1 // SPDX-License-Identifier: GPL-2.0-only
5 * Copyright (C) 2002, Linus Torvalds.
6 * Copyright (C) 2007 Red Hat, Inc., Peter Zijlstra
8 * Contains functions related to writing back dirty pages at the
11 * 10Apr2002 Andrew Morton
15 #include <linux/kernel.h>
16 #include <linux/export.h>
17 #include <linux/spinlock.h>
20 #include <linux/swap.h>
21 #include <linux/slab.h>
22 #include <linux/pagemap.h>
23 #include <linux/writeback.h>
24 #include <linux/init.h>
25 #include <linux/backing-dev.h>
26 #include <linux/task_io_accounting_ops.h>
27 #include <linux/blkdev.h>
28 #include <linux/mpage.h>
29 #include <linux/rmap.h>
30 #include <linux/percpu.h>
31 #include <linux/smp.h>
32 #include <linux/sysctl.h>
33 #include <linux/cpu.h>
34 #include <linux/syscalls.h>
35 #include <linux/pagevec.h>
36 #include <linux/timer.h>
37 #include <linux/sched/rt.h>
38 #include <linux/sched/signal.h>
39 #include <linux/mm_inline.h>
40 #include <trace/events/writeback.h>
45 * Sleep at most 200ms at a time in balance_dirty_pages().
47 #define MAX_PAUSE max(HZ/5, 1)
50 * Try to keep balance_dirty_pages() call intervals higher than this many pages
51 * by raising pause time to max_pause when falls below it.
53 #define DIRTY_POLL_THRESH (128 >> (PAGE_SHIFT - 10))
56 * Estimate write bandwidth at 200ms intervals.
58 #define BANDWIDTH_INTERVAL max(HZ/5, 1)
60 #define RATELIMIT_CALC_SHIFT 10
63 * After a CPU has dirtied this many pages, balance_dirty_pages_ratelimited
64 * will look to see if it needs to force writeback or throttling.
66 static long ratelimit_pages
= 32;
68 /* The following parameters are exported via /proc/sys/vm */
71 * Start background writeback (via writeback threads) at this percentage
73 int dirty_background_ratio
= 10;
76 * dirty_background_bytes starts at 0 (disabled) so that it is a function of
77 * dirty_background_ratio * the amount of dirtyable memory
79 unsigned long dirty_background_bytes
;
82 * free highmem will not be subtracted from the total free memory
83 * for calculating free ratios if vm_highmem_is_dirtyable is true
85 int vm_highmem_is_dirtyable
;
88 * The generator of dirty data starts writeback at this percentage
90 int vm_dirty_ratio
= 20;
93 * vm_dirty_bytes starts at 0 (disabled) so that it is a function of
94 * vm_dirty_ratio * the amount of dirtyable memory
96 unsigned long vm_dirty_bytes
;
99 * The interval between `kupdate'-style writebacks
101 unsigned int dirty_writeback_interval
= 5 * 100; /* centiseconds */
103 EXPORT_SYMBOL_GPL(dirty_writeback_interval
);
106 * The longest time for which data is allowed to remain dirty
108 unsigned int dirty_expire_interval
= 30 * 100; /* centiseconds */
111 * Flag that puts the machine in "laptop mode". Doubles as a timeout in jiffies:
112 * a full sync is triggered after this time elapses without any disk activity.
116 EXPORT_SYMBOL(laptop_mode
);
118 /* End of sysctl-exported parameters */
120 struct wb_domain global_wb_domain
;
122 /* consolidated parameters for balance_dirty_pages() and its subroutines */
123 struct dirty_throttle_control
{
124 #ifdef CONFIG_CGROUP_WRITEBACK
125 struct wb_domain
*dom
;
126 struct dirty_throttle_control
*gdtc
; /* only set in memcg dtc's */
128 struct bdi_writeback
*wb
;
129 struct fprop_local_percpu
*wb_completions
;
131 unsigned long avail
; /* dirtyable */
132 unsigned long dirty
; /* file_dirty + write + nfs */
133 unsigned long thresh
; /* dirty threshold */
134 unsigned long bg_thresh
; /* dirty background threshold */
136 unsigned long wb_dirty
; /* per-wb counterparts */
137 unsigned long wb_thresh
;
138 unsigned long wb_bg_thresh
;
140 unsigned long pos_ratio
;
144 * Length of period for aging writeout fractions of bdis. This is an
145 * arbitrarily chosen number. The longer the period, the slower fractions will
146 * reflect changes in current writeout rate.
148 #define VM_COMPLETIONS_PERIOD_LEN (3*HZ)
150 #ifdef CONFIG_CGROUP_WRITEBACK
152 #define GDTC_INIT(__wb) .wb = (__wb), \
153 .dom = &global_wb_domain, \
154 .wb_completions = &(__wb)->completions
156 #define GDTC_INIT_NO_WB .dom = &global_wb_domain
158 #define MDTC_INIT(__wb, __gdtc) .wb = (__wb), \
159 .dom = mem_cgroup_wb_domain(__wb), \
160 .wb_completions = &(__wb)->memcg_completions, \
163 static bool mdtc_valid(struct dirty_throttle_control
*dtc
)
168 static struct wb_domain
*dtc_dom(struct dirty_throttle_control
*dtc
)
173 static struct dirty_throttle_control
*mdtc_gdtc(struct dirty_throttle_control
*mdtc
)
178 static struct fprop_local_percpu
*wb_memcg_completions(struct bdi_writeback
*wb
)
180 return &wb
->memcg_completions
;
183 static void wb_min_max_ratio(struct bdi_writeback
*wb
,
184 unsigned long *minp
, unsigned long *maxp
)
186 unsigned long this_bw
= READ_ONCE(wb
->avg_write_bandwidth
);
187 unsigned long tot_bw
= atomic_long_read(&wb
->bdi
->tot_write_bandwidth
);
188 unsigned long long min
= wb
->bdi
->min_ratio
;
189 unsigned long long max
= wb
->bdi
->max_ratio
;
192 * @wb may already be clean by the time control reaches here and
193 * the total may not include its bw.
195 if (this_bw
< tot_bw
) {
198 min
= div64_ul(min
, tot_bw
);
202 max
= div64_ul(max
, tot_bw
);
210 #else /* CONFIG_CGROUP_WRITEBACK */
212 #define GDTC_INIT(__wb) .wb = (__wb), \
213 .wb_completions = &(__wb)->completions
214 #define GDTC_INIT_NO_WB
215 #define MDTC_INIT(__wb, __gdtc)
217 static bool mdtc_valid(struct dirty_throttle_control
*dtc
)
222 static struct wb_domain
*dtc_dom(struct dirty_throttle_control
*dtc
)
224 return &global_wb_domain
;
227 static struct dirty_throttle_control
*mdtc_gdtc(struct dirty_throttle_control
*mdtc
)
232 static struct fprop_local_percpu
*wb_memcg_completions(struct bdi_writeback
*wb
)
237 static void wb_min_max_ratio(struct bdi_writeback
*wb
,
238 unsigned long *minp
, unsigned long *maxp
)
240 *minp
= wb
->bdi
->min_ratio
;
241 *maxp
= wb
->bdi
->max_ratio
;
244 #endif /* CONFIG_CGROUP_WRITEBACK */
247 * In a memory zone, there is a certain amount of pages we consider
248 * available for the page cache, which is essentially the number of
249 * free and reclaimable pages, minus some zone reserves to protect
250 * lowmem and the ability to uphold the zone's watermarks without
251 * requiring writeback.
253 * This number of dirtyable pages is the base value of which the
254 * user-configurable dirty ratio is the effective number of pages that
255 * are allowed to be actually dirtied. Per individual zone, or
256 * globally by using the sum of dirtyable pages over all zones.
258 * Because the user is allowed to specify the dirty limit globally as
259 * absolute number of bytes, calculating the per-zone dirty limit can
260 * require translating the configured limit into a percentage of
261 * global dirtyable memory first.
265 * node_dirtyable_memory - number of dirtyable pages in a node
268 * Return: the node's number of pages potentially available for dirty
269 * page cache. This is the base value for the per-node dirty limits.
271 static unsigned long node_dirtyable_memory(struct pglist_data
*pgdat
)
273 unsigned long nr_pages
= 0;
276 for (z
= 0; z
< MAX_NR_ZONES
; z
++) {
277 struct zone
*zone
= pgdat
->node_zones
+ z
;
279 if (!populated_zone(zone
))
282 nr_pages
+= zone_page_state(zone
, NR_FREE_PAGES
);
286 * Pages reserved for the kernel should not be considered
287 * dirtyable, to prevent a situation where reclaim has to
288 * clean pages in order to balance the zones.
290 nr_pages
-= min(nr_pages
, pgdat
->totalreserve_pages
);
292 nr_pages
+= node_page_state(pgdat
, NR_INACTIVE_FILE
);
293 nr_pages
+= node_page_state(pgdat
, NR_ACTIVE_FILE
);
298 static unsigned long highmem_dirtyable_memory(unsigned long total
)
300 #ifdef CONFIG_HIGHMEM
305 for_each_node_state(node
, N_HIGH_MEMORY
) {
306 for (i
= ZONE_NORMAL
+ 1; i
< MAX_NR_ZONES
; i
++) {
308 unsigned long nr_pages
;
310 if (!is_highmem_idx(i
))
313 z
= &NODE_DATA(node
)->node_zones
[i
];
314 if (!populated_zone(z
))
317 nr_pages
= zone_page_state(z
, NR_FREE_PAGES
);
318 /* watch for underflows */
319 nr_pages
-= min(nr_pages
, high_wmark_pages(z
));
320 nr_pages
+= zone_page_state(z
, NR_ZONE_INACTIVE_FILE
);
321 nr_pages
+= zone_page_state(z
, NR_ZONE_ACTIVE_FILE
);
327 * Unreclaimable memory (kernel memory or anonymous memory
328 * without swap) can bring down the dirtyable pages below
329 * the zone's dirty balance reserve and the above calculation
330 * will underflow. However we still want to add in nodes
331 * which are below threshold (negative values) to get a more
332 * accurate calculation but make sure that the total never
339 * Make sure that the number of highmem pages is never larger
340 * than the number of the total dirtyable memory. This can only
341 * occur in very strange VM situations but we want to make sure
342 * that this does not occur.
344 return min(x
, total
);
351 * global_dirtyable_memory - number of globally dirtyable pages
353 * Return: the global number of pages potentially available for dirty
354 * page cache. This is the base value for the global dirty limits.
356 static unsigned long global_dirtyable_memory(void)
360 x
= global_zone_page_state(NR_FREE_PAGES
);
362 * Pages reserved for the kernel should not be considered
363 * dirtyable, to prevent a situation where reclaim has to
364 * clean pages in order to balance the zones.
366 x
-= min(x
, totalreserve_pages
);
368 x
+= global_node_page_state(NR_INACTIVE_FILE
);
369 x
+= global_node_page_state(NR_ACTIVE_FILE
);
371 if (!vm_highmem_is_dirtyable
)
372 x
-= highmem_dirtyable_memory(x
);
374 return x
+ 1; /* Ensure that we never return 0 */
378 * domain_dirty_limits - calculate thresh and bg_thresh for a wb_domain
379 * @dtc: dirty_throttle_control of interest
381 * Calculate @dtc->thresh and ->bg_thresh considering
382 * vm_dirty_{bytes|ratio} and dirty_background_{bytes|ratio}. The caller
383 * must ensure that @dtc->avail is set before calling this function. The
384 * dirty limits will be lifted by 1/4 for real-time tasks.
