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1/*
2 * mm/page-writeback.c
3 *
4 * Copyright (C) 2002, Linus Torvalds.
5 * Copyright (C) 2007 Red Hat, Inc., Peter Zijlstra
6 *
7 * Contains functions related to writing back dirty pages at the
8 * address_space level.
9 *
10 * 10Apr2002 Andrew Morton
11 * Initial version
12 */
13
14#include <linux/kernel.h>
15#include <linux/export.h>
16#include <linux/spinlock.h>
17#include <linux/fs.h>
18#include <linux/mm.h>
19#include <linux/swap.h>
20#include <linux/slab.h>
21#include <linux/pagemap.h>
22#include <linux/writeback.h>
23#include <linux/init.h>
24#include <linux/backing-dev.h>
25#include <linux/task_io_accounting_ops.h>
26#include <linux/blkdev.h>
27#include <linux/mpage.h>
28#include <linux/rmap.h>
29#include <linux/percpu.h>
30#include <linux/notifier.h>
31#include <linux/smp.h>
32#include <linux/sysctl.h>
33#include <linux/cpu.h>
34#include <linux/syscalls.h>
35#include <linux/buffer_head.h> /* __set_page_dirty_buffers */
36#include <linux/pagevec.h>
37#include <linux/timer.h>
38#include <linux/sched/rt.h>
39#include <linux/mm_inline.h>
40#include <trace/events/writeback.h>
41
42#include "internal.h"
43
44/*
45 * Sleep at most 200ms at a time in balance_dirty_pages().
46 */
47#define MAX_PAUSE max(HZ/5, 1)
48
49/*
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.
52 */
53#define DIRTY_POLL_THRESH (128 >> (PAGE_SHIFT - 10))
54
55/*
56 * Estimate write bandwidth at 200ms intervals.
57 */
58#define BANDWIDTH_INTERVAL max(HZ/5, 1)
59
60#define RATELIMIT_CALC_SHIFT 10
61
62/*
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.
65 */
66static long ratelimit_pages = 32;
67
68/* The following parameters are exported via /proc/sys/vm */
69
70/*
71 * Start background writeback (via writeback threads) at this percentage
72 */
73int dirty_background_ratio = 10;
74
75/*
76 * dirty_background_bytes starts at 0 (disabled) so that it is a function of
77 * dirty_background_ratio * the amount of dirtyable memory
78 */
79unsigned long dirty_background_bytes;
80
81/*
82 * free highmem will not be subtracted from the total free memory
83 * for calculating free ratios if vm_highmem_is_dirtyable is true
84 */
85int vm_highmem_is_dirtyable;
86
87/*
88 * The generator of dirty data starts writeback at this percentage
89 */
90int vm_dirty_ratio = 20;
91
92/*
93 * vm_dirty_bytes starts at 0 (disabled) so that it is a function of
94 * vm_dirty_ratio * the amount of dirtyable memory
95 */
96unsigned long vm_dirty_bytes;
97
98/*
99 * The interval between `kupdate'-style writebacks
100 */
101unsigned int dirty_writeback_interval = 5 * 100; /* centiseconds */
102
103EXPORT_SYMBOL_GPL(dirty_writeback_interval);
104
105/*
106 * The longest time for which data is allowed to remain dirty
107 */
108unsigned int dirty_expire_interval = 30 * 100; /* centiseconds */
109
110/*
111 * Flag that makes the machine dump writes/reads and block dirtyings.
112 */
113int block_dump;
114
115/*
116 * Flag that puts the machine in "laptop mode". Doubles as a timeout in jiffies:
117 * a full sync is triggered after this time elapses without any disk activity.
118 */
119int laptop_mode;
120
121EXPORT_SYMBOL(laptop_mode);
122
123/* End of sysctl-exported parameters */
124
125struct wb_domain global_wb_domain;
126
127/* consolidated parameters for balance_dirty_pages() and its subroutines */
128struct dirty_throttle_control {
129#ifdef CONFIG_CGROUP_WRITEBACK
130 struct wb_domain *dom;
131 struct dirty_throttle_control *gdtc; /* only set in memcg dtc's */
132#endif
133 struct bdi_writeback *wb;
134 struct fprop_local_percpu *wb_completions;
135
136 unsigned long avail; /* dirtyable */
137 unsigned long dirty; /* file_dirty + write + nfs */
138 unsigned long thresh; /* dirty threshold */
139 unsigned long bg_thresh; /* dirty background threshold */
140
141 unsigned long wb_dirty; /* per-wb counterparts */
142 unsigned long wb_thresh;
143 unsigned long wb_bg_thresh;
144
145 unsigned long pos_ratio;
146};
147
148/*
149 * Length of period for aging writeout fractions of bdis. This is an
150 * arbitrarily chosen number. The longer the period, the slower fractions will
151 * reflect changes in current writeout rate.
152 */
153#define VM_COMPLETIONS_PERIOD_LEN (3*HZ)
154
155#ifdef CONFIG_CGROUP_WRITEBACK
156
157#define GDTC_INIT(__wb) .wb = (__wb), \
158 .dom = &global_wb_domain, \
159 .wb_completions = &(__wb)->completions
160
161#define GDTC_INIT_NO_WB .dom = &global_wb_domain
162
163#define MDTC_INIT(__wb, __gdtc) .wb = (__wb), \
164 .dom = mem_cgroup_wb_domain(__wb), \
165 .wb_completions = &(__wb)->memcg_completions, \
166 .gdtc = __gdtc
167
168static bool mdtc_valid(struct dirty_throttle_control *dtc)
169{
170 return dtc->dom;
171}
172
173static struct wb_domain *dtc_dom(struct dirty_throttle_control *dtc)
174{
175 return dtc->dom;
176}
177
178static struct dirty_throttle_control *mdtc_gdtc(struct dirty_throttle_control *mdtc)
179{
180 return mdtc->gdtc;
181}
182
183static struct fprop_local_percpu *wb_memcg_completions(struct bdi_writeback *wb)
184{
185 return &wb->memcg_completions;
186}
187
188static void wb_min_max_ratio(struct bdi_writeback *wb,
189 unsigned long *minp, unsigned long *maxp)
190{
191 unsigned long this_bw = wb->avg_write_bandwidth;
192 unsigned long tot_bw = atomic_long_read(&wb->bdi->tot_write_bandwidth);
193 unsigned long long min = wb->bdi->min_ratio;
194 unsigned long long max = wb->bdi->max_ratio;
195
196 /*
197 * @wb may already be clean by the time control reaches here and
198 * the total may not include its bw.
199 */
200 if (this_bw < tot_bw) {
201 if (min) {
202 min *= this_bw;
203 do_div(min, tot_bw);
204 }
205 if (max < 100) {
206 max *= this_bw;
207 do_div(max, tot_bw);
208 }
209 }
210
211 *minp = min;
212 *maxp = max;
213}
214
215#else /* CONFIG_CGROUP_WRITEBACK */
216
217#define GDTC_INIT(__wb) .wb = (__wb), \
218 .wb_completions = &(__wb)->completions
219#define GDTC_INIT_NO_WB
220#define MDTC_INIT(__wb, __gdtc)
221
222static bool mdtc_valid(struct dirty_throttle_control *dtc)
223{
224 return false;
225}
226
227static struct wb_domain *dtc_dom(struct dirty_throttle_control *dtc)
228{
229 return &global_wb_domain;
230}
231
232static struct dirty_throttle_control *mdtc_gdtc(struct dirty_throttle_control *mdtc)
233{
234 return NULL;
235}
236
237static struct fprop_local_percpu *wb_memcg_completions(struct bdi_writeback *wb)
238{
239 return NULL;
240}
241
242static void wb_min_max_ratio(struct bdi_writeback *wb,
243 unsigned long *minp, unsigned long *maxp)
244{
245 *minp = wb->bdi->min_ratio;
246 *maxp = wb->bdi->max_ratio;
247}
248
249#endif /* CONFIG_CGROUP_WRITEBACK */
250
251/*
252 * In a memory zone, there is a certain amount of pages we consider
253 * available for the page cache, which is essentially the number of
254 * free and reclaimable pages, minus some zone reserves to protect
255 * lowmem and the ability to uphold the zone's watermarks without
256 * requiring writeback.
