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/math64.h>
17 #include <linux/export.h>
18 #include <linux/spinlock.h>
21 #include <linux/swap.h>
22 #include <linux/slab.h>
23 #include <linux/pagemap.h>
24 #include <linux/writeback.h>
25 #include <linux/init.h>
26 #include <linux/backing-dev.h>
27 #include <linux/task_io_accounting_ops.h>
28 #include <linux/blkdev.h>
29 #include <linux/mpage.h>
30 #include <linux/rmap.h>
31 #include <linux/percpu.h>
32 #include <linux/smp.h>
33 #include <linux/sysctl.h>
34 #include <linux/cpu.h>
35 #include <linux/syscalls.h>
36 #include <linux/pagevec.h>
37 #include <linux/timer.h>
38 #include <linux/sched/rt.h>
39 #include <linux/sched/signal.h>
40 #include <linux/mm_inline.h>
41 #include <trace/events/writeback.h>
46 * Sleep at most 200ms at a time in balance_dirty_pages().
48 #define MAX_PAUSE max(HZ/5, 1)
51 * Try to keep balance_dirty_pages() call intervals higher than this many pages
52 * by raising pause time to max_pause when falls below it.
54 #define DIRTY_POLL_THRESH (128 >> (PAGE_SHIFT - 10))
57 * Estimate write bandwidth at 200ms intervals.
59 #define BANDWIDTH_INTERVAL max(HZ/5, 1)
61 #define RATELIMIT_CALC_SHIFT 10
64 * After a CPU has dirtied this many pages, balance_dirty_pages_ratelimited
65 * will look to see if it needs to force writeback or throttling.
67 static long ratelimit_pages
= 32;
69 /* The following parameters are exported via /proc/sys/vm */
72 * Start background writeback (via writeback threads) at this percentage
74 static int dirty_background_ratio
= 10;
77 * dirty_background_bytes starts at 0 (disabled) so that it is a function of
78 * dirty_background_ratio * the amount of dirtyable memory
80 static unsigned long dirty_background_bytes
;
83 * free highmem will not be subtracted from the total free memory
84 * for calculating free ratios if vm_highmem_is_dirtyable is true
86 static int vm_highmem_is_dirtyable
;
89 * The generator of dirty data starts writeback at this percentage
91 static int vm_dirty_ratio
= 20;
94 * vm_dirty_bytes starts at 0 (disabled) so that it is a function of
95 * vm_dirty_ratio * the amount of dirtyable memory
97 static unsigned long vm_dirty_bytes
;
100 * The interval between `kupdate'-style writebacks
102 unsigned int dirty_writeback_interval
= 5 * 100; /* centiseconds */
104 EXPORT_SYMBOL_GPL(dirty_writeback_interval
);
107 * The longest time for which data is allowed to remain dirty
109 unsigned int dirty_expire_interval
= 30 * 100; /* centiseconds */
112 * Flag that puts the machine in "laptop mode". Doubles as a timeout in jiffies:
113 * a full sync is triggered after this time elapses without any disk activity.
117 EXPORT_SYMBOL(laptop_mode
);
119 /* End of sysctl-exported parameters */
121 struct wb_domain global_wb_domain
;
123 /* consolidated parameters for balance_dirty_pages() and its subroutines */
124 struct dirty_throttle_control
{
125 #ifdef CONFIG_CGROUP_WRITEBACK
126 struct wb_domain
*dom
;
127 struct dirty_throttle_control
*gdtc
; /* only set in memcg dtc's */
129 struct bdi_writeback
*wb
;
130 struct fprop_local_percpu
*wb_completions
;
132 unsigned long avail
; /* dirtyable */
133 unsigned long dirty
; /* file_dirty + write + nfs */
134 unsigned long thresh
; /* dirty threshold */
135 unsigned long bg_thresh
; /* dirty background threshold */
137 unsigned long wb_dirty
; /* per-wb counterparts */
138 unsigned long wb_thresh
;
139 unsigned long wb_bg_thresh
;
141 unsigned long pos_ratio
;
145 * Length of period for aging writeout fractions of bdis. This is an
146 * arbitrarily chosen number. The longer the period, the slower fractions will
147 * reflect changes in current writeout rate.
149 #define VM_COMPLETIONS_PERIOD_LEN (3*HZ)
151 #ifdef CONFIG_CGROUP_WRITEBACK
153 #define GDTC_INIT(__wb) .wb = (__wb), \
154 .dom = &global_wb_domain, \
155 .wb_completions = &(__wb)->completions
157 #define GDTC_INIT_NO_WB .dom = &global_wb_domain
159 #define MDTC_INIT(__wb, __gdtc) .wb = (__wb), \
160 .dom = mem_cgroup_wb_domain(__wb), \
161 .wb_completions = &(__wb)->memcg_completions, \
164 static bool mdtc_valid(struct dirty_throttle_control
*dtc
)
169 static struct wb_domain
*dtc_dom(struct dirty_throttle_control
*dtc
)
174 static struct dirty_throttle_control
*mdtc_gdtc(struct dirty_throttle_control
*mdtc
)
179 static struct fprop_local_percpu
*wb_memcg_completions(struct bdi_writeback
*wb
)
181 return &wb
->memcg_completions
;
184 static void wb_min_max_ratio(struct bdi_writeback
*wb
,
185 unsigned long *minp
, unsigned long *maxp
)
187 unsigned long this_bw
= READ_ONCE(wb
->avg_write_bandwidth
);
188 unsigned long tot_bw
= atomic_long_read(&wb
->bdi
->tot_write_bandwidth
);
189 unsigned long long min
= wb
->bdi
->min_ratio
;
190 unsigned long long max
= wb
->bdi
->max_ratio
;
193 * @wb may already be clean by the time control reaches here and
194 * the total may not include its bw.
196 if (this_bw
< tot_bw
) {
199 min
= div64_ul(min
, tot_bw
);
201 if (max
< 100 * BDI_RATIO_SCALE
) {
203 max
= div64_ul(max
, tot_bw
);
211 #else /* CONFIG_CGROUP_WRITEBACK */
213 #define GDTC_INIT(__wb) .wb = (__wb), \
214 .wb_completions = &(__wb)->completions
215 #define GDTC_INIT_NO_WB
216 #define MDTC_INIT(__wb, __gdtc)
218 static bool mdtc_valid(struct dirty_throttle_control
*dtc
)
223 static struct wb_domain
*dtc_dom(struct dirty_throttle_control
*dtc
)
225 return &global_wb_domain
;
228 static struct dirty_throttle_control
*mdtc_gdtc(struct dirty_throttle_control
*mdtc
)
233 static struct fprop_local_percpu
*wb_memcg_completions(struct bdi_writeback
*wb
)
238 static void wb_min_max_ratio(struct bdi_writeback
*wb
,
239 unsigned long *minp
, unsigned long *maxp
)
241 *minp
= wb
->bdi
->min_ratio
;
242 *maxp
= wb
->bdi
->max_ratio
;
245 #endif /* CONFIG_CGROUP_WRITEBACK */
248 * In a memory zone, there is a certain amount of pages we consider
249 * available for the page cache, which is essentially the number of
250 * free and reclaimable pages, minus some zone reserves to protect
251 * lowmem and the ability to uphold the zone's watermarks without
252 * requiring writeback.
254 * This number of dirtyable pages is the base value of which the
255 * user-configurable dirty ratio is the effective number of pages that
256 * are allowed to be actually dirtied. Per individual zone, or
257 * globally by using the sum of dirtyable pages over all zones.
259 * Because the user is allowed to specify the dirty limit globally as
260 * absolute number of bytes, calculating the per-zone dirty limit can
261 * require translating the configured limit into a percentage of
262 * global dirtyable memory first.
266 * node_dirtyable_memory - number of dirtyable pages in a node
269 * Return: the node's number of pages potentially available for dirty
270 * page cache. This is the base value for the per-node dirty limits.
272 static unsigned long node_dirtyable_memory(struct pglist_data
*pgdat
)
274 unsigned long nr_pages
= 0;
277 for (z
= 0; z
< MAX_NR_ZONES
; z
++) {
278 struct zone
*zone
= pgdat
->node_zones
+ z
;
280 if (!populated_zone(zone
))
283 nr_pages
+= zone_page_state(zone
, NR_FREE_PAGES
);
287 * Pages reserved for the kernel should not be considered
288 * dirtyable, to prevent a situation where reclaim has to
289 * clean pages in order to balance the zones.
291 nr_pages
-= min(nr_pages
, pgdat
->totalreserve_pages
);
293 nr_pages
+= node_page_state(pgdat
, NR_INACTIVE_FILE
);
294 nr_pages
+= node_page_state(pgdat
, NR_ACTIVE_FILE
);
299 static unsigned long highmem_dirtyable_memory(unsigned long total
)
301 #ifdef CONFIG_HIGHMEM
306 for_each_node_state(node
, N_HIGH_MEMORY
) {
307 for (i
= ZONE_NORMAL
+ 1; i
< MAX_NR_ZONES
; i
++) {
309 unsigned long nr_pages
;
311 if (!is_highmem_idx(i
))
314 z
= &NODE_DATA(node
)->node_zones
[i
];
315 if (!populated_zone(z
))
318 nr_pages
= zone_page_state(z
, NR_FREE_PAGES
);
319 /* watch for underflows */
320 nr_pages
-= min(nr_pages
, high_wmark_pages(z
));
321 nr_pages
+= zone_page_state(z
, NR_ZONE_INACTIVE_FILE
);
322 nr_pages
+= zone_page_state(z
, NR_ZONE_ACTIVE_FILE
);
328 * Make sure that the number of highmem pages is never larger
329 * than the number of the total dirtyable memory. This can only
330 * occur in very strange VM situations but we want to make sure
331 * that this does not occur.
333 return min(x
, total
);
340 * global_dirtyable_memory - number of globally dirtyable pages
342 * Return: the global number of pages potentially available for dirty
343 * page cache. This is the base value for the global dirty limits.
345 static unsigned long global_dirtyable_memory(void)
349 x
= global_zone_page_state(NR_FREE_PAGES
);
351 * Pages reserved for the kernel should not be considered
352 * dirtyable, to prevent a situation where reclaim has to
353 * clean pages in order to balance the zones.
355 x
-= min(x
, totalreserve_pages
);
357 x
+= global_node_page_state(NR_INACTIVE_FILE
);
358 x
+= global_node_page_state(NR_ACTIVE_FILE
);
360 if (!vm_highmem_is_dirtyable
)
361 x
-= highmem_dirtyable_memory(x
);
363 return x
+ 1; /* Ensure that we never return 0 */
367 * domain_dirty_limits - calculate thresh and bg_thresh for a wb_domain
368 * @dtc: dirty_throttle_control of interest
370 * Calculate @dtc->thresh and ->bg_thresh considering
371 * vm_dirty_{bytes|ratio} and dirty_background_{bytes|ratio}. The caller
372 * must ensure that @dtc->avail is set before calling this function. The
373 * dirty limits will be lifted by 1/4 for real-time tasks.
375 static void domain_dirty_limits(struct dirty_throttle_control
*dtc
)
377 const unsigned long available_memory
= dtc
->avail
;
378 struct dirty_throttle_control
*gdtc
= mdtc_gdtc(dtc
);
379 unsigned long bytes
= vm_dirty_bytes
;
380 unsigned long bg_bytes
= dirty_background_bytes
;
381 /* convert ratios to per-PAGE_SIZE for higher precision */
382 unsigned long ratio
= (vm_dirty_ratio
* PAGE_SIZE
) / 100;
383 unsigned long bg_ratio
= (dirty_background_ratio
* PAGE_SIZE
) / 100;
384 unsigned long thresh
;
385 unsigned long bg_thresh
;
386 struct task_struct
*tsk
;
388 /* gdtc is !NULL iff @dtc is for memcg domain */
390 unsigned long global_avail
= gdtc
->avail
;
393 * The byte settings can't be applied directly to memcg
394 * domains. Convert them to ratios by scaling against
395 * globally available memory. As the ratios are in
396 * per-PAGE_SIZE, they can be obtained by dividing bytes by
400 ratio
= min(DIV_ROUND_UP(bytes
, global_avail
),
403 bg_ratio
= min(DIV_ROUND_UP(bg_bytes
, global_avail
),
405 bytes
= bg_bytes
= 0;
409 thresh
= DIV_ROUND_UP(bytes
, PAGE_SIZE
);
411 thresh
= (ratio
* available_memory
) / PAGE_SIZE
;
414 bg_thresh
= DIV_ROUND_UP(bg_bytes
, PAGE_SIZE
);
416 bg_thresh
= (bg_ratio
* available_memory
) / PAGE_SIZE
;
418 if (bg_thresh
>= thresh
)
419 bg_thresh
= thresh
/ 2;
422 bg_thresh
+= bg_thresh
/ 4 + global_wb_domain
.dirty_limit
/ 32;
423 thresh
+= thresh
/ 4 + global_wb_domain
.dirty_limit
/ 32;
425 dtc
->thresh
= thresh
;
426 dtc
->bg_thresh
= bg_thresh
;
428 /* we should eventually report the domain in the TP */
430 trace_global_dirty_state(bg_thresh
, thresh
);
434 * global_dirty_limits - background-writeback and dirty-throttling thresholds
435 * @pbackground: out parameter for bg_thresh
436 * @pdirty: out parameter for thresh
438 * Calculate bg_thresh and thresh for global_wb_domain. See
439 * domain_dirty_limits() for details.
441 void global_dirty_limits(unsigned long *pbackground
, unsigned long *pdirty
)
443 struct dirty_throttle_control gdtc
= { GDTC_INIT_NO_WB
};
445 gdtc
.avail
= global_dirtyable_memory();
446 domain_dirty_limits(&gdtc
);
448 *pbackground
= gdtc
.bg_thresh
;
449 *pdirty
= gdtc
.thresh
;
453 * node_dirty_limit - maximum number of dirty pages allowed in a node
456 * Return: the maximum number of dirty pages allowed in a node, based
457 * on the node's dirtyable memory.