386 static void domain_dirty_limits(struct dirty_throttle_control
*dtc
)
388 const unsigned long available_memory
= dtc
->avail
;
389 struct dirty_throttle_control
*gdtc
= mdtc_gdtc(dtc
);
390 unsigned long bytes
= vm_dirty_bytes
;
391 unsigned long bg_bytes
= dirty_background_bytes
;
392 /* convert ratios to per-PAGE_SIZE for higher precision */
393 unsigned long ratio
= (vm_dirty_ratio
* PAGE_SIZE
) / 100;
394 unsigned long bg_ratio
= (dirty_background_ratio
* PAGE_SIZE
) / 100;
395 unsigned long thresh
;
396 unsigned long bg_thresh
;
397 struct task_struct
*tsk
;
399 /* gdtc is !NULL iff @dtc is for memcg domain */
401 unsigned long global_avail
= gdtc
->avail
;
404 * The byte settings can't be applied directly to memcg
405 * domains. Convert them to ratios by scaling against
406 * globally available memory. As the ratios are in
407 * per-PAGE_SIZE, they can be obtained by dividing bytes by
411 ratio
= min(DIV_ROUND_UP(bytes
, global_avail
),
414 bg_ratio
= min(DIV_ROUND_UP(bg_bytes
, global_avail
),
416 bytes
= bg_bytes
= 0;
420 thresh
= DIV_ROUND_UP(bytes
, PAGE_SIZE
);
422 thresh
= (ratio
* available_memory
) / PAGE_SIZE
;
425 bg_thresh
= DIV_ROUND_UP(bg_bytes
, PAGE_SIZE
);
427 bg_thresh
= (bg_ratio
* available_memory
) / PAGE_SIZE
;
429 if (bg_thresh
>= thresh
)
430 bg_thresh
= thresh
/ 2;
433 bg_thresh
+= bg_thresh
/ 4 + global_wb_domain
.dirty_limit
/ 32;
434 thresh
+= thresh
/ 4 + global_wb_domain
.dirty_limit
/ 32;
436 dtc
->thresh
= thresh
;
437 dtc
->bg_thresh
= bg_thresh
;
439 /* we should eventually report the domain in the TP */
441 trace_global_dirty_state(bg_thresh
, thresh
);
445 * global_dirty_limits - background-writeback and dirty-throttling thresholds
446 * @pbackground: out parameter for bg_thresh
447 * @pdirty: out parameter for thresh
449 * Calculate bg_thresh and thresh for global_wb_domain. See
450 * domain_dirty_limits() for details.
452 void global_dirty_limits(unsigned long *pbackground
, unsigned long *pdirty
)
454 struct dirty_throttle_control gdtc
= { GDTC_INIT_NO_WB
};
456 gdtc
.avail
= global_dirtyable_memory();
457 domain_dirty_limits(&gdtc
);
459 *pbackground
= gdtc
.bg_thresh
;
460 *pdirty
= gdtc
.thresh
;
464 * node_dirty_limit - maximum number of dirty pages allowed in a node
467 * Return: the maximum number of dirty pages allowed in a node, based
468 * on the node's dirtyable memory.
470 static unsigned long node_dirty_limit(struct pglist_data
*pgdat
)
472 unsigned long node_memory
= node_dirtyable_memory(pgdat
);
473 struct task_struct
*tsk
= current
;
477 dirty
= DIV_ROUND_UP(vm_dirty_bytes
, PAGE_SIZE
) *
478 node_memory
/ global_dirtyable_memory();
480 dirty
= vm_dirty_ratio
* node_memory
/ 100;
489 * node_dirty_ok - tells whether a node is within its dirty limits
490 * @pgdat: the node to check
492 * Return: %true when the dirty pages in @pgdat are within the node's
493 * dirty limit, %false if the limit is exceeded.
495 bool node_dirty_ok(struct pglist_data
*pgdat
)
497 unsigned long limit
= node_dirty_limit(pgdat
);
498 unsigned long nr_pages
= 0;
500 nr_pages
+= node_page_state(pgdat
, NR_FILE_DIRTY
);
501 nr_pages
+= node_page_state(pgdat
, NR_WRITEBACK
);
503 return nr_pages
<= limit
;
506 int dirty_background_ratio_handler(struct ctl_table
*table
, int write
,
507 void *buffer
, size_t *lenp
, loff_t
*ppos
)
511 ret
= proc_dointvec_minmax(table
, write
, buffer
, lenp
, ppos
);
512 if (ret
== 0 && write
)
513 dirty_background_bytes
= 0;
517 int dirty_background_bytes_handler(struct ctl_table
*table
, int write
,
518 void *buffer
, size_t *lenp
, loff_t
*ppos
)
522 ret
= proc_doulongvec_minmax(table
, write
, buffer
, lenp
, ppos
);
523 if (ret
== 0 && write
)
524 dirty_background_ratio
= 0;
528 int dirty_ratio_handler(struct ctl_table
*table
, int write
, void *buffer
,
529 size_t *lenp
, loff_t
*ppos
)
531 int old_ratio
= vm_dirty_ratio
;
534 ret
= proc_dointvec_minmax(table
, write
, buffer
, lenp
, ppos
);
535 if (ret
== 0 && write
&& vm_dirty_ratio
!= old_ratio
) {
536 writeback_set_ratelimit();
542 int dirty_bytes_handler(struct ctl_table
*table
, int write
,
543 void *buffer
, size_t *lenp
, loff_t
*ppos
)
545 unsigned long old_bytes
= vm_dirty_bytes
;
548 ret
= proc_doulongvec_minmax(table
, write
, buffer
, lenp
, ppos
);
549 if (ret
== 0 && write
&& vm_dirty_bytes
!= old_bytes
) {
550 writeback_set_ratelimit();
556 static unsigned long wp_next_time(unsigned long cur_time
)
558 cur_time
+= VM_COMPLETIONS_PERIOD_LEN
;
559 /* 0 has a special meaning... */
565 static void wb_domain_writeout_inc(struct wb_domain
*dom
,
566 struct fprop_local_percpu
*completions
,
567 unsigned int max_prop_frac
)
569 __fprop_inc_percpu_max(&dom
->completions
, completions
,
571 /* First event after period switching was turned off? */
572 if (unlikely(!dom
->period_time
)) {
574 * We can race with other __bdi_writeout_inc calls here but
575 * it does not cause any harm since the resulting time when
576 * timer will fire and what is in writeout_period_time will be
579 dom
->period_time
= wp_next_time(jiffies
);
580 mod_timer(&dom
->period_timer
, dom
->period_time
);
585 * Increment @wb's writeout completion count and the global writeout
586 * completion count. Called from test_clear_page_writeback().
588 static inline void __wb_writeout_inc(struct bdi_writeback
*wb
)
590 struct wb_domain
*cgdom
;
592 inc_wb_stat(wb
, WB_WRITTEN
);
593 wb_domain_writeout_inc(&global_wb_domain
, &wb
->completions
,
594 wb
->bdi
->max_prop_frac
);
596 cgdom
= mem_cgroup_wb_domain(wb
);
598 wb_domain_writeout_inc(cgdom
, wb_memcg_completions(wb
),
599 wb
->bdi
->max_prop_frac
);
602 void wb_writeout_inc(struct bdi_writeback
*wb
)
606 local_irq_save(flags
);
607 __wb_writeout_inc(wb
);
608 local_irq_restore(flags
);
610 EXPORT_SYMBOL_GPL(wb_writeout_inc
);
613 * On idle system, we can be called long after we scheduled because we use
614 * deferred timers so count with missed periods.
616 static void writeout_period(struct timer_list
*t
)
618 struct wb_domain
*dom
= from_timer(dom
, t
, period_timer
);
619 int miss_periods
= (jiffies
- dom
->period_time
) /
620 VM_COMPLETIONS_PERIOD_LEN
;
622 if (fprop_new_period(&dom
->completions
, miss_periods
+ 1)) {
623 dom
->period_time
= wp_next_time(dom
->period_time
+
624 miss_periods
* VM_COMPLETIONS_PERIOD_LEN
);
625 mod_timer(&dom
->period_timer
, dom
->period_time
);
628 * Aging has zeroed all fractions. Stop wasting CPU on period
631 dom
->period_time
= 0;
635 int wb_domain_init(struct wb_domain
*dom
, gfp_t gfp
)
637 memset(dom
, 0, sizeof(*dom
));
639 spin_lock_init(&dom
->lock
);
641 timer_setup(&dom
->period_timer
, writeout_period
, TIMER_DEFERRABLE
);
643 dom
->dirty_limit_tstamp
= jiffies
;
645 return fprop_global_init(&dom
->completions
, gfp
);
648 #ifdef CONFIG_CGROUP_WRITEBACK
649 void wb_domain_exit(struct wb_domain
*dom
)
651 del_timer_sync(&dom
->period_timer
);
652 fprop_global_destroy(&dom
->completions
);
657 * bdi_min_ratio keeps the sum of the minimum dirty shares of all
658 * registered backing devices, which, for obvious reasons, can not
661 static unsigned int bdi_min_ratio
;
663 int bdi_set_min_ratio(struct backing_dev_info
*bdi
, unsigned int min_ratio
)
667 spin_lock_bh(&bdi_lock
);
668 if (min_ratio
> bdi
->max_ratio
) {
671 min_ratio
-= bdi
->min_ratio
;
672 if (bdi_min_ratio
+ min_ratio
< 100) {
673 bdi_min_ratio
+= min_ratio
;
674 bdi
->min_ratio
+= min_ratio
;
679 spin_unlock_bh(&bdi_lock
);
684 int bdi_set_max_ratio(struct backing_dev_info
*bdi
, unsigned max_ratio
)
691 spin_lock_bh(&bdi_lock
);
692 if (bdi
->min_ratio
> max_ratio
) {
695 bdi
->max_ratio
= max_ratio
;
696 bdi
->max_prop_frac
= (FPROP_FRAC_BASE
* max_ratio
) / 100;
698 spin_unlock_bh(&bdi_lock
);
702 EXPORT_SYMBOL(bdi_set_max_ratio
);
704 static unsigned long dirty_freerun_ceiling(unsigned long thresh
,
705 unsigned long bg_thresh
)
707 return (thresh
+ bg_thresh
) / 2;
710 static unsigned long hard_dirty_limit(struct wb_domain
*dom
,
711 unsigned long thresh
)
713 return max(thresh
, dom
->dirty_limit
);
717 * Memory which can be further allocated to a memcg domain is capped by
718 * system-wide clean memory excluding the amount being used in the domain.
720 static void mdtc_calc_avail(struct dirty_throttle_control
*mdtc
,
721 unsigned long filepages
, unsigned long headroom
)
723 struct dirty_throttle_control
*gdtc
= mdtc_gdtc(mdtc
);
724 unsigned long clean
= filepages
- min(filepages
, mdtc
->dirty
);
725 unsigned long global_clean
= gdtc
->avail
- min(gdtc
->avail
, gdtc
->dirty
);
726 unsigned long other_clean
= global_clean
- min(global_clean
, clean
);
728 mdtc
->avail
= filepages
+ min(headroom
, other_clean
);
732 * __wb_calc_thresh - @wb's share of dirty throttling threshold
733 * @dtc: dirty_throttle_context of interest
735 * Note that balance_dirty_pages() will only seriously take it as a hard limit
736 * when sleeping max_pause per page is not enough to keep the dirty pages under
737 * control. For example, when the device is completely stalled due to some error
738 * conditions, or when there are 1000 dd tasks writing to a slow 10MB/s USB key.
739 * In the other normal situations, it acts more gently by throttling the tasks
740 * more (rather than completely block them) when the wb dirty pages go high.
742 * It allocates high/low dirty limits to fast/slow devices, in order to prevent
743 * - starving fast devices
744 * - piling up dirty pages (that will take long time to sync) on slow devices
746 * The wb's share of dirty limit will be adapting to its throughput and
747 * bounded by the bdi->min_ratio and/or bdi->max_ratio parameters, if set.
749 * Return: @wb's dirty limit in pages. The term "dirty" in the context of
750 * dirty balancing includes all PG_dirty and PG_writeback pages.
752 static unsigned long __wb_calc_thresh(struct dirty_throttle_control
*dtc
)
754 struct wb_domain
*dom
= dtc_dom(dtc
);
755 unsigned long thresh
= dtc
->thresh
;
757 unsigned long numerator
, denominator
;
758 unsigned long wb_min_ratio
, wb_max_ratio
;
761 * Calculate this BDI's share of the thresh ratio.
763 fprop_fraction_percpu(&dom
->completions
, dtc
->wb_completions
,
764 &numerator
, &denominator
);
766 wb_thresh
= (thresh
* (100 - bdi_min_ratio
)) / 100;
767 wb_thresh
*= numerator
;
768 wb_thresh
= div64_ul(wb_thresh
, denominator
);
770 wb_min_max_ratio(dtc
->wb
, &wb_min_ratio
, &wb_max_ratio
);
772 wb_thresh
+= (thresh
* wb_min_ratio
) / 100;
773 if (wb_thresh
> (thresh
* wb_max_ratio
) / 100)
774 wb_thresh
= thresh
* wb_max_ratio
/ 100;
779 unsigned long wb_calc_thresh(struct bdi_writeback
*wb
, unsigned long thresh
)
781 struct dirty_throttle_control gdtc
= { GDTC_INIT(wb
),
783 return __wb_calc_thresh(&gdtc
);
788 * f(dirty) := 1.0 + (----------------)
791 * it's a 3rd order polynomial that subjects to
793 * (1) f(freerun) = 2.0 => rampup dirty_ratelimit reasonably fast
794 * (2) f(setpoint) = 1.0 => the balance point
795 * (3) f(limit) = 0 => the hard limit
796 * (4) df/dx <= 0 => negative feedback control
797 * (5) the closer to setpoint, the smaller |df/dx| (and the reverse)
798 * => fast response on large errors; small oscillation near setpoint
800 static long long pos_ratio_polynom(unsigned long setpoint
,
807 x
= div64_s64(((s64
)setpoint
- (s64
)dirty
) << RATELIMIT_CALC_SHIFT
,
808 (limit
- setpoint
) | 1);
810 pos_ratio
= pos_ratio
* x
>> RATELIMIT_CALC_SHIFT
;
811 pos_ratio
= pos_ratio
* x
>> RATELIMIT_CALC_SHIFT
;
812 pos_ratio
+= 1 << RATELIMIT_CALC_SHIFT
;
814 return clamp(pos_ratio
, 0LL, 2LL << RATELIMIT_CALC_SHIFT
);
818 * Dirty position control.
