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>
37 #include <trace/events/writeback.h>
40 * Sleep at most 200ms at a time in balance_dirty_pages().
42 #define MAX_PAUSE max(HZ/5, 1)
45 * Estimate write bandwidth at 200ms intervals.
47 #define BANDWIDTH_INTERVAL max(HZ/5, 1)
49 #define RATELIMIT_CALC_SHIFT 10
52 * After a CPU has dirtied this many pages, balance_dirty_pages_ratelimited
53 * will look to see if it needs to force writeback or throttling.
55 static long ratelimit_pages
= 32;
58 * When balance_dirty_pages decides that the caller needs to perform some
59 * non-background writeback, this is how many pages it will attempt to write.
60 * It should be somewhat larger than dirtied pages to ensure that reasonably
61 * large amounts of I/O are submitted.
63 static inline long sync_writeback_pages(unsigned long dirtied
)
65 if (dirtied
< ratelimit_pages
)
66 dirtied
= ratelimit_pages
;
68 return dirtied
+ dirtied
/ 2;
71 /* The following parameters are exported via /proc/sys/vm */
74 * Start background writeback (via writeback threads) at this percentage
76 int dirty_background_ratio
= 10;
79 * dirty_background_bytes starts at 0 (disabled) so that it is a function of
80 * dirty_background_ratio * the amount of dirtyable memory
82 unsigned long dirty_background_bytes
;
85 * free highmem will not be subtracted from the total free memory
86 * for calculating free ratios if vm_highmem_is_dirtyable is true
88 int vm_highmem_is_dirtyable
;
91 * The generator of dirty data starts writeback at this percentage
93 int vm_dirty_ratio
= 20;
96 * vm_dirty_bytes starts at 0 (disabled) so that it is a function of
97 * vm_dirty_ratio * the amount of dirtyable memory
99 unsigned long vm_dirty_bytes
;
102 * The interval between `kupdate'-style writebacks
104 unsigned int dirty_writeback_interval
= 5 * 100; /* centiseconds */
107 * The longest time for which data is allowed to remain dirty
109 unsigned int dirty_expire_interval
= 30 * 100; /* centiseconds */
112 * Flag that makes the machine dump writes/reads and block dirtyings.
117 * Flag that puts the machine in "laptop mode". Doubles as a timeout in jiffies:
118 * a full sync is triggered after this time elapses without any disk activity.
122 EXPORT_SYMBOL(laptop_mode
);
124 /* End of sysctl-exported parameters */
126 unsigned long global_dirty_limit
;
129 * Scale the writeback cache size proportional to the relative writeout speeds.
131 * We do this by keeping a floating proportion between BDIs, based on page
132 * writeback completions [end_page_writeback()]. Those devices that write out
133 * pages fastest will get the larger share, while the slower will get a smaller
136 * We use page writeout completions because we are interested in getting rid of
137 * dirty pages. Having them written out is the primary goal.
139 * We introduce a concept of time, a period over which we measure these events,
140 * because demand can/will vary over time. The length of this period itself is
141 * measured in page writeback completions.
144 static struct prop_descriptor vm_completions
;
145 static struct prop_descriptor vm_dirties
;
148 * couple the period to the dirty_ratio:
150 * period/2 ~ roundup_pow_of_two(dirty limit)
152 static int calc_period_shift(void)
154 unsigned long dirty_total
;
157 dirty_total
= vm_dirty_bytes
/ PAGE_SIZE
;
159 dirty_total
= (vm_dirty_ratio
* determine_dirtyable_memory()) /
161 return 2 + ilog2(dirty_total
- 1);
165 * update the period when the dirty threshold changes.
167 static void update_completion_period(void)
169 int shift
= calc_period_shift();
170 prop_change_shift(&vm_completions
, shift
);
171 prop_change_shift(&vm_dirties
, shift
);
174 int dirty_background_ratio_handler(struct ctl_table
*table
, int write
,
175 void __user
*buffer
, size_t *lenp
,
180 ret
= proc_dointvec_minmax(table
, write
, buffer
, lenp
, ppos
);
181 if (ret
== 0 && write
)
182 dirty_background_bytes
= 0;
186 int dirty_background_bytes_handler(struct ctl_table
*table
, int write
,
187 void __user
*buffer
, size_t *lenp
,
192 ret
= proc_doulongvec_minmax(table
, write
, buffer
, lenp
, ppos
);
193 if (ret
== 0 && write
)
194 dirty_background_ratio
= 0;
198 int dirty_ratio_handler(struct ctl_table
*table
, int write
,
199 void __user
*buffer
, size_t *lenp
,
202 int old_ratio
= vm_dirty_ratio
;
205 ret
= proc_dointvec_minmax(table
, write
, buffer
, lenp
, ppos
);
206 if (ret
== 0 && write
&& vm_dirty_ratio
!= old_ratio
) {
207 update_completion_period();
214 int dirty_bytes_handler(struct ctl_table
*table
, int write
,
215 void __user
*buffer
, size_t *lenp
,
218 unsigned long old_bytes
= vm_dirty_bytes
;
221 ret
= proc_doulongvec_minmax(table
, write
, buffer
, lenp
, ppos
);
222 if (ret
== 0 && write
&& vm_dirty_bytes
!= old_bytes
) {
223 update_completion_period();
230 * Increment the BDI's writeout completion count and the global writeout
231 * completion count. Called from test_clear_page_writeback().
233 static inline void __bdi_writeout_inc(struct backing_dev_info
*bdi
)
235 __inc_bdi_stat(bdi
, BDI_WRITTEN
);
236 __prop_inc_percpu_max(&vm_completions
, &bdi
->completions
,
240 void bdi_writeout_inc(struct backing_dev_info
*bdi
)
244 local_irq_save(flags
);
245 __bdi_writeout_inc(bdi
);
246 local_irq_restore(flags
);
248 EXPORT_SYMBOL_GPL(bdi_writeout_inc
);
250 void task_dirty_inc(struct task_struct
*tsk
)
252 prop_inc_single(&vm_dirties
, &tsk
->dirties
);
256 * Obtain an accurate fraction of the BDI's portion.
258 static void bdi_writeout_fraction(struct backing_dev_info
*bdi
,
259 long *numerator
, long *denominator
)
261 prop_fraction_percpu(&vm_completions
, &bdi
->completions
,
262 numerator
, denominator
);
265 static inline void task_dirties_fraction(struct task_struct
*tsk
,
266 long *numerator
, long *denominator
)
268 prop_fraction_single(&vm_dirties
, &tsk
->dirties
,
269 numerator
, denominator
);
273 * task_dirty_limit - scale down dirty throttling threshold for one task
275 * task specific dirty limit:
277 * dirty -= (dirty/8) * p_{t}
279 * To protect light/slow dirtying tasks from heavier/fast ones, we start
280 * throttling individual tasks before reaching the bdi dirty limit.
281 * Relatively low thresholds will be allocated to heavy dirtiers. So when
282 * dirty pages grow large, heavy dirtiers will be throttled first, which will
283 * effectively curb the growth of dirty pages. Light dirtiers with high enough
284 * dirty threshold may never get throttled.