459 static unsigned long node_dirty_limit(struct pglist_data
*pgdat
)
461 unsigned long node_memory
= node_dirtyable_memory(pgdat
);
462 struct task_struct
*tsk
= current
;
466 dirty
= DIV_ROUND_UP(vm_dirty_bytes
, PAGE_SIZE
) *
467 node_memory
/ global_dirtyable_memory();
469 dirty
= vm_dirty_ratio
* node_memory
/ 100;
478 * node_dirty_ok - tells whether a node is within its dirty limits
479 * @pgdat: the node to check
481 * Return: %true when the dirty pages in @pgdat are within the node's
482 * dirty limit, %false if the limit is exceeded.
484 bool node_dirty_ok(struct pglist_data
*pgdat
)
486 unsigned long limit
= node_dirty_limit(pgdat
);
487 unsigned long nr_pages
= 0;
489 nr_pages
+= node_page_state(pgdat
, NR_FILE_DIRTY
);
490 nr_pages
+= node_page_state(pgdat
, NR_WRITEBACK
);
492 return nr_pages
<= limit
;
496 static int dirty_background_ratio_handler(struct ctl_table
*table
, int write
,
497 void *buffer
, size_t *lenp
, loff_t
*ppos
)
501 ret
= proc_dointvec_minmax(table
, write
, buffer
, lenp
, ppos
);
502 if (ret
== 0 && write
)
503 dirty_background_bytes
= 0;
507 static int dirty_background_bytes_handler(struct ctl_table
*table
, int write
,
508 void *buffer
, size_t *lenp
, loff_t
*ppos
)
512 ret
= proc_doulongvec_minmax(table
, write
, buffer
, lenp
, ppos
);
513 if (ret
== 0 && write
)
514 dirty_background_ratio
= 0;
518 static int dirty_ratio_handler(struct ctl_table
*table
, int write
, void *buffer
,
519 size_t *lenp
, loff_t
*ppos
)
521 int old_ratio
= vm_dirty_ratio
;
524 ret
= proc_dointvec_minmax(table
, write
, buffer
, lenp
, ppos
);
525 if (ret
== 0 && write
&& vm_dirty_ratio
!= old_ratio
) {
526 writeback_set_ratelimit();
532 static int dirty_bytes_handler(struct ctl_table
*table
, int write
,
533 void *buffer
, size_t *lenp
, loff_t
*ppos
)
535 unsigned long old_bytes
= vm_dirty_bytes
;
538 ret
= proc_doulongvec_minmax(table
, write
, buffer
, lenp
, ppos
);
539 if (ret
== 0 && write
&& vm_dirty_bytes
!= old_bytes
) {
540 writeback_set_ratelimit();
547 static unsigned long wp_next_time(unsigned long cur_time
)
549 cur_time
+= VM_COMPLETIONS_PERIOD_LEN
;
550 /* 0 has a special meaning... */
556 static void wb_domain_writeout_add(struct wb_domain
*dom
,
557 struct fprop_local_percpu
*completions
,
558 unsigned int max_prop_frac
, long nr
)
560 __fprop_add_percpu_max(&dom
->completions
, completions
,
562 /* First event after period switching was turned off? */
563 if (unlikely(!dom
->period_time
)) {
565 * We can race with other __bdi_writeout_inc calls here but
566 * it does not cause any harm since the resulting time when
567 * timer will fire and what is in writeout_period_time will be
570 dom
->period_time
= wp_next_time(jiffies
);
571 mod_timer(&dom
->period_timer
, dom
->period_time
);
576 * Increment @wb's writeout completion count and the global writeout
577 * completion count. Called from __folio_end_writeback().
579 static inline void __wb_writeout_add(struct bdi_writeback
*wb
, long nr
)
581 struct wb_domain
*cgdom
;
583 wb_stat_mod(wb
, WB_WRITTEN
, nr
);
584 wb_domain_writeout_add(&global_wb_domain
, &wb
->completions
,
585 wb
->bdi
->max_prop_frac
, nr
);
587 cgdom
= mem_cgroup_wb_domain(wb
);
589 wb_domain_writeout_add(cgdom
, wb_memcg_completions(wb
),
590 wb
->bdi
->max_prop_frac
, nr
);
593 void wb_writeout_inc(struct bdi_writeback
*wb
)
597 local_irq_save(flags
);
598 __wb_writeout_add(wb
, 1);
599 local_irq_restore(flags
);
601 EXPORT_SYMBOL_GPL(wb_writeout_inc
);
604 * On idle system, we can be called long after we scheduled because we use
605 * deferred timers so count with missed periods.
607 static void writeout_period(struct timer_list
*t
)
609 struct wb_domain
*dom
= from_timer(dom
, t
, period_timer
);
610 int miss_periods
= (jiffies
- dom
->period_time
) /
611 VM_COMPLETIONS_PERIOD_LEN
;
613 if (fprop_new_period(&dom
->completions
, miss_periods
+ 1)) {
614 dom
->period_time
= wp_next_time(dom
->period_time
+
615 miss_periods
* VM_COMPLETIONS_PERIOD_LEN
);
616 mod_timer(&dom
->period_timer
, dom
->period_time
);
619 * Aging has zeroed all fractions. Stop wasting CPU on period
622 dom
->period_time
= 0;
626 int wb_domain_init(struct wb_domain
*dom
, gfp_t gfp
)
628 memset(dom
, 0, sizeof(*dom
));
630 spin_lock_init(&dom
->lock
);
632 timer_setup(&dom
->period_timer
, writeout_period
, TIMER_DEFERRABLE
);
634 dom
->dirty_limit_tstamp
= jiffies
;
636 return fprop_global_init(&dom
->completions
, gfp
);
639 #ifdef CONFIG_CGROUP_WRITEBACK
640 void wb_domain_exit(struct wb_domain
*dom
)
642 del_timer_sync(&dom
->period_timer
);
643 fprop_global_destroy(&dom
->completions
);
648 * bdi_min_ratio keeps the sum of the minimum dirty shares of all
649 * registered backing devices, which, for obvious reasons, can not
652 static unsigned int bdi_min_ratio
;
654 static int bdi_check_pages_limit(unsigned long pages
)
656 unsigned long max_dirty_pages
= global_dirtyable_memory();
658 if (pages
> max_dirty_pages
)
664 static unsigned long bdi_ratio_from_pages(unsigned long pages
)
666 unsigned long background_thresh
;
667 unsigned long dirty_thresh
;
670 global_dirty_limits(&background_thresh
, &dirty_thresh
);
671 ratio
= div64_u64(pages
* 100ULL * BDI_RATIO_SCALE
, dirty_thresh
);
676 static u64
bdi_get_bytes(unsigned int ratio
)
678 unsigned long background_thresh
;
679 unsigned long dirty_thresh
;
682 global_dirty_limits(&background_thresh
, &dirty_thresh
);
683 bytes
= (dirty_thresh
* PAGE_SIZE
* ratio
) / BDI_RATIO_SCALE
/ 100;
688 static int __bdi_set_min_ratio(struct backing_dev_info
*bdi
, unsigned int min_ratio
)
693 if (min_ratio
> 100 * BDI_RATIO_SCALE
)
696 spin_lock_bh(&bdi_lock
);
697 if (min_ratio
> bdi
->max_ratio
) {
700 if (min_ratio
< bdi
->min_ratio
) {
701 delta
= bdi
->min_ratio
- min_ratio
;
702 bdi_min_ratio
-= delta
;
703 bdi
->min_ratio
= min_ratio
;
705 delta
= min_ratio
- bdi
->min_ratio
;
706 if (bdi_min_ratio
+ delta
< 100 * BDI_RATIO_SCALE
) {
707 bdi_min_ratio
+= delta
;
708 bdi
->min_ratio
= min_ratio
;
714 spin_unlock_bh(&bdi_lock
);
719 static int __bdi_set_max_ratio(struct backing_dev_info
*bdi
, unsigned int max_ratio
)
723 if (max_ratio
> 100 * BDI_RATIO_SCALE
)
726 spin_lock_bh(&bdi_lock
);
727 if (bdi
->min_ratio
> max_ratio
) {
730 bdi
->max_ratio
= max_ratio
;
731 bdi
->max_prop_frac
= (FPROP_FRAC_BASE
* max_ratio
) /
732 (100 * BDI_RATIO_SCALE
);
734 spin_unlock_bh(&bdi_lock
);
739 int bdi_set_min_ratio_no_scale(struct backing_dev_info
*bdi
, unsigned int min_ratio
)
741 return __bdi_set_min_ratio(bdi
, min_ratio
);
744 int bdi_set_max_ratio_no_scale(struct backing_dev_info
*bdi
, unsigned int max_ratio
)
746 return __bdi_set_max_ratio(bdi
, max_ratio
);
749 int bdi_set_min_ratio(struct backing_dev_info
*bdi
, unsigned int min_ratio
)
751 return __bdi_set_min_ratio(bdi
, min_ratio
* BDI_RATIO_SCALE
);
754 int bdi_set_max_ratio(struct backing_dev_info
*bdi
, unsigned int max_ratio
)
756 return __bdi_set_max_ratio(bdi
, max_ratio
* BDI_RATIO_SCALE
);
758 EXPORT_SYMBOL(bdi_set_max_ratio
);
760 u64
bdi_get_min_bytes(struct backing_dev_info
*bdi
)
762 return bdi_get_bytes(bdi
->min_ratio
);
765 int bdi_set_min_bytes(struct backing_dev_info
*bdi
, u64 min_bytes
)
768 unsigned long pages
= min_bytes
>> PAGE_SHIFT
;
769 unsigned long min_ratio
;
771 ret
= bdi_check_pages_limit(pages
);
775 min_ratio
= bdi_ratio_from_pages(pages
);
776 return __bdi_set_min_ratio(bdi
, min_ratio
);
779 u64
bdi_get_max_bytes(struct backing_dev_info
*bdi
)
781 return bdi_get_bytes(bdi
->max_ratio
);
784 int bdi_set_max_bytes(struct backing_dev_info
*bdi
, u64 max_bytes
)
787 unsigned long pages
= max_bytes
>> PAGE_SHIFT
;
788 unsigned long max_ratio
;
790 ret
= bdi_check_pages_limit(pages
);
794 max_ratio
= bdi_ratio_from_pages(pages
);
795 return __bdi_set_max_ratio(bdi
, max_ratio
);
798 int bdi_set_strict_limit(struct backing_dev_info
*bdi
, unsigned int strict_limit
)
800 if (strict_limit
> 1)
803 spin_lock_bh(&bdi_lock
);
805 bdi
->capabilities
|= BDI_CAP_STRICTLIMIT
;
807 bdi
->capabilities
&= ~BDI_CAP_STRICTLIMIT
;
808 spin_unlock_bh(&bdi_lock
);
813 static unsigned long dirty_freerun_ceiling(unsigned long thresh
,
814 unsigned long bg_thresh
)
816 return (thresh
+ bg_thresh
) / 2;
819 static unsigned long hard_dirty_limit(struct wb_domain
*dom
,
820 unsigned long thresh
)
822 return max(thresh
, dom
->dirty_limit
);
826 * Memory which can be further allocated to a memcg domain is capped by
827 * system-wide clean memory excluding the amount being used in the domain.
829 static void mdtc_calc_avail(struct dirty_throttle_control
*mdtc
,
830 unsigned long filepages
, unsigned long headroom
)
832 struct dirty_throttle_control
*gdtc
= mdtc_gdtc(mdtc
);
833 unsigned long clean
= filepages
- min(filepages
, mdtc
->dirty
);
834 unsigned long global_clean
= gdtc
->avail
- min(gdtc
->avail
, gdtc
->dirty
);
835 unsigned long other_clean
= global_clean
- min(global_clean
, clean
);
837 mdtc
->avail
= filepages
+ min(headroom
, other_clean
);
841 * __wb_calc_thresh - @wb's share of dirty throttling threshold
842 * @dtc: dirty_throttle_context of interest
844 * Note that balance_dirty_pages() will only seriously take it as a hard limit
845 * when sleeping max_pause per page is not enough to keep the dirty pages under
846 * control. For example, when the device is completely stalled due to some error
847 * conditions, or when there are 1000 dd tasks writing to a slow 10MB/s USB key.
848 * In the other normal situations, it acts more gently by throttling the tasks
849 * more (rather than completely block them) when the wb dirty pages go high.
851 * It allocates high/low dirty limits to fast/slow devices, in order to prevent
852 * - starving fast devices
853 * - piling up dirty pages (that will take long time to sync) on slow devices
855 * The wb's share of dirty limit will be adapting to its throughput and
856 * bounded by the bdi->min_ratio and/or bdi->max_ratio parameters, if set.
858 * Return: @wb's dirty limit in pages. The term "dirty" in the context of
859 * dirty balancing includes all PG_dirty and PG_writeback pages.
861 static unsigned long __wb_calc_thresh(struct dirty_throttle_control
*dtc
)
863 struct wb_domain
*dom
= dtc_dom(dtc
);
864 unsigned long thresh
= dtc
->thresh
;
866 unsigned long numerator
, denominator
;
867 unsigned long wb_min_ratio
, wb_max_ratio
;
870 * Calculate this BDI's share of the thresh ratio.