820 * (o) global/bdi setpoints
822 * We want the dirty pages be balanced around the global/wb setpoints.
823 * When the number of dirty pages is higher/lower than the setpoint, the
824 * dirty position control ratio (and hence task dirty ratelimit) will be
825 * decreased/increased to bring the dirty pages back to the setpoint.
827 * pos_ratio = 1 << RATELIMIT_CALC_SHIFT
829 * if (dirty < setpoint) scale up pos_ratio
830 * if (dirty > setpoint) scale down pos_ratio
832 * if (wb_dirty < wb_setpoint) scale up pos_ratio
833 * if (wb_dirty > wb_setpoint) scale down pos_ratio
835 * task_ratelimit = dirty_ratelimit * pos_ratio >> RATELIMIT_CALC_SHIFT
837 * (o) global control line
841 * | |<===== global dirty control scope ======>|
849 * 1.0 ................................*
855 * 0 +------------.------------------.----------------------*------------->
856 * freerun^ setpoint^ limit^ dirty pages
858 * (o) wb control line
866 * | * |<=========== span ============>|
867 * 1.0 .......................*
879 * 1/4 ...............................................* * * * * * * * * * * *
883 * 0 +----------------------.-------------------------------.------------->
884 * wb_setpoint^ x_intercept^
886 * The wb control line won't drop below pos_ratio=1/4, so that wb_dirty can
887 * be smoothly throttled down to normal if it starts high in situations like
888 * - start writing to a slow SD card and a fast disk at the same time. The SD
889 * card's wb_dirty may rush to many times higher than wb_setpoint.
890 * - the wb dirty thresh drops quickly due to change of JBOD workload
892 static void wb_position_ratio(struct dirty_throttle_control
*dtc
)
894 struct bdi_writeback
*wb
= dtc
->wb
;
895 unsigned long write_bw
= READ_ONCE(wb
->avg_write_bandwidth
);
896 unsigned long freerun
= dirty_freerun_ceiling(dtc
->thresh
, dtc
->bg_thresh
);
897 unsigned long limit
= hard_dirty_limit(dtc_dom(dtc
), dtc
->thresh
);
898 unsigned long wb_thresh
= dtc
->wb_thresh
;
899 unsigned long x_intercept
;
900 unsigned long setpoint
; /* dirty pages' target balance point */
901 unsigned long wb_setpoint
;
903 long long pos_ratio
; /* for scaling up/down the rate limit */
908 if (unlikely(dtc
->dirty
>= limit
))
914 * See comment for pos_ratio_polynom().
916 setpoint
= (freerun
+ limit
) / 2;
917 pos_ratio
= pos_ratio_polynom(setpoint
, dtc
->dirty
, limit
);
920 * The strictlimit feature is a tool preventing mistrusted filesystems
921 * from growing a large number of dirty pages before throttling. For
922 * such filesystems balance_dirty_pages always checks wb counters
923 * against wb limits. Even if global "nr_dirty" is under "freerun".
924 * This is especially important for fuse which sets bdi->max_ratio to
925 * 1% by default. Without strictlimit feature, fuse writeback may
926 * consume arbitrary amount of RAM because it is accounted in
927 * NR_WRITEBACK_TEMP which is not involved in calculating "nr_dirty".
929 * Here, in wb_position_ratio(), we calculate pos_ratio based on
930 * two values: wb_dirty and wb_thresh. Let's consider an example:
931 * total amount of RAM is 16GB, bdi->max_ratio is equal to 1%, global
932 * limits are set by default to 10% and 20% (background and throttle).
933 * Then wb_thresh is 1% of 20% of 16GB. This amounts to ~8K pages.
934 * wb_calc_thresh(wb, bg_thresh) is about ~4K pages. wb_setpoint is
935 * about ~6K pages (as the average of background and throttle wb
936 * limits). The 3rd order polynomial will provide positive feedback if
937 * wb_dirty is under wb_setpoint and vice versa.
939 * Note, that we cannot use global counters in these calculations
940 * because we want to throttle process writing to a strictlimit wb
941 * much earlier than global "freerun" is reached (~23MB vs. ~2.3GB
942 * in the example above).
944 if (unlikely(wb
->bdi
->capabilities
& BDI_CAP_STRICTLIMIT
)) {
945 long long wb_pos_ratio
;
947 if (dtc
->wb_dirty
< 8) {
948 dtc
->pos_ratio
= min_t(long long, pos_ratio
* 2,
949 2 << RATELIMIT_CALC_SHIFT
);
953 if (dtc
->wb_dirty
>= wb_thresh
)
956 wb_setpoint
= dirty_freerun_ceiling(wb_thresh
,
959 if (wb_setpoint
== 0 || wb_setpoint
== wb_thresh
)
962 wb_pos_ratio
= pos_ratio_polynom(wb_setpoint
, dtc
->wb_dirty
,
966 * Typically, for strictlimit case, wb_setpoint << setpoint
967 * and pos_ratio >> wb_pos_ratio. In the other words global
968 * state ("dirty") is not limiting factor and we have to
969 * make decision based on wb counters. But there is an
970 * important case when global pos_ratio should get precedence:
971 * global limits are exceeded (e.g. due to activities on other
972 * wb's) while given strictlimit wb is below limit.
974 * "pos_ratio * wb_pos_ratio" would work for the case above,
975 * but it would look too non-natural for the case of all
976 * activity in the system coming from a single strictlimit wb
977 * with bdi->max_ratio == 100%.
979 * Note that min() below somewhat changes the dynamics of the
980 * control system. Normally, pos_ratio value can be well over 3
981 * (when globally we are at freerun and wb is well below wb
982 * setpoint). Now the maximum pos_ratio in the same situation
983 * is 2. We might want to tweak this if we observe the control
984 * system is too slow to adapt.
986 dtc
->pos_ratio
= min(pos_ratio
, wb_pos_ratio
);
991 * We have computed basic pos_ratio above based on global situation. If
992 * the wb is over/under its share of dirty pages, we want to scale
993 * pos_ratio further down/up. That is done by the following mechanism.
999 * f(wb_dirty) := 1.0 + k * (wb_dirty - wb_setpoint)
1001 * x_intercept - wb_dirty
1002 * := --------------------------
1003 * x_intercept - wb_setpoint
1005 * The main wb control line is a linear function that subjects to
1007 * (1) f(wb_setpoint) = 1.0
1008 * (2) k = - 1 / (8 * write_bw) (in single wb case)
1009 * or equally: x_intercept = wb_setpoint + 8 * write_bw
1011 * For single wb case, the dirty pages are observed to fluctuate
1012 * regularly within range
1013 * [wb_setpoint - write_bw/2, wb_setpoint + write_bw/2]
1014 * for various filesystems, where (2) can yield in a reasonable 12.5%
1015 * fluctuation range for pos_ratio.
1017 * For JBOD case, wb_thresh (not wb_dirty!) could fluctuate up to its
1018 * own size, so move the slope over accordingly and choose a slope that
1019 * yields 100% pos_ratio fluctuation on suddenly doubled wb_thresh.
1021 if (unlikely(wb_thresh
> dtc
->thresh
))
1022 wb_thresh
= dtc
->thresh
;
1024 * It's very possible that wb_thresh is close to 0 not because the
1025 * device is slow, but that it has remained inactive for long time.
1026 * Honour such devices a reasonable good (hopefully IO efficient)
1027 * threshold, so that the occasional writes won't be blocked and active
1028 * writes can rampup the threshold quickly.
1030 wb_thresh
= max(wb_thresh
, (limit
- dtc
->dirty
) / 8);
1032 * scale global setpoint to wb's:
1033 * wb_setpoint = setpoint * wb_thresh / thresh
1035 x
= div_u64((u64
)wb_thresh
<< 16, dtc
->thresh
| 1);
1036 wb_setpoint
= setpoint
* (u64
)x
>> 16;
1038 * Use span=(8*write_bw) in single wb case as indicated by
1039 * (thresh - wb_thresh ~= 0) and transit to wb_thresh in JBOD case.
1041 * wb_thresh thresh - wb_thresh
1042 * span = --------- * (8 * write_bw) + ------------------ * wb_thresh
1045 span
= (dtc
->thresh
- wb_thresh
+ 8 * write_bw
) * (u64
)x
>> 16;
1046 x_intercept
= wb_setpoint
+ span
;
1048 if (dtc
->wb_dirty
< x_intercept
- span
/ 4) {
1049 pos_ratio
= div64_u64(pos_ratio
* (x_intercept
- dtc
->wb_dirty
),
1050 (x_intercept
- wb_setpoint
) | 1);
1055 * wb reserve area, safeguard against dirty pool underrun and disk idle
1056 * It may push the desired control point of global dirty pages higher
1059 x_intercept
= wb_thresh
/ 2;
1060 if (dtc
->wb_dirty
< x_intercept
) {
1061 if (dtc
->wb_dirty
> x_intercept
/ 8)
1062 pos_ratio
= div_u64(pos_ratio
* x_intercept
,
1068 dtc
->pos_ratio
= pos_ratio
;
1071 static void wb_update_write_bandwidth(struct bdi_writeback
*wb
,
1072 unsigned long elapsed
,
1073 unsigned long written
)
1075 const unsigned long period
= roundup_pow_of_two(3 * HZ
);
1076 unsigned long avg
= wb
->avg_write_bandwidth
;
1077 unsigned long old
= wb
->write_bandwidth
;
1081 * bw = written * HZ / elapsed
1083 * bw * elapsed + write_bandwidth * (period - elapsed)
1084 * write_bandwidth = ---------------------------------------------------
1087 * @written may have decreased due to account_page_redirty().
1088 * Avoid underflowing @bw calculation.
1090 bw
= written
- min(written
, wb
->written_stamp
);
1092 if (unlikely(elapsed
> period
)) {
1093 bw
= div64_ul(bw
, elapsed
);
1097 bw
+= (u64
)wb
->write_bandwidth
* (period
- elapsed
);
1098 bw
>>= ilog2(period
);
1101 * one more level of smoothing, for filtering out sudden spikes
1103 if (avg
> old
&& old
>= (unsigned long)bw
)
1104 avg
-= (avg
- old
) >> 3;
1106 if (avg
< old
&& old
<= (unsigned long)bw
)
1107 avg
+= (old
- avg
) >> 3;
1110 /* keep avg > 0 to guarantee that tot > 0 if there are dirty wbs */
1111 avg
= max(avg
, 1LU);
1112 if (wb_has_dirty_io(wb
)) {
1113 long delta
= avg
- wb
->avg_write_bandwidth
;
1114 WARN_ON_ONCE(atomic_long_add_return(delta
,
1115 &wb
->bdi
->tot_write_bandwidth
) <= 0);
1117 wb
->write_bandwidth
= bw
;
1118 WRITE_ONCE(wb
->avg_write_bandwidth
, avg
);
1121 static void update_dirty_limit(struct dirty_throttle_control
*dtc
)
1123 struct wb_domain
*dom
= dtc_dom(dtc
);
1124 unsigned long thresh
= dtc
->thresh
;
1125 unsigned long limit
= dom
->dirty_limit
;
1128 * Follow up in one step.
1130 if (limit
< thresh
) {
1136 * Follow down slowly. Use the higher one as the target, because thresh
1137 * may drop below dirty. This is exactly the reason to introduce
1138 * dom->dirty_limit which is guaranteed to lie above the dirty pages.
1140 thresh
= max(thresh
, dtc
->dirty
);
1141 if (limit
> thresh
) {
1142 limit
-= (limit
- thresh
) >> 5;
1147 dom
->dirty_limit
= limit
;
1150 static void domain_update_dirty_limit(struct dirty_throttle_control
*dtc
,
1153 struct wb_domain
*dom
= dtc_dom(dtc
);
1156 * check locklessly first to optimize away locking for the most time
1158 if (time_before(now
, dom
->dirty_limit_tstamp
+ BANDWIDTH_INTERVAL
))
1161 spin_lock(&dom
->lock
);
1162 if (time_after_eq(now
, dom
->dirty_limit_tstamp
+ BANDWIDTH_INTERVAL
)) {
1163 update_dirty_limit(dtc
);
1164 dom
->dirty_limit_tstamp
= now
;
1166 spin_unlock(&dom
->lock
);
1170 * Maintain wb->dirty_ratelimit, the base dirty throttle rate.