257 *
258 * This number of dirtyable pages is the base value of which the
259 * user-configurable dirty ratio is the effictive number of pages that
260 * are allowed to be actually dirtied. Per individual zone, or
261 * globally by using the sum of dirtyable pages over all zones.
262 *
263 * Because the user is allowed to specify the dirty limit globally as
264 * absolute number of bytes, calculating the per-zone dirty limit can
265 * require translating the configured limit into a percentage of
266 * global dirtyable memory first.
267 */
268
269/**
270 * zone_dirtyable_memory - number of dirtyable pages in a zone
271 * @zone: the zone
272 *
273 * Returns the zone's number of pages potentially available for dirty
274 * page cache. This is the base value for the per-zone dirty limits.
275 */
276static unsigned long zone_dirtyable_memory(struct zone *zone)
277{
278 unsigned long nr_pages;
279
280 nr_pages = zone_page_state(zone, NR_FREE_PAGES);
281 /*
282 * Pages reserved for the kernel should not be considered
283 * dirtyable, to prevent a situation where reclaim has to
284 * clean pages in order to balance the zones.
285 */
286 nr_pages -= min(nr_pages, zone->totalreserve_pages);
287
288 nr_pages += zone_page_state(zone, NR_INACTIVE_FILE);
289 nr_pages += zone_page_state(zone, NR_ACTIVE_FILE);
290
291 return nr_pages;
292}
293
294static unsigned long highmem_dirtyable_memory(unsigned long total)
295{
296#ifdef CONFIG_HIGHMEM
297 int node;
298 unsigned long x = 0;
299
300 for_each_node_state(node, N_HIGH_MEMORY) {
301 struct zone *z = &NODE_DATA(node)->node_zones[ZONE_HIGHMEM];
302
303 x += zone_dirtyable_memory(z);
304 }
305 /*
306 * Unreclaimable memory (kernel memory or anonymous memory
307 * without swap) can bring down the dirtyable pages below
308 * the zone's dirty balance reserve and the above calculation
309 * will underflow. However we still want to add in nodes
310 * which are below threshold (negative values) to get a more
311 * accurate calculation but make sure that the total never
312 * underflows.
313 */
314 if ((long)x < 0)
315 x = 0;
316
317 /*
318 * Make sure that the number of highmem pages is never larger
319 * than the number of the total dirtyable memory. This can only
320 * occur in very strange VM situations but we want to make sure
321 * that this does not occur.
322 */
323 return min(x, total);
324#else
325 return 0;
326#endif
327}
328
329/**
330 * global_dirtyable_memory - number of globally dirtyable pages
331 *
332 * Returns the global number of pages potentially available for dirty
333 * page cache. This is the base value for the global dirty limits.
334 */
335static unsigned long global_dirtyable_memory(void)
336{
337 unsigned long x;
338
339 x = global_page_state(NR_FREE_PAGES);
340 /*
341 * Pages reserved for the kernel should not be considered
342 * dirtyable, to prevent a situation where reclaim has to
343 * clean pages in order to balance the zones.
344 */
345 x -= min(x, totalreserve_pages);
346
347 x += global_page_state(NR_INACTIVE_FILE);
348 x += global_page_state(NR_ACTIVE_FILE);
349
350 if (!vm_highmem_is_dirtyable)
351 x -= highmem_dirtyable_memory(x);
352
353 return x + 1; /* Ensure that we never return 0 */
354}
355
356/**
357 * domain_dirty_limits - calculate thresh and bg_thresh for a wb_domain
358 * @dtc: dirty_throttle_control of interest
359 *
360 * Calculate @dtc->thresh and ->bg_thresh considering
361 * vm_dirty_{bytes|ratio} and dirty_background_{bytes|ratio}. The caller
362 * must ensure that @dtc->avail is set before calling this function. The
363 * dirty limits will be lifted by 1/4 for PF_LESS_THROTTLE (ie. nfsd) and
364 * real-time tasks.
365 */
366static void domain_dirty_limits(struct dirty_throttle_control *dtc)
367{
368 const unsigned long available_memory = dtc->avail;
369 struct dirty_throttle_control *gdtc = mdtc_gdtc(dtc);
370 unsigned long bytes = vm_dirty_bytes;
371 unsigned long bg_bytes = dirty_background_bytes;
372 unsigned long ratio = vm_dirty_ratio;
373 unsigned long bg_ratio = dirty_background_ratio;
374 unsigned long thresh;
375 unsigned long bg_thresh;
376 struct task_struct *tsk;
377
378 /* gdtc is !NULL iff @dtc is for memcg domain */
379 if (gdtc) {
380 unsigned long global_avail = gdtc->avail;
381
382 /*
383 * The byte settings can't be applied directly to memcg
384 * domains. Convert them to ratios by scaling against
385 * globally available memory.
386 */
387 if (bytes)
388 ratio = min(DIV_ROUND_UP(bytes, PAGE_SIZE) * 100 /
389 global_avail, 100UL);
390 if (bg_bytes)
391 bg_ratio = min(DIV_ROUND_UP(bg_bytes, PAGE_SIZE) * 100 /
392 global_avail, 100UL);
393 bytes = bg_bytes = 0;
394 }
395
396 if (bytes)
397 thresh = DIV_ROUND_UP(bytes, PAGE_SIZE);
398 else
399 thresh = (ratio * available_memory) / 100;
400
401 if (bg_bytes)
402 bg_thresh = DIV_ROUND_UP(bg_bytes, PAGE_SIZE);
403 else
404 bg_thresh = (bg_ratio * available_memory) / 100;
405
406 if (bg_thresh >= thresh)
407 bg_thresh = thresh / 2;
408 tsk = current;
409 if (tsk->flags & PF_LESS_THROTTLE || rt_task(tsk)) {
410 bg_thresh += bg_thresh / 4;
411 thresh += thresh / 4;
412 }
413 dtc->thresh = thresh;
414 dtc->bg_thresh = bg_thresh;
415
416 /* we should eventually report the domain in the TP */
417 if (!gdtc)
418 trace_global_dirty_state(bg_thresh, thresh);
419}
420
421/**
422 * global_dirty_limits - background-writeback and dirty-throttling thresholds
423 * @pbackground: out parameter for bg_thresh
424 * @pdirty: out parameter for thresh
425 *
426 * Calculate bg_thresh and thresh for global_wb_domain. See
427 * domain_dirty_limits() for details.
428 */
429void global_dirty_limits(unsigned long *pbackground, unsigned long *pdirty)
430{
431 struct dirty_throttle_control gdtc = { GDTC_INIT_NO_WB };
432
433 gdtc.avail = global_dirtyable_memory();
434 domain_dirty_limits(&gdtc);
435
436 *pbackground = gdtc.bg_thresh;
437 *pdirty = gdtc.thresh;
438}
439
440/**
441 * zone_dirty_limit - maximum number of dirty pages allowed in a zone
442 * @zone: the zone
443 *
444 * Returns the maximum number of dirty pages allowed in a zone, based
445 * on the zone's dirtyable memory.