286 #define TASK_LIMIT_FRACTION 8
287 static unsigned long task_dirty_limit(struct task_struct
*tsk
,
288 unsigned long bdi_dirty
)
290 long numerator
, denominator
;
291 unsigned long dirty
= bdi_dirty
;
292 u64 inv
= dirty
/ TASK_LIMIT_FRACTION
;
294 task_dirties_fraction(tsk
, &numerator
, &denominator
);
296 do_div(inv
, denominator
);
300 return max(dirty
, bdi_dirty
/2);
303 /* Minimum limit for any task */
304 static unsigned long task_min_dirty_limit(unsigned long bdi_dirty
)
306 return bdi_dirty
- bdi_dirty
/ TASK_LIMIT_FRACTION
;
312 static unsigned int bdi_min_ratio
;
314 int bdi_set_min_ratio(struct backing_dev_info
*bdi
, unsigned int min_ratio
)
318 spin_lock_bh(&bdi_lock
);
319 if (min_ratio
> bdi
->max_ratio
) {
322 min_ratio
-= bdi
->min_ratio
;
323 if (bdi_min_ratio
+ min_ratio
< 100) {
324 bdi_min_ratio
+= min_ratio
;
325 bdi
->min_ratio
+= min_ratio
;
330 spin_unlock_bh(&bdi_lock
);
335 int bdi_set_max_ratio(struct backing_dev_info
*bdi
, unsigned max_ratio
)
342 spin_lock_bh(&bdi_lock
);
343 if (bdi
->min_ratio
> max_ratio
) {
346 bdi
->max_ratio
= max_ratio
;
347 bdi
->max_prop_frac
= (PROP_FRAC_BASE
* max_ratio
) / 100;
349 spin_unlock_bh(&bdi_lock
);
353 EXPORT_SYMBOL(bdi_set_max_ratio
);
356 * Work out the current dirty-memory clamping and background writeout
359 * The main aim here is to lower them aggressively if there is a lot of mapped
360 * memory around. To avoid stressing page reclaim with lots of unreclaimable
361 * pages. It is better to clamp down on writers than to start swapping, and
362 * performing lots of scanning.
364 * We only allow 1/2 of the currently-unmapped memory to be dirtied.
366 * We don't permit the clamping level to fall below 5% - that is getting rather
369 * We make sure that the background writeout level is below the adjusted
373 static unsigned long highmem_dirtyable_memory(unsigned long total
)
375 #ifdef CONFIG_HIGHMEM
379 for_each_node_state(node
, N_HIGH_MEMORY
) {
381 &NODE_DATA(node
)->node_zones
[ZONE_HIGHMEM
];
383 x
+= zone_page_state(z
, NR_FREE_PAGES
) +
384 zone_reclaimable_pages(z
);
387 * Make sure that the number of highmem pages is never larger
388 * than the number of the total dirtyable memory. This can only
389 * occur in very strange VM situations but we want to make sure
390 * that this does not occur.
392 return min(x
, total
);
399 * determine_dirtyable_memory - amount of memory that may be used
401 * Returns the numebr of pages that can currently be freed and used
402 * by the kernel for direct mappings.
404 unsigned long determine_dirtyable_memory(void)
408 x
= global_page_state(NR_FREE_PAGES
) + global_reclaimable_pages();
410 if (!vm_highmem_is_dirtyable
)
411 x
-= highmem_dirtyable_memory(x
);
413 return x
+ 1; /* Ensure that we never return 0 */
416 static unsigned long dirty_freerun_ceiling(unsigned long thresh
,
417 unsigned long bg_thresh
)
419 return (thresh
+ bg_thresh
) / 2;
422 static unsigned long hard_dirty_limit(unsigned long thresh
)
424 return max(thresh
, global_dirty_limit
);
428 * global_dirty_limits - background-writeback and dirty-throttling thresholds
430 * Calculate the dirty thresholds based on sysctl parameters
431 * - vm.dirty_background_ratio or vm.dirty_background_bytes
432 * - vm.dirty_ratio or vm.dirty_bytes
433 * The dirty limits will be lifted by 1/4 for PF_LESS_THROTTLE (ie. nfsd) and
436 void global_dirty_limits(unsigned long *pbackground
, unsigned long *pdirty
)
438 unsigned long background
;
440 unsigned long uninitialized_var(available_memory
);
441 struct task_struct
*tsk
;
443 if (!vm_dirty_bytes
|| !dirty_background_bytes
)
444 available_memory
= determine_dirtyable_memory();
447 dirty
= DIV_ROUND_UP(vm_dirty_bytes
, PAGE_SIZE
);
449 dirty
= (vm_dirty_ratio
* available_memory
) / 100;
451 if (dirty_background_bytes
)
452 background
= DIV_ROUND_UP(dirty_background_bytes
, PAGE_SIZE
);
454 background
= (dirty_background_ratio
* available_memory
) / 100;
456 if (background
>= dirty
)
457 background
= dirty
/ 2;
459 if (tsk
->flags
& PF_LESS_THROTTLE
|| rt_task(tsk
)) {
460 background
+= background
/ 4;
463 *pbackground
= background
;
465 trace_global_dirty_state(background
, dirty
);
469 * bdi_dirty_limit - @bdi's share of dirty throttling threshold
470 * @bdi: the backing_dev_info to query
471 * @dirty: global dirty limit in pages
473 * Returns @bdi's dirty limit in pages. The term "dirty" in the context of
474 * dirty balancing includes all PG_dirty, PG_writeback and NFS unstable pages.
475 * And the "limit" in the name is not seriously taken as hard limit in
476 * balance_dirty_pages().
478 * It allocates high/low dirty limits to fast/slow devices, in order to prevent
479 * - starving fast devices
480 * - piling up dirty pages (that will take long time to sync) on slow devices
482 * The bdi's share of dirty limit will be adapting to its throughput and
483 * bounded by the bdi->min_ratio and/or bdi->max_ratio parameters, if set.
485 unsigned long bdi_dirty_limit(struct backing_dev_info
*bdi
, unsigned long dirty
)
488 long numerator
, denominator
;
491 * Calculate this BDI's share of the dirty ratio.
493 bdi_writeout_fraction(bdi
, &numerator
, &denominator
);
495 bdi_dirty
= (dirty
* (100 - bdi_min_ratio
)) / 100;
496 bdi_dirty
*= numerator
;
497 do_div(bdi_dirty
, denominator
);
499 bdi_dirty
+= (dirty
* bdi
->min_ratio
) / 100;
500 if (bdi_dirty
> (dirty
* bdi
->max_ratio
) / 100)
501 bdi_dirty
= dirty
* bdi
->max_ratio
/ 100;
507 * Dirty position control.
509 * (o) global/bdi setpoints
511 * We want the dirty pages be balanced around the global/bdi setpoints.
512 * When the number of dirty pages is higher/lower than the setpoint, the
513 * dirty position control ratio (and hence task dirty ratelimit) will be
514 * decreased/increased to bring the dirty pages back to the setpoint.