872 fprop_fraction_percpu(&dom
->completions
, dtc
->wb_completions
,
873 &numerator
, &denominator
);
875 wb_thresh
= (thresh
* (100 * BDI_RATIO_SCALE
- bdi_min_ratio
)) / (100 * BDI_RATIO_SCALE
);
876 wb_thresh
*= numerator
;
877 wb_thresh
= div64_ul(wb_thresh
, denominator
);
879 wb_min_max_ratio(dtc
->wb
, &wb_min_ratio
, &wb_max_ratio
);
881 wb_thresh
+= (thresh
* wb_min_ratio
) / (100 * BDI_RATIO_SCALE
);
882 if (wb_thresh
> (thresh
* wb_max_ratio
) / (100 * BDI_RATIO_SCALE
))
883 wb_thresh
= thresh
* wb_max_ratio
/ (100 * BDI_RATIO_SCALE
);
888 unsigned long wb_calc_thresh(struct bdi_writeback
*wb
, unsigned long thresh
)
890 struct dirty_throttle_control gdtc
= { GDTC_INIT(wb
),
892 return __wb_calc_thresh(&gdtc
);
897 * f(dirty) := 1.0 + (----------------)
900 * it's a 3rd order polynomial that subjects to
902 * (1) f(freerun) = 2.0 => rampup dirty_ratelimit reasonably fast
903 * (2) f(setpoint) = 1.0 => the balance point
904 * (3) f(limit) = 0 => the hard limit
905 * (4) df/dx <= 0 => negative feedback control
906 * (5) the closer to setpoint, the smaller |df/dx| (and the reverse)
907 * => fast response on large errors; small oscillation near setpoint
909 static long long pos_ratio_polynom(unsigned long setpoint
,
916 x
= div64_s64(((s64
)setpoint
- (s64
)dirty
) << RATELIMIT_CALC_SHIFT
,
917 (limit
- setpoint
) | 1);
919 pos_ratio
= pos_ratio
* x
>> RATELIMIT_CALC_SHIFT
;
920 pos_ratio
= pos_ratio
* x
>> RATELIMIT_CALC_SHIFT
;
921 pos_ratio
+= 1 << RATELIMIT_CALC_SHIFT
;
923 return clamp(pos_ratio
, 0LL, 2LL << RATELIMIT_CALC_SHIFT
);
927 * Dirty position control.
929 * (o) global/bdi setpoints
931 * We want the dirty pages be balanced around the global/wb setpoints.
932 * When the number of dirty pages is higher/lower than the setpoint, the
933 * dirty position control ratio (and hence task dirty ratelimit) will be
934 * decreased/increased to bring the dirty pages back to the setpoint.
936 * pos_ratio = 1 << RATELIMIT_CALC_SHIFT
938 * if (dirty < setpoint) scale up pos_ratio
939 * if (dirty > setpoint) scale down pos_ratio
941 * if (wb_dirty < wb_setpoint) scale up pos_ratio
942 * if (wb_dirty > wb_setpoint) scale down pos_ratio
944 * task_ratelimit = dirty_ratelimit * pos_ratio >> RATELIMIT_CALC_SHIFT
946 * (o) global control line
950 * | |<===== global dirty control scope ======>|
958 * 1.0 ................................*
964 * 0 +------------.------------------.----------------------*------------->
965 * freerun^ setpoint^ limit^ dirty pages
967 * (o) wb control line
975 * | * |<=========== span ============>|
976 * 1.0 .......................*
988 * 1/4 ...............................................* * * * * * * * * * * *
992 * 0 +----------------------.-------------------------------.------------->
993 * wb_setpoint^ x_intercept^
995 * The wb control line won't drop below pos_ratio=1/4, so that wb_dirty can
996 * be smoothly throttled down to normal if it starts high in situations like
997 * - start writing to a slow SD card and a fast disk at the same time. The SD
998 * card's wb_dirty may rush to many times higher than wb_setpoint.
999 * - the wb dirty thresh drops quickly due to change of JBOD workload
1001 static void wb_position_ratio(struct dirty_throttle_control
*dtc
)
1003 struct bdi_writeback
*wb
= dtc
->wb
;
1004 unsigned long write_bw
= READ_ONCE(wb
->avg_write_bandwidth
);
1005 unsigned long freerun
= dirty_freerun_ceiling(dtc
->thresh
, dtc
->bg_thresh
);
1006 unsigned long limit
= hard_dirty_limit(dtc_dom(dtc
), dtc
->thresh
);
1007 unsigned long wb_thresh
= dtc
->wb_thresh
;
1008 unsigned long x_intercept
;
1009 unsigned long setpoint
; /* dirty pages' target balance point */
1010 unsigned long wb_setpoint
;
1012 long long pos_ratio
; /* for scaling up/down the rate limit */
1017 if (unlikely(dtc
->dirty
>= limit
))
1023 * See comment for pos_ratio_polynom().
1025 setpoint
= (freerun
+ limit
) / 2;
1026 pos_ratio
= pos_ratio_polynom(setpoint
, dtc
->dirty
, limit
);
1029 * The strictlimit feature is a tool preventing mistrusted filesystems
1030 * from growing a large number of dirty pages before throttling. For
1031 * such filesystems balance_dirty_pages always checks wb counters
1032 * against wb limits. Even if global "nr_dirty" is under "freerun".
1033 * This is especially important for fuse which sets bdi->max_ratio to
1034 * 1% by default. Without strictlimit feature, fuse writeback may
1035 * consume arbitrary amount of RAM because it is accounted in
1036 * NR_WRITEBACK_TEMP which is not involved in calculating "nr_dirty".
1038 * Here, in wb_position_ratio(), we calculate pos_ratio based on
1039 * two values: wb_dirty and wb_thresh. Let's consider an example:
1040 * total amount of RAM is 16GB, bdi->max_ratio is equal to 1%, global
1041 * limits are set by default to 10% and 20% (background and throttle).
1042 * Then wb_thresh is 1% of 20% of 16GB. This amounts to ~8K pages.
1043 * wb_calc_thresh(wb, bg_thresh) is about ~4K pages. wb_setpoint is
1044 * about ~6K pages (as the average of background and throttle wb
1045 * limits). The 3rd order polynomial will provide positive feedback if
1046 * wb_dirty is under wb_setpoint and vice versa.
1048 * Note, that we cannot use global counters in these calculations
1049 * because we want to throttle process writing to a strictlimit wb
1050 * much earlier than global "freerun" is reached (~23MB vs. ~2.3GB
1051 * in the example above).
1053 if (unlikely(wb
->bdi
->capabilities
& BDI_CAP_STRICTLIMIT
)) {
1054 long long wb_pos_ratio
;
1056 if (dtc
->wb_dirty
< 8) {
1057 dtc
->pos_ratio
= min_t(long long, pos_ratio
* 2,
1058 2 << RATELIMIT_CALC_SHIFT
);
1062 if (dtc
->wb_dirty
>= wb_thresh
)
1065 wb_setpoint
= dirty_freerun_ceiling(wb_thresh
,
1068 if (wb_setpoint
== 0 || wb_setpoint
== wb_thresh
)
1071 wb_pos_ratio
= pos_ratio_polynom(wb_setpoint
, dtc
->wb_dirty
,
1075 * Typically, for strictlimit case, wb_setpoint << setpoint
1076 * and pos_ratio >> wb_pos_ratio. In the other words global
1077 * state ("dirty") is not limiting factor and we have to
1078 * make decision based on wb counters. But there is an
1079 * important case when global pos_ratio should get precedence:
1080 * global limits are exceeded (e.g. due to activities on other
1081 * wb's) while given strictlimit wb is below limit.
1083 * "pos_ratio * wb_pos_ratio" would work for the case above,
1084 * but it would look too non-natural for the case of all
1085 * activity in the system coming from a single strictlimit wb
1086 * with bdi->max_ratio == 100%.
1088 * Note that min() below somewhat changes the dynamics of the
1089 * control system. Normally, pos_ratio value can be well over 3
1090 * (when globally we are at freerun and wb is well below wb
1091 * setpoint). Now the maximum pos_ratio in the same situation
1092 * is 2. We might want to tweak this if we observe the control
1093 * system is too slow to adapt.
1095 dtc
->pos_ratio
= min(pos_ratio
, wb_pos_ratio
);
1100 * We have computed basic pos_ratio above based on global situation. If
1101 * the wb is over/under its share of dirty pages, we want to scale
1102 * pos_ratio further down/up. That is done by the following mechanism.
1108 * f(wb_dirty) := 1.0 + k * (wb_dirty - wb_setpoint)
1110 * x_intercept - wb_dirty
1111 * := --------------------------
1112 * x_intercept - wb_setpoint
1114 * The main wb control line is a linear function that subjects to
1116 * (1) f(wb_setpoint) = 1.0
1117 * (2) k = - 1 / (8 * write_bw) (in single wb case)
1118 * or equally: x_intercept = wb_setpoint + 8 * write_bw
1120 * For single wb case, the dirty pages are observed to fluctuate
1121 * regularly within range
1122 * [wb_setpoint - write_bw/2, wb_setpoint + write_bw/2]
1123 * for various filesystems, where (2) can yield in a reasonable 12.5%
1124 * fluctuation range for pos_ratio.
1126 * For JBOD case, wb_thresh (not wb_dirty!) could fluctuate up to its
1127 * own size, so move the slope over accordingly and choose a slope that
1128 * yields 100% pos_ratio fluctuation on suddenly doubled wb_thresh.
1130 if (unlikely(wb_thresh
> dtc
->thresh
))
1131 wb_thresh
= dtc
->thresh
;
1133 * It's very possible that wb_thresh is close to 0 not because the
1134 * device is slow, but that it has remained inactive for long time.
1135 * Honour such devices a reasonable good (hopefully IO efficient)
1136 * threshold, so that the occasional writes won't be blocked and active
1137 * writes can rampup the threshold quickly.
1139 wb_thresh
= max(wb_thresh
, (limit
- dtc
->dirty
) / 8);
1141 * scale global setpoint to wb's:
1142 * wb_setpoint = setpoint * wb_thresh / thresh
1144 x
= div_u64((u64
)wb_thresh
<< 16, dtc
->thresh
| 1);
1145 wb_setpoint
= setpoint
* (u64
)x
>> 16;
1147 * Use span=(8*write_bw) in single wb case as indicated by
1148 * (thresh - wb_thresh ~= 0) and transit to wb_thresh in JBOD case.
1150 * wb_thresh thresh - wb_thresh
1151 * span = --------- * (8 * write_bw) + ------------------ * wb_thresh
1154 span
= (dtc
->thresh
- wb_thresh
+ 8 * write_bw
) * (u64
)x
>> 16;
1155 x_intercept
= wb_setpoint
+ span
;
1157 if (dtc
->wb_dirty
< x_intercept
- span
/ 4) {
1158 pos_ratio
= div64_u64(pos_ratio
* (x_intercept
- dtc
->wb_dirty
),
1159 (x_intercept
- wb_setpoint
) | 1);
1164 * wb reserve area, safeguard against dirty pool underrun and disk idle
1165 * It may push the desired control point of global dirty pages higher
1168 x_intercept
= wb_thresh
/ 2;
1169 if (dtc
->wb_dirty
< x_intercept
) {
1170 if (dtc
->wb_dirty
> x_intercept
/ 8)
1171 pos_ratio
= div_u64(pos_ratio
* x_intercept
,
1177 dtc
->pos_ratio
= pos_ratio
;
1180 static void wb_update_write_bandwidth(struct bdi_writeback
*wb
,
1181 unsigned long elapsed
,
1182 unsigned long written
)
1184 const unsigned long period
= roundup_pow_of_two(3 * HZ
);
1185 unsigned long avg
= wb
->avg_write_bandwidth
;
1186 unsigned long old
= wb
->write_bandwidth
;
1190 * bw = written * HZ / elapsed
1192 * bw * elapsed + write_bandwidth * (period - elapsed)
1193 * write_bandwidth = ---------------------------------------------------
1196 * @written may have decreased due to folio_redirty_for_writepage().
1197 * Avoid underflowing @bw calculation.
1199 bw
= written
- min(written
, wb
->written_stamp
);
1201 if (unlikely(elapsed
> period
)) {
1202 bw
= div64_ul(bw
, elapsed
);
1206 bw
+= (u64
)wb
->write_bandwidth
* (period
- elapsed
);
1207 bw
>>= ilog2(period
);
1210 * one more level of smoothing, for filtering out sudden spikes
1212 if (avg
> old
&& old
>= (unsigned long)bw
)
1213 avg
-= (avg
- old
) >> 3;
1215 if (avg
< old
&& old
<= (unsigned long)bw
)
1216 avg
+= (old
- avg
) >> 3;
1219 /* keep avg > 0 to guarantee that tot > 0 if there are dirty wbs */
1220 avg
= max(avg
, 1LU);
1221 if (wb_has_dirty_io(wb
)) {
1222 long delta
= avg
- wb
->avg_write_bandwidth
;
1223 WARN_ON_ONCE(atomic_long_add_return(delta
,
1224 &wb
->bdi
->tot_write_bandwidth
) <= 0);
1226 wb
->write_bandwidth
= bw
;
1227 WRITE_ONCE(wb
->avg_write_bandwidth
, avg
);
1230 static void update_dirty_limit(struct dirty_throttle_control
*dtc
)
1232 struct wb_domain
*dom
= dtc_dom(dtc
);
1233 unsigned long thresh
= dtc
->thresh
;
1234 unsigned long limit
= dom
->dirty_limit
;
1237 * Follow up in one step.
1239 if (limit
< thresh
) {
1245 * Follow down slowly. Use the higher one as the target, because thresh
1246 * may drop below dirty. This is exactly the reason to introduce
1247 * dom->dirty_limit which is guaranteed to lie above the dirty pages.
1249 thresh
= max(thresh
, dtc
->dirty
);
1250 if (limit
> thresh
) {
1251 limit
-= (limit
- thresh
) >> 5;
1256 dom
->dirty_limit
= limit
;
1259 static void domain_update_dirty_limit(struct dirty_throttle_control
*dtc
,
1262 struct wb_domain
*dom
= dtc_dom(dtc
);
1265 * check locklessly first to optimize away locking for the most time
1267 if (time_before(now
, dom
->dirty_limit_tstamp
+ BANDWIDTH_INTERVAL
))
1270 spin_lock(&dom
->lock
);
1271 if (time_after_eq(now
, dom
->dirty_limit_tstamp
+ BANDWIDTH_INTERVAL
)) {
1272 update_dirty_limit(dtc
);
1273 dom
->dirty_limit_tstamp
= now
;
1275 spin_unlock(&dom
->lock
);
1279 * Maintain wb->dirty_ratelimit, the base dirty throttle rate.
