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 akpm@zip.com.au
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
= 5;
72 * free highmem will not be subtracted from the total free memory
73 * for calculating free ratios if vm_highmem_is_dirtyable is true
75 int vm_highmem_is_dirtyable
;
78 * The generator of dirty data starts writeback at this percentage
80 int vm_dirty_ratio
= 10;
83 * The interval between `kupdate'-style writebacks, in jiffies
85 int dirty_writeback_interval
= 5 * HZ
;
88 * The longest number of jiffies for which data is allowed to remain dirty
90 int dirty_expire_interval
= 30 * HZ
;
93 * Flag that makes the machine dump writes/reads and block dirtyings.
98 * Flag that puts the machine in "laptop mode". Doubles as a timeout in jiffies:
99 * a full sync is triggered after this time elapses without any disk activity.
103 EXPORT_SYMBOL(laptop_mode
);
105 /* End of sysctl-exported parameters */
108 static void background_writeout(unsigned long _min_pages
);
111 * Scale the writeback cache size proportional to the relative writeout speeds.
113 * We do this by keeping a floating proportion between BDIs, based on page
114 * writeback completions [end_page_writeback()]. Those devices that write out
115 * pages fastest will get the larger share, while the slower will get a smaller
118 * We use page writeout completions because we are interested in getting rid of
119 * dirty pages. Having them written out is the primary goal.
121 * We introduce a concept of time, a period over which we measure these events,
122 * because demand can/will vary over time. The length of this period itself is
123 * measured in page writeback completions.
126 static struct prop_descriptor vm_completions
;
127 static struct prop_descriptor vm_dirties
;
129 static unsigned long determine_dirtyable_memory(void);
132 * couple the period to the dirty_ratio:
134 * period/2 ~ roundup_pow_of_two(dirty limit)
136 static int calc_period_shift(void)
138 unsigned long dirty_total
;
140 dirty_total
= (vm_dirty_ratio
* determine_dirtyable_memory()) / 100;
141 return 2 + ilog2(dirty_total
- 1);
145 * update the period when the dirty ratio changes.
147 int dirty_ratio_handler(struct ctl_table
*table
, int write
,
148 struct file
*filp
, void __user
*buffer
, size_t *lenp
,
151 int old_ratio
= vm_dirty_ratio
;
152 int ret
= proc_dointvec_minmax(table
, write
, filp
, buffer
, lenp
, ppos
);
153 if (ret
== 0 && write
&& vm_dirty_ratio
!= old_ratio
) {
154 int shift
= calc_period_shift();
155 prop_change_shift(&vm_completions
, shift
);
156 prop_change_shift(&vm_dirties
, shift
);
162 * Increment the BDI's writeout completion count and the global writeout
163 * completion count. Called from test_clear_page_writeback().
165 static inline void __bdi_writeout_inc(struct backing_dev_info
*bdi
)
167 __prop_inc_percpu(&vm_completions
, &bdi
->completions
);
170 static inline void task_dirty_inc(struct task_struct
*tsk
)
172 prop_inc_single(&vm_dirties
, &tsk
->dirties
);
176 * Obtain an accurate fraction of the BDI's portion.
178 static void bdi_writeout_fraction(struct backing_dev_info
*bdi
,
179 long *numerator
, long *denominator
)
181 if (bdi_cap_writeback_dirty(bdi
)) {
182 prop_fraction_percpu(&vm_completions
, &bdi
->completions
,
183 numerator
, denominator
);
191 * Clip the earned share of dirty pages to that which is actually available.
192 * This avoids exceeding the total dirty_limit when the floating averages
193 * fluctuate too quickly.
196 clip_bdi_dirty_limit(struct backing_dev_info
*bdi
, long dirty
, long *pbdi_dirty
)
200 avail_dirty
= dirty
-
201 (global_page_state(NR_FILE_DIRTY
) +
202 global_page_state(NR_WRITEBACK
) +
203 global_page_state(NR_UNSTABLE_NFS
));
208 avail_dirty
+= bdi_stat(bdi
, BDI_RECLAIMABLE
) +
209 bdi_stat(bdi
, BDI_WRITEBACK
);
211 *pbdi_dirty
= min(*pbdi_dirty
, avail_dirty
);
214 static inline void task_dirties_fraction(struct task_struct
*tsk
,
215 long *numerator
, long *denominator
)
217 prop_fraction_single(&vm_dirties
, &tsk
->dirties
,
218 numerator
, denominator
);
222 * scale the dirty limit
224 * task specific dirty limit:
226 * dirty -= (dirty/8) * p_{t}
228 static void task_dirty_limit(struct task_struct
*tsk
, long *pdirty
)
230 long numerator
, denominator
;
231 long dirty
= *pdirty
;
232 u64 inv
= dirty
>> 3;
234 task_dirties_fraction(tsk
, &numerator
, &denominator
);
236 do_div(inv
, denominator
);
239 if (dirty
< *pdirty
/2)
246 * Work out the current dirty-memory clamping and background writeout
249 * The main aim here is to lower them aggressively if there is a lot of mapped
250 * memory around. To avoid stressing page reclaim with lots of unreclaimable
251 * pages. It is better to clamp down on writers than to start swapping, and
252 * performing lots of scanning.