446 */
447static unsigned long zone_dirty_limit(struct zone *zone)
448{
449 unsigned long zone_memory = zone_dirtyable_memory(zone);
450 struct task_struct *tsk = current;
451 unsigned long dirty;
452
453 if (vm_dirty_bytes)
454 dirty = DIV_ROUND_UP(vm_dirty_bytes, PAGE_SIZE) *
455 zone_memory / global_dirtyable_memory();
456 else
457 dirty = vm_dirty_ratio * zone_memory / 100;
458
459 if (tsk->flags & PF_LESS_THROTTLE || rt_task(tsk))
460 dirty += dirty / 4;
461
462 return dirty;
463}
464
465/**
466 * zone_dirty_ok - tells whether a zone is within its dirty limits
467 * @zone: the zone to check
468 *
469 * Returns %true when the dirty pages in @zone are within the zone's
470 * dirty limit, %false if the limit is exceeded.
471 */
472bool zone_dirty_ok(struct zone *zone)
473{
474 unsigned long limit = zone_dirty_limit(zone);
475
476 return zone_page_state(zone, NR_FILE_DIRTY) +
477 zone_page_state(zone, NR_UNSTABLE_NFS) +
478 zone_page_state(zone, NR_WRITEBACK) <= limit;
479}
480
481int dirty_background_ratio_handler(struct ctl_table *table, int write,
482 void __user *buffer, size_t *lenp,
483 loff_t *ppos)
484{
485 int ret;
486
487 ret = proc_dointvec_minmax(table, write, buffer, lenp, ppos);
488 if (ret == 0 && write)
489 dirty_background_bytes = 0;
490 return ret;
491}
492
493int dirty_background_bytes_handler(struct ctl_table *table, int write,
494 void __user *buffer, size_t *lenp,
495 loff_t *ppos)
496{
497 int ret;
498
499 ret = proc_doulongvec_minmax(table, write, buffer, lenp, ppos);
500 if (ret == 0 && write)
501 dirty_background_ratio = 0;
502 return ret;
503}
504
505int dirty_ratio_handler(struct ctl_table *table, int write,
506 void __user *buffer, size_t *lenp,
507 loff_t *ppos)
508{
509 int old_ratio = vm_dirty_ratio;
510 int ret;
511
512 ret = proc_dointvec_minmax(table, write, buffer, lenp, ppos);
513 if (ret == 0 && write && vm_dirty_ratio != old_ratio) {
514 writeback_set_ratelimit();
515 vm_dirty_bytes = 0;
516 }
517 return ret;
518}
519
520int dirty_bytes_handler(struct ctl_table *table, int write,
521 void __user *buffer, size_t *lenp,
522 loff_t *ppos)
523{
524 unsigned long old_bytes = vm_dirty_bytes;
525 int ret;
526
527 ret = proc_doulongvec_minmax(table, write, buffer, lenp, ppos);
528 if (ret == 0 && write && vm_dirty_bytes != old_bytes) {
529 writeback_set_ratelimit();
530 vm_dirty_ratio = 0;
531 }
532 return ret;
533}
534
535static unsigned long wp_next_time(unsigned long cur_time)
536{
537 cur_time += VM_COMPLETIONS_PERIOD_LEN;
538 /* 0 has a special meaning... */
539 if (!cur_time)
540 return 1;
541 return cur_time;
542}
543
544static void wb_domain_writeout_inc(struct wb_domain *dom,
545 struct fprop_local_percpu *completions,
546 unsigned int max_prop_frac)
547{
548 __fprop_inc_percpu_max(&dom->completions, completions,
549 max_prop_frac);
550 /* First event after period switching was turned off? */
551 if (!unlikely(dom->period_time)) {
552 /*
553 * We can race with other __bdi_writeout_inc calls here but
554 * it does not cause any harm since the resulting time when
555 * timer will fire and what is in writeout_period_time will be
556 * roughly the same.
557 */
558 dom->period_time = wp_next_time(jiffies);
559 mod_timer(&dom->period_timer, dom->period_time);
560 }
561}
562
563/*
564 * Increment @wb's writeout completion count and the global writeout
565 * completion count. Called from test_clear_page_writeback().
566 */
567static inline void __wb_writeout_inc(struct bdi_writeback *wb)
568{
569 struct wb_domain *cgdom;
570
571 __inc_wb_stat(wb, WB_WRITTEN);
572 wb_domain_writeout_inc(&global_wb_domain, &wb->completions,
573 wb->bdi->max_prop_frac);
574
575 cgdom = mem_cgroup_wb_domain(wb);
576 if (cgdom)
577 wb_domain_writeout_inc(cgdom, wb_memcg_completions(wb),
578 wb->bdi->max_prop_frac);
579}
580
581void wb_writeout_inc(struct bdi_writeback *wb)
582{
583 unsigned long flags;
584
585 local_irq_save(flags);
586 __wb_writeout_inc(wb);
587 local_irq_restore(flags);
588}
589EXPORT_SYMBOL_GPL(wb_writeout_inc);
590
591/*
592 * On idle system, we can be called long after we scheduled because we use
593 * deferred timers so count with missed periods.
594 */
595static void writeout_period(unsigned long t)
596{
597 struct wb_domain *dom = (void *)t;
598 int miss_periods = (jiffies - dom->period_time) /
599 VM_COMPLETIONS_PERIOD_LEN;
600
601 if (fprop_new_period(&dom->completions, miss_periods + 1)) {
602 dom->period_time = wp_next_time(dom->period_time +
603 miss_periods * VM_COMPLETIONS_PERIOD_LEN);
604 mod_timer(&dom->period_timer, dom->period_time);
605 } else {
606 /*
607 * Aging has zeroed all fractions. Stop wasting CPU on period
608 * updates.
609 */
610 dom->period_time = 0;
611 }
612}
613
614int wb_domain_init(struct wb_domain *dom, gfp_t gfp)
615{
616 memset(dom, 0, sizeof(*dom));
617
618 spin_lock_init(&dom->lock);
619
620 init_timer_deferrable(&dom->period_timer);
621 dom->period_timer.function = writeout_period;
622 dom->period_timer.data = (unsigned long)dom;
623
624 dom->dirty_limit_tstamp = jiffies;
625
626 return fprop_global_init(&dom->completions, gfp);
627}
628
629#ifdef CONFIG_CGROUP_WRITEBACK
630void wb_domain_exit(struct wb_domain *dom)
631{
632 del_timer_sync(&dom->period_timer);
633 fprop_global_destroy(&dom->completions);
634}
635#endif
636
637/*
638 * bdi_min_ratio keeps the sum of the minimum dirty shares of all
639 * registered backing devices, which, for obvious reasons, can not
640 * exceed 100%.