1281 * Normal wb tasks will be curbed at or below it in long term.
1282 * Obviously it should be around (write_bw / N) when there are N dd tasks.
1284 static void wb_update_dirty_ratelimit(struct dirty_throttle_control
*dtc
,
1285 unsigned long dirtied
,
1286 unsigned long elapsed
)
1288 struct bdi_writeback
*wb
= dtc
->wb
;
1289 unsigned long dirty
= dtc
->dirty
;
1290 unsigned long freerun
= dirty_freerun_ceiling(dtc
->thresh
, dtc
->bg_thresh
);
1291 unsigned long limit
= hard_dirty_limit(dtc_dom(dtc
), dtc
->thresh
);
1292 unsigned long setpoint
= (freerun
+ limit
) / 2;
1293 unsigned long write_bw
= wb
->avg_write_bandwidth
;
1294 unsigned long dirty_ratelimit
= wb
->dirty_ratelimit
;
1295 unsigned long dirty_rate
;
1296 unsigned long task_ratelimit
;
1297 unsigned long balanced_dirty_ratelimit
;
1300 unsigned long shift
;
1303 * The dirty rate will match the writeout rate in long term, except
1304 * when dirty pages are truncated by userspace or re-dirtied by FS.
1306 dirty_rate
= (dirtied
- wb
->dirtied_stamp
) * HZ
/ elapsed
;
1309 * task_ratelimit reflects each dd's dirty rate for the past 200ms.
1311 task_ratelimit
= (u64
)dirty_ratelimit
*
1312 dtc
->pos_ratio
>> RATELIMIT_CALC_SHIFT
;
1313 task_ratelimit
++; /* it helps rampup dirty_ratelimit from tiny values */
1316 * A linear estimation of the "balanced" throttle rate. The theory is,
1317 * if there are N dd tasks, each throttled at task_ratelimit, the wb's
1318 * dirty_rate will be measured to be (N * task_ratelimit). So the below
1319 * formula will yield the balanced rate limit (write_bw / N).
1321 * Note that the expanded form is not a pure rate feedback:
1322 * rate_(i+1) = rate_(i) * (write_bw / dirty_rate) (1)
1323 * but also takes pos_ratio into account:
1324 * rate_(i+1) = rate_(i) * (write_bw / dirty_rate) * pos_ratio (2)
1326 * (1) is not realistic because pos_ratio also takes part in balancing
1327 * the dirty rate. Consider the state
1328 * pos_ratio = 0.5 (3)
1329 * rate = 2 * (write_bw / N) (4)
1330 * If (1) is used, it will stuck in that state! Because each dd will
1332 * task_ratelimit = pos_ratio * rate = (write_bw / N) (5)
1334 * dirty_rate = N * task_ratelimit = write_bw (6)
1335 * put (6) into (1) we get
1336 * rate_(i+1) = rate_(i) (7)
1338 * So we end up using (2) to always keep
1339 * rate_(i+1) ~= (write_bw / N) (8)
1340 * regardless of the value of pos_ratio. As long as (8) is satisfied,
1341 * pos_ratio is able to drive itself to 1.0, which is not only where
1342 * the dirty count meet the setpoint, but also where the slope of
1343 * pos_ratio is most flat and hence task_ratelimit is least fluctuated.
1345 balanced_dirty_ratelimit
= div_u64((u64
)task_ratelimit
* write_bw
,
1348 * balanced_dirty_ratelimit ~= (write_bw / N) <= write_bw
1350 if (unlikely(balanced_dirty_ratelimit
> write_bw
))
1351 balanced_dirty_ratelimit
= write_bw
;
1354 * We could safely do this and return immediately:
1356 * wb->dirty_ratelimit = balanced_dirty_ratelimit;
1358 * However to get a more stable dirty_ratelimit, the below elaborated
1359 * code makes use of task_ratelimit to filter out singular points and
1360 * limit the step size.
1362 * The below code essentially only uses the relative value of
1364 * task_ratelimit - dirty_ratelimit
1365 * = (pos_ratio - 1) * dirty_ratelimit
1367 * which reflects the direction and size of dirty position error.
1371 * dirty_ratelimit will follow balanced_dirty_ratelimit iff
1372 * task_ratelimit is on the same side of dirty_ratelimit, too.
1374 * - dirty_ratelimit > balanced_dirty_ratelimit
1375 * - dirty_ratelimit > task_ratelimit (dirty pages are above setpoint)
1376 * lowering dirty_ratelimit will help meet both the position and rate
1377 * control targets. Otherwise, don't update dirty_ratelimit if it will
1378 * only help meet the rate target. After all, what the users ultimately
1379 * feel and care are stable dirty rate and small position error.
1381 * |task_ratelimit - dirty_ratelimit| is used to limit the step size
1382 * and filter out the singular points of balanced_dirty_ratelimit. Which
1383 * keeps jumping around randomly and can even leap far away at times
1384 * due to the small 200ms estimation period of dirty_rate (we want to
1385 * keep that period small to reduce time lags).
1390 * For strictlimit case, calculations above were based on wb counters
1391 * and limits (starting from pos_ratio = wb_position_ratio() and up to
1392 * balanced_dirty_ratelimit = task_ratelimit * write_bw / dirty_rate).
1393 * Hence, to calculate "step" properly, we have to use wb_dirty as
1394 * "dirty" and wb_setpoint as "setpoint".
1396 * We rampup dirty_ratelimit forcibly if wb_dirty is low because
1397 * it's possible that wb_thresh is close to zero due to inactivity
1398 * of backing device.
1400 if (unlikely(wb
->bdi
->capabilities
& BDI_CAP_STRICTLIMIT
)) {
1401 dirty
= dtc
->wb_dirty
;
1402 if (dtc
->wb_dirty
< 8)
1403 setpoint
= dtc
->wb_dirty
+ 1;
1405 setpoint
= (dtc
->wb_thresh
+ dtc
->wb_bg_thresh
) / 2;
1408 if (dirty
< setpoint
) {
1409 x
= min3(wb
->balanced_dirty_ratelimit
,
1410 balanced_dirty_ratelimit
, task_ratelimit
);
1411 if (dirty_ratelimit
< x
)
1412 step
= x
- dirty_ratelimit
;
1414 x
= max3(wb
->balanced_dirty_ratelimit
,
1415 balanced_dirty_ratelimit
, task_ratelimit
);
1416 if (dirty_ratelimit
> x
)
1417 step
= dirty_ratelimit
- x
;
1421 * Don't pursue 100% rate matching. It's impossible since the balanced
1422 * rate itself is constantly fluctuating. So decrease the track speed
1423 * when it gets close to the target. Helps eliminate pointless tremors.
1425 shift
= dirty_ratelimit
/ (2 * step
+ 1);
1426 if (shift
< BITS_PER_LONG
)
1427 step
= DIV_ROUND_UP(step
>> shift
, 8);
1431 if (dirty_ratelimit
< balanced_dirty_ratelimit
)
1432 dirty_ratelimit
+= step
;
1434 dirty_ratelimit
-= step
;
1436 WRITE_ONCE(wb
->dirty_ratelimit
, max(dirty_ratelimit
, 1UL));
1437 wb
->balanced_dirty_ratelimit
= balanced_dirty_ratelimit
;
1439 trace_bdi_dirty_ratelimit(wb
, dirty_rate
, task_ratelimit
);
1442 static void __wb_update_bandwidth(struct dirty_throttle_control
*gdtc
,
1443 struct dirty_throttle_control
*mdtc
,
1444 bool update_ratelimit
)
1446 struct bdi_writeback
*wb
= gdtc
->wb
;
1447 unsigned long now
= jiffies
;
1448 unsigned long elapsed
;
1449 unsigned long dirtied
;
1450 unsigned long written
;
1452 spin_lock(&wb
->list_lock
);
1455 * Lockless checks for elapsed time are racy and delayed update after
1456 * IO completion doesn't do it at all (to make sure written pages are
1457 * accounted reasonably quickly). Make sure elapsed >= 1 to avoid
1460 elapsed
= max(now
- wb
->bw_time_stamp
, 1UL);
1461 dirtied
= percpu_counter_read(&wb
->stat
[WB_DIRTIED
]);
1462 written
= percpu_counter_read(&wb
->stat
[WB_WRITTEN
]);
1464 if (update_ratelimit
) {
1465 domain_update_dirty_limit(gdtc
, now
);
1466 wb_update_dirty_ratelimit(gdtc
, dirtied
, elapsed
);
1469 * @mdtc is always NULL if !CGROUP_WRITEBACK but the
1470 * compiler has no way to figure that out. Help it.
1472 if (IS_ENABLED(CONFIG_CGROUP_WRITEBACK
) && mdtc
) {
1473 domain_update_dirty_limit(mdtc
, now
);
1474 wb_update_dirty_ratelimit(mdtc
, dirtied
, elapsed
);
1477 wb_update_write_bandwidth(wb
, elapsed
, written
);
1479 wb
->dirtied_stamp
= dirtied
;
1480 wb
->written_stamp
= written
;
1481 WRITE_ONCE(wb
->bw_time_stamp
, now
);
1482 spin_unlock(&wb
->list_lock
);
1485 void wb_update_bandwidth(struct bdi_writeback
*wb
)
1487 struct dirty_throttle_control gdtc
= { GDTC_INIT(wb
) };
1489 __wb_update_bandwidth(&gdtc
, NULL
, false);
1492 /* Interval after which we consider wb idle and don't estimate bandwidth */
1493 #define WB_BANDWIDTH_IDLE_JIF (HZ)
1495 static void wb_bandwidth_estimate_start(struct bdi_writeback
*wb
)
1497 unsigned long now
= jiffies
;
1498 unsigned long elapsed
= now
- READ_ONCE(wb
->bw_time_stamp
);
1500 if (elapsed
> WB_BANDWIDTH_IDLE_JIF
&&
1501 !atomic_read(&wb
->writeback_inodes
)) {
1502 spin_lock(&wb
->list_lock
);
1503 wb
->dirtied_stamp
= wb_stat(wb
, WB_DIRTIED
);
1504 wb
->written_stamp
= wb_stat(wb
, WB_WRITTEN
);
1505 WRITE_ONCE(wb
->bw_time_stamp
, now
);
1506 spin_unlock(&wb
->list_lock
);
1511 * After a task dirtied this many pages, balance_dirty_pages_ratelimited()
1512 * will look to see if it needs to start dirty throttling.
1514 * If dirty_poll_interval is too low, big NUMA machines will call the expensive
1515 * global_zone_page_state() too often. So scale it near-sqrt to the safety margin
1516 * (the number of pages we may dirty without exceeding the dirty limits).
1518 static unsigned long dirty_poll_interval(unsigned long dirty
,
1519 unsigned long thresh
)
1522 return 1UL << (ilog2(thresh
- dirty
) >> 1);
1527 static unsigned long wb_max_pause(struct bdi_writeback
*wb
,
1528 unsigned long wb_dirty
)
1530 unsigned long bw
= READ_ONCE(wb
->avg_write_bandwidth
);
1534 * Limit pause time for small memory systems. If sleeping for too long
1535 * time, a small pool of dirty/writeback pages may go empty and disk go
1538 * 8 serves as the safety ratio.
1540 t
= wb_dirty
/ (1 + bw
/ roundup_pow_of_two(1 + HZ
/ 8));
1543 return min_t(unsigned long, t
, MAX_PAUSE
);
1546 static long wb_min_pause(struct bdi_writeback
*wb
,
1548 unsigned long task_ratelimit
,
1549 unsigned long dirty_ratelimit
,
1550 int *nr_dirtied_pause
)
1552 long hi
= ilog2(READ_ONCE(wb
->avg_write_bandwidth
));
1553 long lo
= ilog2(READ_ONCE(wb
->dirty_ratelimit
));
1554 long t
; /* target pause */
1555 long pause
; /* estimated next pause */
1556 int pages
; /* target nr_dirtied_pause */
1558 /* target for 10ms pause on 1-dd case */
1559 t
= max(1, HZ
/ 100);
1562 * Scale up pause time for concurrent dirtiers in order to reduce CPU
1565 * (N * 10ms) on 2^N concurrent tasks.
1568 t
+= (hi
- lo
) * (10 * HZ
) / 1024;
1571 * This is a bit convoluted. We try to base the next nr_dirtied_pause
1572 * on the much more stable dirty_ratelimit. However the next pause time
1573 * will be computed based on task_ratelimit and the two rate limits may
1574 * depart considerably at some time. Especially if task_ratelimit goes
1575 * below dirty_ratelimit/2 and the target pause is max_pause, the next
1576 * pause time will be max_pause*2 _trimmed down_ to max_pause. As a
1577 * result task_ratelimit won't be executed faithfully, which could
1578 * eventually bring down dirty_ratelimit.
1580 * We apply two rules to fix it up:
1581 * 1) try to estimate the next pause time and if necessary, use a lower
1582 * nr_dirtied_pause so as not to exceed max_pause. When this happens,
1583 * nr_dirtied_pause will be "dancing" with task_ratelimit.
1584 * 2) limit the target pause time to max_pause/2, so that the normal
1585 * small fluctuations of task_ratelimit won't trigger rule (1) and
1586 * nr_dirtied_pause will remain as stable as dirty_ratelimit.
1588 t
= min(t
, 1 + max_pause
/ 2);
1589 pages
= dirty_ratelimit
* t
/ roundup_pow_of_two(HZ
);
1592 * Tiny nr_dirtied_pause is found to hurt I/O performance in the test
1593 * case fio-mmap-randwrite-64k, which does 16*{sync read, async write}.