254 * We only allow 1/2 of the currently-unmapped memory to be dirtied.
256 * We don't permit the clamping level to fall below 5% - that is getting rather
259 * We make sure that the background writeout level is below the adjusted
263 static unsigned long highmem_dirtyable_memory(unsigned long total
)
265 #ifdef CONFIG_HIGHMEM
269 for_each_node_state(node
, N_HIGH_MEMORY
) {
271 &NODE_DATA(node
)->node_zones
[ZONE_HIGHMEM
];
273 x
+= zone_page_state(z
, NR_FREE_PAGES
)
274 + zone_page_state(z
, NR_INACTIVE
)
275 + zone_page_state(z
, NR_ACTIVE
);
278 * Make sure that the number of highmem pages is never larger
279 * than the number of the total dirtyable memory. This can only
280 * occur in very strange VM situations but we want to make sure
281 * that this does not occur.
283 return min(x
, total
);
289 static unsigned long determine_dirtyable_memory(void)
293 x
= global_page_state(NR_FREE_PAGES
)
294 + global_page_state(NR_INACTIVE
)
295 + global_page_state(NR_ACTIVE
);
297 if (!vm_highmem_is_dirtyable
)
298 x
-= highmem_dirtyable_memory(x
);
300 return x
+ 1; /* Ensure that we never return 0 */
304 get_dirty_limits(long *pbackground
, long *pdirty
, long *pbdi_dirty
,
305 struct backing_dev_info
*bdi
)
307 int background_ratio
; /* Percentages */
311 unsigned long available_memory
= determine_dirtyable_memory();
312 struct task_struct
*tsk
;
314 dirty_ratio
= vm_dirty_ratio
;
318 background_ratio
= dirty_background_ratio
;
319 if (background_ratio
>= dirty_ratio
)
320 background_ratio
= dirty_ratio
/ 2;
322 background
= (background_ratio
* available_memory
) / 100;
323 dirty
= (dirty_ratio
* available_memory
) / 100;
325 if (tsk
->flags
& PF_LESS_THROTTLE
|| rt_task(tsk
)) {
326 background
+= background
/ 4;
329 *pbackground
= background
;
333 u64 bdi_dirty
= dirty
;
334 long numerator
, denominator
;
337 * Calculate this BDI's share of the dirty ratio.
339 bdi_writeout_fraction(bdi
, &numerator
, &denominator
);
341 bdi_dirty
*= numerator
;
342 do_div(bdi_dirty
, denominator
);
344 *pbdi_dirty
= bdi_dirty
;
345 clip_bdi_dirty_limit(bdi
, dirty
, pbdi_dirty
);
346 task_dirty_limit(current
, pbdi_dirty
);
351 * balance_dirty_pages() must be called by processes which are generating dirty
352 * data. It looks at the number of dirty pages in the machine and will force
353 * the caller to perform writeback if the system is over `vm_dirty_ratio'.
354 * If we're over `background_thresh' then pdflush is woken to perform some
357 static void balance_dirty_pages(struct address_space
*mapping
)
359 long nr_reclaimable
, bdi_nr_reclaimable
;
360 long nr_writeback
, bdi_nr_writeback
;
361 long background_thresh
;
364 unsigned long pages_written
= 0;
365 unsigned long write_chunk
= sync_writeback_pages();
367 struct backing_dev_info
*bdi
= mapping
->backing_dev_info
;
370 struct writeback_control wbc
= {
372 .sync_mode
= WB_SYNC_NONE
,
373 .older_than_this
= NULL
,
374 .nr_to_write
= write_chunk
,
378 get_dirty_limits(&background_thresh
, &dirty_thresh
,
381 nr_reclaimable
= global_page_state(NR_FILE_DIRTY
) +
382 global_page_state(NR_UNSTABLE_NFS
);
383 nr_writeback
= global_page_state(NR_WRITEBACK
);
385 bdi_nr_reclaimable
= bdi_stat(bdi
, BDI_RECLAIMABLE
);
386 bdi_nr_writeback
= bdi_stat(bdi
, BDI_WRITEBACK
);
388 if (bdi_nr_reclaimable
+ bdi_nr_writeback
<= bdi_thresh
)
392 * Throttle it only when the background writeback cannot
393 * catch-up. This avoids (excessively) small writeouts
394 * when the bdi limits are ramping up.
