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 static 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 static 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 static int vm_highmem_is_dirtyable
;
88 * The generator of dirty data starts writeback at this percentage
90 static 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 static 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 * Make sure that the number of highmem pages is never larger
328 * than the number of the total dirtyable memory. This can only
329 * occur in very strange VM situations but we want to make sure
330 * that this does not occur.
332 return min(x
, total
);
339 * global_dirtyable_memory - number of globally dirtyable pages
341 * Return: the global number of pages potentially available for dirty
342 * page cache. This is the base value for the global dirty limits.
344 static unsigned long global_dirtyable_memory(void)
348 x
= global_zone_page_state(NR_FREE_PAGES
);
350 * Pages reserved for the kernel should not be considered
351 * dirtyable, to prevent a situation where reclaim has to
352 * clean pages in order to balance the zones.
354 x
-= min(x
, totalreserve_pages
);
356 x
+= global_node_page_state(NR_INACTIVE_FILE
);
357 x
+= global_node_page_state(NR_ACTIVE_FILE
);
359 if (!vm_highmem_is_dirtyable
)
360 x
-= highmem_dirtyable_memory(x
);
362 return x
+ 1; /* Ensure that we never return 0 */
366 * domain_dirty_limits - calculate thresh and bg_thresh for a wb_domain
367 * @dtc: dirty_throttle_control of interest
369 * Calculate @dtc->thresh and ->bg_thresh considering
370 * vm_dirty_{bytes|ratio} and dirty_background_{bytes|ratio}. The caller
371 * must ensure that @dtc->avail is set before calling this function. The
372 * dirty limits will be lifted by 1/4 for real-time tasks.
374 static void domain_dirty_limits(struct dirty_throttle_control
*dtc
)
376 const unsigned long available_memory
= dtc
->avail
;
377 struct dirty_throttle_control
*gdtc
= mdtc_gdtc(dtc
);
378 unsigned long bytes
= vm_dirty_bytes
;
379 unsigned long bg_bytes
= dirty_background_bytes
;
380 /* convert ratios to per-PAGE_SIZE for higher precision */
381 unsigned long ratio
= (vm_dirty_ratio
* PAGE_SIZE
) / 100;
382 unsigned long bg_ratio
= (dirty_background_ratio
* PAGE_SIZE
) / 100;
383 unsigned long thresh
;
384 unsigned long bg_thresh
;
385 struct task_struct
*tsk
;
387 /* gdtc is !NULL iff @dtc is for memcg domain */
389 unsigned long global_avail
= gdtc
->avail
;
392 * The byte settings can't be applied directly to memcg
393 * domains. Convert them to ratios by scaling against
394 * globally available memory. As the ratios are in
395 * per-PAGE_SIZE, they can be obtained by dividing bytes by
399 ratio
= min(DIV_ROUND_UP(bytes
, global_avail
),
402 bg_ratio
= min(DIV_ROUND_UP(bg_bytes
, global_avail
),
404 bytes
= bg_bytes
= 0;
408 thresh
= DIV_ROUND_UP(bytes
, PAGE_SIZE
);
410 thresh
= (ratio
* available_memory
) / PAGE_SIZE
;
413 bg_thresh
= DIV_ROUND_UP(bg_bytes
, PAGE_SIZE
);
415 bg_thresh
= (bg_ratio
* available_memory
) / PAGE_SIZE
;
417 if (bg_thresh
>= thresh
)
418 bg_thresh
= thresh
/ 2;
421 bg_thresh
+= bg_thresh
/ 4 + global_wb_domain
.dirty_limit
/ 32;
422 thresh
+= thresh
/ 4 + global_wb_domain
.dirty_limit
/ 32;
424 dtc
->thresh
= thresh
;
425 dtc
->bg_thresh
= bg_thresh
;
427 /* we should eventually report the domain in the TP */
429 trace_global_dirty_state(bg_thresh
, thresh
);
433 * global_dirty_limits - background-writeback and dirty-throttling thresholds
434 * @pbackground: out parameter for bg_thresh
435 * @pdirty: out parameter for thresh
437 * Calculate bg_thresh and thresh for global_wb_domain. See
438 * domain_dirty_limits() for details.
440 void global_dirty_limits(unsigned long *pbackground
, unsigned long *pdirty
)
442 struct dirty_throttle_control gdtc
= { GDTC_INIT_NO_WB
};
444 gdtc
.avail
= global_dirtyable_memory();
445 domain_dirty_limits(&gdtc
);
447 *pbackground
= gdtc
.bg_thresh
;
448 *pdirty
= gdtc
.thresh
;
452 * node_dirty_limit - maximum number of dirty pages allowed in a node
455 * Return: the maximum number of dirty pages allowed in a node, based
456 * on the node's dirtyable memory.
458 static unsigned long node_dirty_limit(struct pglist_data
*pgdat
)
460 unsigned long node_memory
= node_dirtyable_memory(pgdat
);
461 struct task_struct
*tsk
= current
;
465 dirty
= DIV_ROUND_UP(vm_dirty_bytes
, PAGE_SIZE
) *
466 node_memory
/ global_dirtyable_memory();
468 dirty
= vm_dirty_ratio
* node_memory
/ 100;
477 * node_dirty_ok - tells whether a node is within its dirty limits
478 * @pgdat: the node to check
480 * Return: %true when the dirty pages in @pgdat are within the node's
481 * dirty limit, %false if the limit is exceeded.
483 bool node_dirty_ok(struct pglist_data
*pgdat
)
485 unsigned long limit
= node_dirty_limit(pgdat
);
486 unsigned long nr_pages
= 0;
488 nr_pages
+= node_page_state(pgdat
, NR_FILE_DIRTY
);
489 nr_pages
+= node_page_state(pgdat
, NR_WRITEBACK
);
491 return nr_pages
<= limit
;
495 static int dirty_background_ratio_handler(struct ctl_table
*table
, int write
,
496 void *buffer
, size_t *lenp
, loff_t
*ppos
)
500 ret
= proc_dointvec_minmax(table
, write
, buffer
, lenp
, ppos
);
501 if (ret
== 0 && write
)
502 dirty_background_bytes
= 0;
506 static int dirty_background_bytes_handler(struct ctl_table
*table
, int write
,
507 void *buffer
, size_t *lenp
, loff_t
*ppos
)
511 ret
= proc_doulongvec_minmax(table
, write
, buffer
, lenp
, ppos
);
512 if (ret
== 0 && write
)
513 dirty_background_ratio
= 0;
517 static int dirty_ratio_handler(struct ctl_table
*table
, int write
, void *buffer
,
518 size_t *lenp
, loff_t
*ppos
)
520 int old_ratio
= vm_dirty_ratio
;
523 ret
= proc_dointvec_minmax(table
, write
, buffer
, lenp
, ppos
);
524 if (ret
== 0 && write
&& vm_dirty_ratio
!= old_ratio
) {
525 writeback_set_ratelimit();
531 static int dirty_bytes_handler(struct ctl_table
*table
, int write
,
532 void *buffer
, size_t *lenp
, loff_t
*ppos
)
534 unsigned long old_bytes
= vm_dirty_bytes
;
537 ret
= proc_doulongvec_minmax(table
, write
, buffer
, lenp
, ppos
);
538 if (ret
== 0 && write
&& vm_dirty_bytes
!= old_bytes
) {
539 writeback_set_ratelimit();
546 static unsigned long wp_next_time(unsigned long cur_time
)
548 cur_time
+= VM_COMPLETIONS_PERIOD_LEN
;
549 /* 0 has a special meaning... */
555 static void wb_domain_writeout_add(struct wb_domain
*dom
,
556 struct fprop_local_percpu
*completions
,
557 unsigned int max_prop_frac
, long nr
)
559 __fprop_add_percpu_max(&dom
->completions
, completions
,
561 /* First event after period switching was turned off? */
562 if (unlikely(!dom
->period_time
)) {
564 * We can race with other __bdi_writeout_inc calls here but
565 * it does not cause any harm since the resulting time when
566 * timer will fire and what is in writeout_period_time will be
569 dom
->period_time
= wp_next_time(jiffies
);
570 mod_timer(&dom
->period_timer
, dom
->period_time
);
575 * Increment @wb's writeout completion count and the global writeout
576 * completion count. Called from __folio_end_writeback().
578 static inline void __wb_writeout_add(struct bdi_writeback
*wb
, long nr
)
580 struct wb_domain
*cgdom
;
582 wb_stat_mod(wb
, WB_WRITTEN
, nr
);
583 wb_domain_writeout_add(&global_wb_domain
, &wb
->completions
,
584 wb
->bdi
->max_prop_frac
, nr
);
586 cgdom
= mem_cgroup_wb_domain(wb
);
588 wb_domain_writeout_add(cgdom
, wb_memcg_completions(wb
),
589 wb
->bdi
->max_prop_frac
, nr
);
592 void wb_writeout_inc(struct bdi_writeback
*wb
)
596 local_irq_save(flags
);
597 __wb_writeout_add(wb
, 1);
598 local_irq_restore(flags
);
600 EXPORT_SYMBOL_GPL(wb_writeout_inc
);
603 * On idle system, we can be called long after we scheduled because we use
604 * deferred timers so count with missed periods.
606 static void writeout_period(struct timer_list
*t
)
608 struct wb_domain
*dom
= from_timer(dom
, t
, period_timer
);
609 int miss_periods
= (jiffies
- dom
->period_time
) /
610 VM_COMPLETIONS_PERIOD_LEN
;
612 if (fprop_new_period(&dom
->completions
, miss_periods
+ 1)) {
613 dom
->period_time
= wp_next_time(dom
->period_time
+
614 miss_periods
* VM_COMPLETIONS_PERIOD_LEN
);
615 mod_timer(&dom
->period_timer
, dom
->period_time
);
618 * Aging has zeroed all fractions. Stop wasting CPU on period
621 dom
->period_time
= 0;
625 int wb_domain_init(struct wb_domain
*dom
, gfp_t gfp
)
627 memset(dom
, 0, sizeof(*dom
));
629 spin_lock_init(&dom
->lock
);
631 timer_setup(&dom
->period_timer
, writeout_period
, TIMER_DEFERRABLE
);
633 dom
->dirty_limit_tstamp
= jiffies
;
635 return fprop_global_init(&dom
->completions
, gfp
);
638 #ifdef CONFIG_CGROUP_WRITEBACK
639 void wb_domain_exit(struct wb_domain
*dom
)
641 del_timer_sync(&dom
->period_timer
);
642 fprop_global_destroy(&dom
->completions
);
647 * bdi_min_ratio keeps the sum of the minimum dirty shares of all
648 * registered backing devices, which, for obvious reasons, can not
651 static unsigned int bdi_min_ratio
;
653 int bdi_set_min_ratio(struct backing_dev_info
*bdi
, unsigned int min_ratio
)
658 spin_lock_bh(&bdi_lock
);
659 if (min_ratio
> bdi
->max_ratio
) {
662 if (min_ratio
< bdi
->min_ratio
) {
663 delta
= bdi
->min_ratio
- min_ratio
;
664 bdi_min_ratio
-= delta
;
665 bdi
->min_ratio
= min_ratio
;
667 delta
= min_ratio
- bdi
->min_ratio
;
668 if (bdi_min_ratio
+ delta
< 100) {
669 bdi_min_ratio
+= delta
;
670 bdi
->min_ratio
= min_ratio
;
676 spin_unlock_bh(&bdi_lock
);
681 int bdi_set_max_ratio(struct backing_dev_info
*bdi
, unsigned max_ratio
)
688 spin_lock_bh(&bdi_lock
);
689 if (bdi
->min_ratio
> max_ratio
) {
692 bdi
->max_ratio
= max_ratio
;
693 bdi
->max_prop_frac
= (FPROP_FRAC_BASE
* max_ratio
) / 100;
695 spin_unlock_bh(&bdi_lock
);
699 EXPORT_SYMBOL(bdi_set_max_ratio
);
701 static unsigned long dirty_freerun_ceiling(unsigned long thresh
,
702 unsigned long bg_thresh
)
704 return (thresh
+ bg_thresh
) / 2;
707 static unsigned long hard_dirty_limit(struct wb_domain
*dom
,
708 unsigned long thresh
)
710 return max(thresh
, dom
->dirty_limit
);
714 * Memory which can be further allocated to a memcg domain is capped by
715 * system-wide clean memory excluding the amount being used in the domain.