1594 * When the 16 consecutive reads are often interrupted by some dirty
1595 * throttling pause during the async writes, cfq will go into idles
1596 * (deadline is fine). So push nr_dirtied_pause as high as possible
1597 * until reaches DIRTY_POLL_THRESH=32 pages.
1599 if (pages
< DIRTY_POLL_THRESH
) {
1601 pages
= dirty_ratelimit
* t
/ roundup_pow_of_two(HZ
);
1602 if (pages
> DIRTY_POLL_THRESH
) {
1603 pages
= DIRTY_POLL_THRESH
;
1604 t
= HZ
* DIRTY_POLL_THRESH
/ dirty_ratelimit
;
1608 pause
= HZ
* pages
/ (task_ratelimit
+ 1);
1609 if (pause
> max_pause
) {
1611 pages
= task_ratelimit
* t
/ roundup_pow_of_two(HZ
);
1614 *nr_dirtied_pause
= pages
;
1616 * The minimal pause time will normally be half the target pause time.
1618 return pages
>= DIRTY_POLL_THRESH
? 1 + t
/ 2 : t
;
1621 static inline void wb_dirty_limits(struct dirty_throttle_control
*dtc
)
1623 struct bdi_writeback
*wb
= dtc
->wb
;
1624 unsigned long wb_reclaimable
;
1627 * wb_thresh is not treated as some limiting factor as
1628 * dirty_thresh, due to reasons
1629 * - in JBOD setup, wb_thresh can fluctuate a lot
1630 * - in a system with HDD and USB key, the USB key may somehow
1631 * go into state (wb_dirty >> wb_thresh) either because
1632 * wb_dirty starts high, or because wb_thresh drops low.
1633 * In this case we don't want to hard throttle the USB key
1634 * dirtiers for 100 seconds until wb_dirty drops under
1635 * wb_thresh. Instead the auxiliary wb control line in
1636 * wb_position_ratio() will let the dirtier task progress
1637 * at some rate <= (write_bw / 2) for bringing down wb_dirty.
1639 dtc
->wb_thresh
= __wb_calc_thresh(dtc
);
1640 dtc
->wb_bg_thresh
= dtc
->thresh
?
1641 div64_u64(dtc
->wb_thresh
* dtc
->bg_thresh
, dtc
->thresh
) : 0;
1644 * In order to avoid the stacked BDI deadlock we need
1645 * to ensure we accurately count the 'dirty' pages when
1646 * the threshold is low.
1648 * Otherwise it would be possible to get thresh+n pages
1649 * reported dirty, even though there are thresh-m pages
1650 * actually dirty; with m+n sitting in the percpu
1653 if (dtc
->wb_thresh
< 2 * wb_stat_error()) {
1654 wb_reclaimable
= wb_stat_sum(wb
, WB_RECLAIMABLE
);
1655 dtc
->wb_dirty
= wb_reclaimable
+ wb_stat_sum(wb
, WB_WRITEBACK
);
1657 wb_reclaimable
= wb_stat(wb
, WB_RECLAIMABLE
);
1658 dtc
->wb_dirty
= wb_reclaimable
+ wb_stat(wb
, WB_WRITEBACK
);
1663 * balance_dirty_pages() must be called by processes which are generating dirty
1664 * data. It looks at the number of dirty pages in the machine and will force
1665 * the caller to wait once crossing the (background_thresh + dirty_thresh) / 2.
1666 * If we're over `background_thresh' then the writeback threads are woken to
1667 * perform some writeout.
1669 static int balance_dirty_pages(struct bdi_writeback
*wb
,
1670 unsigned long pages_dirtied
, unsigned int flags
)
1672 struct dirty_throttle_control gdtc_stor
= { GDTC_INIT(wb
) };
1673 struct dirty_throttle_control mdtc_stor
= { MDTC_INIT(wb
, &gdtc_stor
) };
1674 struct dirty_throttle_control
* const gdtc
= &gdtc_stor
;
1675 struct dirty_throttle_control
* const mdtc
= mdtc_valid(&mdtc_stor
) ?
1677 struct dirty_throttle_control
*sdtc
;
1678 unsigned long nr_reclaimable
; /* = file_dirty */
1683 int nr_dirtied_pause
;
1684 bool dirty_exceeded
= false;
1685 unsigned long task_ratelimit
;
1686 unsigned long dirty_ratelimit
;
1687 struct backing_dev_info
*bdi
= wb
->bdi
;
1688 bool strictlimit
= bdi
->capabilities
& BDI_CAP_STRICTLIMIT
;
1689 unsigned long start_time
= jiffies
;
1693 unsigned long now
= jiffies
;
1694 unsigned long dirty
, thresh
, bg_thresh
;
1695 unsigned long m_dirty
= 0; /* stop bogus uninit warnings */
1696 unsigned long m_thresh
= 0;
1697 unsigned long m_bg_thresh
= 0;
1699 nr_reclaimable
= global_node_page_state(NR_FILE_DIRTY
);
1700 gdtc
->avail
= global_dirtyable_memory();
1701 gdtc
->dirty
= nr_reclaimable
+ global_node_page_state(NR_WRITEBACK
);
1703 domain_dirty_limits(gdtc
);
1705 if (unlikely(strictlimit
)) {
1706 wb_dirty_limits(gdtc
);
1708 dirty
= gdtc
->wb_dirty
;
1709 thresh
= gdtc
->wb_thresh
;
1710 bg_thresh
= gdtc
->wb_bg_thresh
;
1712 dirty
= gdtc
->dirty
;
1713 thresh
= gdtc
->thresh
;
1714 bg_thresh
= gdtc
->bg_thresh
;
1718 unsigned long filepages
, headroom
, writeback
;
1721 * If @wb belongs to !root memcg, repeat the same
1722 * basic calculations for the memcg domain.
1724 mem_cgroup_wb_stats(wb
, &filepages
, &headroom
,
1725 &mdtc
->dirty
, &writeback
);
1726 mdtc
->dirty
+= writeback
;
1727 mdtc_calc_avail(mdtc
, filepages
, headroom
);
1729 domain_dirty_limits(mdtc
);
1731 if (unlikely(strictlimit
)) {
1732 wb_dirty_limits(mdtc
);
1733 m_dirty
= mdtc
->wb_dirty
;
1734 m_thresh
= mdtc
->wb_thresh
;
1735 m_bg_thresh
= mdtc
->wb_bg_thresh
;
1737 m_dirty
= mdtc
->dirty
;
1738 m_thresh
= mdtc
->thresh
;
1739 m_bg_thresh
= mdtc
->bg_thresh
;
1744 * In laptop mode, we wait until hitting the higher threshold
1745 * before starting background writeout, and then write out all
1746 * the way down to the lower threshold. So slow writers cause
1747 * minimal disk activity.
1749 * In normal mode, we start background writeout at the lower
1750 * background_thresh, to keep the amount of dirty memory low.
1752 if (!laptop_mode
&& nr_reclaimable
> gdtc
->bg_thresh
&&
1753 !writeback_in_progress(wb
))
1754 wb_start_background_writeback(wb
);
1757 * Throttle it only when the background writeback cannot
1758 * catch-up. This avoids (excessively) small writeouts
1759 * when the wb limits are ramping up in case of !strictlimit.
1761 * In strictlimit case make decision based on the wb counters
1762 * and limits. Small writeouts when the wb limits are ramping
1763 * up are the price we consciously pay for strictlimit-ing.
1765 * If memcg domain is in effect, @dirty should be under
1766 * both global and memcg freerun ceilings.
1768 if (dirty
<= dirty_freerun_ceiling(thresh
, bg_thresh
) &&
1770 m_dirty
<= dirty_freerun_ceiling(m_thresh
, m_bg_thresh
))) {
1772 unsigned long m_intv
;
1775 intv
= dirty_poll_interval(dirty
, thresh
);
1778 current
->dirty_paused_when
= now
;
1779 current
->nr_dirtied
= 0;
1781 m_intv
= dirty_poll_interval(m_dirty
, m_thresh
);
1782 current
->nr_dirtied_pause
= min(intv
, m_intv
);
1786 /* Start writeback even when in laptop mode */
1787 if (unlikely(!writeback_in_progress(wb
)))
1788 wb_start_background_writeback(wb
);
1790 mem_cgroup_flush_foreign(wb
);
1793 * Calculate global domain's pos_ratio and select the
1794 * global dtc by default.
1797 wb_dirty_limits(gdtc
);
1799 if ((current
->flags
& PF_LOCAL_THROTTLE
) &&
1801 dirty_freerun_ceiling(gdtc
->wb_thresh
,
1802 gdtc
->wb_bg_thresh
))
1804 * LOCAL_THROTTLE tasks must not be throttled
1805 * when below the per-wb freerun ceiling.
1810 dirty_exceeded
= (gdtc
->wb_dirty
> gdtc
->wb_thresh
) &&
1811 ((gdtc
->dirty
> gdtc
->thresh
) || strictlimit
);
1813 wb_position_ratio(gdtc
);
1818 * If memcg domain is in effect, calculate its
1819 * pos_ratio. @wb should satisfy constraints from
1820 * both global and memcg domains. Choose the one
1821 * w/ lower pos_ratio.
1824 wb_dirty_limits(mdtc
);
1826 if ((current
->flags
& PF_LOCAL_THROTTLE
) &&
1828 dirty_freerun_ceiling(mdtc
->wb_thresh
,
1829 mdtc
->wb_bg_thresh
))
1831 * LOCAL_THROTTLE tasks must not be
1832 * throttled when below the per-wb
1837 dirty_exceeded
|= (mdtc
->wb_dirty
> mdtc
->wb_thresh
) &&
1838 ((mdtc
->dirty
> mdtc
->thresh
) || strictlimit
);
1840 wb_position_ratio(mdtc
);
1841 if (mdtc
->pos_ratio
< gdtc
->pos_ratio
)
1845 if (dirty_exceeded
!= wb
->dirty_exceeded
)
1846 wb
->dirty_exceeded
= dirty_exceeded
;
1848 if (time_is_before_jiffies(READ_ONCE(wb
->bw_time_stamp
) +
1849 BANDWIDTH_INTERVAL
))
1850 __wb_update_bandwidth(gdtc
, mdtc
, true);
1852 /* throttle according to the chosen dtc */
1853 dirty_ratelimit
= READ_ONCE(wb
->dirty_ratelimit
);
1854 task_ratelimit
= ((u64
)dirty_ratelimit
* sdtc
->pos_ratio
) >>
1855 RATELIMIT_CALC_SHIFT
;
1856 max_pause
= wb_max_pause(wb
, sdtc
->wb_dirty
);
1857 min_pause
= wb_min_pause(wb
, max_pause
,
1858 task_ratelimit
, dirty_ratelimit
,
1861 if (unlikely(task_ratelimit
== 0)) {
1866 period
= HZ
* pages_dirtied
/ task_ratelimit
;
1868 if (current
->dirty_paused_when
)
1869 pause
-= now
- current
->dirty_paused_when
;
1871 * For less than 1s think time (ext3/4 may block the dirtier
1872 * for up to 800ms from time to time on 1-HDD; so does xfs,
1873 * however at much less frequency), try to compensate it in
1874 * future periods by updating the virtual time; otherwise just
1875 * do a reset, as it may be a light dirtier.
1877 if (pause
< min_pause
) {
1878 trace_balance_dirty_pages(wb
,
1891 current
->dirty_paused_when
= now
;
1892 current
->nr_dirtied
= 0;
1893 } else if (period
) {
1894 current
->dirty_paused_when
+= period
;
1895 current
->nr_dirtied
= 0;
1896 } else if (current
->nr_dirtied_pause
<= pages_dirtied
)
1897 current
->nr_dirtied_pause
+= pages_dirtied
;
1900 if (unlikely(pause
> max_pause
)) {
1901 /* for occasional dropped task_ratelimit */
1902 now
+= min(pause
- max_pause
, max_pause
);
1907 trace_balance_dirty_pages(wb
,
1919 if (flags
& BDP_ASYNC
) {
1923 __set_current_state(TASK_KILLABLE
);
1924 wb
->dirty_sleep
= now
;
1925 io_schedule_timeout(pause
);
1927 current
->dirty_paused_when
= now
+ pause
;
1928 current
->nr_dirtied
= 0;
1929 current
->nr_dirtied_pause
= nr_dirtied_pause
;
1932 * This is typically equal to (dirty < thresh) and can also
1933 * keep "1000+ dd on a slow USB stick" under control.
1939 * In the case of an unresponsive NFS server and the NFS dirty
1940 * pages exceeds dirty_thresh, give the other good wb's a pipe
1941 * to go through, so that tasks on them still remain responsive.
1943 * In theory 1 page is enough to keep the consumer-producer
1944 * pipe going: the flusher cleans 1 page => the task dirties 1
1945 * more page. However wb_dirty has accounting errors. So use
1946 * the larger and more IO friendly wb_stat_error.
1948 if (sdtc
->wb_dirty
<= wb_stat_error())
1951 if (fatal_signal_pending(current
))
1957 static DEFINE_PER_CPU(int, bdp_ratelimits
);
1960 * Normal tasks are throttled by
1962 * dirty tsk->nr_dirtied_pause pages;
1963 * take a snap in balance_dirty_pages();
1965 * However there is a worst case. If every task exit immediately when dirtied
1966 * (tsk->nr_dirtied_pause - 1) pages, balance_dirty_pages() will never be
1967 * called to throttle the page dirties. The solution is to save the not yet
1968 * throttled page dirties in dirty_throttle_leaks on task exit and charge them
1969 * randomly into the running tasks. This works well for the above worst case,
1970 * as the new task will pick up and accumulate the old task's leaked dirty
1971 * count and eventually get throttled.
1973 DEFINE_PER_CPU(int, dirty_throttle_leaks
) = 0;
1976 * balance_dirty_pages_ratelimited_flags - Balance dirty memory state.
1977 * @mapping: address_space which was dirtied.
1978 * @flags: BDP flags.