396 if (nr_reclaimable
+ nr_writeback
<
397 (background_thresh
+ dirty_thresh
) / 2)
400 if (!bdi
->dirty_exceeded
)
401 bdi
->dirty_exceeded
= 1;
403 /* Note: nr_reclaimable denotes nr_dirty + nr_unstable.
404 * Unstable writes are a feature of certain networked
405 * filesystems (i.e. NFS) in which data may have been
406 * written to the server's write cache, but has not yet
407 * been flushed to permanent storage.
409 if (bdi_nr_reclaimable
) {
410 writeback_inodes(&wbc
);
411 pages_written
+= write_chunk
- wbc
.nr_to_write
;
412 get_dirty_limits(&background_thresh
, &dirty_thresh
,
417 * In order to avoid the stacked BDI deadlock we need
418 * to ensure we accurately count the 'dirty' pages when
419 * the threshold is low.
421 * Otherwise it would be possible to get thresh+n pages
422 * reported dirty, even though there are thresh-m pages
423 * actually dirty; with m+n sitting in the percpu
426 if (bdi_thresh
< 2*bdi_stat_error(bdi
)) {
427 bdi_nr_reclaimable
= bdi_stat_sum(bdi
, BDI_RECLAIMABLE
);
428 bdi_nr_writeback
= bdi_stat_sum(bdi
, BDI_WRITEBACK
);
429 } else if (bdi_nr_reclaimable
) {
430 bdi_nr_reclaimable
= bdi_stat(bdi
, BDI_RECLAIMABLE
);
431 bdi_nr_writeback
= bdi_stat(bdi
, BDI_WRITEBACK
);
434 if (bdi_nr_reclaimable
+ bdi_nr_writeback
<= bdi_thresh
)
436 if (pages_written
>= write_chunk
)
437 break; /* We've done our duty */
439 congestion_wait(WRITE
, HZ
/10);
442 if (bdi_nr_reclaimable
+ bdi_nr_writeback
< bdi_thresh
&&
444 bdi
->dirty_exceeded
= 0;
446 if (writeback_in_progress(bdi
))
447 return; /* pdflush is already working this queue */
450 * In laptop mode, we wait until hitting the higher threshold before
451 * starting background writeout, and then write out all the way down
452 * to the lower threshold. So slow writers cause minimal disk activity.
454 * In normal mode, we start background writeout at the lower
455 * background_thresh, to keep the amount of dirty memory low.
457 if ((laptop_mode
&& pages_written
) ||
458 (!laptop_mode
&& (global_page_state(NR_FILE_DIRTY
)
459 + global_page_state(NR_UNSTABLE_NFS
)
460 > background_thresh
)))
461 pdflush_operation(background_writeout
, 0);
464 void set_page_dirty_balance(struct page
*page
, int page_mkwrite
)
466 if (set_page_dirty(page
) || page_mkwrite
) {
467 struct address_space
*mapping
= page_mapping(page
);
470 balance_dirty_pages_ratelimited(mapping
);
475 * balance_dirty_pages_ratelimited_nr - balance dirty memory state
476 * @mapping: address_space which was dirtied
477 * @nr_pages_dirtied: number of pages which the caller has just dirtied
479 * Processes which are dirtying memory should call in here once for each page
480 * which was newly dirtied. The function will periodically check the system's
481 * dirty state and will initiate writeback if needed.
483 * On really big machines, get_writeback_state is expensive, so try to avoid
484 * calling it too often (ratelimiting). But once we're over the dirty memory
485 * limit we decrease the ratelimiting by a lot, to prevent individual processes
486 * from overshooting the limit by (ratelimit_pages) each.
488 void balance_dirty_pages_ratelimited_nr(struct address_space
*mapping
,
489 unsigned long nr_pages_dirtied
)
491 static DEFINE_PER_CPU(unsigned long, ratelimits
) = 0;
492 unsigned long ratelimit
;
495 ratelimit
= ratelimit_pages
;
496 if (mapping
->backing_dev_info
->dirty_exceeded
)
500 * Check the rate limiting. Also, we do not want to throttle real-time
501 * tasks in balance_dirty_pages(). Period.