1172 * Normal wb tasks will be curbed at or below it in long term.
1173 * Obviously it should be around (write_bw / N) when there are N dd tasks.
1175 static void wb_update_dirty_ratelimit(struct dirty_throttle_control
*dtc
,
1176 unsigned long dirtied
,
1177 unsigned long elapsed
)
1179 struct bdi_writeback
*wb
= dtc
->wb
;
1180 unsigned long dirty
= dtc
->dirty
;
1181 unsigned long freerun
= dirty_freerun_ceiling(dtc
->thresh
, dtc
->bg_thresh
);
1182 unsigned long limit
= hard_dirty_limit(dtc_dom(dtc
), dtc
->thresh
);
1183 unsigned long setpoint
= (freerun
+ limit
) / 2;
1184 unsigned long write_bw
= wb
->avg_write_bandwidth
;
1185 unsigned long dirty_ratelimit
= wb
->dirty_ratelimit
;
1186 unsigned long dirty_rate
;
1187 unsigned long task_ratelimit
;
1188 unsigned long balanced_dirty_ratelimit
;
1191 unsigned long shift
;
1194 * The dirty rate will match the writeout rate in long term, except
1195 * when dirty pages are truncated by userspace or re-dirtied by FS.
1197 dirty_rate
= (dirtied
- wb
->dirtied_stamp
) * HZ
/ elapsed
;
1200 * task_ratelimit reflects each dd's dirty rate for the past 200ms.
1202 task_ratelimit
= (u64
)dirty_ratelimit
*
1203 dtc
->pos_ratio
>> RATELIMIT_CALC_SHIFT
;
1204 task_ratelimit
++; /* it helps rampup dirty_ratelimit from tiny values */
1207 * A linear estimation of the "balanced" throttle rate. The theory is,
1208 * if there are N dd tasks, each throttled at task_ratelimit, the wb's
1209 * dirty_rate will be measured to be (N * task_ratelimit). So the below
1210 * formula will yield the balanced rate limit (write_bw / N).
1212 * Note that the expanded form is not a pure rate feedback:
1213 * rate_(i+1) = rate_(i) * (write_bw / dirty_rate) (1)
1214 * but also takes pos_ratio into account:
1215 * rate_(i+1) = rate_(i) * (write_bw / dirty_rate) * pos_ratio (2)
1217 * (1) is not realistic because pos_ratio also takes part in balancing
1218 * the dirty rate. Consider the state
1219 * pos_ratio = 0.5 (3)
1220 * rate = 2 * (write_bw / N) (4)
1221 * If (1) is used, it will stuck in that state! Because each dd will
1223 * task_ratelimit = pos_ratio * rate = (write_bw / N) (5)
1225 * dirty_rate = N * task_ratelimit = write_bw (6)
1226 * put (6) into (1) we get
1227 * rate_(i+1) = rate_(i) (7)
1229 * So we end up using (2) to always keep
1230 * rate_(i+1) ~= (write_bw / N) (8)
1231 * regardless of the value of pos_ratio. As long as (8) is satisfied,
1232 * pos_ratio is able to drive itself to 1.0, which is not only where
1233 * the dirty count meet the setpoint, but also where the slope of
1234 * pos_ratio is most flat and hence task_ratelimit is least fluctuated.
1236 balanced_dirty_ratelimit
= div_u64((u64
)task_ratelimit
* write_bw
,
1239 * balanced_dirty_ratelimit ~= (write_bw / N) <= write_bw
1241 if (unlikely(balanced_dirty_ratelimit
> write_bw
))
1242 balanced_dirty_ratelimit
= write_bw
;
1245 * We could safely do this and return immediately:
1247 * wb->dirty_ratelimit = balanced_dirty_ratelimit;
1249 * However to get a more stable dirty_ratelimit, the below elaborated
1250 * code makes use of task_ratelimit to filter out singular points and
1251 * limit the step size.
1253 * The below code essentially only uses the relative value of
1255 * task_ratelimit - dirty_ratelimit
1256 * = (pos_ratio - 1) * dirty_ratelimit
1258 * which reflects the direction and size of dirty position error.
1262 * dirty_ratelimit will follow balanced_dirty_ratelimit iff
1263 * task_ratelimit is on the same side of dirty_ratelimit, too.
1265 * - dirty_ratelimit > balanced_dirty_ratelimit
1266 * - dirty_ratelimit > task_ratelimit (dirty pages are above setpoint)
1267 * lowering dirty_ratelimit will help meet both the position and rate
1268 * control targets. Otherwise, don't update dirty_ratelimit if it will
1269 * only help meet the rate target. After all, what the users ultimately
1270 * feel and care are stable dirty rate and small position error.
1272 * |task_ratelimit - dirty_ratelimit| is used to limit the step size
1273 * and filter out the singular points of balanced_dirty_ratelimit. Which
1274 * keeps jumping around randomly and can even leap far away at times
1275 * due to the small 200ms estimation period of dirty_rate (we want to
1276 * keep that period small to reduce time lags).
1281 * For strictlimit case, calculations above were based on wb counters
1282 * and limits (starting from pos_ratio = wb_position_ratio() and up to
1283 * balanced_dirty_ratelimit = task_ratelimit * write_bw / dirty_rate).
1284 * Hence, to calculate "step" properly, we have to use wb_dirty as
1285 * "dirty" and wb_setpoint as "setpoint".
1287 * We rampup dirty_ratelimit forcibly if wb_dirty is low because
1288 * it's possible that wb_thresh is close to zero due to inactivity
1289 * of backing device.
1291 if (unlikely(wb
->bdi
->capabilities
& BDI_CAP_STRICTLIMIT
)) {
1292 dirty
= dtc
->wb_dirty
;
1293 if (dtc
->wb_dirty
< 8)
1294 setpoint
= dtc
->wb_dirty
+ 1;
1296 setpoint
= (dtc
->wb_thresh
+ dtc
->wb_bg_thresh
) / 2;
1299 if (dirty
< setpoint
) {
1300 x
= min3(wb
->balanced_dirty_ratelimit
,
1301 balanced_dirty_ratelimit
, task_ratelimit
);
1302 if (dirty_ratelimit
< x
)
1303 step
= x
- dirty_ratelimit
;
1305 x
= max3(wb
->balanced_dirty_ratelimit
,
1306 balanced_dirty_ratelimit
, task_ratelimit
);
1307 if (dirty_ratelimit
> x
)
1308 step
= dirty_ratelimit
- x
;
1312 * Don't pursue 100% rate matching. It's impossible since the balanced
1313 * rate itself is constantly fluctuating. So decrease the track speed
1314 * when it gets close to the target. Helps eliminate pointless tremors.
1316 shift
= dirty_ratelimit
/ (2 * step
+ 1);
1317 if (shift
< BITS_PER_LONG
)
1318 step
= DIV_ROUND_UP(step
>> shift
, 8);
1322 if (dirty_ratelimit
< balanced_dirty_ratelimit
)
1323 dirty_ratelimit
+= step
;
1325 dirty_ratelimit
-= step
;
1327 WRITE_ONCE(wb
->dirty_ratelimit
, max(dirty_ratelimit
, 1UL));
1328 wb
->balanced_dirty_ratelimit
= balanced_dirty_ratelimit
;
1330 trace_bdi_dirty_ratelimit(wb
, dirty_rate
, task_ratelimit
);
1333 static void __wb_update_bandwidth(struct dirty_throttle_control
*gdtc
,
1334 struct dirty_throttle_control
*mdtc
,
1335 bool update_ratelimit
)
1337 struct bdi_writeback
*wb
= gdtc
->wb
;
1338 unsigned long now
= jiffies
;
1339 unsigned long elapsed
;
1340 unsigned long dirtied
;
1341 unsigned long written
;
1343 spin_lock(&wb
->list_lock
);
1346 * Lockless checks for elapsed time are racy and delayed update after
1347 * IO completion doesn't do it at all (to make sure written pages are
1348 * accounted reasonably quickly). Make sure elapsed >= 1 to avoid
1351 elapsed
= max(now
- wb
->bw_time_stamp
, 1UL);
1352 dirtied
= percpu_counter_read(&wb
->stat
[WB_DIRTIED
]);
1353 written
= percpu_counter_read(&wb
->stat
[WB_WRITTEN
]);
1355 if (update_ratelimit
) {
1356 domain_update_dirty_limit(gdtc
, now
);
1357 wb_update_dirty_ratelimit(gdtc
, dirtied
, elapsed
);
1360 * @mdtc is always NULL if !CGROUP_WRITEBACK but the
1361 * compiler has no way to figure that out. Help it.
1363 if (IS_ENABLED(CONFIG_CGROUP_WRITEBACK
) && mdtc
) {
1364 domain_update_dirty_limit(mdtc
, now
);
1365 wb_update_dirty_ratelimit(mdtc
, dirtied
, elapsed
);
1368 wb_update_write_bandwidth(wb
, elapsed
, written
);
1370 wb
->dirtied_stamp
= dirtied
;
1371 wb
->written_stamp
= written
;
1372 WRITE_ONCE(wb
->bw_time_stamp
, now
);
1373 spin_unlock(&wb
->list_lock
);
1376 void wb_update_bandwidth(struct bdi_writeback
*wb
)
1378 struct dirty_throttle_control gdtc
= { GDTC_INIT(wb
) };
1380 __wb_update_bandwidth(&gdtc
, NULL
, false);
1383 /* Interval after which we consider wb idle and don't estimate bandwidth */
1384 #define WB_BANDWIDTH_IDLE_JIF (HZ)
1386 static void wb_bandwidth_estimate_start(struct bdi_writeback
*wb
)
1388 unsigned long now
= jiffies
;
1389 unsigned long elapsed
= now
- READ_ONCE(wb
->bw_time_stamp
);
1391 if (elapsed
> WB_BANDWIDTH_IDLE_JIF
&&
1392 !atomic_read(&wb
->writeback_inodes
)) {
1393 spin_lock(&wb
->list_lock
);
1394 wb
->dirtied_stamp
= wb_stat(wb
, WB_DIRTIED
);
1395 wb
->written_stamp
= wb_stat(wb
, WB_WRITTEN
);
1396 WRITE_ONCE(wb
->bw_time_stamp
, now
);
1397 spin_unlock(&wb
->list_lock
);
1402 * After a task dirtied this many pages, balance_dirty_pages_ratelimited()
1403 * will look to see if it needs to start dirty throttling.
1405 * If dirty_poll_interval is too low, big NUMA machines will call the expensive
1406 * global_zone_page_state() too often. So scale it near-sqrt to the safety margin
1407 * (the number of pages we may dirty without exceeding the dirty limits).
1409 static unsigned long dirty_poll_interval(unsigned long dirty
,
1410 unsigned long thresh
)
1413 return 1UL << (ilog2(thresh
- dirty
) >> 1);
1418 static unsigned long wb_max_pause(struct bdi_writeback
*wb
,
1419 unsigned long wb_dirty
)
1421 unsigned long bw
= READ_ONCE(wb
->avg_write_bandwidth
);
1425 * Limit pause time for small memory systems. If sleeping for too long
1426 * time, a small pool of dirty/writeback pages may go empty and disk go
1429 * 8 serves as the safety ratio.
1431 t
= wb_dirty
/ (1 + bw
/ roundup_pow_of_two(1 + HZ
/ 8));
1434 return min_t(unsigned long, t
, MAX_PAUSE
);
1437 static long wb_min_pause(struct bdi_writeback
*wb
,
1439 unsigned long task_ratelimit
,
1440 unsigned long dirty_ratelimit
,
1441 int *nr_dirtied_pause
)
1443 long hi
= ilog2(READ_ONCE(wb
->avg_write_bandwidth
));
1444 long lo
= ilog2(READ_ONCE(wb
->dirty_ratelimit
));
1445 long t
; /* target pause */
1446 long pause
; /* estimated next pause */
1447 int pages
; /* target nr_dirtied_pause */
1449 /* target for 10ms pause on 1-dd case */
1450 t
= max(1, HZ
/ 100);
1453 * Scale up pause time for concurrent dirtiers in order to reduce CPU
1456 * (N * 10ms) on 2^N concurrent tasks.
1459 t
+= (hi
- lo
) * (10 * HZ
) / 1024;
1462 * This is a bit convoluted. We try to base the next nr_dirtied_pause
1463 * on the much more stable dirty_ratelimit. However the next pause time
1464 * will be computed based on task_ratelimit and the two rate limits may
1465 * depart considerably at some time. Especially if task_ratelimit goes
1466 * below dirty_ratelimit/2 and the target pause is max_pause, the next
1467 * pause time will be max_pause*2 _trimmed down_ to max_pause. As a
1468 * result task_ratelimit won't be executed faithfully, which could
1469 * eventually bring down dirty_ratelimit.