1980 * Processes which are dirtying memory should call in here once for each page
1981 * which was newly dirtied. The function will periodically check the system's
1982 * dirty state and will initiate writeback if needed.
1984 * See balance_dirty_pages_ratelimited() for details.
1986 * Return: If @flags contains BDP_ASYNC, it may return -EAGAIN to
1987 * indicate that memory is out of balance and the caller must wait
1988 * for I/O to complete. Otherwise, it will return 0 to indicate
1989 * that either memory was already in balance, or it was able to sleep
1990 * until the amount of dirty memory returned to balance.
1992 int balance_dirty_pages_ratelimited_flags(struct address_space
*mapping
,
1995 struct inode
*inode
= mapping
->host
;
1996 struct backing_dev_info
*bdi
= inode_to_bdi(inode
);
1997 struct bdi_writeback
*wb
= NULL
;
2002 if (!(bdi
->capabilities
& BDI_CAP_WRITEBACK
))
2005 if (inode_cgwb_enabled(inode
))
2006 wb
= wb_get_create_current(bdi
, GFP_KERNEL
);
2010 ratelimit
= current
->nr_dirtied_pause
;
2011 if (wb
->dirty_exceeded
)
2012 ratelimit
= min(ratelimit
, 32 >> (PAGE_SHIFT
- 10));
2016 * This prevents one CPU to accumulate too many dirtied pages without
2017 * calling into balance_dirty_pages(), which can happen when there are
2018 * 1000+ tasks, all of them start dirtying pages at exactly the same
2019 * time, hence all honoured too large initial task->nr_dirtied_pause.
2021 p
= this_cpu_ptr(&bdp_ratelimits
);
2022 if (unlikely(current
->nr_dirtied
>= ratelimit
))
2024 else if (unlikely(*p
>= ratelimit_pages
)) {
2029 * Pick up the dirtied pages by the exited tasks. This avoids lots of
2030 * short-lived tasks (eg. gcc invocations in a kernel build) escaping
2031 * the dirty throttling and livelock other long-run dirtiers.
2033 p
= this_cpu_ptr(&dirty_throttle_leaks
);
2034 if (*p
> 0 && current
->nr_dirtied
< ratelimit
) {
2035 unsigned long nr_pages_dirtied
;
2036 nr_pages_dirtied
= min(*p
, ratelimit
- current
->nr_dirtied
);
2037 *p
-= nr_pages_dirtied
;
2038 current
->nr_dirtied
+= nr_pages_dirtied
;
2042 if (unlikely(current
->nr_dirtied
>= ratelimit
))
2043 ret
= balance_dirty_pages(wb
, current
->nr_dirtied
, flags
);
2048 EXPORT_SYMBOL_GPL(balance_dirty_pages_ratelimited_flags
);
2051 * balance_dirty_pages_ratelimited - balance dirty memory state.
2052 * @mapping: address_space which was dirtied.
2054 * Processes which are dirtying memory should call in here once for each page
2055 * which was newly dirtied. The function will periodically check the system's
2056 * dirty state and will initiate writeback if needed.
2058 * Once we're over the dirty memory limit we decrease the ratelimiting
2059 * by a lot, to prevent individual processes from overshooting the limit
2060 * by (ratelimit_pages) each.
2062 void balance_dirty_pages_ratelimited(struct address_space
*mapping
)
2064 balance_dirty_pages_ratelimited_flags(mapping
, 0);
2066 EXPORT_SYMBOL(balance_dirty_pages_ratelimited
);
2069 * wb_over_bg_thresh - does @wb need to be written back?
2070 * @wb: bdi_writeback of interest
2072 * Determines whether background writeback should keep writing @wb or it's
2075 * Return: %true if writeback should continue.
2077 bool wb_over_bg_thresh(struct bdi_writeback
*wb
)
2079 struct dirty_throttle_control gdtc_stor
= { GDTC_INIT(wb
) };
2080 struct dirty_throttle_control mdtc_stor
= { MDTC_INIT(wb
, &gdtc_stor
) };
2081 struct dirty_throttle_control
* const gdtc
= &gdtc_stor
;
2082 struct dirty_throttle_control
* const mdtc
= mdtc_valid(&mdtc_stor
) ?
2084 unsigned long reclaimable
;
2085 unsigned long thresh
;
2088 * Similar to balance_dirty_pages() but ignores pages being written
2089 * as we're trying to decide whether to put more under writeback.
2091 gdtc
->avail
= global_dirtyable_memory();
2092 gdtc
->dirty
= global_node_page_state(NR_FILE_DIRTY
);
2093 domain_dirty_limits(gdtc
);
2095 if (gdtc
->dirty
> gdtc
->bg_thresh
)
2098 thresh
= wb_calc_thresh(gdtc
->wb
, gdtc
->bg_thresh
);
2099 if (thresh
< 2 * wb_stat_error())
2100 reclaimable
= wb_stat_sum(wb
, WB_RECLAIMABLE
);
2102 reclaimable
= wb_stat(wb
, WB_RECLAIMABLE
);
2104 if (reclaimable
> thresh
)
2108 unsigned long filepages
, headroom
, writeback
;
2110 mem_cgroup_wb_stats(wb
, &filepages
, &headroom
, &mdtc
->dirty
,
2112 mdtc_calc_avail(mdtc
, filepages
, headroom
);
2113 domain_dirty_limits(mdtc
); /* ditto, ignore writeback */
2115 if (mdtc
->dirty
> mdtc
->bg_thresh
)
2118 thresh
= wb_calc_thresh(mdtc
->wb
, mdtc
->bg_thresh
);
2119 if (thresh
< 2 * wb_stat_error())
2120 reclaimable
= wb_stat_sum(wb
, WB_RECLAIMABLE
);
2122 reclaimable
= wb_stat(wb
, WB_RECLAIMABLE
);
2124 if (reclaimable
> thresh
)
2131 #ifdef CONFIG_SYSCTL
2133 * sysctl handler for /proc/sys/vm/dirty_writeback_centisecs
2135 static int dirty_writeback_centisecs_handler(struct ctl_table
*table
, int write
,
2136 void *buffer
, size_t *length
, loff_t
*ppos
)
2138 unsigned int old_interval
= dirty_writeback_interval
;
2141 ret
= proc_dointvec(table
, write
, buffer
, length
, ppos
);
2144 * Writing 0 to dirty_writeback_interval will disable periodic writeback
2145 * and a different non-zero value will wakeup the writeback threads.
2146 * wb_wakeup_delayed() would be more appropriate, but it's a pain to
2147 * iterate over all bdis and wbs.
2148 * The reason we do this is to make the change take effect immediately.
2150 if (!ret
&& write
&& dirty_writeback_interval
&&
2151 dirty_writeback_interval
!= old_interval
)
2152 wakeup_flusher_threads(WB_REASON_PERIODIC
);
2158 void laptop_mode_timer_fn(struct timer_list
*t
)
2160 struct backing_dev_info
*backing_dev_info
=
2161 from_timer(backing_dev_info
, t
, laptop_mode_wb_timer
);
2163 wakeup_flusher_threads_bdi(backing_dev_info
, WB_REASON_LAPTOP_TIMER
);
2167 * We've spun up the disk and we're in laptop mode: schedule writeback
2168 * of all dirty data a few seconds from now. If the flush is already scheduled
2169 * then push it back - the user is still using the disk.
2171 void laptop_io_completion(struct backing_dev_info
*info
)
2173 mod_timer(&info
->laptop_mode_wb_timer
, jiffies
+ laptop_mode
);
2177 * We're in laptop mode and we've just synced. The sync's writes will have
2178 * caused another writeback to be scheduled by laptop_io_completion.
2179 * Nothing needs to be written back anymore, so we unschedule the writeback.
2181 void laptop_sync_completion(void)
2183 struct backing_dev_info
*bdi
;
2187 list_for_each_entry_rcu(bdi
, &bdi_list
, bdi_list
)
2188 del_timer(&bdi
->laptop_mode_wb_timer
);
2194 * If ratelimit_pages is too high then we can get into dirty-data overload
2195 * if a large number of processes all perform writes at the same time.
2197 * Here we set ratelimit_pages to a level which ensures that when all CPUs are
2198 * dirtying in parallel, we cannot go more than 3% (1/32) over the dirty memory
2202 void writeback_set_ratelimit(void)
2204 struct wb_domain
*dom
= &global_wb_domain
;
2205 unsigned long background_thresh
;
2206 unsigned long dirty_thresh
;
2208 global_dirty_limits(&background_thresh
, &dirty_thresh
);
2209 dom
->dirty_limit
= dirty_thresh
;
2210 ratelimit_pages
= dirty_thresh
/ (num_online_cpus() * 32);
2211 if (ratelimit_pages
< 16)
2212 ratelimit_pages
= 16;
2215 static int page_writeback_cpu_online(unsigned int cpu
)
2217 writeback_set_ratelimit();
2221 #ifdef CONFIG_SYSCTL
2223 /* this is needed for the proc_doulongvec_minmax of vm_dirty_bytes */
2224 static const unsigned long dirty_bytes_min
= 2 * PAGE_SIZE
;
2226 static struct ctl_table vm_page_writeback_sysctls
[] = {
2228 .procname
= "dirty_background_ratio",
2229 .data
= &dirty_background_ratio
,
2230 .maxlen
= sizeof(dirty_background_ratio
),
2232 .proc_handler
= dirty_background_ratio_handler
,
2233 .extra1
= SYSCTL_ZERO
,
2234 .extra2
= SYSCTL_ONE_HUNDRED
,
2237 .procname
= "dirty_background_bytes",
2238 .data
= &dirty_background_bytes
,
2239 .maxlen
= sizeof(dirty_background_bytes
),
2241 .proc_handler
= dirty_background_bytes_handler
,
2242 .extra1
= SYSCTL_LONG_ONE
,
2245 .procname
= "dirty_ratio",
2246 .data
= &vm_dirty_ratio
,
2247 .maxlen
= sizeof(vm_dirty_ratio
),
2249 .proc_handler
= dirty_ratio_handler
,
2250 .extra1
= SYSCTL_ZERO
,
2251 .extra2
= SYSCTL_ONE_HUNDRED
,
2254 .procname
= "dirty_bytes",
2255 .data
= &vm_dirty_bytes
,
2256 .maxlen
= sizeof(vm_dirty_bytes
),
2258 .proc_handler
= dirty_bytes_handler
,
2259 .extra1
= (void *)&dirty_bytes_min
,
2262 .procname
= "dirty_writeback_centisecs",
2263 .data
= &dirty_writeback_interval
,
2264 .maxlen
= sizeof(dirty_writeback_interval
),
2266 .proc_handler
= dirty_writeback_centisecs_handler
,
2269 .procname
= "dirty_expire_centisecs",
2270 .data
= &dirty_expire_interval
,
2271 .maxlen
= sizeof(dirty_expire_interval
),
2273 .proc_handler
= proc_dointvec_minmax
,
2274 .extra1
= SYSCTL_ZERO
,
2276 #ifdef CONFIG_HIGHMEM
2278 .procname
= "highmem_is_dirtyable",
2279 .data
= &vm_highmem_is_dirtyable
,
2280 .maxlen
= sizeof(vm_highmem_is_dirtyable
),
2282 .proc_handler
= proc_dointvec_minmax
,
2283 .extra1
= SYSCTL_ZERO
,
2284 .extra2
= SYSCTL_ONE
,
2288 .procname
= "laptop_mode",
2289 .data
= &laptop_mode
,
2290 .maxlen
= sizeof(laptop_mode
),
2292 .proc_handler
= proc_dointvec_jiffies
,
2299 * Called early on to tune the page writeback dirty limits.
2301 * We used to scale dirty pages according to how total memory
2302 * related to pages that could be allocated for buffers.
2304 * However, that was when we used "dirty_ratio" to scale with
2305 * all memory, and we don't do that any more. "dirty_ratio"
2306 * is now applied to total non-HIGHPAGE memory, and as such we can't
2307 * get into the old insane situation any more where we had
2308 * large amounts of dirty pages compared to a small amount of
2309 * non-HIGHMEM memory.
2311 * But we might still want to scale the dirty_ratio by how
2312 * much memory the box has..
2314 void __init
page_writeback_init(void)
2316 BUG_ON(wb_domain_init(&global_wb_domain
, GFP_KERNEL
));
2318 cpuhp_setup_state(CPUHP_AP_ONLINE_DYN
, "mm/writeback:online",
2319 page_writeback_cpu_online
, NULL
);
2320 cpuhp_setup_state(CPUHP_MM_WRITEBACK_DEAD
, "mm/writeback:dead", NULL
,
2321 page_writeback_cpu_online
);
2322 #ifdef CONFIG_SYSCTL
2323 register_sysctl_init("vm", vm_page_writeback_sysctls
);
2328 * tag_pages_for_writeback - tag pages to be written by write_cache_pages
2329 * @mapping: address space structure to write
2330 * @start: starting page index
2331 * @end: ending page index (inclusive)
2333 * This function scans the page range from @start to @end (inclusive) and tags
2334 * all pages that have DIRTY tag set with a special TOWRITE tag. The idea is
2335 * that write_cache_pages (or whoever calls this function) will then use
2336 * TOWRITE tag to identify pages eligible for writeback. This mechanism is
2337 * used to avoid livelocking of writeback by a process steadily creating new
2338 * dirty pages in the file (thus it is important for this function to be quick
2339 * so that it can tag pages faster than a dirtying process can create them).
2341 void tag_pages_for_writeback(struct address_space
*mapping
,
2342 pgoff_t start
, pgoff_t end
)
2344 XA_STATE(xas
, &mapping
->i_pages
, start
);
2345 unsigned int tagged
= 0;
2349 xas_for_each_marked(&xas
, page
, end
, PAGECACHE_TAG_DIRTY
) {
2350 xas_set_mark(&xas
, PAGECACHE_TAG_TOWRITE
);
2351 if (++tagged
% XA_CHECK_SCHED
)
2355 xas_unlock_irq(&xas
);
2359 xas_unlock_irq(&xas
);
2361 EXPORT_SYMBOL(tag_pages_for_writeback
);
2364 * write_cache_pages - walk the list of dirty pages of the given address space and write all of them.