504 p
= &__get_cpu_var(ratelimits
);
505 *p
+= nr_pages_dirtied
;
506 if (unlikely(*p
>= ratelimit
)) {
509 balance_dirty_pages(mapping
);
514 EXPORT_SYMBOL(balance_dirty_pages_ratelimited_nr
);
516 void throttle_vm_writeout(gfp_t gfp_mask
)
518 long background_thresh
;
522 get_dirty_limits(&background_thresh
, &dirty_thresh
, NULL
, NULL
);
525 * Boost the allowable dirty threshold a bit for page
526 * allocators so they don't get DoS'ed by heavy writers
528 dirty_thresh
+= dirty_thresh
/ 10; /* wheeee... */
530 if (global_page_state(NR_UNSTABLE_NFS
) +
531 global_page_state(NR_WRITEBACK
) <= dirty_thresh
)
533 congestion_wait(WRITE
, HZ
/10);
536 * The caller might hold locks which can prevent IO completion
537 * or progress in the filesystem. So we cannot just sit here
538 * waiting for IO to complete.
540 if ((gfp_mask
& (__GFP_FS
|__GFP_IO
)) != (__GFP_FS
|__GFP_IO
))
546 * writeback at least _min_pages, and keep writing until the amount of dirty
547 * memory is less than the background threshold, or until we're all clean.
549 static void background_writeout(unsigned long _min_pages
)
551 long min_pages
= _min_pages
;
552 struct writeback_control wbc
= {
554 .sync_mode
= WB_SYNC_NONE
,
555 .older_than_this
= NULL
,
562 long background_thresh
;
565 get_dirty_limits(&background_thresh
, &dirty_thresh
, NULL
, NULL
);
566 if (global_page_state(NR_FILE_DIRTY
) +
567 global_page_state(NR_UNSTABLE_NFS
) < background_thresh
570 wbc
.encountered_congestion
= 0;
571 wbc
.nr_to_write
= MAX_WRITEBACK_PAGES
;
572 wbc
.pages_skipped
= 0;
573 writeback_inodes(&wbc
);
574 min_pages
-= MAX_WRITEBACK_PAGES
- wbc
.nr_to_write
;
575 if (wbc
.nr_to_write
> 0 || wbc
.pages_skipped
> 0) {
576 /* Wrote less than expected */
577 congestion_wait(WRITE
, HZ
/10);
578 if (!wbc
.encountered_congestion
)
585 * Start writeback of `nr_pages' pages. If `nr_pages' is zero, write back
586 * the whole world. Returns 0 if a pdflush thread was dispatched. Returns
587 * -1 if all pdflush threads were busy.
589 int wakeup_pdflush(long nr_pages
)
592 nr_pages
= global_page_state(NR_FILE_DIRTY
) +
593 global_page_state(NR_UNSTABLE_NFS
);
594 return pdflush_operation(background_writeout
, nr_pages
);
597 static void wb_timer_fn(unsigned long unused
);
598 static void laptop_timer_fn(unsigned long unused
);
600 static DEFINE_TIMER(wb_timer
, wb_timer_fn
, 0, 0);
601 static DEFINE_TIMER(laptop_mode_wb_timer
, laptop_timer_fn
, 0, 0);
604 * Periodic writeback of "old" data.
606 * Define "old": the first time one of an inode's pages is dirtied, we mark the
607 * dirtying-time in the inode's address_space. So this periodic writeback code
608 * just walks the superblock inode list, writing back any inodes which are
609 * older than a specific point in time.
611 * Try to run once per dirty_writeback_interval. But if a writeback event
612 * takes longer than a dirty_writeback_interval interval, then leave a
615 * older_than_this takes precedence over nr_to_write. So we'll only write back
616 * all dirty pages if they are all attached to "old" mappings.