516 * pos_ratio = 1 << RATELIMIT_CALC_SHIFT
518 * if (dirty < setpoint) scale up pos_ratio
519 * if (dirty > setpoint) scale down pos_ratio
521 * if (bdi_dirty < bdi_setpoint) scale up pos_ratio
522 * if (bdi_dirty > bdi_setpoint) scale down pos_ratio
524 * task_ratelimit = dirty_ratelimit * pos_ratio >> RATELIMIT_CALC_SHIFT
526 * (o) global control line
530 * | |<===== global dirty control scope ======>|
538 * 1.0 ................................*
544 * 0 +------------.------------------.----------------------*------------->
545 * freerun^ setpoint^ limit^ dirty pages
547 * (o) bdi control line
555 * | * |<=========== span ============>|
556 * 1.0 .......................*
568 * 1/4 ...............................................* * * * * * * * * * * *
572 * 0 +----------------------.-------------------------------.------------->
573 * bdi_setpoint^ x_intercept^
575 * The bdi control line won't drop below pos_ratio=1/4, so that bdi_dirty can
576 * be smoothly throttled down to normal if it starts high in situations like
577 * - start writing to a slow SD card and a fast disk at the same time. The SD
578 * card's bdi_dirty may rush to many times higher than bdi_setpoint.
579 * - the bdi dirty thresh drops quickly due to change of JBOD workload
581 static unsigned long bdi_position_ratio(struct backing_dev_info
*bdi
,
582 unsigned long thresh
,
583 unsigned long bg_thresh
,
585 unsigned long bdi_thresh
,
586 unsigned long bdi_dirty
)
588 unsigned long write_bw
= bdi
->avg_write_bandwidth
;
589 unsigned long freerun
= dirty_freerun_ceiling(thresh
, bg_thresh
);
590 unsigned long limit
= hard_dirty_limit(thresh
);
591 unsigned long x_intercept
;
592 unsigned long setpoint
; /* dirty pages' target balance point */
593 unsigned long bdi_setpoint
;
595 long long pos_ratio
; /* for scaling up/down the rate limit */
598 if (unlikely(dirty
>= limit
))
605 * f(dirty) := 1.0 + (----------------)
608 * it's a 3rd order polynomial that subjects to
610 * (1) f(freerun) = 2.0 => rampup dirty_ratelimit reasonably fast
611 * (2) f(setpoint) = 1.0 => the balance point
612 * (3) f(limit) = 0 => the hard limit
613 * (4) df/dx <= 0 => negative feedback control
614 * (5) the closer to setpoint, the smaller |df/dx| (and the reverse)
615 * => fast response on large errors; small oscillation near setpoint
617 setpoint
= (freerun
+ limit
) / 2;
618 x
= div_s64((setpoint
- dirty
) << RATELIMIT_CALC_SHIFT
,
619 limit
- setpoint
+ 1);
621 pos_ratio
= pos_ratio
* x
>> RATELIMIT_CALC_SHIFT
;
622 pos_ratio
= pos_ratio
* x
>> RATELIMIT_CALC_SHIFT
;
623 pos_ratio
+= 1 << RATELIMIT_CALC_SHIFT
;
626 * We have computed basic pos_ratio above based on global situation. If
627 * the bdi is over/under its share of dirty pages, we want to scale
628 * pos_ratio further down/up. That is done by the following mechanism.
634 * f(bdi_dirty) := 1.0 + k * (bdi_dirty - bdi_setpoint)
636 * x_intercept - bdi_dirty
637 * := --------------------------
638 * x_intercept - bdi_setpoint
640 * The main bdi control line is a linear function that subjects to
642 * (1) f(bdi_setpoint) = 1.0
643 * (2) k = - 1 / (8 * write_bw) (in single bdi case)
644 * or equally: x_intercept = bdi_setpoint + 8 * write_bw
646 * For single bdi case, the dirty pages are observed to fluctuate
647 * regularly within range
648 * [bdi_setpoint - write_bw/2, bdi_setpoint + write_bw/2]
649 * for various filesystems, where (2) can yield in a reasonable 12.5%
650 * fluctuation range for pos_ratio.
652 * For JBOD case, bdi_thresh (not bdi_dirty!) could fluctuate up to its
653 * own size, so move the slope over accordingly and choose a slope that
654 * yields 100% pos_ratio fluctuation on suddenly doubled bdi_thresh.
656 if (unlikely(bdi_thresh
> thresh
))
659 * scale global setpoint to bdi's:
660 * bdi_setpoint = setpoint * bdi_thresh / thresh
662 x
= div_u64((u64
)bdi_thresh
<< 16, thresh
+ 1);
663 bdi_setpoint
= setpoint
* (u64
)x
>> 16;
665 * Use span=(8*write_bw) in single bdi case as indicated by
666 * (thresh - bdi_thresh ~= 0) and transit to bdi_thresh in JBOD case.
668 * bdi_thresh thresh - bdi_thresh
669 * span = ---------- * (8 * write_bw) + ------------------- * bdi_thresh
672 span
= (thresh
- bdi_thresh
+ 8 * write_bw
) * (u64
)x
>> 16;
673 x_intercept
= bdi_setpoint
+ span
;
675 if (bdi_dirty
< x_intercept
- span
/ 4) {
676 pos_ratio
*= x_intercept
- bdi_dirty
;
677 do_div(pos_ratio
, x_intercept
- bdi_setpoint
+ 1);
684 static void bdi_update_write_bandwidth(struct backing_dev_info
*bdi
,
685 unsigned long elapsed
,
686 unsigned long written
)
688 const unsigned long period
= roundup_pow_of_two(3 * HZ
);
689 unsigned long avg
= bdi
->avg_write_bandwidth
;
690 unsigned long old
= bdi
->write_bandwidth
;
694 * bw = written * HZ / elapsed
696 * bw * elapsed + write_bandwidth * (period - elapsed)
697 * write_bandwidth = ---------------------------------------------------
700 bw
= written
- bdi
->written_stamp
;
702 if (unlikely(elapsed
> period
)) {
707 bw
+= (u64
)bdi
->write_bandwidth
* (period
- elapsed
);
708 bw
>>= ilog2(period
);
711 * one more level of smoothing, for filtering out sudden spikes
713 if (avg
> old
&& old
>= (unsigned long)bw
)
714 avg
-= (avg
- old
) >> 3;
716 if (avg
< old
&& old
<= (unsigned long)bw
)
717 avg
+= (old
- avg
) >> 3;
720 bdi
->write_bandwidth
= bw
;
721 bdi
->avg_write_bandwidth
= avg
;
725 * The global dirtyable memory and dirty threshold could be suddenly knocked
726 * down by a large amount (eg. on the startup of KVM in a swapless system).
727 * This may throw the system into deep dirty exceeded state and throttle
728 * heavy/light dirtiers alike. To retain good responsiveness, maintain
729 * global_dirty_limit for tracking slowly down to the knocked down dirty
732 static void update_dirty_limit(unsigned long thresh
, unsigned long dirty
)
734 unsigned long limit
= global_dirty_limit
;
737 * Follow up in one step.
739 if (limit
< thresh
) {
745 * Follow down slowly. Use the higher one as the target, because thresh
746 * may drop below dirty. This is exactly the reason to introduce
747 * global_dirty_limit which is guaranteed to lie above the dirty pages.