2365 * @mapping: address space structure to write
2366 * @wbc: subtract the number of written pages from *@wbc->nr_to_write
2367 * @writepage: function called for each page
2368 * @data: data passed to writepage function
2370 * If a page is already under I/O, write_cache_pages() skips it, even
2371 * if it's dirty. This is desirable behaviour for memory-cleaning writeback,
2372 * but it is INCORRECT for data-integrity system calls such as fsync(). fsync()
2373 * and msync() need to guarantee that all the data which was dirty at the time
2374 * the call was made get new I/O started against them. If wbc->sync_mode is
2375 * WB_SYNC_ALL then we were called for data integrity and we must wait for
2376 * existing IO to complete.
2378 * To avoid livelocks (when other process dirties new pages), we first tag
2379 * pages which should be written back with TOWRITE tag and only then start
2380 * writing them. For data-integrity sync we have to be careful so that we do
2381 * not miss some pages (e.g., because some other process has cleared TOWRITE
2382 * tag we set). The rule we follow is that TOWRITE tag can be cleared only
2383 * by the process clearing the DIRTY tag (and submitting the page for IO).
2385 * To avoid deadlocks between range_cyclic writeback and callers that hold
2386 * pages in PageWriteback to aggregate IO until write_cache_pages() returns,
2387 * we do not loop back to the start of the file. Doing so causes a page
2388 * lock/page writeback access order inversion - we should only ever lock
2389 * multiple pages in ascending page->index order, and looping back to the start
2390 * of the file violates that rule and causes deadlocks.
2392 * Return: %0 on success, negative error code otherwise
2394 int write_cache_pages(struct address_space
*mapping
,
2395 struct writeback_control
*wbc
, writepage_t writepage
,
2401 struct folio_batch fbatch
;
2404 pgoff_t end
; /* Inclusive */
2406 int range_whole
= 0;
2409 folio_batch_init(&fbatch
);
2410 if (wbc
->range_cyclic
) {
2411 index
= mapping
->writeback_index
; /* prev offset */
2414 index
= wbc
->range_start
>> PAGE_SHIFT
;
2415 end
= wbc
->range_end
>> PAGE_SHIFT
;
2416 if (wbc
->range_start
== 0 && wbc
->range_end
== LLONG_MAX
)
2419 if (wbc
->sync_mode
== WB_SYNC_ALL
|| wbc
->tagged_writepages
) {
2420 tag_pages_for_writeback(mapping
, index
, end
);
2421 tag
= PAGECACHE_TAG_TOWRITE
;
2423 tag
= PAGECACHE_TAG_DIRTY
;
2426 while (!done
&& (index
<= end
)) {
2429 nr_folios
= filemap_get_folios_tag(mapping
, &index
, end
,
2435 for (i
= 0; i
< nr_folios
; i
++) {
2436 struct folio
*folio
= fbatch
.folios
[i
];
2439 done_index
= folio
->index
;
2444 * Page truncated or invalidated. We can freely skip it
2445 * then, even for data integrity operations: the page
2446 * has disappeared concurrently, so there could be no
2447 * real expectation of this data integrity operation
2448 * even if there is now a new, dirty page at the same
2449 * pagecache address.
2451 if (unlikely(folio
->mapping
!= mapping
)) {
2453 folio_unlock(folio
);
2457 if (!folio_test_dirty(folio
)) {
2458 /* someone wrote it for us */
2459 goto continue_unlock
;
2462 if (folio_test_writeback(folio
)) {
2463 if (wbc
->sync_mode
!= WB_SYNC_NONE
)
2464 folio_wait_writeback(folio
);
2466 goto continue_unlock
;
2469 BUG_ON(folio_test_writeback(folio
));
2470 if (!folio_clear_dirty_for_io(folio
))
2471 goto continue_unlock
;
2473 trace_wbc_writepage(wbc
, inode_to_bdi(mapping
->host
));
2474 error
= writepage(folio
, wbc
, data
);
2475 nr
= folio_nr_pages(folio
);
2476 if (unlikely(error
)) {
2478 * Handle errors according to the type of
2479 * writeback. There's no need to continue for
2480 * background writeback. Just push done_index
2481 * past this page so media errors won't choke
2482 * writeout for the entire file. For integrity
2483 * writeback, we must process the entire dirty
2484 * set regardless of errors because the fs may
2485 * still have state to clear for each page. In
2486 * that case we continue processing and return
2489 if (error
== AOP_WRITEPAGE_ACTIVATE
) {
2490 folio_unlock(folio
);
2492 } else if (wbc
->sync_mode
!= WB_SYNC_ALL
) {
2494 done_index
= folio
->index
+ nr
;
2503 * We stop writing back only if we are not doing
2504 * integrity sync. In case of integrity sync we have to
2505 * keep going until we have written all the pages
2506 * we tagged for writeback prior to entering this loop.
2508 wbc
->nr_to_write
-= nr
;
2509 if (wbc
->nr_to_write
<= 0 &&
2510 wbc
->sync_mode
== WB_SYNC_NONE
) {
2515 folio_batch_release(&fbatch
);
2520 * If we hit the last page and there is more work to be done: wrap
2521 * back the index back to the start of the file for the next
2522 * time we are called.
2524 if (wbc
->range_cyclic
&& !done
)
2526 if (wbc
->range_cyclic
|| (range_whole
&& wbc
->nr_to_write
> 0))
2527 mapping
->writeback_index
= done_index
;
2531 EXPORT_SYMBOL(write_cache_pages
);
2533 static int writepage_cb(struct folio
*folio
, struct writeback_control
*wbc
,
2536 struct address_space
*mapping
= data
;
2537 int ret
= mapping
->a_ops
->writepage(&folio
->page
, wbc
);
2538 mapping_set_error(mapping
, ret
);
2542 int do_writepages(struct address_space
*mapping
, struct writeback_control
*wbc
)
2545 struct bdi_writeback
*wb
;
2547 if (wbc
->nr_to_write
<= 0)
2549 wb
= inode_to_wb_wbc(mapping
->host
, wbc
);
2550 wb_bandwidth_estimate_start(wb
);
2552 if (mapping
->a_ops
->writepages
) {
2553 ret
= mapping
->a_ops
->writepages(mapping
, wbc
);
2554 } else if (mapping
->a_ops
->writepage
) {
2555 struct blk_plug plug
;
2557 blk_start_plug(&plug
);
2558 ret
= write_cache_pages(mapping
, wbc
, writepage_cb
,
2560 blk_finish_plug(&plug
);
2562 /* deal with chardevs and other special files */
2565 if (ret
!= -ENOMEM
|| wbc
->sync_mode
!= WB_SYNC_ALL
)
2569 * Lacking an allocation context or the locality or writeback
2570 * state of any of the inode's pages, throttle based on
2571 * writeback activity on the local node. It's as good a
2574 reclaim_throttle(NODE_DATA(numa_node_id()),
2575 VMSCAN_THROTTLE_WRITEBACK
);
2578 * Usually few pages are written by now from those we've just submitted
2579 * but if there's constant writeback being submitted, this makes sure
2580 * writeback bandwidth is updated once in a while.
2582 if (time_is_before_jiffies(READ_ONCE(wb
->bw_time_stamp
) +
2583 BANDWIDTH_INTERVAL
))
2584 wb_update_bandwidth(wb
);
2589 * For address_spaces which do not use buffers nor write back.
2591 bool noop_dirty_folio(struct address_space
*mapping
, struct folio
*folio
)
2593 if (!folio_test_dirty(folio
))
2594 return !folio_test_set_dirty(folio
);
2597 EXPORT_SYMBOL(noop_dirty_folio
);
2600 * Helper function for set_page_dirty family.
2602 * Caller must hold folio_memcg_lock().
2604 * NOTE: This relies on being atomic wrt interrupts.
2606 static void folio_account_dirtied(struct folio
*folio
,
2607 struct address_space
*mapping
)
2609 struct inode
*inode
= mapping
->host
;
2611 trace_writeback_dirty_folio(folio
, mapping
);
2613 if (mapping_can_writeback(mapping
)) {
2614 struct bdi_writeback
*wb
;
2615 long nr
= folio_nr_pages(folio
);
2617 inode_attach_wb(inode
, folio
);
2618 wb
= inode_to_wb(inode
);
2620 __lruvec_stat_mod_folio(folio
, NR_FILE_DIRTY
, nr
);
2621 __zone_stat_mod_folio(folio
, NR_ZONE_WRITE_PENDING
, nr
);
2622 __node_stat_mod_folio(folio
, NR_DIRTIED
, nr
);
2623 wb_stat_mod(wb
, WB_RECLAIMABLE
, nr
);
2624 wb_stat_mod(wb
, WB_DIRTIED
, nr
);
2625 task_io_account_write(nr
* PAGE_SIZE
);
2626 current
->nr_dirtied
+= nr
;
2627 __this_cpu_add(bdp_ratelimits
, nr
);
2629 mem_cgroup_track_foreign_dirty(folio
, wb
);
2634 * Helper function for deaccounting dirty page without writeback.
2636 * Caller must hold folio_memcg_lock().
2638 void folio_account_cleaned(struct folio
*folio
, struct bdi_writeback
*wb
)
2640 long nr
= folio_nr_pages(folio
);
2642 lruvec_stat_mod_folio(folio
, NR_FILE_DIRTY
, -nr
);
2643 zone_stat_mod_folio(folio
, NR_ZONE_WRITE_PENDING
, -nr
);
2644 wb_stat_mod(wb
, WB_RECLAIMABLE
, -nr
);
2645 task_io_account_cancelled_write(nr
* PAGE_SIZE
);
2649 * Mark the folio dirty, and set it dirty in the page cache, and mark
2652 * If warn is true, then emit a warning if the folio is not uptodate and has
2653 * not been truncated.
2655 * The caller must hold folio_memcg_lock(). Most callers have the folio
2656 * locked. A few have the folio blocked from truncation through other
2657 * means (eg zap_vma_pages() has it mapped and is holding the page table
2658 * lock). This can also be called from mark_buffer_dirty(), which I
2659 * cannot prove is always protected against truncate.
2661 void __folio_mark_dirty(struct folio
*folio
, struct address_space
*mapping
,
2664 unsigned long flags
;
2666 xa_lock_irqsave(&mapping
->i_pages
, flags
);
2667 if (folio
->mapping
) { /* Race with truncate? */
2668 WARN_ON_ONCE(warn
&& !folio_test_uptodate(folio
));
2669 folio_account_dirtied(folio
, mapping
);
2670 __xa_set_mark(&mapping
->i_pages
, folio_index(folio
),
2671 PAGECACHE_TAG_DIRTY
);
2673 xa_unlock_irqrestore(&mapping
->i_pages
, flags
);
2677 * filemap_dirty_folio - Mark a folio dirty for filesystems which do not use buffer_heads.
2678 * @mapping: Address space this folio belongs to.
2679 * @folio: Folio to be marked as dirty.
2681 * Filesystems which do not use buffer heads should call this function
2682 * from their dirty_folio address space operation. It ignores the
2683 * contents of folio_get_private(), so if the filesystem marks individual
2684 * blocks as dirty, the filesystem should handle that itself.
2686 * This is also sometimes used by filesystems which use buffer_heads when
2687 * a single buffer is being dirtied: we want to set the folio dirty in
2688 * that case, but not all the buffers. This is a "bottom-up" dirtying,
2689 * whereas block_dirty_folio() is a "top-down" dirtying.
2691 * The caller must ensure this doesn't race with truncation. Most will
2692 * simply hold the folio lock, but e.g. zap_pte_range() calls with the
2693 * folio mapped and the pte lock held, which also locks out truncation.
2695 bool filemap_dirty_folio(struct address_space
*mapping
, struct folio
*folio
)
2697 folio_memcg_lock(folio
);
2698 if (folio_test_set_dirty(folio
)) {
2699 folio_memcg_unlock(folio
);
2703 __folio_mark_dirty(folio
, mapping
, !folio_test_private(folio
));
2704 folio_memcg_unlock(folio
);
2706 if (mapping
->host
) {
2707 /* !PageAnon && !swapper_space */
2708 __mark_inode_dirty(mapping
->host
, I_DIRTY_PAGES
);
2712 EXPORT_SYMBOL(filemap_dirty_folio
);
2715 * folio_redirty_for_writepage - Decline to write a dirty folio.
2716 * @wbc: The writeback control.
2717 * @folio: The folio.
2719 * When a writepage implementation decides that it doesn't want to write
2720 * @folio for some reason, it should call this function, unlock @folio and
2723 * Return: True if we redirtied the folio. False if someone else dirtied
2726 bool folio_redirty_for_writepage(struct writeback_control
*wbc
,
2727 struct folio
*folio
)
2729 struct address_space
*mapping
= folio
->mapping
;
2730 long nr
= folio_nr_pages(folio
);
2733 wbc
->pages_skipped
+= nr
;
2734 ret
= filemap_dirty_folio(mapping
, folio
);
2735 if (mapping
&& mapping_can_writeback(mapping
)) {
2736 struct inode
*inode
= mapping
->host
;
2737 struct bdi_writeback
*wb
;
2738 struct wb_lock_cookie cookie
= {};
2740 wb
= unlocked_inode_to_wb_begin(inode
, &cookie
);
2741 current
->nr_dirtied
-= nr
;
2742 node_stat_mod_folio(folio
, NR_DIRTIED
, -nr
);
2743 wb_stat_mod(wb
, WB_DIRTIED
, -nr
);
2744 unlocked_inode_to_wb_end(inode
, &cookie
);
2748 EXPORT_SYMBOL(folio_redirty_for_writepage
);
2751 * folio_mark_dirty - Mark a folio as being modified.