717 static void mdtc_calc_avail(struct dirty_throttle_control
*mdtc
,
718 unsigned long filepages
, unsigned long headroom
)
720 struct dirty_throttle_control
*gdtc
= mdtc_gdtc(mdtc
);
721 unsigned long clean
= filepages
- min(filepages
, mdtc
->dirty
);
722 unsigned long global_clean
= gdtc
->avail
- min(gdtc
->avail
, gdtc
->dirty
);
723 unsigned long other_clean
= global_clean
- min(global_clean
, clean
);
725 mdtc
->avail
= filepages
+ min(headroom
, other_clean
);
729 * __wb_calc_thresh - @wb's share of dirty throttling threshold
730 * @dtc: dirty_throttle_context of interest
732 * Note that balance_dirty_pages() will only seriously take it as a hard limit
733 * when sleeping max_pause per page is not enough to keep the dirty pages under
734 * control. For example, when the device is completely stalled due to some error
735 * conditions, or when there are 1000 dd tasks writing to a slow 10MB/s USB key.
736 * In the other normal situations, it acts more gently by throttling the tasks
737 * more (rather than completely block them) when the wb dirty pages go high.
739 * It allocates high/low dirty limits to fast/slow devices, in order to prevent
740 * - starving fast devices
741 * - piling up dirty pages (that will take long time to sync) on slow devices
743 * The wb's share of dirty limit will be adapting to its throughput and
744 * bounded by the bdi->min_ratio and/or bdi->max_ratio parameters, if set.
746 * Return: @wb's dirty limit in pages. The term "dirty" in the context of
747 * dirty balancing includes all PG_dirty and PG_writeback pages.
749 static unsigned long __wb_calc_thresh(struct dirty_throttle_control
*dtc
)
751 struct wb_domain
*dom
= dtc_dom(dtc
);
752 unsigned long thresh
= dtc
->thresh
;
754 unsigned long numerator
, denominator
;
755 unsigned long wb_min_ratio
, wb_max_ratio
;
758 * Calculate this BDI's share of the thresh ratio.
760 fprop_fraction_percpu(&dom
->completions
, dtc
->wb_completions
,
761 &numerator
, &denominator
);
763 wb_thresh
= (thresh
* (100 - bdi_min_ratio
)) / 100;
764 wb_thresh
*= numerator
;
765 wb_thresh
= div64_ul(wb_thresh
, denominator
);
767 wb_min_max_ratio(dtc
->wb
, &wb_min_ratio
, &wb_max_ratio
);
769 wb_thresh
+= (thresh
* wb_min_ratio
) / 100;
770 if (wb_thresh
> (thresh
* wb_max_ratio
) / 100)
771 wb_thresh
= thresh
* wb_max_ratio
/ 100;
776 unsigned long wb_calc_thresh(struct bdi_writeback
*wb
, unsigned long thresh
)
778 struct dirty_throttle_control gdtc
= { GDTC_INIT(wb
),
780 return __wb_calc_thresh(&gdtc
);
785 * f(dirty) := 1.0 + (----------------)
788 * it's a 3rd order polynomial that subjects to
790 * (1) f(freerun) = 2.0 => rampup dirty_ratelimit reasonably fast
791 * (2) f(setpoint) = 1.0 => the balance point
792 * (3) f(limit) = 0 => the hard limit
793 * (4) df/dx <= 0 => negative feedback control
794 * (5) the closer to setpoint, the smaller |df/dx| (and the reverse)
795 * => fast response on large errors; small oscillation near setpoint
797 static long long pos_ratio_polynom(unsigned long setpoint
,
804 x
= div64_s64(((s64
)setpoint
- (s64
)dirty
) << RATELIMIT_CALC_SHIFT
,
805 (limit
- setpoint
) | 1);
807 pos_ratio
= pos_ratio
* x
>> RATELIMIT_CALC_SHIFT
;
808 pos_ratio
= pos_ratio
* x
>> RATELIMIT_CALC_SHIFT
;
809 pos_ratio
+= 1 << RATELIMIT_CALC_SHIFT
;
811 return clamp(pos_ratio
, 0LL, 2LL << RATELIMIT_CALC_SHIFT
);
815 * Dirty position control.
817 * (o) global/bdi setpoints
819 * We want the dirty pages be balanced around the global/wb setpoints.
820 * When the number of dirty pages is higher/lower than the setpoint, the
821 * dirty position control ratio (and hence task dirty ratelimit) will be
822 * decreased/increased to bring the dirty pages back to the setpoint.
824 * pos_ratio = 1 << RATELIMIT_CALC_SHIFT
826 * if (dirty < setpoint) scale up pos_ratio
827 * if (dirty > setpoint) scale down pos_ratio
829 * if (wb_dirty < wb_setpoint) scale up pos_ratio
830 * if (wb_dirty > wb_setpoint) scale down pos_ratio
832 * task_ratelimit = dirty_ratelimit * pos_ratio >> RATELIMIT_CALC_SHIFT
834 * (o) global control line
838 * | |<===== global dirty control scope ======>|
846 * 1.0 ................................*
852 * 0 +------------.------------------.----------------------*------------->
853 * freerun^ setpoint^ limit^ dirty pages
855 * (o) wb control line
863 * | * |<=========== span ============>|
864 * 1.0 .......................*
876 * 1/4 ...............................................* * * * * * * * * * * *
880 * 0 +----------------------.-------------------------------.------------->
881 * wb_setpoint^ x_intercept^
883 * The wb control line won't drop below pos_ratio=1/4, so that wb_dirty can
884 * be smoothly throttled down to normal if it starts high in situations like
885 * - start writing to a slow SD card and a fast disk at the same time. The SD
886 * card's wb_dirty may rush to many times higher than wb_setpoint.
887 * - the wb dirty thresh drops quickly due to change of JBOD workload
889 static void wb_position_ratio(struct dirty_throttle_control
*dtc
)
891 struct bdi_writeback
*wb
= dtc
->wb
;
892 unsigned long write_bw
= READ_ONCE(wb
->avg_write_bandwidth
);
893 unsigned long freerun
= dirty_freerun_ceiling(dtc
->thresh
, dtc
->bg_thresh
);
894 unsigned long limit
= hard_dirty_limit(dtc_dom(dtc
), dtc
->thresh
);
895 unsigned long wb_thresh
= dtc
->wb_thresh
;
896 unsigned long x_intercept
;
897 unsigned long setpoint
; /* dirty pages' target balance point */
898 unsigned long wb_setpoint
;
900 long long pos_ratio
; /* for scaling up/down the rate limit */
905 if (unlikely(dtc
->dirty
>= limit
))
911 * See comment for pos_ratio_polynom().
913 setpoint
= (freerun
+ limit
) / 2;
914 pos_ratio
= pos_ratio_polynom(setpoint
, dtc
->dirty
, limit
);
917 * The strictlimit feature is a tool preventing mistrusted filesystems
918 * from growing a large number of dirty pages before throttling. For
919 * such filesystems balance_dirty_pages always checks wb counters
920 * against wb limits. Even if global "nr_dirty" is under "freerun".
921 * This is especially important for fuse which sets bdi->max_ratio to
922 * 1% by default. Without strictlimit feature, fuse writeback may
923 * consume arbitrary amount of RAM because it is accounted in
924 * NR_WRITEBACK_TEMP which is not involved in calculating "nr_dirty".
926 * Here, in wb_position_ratio(), we calculate pos_ratio based on
927 * two values: wb_dirty and wb_thresh. Let's consider an example:
928 * total amount of RAM is 16GB, bdi->max_ratio is equal to 1%, global
929 * limits are set by default to 10% and 20% (background and throttle).
930 * Then wb_thresh is 1% of 20% of 16GB. This amounts to ~8K pages.
931 * wb_calc_thresh(wb, bg_thresh) is about ~4K pages. wb_setpoint is
932 * about ~6K pages (as the average of background and throttle wb
933 * limits). The 3rd order polynomial will provide positive feedback if
934 * wb_dirty is under wb_setpoint and vice versa.
936 * Note, that we cannot use global counters in these calculations
937 * because we want to throttle process writing to a strictlimit wb
938 * much earlier than global "freerun" is reached (~23MB vs. ~2.3GB
939 * in the example above).
941 if (unlikely(wb
->bdi
->capabilities
& BDI_CAP_STRICTLIMIT
)) {
942 long long wb_pos_ratio
;
944 if (dtc
->wb_dirty
< 8) {
945 dtc
->pos_ratio
= min_t(long long, pos_ratio
* 2,
946 2 << RATELIMIT_CALC_SHIFT
);
950 if (dtc
->wb_dirty
>= wb_thresh
)
953 wb_setpoint
= dirty_freerun_ceiling(wb_thresh
,
956 if (wb_setpoint
== 0 || wb_setpoint
== wb_thresh
)
959 wb_pos_ratio
= pos_ratio_polynom(wb_setpoint
, dtc
->wb_dirty
,
963 * Typically, for strictlimit case, wb_setpoint << setpoint
964 * and pos_ratio >> wb_pos_ratio. In the other words global
965 * state ("dirty") is not limiting factor and we have to
966 * make decision based on wb counters. But there is an
967 * important case when global pos_ratio should get precedence:
968 * global limits are exceeded (e.g. due to activities on other
969 * wb's) while given strictlimit wb is below limit.
971 * "pos_ratio * wb_pos_ratio" would work for the case above,
972 * but it would look too non-natural for the case of all
973 * activity in the system coming from a single strictlimit wb
974 * with bdi->max_ratio == 100%.
976 * Note that min() below somewhat changes the dynamics of the
977 * control system. Normally, pos_ratio value can be well over 3
978 * (when globally we are at freerun and wb is well below wb
979 * setpoint). Now the maximum pos_ratio in the same situation
980 * is 2. We might want to tweak this if we observe the control
981 * system is too slow to adapt.
983 dtc
->pos_ratio
= min(pos_ratio
, wb_pos_ratio
);
988 * We have computed basic pos_ratio above based on global situation. If
989 * the wb is over/under its share of dirty pages, we want to scale
990 * pos_ratio further down/up. That is done by the following mechanism.
996 * f(wb_dirty) := 1.0 + k * (wb_dirty - wb_setpoint)
998 * x_intercept - wb_dirty
999 * := --------------------------
1000 * x_intercept - wb_setpoint
1002 * The main wb control line is a linear function that subjects to
1004 * (1) f(wb_setpoint) = 1.0
1005 * (2) k = - 1 / (8 * write_bw) (in single wb case)
1006 * or equally: x_intercept = wb_setpoint + 8 * write_bw
1008 * For single wb case, the dirty pages are observed to fluctuate
1009 * regularly within range
1010 * [wb_setpoint - write_bw/2, wb_setpoint + write_bw/2]
1011 * for various filesystems, where (2) can yield in a reasonable 12.5%
1012 * fluctuation range for pos_ratio.
1014 * For JBOD case, wb_thresh (not wb_dirty!) could fluctuate up to its
1015 * own size, so move the slope over accordingly and choose a slope that
1016 * yields 100% pos_ratio fluctuation on suddenly doubled wb_thresh.
1018 if (unlikely(wb_thresh
> dtc
->thresh
))
1019 wb_thresh
= dtc
->thresh
;
1021 * It's very possible that wb_thresh is close to 0 not because the
1022 * device is slow, but that it has remained inactive for long time.
1023 * Honour such devices a reasonable good (hopefully IO efficient)
1024 * threshold, so that the occasional writes won't be blocked and active
1025 * writes can rampup the threshold quickly.
1027 wb_thresh
= max(wb_thresh
, (limit
- dtc
->dirty
) / 8);
1029 * scale global setpoint to wb's:
1030 * wb_setpoint = setpoint * wb_thresh / thresh
1032 x
= div_u64((u64
)wb_thresh
<< 16, dtc
->thresh
| 1);
1033 wb_setpoint
= setpoint
* (u64
)x
>> 16;
1035 * Use span=(8*write_bw) in single wb case as indicated by
1036 * (thresh - wb_thresh ~= 0) and transit to wb_thresh in JBOD case.