1471 * We apply two rules to fix it up:
1472 * 1) try to estimate the next pause time and if necessary, use a lower
1473 * nr_dirtied_pause so as not to exceed max_pause. When this happens,
1474 * nr_dirtied_pause will be "dancing" with task_ratelimit.
1475 * 2) limit the target pause time to max_pause/2, so that the normal
1476 * small fluctuations of task_ratelimit won't trigger rule (1) and
1477 * nr_dirtied_pause will remain as stable as dirty_ratelimit.
1479 t
= min(t
, 1 + max_pause
/ 2);
1480 pages
= dirty_ratelimit
* t
/ roundup_pow_of_two(HZ
);
1483 * Tiny nr_dirtied_pause is found to hurt I/O performance in the test
1484 * case fio-mmap-randwrite-64k, which does 16*{sync read, async write}.
1485 * When the 16 consecutive reads are often interrupted by some dirty
1486 * throttling pause during the async writes, cfq will go into idles
1487 * (deadline is fine). So push nr_dirtied_pause as high as possible
1488 * until reaches DIRTY_POLL_THRESH=32 pages.
1490 if (pages
< DIRTY_POLL_THRESH
) {
1492 pages
= dirty_ratelimit
* t
/ roundup_pow_of_two(HZ
);
1493 if (pages
> DIRTY_POLL_THRESH
) {
1494 pages
= DIRTY_POLL_THRESH
;
1495 t
= HZ
* DIRTY_POLL_THRESH
/ dirty_ratelimit
;
1499 pause
= HZ
* pages
/ (task_ratelimit
+ 1);
1500 if (pause
> max_pause
) {
1502 pages
= task_ratelimit
* t
/ roundup_pow_of_two(HZ
);
1505 *nr_dirtied_pause
= pages
;
1507 * The minimal pause time will normally be half the target pause time.
1509 return pages
>= DIRTY_POLL_THRESH
? 1 + t
/ 2 : t
;
1512 static inline void wb_dirty_limits(struct dirty_throttle_control
*dtc
)
1514 struct bdi_writeback
*wb
= dtc
->wb
;
1515 unsigned long wb_reclaimable
;
1518 * wb_thresh is not treated as some limiting factor as
1519 * dirty_thresh, due to reasons
1520 * - in JBOD setup, wb_thresh can fluctuate a lot
1521 * - in a system with HDD and USB key, the USB key may somehow
1522 * go into state (wb_dirty >> wb_thresh) either because
1523 * wb_dirty starts high, or because wb_thresh drops low.
1524 * In this case we don't want to hard throttle the USB key
1525 * dirtiers for 100 seconds until wb_dirty drops under
1526 * wb_thresh. Instead the auxiliary wb control line in
1527 * wb_position_ratio() will let the dirtier task progress
1528 * at some rate <= (write_bw / 2) for bringing down wb_dirty.
1530 dtc
->wb_thresh
= __wb_calc_thresh(dtc
);
1531 dtc
->wb_bg_thresh
= dtc
->thresh
?
1532 div_u64((u64
)dtc
->wb_thresh
* dtc
->bg_thresh
, dtc
->thresh
) : 0;
1535 * In order to avoid the stacked BDI deadlock we need
1536 * to ensure we accurately count the 'dirty' pages when
1537 * the threshold is low.
1539 * Otherwise it would be possible to get thresh+n pages
1540 * reported dirty, even though there are thresh-m pages
1541 * actually dirty; with m+n sitting in the percpu
1544 if (dtc
->wb_thresh
< 2 * wb_stat_error()) {
1545 wb_reclaimable
= wb_stat_sum(wb
, WB_RECLAIMABLE
);
1546 dtc
->wb_dirty
= wb_reclaimable
+ wb_stat_sum(wb
, WB_WRITEBACK
);
1548 wb_reclaimable
= wb_stat(wb
, WB_RECLAIMABLE
);
1549 dtc
->wb_dirty
= wb_reclaimable
+ wb_stat(wb
, WB_WRITEBACK
);
1554 * balance_dirty_pages() must be called by processes which are generating dirty
1555 * data. It looks at the number of dirty pages in the machine and will force
1556 * the caller to wait once crossing the (background_thresh + dirty_thresh) / 2.
1557 * If we're over `background_thresh' then the writeback threads are woken to
1558 * perform some writeout.
1560 static void balance_dirty_pages(struct bdi_writeback
*wb
,
1561 unsigned long pages_dirtied
)
1563 struct dirty_throttle_control gdtc_stor
= { GDTC_INIT(wb
) };
1564 struct dirty_throttle_control mdtc_stor
= { MDTC_INIT(wb
, &gdtc_stor
) };
1565 struct dirty_throttle_control
* const gdtc
= &gdtc_stor
;
1566 struct dirty_throttle_control
* const mdtc
= mdtc_valid(&mdtc_stor
) ?
1568 struct dirty_throttle_control
*sdtc
;
1569 unsigned long nr_reclaimable
; /* = file_dirty */
1574 int nr_dirtied_pause
;
1575 bool dirty_exceeded
= false;
1576 unsigned long task_ratelimit
;
1577 unsigned long dirty_ratelimit
;
1578 struct backing_dev_info
*bdi
= wb
->bdi
;
1579 bool strictlimit
= bdi
->capabilities
& BDI_CAP_STRICTLIMIT
;
1580 unsigned long start_time
= jiffies
;
1583 unsigned long now
= jiffies
;
1584 unsigned long dirty
, thresh
, bg_thresh
;
1585 unsigned long m_dirty
= 0; /* stop bogus uninit warnings */
1586 unsigned long m_thresh
= 0;
1587 unsigned long m_bg_thresh
= 0;
1589 nr_reclaimable
= global_node_page_state(NR_FILE_DIRTY
);
1590 gdtc
->avail
= global_dirtyable_memory();
1591 gdtc
->dirty
= nr_reclaimable
+ global_node_page_state(NR_WRITEBACK
);
1593 domain_dirty_limits(gdtc
);
1595 if (unlikely(strictlimit
)) {
1596 wb_dirty_limits(gdtc
);
1598 dirty
= gdtc
->wb_dirty
;
1599 thresh
= gdtc
->wb_thresh
;
1600 bg_thresh
= gdtc
->wb_bg_thresh
;
1602 dirty
= gdtc
->dirty
;
1603 thresh
= gdtc
->thresh
;
1604 bg_thresh
= gdtc
->bg_thresh
;
1608 unsigned long filepages
, headroom
, writeback
;
1611 * If @wb belongs to !root memcg, repeat the same
1612 * basic calculations for the memcg domain.
1614 mem_cgroup_wb_stats(wb
, &filepages
, &headroom
,
1615 &mdtc
->dirty
, &writeback
);
1616 mdtc
->dirty
+= writeback
;
1617 mdtc_calc_avail(mdtc
, filepages
, headroom
);
1619 domain_dirty_limits(mdtc
);
1621 if (unlikely(strictlimit
)) {
1622 wb_dirty_limits(mdtc
);
1623 m_dirty
= mdtc
->wb_dirty
;
1624 m_thresh
= mdtc
->wb_thresh
;
1625 m_bg_thresh
= mdtc
->wb_bg_thresh
;
1627 m_dirty
= mdtc
->dirty
;
1628 m_thresh
= mdtc
->thresh
;
1629 m_bg_thresh
= mdtc
->bg_thresh
;
1634 * Throttle it only when the background writeback cannot
1635 * catch-up. This avoids (excessively) small writeouts
1636 * when the wb limits are ramping up in case of !strictlimit.
1638 * In strictlimit case make decision based on the wb counters
1639 * and limits. Small writeouts when the wb limits are ramping
1640 * up are the price we consciously pay for strictlimit-ing.
1642 * If memcg domain is in effect, @dirty should be under
1643 * both global and memcg freerun ceilings.
1645 if (dirty
<= dirty_freerun_ceiling(thresh
, bg_thresh
) &&
1647 m_dirty
<= dirty_freerun_ceiling(m_thresh
, m_bg_thresh
))) {
1649 unsigned long m_intv
;
1652 intv
= dirty_poll_interval(dirty
, thresh
);
1655 current
->dirty_paused_when
= now
;
1656 current
->nr_dirtied
= 0;
1658 m_intv
= dirty_poll_interval(m_dirty
, m_thresh
);
1659 current
->nr_dirtied_pause
= min(intv
, m_intv
);
1663 if (unlikely(!writeback_in_progress(wb
)))
1664 wb_start_background_writeback(wb
);
1666 mem_cgroup_flush_foreign(wb
);
1669 * Calculate global domain's pos_ratio and select the
1670 * global dtc by default.
1673 wb_dirty_limits(gdtc
);
1675 if ((current
->flags
& PF_LOCAL_THROTTLE
) &&
1677 dirty_freerun_ceiling(gdtc
->wb_thresh
,
1678 gdtc
->wb_bg_thresh
))
1680 * LOCAL_THROTTLE tasks must not be throttled
1681 * when below the per-wb freerun ceiling.
1686 dirty_exceeded
= (gdtc
->wb_dirty
> gdtc
->wb_thresh
) &&
1687 ((gdtc
->dirty
> gdtc
->thresh
) || strictlimit
);
1689 wb_position_ratio(gdtc
);
1694 * If memcg domain is in effect, calculate its
1695 * pos_ratio. @wb should satisfy constraints from
1696 * both global and memcg domains. Choose the one
1697 * w/ lower pos_ratio.
1700 wb_dirty_limits(mdtc
);
1702 if ((current
->flags
& PF_LOCAL_THROTTLE
) &&
1704 dirty_freerun_ceiling(mdtc
->wb_thresh
,
1705 mdtc
->wb_bg_thresh
))
1707 * LOCAL_THROTTLE tasks must not be
1708 * throttled when below the per-wb
1713 dirty_exceeded
|= (mdtc
->wb_dirty
> mdtc
->wb_thresh
) &&
1714 ((mdtc
->dirty
> mdtc
->thresh
) || strictlimit
);
1716 wb_position_ratio(mdtc
);
1717 if (mdtc
->pos_ratio
< gdtc
->pos_ratio
)
1721 if (dirty_exceeded
&& !wb
->dirty_exceeded
)
1722 wb
->dirty_exceeded
= 1;
1724 if (time_is_before_jiffies(READ_ONCE(wb
->bw_time_stamp
) +
1725 BANDWIDTH_INTERVAL
))
1726 __wb_update_bandwidth(gdtc
, mdtc
, true);
1728 /* throttle according to the chosen dtc */
1729 dirty_ratelimit
= READ_ONCE(wb
->dirty_ratelimit
);
1730 task_ratelimit
= ((u64
)dirty_ratelimit
* sdtc
->pos_ratio
) >>
1731 RATELIMIT_CALC_SHIFT
;
1732 max_pause
= wb_max_pause(wb
, sdtc
->wb_dirty
);
1733 min_pause
= wb_min_pause(wb
, max_pause
,
1734 task_ratelimit
, dirty_ratelimit
,
1737 if (unlikely(task_ratelimit
== 0)) {
1742 period
= HZ
* pages_dirtied
/ task_ratelimit
;
1744 if (current
->dirty_paused_when
)
1745 pause
-= now
- current
->dirty_paused_when
;
1747 * For less than 1s think time (ext3/4 may block the dirtier
1748 * for up to 800ms from time to time on 1-HDD; so does xfs,
1749 * however at much less frequency), try to compensate it in
1750 * future periods by updating the virtual time; otherwise just
1751 * do a reset, as it may be a light dirtier.
1753 if (pause
< min_pause
) {
1754 trace_balance_dirty_pages(wb
,
1767 current
->dirty_paused_when
= now
;
1768 current
->nr_dirtied
= 0;
1769 } else if (period
) {
1770 current
->dirty_paused_when
+= period
;
1771 current
->nr_dirtied
= 0;
1772 } else if (current
->nr_dirtied_pause
<= pages_dirtied
)
1773 current
->nr_dirtied_pause
+= pages_dirtied
;
1776 if (unlikely(pause
> max_pause
)) {
1777 /* for occasional dropped task_ratelimit */
1778 now
+= min(pause
- max_pause
, max_pause
);
1783 trace_balance_dirty_pages(wb
,
1795 __set_current_state(TASK_KILLABLE
);
1796 wb
->dirty_sleep
= now
;
1797 io_schedule_timeout(pause
);
1799 current
->dirty_paused_when
= now
+ pause
;
1800 current
->nr_dirtied
= 0;
1801 current
->nr_dirtied_pause
= nr_dirtied_pause
;
1804 * This is typically equal to (dirty < thresh) and can also
1805 * keep "1000+ dd on a slow USB stick" under control.