749 thresh
= max(thresh
, dirty
);
750 if (limit
> thresh
) {
751 limit
-= (limit
- thresh
) >> 5;
756 global_dirty_limit
= limit
;
759 static void global_update_bandwidth(unsigned long thresh
,
763 static DEFINE_SPINLOCK(dirty_lock
);
764 static unsigned long update_time
;
767 * check locklessly first to optimize away locking for the most time
769 if (time_before(now
, update_time
+ BANDWIDTH_INTERVAL
))
772 spin_lock(&dirty_lock
);
773 if (time_after_eq(now
, update_time
+ BANDWIDTH_INTERVAL
)) {
774 update_dirty_limit(thresh
, dirty
);
777 spin_unlock(&dirty_lock
);
780 void __bdi_update_bandwidth(struct backing_dev_info
*bdi
,
781 unsigned long thresh
,
782 unsigned long bg_thresh
,
784 unsigned long bdi_thresh
,
785 unsigned long bdi_dirty
,
786 unsigned long start_time
)
788 unsigned long now
= jiffies
;
789 unsigned long elapsed
= now
- bdi
->bw_time_stamp
;
790 unsigned long written
;
793 * rate-limit, only update once every 200ms.
795 if (elapsed
< BANDWIDTH_INTERVAL
)
798 written
= percpu_counter_read(&bdi
->bdi_stat
[BDI_WRITTEN
]);
801 * Skip quiet periods when disk bandwidth is under-utilized.
802 * (at least 1s idle time between two flusher runs)
804 if (elapsed
> HZ
&& time_before(bdi
->bw_time_stamp
, start_time
))
808 global_update_bandwidth(thresh
, dirty
, now
);
810 bdi_update_write_bandwidth(bdi
, elapsed
, written
);
813 bdi
->written_stamp
= written
;
814 bdi
->bw_time_stamp
= now
;
817 static void bdi_update_bandwidth(struct backing_dev_info
*bdi
,
818 unsigned long thresh
,
819 unsigned long bg_thresh
,
821 unsigned long bdi_thresh
,
822 unsigned long bdi_dirty
,
823 unsigned long start_time
)
825 if (time_is_after_eq_jiffies(bdi
->bw_time_stamp
+ BANDWIDTH_INTERVAL
))
827 spin_lock(&bdi
->wb
.list_lock
);
828 __bdi_update_bandwidth(bdi
, thresh
, bg_thresh
, dirty
,
829 bdi_thresh
, bdi_dirty
, start_time
);
830 spin_unlock(&bdi
->wb
.list_lock
);
834 * balance_dirty_pages() must be called by processes which are generating dirty
835 * data. It looks at the number of dirty pages in the machine and will force
836 * the caller to perform writeback if the system is over `vm_dirty_ratio'.
837 * If we're over `background_thresh' then the writeback threads are woken to
838 * perform some writeout.
840 static void balance_dirty_pages(struct address_space
*mapping
,
841 unsigned long write_chunk
)
843 unsigned long nr_reclaimable
, bdi_nr_reclaimable
;
844 unsigned long nr_dirty
; /* = file_dirty + writeback + unstable_nfs */
845 unsigned long bdi_dirty
;
846 unsigned long freerun
;
847 unsigned long background_thresh
;
848 unsigned long dirty_thresh
;
849 unsigned long bdi_thresh
;
850 unsigned long task_bdi_thresh
;
851 unsigned long min_task_bdi_thresh
;
852 unsigned long pages_written
= 0;
853 unsigned long pause
= 1;
854 bool dirty_exceeded
= false;
855 bool clear_dirty_exceeded
= true;
856 struct backing_dev_info
*bdi
= mapping
->backing_dev_info
;
857 unsigned long start_time
= jiffies
;
860 nr_reclaimable
= global_page_state(NR_FILE_DIRTY
) +
861 global_page_state(NR_UNSTABLE_NFS
);
862 nr_dirty
= nr_reclaimable
+ global_page_state(NR_WRITEBACK
);
864 global_dirty_limits(&background_thresh
, &dirty_thresh
);
867 * Throttle it only when the background writeback cannot
868 * catch-up. This avoids (excessively) small writeouts
869 * when the bdi limits are ramping up.
871 freerun
= dirty_freerun_ceiling(dirty_thresh
,
873 if (nr_dirty
<= freerun
)
876 bdi_thresh
= bdi_dirty_limit(bdi
, dirty_thresh
);
877 min_task_bdi_thresh
= task_min_dirty_limit(bdi_thresh
);
878 task_bdi_thresh
= task_dirty_limit(current
, bdi_thresh
);
881 * In order to avoid the stacked BDI deadlock we need
882 * to ensure we accurately count the 'dirty' pages when
883 * the threshold is low.
885 * Otherwise it would be possible to get thresh+n pages
886 * reported dirty, even though there are thresh-m pages
887 * actually dirty; with m+n sitting in the percpu
890 if (task_bdi_thresh
< 2 * bdi_stat_error(bdi
)) {
891 bdi_nr_reclaimable
= bdi_stat_sum(bdi
, BDI_RECLAIMABLE
);
892 bdi_dirty
= bdi_nr_reclaimable
+
893 bdi_stat_sum(bdi
, BDI_WRITEBACK
);
895 bdi_nr_reclaimable
= bdi_stat(bdi
, BDI_RECLAIMABLE
);
896 bdi_dirty
= bdi_nr_reclaimable
+
897 bdi_stat(bdi
, BDI_WRITEBACK
);
901 * The bdi thresh is somehow "soft" limit derived from the
902 * global "hard" limit. The former helps to prevent heavy IO
903 * bdi or process from holding back light ones; The latter is
904 * the last resort safeguard.
906 dirty_exceeded
= (bdi_dirty
> task_bdi_thresh
) ||
907 (nr_dirty
> dirty_thresh
);
908 clear_dirty_exceeded
= (bdi_dirty
<= min_task_bdi_thresh
) &&
909 (nr_dirty
<= dirty_thresh
);
914 if (!bdi
->dirty_exceeded
)
915 bdi
->dirty_exceeded
= 1;
917 bdi_update_bandwidth(bdi
, dirty_thresh
, background_thresh
,
918 nr_dirty
, bdi_thresh
, bdi_dirty
,
921 /* Note: nr_reclaimable denotes nr_dirty + nr_unstable.
922 * Unstable writes are a feature of certain networked
923 * filesystems (i.e. NFS) in which data may have been
924 * written to the server's write cache, but has not yet
925 * been flushed to permanent storage.
926 * Only move pages to writeback if this bdi is over its
927 * threshold otherwise wait until the disk writes catch
930 trace_balance_dirty_start(bdi
);
931 if (bdi_nr_reclaimable
> task_bdi_thresh
) {
932 pages_written
+= writeback_inodes_wb(&bdi
->wb
,
934 trace_balance_dirty_written(bdi
, pages_written
);
935 if (pages_written
>= write_chunk
)
936 break; /* We've done our duty */
938 __set_current_state(TASK_UNINTERRUPTIBLE
);
939 io_schedule_timeout(pause
);
940 trace_balance_dirty_wait(bdi
);
942 dirty_thresh
= hard_dirty_limit(dirty_thresh
);
944 * max-pause area. If dirty exceeded but still within this
945 * area, no need to sleep for more than 200ms: (a) 8 pages per
946 * 200ms is typically more than enough to curb heavy dirtiers;
947 * (b) the pause time limit makes the dirtiers more responsive.