1038 * wb_thresh thresh - wb_thresh
1039 * span = --------- * (8 * write_bw) + ------------------ * wb_thresh
1042 span
= (dtc
->thresh
- wb_thresh
+ 8 * write_bw
) * (u64
)x
>> 16;
1043 x_intercept
= wb_setpoint
+ span
;
1045 if (dtc
->wb_dirty
< x_intercept
- span
/ 4) {
1046 pos_ratio
= div64_u64(pos_ratio
* (x_intercept
- dtc
->wb_dirty
),
1047 (x_intercept
- wb_setpoint
) | 1);
1052 * wb reserve area, safeguard against dirty pool underrun and disk idle
1053 * It may push the desired control point of global dirty pages higher
1056 x_intercept
= wb_thresh
/ 2;
1057 if (dtc
->wb_dirty
< x_intercept
) {
1058 if (dtc
->wb_dirty
> x_intercept
/ 8)
1059 pos_ratio
= div_u64(pos_ratio
* x_intercept
,
1065 dtc
->pos_ratio
= pos_ratio
;
1068 static void wb_update_write_bandwidth(struct bdi_writeback
*wb
,
1069 unsigned long elapsed
,
1070 unsigned long written
)
1072 const unsigned long period
= roundup_pow_of_two(3 * HZ
);
1073 unsigned long avg
= wb
->avg_write_bandwidth
;
1074 unsigned long old
= wb
->write_bandwidth
;
1078 * bw = written * HZ / elapsed
1080 * bw * elapsed + write_bandwidth * (period - elapsed)
1081 * write_bandwidth = ---------------------------------------------------
1084 * @written may have decreased due to folio_account_redirty().
1085 * Avoid underflowing @bw calculation.
1087 bw
= written
- min(written
, wb
->written_stamp
);
1089 if (unlikely(elapsed
> period
)) {
1090 bw
= div64_ul(bw
, elapsed
);
1094 bw
+= (u64
)wb
->write_bandwidth
* (period
- elapsed
);
1095 bw
>>= ilog2(period
);
1098 * one more level of smoothing, for filtering out sudden spikes
1100 if (avg
> old
&& old
>= (unsigned long)bw
)
1101 avg
-= (avg
- old
) >> 3;
1103 if (avg
< old
&& old
<= (unsigned long)bw
)
1104 avg
+= (old
- avg
) >> 3;
1107 /* keep avg > 0 to guarantee that tot > 0 if there are dirty wbs */
1108 avg
= max(avg
, 1LU);
1109 if (wb_has_dirty_io(wb
)) {
1110 long delta
= avg
- wb
->avg_write_bandwidth
;
1111 WARN_ON_ONCE(atomic_long_add_return(delta
,
1112 &wb
->bdi
->tot_write_bandwidth
) <= 0);
1114 wb
->write_bandwidth
= bw
;
1115 WRITE_ONCE(wb
->avg_write_bandwidth
, avg
);
1118 static void update_dirty_limit(struct dirty_throttle_control
*dtc
)
1120 struct wb_domain
*dom
= dtc_dom(dtc
);
1121 unsigned long thresh
= dtc
->thresh
;
1122 unsigned long limit
= dom
->dirty_limit
;
1125 * Follow up in one step.
1127 if (limit
< thresh
) {
1133 * Follow down slowly. Use the higher one as the target, because thresh
1134 * may drop below dirty. This is exactly the reason to introduce
1135 * dom->dirty_limit which is guaranteed to lie above the dirty pages.
1137 thresh
= max(thresh
, dtc
->dirty
);
1138 if (limit
> thresh
) {
1139 limit
-= (limit
- thresh
) >> 5;
1144 dom
->dirty_limit
= limit
;
1147 static void domain_update_dirty_limit(struct dirty_throttle_control
*dtc
,
1150 struct wb_domain
*dom
= dtc_dom(dtc
);
1153 * check locklessly first to optimize away locking for the most time
1155 if (time_before(now
, dom
->dirty_limit_tstamp
+ BANDWIDTH_INTERVAL
))
1158 spin_lock(&dom
->lock
);
1159 if (time_after_eq(now
, dom
->dirty_limit_tstamp
+ BANDWIDTH_INTERVAL
)) {
1160 update_dirty_limit(dtc
);
1161 dom
->dirty_limit_tstamp
= now
;
1163 spin_unlock(&dom
->lock
);
1167 * Maintain wb->dirty_ratelimit, the base dirty throttle rate.
1169 * Normal wb tasks will be curbed at or below it in long term.
1170 * Obviously it should be around (write_bw / N) when there are N dd tasks.
1172 static void wb_update_dirty_ratelimit(struct dirty_throttle_control
*dtc
,
1173 unsigned long dirtied
,
1174 unsigned long elapsed
)
1176 struct bdi_writeback
*wb
= dtc
->wb
;
1177 unsigned long dirty
= dtc
->dirty
;
1178 unsigned long freerun
= dirty_freerun_ceiling(dtc
->thresh
, dtc
->bg_thresh
);
1179 unsigned long limit
= hard_dirty_limit(dtc_dom(dtc
), dtc
->thresh
);
1180 unsigned long setpoint
= (freerun
+ limit
) / 2;
1181 unsigned long write_bw
= wb
->avg_write_bandwidth
;
1182 unsigned long dirty_ratelimit
= wb
->dirty_ratelimit
;
1183 unsigned long dirty_rate
;
1184 unsigned long task_ratelimit
;
1185 unsigned long balanced_dirty_ratelimit
;
1188 unsigned long shift
;
1191 * The dirty rate will match the writeout rate in long term, except
1192 * when dirty pages are truncated by userspace or re-dirtied by FS.
1194 dirty_rate
= (dirtied
- wb
->dirtied_stamp
) * HZ
/ elapsed
;
1197 * task_ratelimit reflects each dd's dirty rate for the past 200ms.
1199 task_ratelimit
= (u64
)dirty_ratelimit
*
1200 dtc
->pos_ratio
>> RATELIMIT_CALC_SHIFT
;
1201 task_ratelimit
++; /* it helps rampup dirty_ratelimit from tiny values */
1204 * A linear estimation of the "balanced" throttle rate. The theory is,
1205 * if there are N dd tasks, each throttled at task_ratelimit, the wb's
1206 * dirty_rate will be measured to be (N * task_ratelimit). So the below
1207 * formula will yield the balanced rate limit (write_bw / N).
1209 * Note that the expanded form is not a pure rate feedback:
1210 * rate_(i+1) = rate_(i) * (write_bw / dirty_rate) (1)
1211 * but also takes pos_ratio into account:
1212 * rate_(i+1) = rate_(i) * (write_bw / dirty_rate) * pos_ratio (2)
1214 * (1) is not realistic because pos_ratio also takes part in balancing
1215 * the dirty rate. Consider the state
1216 * pos_ratio = 0.5 (3)
1217 * rate = 2 * (write_bw / N) (4)
1218 * If (1) is used, it will stuck in that state! Because each dd will
1220 * task_ratelimit = pos_ratio * rate = (write_bw / N) (5)
1222 * dirty_rate = N * task_ratelimit = write_bw (6)
1223 * put (6) into (1) we get
1224 * rate_(i+1) = rate_(i) (7)
1226 * So we end up using (2) to always keep
1227 * rate_(i+1) ~= (write_bw / N) (8)
1228 * regardless of the value of pos_ratio. As long as (8) is satisfied,
1229 * pos_ratio is able to drive itself to 1.0, which is not only where
1230 * the dirty count meet the setpoint, but also where the slope of
1231 * pos_ratio is most flat and hence task_ratelimit is least fluctuated.
1233 balanced_dirty_ratelimit
= div_u64((u64
)task_ratelimit
* write_bw
,
1236 * balanced_dirty_ratelimit ~= (write_bw / N) <= write_bw
1238 if (unlikely(balanced_dirty_ratelimit
> write_bw
))
1239 balanced_dirty_ratelimit
= write_bw
;
1242 * We could safely do this and return immediately:
1244 * wb->dirty_ratelimit = balanced_dirty_ratelimit;
1246 * However to get a more stable dirty_ratelimit, the below elaborated
1247 * code makes use of task_ratelimit to filter out singular points and
1248 * limit the step size.
1250 * The below code essentially only uses the relative value of
1252 * task_ratelimit - dirty_ratelimit
1253 * = (pos_ratio - 1) * dirty_ratelimit
1255 * which reflects the direction and size of dirty position error.
1259 * dirty_ratelimit will follow balanced_dirty_ratelimit iff
1260 * task_ratelimit is on the same side of dirty_ratelimit, too.
1262 * - dirty_ratelimit > balanced_dirty_ratelimit
1263 * - dirty_ratelimit > task_ratelimit (dirty pages are above setpoint)
1264 * lowering dirty_ratelimit will help meet both the position and rate
1265 * control targets. Otherwise, don't update dirty_ratelimit if it will
1266 * only help meet the rate target. After all, what the users ultimately
1267 * feel and care are stable dirty rate and small position error.
1269 * |task_ratelimit - dirty_ratelimit| is used to limit the step size
1270 * and filter out the singular points of balanced_dirty_ratelimit. Which
1271 * keeps jumping around randomly and can even leap far away at times
1272 * due to the small 200ms estimation period of dirty_rate (we want to
1273 * keep that period small to reduce time lags).
1278 * For strictlimit case, calculations above were based on wb counters
1279 * and limits (starting from pos_ratio = wb_position_ratio() and up to
1280 * balanced_dirty_ratelimit = task_ratelimit * write_bw / dirty_rate).
1281 * Hence, to calculate "step" properly, we have to use wb_dirty as
1282 * "dirty" and wb_setpoint as "setpoint".
1284 * We rampup dirty_ratelimit forcibly if wb_dirty is low because
1285 * it's possible that wb_thresh is close to zero due to inactivity
1286 * of backing device.
1288 if (unlikely(wb
->bdi
->capabilities
& BDI_CAP_STRICTLIMIT
)) {
1289 dirty
= dtc
->wb_dirty
;
1290 if (dtc
->wb_dirty
< 8)
1291 setpoint
= dtc
->wb_dirty
+ 1;
1293 setpoint
= (dtc
->wb_thresh
+ dtc
->wb_bg_thresh
) / 2;
1296 if (dirty
< setpoint
) {
1297 x
= min3(wb
->balanced_dirty_ratelimit
,
1298 balanced_dirty_ratelimit
, task_ratelimit
);
1299 if (dirty_ratelimit
< x
)
1300 step
= x
- dirty_ratelimit
;
1302 x
= max3(wb
->balanced_dirty_ratelimit
,
1303 balanced_dirty_ratelimit
, task_ratelimit
);
1304 if (dirty_ratelimit
> x
)
1305 step
= dirty_ratelimit
- x
;
1309 * Don't pursue 100% rate matching. It's impossible since the balanced
1310 * rate itself is constantly fluctuating. So decrease the track speed
1311 * when it gets close to the target. Helps eliminate pointless tremors.
1313 shift
= dirty_ratelimit
/ (2 * step
+ 1);
1314 if (shift
< BITS_PER_LONG
)
1315 step
= DIV_ROUND_UP(step
>> shift
, 8);
1319 if (dirty_ratelimit
< balanced_dirty_ratelimit
)
1320 dirty_ratelimit
+= step
;
1322 dirty_ratelimit
-= step
;
1324 WRITE_ONCE(wb
->dirty_ratelimit
, max(dirty_ratelimit
, 1UL));
1325 wb
->balanced_dirty_ratelimit
= balanced_dirty_ratelimit
;
1327 trace_bdi_dirty_ratelimit(wb
, dirty_rate
, task_ratelimit
);
1330 static void __wb_update_bandwidth(struct dirty_throttle_control
*gdtc
,
1331 struct dirty_throttle_control
*mdtc
,
1332 bool update_ratelimit
)
1334 struct bdi_writeback
*wb
= gdtc
->wb
;
1335 unsigned long now
= jiffies
;
1336 unsigned long elapsed
;
1337 unsigned long dirtied
;
1338 unsigned long written
;
1340 spin_lock(&wb
->list_lock
);
1343 * Lockless checks for elapsed time are racy and delayed update after
1344 * IO completion doesn't do it at all (to make sure written pages are
1345 * accounted reasonably quickly). Make sure elapsed >= 1 to avoid
1348 elapsed
= max(now
- wb
->bw_time_stamp
, 1UL);
1349 dirtied
= percpu_counter_read(&wb
->stat
[WB_DIRTIED
]);
1350 written
= percpu_counter_read(&wb
->stat
[WB_WRITTEN
]);
1352 if (update_ratelimit
) {
1353 domain_update_dirty_limit(gdtc
, now
);
1354 wb_update_dirty_ratelimit(gdtc
, dirtied
, elapsed
);
1357 * @mdtc is always NULL if !CGROUP_WRITEBACK but the
1358 * compiler has no way to figure that out. Help it.