641 */
642static unsigned int bdi_min_ratio;
643
644int bdi_set_min_ratio(struct backing_dev_info *bdi, unsigned int min_ratio)
645{
646 int ret = 0;
647
648 spin_lock_bh(&bdi_lock);
649 if (min_ratio > bdi->max_ratio) {
650 ret = -EINVAL;
651 } else {
652 min_ratio -= bdi->min_ratio;
653 if (bdi_min_ratio + min_ratio < 100) {
654 bdi_min_ratio += min_ratio;
655 bdi->min_ratio += min_ratio;
656 } else {
657 ret = -EINVAL;
658 }
659 }
660 spin_unlock_bh(&bdi_lock);
661
662 return ret;
663}
664
665int bdi_set_max_ratio(struct backing_dev_info *bdi, unsigned max_ratio)
666{
667 int ret = 0;
668
669 if (max_ratio > 100)
670 return -EINVAL;
671
672 spin_lock_bh(&bdi_lock);
673 if (bdi->min_ratio > max_ratio) {
674 ret = -EINVAL;
675 } else {
676 bdi->max_ratio = max_ratio;
677 bdi->max_prop_frac = (FPROP_FRAC_BASE * max_ratio) / 100;
678 }
679 spin_unlock_bh(&bdi_lock);
680
681 return ret;
682}
683EXPORT_SYMBOL(bdi_set_max_ratio);
684
685static unsigned long dirty_freerun_ceiling(unsigned long thresh,
686 unsigned long bg_thresh)
687{
688 return (thresh + bg_thresh) / 2;
689}
690
691static unsigned long hard_dirty_limit(struct wb_domain *dom,
692 unsigned long thresh)
693{
694 return max(thresh, dom->dirty_limit);
695}
696
697/*
698 * Memory which can be further allocated to a memcg domain is capped by
699 * system-wide clean memory excluding the amount being used in the domain.
700 */
701static void mdtc_calc_avail(struct dirty_throttle_control *mdtc,
702 unsigned long filepages, unsigned long headroom)
703{
704 struct dirty_throttle_control *gdtc = mdtc_gdtc(mdtc);
705 unsigned long clean = filepages - min(filepages, mdtc->dirty);
706 unsigned long global_clean = gdtc->avail - min(gdtc->avail, gdtc->dirty);
707 unsigned long other_clean = global_clean - min(global_clean, clean);
708
709 mdtc->avail = filepages + min(headroom, other_clean);
710}
711
712/**
713 * __wb_calc_thresh - @wb's share of dirty throttling threshold
714 * @dtc: dirty_throttle_context of interest
715 *
716 * Returns @wb's dirty limit in pages. The term "dirty" in the context of
717 * dirty balancing includes all PG_dirty, PG_writeback and NFS unstable pages.
718 *
719 * Note that balance_dirty_pages() will only seriously take it as a hard limit
720 * when sleeping max_pause per page is not enough to keep the dirty pages under
721 * control. For example, when the device is completely stalled due to some error
722 * conditions, or when there are 1000 dd tasks writing to a slow 10MB/s USB key.
723 * In the other normal situations, it acts more gently by throttling the tasks
724 * more (rather than completely block them) when the wb dirty pages go high.
725 *
726 * It allocates high/low dirty limits to fast/slow devices, in order to prevent
727 * - starving fast devices
728 * - piling up dirty pages (that will take long time to sync) on slow devices
729 *
730 * The wb's share of dirty limit will be adapting to its throughput and
731 * bounded by the bdi->min_ratio and/or bdi->max_ratio parameters, if set.
732 */
733static unsigned long __wb_calc_thresh(struct dirty_throttle_control *dtc)
734{
735 struct wb_domain *dom = dtc_dom(dtc);
736 unsigned long thresh = dtc->thresh;
737 u64 wb_thresh;
738 long numerator, denominator;
739 unsigned long wb_min_ratio, wb_max_ratio;
740
741 /*
742 * Calculate this BDI's share of the thresh ratio.
743 */
744 fprop_fraction_percpu(&dom->completions, dtc->wb_completions,
745 &numerator, &denominator);
746
747 wb_thresh = (thresh * (100 - bdi_min_ratio)) / 100;
748 wb_thresh *= numerator;
749 do_div(wb_thresh, denominator);
750
751 wb_min_max_ratio(dtc->wb, &wb_min_ratio, &wb_max_ratio);
752
753 wb_thresh += (thresh * wb_min_ratio) / 100;
754 if (wb_thresh > (thresh * wb_max_ratio) / 100)
755 wb_thresh = thresh * wb_max_ratio / 100;
756
757 return wb_thresh;
758}
759
760unsigned long wb_calc_thresh(struct bdi_writeback *wb, unsigned long thresh)
761{
762 struct dirty_throttle_control gdtc = { GDTC_INIT(wb),
763 .thresh = thresh };
764 return __wb_calc_thresh(&gdtc);
765}
766
767/*
768 * setpoint - dirty 3
769 * f(dirty) := 1.0 + (----------------)
770 * limit - setpoint
771 *
772 * it's a 3rd order polynomial that subjects to
773 *
774 * (1) f(freerun) = 2.0 => rampup dirty_ratelimit reasonably fast
775 * (2) f(setpoint) = 1.0 => the balance point
776 * (3) f(limit) = 0 => the hard limit
777 * (4) df/dx <= 0 => negative feedback control
778 * (5) the closer to setpoint, the smaller |df/dx| (and the reverse)
779 * => fast response on large errors; small oscillation near setpoint
780 */
781static long long pos_ratio_polynom(unsigned long setpoint,
782 unsigned long dirty,
783 unsigned long limit)
784{
785 long long pos_ratio;
786 long x;
787
788 x = div64_s64(((s64)setpoint - (s64)dirty) << RATELIMIT_CALC_SHIFT,
789 (limit - setpoint) | 1);
790 pos_ratio = x;
791 pos_ratio = pos_ratio * x >> RATELIMIT_CALC_SHIFT;
792 pos_ratio = pos_ratio * x >> RATELIMIT_CALC_SHIFT;
793 pos_ratio += 1 << RATELIMIT_CALC_SHIFT;
794
795 return clamp(pos_ratio, 0LL, 2LL << RATELIMIT_CALC_SHIFT);
796}
797
798/*
799 * Dirty position control.
800 *
801 * (o) global/bdi setpoints
802 *
803 * We want the dirty pages be balanced around the global/wb setpoints.
804 * When the number of dirty pages is higher/lower than the setpoint, the
805 * dirty position control ratio (and hence task dirty ratelimit) will be
806 * decreased/increased to bring the dirty pages back to the setpoint.
807 *
808 * pos_ratio = 1 << RATELIMIT_CALC_SHIFT
809 *
810 * if (dirty < setpoint) scale up pos_ratio
811 * if (dirty > setpoint) scale down pos_ratio
812 *
813 * if (wb_dirty < wb_setpoint) scale up pos_ratio
814 * if (wb_dirty > wb_setpoint) scale down pos_ratio
815 *
816 * task_ratelimit = dirty_ratelimit * pos_ratio >> RATELIMIT_CALC_SHIFT
817 *
818 * (o) global control line
819 *
820 * ^ pos_ratio
821 * |
822 * | |<===== global dirty control scope ======>|
823 * 2.0 .............*
824 * | .*
825 * | . *
826 * | . *
827 * | . *
828 * | . *
829 * | . *
830 * 1.0 ................................*
831 * | . . *
832 * | . . *
833 * | . . *
834 * | . . *
835 * | . . *
836 * 0 +------------.------------------.----------------------*------------->
837 * freerun^ setpoint^ limit^ dirty pages
838 *
839 * (o) wb control line
840 *
841 * ^ pos_ratio
842 * |
843 * | *
844 * | *
845 * | *
846 * | *
847 * | * |<=========== span ============>|
848 * 1.0 .......................*
849 * | . *
850 * | . *
851 * | . *
852 * | . *
853 * | . *
854 * | . *
855 * | . *
856 * | . *
857 * | . *
858 * | . *
859 * | . *
860 * 1/4 ...............................................* * * * * * * * * * * *
861 * | . .