949 if (nr_dirty
< dirty_thresh
&&
950 bdi_dirty
< (task_bdi_thresh
+ bdi_thresh
) / 2 &&
951 time_after(jiffies
, start_time
+ MAX_PAUSE
))
955 * Increase the delay for each loop, up to our previous
956 * default of taking a 100ms nap.
963 /* Clear dirty_exceeded flag only when no task can exceed the limit */
964 if (clear_dirty_exceeded
&& bdi
->dirty_exceeded
)
965 bdi
->dirty_exceeded
= 0;
967 if (writeback_in_progress(bdi
))
971 * In laptop mode, we wait until hitting the higher threshold before
972 * starting background writeout, and then write out all the way down
973 * to the lower threshold. So slow writers cause minimal disk activity.
975 * In normal mode, we start background writeout at the lower
976 * background_thresh, to keep the amount of dirty memory low.
978 if ((laptop_mode
&& pages_written
) ||
979 (!laptop_mode
&& (nr_reclaimable
> background_thresh
)))
980 bdi_start_background_writeback(bdi
);
983 void set_page_dirty_balance(struct page
*page
, int page_mkwrite
)
985 if (set_page_dirty(page
) || page_mkwrite
) {
986 struct address_space
*mapping
= page_mapping(page
);
989 balance_dirty_pages_ratelimited(mapping
);
993 static DEFINE_PER_CPU(unsigned long, bdp_ratelimits
) = 0;
996 * balance_dirty_pages_ratelimited_nr - balance dirty memory state
997 * @mapping: address_space which was dirtied
998 * @nr_pages_dirtied: number of pages which the caller has just dirtied
1000 * Processes which are dirtying memory should call in here once for each page
1001 * which was newly dirtied. The function will periodically check the system's
1002 * dirty state and will initiate writeback if needed.
1004 * On really big machines, get_writeback_state is expensive, so try to avoid
1005 * calling it too often (ratelimiting). But once we're over the dirty memory
1006 * limit we decrease the ratelimiting by a lot, to prevent individual processes
1007 * from overshooting the limit by (ratelimit_pages) each.
1009 void balance_dirty_pages_ratelimited_nr(struct address_space
*mapping
,
1010 unsigned long nr_pages_dirtied
)
1012 struct backing_dev_info
*bdi
= mapping
->backing_dev_info
;
1013 unsigned long ratelimit
;
1016 if (!bdi_cap_account_dirty(bdi
))
1019 ratelimit
= ratelimit_pages
;
1020 if (mapping
->backing_dev_info
->dirty_exceeded
)
1024 * Check the rate limiting. Also, we do not want to throttle real-time
1025 * tasks in balance_dirty_pages(). Period.
1028 p
= &__get_cpu_var(bdp_ratelimits
);
1029 *p
+= nr_pages_dirtied
;
1030 if (unlikely(*p
>= ratelimit
)) {
1031 ratelimit
= sync_writeback_pages(*p
);
1034 balance_dirty_pages(mapping
, ratelimit
);
1039 EXPORT_SYMBOL(balance_dirty_pages_ratelimited_nr
);
1041 void throttle_vm_writeout(gfp_t gfp_mask
)
1043 unsigned long background_thresh
;
1044 unsigned long dirty_thresh
;
1047 global_dirty_limits(&background_thresh
, &dirty_thresh
);
1050 * Boost the allowable dirty threshold a bit for page
1051 * allocators so they don't get DoS'ed by heavy writers
1053 dirty_thresh
+= dirty_thresh
/ 10; /* wheeee... */
1055 if (global_page_state(NR_UNSTABLE_NFS
) +
1056 global_page_state(NR_WRITEBACK
) <= dirty_thresh
)
1058 congestion_wait(BLK_RW_ASYNC
, HZ
/10);
1061 * The caller might hold locks which can prevent IO completion
1062 * or progress in the filesystem. So we cannot just sit here
1063 * waiting for IO to complete.
1065 if ((gfp_mask
& (__GFP_FS
|__GFP_IO
)) != (__GFP_FS
|__GFP_IO
))
1071 * sysctl handler for /proc/sys/vm/dirty_writeback_centisecs
1073 int dirty_writeback_centisecs_handler(ctl_table
*table
, int write
,
1074 void __user
*buffer
, size_t *length
, loff_t
*ppos
)
1076 proc_dointvec(table
, write
, buffer
, length
, ppos
);
1077 bdi_arm_supers_timer();
1082 void laptop_mode_timer_fn(unsigned long data
)
1084 struct request_queue
*q
= (struct request_queue
*)data
;
1085 int nr_pages
= global_page_state(NR_FILE_DIRTY
) +
1086 global_page_state(NR_UNSTABLE_NFS
);
1089 * We want to write everything out, not just down to the dirty
1092 if (bdi_has_dirty_io(&q
->backing_dev_info
))
1093 bdi_start_writeback(&q
->backing_dev_info
, nr_pages
);
1097 * We've spun up the disk and we're in laptop mode: schedule writeback
1098 * of all dirty data a few seconds from now. If the flush is already scheduled
1099 * then push it back - the user is still using the disk.
1101 void laptop_io_completion(struct backing_dev_info
*info
)
1103 mod_timer(&info
->laptop_mode_wb_timer
, jiffies
+ laptop_mode
);
1107 * We're in laptop mode and we've just synced. The sync's writes will have
1108 * caused another writeback to be scheduled by laptop_io_completion.
1109 * Nothing needs to be written back anymore, so we unschedule the writeback.
1111 void laptop_sync_completion(void)
1113 struct backing_dev_info
*bdi
;
1117 list_for_each_entry_rcu(bdi
, &bdi_list
, bdi_list
)
1118 del_timer(&bdi
->laptop_mode_wb_timer
);
1125 * If ratelimit_pages is too high then we can get into dirty-data overload
1126 * if a large number of processes all perform writes at the same time.
1127 * If it is too low then SMP machines will call the (expensive)
1128 * get_writeback_state too often.
1130 * Here we set ratelimit_pages to a level which ensures that when all CPUs are
1131 * dirtying in parallel, we cannot go more than 3% (1/32) over the dirty memory
1132 * thresholds before writeback cuts in.
1134 * But the limit should not be set too high. Because it also controls the
1135 * amount of memory which the balance_dirty_pages() caller has to write back.
1136 * If this is too large then the caller will block on the IO queue all the
1137 * time. So limit it to four megabytes - the balance_dirty_pages() caller
1138 * will write six megabyte chunks, max.