1360 if (IS_ENABLED(CONFIG_CGROUP_WRITEBACK
) && mdtc
) {
1361 domain_update_dirty_limit(mdtc
, now
);
1362 wb_update_dirty_ratelimit(mdtc
, dirtied
, elapsed
);
1365 wb_update_write_bandwidth(wb
, elapsed
, written
);
1367 wb
->dirtied_stamp
= dirtied
;
1368 wb
->written_stamp
= written
;
1369 WRITE_ONCE(wb
->bw_time_stamp
, now
);
1370 spin_unlock(&wb
->list_lock
);
1373 void wb_update_bandwidth(struct bdi_writeback
*wb
)
1375 struct dirty_throttle_control gdtc
= { GDTC_INIT(wb
) };
1377 __wb_update_bandwidth(&gdtc
, NULL
, false);
1380 /* Interval after which we consider wb idle and don't estimate bandwidth */
1381 #define WB_BANDWIDTH_IDLE_JIF (HZ)
1383 static void wb_bandwidth_estimate_start(struct bdi_writeback
*wb
)
1385 unsigned long now
= jiffies
;
1386 unsigned long elapsed
= now
- READ_ONCE(wb
->bw_time_stamp
);
1388 if (elapsed
> WB_BANDWIDTH_IDLE_JIF
&&
1389 !atomic_read(&wb
->writeback_inodes
)) {
1390 spin_lock(&wb
->list_lock
);
1391 wb
->dirtied_stamp
= wb_stat(wb
, WB_DIRTIED
);
1392 wb
->written_stamp
= wb_stat(wb
, WB_WRITTEN
);
1393 WRITE_ONCE(wb
->bw_time_stamp
, now
);
1394 spin_unlock(&wb
->list_lock
);
1399 * After a task dirtied this many pages, balance_dirty_pages_ratelimited()
1400 * will look to see if it needs to start dirty throttling.
1402 * If dirty_poll_interval is too low, big NUMA machines will call the expensive
1403 * global_zone_page_state() too often. So scale it near-sqrt to the safety margin
1404 * (the number of pages we may dirty without exceeding the dirty limits).
1406 static unsigned long dirty_poll_interval(unsigned long dirty
,
1407 unsigned long thresh
)
1410 return 1UL << (ilog2(thresh
- dirty
) >> 1);
1415 static unsigned long wb_max_pause(struct bdi_writeback
*wb
,
1416 unsigned long wb_dirty
)
1418 unsigned long bw
= READ_ONCE(wb
->avg_write_bandwidth
);
1422 * Limit pause time for small memory systems. If sleeping for too long
1423 * time, a small pool of dirty/writeback pages may go empty and disk go
1426 * 8 serves as the safety ratio.
1428 t
= wb_dirty
/ (1 + bw
/ roundup_pow_of_two(1 + HZ
/ 8));
1431 return min_t(unsigned long, t
, MAX_PAUSE
);
1434 static long wb_min_pause(struct bdi_writeback
*wb
,
1436 unsigned long task_ratelimit
,
1437 unsigned long dirty_ratelimit
,
1438 int *nr_dirtied_pause
)
1440 long hi
= ilog2(READ_ONCE(wb
->avg_write_bandwidth
));
1441 long lo
= ilog2(READ_ONCE(wb
->dirty_ratelimit
));
1442 long t
; /* target pause */
1443 long pause
; /* estimated next pause */
1444 int pages
; /* target nr_dirtied_pause */
1446 /* target for 10ms pause on 1-dd case */
1447 t
= max(1, HZ
/ 100);
1450 * Scale up pause time for concurrent dirtiers in order to reduce CPU
1453 * (N * 10ms) on 2^N concurrent tasks.
1456 t
+= (hi
- lo
) * (10 * HZ
) / 1024;
1459 * This is a bit convoluted. We try to base the next nr_dirtied_pause
1460 * on the much more stable dirty_ratelimit. However the next pause time
1461 * will be computed based on task_ratelimit and the two rate limits may
1462 * depart considerably at some time. Especially if task_ratelimit goes
1463 * below dirty_ratelimit/2 and the target pause is max_pause, the next
1464 * pause time will be max_pause*2 _trimmed down_ to max_pause. As a
1465 * result task_ratelimit won't be executed faithfully, which could
1466 * eventually bring down dirty_ratelimit.
1468 * We apply two rules to fix it up:
1469 * 1) try to estimate the next pause time and if necessary, use a lower
1470 * nr_dirtied_pause so as not to exceed max_pause. When this happens,
1471 * nr_dirtied_pause will be "dancing" with task_ratelimit.
1472 * 2) limit the target pause time to max_pause/2, so that the normal
1473 * small fluctuations of task_ratelimit won't trigger rule (1) and
1474 * nr_dirtied_pause will remain as stable as dirty_ratelimit.
1476 t
= min(t
, 1 + max_pause
/ 2);
1477 pages
= dirty_ratelimit
* t
/ roundup_pow_of_two(HZ
);
1480 * Tiny nr_dirtied_pause is found to hurt I/O performance in the test
1481 * case fio-mmap-randwrite-64k, which does 16*{sync read, async write}.
1482 * When the 16 consecutive reads are often interrupted by some dirty
1483 * throttling pause during the async writes, cfq will go into idles
1484 * (deadline is fine). So push nr_dirtied_pause as high as possible
1485 * until reaches DIRTY_POLL_THRESH=32 pages.
1487 if (pages
< DIRTY_POLL_THRESH
) {
1489 pages
= dirty_ratelimit
* t
/ roundup_pow_of_two(HZ
);
1490 if (pages
> DIRTY_POLL_THRESH
) {
1491 pages
= DIRTY_POLL_THRESH
;
1492 t
= HZ
* DIRTY_POLL_THRESH
/ dirty_ratelimit
;
1496 pause
= HZ
* pages
/ (task_ratelimit
+ 1);
1497 if (pause
> max_pause
) {
1499 pages
= task_ratelimit
* t
/ roundup_pow_of_two(HZ
);
1502 *nr_dirtied_pause
= pages
;
1504 * The minimal pause time will normally be half the target pause time.
1506 return pages
>= DIRTY_POLL_THRESH
? 1 + t
/ 2 : t
;
1509 static inline void wb_dirty_limits(struct dirty_throttle_control
*dtc
)
1511 struct bdi_writeback
*wb
= dtc
->wb
;
1512 unsigned long wb_reclaimable
;
1515 * wb_thresh is not treated as some limiting factor as
1516 * dirty_thresh, due to reasons
1517 * - in JBOD setup, wb_thresh can fluctuate a lot
1518 * - in a system with HDD and USB key, the USB key may somehow
1519 * go into state (wb_dirty >> wb_thresh) either because
1520 * wb_dirty starts high, or because wb_thresh drops low.
1521 * In this case we don't want to hard throttle the USB key
1522 * dirtiers for 100 seconds until wb_dirty drops under
1523 * wb_thresh. Instead the auxiliary wb control line in
1524 * wb_position_ratio() will let the dirtier task progress
1525 * at some rate <= (write_bw / 2) for bringing down wb_dirty.
1527 dtc
->wb_thresh
= __wb_calc_thresh(dtc
);
1528 dtc
->wb_bg_thresh
= dtc
->thresh
?
1529 div_u64((u64
)dtc
->wb_thresh
* dtc
->bg_thresh
, dtc
->thresh
) : 0;
1532 * In order to avoid the stacked BDI deadlock we need
1533 * to ensure we accurately count the 'dirty' pages when
1534 * the threshold is low.
1536 * Otherwise it would be possible to get thresh+n pages
1537 * reported dirty, even though there are thresh-m pages
1538 * actually dirty; with m+n sitting in the percpu
1541 if (dtc
->wb_thresh
< 2 * wb_stat_error()) {
1542 wb_reclaimable
= wb_stat_sum(wb
, WB_RECLAIMABLE
);
1543 dtc
->wb_dirty
= wb_reclaimable
+ wb_stat_sum(wb
, WB_WRITEBACK
);
1545 wb_reclaimable
= wb_stat(wb
, WB_RECLAIMABLE
);
1546 dtc
->wb_dirty
= wb_reclaimable
+ wb_stat(wb
, WB_WRITEBACK
);
1551 * balance_dirty_pages() must be called by processes which are generating dirty
1552 * data. It looks at the number of dirty pages in the machine and will force
1553 * the caller to wait once crossing the (background_thresh + dirty_thresh) / 2.
1554 * If we're over `background_thresh' then the writeback threads are woken to
1555 * perform some writeout.
1557 static int balance_dirty_pages(struct bdi_writeback
*wb
,
1558 unsigned long pages_dirtied
, unsigned int flags
)
1560 struct dirty_throttle_control gdtc_stor
= { GDTC_INIT(wb
) };
1561 struct dirty_throttle_control mdtc_stor
= { MDTC_INIT(wb
, &gdtc_stor
) };
1562 struct dirty_throttle_control
* const gdtc
= &gdtc_stor
;
1563 struct dirty_throttle_control
* const mdtc
= mdtc_valid(&mdtc_stor
) ?
1565 struct dirty_throttle_control
*sdtc
;
1566 unsigned long nr_reclaimable
; /* = file_dirty */
1571 int nr_dirtied_pause
;
1572 bool dirty_exceeded
= false;
1573 unsigned long task_ratelimit
;
1574 unsigned long dirty_ratelimit
;
1575 struct backing_dev_info
*bdi
= wb
->bdi
;
1576 bool strictlimit
= bdi
->capabilities
& BDI_CAP_STRICTLIMIT
;
1577 unsigned long start_time
= jiffies
;
1581 unsigned long now
= jiffies
;
1582 unsigned long dirty
, thresh
, bg_thresh
;
1583 unsigned long m_dirty
= 0; /* stop bogus uninit warnings */
1584 unsigned long m_thresh
= 0;
1585 unsigned long m_bg_thresh
= 0;
1587 nr_reclaimable
= global_node_page_state(NR_FILE_DIRTY
);
1588 gdtc
->avail
= global_dirtyable_memory();
1589 gdtc
->dirty
= nr_reclaimable
+ global_node_page_state(NR_WRITEBACK
);
1591 domain_dirty_limits(gdtc
);
1593 if (unlikely(strictlimit
)) {
1594 wb_dirty_limits(gdtc
);
1596 dirty
= gdtc
->wb_dirty
;
1597 thresh
= gdtc
->wb_thresh
;
1598 bg_thresh
= gdtc
->wb_bg_thresh
;
1600 dirty
= gdtc
->dirty
;
1601 thresh
= gdtc
->thresh
;
1602 bg_thresh
= gdtc
->bg_thresh
;
1606 unsigned long filepages
, headroom
, writeback
;
1609 * If @wb belongs to !root memcg, repeat the same
1610 * basic calculations for the memcg domain.
1612 mem_cgroup_wb_stats(wb
, &filepages
, &headroom
,
1613 &mdtc
->dirty
, &writeback
);
1614 mdtc
->dirty
+= writeback
;
1615 mdtc_calc_avail(mdtc
, filepages
, headroom
);
1617 domain_dirty_limits(mdtc
);
1619 if (unlikely(strictlimit
)) {
1620 wb_dirty_limits(mdtc
);
1621 m_dirty
= mdtc
->wb_dirty
;
1622 m_thresh
= mdtc
->wb_thresh
;
1623 m_bg_thresh
= mdtc
->wb_bg_thresh
;
1625 m_dirty
= mdtc
->dirty
;
1626 m_thresh
= mdtc
->thresh
;
1627 m_bg_thresh
= mdtc
->bg_thresh
;
1632 * In laptop mode, we wait until hitting the higher threshold
1633 * before starting background writeout, and then write out all
1634 * the way down to the lower threshold. So slow writers cause
1635 * minimal disk activity.
1637 * In normal mode, we start background writeout at the lower
1638 * background_thresh, to keep the amount of dirty memory low.
1640 if (!laptop_mode
&& nr_reclaimable
> gdtc
->bg_thresh
&&
1641 !writeback_in_progress(wb
))
1642 wb_start_background_writeback(wb
);
1645 * Throttle it only when the background writeback cannot
1646 * catch-up. This avoids (excessively) small writeouts
1647 * when the wb limits are ramping up in case of !strictlimit.
1649 * In strictlimit case make decision based on the wb counters
1650 * and limits. Small writeouts when the wb limits are ramping
1651 * up are the price we consciously pay for strictlimit-ing.
1653 * If memcg domain is in effect, @dirty should be under
1654 * both global and memcg freerun ceilings.