618 static void wb_kupdate(unsigned long arg
)
620 unsigned long oldest_jif
;
621 unsigned long start_jif
;
622 unsigned long next_jif
;
624 struct writeback_control wbc
= {
626 .sync_mode
= WB_SYNC_NONE
,
627 .older_than_this
= &oldest_jif
,
636 oldest_jif
= jiffies
- dirty_expire_interval
;
638 next_jif
= start_jif
+ dirty_writeback_interval
;
639 nr_to_write
= global_page_state(NR_FILE_DIRTY
) +
640 global_page_state(NR_UNSTABLE_NFS
) +
641 (inodes_stat
.nr_inodes
- inodes_stat
.nr_unused
);
642 while (nr_to_write
> 0) {
643 wbc
.encountered_congestion
= 0;
644 wbc
.nr_to_write
= MAX_WRITEBACK_PAGES
;
645 writeback_inodes(&wbc
);
646 if (wbc
.nr_to_write
> 0) {
647 if (wbc
.encountered_congestion
)
648 congestion_wait(WRITE
, HZ
/10);
650 break; /* All the old data is written */
652 nr_to_write
-= MAX_WRITEBACK_PAGES
- wbc
.nr_to_write
;
654 if (time_before(next_jif
, jiffies
+ HZ
))
655 next_jif
= jiffies
+ HZ
;
656 if (dirty_writeback_interval
)
657 mod_timer(&wb_timer
, next_jif
);
661 * sysctl handler for /proc/sys/vm/dirty_writeback_centisecs
663 int dirty_writeback_centisecs_handler(ctl_table
*table
, int write
,
664 struct file
*file
, void __user
*buffer
, size_t *length
, loff_t
*ppos
)
666 proc_dointvec_userhz_jiffies(table
, write
, file
, buffer
, length
, ppos
);
667 if (dirty_writeback_interval
)
668 mod_timer(&wb_timer
, jiffies
+ dirty_writeback_interval
);
670 del_timer(&wb_timer
);
674 static void wb_timer_fn(unsigned long unused
)
676 if (pdflush_operation(wb_kupdate
, 0) < 0)
677 mod_timer(&wb_timer
, jiffies
+ HZ
); /* delay 1 second */
680 static void laptop_flush(unsigned long unused
)
685 static void laptop_timer_fn(unsigned long unused
)
687 pdflush_operation(laptop_flush
, 0);
691 * We've spun up the disk and we're in laptop mode: schedule writeback
692 * of all dirty data a few seconds from now. If the flush is already scheduled
693 * then push it back - the user is still using the disk.
695 void laptop_io_completion(void)
697 mod_timer(&laptop_mode_wb_timer
, jiffies
+ laptop_mode
);
701 * We're in laptop mode and we've just synced. The sync's writes will have
702 * caused another writeback to be scheduled by laptop_io_completion.
703 * Nothing needs to be written back anymore, so we unschedule the writeback.
705 void laptop_sync_completion(void)
707 del_timer(&laptop_mode_wb_timer
);
711 * If ratelimit_pages is too high then we can get into dirty-data overload
712 * if a large number of processes all perform writes at the same time.
713 * If it is too low then SMP machines will call the (expensive)
714 * get_writeback_state too often.
716 * Here we set ratelimit_pages to a level which ensures that when all CPUs are
717 * dirtying in parallel, we cannot go more than 3% (1/32) over the dirty memory
718 * thresholds before writeback cuts in.
720 * But the limit should not be set too high. Because it also controls the
721 * amount of memory which the balance_dirty_pages() caller has to write back.
722 * If this is too large then the caller will block on the IO queue all the
723 * time. So limit it to four megabytes - the balance_dirty_pages() caller
724 * will write six megabyte chunks, max.
727 void writeback_set_ratelimit(void)
729 ratelimit_pages
= vm_total_pages
/ (num_online_cpus() * 32);
730 if (ratelimit_pages
< 16)
731 ratelimit_pages
= 16;
732 if (ratelimit_pages
* PAGE_CACHE_SIZE
> 4096 * 1024)
733 ratelimit_pages
= (4096 * 1024) / PAGE_CACHE_SIZE
;
737 ratelimit_handler(struct notifier_block
*self
, unsigned long u
, void *v
)
739 writeback_set_ratelimit();
743 static struct notifier_block __cpuinitdata ratelimit_nb
= {
744 .notifier_call
= ratelimit_handler
,
749 * Called early on to tune the page writeback dirty limits.
751 * We used to scale dirty pages according to how total memory
752 * related to pages that could be allocated for buffers (by
753 * comparing nr_free_buffer_pages() to vm_total_pages.
755 * However, that was when we used "dirty_ratio" to scale with
756 * all memory, and we don't do that any more. "dirty_ratio"
757 * is now applied to total non-HIGHPAGE memory (by subtracting
758 * totalhigh_pages from vm_total_pages), and as such we can't
759 * get into the old insane situation any more where we had
760 * large amounts of dirty pages compared to a small amount of
761 * non-HIGHMEM memory.
763 * But we might still want to scale the dirty_ratio by how
764 * much memory the box has..
766 void __init
page_writeback_init(void)
770 mod_timer(&wb_timer
, jiffies
+ dirty_writeback_interval
);
771 writeback_set_ratelimit();
772 register_cpu_notifier(&ratelimit_nb
);
774 shift
= calc_period_shift();
775 prop_descriptor_init(&vm_completions
, shift
);
776 prop_descriptor_init(&vm_dirties
, shift
);
780 * write_cache_pages - walk the list of dirty pages of the given address space and write all of them.