862 * | . .
863 * | . .
864 * 0 +----------------------.-------------------------------.------------->
865 * wb_setpoint^ x_intercept^
866 *
867 * The wb control line won't drop below pos_ratio=1/4, so that wb_dirty can
868 * be smoothly throttled down to normal if it starts high in situations like
869 * - start writing to a slow SD card and a fast disk at the same time. The SD
870 * card's wb_dirty may rush to many times higher than wb_setpoint.
871 * - the wb dirty thresh drops quickly due to change of JBOD workload
872 */
873static void wb_position_ratio(struct dirty_throttle_control *dtc)
874{
875 struct bdi_writeback *wb = dtc->wb;
876 unsigned long write_bw = wb->avg_write_bandwidth;
877 unsigned long freerun = dirty_freerun_ceiling(dtc->thresh, dtc->bg_thresh);
878 unsigned long limit = hard_dirty_limit(dtc_dom(dtc), dtc->thresh);
879 unsigned long wb_thresh = dtc->wb_thresh;
880 unsigned long x_intercept;
881 unsigned long setpoint; /* dirty pages' target balance point */
882 unsigned long wb_setpoint;
883 unsigned long span;
884 long long pos_ratio; /* for scaling up/down the rate limit */
885 long x;
886
887 dtc->pos_ratio = 0;
888
889 if (unlikely(dtc->dirty >= limit))
890 return;
891
892 /*
893 * global setpoint
894 *
895 * See comment for pos_ratio_polynom().
896 */
897 setpoint = (freerun + limit) / 2;
898 pos_ratio = pos_ratio_polynom(setpoint, dtc->dirty, limit);
899
900 /*
901 * The strictlimit feature is a tool preventing mistrusted filesystems
902 * from growing a large number of dirty pages before throttling. For
903 * such filesystems balance_dirty_pages always checks wb counters
904 * against wb limits. Even if global "nr_dirty" is under "freerun".
905 * This is especially important for fuse which sets bdi->max_ratio to
906 * 1% by default. Without strictlimit feature, fuse writeback may
907 * consume arbitrary amount of RAM because it is accounted in
908 * NR_WRITEBACK_TEMP which is not involved in calculating "nr_dirty".
909 *
910 * Here, in wb_position_ratio(), we calculate pos_ratio based on
911 * two values: wb_dirty and wb_thresh. Let's consider an example:
912 * total amount of RAM is 16GB, bdi->max_ratio is equal to 1%, global
913 * limits are set by default to 10% and 20% (background and throttle).
914 * Then wb_thresh is 1% of 20% of 16GB. This amounts to ~8K pages.
915 * wb_calc_thresh(wb, bg_thresh) is about ~4K pages. wb_setpoint is
916 * about ~6K pages (as the average of background and throttle wb
917 * limits). The 3rd order polynomial will provide positive feedback if
918 * wb_dirty is under wb_setpoint and vice versa.
919 *
920 * Note, that we cannot use global counters in these calculations
921 * because we want to throttle process writing to a strictlimit wb
922 * much earlier than global "freerun" is reached (~23MB vs. ~2.3GB
923 * in the example above).
924 */
925 if (unlikely(wb->bdi->capabilities & BDI_CAP_STRICTLIMIT)) {
926 long long wb_pos_ratio;
927
928 if (dtc->wb_dirty < 8) {
929 dtc->pos_ratio = min_t(long long, pos_ratio * 2,
930 2 << RATELIMIT_CALC_SHIFT);
931 return;
932 }
933
934 if (dtc->wb_dirty >= wb_thresh)
935 return;
936
937 wb_setpoint = dirty_freerun_ceiling(wb_thresh,
938 dtc->wb_bg_thresh);
939
940 if (wb_setpoint == 0 || wb_setpoint == wb_thresh)
941 return;
942
943 wb_pos_ratio = pos_ratio_polynom(wb_setpoint, dtc->wb_dirty,
944 wb_thresh);
945
946 /*
947 * Typically, for strictlimit case, wb_setpoint << setpoint
948 * and pos_ratio >> wb_pos_ratio. In the other words global
949 * state ("dirty") is not limiting factor and we have to
950 * make decision based on wb counters. But there is an
951 * important case when global pos_ratio should get precedence:
952 * global limits are exceeded (e.g. due to activities on other
953 * wb's) while given strictlimit wb is below limit.
954 *
955 * "pos_ratio * wb_pos_ratio" would work for the case above,
956 * but it would look too non-natural for the case of all
957 * activity in the system coming from a single strictlimit wb
958 * with bdi->max_ratio == 100%.
959 *
960 * Note that min() below somewhat changes the dynamics of the
961 * control system. Normally, pos_ratio value can be well over 3
962 * (when globally we are at freerun and wb is well below wb
963 * setpoint). Now the maximum pos_ratio in the same situation
964 * is 2. We might want to tweak this if we observe the control
965 * system is too slow to adapt.
966 */
967 dtc->pos_ratio = min(pos_ratio, wb_pos_ratio);
968 return;
969 }
970
971 /*
972 * We have computed basic pos_ratio above based on global situation. If
973 * the wb is over/under its share of dirty pages, we want to scale
974 * pos_ratio further down/up. That is done by the following mechanism.
975 */
976
977 /*
978 * wb setpoint
979 *
980 * f(wb_dirty) := 1.0 + k * (wb_dirty - wb_setpoint)
981 *
982 * x_intercept - wb_dirty
983 * := --------------------------
984 * x_intercept - wb_setpoint
985 *
986 * The main wb control line is a linear function that subjects to
987 *
988 * (1) f(wb_setpoint) = 1.0
989 * (2) k = - 1 / (8 * write_bw) (in single wb case)
990 * or equally: x_intercept = wb_setpoint + 8 * write_bw
991 *
992 * For single wb case, the dirty pages are observed to fluctuate
993 * regularly within range
994 * [wb_setpoint - write_bw/2, wb_setpoint + write_bw/2]
995 * for various filesystems, where (2) can yield in a reasonable 12.5%
996 * fluctuation range for pos_ratio.
997 *
998 * For JBOD case, wb_thresh (not wb_dirty!) could fluctuate up to its
999 * own size, so move the slope over accordingly and choose a slope that
1000 * yields 100% pos_ratio fluctuation on suddenly doubled wb_thresh.
1001 */
1002 if (unlikely(wb_thresh > dtc->thresh))
1003 wb_thresh = dtc->thresh;
1004 /*
1005 * It's very possible that wb_thresh is close to 0 not because the
1006 * device is slow, but that it has remained inactive for long time.
1007 * Honour such devices a reasonable good (hopefully IO efficient)
1008 * threshold, so that the occasional writes won't be blocked and active
1009 * writes can rampup the threshold quickly.
1010 */
1011 wb_thresh = max(wb_thresh, (limit - dtc->dirty) / 8);
1012 /*
1013 * scale global setpoint to wb's:
1014 * wb_setpoint = setpoint * wb_thresh / thresh
1015 */
1016 x = div_u64((u64)wb_thresh << 16, dtc->thresh | 1);
1017 wb_setpoint = setpoint * (u64)x >> 16;
1018 /*
1019 * Use span=(8*write_bw) in single wb case as indicated by
1020 * (thresh - wb_thresh ~= 0) and transit to wb_thresh in JBOD case.