1656 if (dirty
<= dirty_freerun_ceiling(thresh
, bg_thresh
) &&
1658 m_dirty
<= dirty_freerun_ceiling(m_thresh
, m_bg_thresh
))) {
1660 unsigned long m_intv
;
1663 intv
= dirty_poll_interval(dirty
, thresh
);
1666 current
->dirty_paused_when
= now
;
1667 current
->nr_dirtied
= 0;
1669 m_intv
= dirty_poll_interval(m_dirty
, m_thresh
);
1670 current
->nr_dirtied_pause
= min(intv
, m_intv
);
1674 /* Start writeback even when in laptop mode */
1675 if (unlikely(!writeback_in_progress(wb
)))
1676 wb_start_background_writeback(wb
);
1678 mem_cgroup_flush_foreign(wb
);
1681 * Calculate global domain's pos_ratio and select the
1682 * global dtc by default.
1685 wb_dirty_limits(gdtc
);
1687 if ((current
->flags
& PF_LOCAL_THROTTLE
) &&
1689 dirty_freerun_ceiling(gdtc
->wb_thresh
,
1690 gdtc
->wb_bg_thresh
))
1692 * LOCAL_THROTTLE tasks must not be throttled
1693 * when below the per-wb freerun ceiling.
1698 dirty_exceeded
= (gdtc
->wb_dirty
> gdtc
->wb_thresh
) &&
1699 ((gdtc
->dirty
> gdtc
->thresh
) || strictlimit
);
1701 wb_position_ratio(gdtc
);
1706 * If memcg domain is in effect, calculate its
1707 * pos_ratio. @wb should satisfy constraints from
1708 * both global and memcg domains. Choose the one
1709 * w/ lower pos_ratio.
1712 wb_dirty_limits(mdtc
);
1714 if ((current
->flags
& PF_LOCAL_THROTTLE
) &&
1716 dirty_freerun_ceiling(mdtc
->wb_thresh
,
1717 mdtc
->wb_bg_thresh
))
1719 * LOCAL_THROTTLE tasks must not be
1720 * throttled when below the per-wb
1725 dirty_exceeded
|= (mdtc
->wb_dirty
> mdtc
->wb_thresh
) &&
1726 ((mdtc
->dirty
> mdtc
->thresh
) || strictlimit
);
1728 wb_position_ratio(mdtc
);
1729 if (mdtc
->pos_ratio
< gdtc
->pos_ratio
)
1733 if (dirty_exceeded
!= wb
->dirty_exceeded
)
1734 wb
->dirty_exceeded
= dirty_exceeded
;
1736 if (time_is_before_jiffies(READ_ONCE(wb
->bw_time_stamp
) +
1737 BANDWIDTH_INTERVAL
))
1738 __wb_update_bandwidth(gdtc
, mdtc
, true);
1740 /* throttle according to the chosen dtc */
1741 dirty_ratelimit
= READ_ONCE(wb
->dirty_ratelimit
);
1742 task_ratelimit
= ((u64
)dirty_ratelimit
* sdtc
->pos_ratio
) >>
1743 RATELIMIT_CALC_SHIFT
;
1744 max_pause
= wb_max_pause(wb
, sdtc
->wb_dirty
);
1745 min_pause
= wb_min_pause(wb
, max_pause
,
1746 task_ratelimit
, dirty_ratelimit
,
1749 if (unlikely(task_ratelimit
== 0)) {
1754 period
= HZ
* pages_dirtied
/ task_ratelimit
;
1756 if (current
->dirty_paused_when
)
1757 pause
-= now
- current
->dirty_paused_when
;
1759 * For less than 1s think time (ext3/4 may block the dirtier
1760 * for up to 800ms from time to time on 1-HDD; so does xfs,
1761 * however at much less frequency), try to compensate it in
1762 * future periods by updating the virtual time; otherwise just
1763 * do a reset, as it may be a light dirtier.
1765 if (pause
< min_pause
) {
1766 trace_balance_dirty_pages(wb
,
1779 current
->dirty_paused_when
= now
;
1780 current
->nr_dirtied
= 0;
1781 } else if (period
) {
1782 current
->dirty_paused_when
+= period
;
1783 current
->nr_dirtied
= 0;
1784 } else if (current
->nr_dirtied_pause
<= pages_dirtied
)
1785 current
->nr_dirtied_pause
+= pages_dirtied
;
1788 if (unlikely(pause
> max_pause
)) {
1789 /* for occasional dropped task_ratelimit */
1790 now
+= min(pause
- max_pause
, max_pause
);
1795 trace_balance_dirty_pages(wb
,
1807 if (flags
& BDP_ASYNC
) {
1811 __set_current_state(TASK_KILLABLE
);
1812 wb
->dirty_sleep
= now
;
1813 io_schedule_timeout(pause
);
1815 current
->dirty_paused_when
= now
+ pause
;
1816 current
->nr_dirtied
= 0;
1817 current
->nr_dirtied_pause
= nr_dirtied_pause
;
1820 * This is typically equal to (dirty < thresh) and can also
1821 * keep "1000+ dd on a slow USB stick" under control.
1827 * In the case of an unresponsive NFS server and the NFS dirty
1828 * pages exceeds dirty_thresh, give the other good wb's a pipe
1829 * to go through, so that tasks on them still remain responsive.
1831 * In theory 1 page is enough to keep the consumer-producer
1832 * pipe going: the flusher cleans 1 page => the task dirties 1
1833 * more page. However wb_dirty has accounting errors. So use
1834 * the larger and more IO friendly wb_stat_error.
1836 if (sdtc
->wb_dirty
<= wb_stat_error())
1839 if (fatal_signal_pending(current
))
1845 static DEFINE_PER_CPU(int, bdp_ratelimits
);
1848 * Normal tasks are throttled by
1850 * dirty tsk->nr_dirtied_pause pages;
1851 * take a snap in balance_dirty_pages();
1853 * However there is a worst case. If every task exit immediately when dirtied
1854 * (tsk->nr_dirtied_pause - 1) pages, balance_dirty_pages() will never be
1855 * called to throttle the page dirties. The solution is to save the not yet
1856 * throttled page dirties in dirty_throttle_leaks on task exit and charge them
1857 * randomly into the running tasks. This works well for the above worst case,
1858 * as the new task will pick up and accumulate the old task's leaked dirty
1859 * count and eventually get throttled.
1861 DEFINE_PER_CPU(int, dirty_throttle_leaks
) = 0;
1864 * balance_dirty_pages_ratelimited_flags - Balance dirty memory state.
1865 * @mapping: address_space which was dirtied.
1866 * @flags: BDP flags.
1868 * Processes which are dirtying memory should call in here once for each page
1869 * which was newly dirtied. The function will periodically check the system's
1870 * dirty state and will initiate writeback if needed.
1872 * See balance_dirty_pages_ratelimited() for details.
1874 * Return: If @flags contains BDP_ASYNC, it may return -EAGAIN to
1875 * indicate that memory is out of balance and the caller must wait
1876 * for I/O to complete. Otherwise, it will return 0 to indicate
1877 * that either memory was already in balance, or it was able to sleep
1878 * until the amount of dirty memory returned to balance.
1880 int balance_dirty_pages_ratelimited_flags(struct address_space
*mapping
,
1883 struct inode
*inode
= mapping
->host
;
1884 struct backing_dev_info
*bdi
= inode_to_bdi(inode
);
1885 struct bdi_writeback
*wb
= NULL
;
1890 if (!(bdi
->capabilities
& BDI_CAP_WRITEBACK
))
1893 if (inode_cgwb_enabled(inode
))
1894 wb
= wb_get_create_current(bdi
, GFP_KERNEL
);
1898 ratelimit
= current
->nr_dirtied_pause
;
1899 if (wb
->dirty_exceeded
)
1900 ratelimit
= min(ratelimit
, 32 >> (PAGE_SHIFT
- 10));
1904 * This prevents one CPU to accumulate too many dirtied pages without
1905 * calling into balance_dirty_pages(), which can happen when there are
1906 * 1000+ tasks, all of them start dirtying pages at exactly the same
1907 * time, hence all honoured too large initial task->nr_dirtied_pause.
1909 p
= this_cpu_ptr(&bdp_ratelimits
);
1910 if (unlikely(current
->nr_dirtied
>= ratelimit
))
1912 else if (unlikely(*p
>= ratelimit_pages
)) {
1917 * Pick up the dirtied pages by the exited tasks. This avoids lots of
1918 * short-lived tasks (eg. gcc invocations in a kernel build) escaping
1919 * the dirty throttling and livelock other long-run dirtiers.
1921 p
= this_cpu_ptr(&dirty_throttle_leaks
);
1922 if (*p
> 0 && current
->nr_dirtied
< ratelimit
) {
1923 unsigned long nr_pages_dirtied
;
1924 nr_pages_dirtied
= min(*p
, ratelimit
- current
->nr_dirtied
);
1925 *p
-= nr_pages_dirtied
;
1926 current
->nr_dirtied
+= nr_pages_dirtied
;
1930 if (unlikely(current
->nr_dirtied
>= ratelimit
))
1931 ret
= balance_dirty_pages(wb
, current
->nr_dirtied
, flags
);
1936 EXPORT_SYMBOL_GPL(balance_dirty_pages_ratelimited_flags
);
1939 * balance_dirty_pages_ratelimited - balance dirty memory state.
1940 * @mapping: address_space which was dirtied.
1942 * Processes which are dirtying memory should call in here once for each page
1943 * which was newly dirtied. The function will periodically check the system's
1944 * dirty state and will initiate writeback if needed.
1946 * Once we're over the dirty memory limit we decrease the ratelimiting
1947 * by a lot, to prevent individual processes from overshooting the limit
1948 * by (ratelimit_pages) each.
1950 void balance_dirty_pages_ratelimited(struct address_space
*mapping
)
1952 balance_dirty_pages_ratelimited_flags(mapping
, 0);
1954 EXPORT_SYMBOL(balance_dirty_pages_ratelimited
);
1957 * wb_over_bg_thresh - does @wb need to be written back?
1958 * @wb: bdi_writeback of interest
1960 * Determines whether background writeback should keep writing @wb or it's
1963 * Return: %true if writeback should continue.
1965 bool wb_over_bg_thresh(struct bdi_writeback
*wb
)
1967 struct dirty_throttle_control gdtc_stor
= { GDTC_INIT(wb
) };
1968 struct dirty_throttle_control mdtc_stor
= { MDTC_INIT(wb
, &gdtc_stor
) };
1969 struct dirty_throttle_control
* const gdtc
= &gdtc_stor
;
1970 struct dirty_throttle_control
* const mdtc
= mdtc_valid(&mdtc_stor
) ?
1972 unsigned long reclaimable
;
1973 unsigned long thresh
;
1976 * Similar to balance_dirty_pages() but ignores pages being written
1977 * as we're trying to decide whether to put more under writeback.
1979 gdtc
->avail
= global_dirtyable_memory();
1980 gdtc
->dirty
= global_node_page_state(NR_FILE_DIRTY
);
1981 domain_dirty_limits(gdtc
);
1983 if (gdtc
->dirty
> gdtc
->bg_thresh
)
1986 thresh
= wb_calc_thresh(gdtc
->wb
, gdtc
->bg_thresh
);
1987 if (thresh
< 2 * wb_stat_error())
1988 reclaimable
= wb_stat_sum(wb
, WB_RECLAIMABLE
);
1990 reclaimable
= wb_stat(wb
, WB_RECLAIMABLE
);
1992 if (reclaimable
> thresh
)
1996 unsigned long filepages
, headroom
, writeback
;
1998 mem_cgroup_wb_stats(wb
, &filepages
, &headroom
, &mdtc
->dirty
,
2000 mdtc_calc_avail(mdtc
, filepages
, headroom
);
2001 domain_dirty_limits(mdtc
); /* ditto, ignore writeback */
2003 if (mdtc
->dirty
> mdtc
->bg_thresh
)
2006 thresh
= wb_calc_thresh(mdtc
->wb
, mdtc
->bg_thresh
);
2007 if (thresh
< 2 * wb_stat_error())
2008 reclaimable
= wb_stat_sum(wb
, WB_RECLAIMABLE
);
2010 reclaimable
= wb_stat(wb
, WB_RECLAIMABLE
);
2012 if (reclaimable
> thresh
)
2019 #ifdef CONFIG_SYSCTL
2021 * sysctl handler for /proc/sys/vm/dirty_writeback_centisecs
2023 static int dirty_writeback_centisecs_handler(struct ctl_table
*table
, int write
,
2024 void *buffer
, size_t *length
, loff_t
*ppos
)
2026 unsigned int old_interval
= dirty_writeback_interval
;
2029 ret
= proc_dointvec(table
, write
, buffer
, length
, ppos
);
2032 * Writing 0 to dirty_writeback_interval will disable periodic writeback
2033 * and a different non-zero value will wakeup the writeback threads.
2034 * wb_wakeup_delayed() would be more appropriate, but it's a pain to
2035 * iterate over all bdis and wbs.