2752 * @folio: The folio.
2754 * The folio may not be truncated while this function is running.
2755 * Holding the folio lock is sufficient to prevent truncation, but some
2756 * callers cannot acquire a sleeping lock. These callers instead hold
2757 * the page table lock for a page table which contains at least one page
2758 * in this folio. Truncation will block on the page table lock as it
2759 * unmaps pages before removing the folio from its mapping.
2761 * Return: True if the folio was newly dirtied, false if it was already dirty.
2763 bool folio_mark_dirty(struct folio
*folio
)
2765 struct address_space
*mapping
= folio_mapping(folio
);
2767 if (likely(mapping
)) {
2769 * readahead/folio_deactivate could remain
2770 * PG_readahead/PG_reclaim due to race with folio_end_writeback
2771 * About readahead, if the folio is written, the flags would be
2772 * reset. So no problem.
2773 * About folio_deactivate, if the folio is redirtied,
2774 * the flag will be reset. So no problem. but if the
2775 * folio is used by readahead it will confuse readahead
2776 * and make it restart the size rampup process. But it's
2777 * a trivial problem.
2779 if (folio_test_reclaim(folio
))
2780 folio_clear_reclaim(folio
);
2781 return mapping
->a_ops
->dirty_folio(mapping
, folio
);
2784 return noop_dirty_folio(mapping
, folio
);
2786 EXPORT_SYMBOL(folio_mark_dirty
);
2789 * set_page_dirty() is racy if the caller has no reference against
2790 * page->mapping->host, and if the page is unlocked. This is because another
2791 * CPU could truncate the page off the mapping and then free the mapping.
2793 * Usually, the page _is_ locked, or the caller is a user-space process which
2794 * holds a reference on the inode by having an open file.
2796 * In other cases, the page should be locked before running set_page_dirty().
2798 int set_page_dirty_lock(struct page
*page
)
2803 ret
= set_page_dirty(page
);
2807 EXPORT_SYMBOL(set_page_dirty_lock
);
2810 * This cancels just the dirty bit on the kernel page itself, it does NOT
2811 * actually remove dirty bits on any mmap's that may be around. It also
2812 * leaves the page tagged dirty, so any sync activity will still find it on
2813 * the dirty lists, and in particular, clear_page_dirty_for_io() will still
2814 * look at the dirty bits in the VM.
2816 * Doing this should *normally* only ever be done when a page is truncated,
2817 * and is not actually mapped anywhere at all. However, fs/buffer.c does
2818 * this when it notices that somebody has cleaned out all the buffers on a
2819 * page without actually doing it through the VM. Can you say "ext3 is
2820 * horribly ugly"? Thought you could.
2822 void __folio_cancel_dirty(struct folio
*folio
)
2824 struct address_space
*mapping
= folio_mapping(folio
);
2826 if (mapping_can_writeback(mapping
)) {
2827 struct inode
*inode
= mapping
->host
;
2828 struct bdi_writeback
*wb
;
2829 struct wb_lock_cookie cookie
= {};
2831 folio_memcg_lock(folio
);
2832 wb
= unlocked_inode_to_wb_begin(inode
, &cookie
);
2834 if (folio_test_clear_dirty(folio
))
2835 folio_account_cleaned(folio
, wb
);
2837 unlocked_inode_to_wb_end(inode
, &cookie
);
2838 folio_memcg_unlock(folio
);
2840 folio_clear_dirty(folio
);
2843 EXPORT_SYMBOL(__folio_cancel_dirty
);
2846 * Clear a folio's dirty flag, while caring for dirty memory accounting.
2847 * Returns true if the folio was previously dirty.
2849 * This is for preparing to put the folio under writeout. We leave
2850 * the folio tagged as dirty in the xarray so that a concurrent
2851 * write-for-sync can discover it via a PAGECACHE_TAG_DIRTY walk.
2852 * The ->writepage implementation will run either folio_start_writeback()
2853 * or folio_mark_dirty(), at which stage we bring the folio's dirty flag
2854 * and xarray dirty tag back into sync.
2856 * This incoherency between the folio's dirty flag and xarray tag is
2857 * unfortunate, but it only exists while the folio is locked.
2859 bool folio_clear_dirty_for_io(struct folio
*folio
)
2861 struct address_space
*mapping
= folio_mapping(folio
);
2864 VM_BUG_ON_FOLIO(!folio_test_locked(folio
), folio
);
2866 if (mapping
&& mapping_can_writeback(mapping
)) {
2867 struct inode
*inode
= mapping
->host
;
2868 struct bdi_writeback
*wb
;
2869 struct wb_lock_cookie cookie
= {};
2872 * Yes, Virginia, this is indeed insane.
2874 * We use this sequence to make sure that
2875 * (a) we account for dirty stats properly
2876 * (b) we tell the low-level filesystem to
2877 * mark the whole folio dirty if it was
2878 * dirty in a pagetable. Only to then
2879 * (c) clean the folio again and return 1 to
2880 * cause the writeback.
2882 * This way we avoid all nasty races with the
2883 * dirty bit in multiple places and clearing
2884 * them concurrently from different threads.
2886 * Note! Normally the "folio_mark_dirty(folio)"
2887 * has no effect on the actual dirty bit - since
2888 * that will already usually be set. But we
2889 * need the side effects, and it can help us
2892 * We basically use the folio "master dirty bit"
2893 * as a serialization point for all the different
2894 * threads doing their things.
2896 if (folio_mkclean(folio
))
2897 folio_mark_dirty(folio
);
2899 * We carefully synchronise fault handlers against
2900 * installing a dirty pte and marking the folio dirty
2901 * at this point. We do this by having them hold the
2902 * page lock while dirtying the folio, and folios are
2903 * always locked coming in here, so we get the desired
2906 wb
= unlocked_inode_to_wb_begin(inode
, &cookie
);
2907 if (folio_test_clear_dirty(folio
)) {
2908 long nr
= folio_nr_pages(folio
);
2909 lruvec_stat_mod_folio(folio
, NR_FILE_DIRTY
, -nr
);
2910 zone_stat_mod_folio(folio
, NR_ZONE_WRITE_PENDING
, -nr
);
2911 wb_stat_mod(wb
, WB_RECLAIMABLE
, -nr
);
2914 unlocked_inode_to_wb_end(inode
, &cookie
);
2917 return folio_test_clear_dirty(folio
);
2919 EXPORT_SYMBOL(folio_clear_dirty_for_io
);
2921 static void wb_inode_writeback_start(struct bdi_writeback
*wb
)
2923 atomic_inc(&wb
->writeback_inodes
);
2926 static void wb_inode_writeback_end(struct bdi_writeback
*wb
)
2928 unsigned long flags
;
2929 atomic_dec(&wb
->writeback_inodes
);
2931 * Make sure estimate of writeback throughput gets updated after
2932 * writeback completed. We delay the update by BANDWIDTH_INTERVAL
2933 * (which is the interval other bandwidth updates use for batching) so
2934 * that if multiple inodes end writeback at a similar time, they get
2935 * batched into one bandwidth update.
2937 spin_lock_irqsave(&wb
->work_lock
, flags
);
2938 if (test_bit(WB_registered
, &wb
->state
))
2939 queue_delayed_work(bdi_wq
, &wb
->bw_dwork
, BANDWIDTH_INTERVAL
);
2940 spin_unlock_irqrestore(&wb
->work_lock
, flags
);
2943 bool __folio_end_writeback(struct folio
*folio
)
2945 long nr
= folio_nr_pages(folio
);
2946 struct address_space
*mapping
= folio_mapping(folio
);
2949 folio_memcg_lock(folio
);
2950 if (mapping
&& mapping_use_writeback_tags(mapping
)) {
2951 struct inode
*inode
= mapping
->host
;
2952 struct backing_dev_info
*bdi
= inode_to_bdi(inode
);
2953 unsigned long flags
;
2955 xa_lock_irqsave(&mapping
->i_pages
, flags
);
2956 ret
= folio_xor_flags_has_waiters(folio
, 1 << PG_writeback
);
2957 __xa_clear_mark(&mapping
->i_pages
, folio_index(folio
),
2958 PAGECACHE_TAG_WRITEBACK
);
2959 if (bdi
->capabilities
& BDI_CAP_WRITEBACK_ACCT
) {
2960 struct bdi_writeback
*wb
= inode_to_wb(inode
);
2962 wb_stat_mod(wb
, WB_WRITEBACK
, -nr
);
2963 __wb_writeout_add(wb
, nr
);
2964 if (!mapping_tagged(mapping
, PAGECACHE_TAG_WRITEBACK
))
2965 wb_inode_writeback_end(wb
);
2968 if (mapping
->host
&& !mapping_tagged(mapping
,
2969 PAGECACHE_TAG_WRITEBACK
))
2970 sb_clear_inode_writeback(mapping
->host
);
2972 xa_unlock_irqrestore(&mapping
->i_pages
, flags
);
2974 ret
= folio_xor_flags_has_waiters(folio
, 1 << PG_writeback
);
2977 lruvec_stat_mod_folio(folio
, NR_WRITEBACK
, -nr
);
2978 zone_stat_mod_folio(folio
, NR_ZONE_WRITE_PENDING
, -nr
);
2979 node_stat_mod_folio(folio
, NR_WRITTEN
, nr
);
2980 folio_memcg_unlock(folio
);
2985 void __folio_start_writeback(struct folio
*folio
, bool keep_write
)
2987 long nr
= folio_nr_pages(folio
);
2988 struct address_space
*mapping
= folio_mapping(folio
);
2991 VM_BUG_ON_FOLIO(folio_test_writeback(folio
), folio
);
2993 folio_memcg_lock(folio
);
2994 if (mapping
&& mapping_use_writeback_tags(mapping
)) {
2995 XA_STATE(xas
, &mapping
->i_pages
, folio_index(folio
));
2996 struct inode
*inode
= mapping
->host
;
2997 struct backing_dev_info
*bdi
= inode_to_bdi(inode
);
2998 unsigned long flags
;
3001 xas_lock_irqsave(&xas
, flags
);
3003 folio_test_set_writeback(folio
);
3005 on_wblist
= mapping_tagged(mapping
, PAGECACHE_TAG_WRITEBACK
);
3007 xas_set_mark(&xas
, PAGECACHE_TAG_WRITEBACK
);
3008 if (bdi
->capabilities
& BDI_CAP_WRITEBACK_ACCT
) {
3009 struct bdi_writeback
*wb
= inode_to_wb(inode
);
3011 wb_stat_mod(wb
, WB_WRITEBACK
, nr
);
3013 wb_inode_writeback_start(wb
);
3017 * We can come through here when swapping anonymous
3018 * folios, so we don't necessarily have an inode to
3021 if (mapping
->host
&& !on_wblist
)
3022 sb_mark_inode_writeback(mapping
->host
);
3023 if (!folio_test_dirty(folio
))
3024 xas_clear_mark(&xas
, PAGECACHE_TAG_DIRTY
);
3026 xas_clear_mark(&xas
, PAGECACHE_TAG_TOWRITE
);
3027 xas_unlock_irqrestore(&xas
, flags
);
3029 folio_test_set_writeback(folio
);
3032 lruvec_stat_mod_folio(folio
, NR_WRITEBACK
, nr
);
3033 zone_stat_mod_folio(folio
, NR_ZONE_WRITE_PENDING
, nr
);
3034 folio_memcg_unlock(folio
);
3036 access_ret
= arch_make_folio_accessible(folio
);
3038 * If writeback has been triggered on a page that cannot be made
3039 * accessible, it is too late to recover here.
3041 VM_BUG_ON_FOLIO(access_ret
!= 0, folio
);
3043 EXPORT_SYMBOL(__folio_start_writeback
);
3046 * folio_wait_writeback - Wait for a folio to finish writeback.
3047 * @folio: The folio to wait for.
3049 * If the folio is currently being written back to storage, wait for the
3052 * Context: Sleeps. Must be called in process context and with
3053 * no spinlocks held. Caller should hold a reference on the folio.
3054 * If the folio is not locked, writeback may start again after writeback
3057 void folio_wait_writeback(struct folio
*folio
)
3059 while (folio_test_writeback(folio
)) {
3060 trace_folio_wait_writeback(folio
, folio_mapping(folio
));
3061 folio_wait_bit(folio
, PG_writeback
);
3064 EXPORT_SYMBOL_GPL(folio_wait_writeback
);
3067 * folio_wait_writeback_killable - Wait for a folio to finish writeback.
3068 * @folio: The folio to wait for.
3070 * If the folio is currently being written back to storage, wait for the
3071 * I/O to complete or a fatal signal to arrive.
3073 * Context: Sleeps. Must be called in process context and with
3074 * no spinlocks held. Caller should hold a reference on the folio.
3075 * If the folio is not locked, writeback may start again after writeback
3077 * Return: 0 on success, -EINTR if we get a fatal signal while waiting.
3079 int folio_wait_writeback_killable(struct folio
*folio
)
3081 while (folio_test_writeback(folio
)) {
3082 trace_folio_wait_writeback(folio
, folio_mapping(folio
));
3083 if (folio_wait_bit_killable(folio
, PG_writeback
))
3089 EXPORT_SYMBOL_GPL(folio_wait_writeback_killable
);
3092 * folio_wait_stable() - wait for writeback to finish, if necessary.
3093 * @folio: The folio to wait on.
3095 * This function determines if the given folio is related to a backing
3096 * device that requires folio contents to be held stable during writeback.
3097 * If so, then it will wait for any pending writeback to complete.
3099 * Context: Sleeps. Must be called in process context and with
3100 * no spinlocks held. Caller should hold a reference on the folio.
3101 * If the folio is not locked, writeback may start again after writeback
3104 void folio_wait_stable(struct folio
*folio
)
3106 if (mapping_stable_writes(folio_mapping(folio
)))
3107 folio_wait_writeback(folio
);
3109 EXPORT_SYMBOL_GPL(folio_wait_stable
);