1811 * In the case of an unresponsive NFS server and the NFS dirty
1812 * pages exceeds dirty_thresh, give the other good wb's a pipe
1813 * to go through, so that tasks on them still remain responsive.
1815 * In theory 1 page is enough to keep the consumer-producer
1816 * pipe going: the flusher cleans 1 page => the task dirties 1
1817 * more page. However wb_dirty has accounting errors. So use
1818 * the larger and more IO friendly wb_stat_error.
1820 if (sdtc
->wb_dirty
<= wb_stat_error())
1823 if (fatal_signal_pending(current
))
1827 if (!dirty_exceeded
&& wb
->dirty_exceeded
)
1828 wb
->dirty_exceeded
= 0;
1830 if (writeback_in_progress(wb
))
1834 * In laptop mode, we wait until hitting the higher threshold before
1835 * starting background writeout, and then write out all the way down
1836 * to the lower threshold. So slow writers cause minimal disk activity.
1838 * In normal mode, we start background writeout at the lower
1839 * background_thresh, to keep the amount of dirty memory low.
1844 if (nr_reclaimable
> gdtc
->bg_thresh
)
1845 wb_start_background_writeback(wb
);
1848 static DEFINE_PER_CPU(int, bdp_ratelimits
);
1851 * Normal tasks are throttled by
1853 * dirty tsk->nr_dirtied_pause pages;
1854 * take a snap in balance_dirty_pages();
1856 * However there is a worst case. If every task exit immediately when dirtied
1857 * (tsk->nr_dirtied_pause - 1) pages, balance_dirty_pages() will never be
1858 * called to throttle the page dirties. The solution is to save the not yet
1859 * throttled page dirties in dirty_throttle_leaks on task exit and charge them
1860 * randomly into the running tasks. This works well for the above worst case,
1861 * as the new task will pick up and accumulate the old task's leaked dirty
1862 * count and eventually get throttled.
1864 DEFINE_PER_CPU(int, dirty_throttle_leaks
) = 0;
1867 * balance_dirty_pages_ratelimited - balance dirty memory state
1868 * @mapping: address_space which was dirtied
1870 * Processes which are dirtying memory should call in here once for each page
1871 * which was newly dirtied. The function will periodically check the system's
1872 * dirty state and will initiate writeback if needed.
1874 * Once we're over the dirty memory limit we decrease the ratelimiting
1875 * by a lot, to prevent individual processes from overshooting the limit
1876 * by (ratelimit_pages) each.
1878 void balance_dirty_pages_ratelimited(struct address_space
*mapping
)
1880 struct inode
*inode
= mapping
->host
;
1881 struct backing_dev_info
*bdi
= inode_to_bdi(inode
);
1882 struct bdi_writeback
*wb
= NULL
;
1886 if (!(bdi
->capabilities
& BDI_CAP_WRITEBACK
))
1889 if (inode_cgwb_enabled(inode
))
1890 wb
= wb_get_create_current(bdi
, GFP_KERNEL
);
1894 ratelimit
= current
->nr_dirtied_pause
;
1895 if (wb
->dirty_exceeded
)
1896 ratelimit
= min(ratelimit
, 32 >> (PAGE_SHIFT
- 10));
1900 * This prevents one CPU to accumulate too many dirtied pages without
1901 * calling into balance_dirty_pages(), which can happen when there are
1902 * 1000+ tasks, all of them start dirtying pages at exactly the same
1903 * time, hence all honoured too large initial task->nr_dirtied_pause.
1905 p
= this_cpu_ptr(&bdp_ratelimits
);
1906 if (unlikely(current
->nr_dirtied
>= ratelimit
))
1908 else if (unlikely(*p
>= ratelimit_pages
)) {
1913 * Pick up the dirtied pages by the exited tasks. This avoids lots of
1914 * short-lived tasks (eg. gcc invocations in a kernel build) escaping
1915 * the dirty throttling and livelock other long-run dirtiers.
1917 p
= this_cpu_ptr(&dirty_throttle_leaks
);
1918 if (*p
> 0 && current
->nr_dirtied
< ratelimit
) {
1919 unsigned long nr_pages_dirtied
;
1920 nr_pages_dirtied
= min(*p
, ratelimit
- current
->nr_dirtied
);
1921 *p
-= nr_pages_dirtied
;
1922 current
->nr_dirtied
+= nr_pages_dirtied
;
1926 if (unlikely(current
->nr_dirtied
>= ratelimit
))
1927 balance_dirty_pages(wb
, current
->nr_dirtied
);
1931 EXPORT_SYMBOL(balance_dirty_pages_ratelimited
);
1934 * wb_over_bg_thresh - does @wb need to be written back?
1935 * @wb: bdi_writeback of interest
1937 * Determines whether background writeback should keep writing @wb or it's
1940 * Return: %true if writeback should continue.
1942 bool wb_over_bg_thresh(struct bdi_writeback
*wb
)
1944 struct dirty_throttle_control gdtc_stor
= { GDTC_INIT(wb
) };
1945 struct dirty_throttle_control mdtc_stor
= { MDTC_INIT(wb
, &gdtc_stor
) };
1946 struct dirty_throttle_control
* const gdtc
= &gdtc_stor
;
1947 struct dirty_throttle_control
* const mdtc
= mdtc_valid(&mdtc_stor
) ?
1949 unsigned long reclaimable
;
1950 unsigned long thresh
;
1953 * Similar to balance_dirty_pages() but ignores pages being written
1954 * as we're trying to decide whether to put more under writeback.
1956 gdtc
->avail
= global_dirtyable_memory();
1957 gdtc
->dirty
= global_node_page_state(NR_FILE_DIRTY
);
1958 domain_dirty_limits(gdtc
);
1960 if (gdtc
->dirty
> gdtc
->bg_thresh
)
1963 thresh
= wb_calc_thresh(gdtc
->wb
, gdtc
->bg_thresh
);
1964 if (thresh
< 2 * wb_stat_error())
1965 reclaimable
= wb_stat_sum(wb
, WB_RECLAIMABLE
);
1967 reclaimable
= wb_stat(wb
, WB_RECLAIMABLE
);
1969 if (reclaimable
> thresh
)
1973 unsigned long filepages
, headroom
, writeback
;
1975 mem_cgroup_wb_stats(wb
, &filepages
, &headroom
, &mdtc
->dirty
,
1977 mdtc_calc_avail(mdtc
, filepages
, headroom
);
1978 domain_dirty_limits(mdtc
); /* ditto, ignore writeback */
1980 if (mdtc
->dirty
> mdtc
->bg_thresh
)
1983 thresh
= wb_calc_thresh(mdtc
->wb
, mdtc
->bg_thresh
);
1984 if (thresh
< 2 * wb_stat_error())
1985 reclaimable
= wb_stat_sum(wb
, WB_RECLAIMABLE
);
1987 reclaimable
= wb_stat(wb
, WB_RECLAIMABLE
);
1989 if (reclaimable
> thresh
)
1997 * sysctl handler for /proc/sys/vm/dirty_writeback_centisecs
1999 int dirty_writeback_centisecs_handler(struct ctl_table
*table
, int write
,
2000 void *buffer
, size_t *length
, loff_t
*ppos
)
2002 unsigned int old_interval
= dirty_writeback_interval
;
2005 ret
= proc_dointvec(table
, write
, buffer
, length
, ppos
);
2008 * Writing 0 to dirty_writeback_interval will disable periodic writeback
2009 * and a different non-zero value will wakeup the writeback threads.
2010 * wb_wakeup_delayed() would be more appropriate, but it's a pain to
2011 * iterate over all bdis and wbs.
2012 * The reason we do this is to make the change take effect immediately.
2014 if (!ret
&& write
&& dirty_writeback_interval
&&
2015 dirty_writeback_interval
!= old_interval
)
2016 wakeup_flusher_threads(WB_REASON_PERIODIC
);
2021 void laptop_mode_timer_fn(struct timer_list
*t
)
2023 struct backing_dev_info
*backing_dev_info
=
2024 from_timer(backing_dev_info
, t
, laptop_mode_wb_timer
);
2026 wakeup_flusher_threads_bdi(backing_dev_info
, WB_REASON_LAPTOP_TIMER
);
2030 * We've spun up the disk and we're in laptop mode: schedule writeback
2031 * of all dirty data a few seconds from now. If the flush is already scheduled
2032 * then push it back - the user is still using the disk.
2034 void laptop_io_completion(struct backing_dev_info
*info
)
2036 mod_timer(&info
->laptop_mode_wb_timer
, jiffies
+ laptop_mode
);
2040 * We're in laptop mode and we've just synced. The sync's writes will have
2041 * caused another writeback to be scheduled by laptop_io_completion.
2042 * Nothing needs to be written back anymore, so we unschedule the writeback.
2044 void laptop_sync_completion(void)
2046 struct backing_dev_info
*bdi
;
2050 list_for_each_entry_rcu(bdi
, &bdi_list
, bdi_list
)
2051 del_timer(&bdi
->laptop_mode_wb_timer
);
2057 * If ratelimit_pages is too high then we can get into dirty-data overload
2058 * if a large number of processes all perform writes at the same time.
2060 * Here we set ratelimit_pages to a level which ensures that when all CPUs are
2061 * dirtying in parallel, we cannot go more than 3% (1/32) over the dirty memory
2065 void writeback_set_ratelimit(void)
2067 struct wb_domain
*dom
= &global_wb_domain
;
2068 unsigned long background_thresh
;
2069 unsigned long dirty_thresh
;
2071 global_dirty_limits(&background_thresh
, &dirty_thresh
);
2072 dom
->dirty_limit
= dirty_thresh
;
2073 ratelimit_pages
= dirty_thresh
/ (num_online_cpus() * 32);
2074 if (ratelimit_pages
< 16)
2075 ratelimit_pages
= 16;
2078 static int page_writeback_cpu_online(unsigned int cpu
)
2080 writeback_set_ratelimit();
2085 * Called early on to tune the page writeback dirty limits.
2087 * We used to scale dirty pages according to how total memory
2088 * related to pages that could be allocated for buffers.
2090 * However, that was when we used "dirty_ratio" to scale with
2091 * all memory, and we don't do that any more. "dirty_ratio"
2092 * is now applied to total non-HIGHPAGE memory, and as such we can't
2093 * get into the old insane situation any more where we had
2094 * large amounts of dirty pages compared to a small amount of
2095 * non-HIGHMEM memory.
2097 * But we might still want to scale the dirty_ratio by how
2098 * much memory the box has..
2100 void __init
page_writeback_init(void)
2102 BUG_ON(wb_domain_init(&global_wb_domain
, GFP_KERNEL
));
2104 cpuhp_setup_state(CPUHP_AP_ONLINE_DYN
, "mm/writeback:online",
2105 page_writeback_cpu_online
, NULL
);
2106 cpuhp_setup_state(CPUHP_MM_WRITEBACK_DEAD
, "mm/writeback:dead", NULL
,
2107 page_writeback_cpu_online
);
2111 * tag_pages_for_writeback - tag pages to be written by write_cache_pages
2112 * @mapping: address space structure to write
2113 * @start: starting page index
2114 * @end: ending page index (inclusive)
2116 * This function scans the page range from @start to @end (inclusive) and tags
2117 * all pages that have DIRTY tag set with a special TOWRITE tag. The idea is
2118 * that write_cache_pages (or whoever calls this function) will then use
2119 * TOWRITE tag to identify pages eligible for writeback. This mechanism is
2120 * used to avoid livelocking of writeback by a process steadily creating new
2121 * dirty pages in the file (thus it is important for this function to be quick
2122 * so that it can tag pages faster than a dirtying process can create them).
2124 void tag_pages_for_writeback(struct address_space
*mapping
,
2125 pgoff_t start
, pgoff_t end
)
2127 XA_STATE(xas
, &mapping
->i_pages
, start
);
2128 unsigned int tagged
= 0;
2132 xas_for_each_marked(&xas
, page
, end
, PAGECACHE_TAG_DIRTY
) {
2133 xas_set_mark(&xas
, PAGECACHE_TAG_TOWRITE
);
2134 if (++tagged
% XA_CHECK_SCHED
)
2138 xas_unlock_irq(&xas
);
2142 xas_unlock_irq(&xas
);
2144 EXPORT_SYMBOL(tag_pages_for_writeback
);
2147 * write_cache_pages - walk the list of dirty pages of the given address space and write all of them.
2148 * @mapping: address space structure to write
2149 * @wbc: subtract the number of written pages from *@wbc->nr_to_write
2150 * @writepage: function called for each page
2151 * @data: data passed to writepage function
2153 * If a page is already under I/O, write_cache_pages() skips it, even
2154 * if it's dirty. This is desirable behaviour for memory-cleaning writeback,
2155 * but it is INCORRECT for data-integrity system calls such as fsync(). fsync()
2156 * and msync() need to guarantee that all the data which was dirty at the time
2157 * the call was made get new I/O started against them. If wbc->sync_mode is
2158 * WB_SYNC_ALL then we were called for data integrity and we must wait for
2159 * existing IO to complete.