2036 * The reason we do this is to make the change take effect immediately.
2038 if (!ret
&& write
&& dirty_writeback_interval
&&
2039 dirty_writeback_interval
!= old_interval
)
2040 wakeup_flusher_threads(WB_REASON_PERIODIC
);
2046 void laptop_mode_timer_fn(struct timer_list
*t
)
2048 struct backing_dev_info
*backing_dev_info
=
2049 from_timer(backing_dev_info
, t
, laptop_mode_wb_timer
);
2051 wakeup_flusher_threads_bdi(backing_dev_info
, WB_REASON_LAPTOP_TIMER
);
2055 * We've spun up the disk and we're in laptop mode: schedule writeback
2056 * of all dirty data a few seconds from now. If the flush is already scheduled
2057 * then push it back - the user is still using the disk.
2059 void laptop_io_completion(struct backing_dev_info
*info
)
2061 mod_timer(&info
->laptop_mode_wb_timer
, jiffies
+ laptop_mode
);
2065 * We're in laptop mode and we've just synced. The sync's writes will have
2066 * caused another writeback to be scheduled by laptop_io_completion.
2067 * Nothing needs to be written back anymore, so we unschedule the writeback.
2069 void laptop_sync_completion(void)
2071 struct backing_dev_info
*bdi
;
2075 list_for_each_entry_rcu(bdi
, &bdi_list
, bdi_list
)
2076 del_timer(&bdi
->laptop_mode_wb_timer
);
2082 * If ratelimit_pages is too high then we can get into dirty-data overload
2083 * if a large number of processes all perform writes at the same time.
2085 * Here we set ratelimit_pages to a level which ensures that when all CPUs are
2086 * dirtying in parallel, we cannot go more than 3% (1/32) over the dirty memory
2090 void writeback_set_ratelimit(void)
2092 struct wb_domain
*dom
= &global_wb_domain
;
2093 unsigned long background_thresh
;
2094 unsigned long dirty_thresh
;
2096 global_dirty_limits(&background_thresh
, &dirty_thresh
);
2097 dom
->dirty_limit
= dirty_thresh
;
2098 ratelimit_pages
= dirty_thresh
/ (num_online_cpus() * 32);
2099 if (ratelimit_pages
< 16)
2100 ratelimit_pages
= 16;
2103 static int page_writeback_cpu_online(unsigned int cpu
)
2105 writeback_set_ratelimit();
2109 #ifdef CONFIG_SYSCTL
2111 /* this is needed for the proc_doulongvec_minmax of vm_dirty_bytes */
2112 static const unsigned long dirty_bytes_min
= 2 * PAGE_SIZE
;
2114 static struct ctl_table vm_page_writeback_sysctls
[] = {
2116 .procname
= "dirty_background_ratio",
2117 .data
= &dirty_background_ratio
,
2118 .maxlen
= sizeof(dirty_background_ratio
),
2120 .proc_handler
= dirty_background_ratio_handler
,
2121 .extra1
= SYSCTL_ZERO
,
2122 .extra2
= SYSCTL_ONE_HUNDRED
,
2125 .procname
= "dirty_background_bytes",
2126 .data
= &dirty_background_bytes
,
2127 .maxlen
= sizeof(dirty_background_bytes
),
2129 .proc_handler
= dirty_background_bytes_handler
,
2130 .extra1
= SYSCTL_LONG_ONE
,
2133 .procname
= "dirty_ratio",
2134 .data
= &vm_dirty_ratio
,
2135 .maxlen
= sizeof(vm_dirty_ratio
),
2137 .proc_handler
= dirty_ratio_handler
,
2138 .extra1
= SYSCTL_ZERO
,
2139 .extra2
= SYSCTL_ONE_HUNDRED
,
2142 .procname
= "dirty_bytes",
2143 .data
= &vm_dirty_bytes
,
2144 .maxlen
= sizeof(vm_dirty_bytes
),
2146 .proc_handler
= dirty_bytes_handler
,
2147 .extra1
= (void *)&dirty_bytes_min
,
2150 .procname
= "dirty_writeback_centisecs",
2151 .data
= &dirty_writeback_interval
,
2152 .maxlen
= sizeof(dirty_writeback_interval
),
2154 .proc_handler
= dirty_writeback_centisecs_handler
,
2157 .procname
= "dirty_expire_centisecs",
2158 .data
= &dirty_expire_interval
,
2159 .maxlen
= sizeof(dirty_expire_interval
),
2161 .proc_handler
= proc_dointvec_minmax
,
2162 .extra1
= SYSCTL_ZERO
,
2164 #ifdef CONFIG_HIGHMEM
2166 .procname
= "highmem_is_dirtyable",
2167 .data
= &vm_highmem_is_dirtyable
,
2168 .maxlen
= sizeof(vm_highmem_is_dirtyable
),
2170 .proc_handler
= proc_dointvec_minmax
,
2171 .extra1
= SYSCTL_ZERO
,
2172 .extra2
= SYSCTL_ONE
,
2176 .procname
= "laptop_mode",
2177 .data
= &laptop_mode
,
2178 .maxlen
= sizeof(laptop_mode
),
2180 .proc_handler
= proc_dointvec_jiffies
,
2187 * Called early on to tune the page writeback dirty limits.
2189 * We used to scale dirty pages according to how total memory
2190 * related to pages that could be allocated for buffers.
2192 * However, that was when we used "dirty_ratio" to scale with
2193 * all memory, and we don't do that any more. "dirty_ratio"
2194 * is now applied to total non-HIGHPAGE memory, and as such we can't
2195 * get into the old insane situation any more where we had
2196 * large amounts of dirty pages compared to a small amount of
2197 * non-HIGHMEM memory.
2199 * But we might still want to scale the dirty_ratio by how
2200 * much memory the box has..
2202 void __init
page_writeback_init(void)
2204 BUG_ON(wb_domain_init(&global_wb_domain
, GFP_KERNEL
));
2206 cpuhp_setup_state(CPUHP_AP_ONLINE_DYN
, "mm/writeback:online",
2207 page_writeback_cpu_online
, NULL
);
2208 cpuhp_setup_state(CPUHP_MM_WRITEBACK_DEAD
, "mm/writeback:dead", NULL
,
2209 page_writeback_cpu_online
);
2210 #ifdef CONFIG_SYSCTL
2211 register_sysctl_init("vm", vm_page_writeback_sysctls
);
2216 * tag_pages_for_writeback - tag pages to be written by write_cache_pages
2217 * @mapping: address space structure to write
2218 * @start: starting page index
2219 * @end: ending page index (inclusive)
2221 * This function scans the page range from @start to @end (inclusive) and tags
2222 * all pages that have DIRTY tag set with a special TOWRITE tag. The idea is
2223 * that write_cache_pages (or whoever calls this function) will then use
2224 * TOWRITE tag to identify pages eligible for writeback. This mechanism is
2225 * used to avoid livelocking of writeback by a process steadily creating new
2226 * dirty pages in the file (thus it is important for this function to be quick
2227 * so that it can tag pages faster than a dirtying process can create them).
2229 void tag_pages_for_writeback(struct address_space
*mapping
,
2230 pgoff_t start
, pgoff_t end
)
2232 XA_STATE(xas
, &mapping
->i_pages
, start
);
2233 unsigned int tagged
= 0;
2237 xas_for_each_marked(&xas
, page
, end
, PAGECACHE_TAG_DIRTY
) {
2238 xas_set_mark(&xas
, PAGECACHE_TAG_TOWRITE
);
2239 if (++tagged
% XA_CHECK_SCHED
)
2243 xas_unlock_irq(&xas
);
2247 xas_unlock_irq(&xas
);
2249 EXPORT_SYMBOL(tag_pages_for_writeback
);
2252 * write_cache_pages - walk the list of dirty pages of the given address space and write all of them.
2253 * @mapping: address space structure to write
2254 * @wbc: subtract the number of written pages from *@wbc->nr_to_write
2255 * @writepage: function called for each page
2256 * @data: data passed to writepage function
2258 * If a page is already under I/O, write_cache_pages() skips it, even
2259 * if it's dirty. This is desirable behaviour for memory-cleaning writeback,
2260 * but it is INCORRECT for data-integrity system calls such as fsync(). fsync()
2261 * and msync() need to guarantee that all the data which was dirty at the time
2262 * the call was made get new I/O started against them. If wbc->sync_mode is
2263 * WB_SYNC_ALL then we were called for data integrity and we must wait for
2264 * existing IO to complete.
2266 * To avoid livelocks (when other process dirties new pages), we first tag
2267 * pages which should be written back with TOWRITE tag and only then start
2268 * writing them. For data-integrity sync we have to be careful so that we do
2269 * not miss some pages (e.g., because some other process has cleared TOWRITE
2270 * tag we set). The rule we follow is that TOWRITE tag can be cleared only
2271 * by the process clearing the DIRTY tag (and submitting the page for IO).
2273 * To avoid deadlocks between range_cyclic writeback and callers that hold
2274 * pages in PageWriteback to aggregate IO until write_cache_pages() returns,
2275 * we do not loop back to the start of the file. Doing so causes a page
2276 * lock/page writeback access order inversion - we should only ever lock
2277 * multiple pages in ascending page->index order, and looping back to the start
2278 * of the file violates that rule and causes deadlocks.
2280 * Return: %0 on success, negative error code otherwise
2282 int write_cache_pages(struct address_space
*mapping
,
2283 struct writeback_control
*wbc
, writepage_t writepage
,
2289 struct pagevec pvec
;
2292 pgoff_t end
; /* Inclusive */
2294 int range_whole
= 0;
2297 pagevec_init(&pvec
);
2298 if (wbc
->range_cyclic
) {
2299 index
= mapping
->writeback_index
; /* prev offset */
2302 index
= wbc
->range_start
>> PAGE_SHIFT
;
2303 end
= wbc
->range_end
>> PAGE_SHIFT
;
2304 if (wbc
->range_start
== 0 && wbc
->range_end
== LLONG_MAX
)
2307 if (wbc
->sync_mode
== WB_SYNC_ALL
|| wbc
->tagged_writepages
) {
2308 tag_pages_for_writeback(mapping
, index
, end
);
2309 tag
= PAGECACHE_TAG_TOWRITE
;
2311 tag
= PAGECACHE_TAG_DIRTY
;
2314 while (!done
&& (index
<= end
)) {
2317 nr_pages
= pagevec_lookup_range_tag(&pvec
, mapping
, &index
, end
,
2322 for (i
= 0; i
< nr_pages
; i
++) {
2323 struct page
*page
= pvec
.pages
[i
];
2325 done_index
= page
->index
;
2330 * Page truncated or invalidated. We can freely skip it
2331 * then, even for data integrity operations: the page
2332 * has disappeared concurrently, so there could be no
2333 * real expectation of this data integrity operation
2334 * even if there is now a new, dirty page at the same
2335 * pagecache address.
2337 if (unlikely(page
->mapping
!= mapping
)) {
2343 if (!PageDirty(page
)) {
2344 /* someone wrote it for us */
2345 goto continue_unlock
;
2348 if (PageWriteback(page
)) {
2349 if (wbc
->sync_mode
!= WB_SYNC_NONE
)
2350 wait_on_page_writeback(page
);
2352 goto continue_unlock
;
2355 BUG_ON(PageWriteback(page
));
2356 if (!clear_page_dirty_for_io(page
))
2357 goto continue_unlock
;
2359 trace_wbc_writepage(wbc
, inode_to_bdi(mapping
->host
));
2360 error
= (*writepage
)(page
, wbc
, data
);
2361 if (unlikely(error
)) {
2363 * Handle errors according to the type of
2364 * writeback. There's no need to continue for
2365 * background writeback. Just push done_index
2366 * past this page so media errors won't choke
2367 * writeout for the entire file. For integrity
2368 * writeback, we must process the entire dirty
2369 * set regardless of errors because the fs may
2370 * still have state to clear for each page. In
2371 * that case we continue processing and return
2374 if (error
== AOP_WRITEPAGE_ACTIVATE
) {
2377 } else if (wbc
->sync_mode
!= WB_SYNC_ALL
) {
2379 done_index
= page
->index
+ 1;
2388 * We stop writing back only if we are not doing
2389 * integrity sync. In case of integrity sync we have to
2390 * keep going until we have written all the pages
2391 * we tagged for writeback prior to entering this loop.
2393 if (--wbc
->nr_to_write
<= 0 &&
2394 wbc
->sync_mode
== WB_SYNC_NONE
) {
2399 pagevec_release(&pvec
);
2404 * If we hit the last page and there is more work to be done: wrap
2405 * back the index back to the start of the file for the next
2406 * time we are called.