1141 void writeback_set_ratelimit(void)
1143 ratelimit_pages
= vm_total_pages
/ (num_online_cpus() * 32);
1144 if (ratelimit_pages
< 16)
1145 ratelimit_pages
= 16;
1146 if (ratelimit_pages
* PAGE_CACHE_SIZE
> 4096 * 1024)
1147 ratelimit_pages
= (4096 * 1024) / PAGE_CACHE_SIZE
;
1150 static int __cpuinit
1151 ratelimit_handler(struct notifier_block
*self
, unsigned long u
, void *v
)
1153 writeback_set_ratelimit();
1157 static struct notifier_block __cpuinitdata ratelimit_nb
= {
1158 .notifier_call
= ratelimit_handler
,
1163 * Called early on to tune the page writeback dirty limits.
1165 * We used to scale dirty pages according to how total memory
1166 * related to pages that could be allocated for buffers (by
1167 * comparing nr_free_buffer_pages() to vm_total_pages.
1169 * However, that was when we used "dirty_ratio" to scale with
1170 * all memory, and we don't do that any more. "dirty_ratio"
1171 * is now applied to total non-HIGHPAGE memory (by subtracting
1172 * totalhigh_pages from vm_total_pages), and as such we can't
1173 * get into the old insane situation any more where we had
1174 * large amounts of dirty pages compared to a small amount of
1175 * non-HIGHMEM memory.
1177 * But we might still want to scale the dirty_ratio by how
1178 * much memory the box has..
1180 void __init
page_writeback_init(void)
1184 writeback_set_ratelimit();
1185 register_cpu_notifier(&ratelimit_nb
);
1187 shift
= calc_period_shift();
1188 prop_descriptor_init(&vm_completions
, shift
);
1189 prop_descriptor_init(&vm_dirties
, shift
);
1193 * tag_pages_for_writeback - tag pages to be written by write_cache_pages
1194 * @mapping: address space structure to write
1195 * @start: starting page index
1196 * @end: ending page index (inclusive)
1198 * This function scans the page range from @start to @end (inclusive) and tags
1199 * all pages that have DIRTY tag set with a special TOWRITE tag. The idea is
1200 * that write_cache_pages (or whoever calls this function) will then use
1201 * TOWRITE tag to identify pages eligible for writeback. This mechanism is
1202 * used to avoid livelocking of writeback by a process steadily creating new
1203 * dirty pages in the file (thus it is important for this function to be quick
1204 * so that it can tag pages faster than a dirtying process can create them).
1207 * We tag pages in batches of WRITEBACK_TAG_BATCH to reduce tree_lock latency.
1209 void tag_pages_for_writeback(struct address_space
*mapping
,
1210 pgoff_t start
, pgoff_t end
)
1212 #define WRITEBACK_TAG_BATCH 4096
1213 unsigned long tagged
;
1216 spin_lock_irq(&mapping
->tree_lock
);
1217 tagged
= radix_tree_range_tag_if_tagged(&mapping
->page_tree
,
1218 &start
, end
, WRITEBACK_TAG_BATCH
,
1219 PAGECACHE_TAG_DIRTY
, PAGECACHE_TAG_TOWRITE
);
1220 spin_unlock_irq(&mapping
->tree_lock
);
1221 WARN_ON_ONCE(tagged
> WRITEBACK_TAG_BATCH
);
1223 /* We check 'start' to handle wrapping when end == ~0UL */
1224 } while (tagged
>= WRITEBACK_TAG_BATCH
&& start
);
1226 EXPORT_SYMBOL(tag_pages_for_writeback
);
1229 * write_cache_pages - walk the list of dirty pages of the given address space and write all of them.
1230 * @mapping: address space structure to write
1231 * @wbc: subtract the number of written pages from *@wbc->nr_to_write
1232 * @writepage: function called for each page
1233 * @data: data passed to writepage function
1235 * If a page is already under I/O, write_cache_pages() skips it, even
1236 * if it's dirty. This is desirable behaviour for memory-cleaning writeback,
1237 * but it is INCORRECT for data-integrity system calls such as fsync(). fsync()
1238 * and msync() need to guarantee that all the data which was dirty at the time
1239 * the call was made get new I/O started against them. If wbc->sync_mode is
1240 * WB_SYNC_ALL then we were called for data integrity and we must wait for
1241 * existing IO to complete.
1243 * To avoid livelocks (when other process dirties new pages), we first tag
1244 * pages which should be written back with TOWRITE tag and only then start
1245 * writing them. For data-integrity sync we have to be careful so that we do
1246 * not miss some pages (e.g., because some other process has cleared TOWRITE
1247 * tag we set). The rule we follow is that TOWRITE tag can be cleared only
1248 * by the process clearing the DIRTY tag (and submitting the page for IO).
1250 int write_cache_pages(struct address_space
*mapping
,
1251 struct writeback_control
*wbc
, writepage_t writepage
,
1256 struct pagevec pvec
;
1258 pgoff_t
uninitialized_var(writeback_index
);
1260 pgoff_t end
; /* Inclusive */
1263 int range_whole
= 0;
1266 pagevec_init(&pvec
, 0);
1267 if (wbc
->range_cyclic
) {
1268 writeback_index
= mapping
->writeback_index
; /* prev offset */
1269 index
= writeback_index
;
1276 index
= wbc
->range_start
>> PAGE_CACHE_SHIFT
;
1277 end
= wbc
->range_end
>> PAGE_CACHE_SHIFT
;
1278 if (wbc
->range_start
== 0 && wbc
->range_end
== LLONG_MAX
)
1280 cycled
= 1; /* ignore range_cyclic tests */
1282 if (wbc
->sync_mode
== WB_SYNC_ALL
|| wbc
->tagged_writepages
)
1283 tag
= PAGECACHE_TAG_TOWRITE
;
1285 tag
= PAGECACHE_TAG_DIRTY
;
1287 if (wbc
->sync_mode
== WB_SYNC_ALL
|| wbc
->tagged_writepages
)
1288 tag_pages_for_writeback(mapping
, index
, end
);
1290 while (!done
&& (index
<= end
)) {
1293 nr_pages
= pagevec_lookup_tag(&pvec
, mapping
, &index
, tag
,
1294 min(end
- index
, (pgoff_t
)PAGEVEC_SIZE
-1) + 1);
1298 for (i
= 0; i
< nr_pages
; i
++) {
1299 struct page
*page
= pvec
.pages
[i
];
1302 * At this point, the page may be truncated or
1303 * invalidated (changing page->mapping to NULL), or
1304 * even swizzled back from swapper_space to tmpfs file
1305 * mapping. However, page->index will not change
1306 * because we have a reference on the page.
1308 if (page
->index
> end
) {
1310 * can't be range_cyclic (1st pass) because
1311 * end == -1 in that case.
1317 done_index
= page
->index
;
1322 * Page truncated or invalidated. We can freely skip it
1323 * then, even for data integrity operations: the page
1324 * has disappeared concurrently, so there could be no
1325 * real expectation of this data interity operation
1326 * even if there is now a new, dirty page at the same
1327 * pagecache address.