2161 * To avoid livelocks (when other process dirties new pages), we first tag
2162 * pages which should be written back with TOWRITE tag and only then start
2163 * writing them. For data-integrity sync we have to be careful so that we do
2164 * not miss some pages (e.g., because some other process has cleared TOWRITE
2165 * tag we set). The rule we follow is that TOWRITE tag can be cleared only
2166 * by the process clearing the DIRTY tag (and submitting the page for IO).
2168 * To avoid deadlocks between range_cyclic writeback and callers that hold
2169 * pages in PageWriteback to aggregate IO until write_cache_pages() returns,
2170 * we do not loop back to the start of the file. Doing so causes a page
2171 * lock/page writeback access order inversion - we should only ever lock
2172 * multiple pages in ascending page->index order, and looping back to the start
2173 * of the file violates that rule and causes deadlocks.
2175 * Return: %0 on success, negative error code otherwise
2177 int write_cache_pages(struct address_space
*mapping
,
2178 struct writeback_control
*wbc
, writepage_t writepage
,
2184 struct pagevec pvec
;
2187 pgoff_t end
; /* Inclusive */
2189 int range_whole
= 0;
2192 pagevec_init(&pvec
);
2193 if (wbc
->range_cyclic
) {
2194 index
= mapping
->writeback_index
; /* prev offset */
2197 index
= wbc
->range_start
>> PAGE_SHIFT
;
2198 end
= wbc
->range_end
>> PAGE_SHIFT
;
2199 if (wbc
->range_start
== 0 && wbc
->range_end
== LLONG_MAX
)
2202 if (wbc
->sync_mode
== WB_SYNC_ALL
|| wbc
->tagged_writepages
) {
2203 tag_pages_for_writeback(mapping
, index
, end
);
2204 tag
= PAGECACHE_TAG_TOWRITE
;
2206 tag
= PAGECACHE_TAG_DIRTY
;
2209 while (!done
&& (index
<= end
)) {
2212 nr_pages
= pagevec_lookup_range_tag(&pvec
, mapping
, &index
, end
,
2217 for (i
= 0; i
< nr_pages
; i
++) {
2218 struct page
*page
= pvec
.pages
[i
];
2220 done_index
= page
->index
;
2225 * Page truncated or invalidated. We can freely skip it
2226 * then, even for data integrity operations: the page
2227 * has disappeared concurrently, so there could be no
2228 * real expectation of this data integrity operation
2229 * even if there is now a new, dirty page at the same
2230 * pagecache address.
2232 if (unlikely(page
->mapping
!= mapping
)) {
2238 if (!PageDirty(page
)) {
2239 /* someone wrote it for us */
2240 goto continue_unlock
;
2243 if (PageWriteback(page
)) {
2244 if (wbc
->sync_mode
!= WB_SYNC_NONE
)
2245 wait_on_page_writeback(page
);
2247 goto continue_unlock
;
2250 BUG_ON(PageWriteback(page
));
2251 if (!clear_page_dirty_for_io(page
))
2252 goto continue_unlock
;
2254 trace_wbc_writepage(wbc
, inode_to_bdi(mapping
->host
));
2255 error
= (*writepage
)(page
, wbc
, data
);
2256 if (unlikely(error
)) {
2258 * Handle errors according to the type of
2259 * writeback. There's no need to continue for
2260 * background writeback. Just push done_index
2261 * past this page so media errors won't choke
2262 * writeout for the entire file. For integrity
2263 * writeback, we must process the entire dirty
2264 * set regardless of errors because the fs may
2265 * still have state to clear for each page. In
2266 * that case we continue processing and return
2269 if (error
== AOP_WRITEPAGE_ACTIVATE
) {
2272 } else if (wbc
->sync_mode
!= WB_SYNC_ALL
) {
2274 done_index
= page
->index
+ 1;
2283 * We stop writing back only if we are not doing
2284 * integrity sync. In case of integrity sync we have to
2285 * keep going until we have written all the pages
2286 * we tagged for writeback prior to entering this loop.
2288 if (--wbc
->nr_to_write
<= 0 &&
2289 wbc
->sync_mode
== WB_SYNC_NONE
) {
2294 pagevec_release(&pvec
);
2299 * If we hit the last page and there is more work to be done: wrap
2300 * back the index back to the start of the file for the next
2301 * time we are called.
2303 if (wbc
->range_cyclic
&& !done
)
2305 if (wbc
->range_cyclic
|| (range_whole
&& wbc
->nr_to_write
> 0))
2306 mapping
->writeback_index
= done_index
;
2310 EXPORT_SYMBOL(write_cache_pages
);
2313 * Function used by generic_writepages to call the real writepage
2314 * function and set the mapping flags on error
2316 static int __writepage(struct page
*page
, struct writeback_control
*wbc
,
2319 struct address_space
*mapping
= data
;
2320 int ret
= mapping
->a_ops
->writepage(page
, wbc
);
2321 mapping_set_error(mapping
, ret
);
2326 * generic_writepages - walk the list of dirty pages of the given address space and writepage() all of them.
2327 * @mapping: address space structure to write
2328 * @wbc: subtract the number of written pages from *@wbc->nr_to_write
2330 * This is a library function, which implements the writepages()
2331 * address_space_operation.
2333 * Return: %0 on success, negative error code otherwise
2335 int generic_writepages(struct address_space
*mapping
,
2336 struct writeback_control
*wbc
)
2338 struct blk_plug plug
;
2341 /* deal with chardevs and other special file */
2342 if (!mapping
->a_ops
->writepage
)
2345 blk_start_plug(&plug
);
2346 ret
= write_cache_pages(mapping
, wbc
, __writepage
, mapping
);
2347 blk_finish_plug(&plug
);
2351 EXPORT_SYMBOL(generic_writepages
);
2353 int do_writepages(struct address_space
*mapping
, struct writeback_control
*wbc
)
2356 struct bdi_writeback
*wb
;
2358 if (wbc
->nr_to_write
<= 0)
2360 wb
= inode_to_wb_wbc(mapping
->host
, wbc
);
2361 wb_bandwidth_estimate_start(wb
);
2363 if (mapping
->a_ops
->writepages
)
2364 ret
= mapping
->a_ops
->writepages(mapping
, wbc
);
2366 ret
= generic_writepages(mapping
, wbc
);
2367 if ((ret
!= -ENOMEM
) || (wbc
->sync_mode
!= WB_SYNC_ALL
))
2370 congestion_wait(BLK_RW_ASYNC
, HZ
/50);
2373 * Usually few pages are written by now from those we've just submitted
2374 * but if there's constant writeback being submitted, this makes sure
2375 * writeback bandwidth is updated once in a while.
2377 if (time_is_before_jiffies(READ_ONCE(wb
->bw_time_stamp
) +
2378 BANDWIDTH_INTERVAL
))
2379 wb_update_bandwidth(wb
);
2384 * write_one_page - write out a single page and wait on I/O
2385 * @page: the page to write
2387 * The page must be locked by the caller and will be unlocked upon return.
2389 * Note that the mapping's AS_EIO/AS_ENOSPC flags will be cleared when this
2392 * Return: %0 on success, negative error code otherwise
2394 int write_one_page(struct page
*page
)
2396 struct address_space
*mapping
= page
->mapping
;
2398 struct writeback_control wbc
= {
2399 .sync_mode
= WB_SYNC_ALL
,
2403 BUG_ON(!PageLocked(page
));
2405 wait_on_page_writeback(page
);
2407 if (clear_page_dirty_for_io(page
)) {
2409 ret
= mapping
->a_ops
->writepage(page
, &wbc
);
2411 wait_on_page_writeback(page
);
2418 ret
= filemap_check_errors(mapping
);
2421 EXPORT_SYMBOL(write_one_page
);
2424 * For address_spaces which do not use buffers nor write back.
2426 int __set_page_dirty_no_writeback(struct page
*page
)
2428 if (!PageDirty(page
))
2429 return !TestSetPageDirty(page
);
2432 EXPORT_SYMBOL(__set_page_dirty_no_writeback
);
2435 * Helper function for set_page_dirty family.
2437 * Caller must hold lock_page_memcg().
2439 * NOTE: This relies on being atomic wrt interrupts.
2441 static void account_page_dirtied(struct page
*page
,
2442 struct address_space
*mapping
)
2444 struct inode
*inode
= mapping
->host
;
2446 trace_writeback_dirty_page(page
, mapping
);
2448 if (mapping_can_writeback(mapping
)) {
2449 struct bdi_writeback
*wb
;
2451 inode_attach_wb(inode
, page
);
2452 wb
= inode_to_wb(inode
);
2454 __inc_lruvec_page_state(page
, NR_FILE_DIRTY
);
2455 __inc_zone_page_state(page
, NR_ZONE_WRITE_PENDING
);
2456 __inc_node_page_state(page
, NR_DIRTIED
);
2457 inc_wb_stat(wb
, WB_RECLAIMABLE
);
2458 inc_wb_stat(wb
, WB_DIRTIED
);
2459 task_io_account_write(PAGE_SIZE
);
2460 current
->nr_dirtied
++;
2461 __this_cpu_inc(bdp_ratelimits
);
2463 mem_cgroup_track_foreign_dirty(page
, wb
);
2468 * Helper function for deaccounting dirty page without writeback.
2470 * Caller must hold lock_page_memcg().
2472 void account_page_cleaned(struct page
*page
, struct address_space
*mapping
,
2473 struct bdi_writeback
*wb
)
2475 if (mapping_can_writeback(mapping
)) {
2476 dec_lruvec_page_state(page
, NR_FILE_DIRTY
);
2477 dec_zone_page_state(page
, NR_ZONE_WRITE_PENDING
);
2478 dec_wb_stat(wb
, WB_RECLAIMABLE
);
2479 task_io_account_cancelled_write(PAGE_SIZE
);
2484 * Mark the page dirty, and set it dirty in the page cache, and mark the inode
2487 * If warn is true, then emit a warning if the page is not uptodate and has
2488 * not been truncated.
2490 * The caller must hold lock_page_memcg().
2492 void __set_page_dirty(struct page
*page
, struct address_space
*mapping
,
2495 unsigned long flags
;
2497 xa_lock_irqsave(&mapping
->i_pages
, flags
);
2498 if (page
->mapping
) { /* Race with truncate? */
2499 WARN_ON_ONCE(warn
&& !PageUptodate(page
));
2500 account_page_dirtied(page
, mapping
);
2501 __xa_set_mark(&mapping
->i_pages
, page_index(page
),
2502 PAGECACHE_TAG_DIRTY
);
2504 xa_unlock_irqrestore(&mapping
->i_pages
, flags
);
2508 * For address_spaces which do not use buffers. Just tag the page as dirty in
2511 * This is also used when a single buffer is being dirtied: we want to set the
2512 * page dirty in that case, but not all the buffers. This is a "bottom-up"
2513 * dirtying, whereas __set_page_dirty_buffers() is a "top-down" dirtying.
2515 * The caller must ensure this doesn't race with truncation. Most will simply
2516 * hold the page lock, but e.g. zap_pte_range() calls with the page mapped and
2517 * the pte lock held, which also locks out truncation.
2519 int __set_page_dirty_nobuffers(struct page
*page
)
2521 lock_page_memcg(page
);
2522 if (!TestSetPageDirty(page
)) {
2523 struct address_space
*mapping
= page_mapping(page
);
2526 unlock_page_memcg(page
);
2529 __set_page_dirty(page
, mapping
, !PagePrivate(page
));
2530 unlock_page_memcg(page
);
2532 if (mapping
->host
) {
2533 /* !PageAnon && !swapper_space */
2534 __mark_inode_dirty(mapping
->host
, I_DIRTY_PAGES
);
2538 unlock_page_memcg(page
);
2541 EXPORT_SYMBOL(__set_page_dirty_nobuffers
);
2544 * Call this whenever redirtying a page, to de-account the dirty counters
2545 * (NR_DIRTIED, WB_DIRTIED, tsk->nr_dirtied), so that they match the written
2546 * counters (NR_WRITTEN, WB_WRITTEN) in long term. The mismatches will lead to
2547 * systematic errors in balanced_dirty_ratelimit and the dirty pages position
2550 void account_page_redirty(struct page
*page
)
2552 struct address_space
*mapping
= page
->mapping
;
2554 if (mapping
&& mapping_can_writeback(mapping
)) {
2555 struct inode
*inode
= mapping
->host
;
2556 struct bdi_writeback
*wb
;
2557 struct wb_lock_cookie cookie
= {};
2559 wb
= unlocked_inode_to_wb_begin(inode
, &cookie
);
2560 current
->nr_dirtied
--;
2561 dec_node_page_state(page
, NR_DIRTIED
);
2562 dec_wb_stat(wb
, WB_DIRTIED
);
2563 unlocked_inode_to_wb_end(inode
, &cookie
);
2566 EXPORT_SYMBOL(account_page_redirty
);
2569 * When a writepage implementation decides that it doesn't want to write this
2570 * page for some reason, it should redirty the locked page via
2571 * redirty_page_for_writepage() and it should then unlock the page and return 0
2573 int redirty_page_for_writepage(struct writeback_control
*wbc
, struct page
*page
)
2577 wbc
->pages_skipped
++;
2578 ret
= __set_page_dirty_nobuffers(page
);
2579 account_page_redirty(page
);
2582 EXPORT_SYMBOL(redirty_page_for_writepage
);
2587 * For pages with a mapping this should be done under the page lock for the
2588 * benefit of asynchronous memory errors who prefer a consistent dirty state.