2408 if (wbc
->range_cyclic
&& !done
)
2410 if (wbc
->range_cyclic
|| (range_whole
&& wbc
->nr_to_write
> 0))
2411 mapping
->writeback_index
= done_index
;
2415 EXPORT_SYMBOL(write_cache_pages
);
2418 * Function used by generic_writepages to call the real writepage
2419 * function and set the mapping flags on error
2421 static int __writepage(struct page
*page
, struct writeback_control
*wbc
,
2424 struct address_space
*mapping
= data
;
2425 int ret
= mapping
->a_ops
->writepage(page
, wbc
);
2426 mapping_set_error(mapping
, ret
);
2431 * generic_writepages - walk the list of dirty pages of the given address space and writepage() all of them.
2432 * @mapping: address space structure to write
2433 * @wbc: subtract the number of written pages from *@wbc->nr_to_write
2435 * This is a library function, which implements the writepages()
2436 * address_space_operation.
2438 * Return: %0 on success, negative error code otherwise
2440 int generic_writepages(struct address_space
*mapping
,
2441 struct writeback_control
*wbc
)
2443 struct blk_plug plug
;
2446 /* deal with chardevs and other special file */
2447 if (!mapping
->a_ops
->writepage
)
2450 blk_start_plug(&plug
);
2451 ret
= write_cache_pages(mapping
, wbc
, __writepage
, mapping
);
2452 blk_finish_plug(&plug
);
2456 EXPORT_SYMBOL(generic_writepages
);
2458 int do_writepages(struct address_space
*mapping
, struct writeback_control
*wbc
)
2461 struct bdi_writeback
*wb
;
2463 if (wbc
->nr_to_write
<= 0)
2465 wb
= inode_to_wb_wbc(mapping
->host
, wbc
);
2466 wb_bandwidth_estimate_start(wb
);
2468 if (mapping
->a_ops
->writepages
)
2469 ret
= mapping
->a_ops
->writepages(mapping
, wbc
);
2471 ret
= generic_writepages(mapping
, wbc
);
2472 if ((ret
!= -ENOMEM
) || (wbc
->sync_mode
!= WB_SYNC_ALL
))
2476 * Lacking an allocation context or the locality or writeback
2477 * state of any of the inode's pages, throttle based on
2478 * writeback activity on the local node. It's as good a
2481 reclaim_throttle(NODE_DATA(numa_node_id()),
2482 VMSCAN_THROTTLE_WRITEBACK
);
2485 * Usually few pages are written by now from those we've just submitted
2486 * but if there's constant writeback being submitted, this makes sure
2487 * writeback bandwidth is updated once in a while.
2489 if (time_is_before_jiffies(READ_ONCE(wb
->bw_time_stamp
) +
2490 BANDWIDTH_INTERVAL
))
2491 wb_update_bandwidth(wb
);
2496 * folio_write_one - write out a single folio and wait on I/O.
2497 * @folio: The folio to write.
2499 * The folio must be locked by the caller and will be unlocked upon return.
2501 * Note that the mapping's AS_EIO/AS_ENOSPC flags will be cleared when this
2504 * Return: %0 on success, negative error code otherwise
2506 int folio_write_one(struct folio
*folio
)
2508 struct address_space
*mapping
= folio
->mapping
;
2510 struct writeback_control wbc
= {
2511 .sync_mode
= WB_SYNC_ALL
,
2512 .nr_to_write
= folio_nr_pages(folio
),
2515 BUG_ON(!folio_test_locked(folio
));
2517 folio_wait_writeback(folio
);
2519 if (folio_clear_dirty_for_io(folio
)) {
2521 ret
= mapping
->a_ops
->writepage(&folio
->page
, &wbc
);
2523 folio_wait_writeback(folio
);
2526 folio_unlock(folio
);
2530 ret
= filemap_check_errors(mapping
);
2533 EXPORT_SYMBOL(folio_write_one
);
2536 * For address_spaces which do not use buffers nor write back.
2538 bool noop_dirty_folio(struct address_space
*mapping
, struct folio
*folio
)
2540 if (!folio_test_dirty(folio
))
2541 return !folio_test_set_dirty(folio
);
2544 EXPORT_SYMBOL(noop_dirty_folio
);
2547 * Helper function for set_page_dirty family.
2549 * Caller must hold lock_page_memcg().
2551 * NOTE: This relies on being atomic wrt interrupts.
2553 static void folio_account_dirtied(struct folio
*folio
,
2554 struct address_space
*mapping
)
2556 struct inode
*inode
= mapping
->host
;
2558 trace_writeback_dirty_folio(folio
, mapping
);
2560 if (mapping_can_writeback(mapping
)) {
2561 struct bdi_writeback
*wb
;
2562 long nr
= folio_nr_pages(folio
);
2564 inode_attach_wb(inode
, &folio
->page
);
2565 wb
= inode_to_wb(inode
);
2567 __lruvec_stat_mod_folio(folio
, NR_FILE_DIRTY
, nr
);
2568 __zone_stat_mod_folio(folio
, NR_ZONE_WRITE_PENDING
, nr
);
2569 __node_stat_mod_folio(folio
, NR_DIRTIED
, nr
);
2570 wb_stat_mod(wb
, WB_RECLAIMABLE
, nr
);
2571 wb_stat_mod(wb
, WB_DIRTIED
, nr
);
2572 task_io_account_write(nr
* PAGE_SIZE
);
2573 current
->nr_dirtied
+= nr
;
2574 __this_cpu_add(bdp_ratelimits
, nr
);
2576 mem_cgroup_track_foreign_dirty(folio
, wb
);
2581 * Helper function for deaccounting dirty page without writeback.
2583 * Caller must hold lock_page_memcg().
2585 void folio_account_cleaned(struct folio
*folio
, struct bdi_writeback
*wb
)
2587 long nr
= folio_nr_pages(folio
);
2589 lruvec_stat_mod_folio(folio
, NR_FILE_DIRTY
, -nr
);
2590 zone_stat_mod_folio(folio
, NR_ZONE_WRITE_PENDING
, -nr
);
2591 wb_stat_mod(wb
, WB_RECLAIMABLE
, -nr
);
2592 task_io_account_cancelled_write(nr
* PAGE_SIZE
);
2596 * Mark the folio dirty, and set it dirty in the page cache, and mark
2599 * If warn is true, then emit a warning if the folio is not uptodate and has
2600 * not been truncated.
2602 * The caller must hold lock_page_memcg(). Most callers have the folio
2603 * locked. A few have the folio blocked from truncation through other
2604 * means (eg zap_page_range() has it mapped and is holding the page table
2605 * lock). This can also be called from mark_buffer_dirty(), which I
2606 * cannot prove is always protected against truncate.
2608 void __folio_mark_dirty(struct folio
*folio
, struct address_space
*mapping
,
2611 unsigned long flags
;
2613 xa_lock_irqsave(&mapping
->i_pages
, flags
);
2614 if (folio
->mapping
) { /* Race with truncate? */
2615 WARN_ON_ONCE(warn
&& !folio_test_uptodate(folio
));
2616 folio_account_dirtied(folio
, mapping
);
2617 __xa_set_mark(&mapping
->i_pages
, folio_index(folio
),
2618 PAGECACHE_TAG_DIRTY
);
2620 xa_unlock_irqrestore(&mapping
->i_pages
, flags
);
2624 * filemap_dirty_folio - Mark a folio dirty for filesystems which do not use buffer_heads.
2625 * @mapping: Address space this folio belongs to.
2626 * @folio: Folio to be marked as dirty.
2628 * Filesystems which do not use buffer heads should call this function
2629 * from their set_page_dirty address space operation. It ignores the
2630 * contents of folio_get_private(), so if the filesystem marks individual
2631 * blocks as dirty, the filesystem should handle that itself.
2633 * This is also sometimes used by filesystems which use buffer_heads when
2634 * a single buffer is being dirtied: we want to set the folio dirty in
2635 * that case, but not all the buffers. This is a "bottom-up" dirtying,
2636 * whereas block_dirty_folio() is a "top-down" dirtying.
2638 * The caller must ensure this doesn't race with truncation. Most will
2639 * simply hold the folio lock, but e.g. zap_pte_range() calls with the
2640 * folio mapped and the pte lock held, which also locks out truncation.
2642 bool filemap_dirty_folio(struct address_space
*mapping
, struct folio
*folio
)
2644 folio_memcg_lock(folio
);
2645 if (folio_test_set_dirty(folio
)) {
2646 folio_memcg_unlock(folio
);
2650 __folio_mark_dirty(folio
, mapping
, !folio_test_private(folio
));
2651 folio_memcg_unlock(folio
);
2653 if (mapping
->host
) {
2654 /* !PageAnon && !swapper_space */
2655 __mark_inode_dirty(mapping
->host
, I_DIRTY_PAGES
);
2659 EXPORT_SYMBOL(filemap_dirty_folio
);
2662 * folio_account_redirty - Manually account for redirtying a page.
2663 * @folio: The folio which is being redirtied.
2665 * Most filesystems should call folio_redirty_for_writepage() instead
2666 * of this fuction. If your filesystem is doing writeback outside the
2667 * context of a writeback_control(), it can call this when redirtying
2668 * a folio, to de-account the dirty counters (NR_DIRTIED, WB_DIRTIED,
2669 * tsk->nr_dirtied), so that they match the written counters (NR_WRITTEN,
2670 * WB_WRITTEN) in long term. The mismatches will lead to systematic errors
2671 * in balanced_dirty_ratelimit and the dirty pages position control.
2673 void folio_account_redirty(struct folio
*folio
)
2675 struct address_space
*mapping
= folio
->mapping
;
2677 if (mapping
&& mapping_can_writeback(mapping
)) {
2678 struct inode
*inode
= mapping
->host
;
2679 struct bdi_writeback
*wb
;
2680 struct wb_lock_cookie cookie
= {};
2681 long nr
= folio_nr_pages(folio
);
2683 wb
= unlocked_inode_to_wb_begin(inode
, &cookie
);
2684 current
->nr_dirtied
-= nr
;
2685 node_stat_mod_folio(folio
, NR_DIRTIED
, -nr
);
2686 wb_stat_mod(wb
, WB_DIRTIED
, -nr
);
2687 unlocked_inode_to_wb_end(inode
, &cookie
);
2690 EXPORT_SYMBOL(folio_account_redirty
);
2693 * folio_redirty_for_writepage - Decline to write a dirty folio.
2694 * @wbc: The writeback control.
2695 * @folio: The folio.
2697 * When a writepage implementation decides that it doesn't want to write
2698 * @folio for some reason, it should call this function, unlock @folio and
2701 * Return: True if we redirtied the folio. False if someone else dirtied
2704 bool folio_redirty_for_writepage(struct writeback_control
*wbc
,
2705 struct folio
*folio
)
2708 long nr
= folio_nr_pages(folio
);
2710 wbc
->pages_skipped
+= nr
;
2711 ret
= filemap_dirty_folio(folio
->mapping
, folio
);
2712 folio_account_redirty(folio
);
2716 EXPORT_SYMBOL(folio_redirty_for_writepage
);
2719 * folio_mark_dirty - Mark a folio as being modified.
2720 * @folio: The folio.
2722 * The folio may not be truncated while this function is running.
2723 * Holding the folio lock is sufficient to prevent truncation, but some
2724 * callers cannot acquire a sleeping lock. These callers instead hold
2725 * the page table lock for a page table which contains at least one page
2726 * in this folio. Truncation will block on the page table lock as it
2727 * unmaps pages before removing the folio from its mapping.
2729 * Return: True if the folio was newly dirtied, false if it was already dirty.
2731 bool folio_mark_dirty(struct folio
*folio
)
2733 struct address_space
*mapping
= folio_mapping(folio
);
2735 if (likely(mapping
)) {
2737 * readahead/lru_deactivate_page could remain
2738 * PG_readahead/PG_reclaim due to race with folio_end_writeback
2739 * About readahead, if the folio is written, the flags would be
2740 * reset. So no problem.
2741 * About lru_deactivate_page, if the folio is redirtied,
2742 * the flag will be reset. So no problem. but if the
2743 * folio is used by readahead it will confuse readahead
2744 * and make it restart the size rampup process. But it's
2745 * a trivial problem.