1021 *
1022 * wb_thresh thresh - wb_thresh
1023 * span = --------- * (8 * write_bw) + ------------------ * wb_thresh
1024 * thresh thresh
1025 */
1026 span = (dtc->thresh - wb_thresh + 8 * write_bw) * (u64)x >> 16;
1027 x_intercept = wb_setpoint + span;
1028
1029 if (dtc->wb_dirty < x_intercept - span / 4) {
1030 pos_ratio = div64_u64(pos_ratio * (x_intercept - dtc->wb_dirty),
1031 (x_intercept - wb_setpoint) | 1);
1032 } else
1033 pos_ratio /= 4;
1034
1035 /*
1036 * wb reserve area, safeguard against dirty pool underrun and disk idle
1037 * It may push the desired control point of global dirty pages higher
1038 * than setpoint.
1039 */
1040 x_intercept = wb_thresh / 2;
1041 if (dtc->wb_dirty < x_intercept) {
1042 if (dtc->wb_dirty > x_intercept / 8)
1043 pos_ratio = div_u64(pos_ratio * x_intercept,
1044 dtc->wb_dirty);
1045 else
1046 pos_ratio *= 8;
1047 }
1048
1049 dtc->pos_ratio = pos_ratio;
1050}
1051
1052static void wb_update_write_bandwidth(struct bdi_writeback *wb,
1053 unsigned long elapsed,
1054 unsigned long written)
1055{
1056 const unsigned long period = roundup_pow_of_two(3 * HZ);
1057 unsigned long avg = wb->avg_write_bandwidth;
1058 unsigned long old = wb->write_bandwidth;
1059 u64 bw;
1060
1061 /*
1062 * bw = written * HZ / elapsed
1063 *
1064 * bw * elapsed + write_bandwidth * (period - elapsed)
1065 * write_bandwidth = ---------------------------------------------------
1066 * period
1067 *
1068 * @written may have decreased due to account_page_redirty().
1069 * Avoid underflowing @bw calculation.
1070 */
1071 bw = written - min(written, wb->written_stamp);
1072 bw *= HZ;
1073 if (unlikely(elapsed > period)) {
1074 do_div(bw, elapsed);
1075 avg = bw;
1076 goto out;
1077 }
1078 bw += (u64)wb->write_bandwidth * (period - elapsed);
1079 bw >>= ilog2(period);
1080
1081 /*
1082 * one more level of smoothing, for filtering out sudden spikes
1083 */
1084 if (avg > old && old >= (unsigned long)bw)
1085 avg -= (avg - old) >> 3;
1086
1087 if (avg < old && old <= (unsigned long)bw)
1088 avg += (old - avg) >> 3;
1089
1090out:
1091 /* keep avg > 0 to guarantee that tot > 0 if there are dirty wbs */
1092 avg = max(avg, 1LU);
1093 if (wb_has_dirty_io(wb)) {
1094 long delta = avg - wb->avg_write_bandwidth;
1095 WARN_ON_ONCE(atomic_long_add_return(delta,
1096 &wb->bdi->tot_write_bandwidth) <= 0);
1097 }
1098 wb->write_bandwidth = bw;
1099 wb->avg_write_bandwidth = avg;
1100}
1101
1102static void update_dirty_limit(struct dirty_throttle_control *dtc)
1103{
1104 struct wb_domain *dom = dtc_dom(dtc);
1105 unsigned long thresh = dtc->thresh;
1106 unsigned long limit = dom->dirty_limit;
1107
1108 /*
1109 * Follow up in one step.
1110 */
1111 if (limit < thresh) {
1112 limit = thresh;
1113 goto update;
1114 }
1115
1116 /*
1117 * Follow down slowly. Use the higher one as the target, because thresh
1118 * may drop below dirty. This is exactly the reason to introduce
1119 * dom->dirty_limit which is guaranteed to lie above the dirty pages.
1120 */
1121 thresh = max(thresh, dtc->dirty);
1122 if (limit > thresh) {
1123 limit -= (limit - thresh) >> 5;
1124 goto update;
1125 }
1126 return;
1127update:
1128 dom->dirty_limit = limit;
1129}
1130
1131static void domain_update_bandwidth(struct dirty_throttle_control *dtc,
1132 unsigned long now)
1133{
1134 struct wb_domain *dom = dtc_dom(dtc);
1135
1136 /*
1137 * check locklessly first to optimize away locking for the most time
1138 */
1139 if (time_before(now, dom->dirty_limit_tstamp + BANDWIDTH_INTERVAL))
1140 return;
1141
1142 spin_lock(&dom->lock);
1143 if (time_after_eq(now, dom->dirty_limit_tstamp + BANDWIDTH_INTERVAL)) {
1144 update_dirty_limit(dtc);
1145 dom->dirty_limit_tstamp = now;
1146 }
1147 spin_unlock(&dom->lock);
1148}
1149
1150/*
1151 * Maintain wb->dirty_ratelimit, the base dirty throttle rate.
1152 *
1153 * Normal wb tasks will be curbed at or below it in long term.
1154 * Obviously it should be around (write_bw / N) when there are N dd tasks.
1155 */
1156static void wb_update_dirty_ratelimit(struct dirty_throttle_control *dtc,
1157 unsigned long dirtied,
1158 unsigned long elapsed)
1159{
1160 struct bdi_writeback *wb = dtc->wb;
1161 unsigned long dirty = dtc->dirty;
1162 unsigned long freerun = dirty_freerun_ceiling(dtc->thresh, dtc->bg_thresh);
1163 unsigned long limit = hard_dirty_limit(dtc_dom(dtc), dtc->thresh);
1164 unsigned long setpoint = (freerun + limit) / 2;
1165 unsigned long write_bw = wb->avg_write_bandwidth;
1166 unsigned long dirty_ratelimit = wb->dirty_ratelimit;
1167 unsigned long dirty_rate;
1168 unsigned long task_ratelimit;
1169 unsigned long balanced_dirty_ratelimit;
1170 unsigned long step;
1171 unsigned long x;
1172 unsigned long shift;
1173
1174 /*
1175 * The dirty rate will match the writeout rate in long term, except
1176 * when dirty pages are truncated by userspace or re-dirtied by FS.
1177 */
1178 dirty_rate = (dirtied - wb->dirtied_stamp) * HZ / elapsed;
1179
1180 /*
1181 * task_ratelimit reflects each dd's dirty rate for the past 200ms.
1182 */
1183 task_ratelimit = (u64)dirty_ratelimit *
1184 dtc->pos_ratio >> RATELIMIT_CALC_SHIFT;
1185 task_ratelimit++; /* it helps rampup dirty_ratelimit from tiny values */
1186
1187 /*
1188 * A linear estimation of the "balanced" throttle rate. The theory is,
1189 * if there are N dd tasks, each throttled at task_ratelimit, the wb's
1190 * dirty_rate will be measured to be (N * task_ratelimit). So the below
1191 * formula will yield the balanced rate limit (write_bw / N).
1192 *
1193 * Note that the expanded form is not a pure rate feedback:
1194 * rate_(i+1) = rate_(i) * (write_bw / dirty_rate) (1)
1195 * but also takes pos_ratio into account:
1196 * rate_(i+1) = rate_(i) * (write_bw / dirty_rate) * pos_ratio (2)
1197 *
1198 * (1) is not realistic because pos_ratio also takes part in balancing
1199 * the dirty rate. Consider the state
1200 * pos_ratio = 0.5 (3)
1201 * rate = 2 * (write_bw / N) (4)
1202 * If (1) is used, it will stuck in that state! Because each dd will
1203 * be throttled at
1204 * task_ratelimit = pos_ratio * rate = (write_bw / N) (5)
1205 * yielding
1206 * dirty_rate = N * task_ratelimit = write_bw (6)
1207 * put (6) into (1) we get
1208 * rate_(i+1) = rate_(i) (7)
1209 *
1210 * So we end up using (2) to always keep
1211 * rate_(i+1) ~= (write_bw / N) (8)
1212 * regardless of the value of pos_ratio. As long as (8) is satisfied,
1213 * pos_ratio is able to drive itself to 1.0, which is not only where
1214 * the dirty count meet the setpoint, but also where the slope of
1215 * pos_ratio is most flat and hence task_ratelimit is least fluctuated.