2589 * This rule can be broken in some special cases, but should be better not to.
2591 int set_page_dirty(struct page
*page
)
2593 struct address_space
*mapping
= page_mapping(page
);
2595 page
= compound_head(page
);
2596 if (likely(mapping
)) {
2598 * readahead/lru_deactivate_page could remain
2599 * PG_readahead/PG_reclaim due to race with end_page_writeback
2600 * About readahead, if the page is written, the flags would be
2601 * reset. So no problem.
2602 * About lru_deactivate_page, if the page is redirty, the flag
2603 * will be reset. So no problem. but if the page is used by readahead
2604 * it will confuse readahead and make it restart the size rampup
2605 * process. But it's a trivial problem.
2607 if (PageReclaim(page
))
2608 ClearPageReclaim(page
);
2609 return mapping
->a_ops
->set_page_dirty(page
);
2611 if (!PageDirty(page
)) {
2612 if (!TestSetPageDirty(page
))
2617 EXPORT_SYMBOL(set_page_dirty
);
2620 * set_page_dirty() is racy if the caller has no reference against
2621 * page->mapping->host, and if the page is unlocked. This is because another
2622 * CPU could truncate the page off the mapping and then free the mapping.
2624 * Usually, the page _is_ locked, or the caller is a user-space process which
2625 * holds a reference on the inode by having an open file.
2627 * In other cases, the page should be locked before running set_page_dirty().
2629 int set_page_dirty_lock(struct page
*page
)
2634 ret
= set_page_dirty(page
);
2638 EXPORT_SYMBOL(set_page_dirty_lock
);
2641 * This cancels just the dirty bit on the kernel page itself, it does NOT
2642 * actually remove dirty bits on any mmap's that may be around. It also
2643 * leaves the page tagged dirty, so any sync activity will still find it on
2644 * the dirty lists, and in particular, clear_page_dirty_for_io() will still
2645 * look at the dirty bits in the VM.
2647 * Doing this should *normally* only ever be done when a page is truncated,
2648 * and is not actually mapped anywhere at all. However, fs/buffer.c does
2649 * this when it notices that somebody has cleaned out all the buffers on a
2650 * page without actually doing it through the VM. Can you say "ext3 is
2651 * horribly ugly"? Thought you could.
2653 void __cancel_dirty_page(struct page
*page
)
2655 struct address_space
*mapping
= page_mapping(page
);
2657 if (mapping_can_writeback(mapping
)) {
2658 struct inode
*inode
= mapping
->host
;
2659 struct bdi_writeback
*wb
;
2660 struct wb_lock_cookie cookie
= {};
2662 lock_page_memcg(page
);
2663 wb
= unlocked_inode_to_wb_begin(inode
, &cookie
);
2665 if (TestClearPageDirty(page
))
2666 account_page_cleaned(page
, mapping
, wb
);
2668 unlocked_inode_to_wb_end(inode
, &cookie
);
2669 unlock_page_memcg(page
);
2671 ClearPageDirty(page
);
2674 EXPORT_SYMBOL(__cancel_dirty_page
);
2677 * Clear a page's dirty flag, while caring for dirty memory accounting.
2678 * Returns true if the page was previously dirty.
2680 * This is for preparing to put the page under writeout. We leave the page
2681 * tagged as dirty in the xarray so that a concurrent write-for-sync
2682 * can discover it via a PAGECACHE_TAG_DIRTY walk. The ->writepage
2683 * implementation will run either set_page_writeback() or set_page_dirty(),
2684 * at which stage we bring the page's dirty flag and xarray dirty tag
2687 * This incoherency between the page's dirty flag and xarray tag is
2688 * unfortunate, but it only exists while the page is locked.
2690 int clear_page_dirty_for_io(struct page
*page
)
2692 struct address_space
*mapping
= page_mapping(page
);
2695 VM_BUG_ON_PAGE(!PageLocked(page
), page
);
2697 if (mapping
&& mapping_can_writeback(mapping
)) {
2698 struct inode
*inode
= mapping
->host
;
2699 struct bdi_writeback
*wb
;
2700 struct wb_lock_cookie cookie
= {};
2703 * Yes, Virginia, this is indeed insane.
2705 * We use this sequence to make sure that
2706 * (a) we account for dirty stats properly
2707 * (b) we tell the low-level filesystem to
2708 * mark the whole page dirty if it was
2709 * dirty in a pagetable. Only to then
2710 * (c) clean the page again and return 1 to
2711 * cause the writeback.
2713 * This way we avoid all nasty races with the
2714 * dirty bit in multiple places and clearing
2715 * them concurrently from different threads.
2717 * Note! Normally the "set_page_dirty(page)"
2718 * has no effect on the actual dirty bit - since
2719 * that will already usually be set. But we
2720 * need the side effects, and it can help us
2723 * We basically use the page "master dirty bit"
2724 * as a serialization point for all the different
2725 * threads doing their things.
2727 if (page_mkclean(page
))
2728 set_page_dirty(page
);
2730 * We carefully synchronise fault handlers against
2731 * installing a dirty pte and marking the page dirty
2732 * at this point. We do this by having them hold the
2733 * page lock while dirtying the page, and pages are
2734 * always locked coming in here, so we get the desired
2737 wb
= unlocked_inode_to_wb_begin(inode
, &cookie
);
2738 if (TestClearPageDirty(page
)) {
2739 dec_lruvec_page_state(page
, NR_FILE_DIRTY
);
2740 dec_zone_page_state(page
, NR_ZONE_WRITE_PENDING
);
2741 dec_wb_stat(wb
, WB_RECLAIMABLE
);
2744 unlocked_inode_to_wb_end(inode
, &cookie
);
2747 return TestClearPageDirty(page
);
2749 EXPORT_SYMBOL(clear_page_dirty_for_io
);
2751 static void wb_inode_writeback_start(struct bdi_writeback
*wb
)
2753 atomic_inc(&wb
->writeback_inodes
);
2756 static void wb_inode_writeback_end(struct bdi_writeback
*wb
)
2758 atomic_dec(&wb
->writeback_inodes
);
2760 * Make sure estimate of writeback throughput gets updated after
2761 * writeback completed. We delay the update by BANDWIDTH_INTERVAL
2762 * (which is the interval other bandwidth updates use for batching) so
2763 * that if multiple inodes end writeback at a similar time, they get
2764 * batched into one bandwidth update.
2766 queue_delayed_work(bdi_wq
, &wb
->bw_dwork
, BANDWIDTH_INTERVAL
);
2769 int test_clear_page_writeback(struct page
*page
)
2771 struct address_space
*mapping
= page_mapping(page
);
2774 lock_page_memcg(page
);
2775 if (mapping
&& mapping_use_writeback_tags(mapping
)) {
2776 struct inode
*inode
= mapping
->host
;
2777 struct backing_dev_info
*bdi
= inode_to_bdi(inode
);
2778 unsigned long flags
;
2780 xa_lock_irqsave(&mapping
->i_pages
, flags
);
2781 ret
= TestClearPageWriteback(page
);
2783 __xa_clear_mark(&mapping
->i_pages
, page_index(page
),
2784 PAGECACHE_TAG_WRITEBACK
);
2785 if (bdi
->capabilities
& BDI_CAP_WRITEBACK_ACCT
) {
2786 struct bdi_writeback
*wb
= inode_to_wb(inode
);
2788 dec_wb_stat(wb
, WB_WRITEBACK
);
2789 __wb_writeout_inc(wb
);
2790 if (!mapping_tagged(mapping
,
2791 PAGECACHE_TAG_WRITEBACK
))
2792 wb_inode_writeback_end(wb
);
2796 if (mapping
->host
&& !mapping_tagged(mapping
,
2797 PAGECACHE_TAG_WRITEBACK
))
2798 sb_clear_inode_writeback(mapping
->host
);
2800 xa_unlock_irqrestore(&mapping
->i_pages
, flags
);
2802 ret
= TestClearPageWriteback(page
);
2805 dec_lruvec_page_state(page
, NR_WRITEBACK
);
2806 dec_zone_page_state(page
, NR_ZONE_WRITE_PENDING
);
2807 inc_node_page_state(page
, NR_WRITTEN
);
2809 unlock_page_memcg(page
);
2813 int __test_set_page_writeback(struct page
*page
, bool keep_write
)
2815 struct address_space
*mapping
= page_mapping(page
);
2816 int ret
, access_ret
;
2818 lock_page_memcg(page
);
2819 if (mapping
&& mapping_use_writeback_tags(mapping
)) {
2820 XA_STATE(xas
, &mapping
->i_pages
, page_index(page
));
2821 struct inode
*inode
= mapping
->host
;
2822 struct backing_dev_info
*bdi
= inode_to_bdi(inode
);
2823 unsigned long flags
;
2825 xas_lock_irqsave(&xas
, flags
);
2827 ret
= TestSetPageWriteback(page
);
2831 on_wblist
= mapping_tagged(mapping
,
2832 PAGECACHE_TAG_WRITEBACK
);
2834 xas_set_mark(&xas
, PAGECACHE_TAG_WRITEBACK
);
2835 if (bdi
->capabilities
& BDI_CAP_WRITEBACK_ACCT
) {
2836 struct bdi_writeback
*wb
= inode_to_wb(inode
);
2838 inc_wb_stat(wb
, WB_WRITEBACK
);
2840 wb_inode_writeback_start(wb
);
2844 * We can come through here when swapping anonymous
2845 * pages, so we don't necessarily have an inode to track
2848 if (mapping
->host
&& !on_wblist
)
2849 sb_mark_inode_writeback(mapping
->host
);
2851 if (!PageDirty(page
))
2852 xas_clear_mark(&xas
, PAGECACHE_TAG_DIRTY
);
2854 xas_clear_mark(&xas
, PAGECACHE_TAG_TOWRITE
);
2855 xas_unlock_irqrestore(&xas
, flags
);
2857 ret
= TestSetPageWriteback(page
);
2860 inc_lruvec_page_state(page
, NR_WRITEBACK
);
2861 inc_zone_page_state(page
, NR_ZONE_WRITE_PENDING
);
2863 unlock_page_memcg(page
);
2864 access_ret
= arch_make_page_accessible(page
);
2866 * If writeback has been triggered on a page that cannot be made
2867 * accessible, it is too late to recover here.
2869 VM_BUG_ON_PAGE(access_ret
!= 0, page
);
2874 EXPORT_SYMBOL(__test_set_page_writeback
);
2877 * Wait for a page to complete writeback
2879 void wait_on_page_writeback(struct page
*page
)
2881 while (PageWriteback(page
)) {
2882 trace_wait_on_page_writeback(page
, page_mapping(page
));
2883 wait_on_page_bit(page
, PG_writeback
);
2886 EXPORT_SYMBOL_GPL(wait_on_page_writeback
);
2889 * Wait for a page to complete writeback. Returns -EINTR if we get a
2890 * fatal signal while waiting.
2892 int wait_on_page_writeback_killable(struct page
*page
)
2894 while (PageWriteback(page
)) {
2895 trace_wait_on_page_writeback(page
, page_mapping(page
));
2896 if (wait_on_page_bit_killable(page
, PG_writeback
))
2902 EXPORT_SYMBOL_GPL(wait_on_page_writeback_killable
);
2905 * wait_for_stable_page() - wait for writeback to finish, if necessary.
2906 * @page: The page to wait on.
2908 * This function determines if the given page is related to a backing device
2909 * that requires page contents to be held stable during writeback. If so, then
2910 * it will wait for any pending writeback to complete.
2912 void wait_for_stable_page(struct page
*page
)
2914 page
= thp_head(page
);
2915 if (page
->mapping
->host
->i_sb
->s_iflags
& SB_I_STABLE_WRITES
)
2916 wait_on_page_writeback(page
);
2918 EXPORT_SYMBOL_GPL(wait_for_stable_page
);