1329 if (unlikely(page
->mapping
!= mapping
)) {
1335 if (!PageDirty(page
)) {
1336 /* someone wrote it for us */
1337 goto continue_unlock
;
1340 if (PageWriteback(page
)) {
1341 if (wbc
->sync_mode
!= WB_SYNC_NONE
)
1342 wait_on_page_writeback(page
);
1344 goto continue_unlock
;
1347 BUG_ON(PageWriteback(page
));
1348 if (!clear_page_dirty_for_io(page
))
1349 goto continue_unlock
;
1351 trace_wbc_writepage(wbc
, mapping
->backing_dev_info
);
1352 ret
= (*writepage
)(page
, wbc
, data
);
1353 if (unlikely(ret
)) {
1354 if (ret
== AOP_WRITEPAGE_ACTIVATE
) {
1359 * done_index is set past this page,
1360 * so media errors will not choke
1361 * background writeout for the entire
1362 * file. This has consequences for
1363 * range_cyclic semantics (ie. it may
1364 * not be suitable for data integrity
1367 done_index
= page
->index
+ 1;
1374 * We stop writing back only if we are not doing
1375 * integrity sync. In case of integrity sync we have to
1376 * keep going until we have written all the pages
1377 * we tagged for writeback prior to entering this loop.
1379 if (--wbc
->nr_to_write
<= 0 &&
1380 wbc
->sync_mode
== WB_SYNC_NONE
) {
1385 pagevec_release(&pvec
);
1388 if (!cycled
&& !done
) {
1391 * We hit the last page and there is more work to be done: wrap
1392 * back to the start of the file
1396 end
= writeback_index
- 1;
1399 if (wbc
->range_cyclic
|| (range_whole
&& wbc
->nr_to_write
> 0))
1400 mapping
->writeback_index
= done_index
;
1404 EXPORT_SYMBOL(write_cache_pages
);
1407 * Function used by generic_writepages to call the real writepage
1408 * function and set the mapping flags on error
1410 static int __writepage(struct page
*page
, struct writeback_control
*wbc
,
1413 struct address_space
*mapping
= data
;
1414 int ret
= mapping
->a_ops
->writepage(page
, wbc
);
1415 mapping_set_error(mapping
, ret
);
1420 * generic_writepages - walk the list of dirty pages of the given address space and writepage() all of them.
1421 * @mapping: address space structure to write
1422 * @wbc: subtract the number of written pages from *@wbc->nr_to_write
1424 * This is a library function, which implements the writepages()
1425 * address_space_operation.
1427 int generic_writepages(struct address_space
*mapping
,
1428 struct writeback_control
*wbc
)
1430 struct blk_plug plug
;
1433 /* deal with chardevs and other special file */
1434 if (!mapping
->a_ops
->writepage
)
1437 blk_start_plug(&plug
);
1438 ret
= write_cache_pages(mapping
, wbc
, __writepage
, mapping
);
1439 blk_finish_plug(&plug
);
1443 EXPORT_SYMBOL(generic_writepages
);
1445 int do_writepages(struct address_space
*mapping
, struct writeback_control
*wbc
)
1449 if (wbc
->nr_to_write
<= 0)
1451 if (mapping
->a_ops
->writepages
)
1452 ret
= mapping
->a_ops
->writepages(mapping
, wbc
);
1454 ret
= generic_writepages(mapping
, wbc
);
1459 * write_one_page - write out a single page and optionally wait on I/O
1460 * @page: the page to write
1461 * @wait: if true, wait on writeout
1463 * The page must be locked by the caller and will be unlocked upon return.
1465 * write_one_page() returns a negative error code if I/O failed.
1467 int write_one_page(struct page
*page
, int wait
)
1469 struct address_space
*mapping
= page
->mapping
;
1471 struct writeback_control wbc
= {
1472 .sync_mode
= WB_SYNC_ALL
,
1476 BUG_ON(!PageLocked(page
));
1479 wait_on_page_writeback(page
);
1481 if (clear_page_dirty_for_io(page
)) {
1482 page_cache_get(page
);
1483 ret
= mapping
->a_ops
->writepage(page
, &wbc
);
1484 if (ret
== 0 && wait
) {
1485 wait_on_page_writeback(page
);
1486 if (PageError(page
))
1489 page_cache_release(page
);
1495 EXPORT_SYMBOL(write_one_page
);
1498 * For address_spaces which do not use buffers nor write back.
1500 int __set_page_dirty_no_writeback(struct page
*page
)
1502 if (!PageDirty(page
))
1503 return !TestSetPageDirty(page
);
1508 * Helper function for set_page_dirty family.
1509 * NOTE: This relies on being atomic wrt interrupts.
1511 void account_page_dirtied(struct page
*page
, struct address_space
*mapping
)
1513 if (mapping_cap_account_dirty(mapping
)) {
1514 __inc_zone_page_state(page
, NR_FILE_DIRTY
);
1515 __inc_zone_page_state(page
, NR_DIRTIED
);
1516 __inc_bdi_stat(mapping
->backing_dev_info
, BDI_RECLAIMABLE
);
1517 __inc_bdi_stat(mapping
->backing_dev_info
, BDI_DIRTIED
);
1518 task_dirty_inc(current
);
1519 task_io_account_write(PAGE_CACHE_SIZE
);
1522 EXPORT_SYMBOL(account_page_dirtied
);
1525 * Helper function for set_page_writeback family.
1526 * NOTE: Unlike account_page_dirtied this does not rely on being atomic
1529 void account_page_writeback(struct page
*page
)
1531 inc_zone_page_state(page
, NR_WRITEBACK
);
1533 EXPORT_SYMBOL(account_page_writeback
);
1536 * For address_spaces which do not use buffers. Just tag the page as dirty in
1539 * This is also used when a single buffer is being dirtied: we want to set the
1540 * page dirty in that case, but not all the buffers. This is a "bottom-up"
1541 * dirtying, whereas __set_page_dirty_buffers() is a "top-down" dirtying.
1543 * Most callers have locked the page, which pins the address_space in memory.
1544 * But zap_pte_range() does not lock the page, however in that case the
1545 * mapping is pinned by the vma's ->vm_file reference.
1547 * We take care to handle the case where the page was truncated from the
1548 * mapping by re-checking page_mapping() inside tree_lock.
1550 int __set_page_dirty_nobuffers(struct page
*page
)
1552 if (!TestSetPageDirty(page
)) {
1553 struct address_space
*mapping
= page_mapping(page
);
1554 struct address_space
*mapping2
;
1559 spin_lock_irq(&mapping
->tree_lock
);
1560 mapping2
= page_mapping(page
);
1561 if (mapping2
) { /* Race with truncate? */
1562 BUG_ON(mapping2
!= mapping
);
1563 WARN_ON_ONCE(!PagePrivate(page
) && !PageUptodate(page
));
1564 account_page_dirtied(page
, mapping
);
1565 radix_tree_tag_set(&mapping
->page_tree
,
1566 page_index(page
), PAGECACHE_TAG_DIRTY
);
1568 spin_unlock_irq(&mapping
->tree_lock
);
1569 if (mapping
->host
) {
1570 /* !PageAnon && !swapper_space */
1571 __mark_inode_dirty(mapping
->host
, I_DIRTY_PAGES
);
1577 EXPORT_SYMBOL(__set_page_dirty_nobuffers
);
1580 * When a writepage implementation decides that it doesn't want to write this
1581 * page for some reason, it should redirty the locked page via
1582 * redirty_page_for_writepage() and it should then unlock the page and return 0
1584 int redirty_page_for_writepage(struct writeback_control
*wbc
, struct page
*page
)
1586 wbc
->pages_skipped
++;
1587 return __set_page_dirty_nobuffers(page
);
1589 EXPORT_SYMBOL(redirty_page_for_writepage
);
1594 * For pages with a mapping this should be done under the page lock
1595 * for the benefit of asynchronous memory errors who prefer a consistent
1596 * dirty state. This rule can be broken in some special cases,
1597 * but should be better not to.