1216 */
1217 balanced_dirty_ratelimit = div_u64((u64)task_ratelimit * write_bw,
1218 dirty_rate | 1);
1219 /*
1220 * balanced_dirty_ratelimit ~= (write_bw / N) <= write_bw
1221 */
1222 if (unlikely(balanced_dirty_ratelimit > write_bw))
1223 balanced_dirty_ratelimit = write_bw;
1224
1225 /*
1226 * We could safely do this and return immediately:
1227 *
1228 * wb->dirty_ratelimit = balanced_dirty_ratelimit;
1229 *
1230 * However to get a more stable dirty_ratelimit, the below elaborated
1231 * code makes use of task_ratelimit to filter out singular points and
1232 * limit the step size.
1233 *
1234 * The below code essentially only uses the relative value of
1235 *
1236 * task_ratelimit - dirty_ratelimit
1237 * = (pos_ratio - 1) * dirty_ratelimit
1238 *
1239 * which reflects the direction and size of dirty position error.
1240 */
1241
1242 /*
1243 * dirty_ratelimit will follow balanced_dirty_ratelimit iff
1244 * task_ratelimit is on the same side of dirty_ratelimit, too.
1245 * For example, when
1246 * - dirty_ratelimit > balanced_dirty_ratelimit
1247 * - dirty_ratelimit > task_ratelimit (dirty pages are above setpoint)
1248 * lowering dirty_ratelimit will help meet both the position and rate
1249 * control targets. Otherwise, don't update dirty_ratelimit if it will
1250 * only help meet the rate target. After all, what the users ultimately
1251 * feel and care are stable dirty rate and small position error.
1252 *
1253 * |task_ratelimit - dirty_ratelimit| is used to limit the step size
1254 * and filter out the singular points of balanced_dirty_ratelimit. Which
1255 * keeps jumping around randomly and can even leap far away at times
1256 * due to the small 200ms estimation period of dirty_rate (we want to
1257 * keep that period small to reduce time lags).
1258 */
1259 step = 0;
1260
1261 /*
1262 * For strictlimit case, calculations above were based on wb counters
1263 * and limits (starting from pos_ratio = wb_position_ratio() and up to
1264 * balanced_dirty_ratelimit = task_ratelimit * write_bw / dirty_rate).
1265 * Hence, to calculate "step" properly, we have to use wb_dirty as
1266 * "dirty" and wb_setpoint as "setpoint".
1267 *
1268 * We rampup dirty_ratelimit forcibly if wb_dirty is low because
1269 * it's possible that wb_thresh is close to zero due to inactivity
1270 * of backing device.
1271 */
1272 if (unlikely(wb->bdi->capabilities & BDI_CAP_STRICTLIMIT)) {
1273 dirty = dtc->wb_dirty;
1274 if (dtc->wb_dirty < 8)
1275 setpoint = dtc->wb_dirty + 1;
1276 else
1277 setpoint = (dtc->wb_thresh + dtc->wb_bg_thresh) / 2;
1278 }
1279
1280 if (dirty < setpoint) {
1281 x = min3(wb->balanced_dirty_ratelimit,
1282 balanced_dirty_ratelimit, task_ratelimit);
1283 if (dirty_ratelimit < x)
1284 step = x - dirty_ratelimit;
1285 } else {
1286 x = max3(wb->balanced_dirty_ratelimit,
1287 balanced_dirty_ratelimit, task_ratelimit);
1288 if (dirty_ratelimit > x)
1289 step = dirty_ratelimit - x;
1290 }
1291
1292 /*
1293 * Don't pursue 100% rate matching. It's impossible since the balanced
1294 * rate itself is constantly fluctuating. So decrease the track speed
1295 * when it gets close to the target. Helps eliminate pointless tremors.
1296 */
1297 shift = dirty_ratelimit / (2 * step + 1);
1298 if (shift < BITS_PER_LONG)
1299 step = DIV_ROUND_UP(step >> shift, 8);
1300 else
1301 step = 0;
1302
1303 if (dirty_ratelimit < balanced_dirty_ratelimit)
1304 dirty_ratelimit += step;
1305 else
1306 dirty_ratelimit -= step;
1307
1308 wb->dirty_ratelimit = max(dirty_ratelimit, 1UL);
1309 wb->balanced_dirty_ratelimit = balanced_dirty_ratelimit;
1310
1311 trace_bdi_dirty_ratelimit(wb, dirty_rate, task_ratelimit);
1312}
1313
1314static void __wb_update_bandwidth(struct dirty_throttle_control *gdtc,
1315 struct dirty_throttle_control *mdtc,
1316 unsigned long start_time,
1317 bool update_ratelimit)
1318{
1319 struct bdi_writeback *wb = gdtc->wb;
1320 unsigned long now = jiffies;
1321 unsigned long elapsed = now - wb->bw_time_stamp;
1322 unsigned long dirtied;
1323 unsigned long written;
1324
1325 lockdep_assert_held(&wb->list_lock);
1326
1327 /*
1328 * rate-limit, only update once every 200ms.
1329 */
1330 if (elapsed < BANDWIDTH_INTERVAL)
1331 return;
1332
1333 dirtied = percpu_counter_read(&wb->stat[WB_DIRTIED]);
1334 written = percpu_counter_read(&wb->stat[WB_WRITTEN]);
1335
1336 /*
1337 * Skip quiet periods when disk bandwidth is under-utilized.
1338 * (at least 1s idle time between two flusher runs)
1339 */
1340 if (elapsed > HZ && time_before(wb->bw_time_stamp, start_time))
1341 goto snapshot;
1342
1343 if (update_ratelimit) {
1344 domain_update_bandwidth(gdtc, now);
1345 wb_update_dirty_ratelimit(gdtc, dirtied, elapsed);
1346
1347 /*
1348 * @mdtc is always NULL if !CGROUP_WRITEBACK but the
1349 * compiler has no way to figure that out. Help it.
1350 */
1351 if (IS_ENABLED(CONFIG_CGROUP_WRITEBACK) && mdtc) {
1352 domain_update_bandwidth(mdtc, now);
1353 wb_update_dirty_ratelimit(mdtc, dirtied, elapsed);
1354 }
1355 }
1356 wb_update_write_bandwidth(wb, elapsed, written);
1357
1358snapshot:
1359 wb->dirtied_stamp = dirtied;
1360 wb->written_stamp = written;
1361 wb->bw_time_stamp = now;
1362}
1363
1364void wb_update_bandwidth(struct bdi_writeback *wb, unsigned long start_time)
1365{
1366 struct dirty_throttle_control gdtc = { GDTC_INIT(wb) };
1367
1368 __wb_update_bandwidth(&gdtc, NULL, start_time, false);
1369}
1370
1371/*
1372 * After a task dirtied this many pages, balance_dirty_pages_ratelimited()
1373 * will look to see if it needs to start dirty throttling.
1374 *
1375 * If dirty_poll_interval is too low, big NUMA machines will call the expensive
1376 * global_page_state() too often. So scale it near-sqrt to the safety margin
1377 * (the number of pages we may dirty without exceeding the dirty limits).