781 * @mapping: address space structure to write
782 * @wbc: subtract the number of written pages from *@wbc->nr_to_write
783 * @writepage: function called for each page
784 * @data: data passed to writepage function
786 * If a page is already under I/O, write_cache_pages() skips it, even
787 * if it's dirty. This is desirable behaviour for memory-cleaning writeback,
788 * but it is INCORRECT for data-integrity system calls such as fsync(). fsync()
789 * and msync() need to guarantee that all the data which was dirty at the time
790 * the call was made get new I/O started against them. If wbc->sync_mode is
791 * WB_SYNC_ALL then we were called for data integrity and we must wait for
792 * existing IO to complete.
794 int write_cache_pages(struct address_space
*mapping
,
795 struct writeback_control
*wbc
, writepage_t writepage
,
798 struct backing_dev_info
*bdi
= mapping
->backing_dev_info
;
804 pgoff_t end
; /* Inclusive */
808 if (wbc
->nonblocking
&& bdi_write_congested(bdi
)) {
809 wbc
->encountered_congestion
= 1;
813 pagevec_init(&pvec
, 0);
814 if (wbc
->range_cyclic
) {
815 index
= mapping
->writeback_index
; /* Start from prev offset */
818 index
= wbc
->range_start
>> PAGE_CACHE_SHIFT
;
819 end
= wbc
->range_end
>> PAGE_CACHE_SHIFT
;
820 if (wbc
->range_start
== 0 && wbc
->range_end
== LLONG_MAX
)
825 while (!done
&& (index
<= end
) &&
826 (nr_pages
= pagevec_lookup_tag(&pvec
, mapping
, &index
,
828 min(end
- index
, (pgoff_t
)PAGEVEC_SIZE
-1) + 1))) {
832 for (i
= 0; i
< nr_pages
; i
++) {
833 struct page
*page
= pvec
.pages
[i
];
836 * At this point we hold neither mapping->tree_lock nor
837 * lock on the page itself: the page may be truncated or
838 * invalidated (changing page->mapping to NULL), or even
839 * swizzled back from swapper_space to tmpfs file
844 if (unlikely(page
->mapping
!= mapping
)) {
849 if (!wbc
->range_cyclic
&& page
->index
> end
) {
855 if (wbc
->sync_mode
!= WB_SYNC_NONE
)
856 wait_on_page_writeback(page
);
858 if (PageWriteback(page
) ||
859 !clear_page_dirty_for_io(page
)) {
864 ret
= (*writepage
)(page
, wbc
, data
);
866 if (unlikely(ret
== AOP_WRITEPAGE_ACTIVATE
)) {
870 if (ret
|| (--(wbc
->nr_to_write
) <= 0))
872 if (wbc
->nonblocking
&& bdi_write_congested(bdi
)) {
873 wbc
->encountered_congestion
= 1;
877 pagevec_release(&pvec
);
880 if (!scanned
&& !done
) {
882 * We hit the last page and there is more work to be done: wrap
883 * back to the start of the file
889 if (wbc
->range_cyclic
|| (range_whole
&& wbc
->nr_to_write
> 0))
890 mapping
->writeback_index
= index
;
893 EXPORT_SYMBOL(write_cache_pages
);
896 * Function used by generic_writepages to call the real writepage
897 * function and set the mapping flags on error
899 static int __writepage(struct page
*page
, struct writeback_control
*wbc
,
902 struct address_space
*mapping
= data
;
903 int ret
= mapping
->a_ops
->writepage(page
, wbc
);
904 mapping_set_error(mapping
, ret
);
909 * generic_writepages - walk the list of dirty pages of the given address space and writepage() all of them.
910 * @mapping: address space structure to write
911 * @wbc: subtract the number of written pages from *@wbc->nr_to_write
913 * This is a library function, which implements the writepages()
914 * address_space_operation.
916 int generic_writepages(struct address_space
*mapping
,
917 struct writeback_control
*wbc
)
919 /* deal with chardevs and other special file */
920 if (!mapping
->a_ops
->writepage
)
923 return write_cache_pages(mapping
, wbc
, __writepage
, mapping
);
926 EXPORT_SYMBOL(generic_writepages
);
928 int do_writepages(struct address_space
*mapping
, struct writeback_control
*wbc
)
932 if (wbc
->nr_to_write
<= 0)
934 wbc
->for_writepages
= 1;
935 if (mapping
->a_ops
->writepages
)
936 ret
= mapping
->a_ops
->writepages(mapping
, wbc
);
938 ret
= generic_writepages(mapping
, wbc
);
939 wbc
->for_writepages
= 0;
944 * write_one_page - write out a single page and optionally wait on I/O
945 * @page: the page to write
946 * @wait: if true, wait on writeout
948 * The page must be locked by the caller and will be unlocked upon return.
950 * write_one_page() returns a negative error code if I/O failed.