2747 if (folio_test_reclaim(folio
))
2748 folio_clear_reclaim(folio
);
2749 return mapping
->a_ops
->dirty_folio(mapping
, folio
);
2752 return noop_dirty_folio(mapping
, folio
);
2754 EXPORT_SYMBOL(folio_mark_dirty
);
2757 * set_page_dirty() is racy if the caller has no reference against
2758 * page->mapping->host, and if the page is unlocked. This is because another
2759 * CPU could truncate the page off the mapping and then free the mapping.
2761 * Usually, the page _is_ locked, or the caller is a user-space process which
2762 * holds a reference on the inode by having an open file.
2764 * In other cases, the page should be locked before running set_page_dirty().
2766 int set_page_dirty_lock(struct page
*page
)
2771 ret
= set_page_dirty(page
);
2775 EXPORT_SYMBOL(set_page_dirty_lock
);
2778 * This cancels just the dirty bit on the kernel page itself, it does NOT
2779 * actually remove dirty bits on any mmap's that may be around. It also
2780 * leaves the page tagged dirty, so any sync activity will still find it on
2781 * the dirty lists, and in particular, clear_page_dirty_for_io() will still
2782 * look at the dirty bits in the VM.
2784 * Doing this should *normally* only ever be done when a page is truncated,
2785 * and is not actually mapped anywhere at all. However, fs/buffer.c does
2786 * this when it notices that somebody has cleaned out all the buffers on a
2787 * page without actually doing it through the VM. Can you say "ext3 is
2788 * horribly ugly"? Thought you could.
2790 void __folio_cancel_dirty(struct folio
*folio
)
2792 struct address_space
*mapping
= folio_mapping(folio
);
2794 if (mapping_can_writeback(mapping
)) {
2795 struct inode
*inode
= mapping
->host
;
2796 struct bdi_writeback
*wb
;
2797 struct wb_lock_cookie cookie
= {};
2799 folio_memcg_lock(folio
);
2800 wb
= unlocked_inode_to_wb_begin(inode
, &cookie
);
2802 if (folio_test_clear_dirty(folio
))
2803 folio_account_cleaned(folio
, wb
);
2805 unlocked_inode_to_wb_end(inode
, &cookie
);
2806 folio_memcg_unlock(folio
);
2808 folio_clear_dirty(folio
);
2811 EXPORT_SYMBOL(__folio_cancel_dirty
);
2814 * Clear a folio's dirty flag, while caring for dirty memory accounting.
2815 * Returns true if the folio was previously dirty.
2817 * This is for preparing to put the folio under writeout. We leave
2818 * the folio tagged as dirty in the xarray so that a concurrent
2819 * write-for-sync can discover it via a PAGECACHE_TAG_DIRTY walk.
2820 * The ->writepage implementation will run either folio_start_writeback()
2821 * or folio_mark_dirty(), at which stage we bring the folio's dirty flag
2822 * and xarray dirty tag back into sync.
2824 * This incoherency between the folio's dirty flag and xarray tag is
2825 * unfortunate, but it only exists while the folio is locked.
2827 bool folio_clear_dirty_for_io(struct folio
*folio
)
2829 struct address_space
*mapping
= folio_mapping(folio
);
2832 VM_BUG_ON_FOLIO(!folio_test_locked(folio
), folio
);
2834 if (mapping
&& mapping_can_writeback(mapping
)) {
2835 struct inode
*inode
= mapping
->host
;
2836 struct bdi_writeback
*wb
;
2837 struct wb_lock_cookie cookie
= {};
2840 * Yes, Virginia, this is indeed insane.
2842 * We use this sequence to make sure that
2843 * (a) we account for dirty stats properly
2844 * (b) we tell the low-level filesystem to
2845 * mark the whole folio dirty if it was
2846 * dirty in a pagetable. Only to then
2847 * (c) clean the folio again and return 1 to
2848 * cause the writeback.
2850 * This way we avoid all nasty races with the
2851 * dirty bit in multiple places and clearing
2852 * them concurrently from different threads.
2854 * Note! Normally the "folio_mark_dirty(folio)"
2855 * has no effect on the actual dirty bit - since
2856 * that will already usually be set. But we
2857 * need the side effects, and it can help us
2860 * We basically use the folio "master dirty bit"
2861 * as a serialization point for all the different
2862 * threads doing their things.
2864 if (folio_mkclean(folio
))
2865 folio_mark_dirty(folio
);
2867 * We carefully synchronise fault handlers against
2868 * installing a dirty pte and marking the folio dirty
2869 * at this point. We do this by having them hold the
2870 * page lock while dirtying the folio, and folios are
2871 * always locked coming in here, so we get the desired
2874 wb
= unlocked_inode_to_wb_begin(inode
, &cookie
);
2875 if (folio_test_clear_dirty(folio
)) {
2876 long nr
= folio_nr_pages(folio
);
2877 lruvec_stat_mod_folio(folio
, NR_FILE_DIRTY
, -nr
);
2878 zone_stat_mod_folio(folio
, NR_ZONE_WRITE_PENDING
, -nr
);
2879 wb_stat_mod(wb
, WB_RECLAIMABLE
, -nr
);
2882 unlocked_inode_to_wb_end(inode
, &cookie
);
2885 return folio_test_clear_dirty(folio
);
2887 EXPORT_SYMBOL(folio_clear_dirty_for_io
);
2889 static void wb_inode_writeback_start(struct bdi_writeback
*wb
)
2891 atomic_inc(&wb
->writeback_inodes
);
2894 static void wb_inode_writeback_end(struct bdi_writeback
*wb
)
2896 unsigned long flags
;
2897 atomic_dec(&wb
->writeback_inodes
);
2899 * Make sure estimate of writeback throughput gets updated after
2900 * writeback completed. We delay the update by BANDWIDTH_INTERVAL
2901 * (which is the interval other bandwidth updates use for batching) so
2902 * that if multiple inodes end writeback at a similar time, they get
2903 * batched into one bandwidth update.
2905 spin_lock_irqsave(&wb
->work_lock
, flags
);
2906 if (test_bit(WB_registered
, &wb
->state
))
2907 queue_delayed_work(bdi_wq
, &wb
->bw_dwork
, BANDWIDTH_INTERVAL
);
2908 spin_unlock_irqrestore(&wb
->work_lock
, flags
);
2911 bool __folio_end_writeback(struct folio
*folio
)
2913 long nr
= folio_nr_pages(folio
);
2914 struct address_space
*mapping
= folio_mapping(folio
);
2917 folio_memcg_lock(folio
);
2918 if (mapping
&& mapping_use_writeback_tags(mapping
)) {
2919 struct inode
*inode
= mapping
->host
;
2920 struct backing_dev_info
*bdi
= inode_to_bdi(inode
);
2921 unsigned long flags
;
2923 xa_lock_irqsave(&mapping
->i_pages
, flags
);
2924 ret
= folio_test_clear_writeback(folio
);
2926 __xa_clear_mark(&mapping
->i_pages
, folio_index(folio
),
2927 PAGECACHE_TAG_WRITEBACK
);
2928 if (bdi
->capabilities
& BDI_CAP_WRITEBACK_ACCT
) {
2929 struct bdi_writeback
*wb
= inode_to_wb(inode
);
2931 wb_stat_mod(wb
, WB_WRITEBACK
, -nr
);
2932 __wb_writeout_add(wb
, nr
);
2933 if (!mapping_tagged(mapping
,
2934 PAGECACHE_TAG_WRITEBACK
))
2935 wb_inode_writeback_end(wb
);
2939 if (mapping
->host
&& !mapping_tagged(mapping
,
2940 PAGECACHE_TAG_WRITEBACK
))
2941 sb_clear_inode_writeback(mapping
->host
);
2943 xa_unlock_irqrestore(&mapping
->i_pages
, flags
);
2945 ret
= folio_test_clear_writeback(folio
);
2948 lruvec_stat_mod_folio(folio
, NR_WRITEBACK
, -nr
);
2949 zone_stat_mod_folio(folio
, NR_ZONE_WRITE_PENDING
, -nr
);
2950 node_stat_mod_folio(folio
, NR_WRITTEN
, nr
);
2952 folio_memcg_unlock(folio
);
2956 bool __folio_start_writeback(struct folio
*folio
, bool keep_write
)
2958 long nr
= folio_nr_pages(folio
);
2959 struct address_space
*mapping
= folio_mapping(folio
);
2963 folio_memcg_lock(folio
);
2964 if (mapping
&& mapping_use_writeback_tags(mapping
)) {
2965 XA_STATE(xas
, &mapping
->i_pages
, folio_index(folio
));
2966 struct inode
*inode
= mapping
->host
;
2967 struct backing_dev_info
*bdi
= inode_to_bdi(inode
);
2968 unsigned long flags
;
2970 xas_lock_irqsave(&xas
, flags
);
2972 ret
= folio_test_set_writeback(folio
);
2976 on_wblist
= mapping_tagged(mapping
,
2977 PAGECACHE_TAG_WRITEBACK
);
2979 xas_set_mark(&xas
, PAGECACHE_TAG_WRITEBACK
);
2980 if (bdi
->capabilities
& BDI_CAP_WRITEBACK_ACCT
) {
2981 struct bdi_writeback
*wb
= inode_to_wb(inode
);
2983 wb_stat_mod(wb
, WB_WRITEBACK
, nr
);
2985 wb_inode_writeback_start(wb
);
2989 * We can come through here when swapping
2990 * anonymous folios, so we don't necessarily
2991 * have an inode to track for sync.
2993 if (mapping
->host
&& !on_wblist
)
2994 sb_mark_inode_writeback(mapping
->host
);
2996 if (!folio_test_dirty(folio
))
2997 xas_clear_mark(&xas
, PAGECACHE_TAG_DIRTY
);
2999 xas_clear_mark(&xas
, PAGECACHE_TAG_TOWRITE
);
3000 xas_unlock_irqrestore(&xas
, flags
);
3002 ret
= folio_test_set_writeback(folio
);
3005 lruvec_stat_mod_folio(folio
, NR_WRITEBACK
, nr
);
3006 zone_stat_mod_folio(folio
, NR_ZONE_WRITE_PENDING
, nr
);
3008 folio_memcg_unlock(folio
);
3009 access_ret
= arch_make_folio_accessible(folio
);
3011 * If writeback has been triggered on a page that cannot be made
3012 * accessible, it is too late to recover here.
3014 VM_BUG_ON_FOLIO(access_ret
!= 0, folio
);
3018 EXPORT_SYMBOL(__folio_start_writeback
);
3021 * folio_wait_writeback - Wait for a folio to finish writeback.
3022 * @folio: The folio to wait for.
3024 * If the folio is currently being written back to storage, wait for the
3027 * Context: Sleeps. Must be called in process context and with
3028 * no spinlocks held. Caller should hold a reference on the folio.
3029 * If the folio is not locked, writeback may start again after writeback
3032 void folio_wait_writeback(struct folio
*folio
)
3034 while (folio_test_writeback(folio
)) {
3035 trace_folio_wait_writeback(folio
, folio_mapping(folio
));
3036 folio_wait_bit(folio
, PG_writeback
);
3039 EXPORT_SYMBOL_GPL(folio_wait_writeback
);
3042 * folio_wait_writeback_killable - Wait for a folio to finish writeback.
3043 * @folio: The folio to wait for.
3045 * If the folio is currently being written back to storage, wait for the
3046 * I/O to complete or a fatal signal to arrive.
3048 * Context: Sleeps. Must be called in process context and with
3049 * no spinlocks held. Caller should hold a reference on the folio.
3050 * If the folio is not locked, writeback may start again after writeback
3052 * Return: 0 on success, -EINTR if we get a fatal signal while waiting.
3054 int folio_wait_writeback_killable(struct folio
*folio
)
3056 while (folio_test_writeback(folio
)) {
3057 trace_folio_wait_writeback(folio
, folio_mapping(folio
));
3058 if (folio_wait_bit_killable(folio
, PG_writeback
))
3064 EXPORT_SYMBOL_GPL(folio_wait_writeback_killable
);
3067 * folio_wait_stable() - wait for writeback to finish, if necessary.
3068 * @folio: The folio to wait on.
3070 * This function determines if the given folio is related to a backing
3071 * device that requires folio contents to be held stable during writeback.
3072 * If so, then it will wait for any pending writeback to complete.
3074 * Context: Sleeps. Must be called in process context and with
3075 * no spinlocks held. Caller should hold a reference on the folio.
3076 * If the folio is not locked, writeback may start again after writeback
3079 void folio_wait_stable(struct folio
*folio
)
3081 if (folio_inode(folio
)->i_sb
->s_iflags
& SB_I_STABLE_WRITES
)
3082 folio_wait_writeback(folio
);
3084 EXPORT_SYMBOL_GPL(folio_wait_stable
);