1599 * If the mapping doesn't provide a set_page_dirty a_op, then
1600 * just fall through and assume that it wants buffer_heads.
1602 int set_page_dirty(struct page
*page
)
1604 struct address_space
*mapping
= page_mapping(page
);
1606 if (likely(mapping
)) {
1607 int (*spd
)(struct page
*) = mapping
->a_ops
->set_page_dirty
;
1609 * readahead/lru_deactivate_page could remain
1610 * PG_readahead/PG_reclaim due to race with end_page_writeback
1611 * About readahead, if the page is written, the flags would be
1612 * reset. So no problem.
1613 * About lru_deactivate_page, if the page is redirty, the flag
1614 * will be reset. So no problem. but if the page is used by readahead
1615 * it will confuse readahead and make it restart the size rampup
1616 * process. But it's a trivial problem.
1618 ClearPageReclaim(page
);
1621 spd
= __set_page_dirty_buffers
;
1623 return (*spd
)(page
);
1625 if (!PageDirty(page
)) {
1626 if (!TestSetPageDirty(page
))
1631 EXPORT_SYMBOL(set_page_dirty
);
1634 * set_page_dirty() is racy if the caller has no reference against
1635 * page->mapping->host, and if the page is unlocked. This is because another
1636 * CPU could truncate the page off the mapping and then free the mapping.
1638 * Usually, the page _is_ locked, or the caller is a user-space process which
1639 * holds a reference on the inode by having an open file.
1641 * In other cases, the page should be locked before running set_page_dirty().
1643 int set_page_dirty_lock(struct page
*page
)
1648 ret
= set_page_dirty(page
);
1652 EXPORT_SYMBOL(set_page_dirty_lock
);
1655 * Clear a page's dirty flag, while caring for dirty memory accounting.
1656 * Returns true if the page was previously dirty.
1658 * This is for preparing to put the page under writeout. We leave the page
1659 * tagged as dirty in the radix tree so that a concurrent write-for-sync
1660 * can discover it via a PAGECACHE_TAG_DIRTY walk. The ->writepage
1661 * implementation will run either set_page_writeback() or set_page_dirty(),
1662 * at which stage we bring the page's dirty flag and radix-tree dirty tag
1665 * This incoherency between the page's dirty flag and radix-tree tag is
1666 * unfortunate, but it only exists while the page is locked.
1668 int clear_page_dirty_for_io(struct page
*page
)
1670 struct address_space
*mapping
= page_mapping(page
);
1672 BUG_ON(!PageLocked(page
));
1674 if (mapping
&& mapping_cap_account_dirty(mapping
)) {
1676 * Yes, Virginia, this is indeed insane.
1678 * We use this sequence to make sure that
1679 * (a) we account for dirty stats properly
1680 * (b) we tell the low-level filesystem to
1681 * mark the whole page dirty if it was
1682 * dirty in a pagetable. Only to then
1683 * (c) clean the page again and return 1 to
1684 * cause the writeback.
1686 * This way we avoid all nasty races with the
1687 * dirty bit in multiple places and clearing
1688 * them concurrently from different threads.
1690 * Note! Normally the "set_page_dirty(page)"
1691 * has no effect on the actual dirty bit - since
1692 * that will already usually be set. But we
1693 * need the side effects, and it can help us
1696 * We basically use the page "master dirty bit"
1697 * as a serialization point for all the different
1698 * threads doing their things.
1700 if (page_mkclean(page
))
1701 set_page_dirty(page
);
1703 * We carefully synchronise fault handlers against
1704 * installing a dirty pte and marking the page dirty
1705 * at this point. We do this by having them hold the
1706 * page lock at some point after installing their
1707 * pte, but before marking the page dirty.
1708 * Pages are always locked coming in here, so we get
1709 * the desired exclusion. See mm/memory.c:do_wp_page()
1710 * for more comments.
1712 if (TestClearPageDirty(page
)) {
1713 dec_zone_page_state(page
, NR_FILE_DIRTY
);
1714 dec_bdi_stat(mapping
->backing_dev_info
,
1720 return TestClearPageDirty(page
);
1722 EXPORT_SYMBOL(clear_page_dirty_for_io
);
1724 int test_clear_page_writeback(struct page
*page
)
1726 struct address_space
*mapping
= page_mapping(page
);
1730 struct backing_dev_info
*bdi
= mapping
->backing_dev_info
;
1731 unsigned long flags
;
1733 spin_lock_irqsave(&mapping
->tree_lock
, flags
);
1734 ret
= TestClearPageWriteback(page
);
1736 radix_tree_tag_clear(&mapping
->page_tree
,
1738 PAGECACHE_TAG_WRITEBACK
);
1739 if (bdi_cap_account_writeback(bdi
)) {
1740 __dec_bdi_stat(bdi
, BDI_WRITEBACK
);
1741 __bdi_writeout_inc(bdi
);
1744 spin_unlock_irqrestore(&mapping
->tree_lock
, flags
);
1746 ret
= TestClearPageWriteback(page
);
1749 dec_zone_page_state(page
, NR_WRITEBACK
);
1750 inc_zone_page_state(page
, NR_WRITTEN
);
1755 int test_set_page_writeback(struct page
*page
)
1757 struct address_space
*mapping
= page_mapping(page
);
1761 struct backing_dev_info
*bdi
= mapping
->backing_dev_info
;
1762 unsigned long flags
;
1764 spin_lock_irqsave(&mapping
->tree_lock
, flags
);
1765 ret
= TestSetPageWriteback(page
);
1767 radix_tree_tag_set(&mapping
->page_tree
,
1769 PAGECACHE_TAG_WRITEBACK
);
1770 if (bdi_cap_account_writeback(bdi
))
1771 __inc_bdi_stat(bdi
, BDI_WRITEBACK
);
1773 if (!PageDirty(page
))
1774 radix_tree_tag_clear(&mapping
->page_tree
,
1776 PAGECACHE_TAG_DIRTY
);
1777 radix_tree_tag_clear(&mapping
->page_tree
,
1779 PAGECACHE_TAG_TOWRITE
);
1780 spin_unlock_irqrestore(&mapping
->tree_lock
, flags
);
1782 ret
= TestSetPageWriteback(page
);
1785 account_page_writeback(page
);
1789 EXPORT_SYMBOL(test_set_page_writeback
);
1792 * Return true if any of the pages in the mapping are marked with the
1795 int mapping_tagged(struct address_space
*mapping
, int tag
)
1797 return radix_tree_tagged(&mapping
->page_tree
, tag
);
1799 EXPORT_SYMBOL(mapping_tagged
);