952 int write_one_page(struct page
*page
, int wait
)
954 struct address_space
*mapping
= page
->mapping
;
956 struct writeback_control wbc
= {
957 .sync_mode
= WB_SYNC_ALL
,
961 BUG_ON(!PageLocked(page
));
964 wait_on_page_writeback(page
);
966 if (clear_page_dirty_for_io(page
)) {
967 page_cache_get(page
);
968 ret
= mapping
->a_ops
->writepage(page
, &wbc
);
969 if (ret
== 0 && wait
) {
970 wait_on_page_writeback(page
);
974 page_cache_release(page
);
980 EXPORT_SYMBOL(write_one_page
);
983 * For address_spaces which do not use buffers nor write back.
985 int __set_page_dirty_no_writeback(struct page
*page
)
987 if (!PageDirty(page
))
993 * For address_spaces which do not use buffers. Just tag the page as dirty in
996 * This is also used when a single buffer is being dirtied: we want to set the
997 * page dirty in that case, but not all the buffers. This is a "bottom-up"
998 * dirtying, whereas __set_page_dirty_buffers() is a "top-down" dirtying.
1000 * Most callers have locked the page, which pins the address_space in memory.
1001 * But zap_pte_range() does not lock the page, however in that case the
1002 * mapping is pinned by the vma's ->vm_file reference.
1004 * We take care to handle the case where the page was truncated from the
1005 * mapping by re-checking page_mapping() inside tree_lock.
1007 int __set_page_dirty_nobuffers(struct page
*page
)
1009 if (!TestSetPageDirty(page
)) {
1010 struct address_space
*mapping
= page_mapping(page
);
1011 struct address_space
*mapping2
;
1016 write_lock_irq(&mapping
->tree_lock
);
1017 mapping2
= page_mapping(page
);
1018 if (mapping2
) { /* Race with truncate? */
1019 BUG_ON(mapping2
!= mapping
);
1020 WARN_ON_ONCE(!PagePrivate(page
) && !PageUptodate(page
));
1021 if (mapping_cap_account_dirty(mapping
)) {
1022 __inc_zone_page_state(page
, NR_FILE_DIRTY
);
1023 __inc_bdi_stat(mapping
->backing_dev_info
,
1025 task_io_account_write(PAGE_CACHE_SIZE
);
1027 radix_tree_tag_set(&mapping
->page_tree
,
1028 page_index(page
), PAGECACHE_TAG_DIRTY
);
1030 write_unlock_irq(&mapping
->tree_lock
);
1031 if (mapping
->host
) {
1032 /* !PageAnon && !swapper_space */
1033 __mark_inode_dirty(mapping
->host
, I_DIRTY_PAGES
);
1039 EXPORT_SYMBOL(__set_page_dirty_nobuffers
);
1042 * When a writepage implementation decides that it doesn't want to write this
1043 * page for some reason, it should redirty the locked page via
1044 * redirty_page_for_writepage() and it should then unlock the page and return 0
1046 int redirty_page_for_writepage(struct writeback_control
*wbc
, struct page
*page
)
1048 wbc
->pages_skipped
++;
1049 return __set_page_dirty_nobuffers(page
);
1051 EXPORT_SYMBOL(redirty_page_for_writepage
);
1054 * If the mapping doesn't provide a set_page_dirty a_op, then
1055 * just fall through and assume that it wants buffer_heads.
1057 static int __set_page_dirty(struct page
*page
)
1059 struct address_space
*mapping
= page_mapping(page
);
1061 if (likely(mapping
)) {
1062 int (*spd
)(struct page
*) = mapping
->a_ops
->set_page_dirty
;
1065 spd
= __set_page_dirty_buffers
;
1067 return (*spd
)(page
);
1069 if (!PageDirty(page
)) {
1070 if (!TestSetPageDirty(page
))
1076 int set_page_dirty(struct page
*page
)
1078 int ret
= __set_page_dirty(page
);
1080 task_dirty_inc(current
);
1083 EXPORT_SYMBOL(set_page_dirty
);
1086 * set_page_dirty() is racy if the caller has no reference against
1087 * page->mapping->host, and if the page is unlocked. This is because another
1088 * CPU could truncate the page off the mapping and then free the mapping.
1090 * Usually, the page _is_ locked, or the caller is a user-space process which
1091 * holds a reference on the inode by having an open file.
1093 * In other cases, the page should be locked before running set_page_dirty().
1095 int set_page_dirty_lock(struct page
*page
)
1099 lock_page_nosync(page
);
1100 ret
= set_page_dirty(page
);
1104 EXPORT_SYMBOL(set_page_dirty_lock
);
1107 * Clear a page's dirty flag, while caring for dirty memory accounting.
1108 * Returns true if the page was previously dirty.
