdi
, BDI_WRITEBACK
);
1439 if (!PageDirty(page
))
1440 radix_tree_tag_clear(&mapping
->page_tree
,
1442 PAGECACHE_TAG_DIRTY
);
1443 spin_unlock_irqrestore(&mapping
->tree_lock
, flags
);
1445 ret
= TestSetPageWriteback(page
);
1448 inc_zone_page_state(page
, NR_WRITEBACK
);
1452 EXPORT_SYMBOL(test_set_page_writeback
);
1455 * Return true if any of the pages in the mapping are marked with the
1458 int mapping_tagged(struct address_space
*mapping
, int tag
)
1462 ret
= radix_tree_tagged(&mapping
->page_tree
, tag
);
1466 EXPORT_SYMBOL(mapping_tagged
);