1110 * This is for preparing to put the page under writeout. We leave the page
1111 * tagged as dirty in the radix tree so that a concurrent write-for-sync
1112 * can discover it via a PAGECACHE_TAG_DIRTY walk. The ->writepage
1113 * implementation will run either set_page_writeback() or set_page_dirty(),
1114 * at which stage we bring the page's dirty flag and radix-tree dirty tag
1117 * This incoherency between the page's dirty flag and radix-tree tag is
1118 * unfortunate, but it only exists while the page is locked.
1120 int clear_page_dirty_for_io(struct page
*page
)
1122 struct address_space
*mapping
= page_mapping(page
);
1124 BUG_ON(!PageLocked(page
));
1126 ClearPageReclaim(page
);
1127 if (mapping
&& mapping_cap_account_dirty(mapping
)) {
1129 * Yes, Virginia, this is indeed insane.
1131 * We use this sequence to make sure that
1132 * (a) we account for dirty stats properly
1133 * (b) we tell the low-level filesystem to
1134 * mark the whole page dirty if it was
1135 * dirty in a pagetable. Only to then
1136 * (c) clean the page again and return 1 to
1137 * cause the writeback.
1139 * This way we avoid all nasty races with the
1140 * dirty bit in multiple places and clearing
1141 * them concurrently from different threads.
1143 * Note! Normally the "set_page_dirty(page)"
1144 * has no effect on the actual dirty bit - since
1145 * that will already usually be set. But we
1146 * need the side effects, and it can help us
1149 * We basically use the page "master dirty bit"
1150 * as a serialization point for all the different
1151 * threads doing their things.
1153 if (page_mkclean(page
))
1154 set_page_dirty(page
);
1156 * We carefully synchronise fault handlers against
1157 * installing a dirty pte and marking the page dirty
1158 * at this point. We do this by having them hold the
1159 * page lock at some point after installing their
1160 * pte, but before marking the page dirty.
1161 * Pages are always locked coming in here, so we get
1162 * the desired exclusion. See mm/memory.c:do_wp_page()
1163 * for more comments.
1165 if (TestClearPageDirty(page
)) {
1166 dec_zone_page_state(page
, NR_FILE_DIRTY
);
1167 dec_bdi_stat(mapping
->backing_dev_info
,
1173 return TestClearPageDirty(page
);
1175 EXPORT_SYMBOL(clear_page_dirty_for_io
);
1177 int test_clear_page_writeback(struct page
*page
)
1179 struct address_space
*mapping
= page_mapping(page
);
1183 struct backing_dev_info
*bdi
= mapping
->backing_dev_info
;
1184 unsigned long flags
;
1186 write_lock_irqsave(&mapping
->tree_lock
, flags
);
1187 ret
= TestClearPageWriteback(page
);
1189 radix_tree_tag_clear(&mapping
->page_tree
,
1191 PAGECACHE_TAG_WRITEBACK
);
1192 if (bdi_cap_writeback_dirty(bdi
)) {
1193 __dec_bdi_stat(bdi
, BDI_WRITEBACK
);
1194 __bdi_writeout_inc(bdi
);
1197 write_unlock_irqrestore(&mapping
->tree_lock
, flags
);
1199 ret
= TestClearPageWriteback(page
);
1202 dec_zone_page_state(page
, NR_WRITEBACK
);
1206 int test_set_page_writeback(struct page
*page
)
1208 struct address_space
*mapping
= page_mapping(page
);
1212 struct backing_dev_info
*bdi
= mapping
->backing_dev_info
;
1213 unsigned long flags
;
1215 write_lock_irqsave(&mapping
->tree_lock
, flags
);
1216 ret
= TestSetPageWriteback(page
);
1218 radix_tree_tag_set(&mapping
->page_tree
,
1220 PAGECACHE_TAG_WRITEBACK
);
1221 if (bdi_cap_writeback_dirty(bdi
))
1222 __inc_bdi_stat(bdi
, BDI_WRITEBACK
);
1224 if (!PageDirty(page
))
1225 radix_tree_tag_clear(&mapping
->page_tree
,
1227 PAGECACHE_TAG_DIRTY
);
1228 write_unlock_irqrestore(&mapping
->tree_lock
, flags
);
1230 ret
= TestSetPageWriteback(page
);
1233 inc_zone_page_state(page
, NR_WRITEBACK
);
1237 EXPORT_SYMBOL(test_set_page_writeback
);
1240 * Return true if any of the pages in the mapping are marked with the
1243 int mapping_tagged(struct address_space
*mapping
, int tag
)
1247 ret
= radix_tree_tagged(&mapping
->page_tree
, tag
);
1251 EXPORT_SYMBOL(mapping_tagged
);