1378 */
1379static unsigned long dirty_poll_interval(unsigned long dirty,
1380 unsigned long thresh)
1381{
1382 if (thresh > dirty)
1383 return 1UL << (ilog2(thresh - dirty) >> 1);
1384
1385 return 1;
1386}
1387
1388static unsigned long wb_max_pause(struct bdi_writeback *wb,
1389 unsigned long wb_dirty)
1390{
1391 unsigned long bw = wb->avg_write_bandwidth;
1392 unsigned long t;
1393
1394 /*
1395 * Limit pause time for small memory systems. If sleeping for too long
1396 * time, a small pool of dirty/writeback pages may go empty and disk go
1397 * idle.
1398 *
1399 * 8 serves as the safety ratio.
1400 */
1401 t = wb_dirty / (1 + bw / roundup_pow_of_two(1 + HZ / 8));
1402 t++;
1403
1404 return min_t(unsigned long, t, MAX_PAUSE);
1405}
1406
1407static long wb_min_pause(struct bdi_writeback *wb,
1408 long max_pause,
1409 unsigned long task_ratelimit,
1410 unsigned long dirty_ratelimit,
1411 int *nr_dirtied_pause)
1412{
1413 long hi = ilog2(wb->avg_write_bandwidth);
1414 long lo = ilog2(wb->dirty_ratelimit);
1415 long t; /* target pause */
1416 long pause; /* estimated next pause */
1417 int pages; /* target nr_dirtied_pause */
1418
1419 /* target for 10ms pause on 1-dd case */
1420 t = max(1, HZ / 100);
1421
1422 /*
1423 * Scale up pause time for concurrent dirtiers in order to reduce CPU
1424 * overheads.
1425 *
1426 * (N * 10ms) on 2^N concurrent tasks.
1427 */
1428 if (hi > lo)
1429 t += (hi - lo) * (10 * HZ) / 1024;
1430
1431 /*
1432 * This is a bit convoluted. We try to base the next nr_dirtied_pause
1433 * on the much more stable dirty_ratelimit. However the next pause time
1434 * will be computed based on task_ratelimit and the two rate limits may
1435 * depart considerably at some time. Especially if task_ratelimit goes
1436 * below dirty_ratelimit/2 and the target pause is max_pause, the next
1437 * pause time will be max_pause*2 _trimmed down_ to max_pause. As a
1438 * result task_ratelimit won't be executed faithfully, which could
1439 * eventually bring down dirty_ratelimit.
1440 *
1441 * We apply two rules to fix it up:
1442 * 1) try to estimate the next pause time and if necessary, use a lower
1443 * nr_dirtied_pause so as not to exceed max_pause. When this happens,
1444 * nr_dirtied_pause will be "dancing" with task_ratelimit.
1445 * 2) limit the target pause time to max_pause/2, so that the normal
1446 * small fluctuations of task_ratelimit won't trigger rule (1) and
1447 * nr_dirtied_pause will remain as stable as dirty_ratelimit.
1448 */
1449 t = min(t, 1 + max_pause / 2);
1450 pages = dirty_ratelimit * t / roundup_pow_of_two(HZ);
1451
1452 /*
1453 * Tiny nr_dirtied_pause is found to hurt I/O performance in the test
1454 * case fio-mmap-randwrite-64k, which does 16*{sync read, async write}.
1455 * When the 16 consecutive reads are often interrupted by some dirty
1456 * throttling pause during the async writes, cfq will go into idles
1457 * (deadline is fine). So push nr_dirtied_pause as high as possible
1458 * until reaches DIRTY_POLL_THRESH=32 pages.
1459 */
1460 if (pages < DIRTY_POLL_THRESH) {
1461 t = max_pause;
1462 pages = dirty_ratelimit * t / roundup_pow_of_two(HZ);
1463 if (pages > DIRTY_POLL_THRESH) {
1464 pages = DIRTY_POLL_THRESH;
1465 t = HZ * DIRTY_POLL_THRESH / dirty_ratelimit;
1466 }
1467 }
1468
1469 pause = HZ * pages / (task_ratelimit + 1);
1470 if (pause > max_pause) {
1471 t = max_pause;
1472 pages = task_ratelimit * t / roundup_pow_of_two(HZ);
1473 }
1474
1475 *nr_dirtied_pause = pages;
1476 /*
1477 * The minimal pause time will normally be half the target pause time.
1478 */
1479 return pages >= DIRTY_POLL_THRESH ? 1 + t / 2 : t;
1480}
1481
1482static inline void wb_dirty_limits(struct dirty_throttle_control *dtc)
1483{
1484 struct bdi_writeback *wb = dtc->wb;
1485 unsigned long wb_reclaimable;
1486
1487 /*
1488 * wb_thresh is not treated as some limiting factor as
1489 * dirty_thresh, due to reasons
1490 * - in JBOD setup, wb_thresh can fluctuate a lot
1491 * - in a system with HDD and USB key, the USB key may somehow
1492 * go into state (wb_dirty >> wb_thresh) either because
1493 * wb_dirty starts high, or because wb_thresh drops low.
1494 * In this case we don't want to hard throttle the USB key
1495 * dirtiers for 100 seconds until wb_dirty drops under
1496 * wb_thresh. Instead the auxiliary wb control line in
1497 * wb_position_ratio() will let the dirtier task progress
1498 * at some rate <= (write_bw / 2) for bringing down wb_dirty.
1499 */
1500 dtc->wb_thresh = __wb_calc_thresh(dtc);
1501 dtc->wb_bg_thresh = dtc->thresh ?
1502 div_u64((u64)dtc->wb_thresh * dtc->bg_thresh, dtc->thresh) : 0;
1503
1504 /*
1505 * In order to avoid the stacked BDI deadlock we need
1506 * to ensure we accurately count the 'dirty' pages when
1507 * the threshold is low.
1508 *
1509 * Otherwise it would be possible to get thresh+n pages
1510 * reported dirty, even though there are thresh-m pages
1511 * actually dirty; with m+n sitting in the percpu
1512 * deltas.
1513 */
1514 if (dtc->wb_thresh < 2 * wb_stat_error(wb)) {
1515 wb_reclaimable = wb_stat_sum(wb, WB_RECLAIMABLE);
1516 dtc->wb_dirty = wb_reclaimable + wb_stat_sum(wb, WB_WRITEBACK);
1517 } else {
1518 wb_reclaimable = wb_stat(wb, WB_RECLAIMABLE);
1519 dtc->wb_dirty = wb_reclaimable + wb_stat(wb, WB_WRITEBACK);
1520 }
1521}
1522
1523/*
1524 * balance_dirty_pages() must be called by processes which are generating dirty
1525 * data. It looks at the number of dirty pages in the machine and will force
1526 * the caller to wait once crossing the (background_thresh + dirty_thresh) / 2.
1527 * If we're over `background_thresh' then the writeback threads are woken to
1528 * perform some writeout.
1529 */
1530static void balance_dirty_pages(struct address_space *mapping,
1531 struct bdi_writeback *wb,
1532 unsigned long pages_dirtied)
1533{
1534 struct dirty_throttle_control gdtc_stor = { GDTC_INIT(wb) };
1535 struct dirty_throttle_control mdtc_stor = { MDTC_INIT(wb, &gdtc_stor) };
1536 struct dirty_throttle_control * const gdtc = &gdtc_stor;
1537 struct dirty_throttle_control * const mdtc = mdtc_valid(&mdtc_stor) ?
1538 &mdtc_stor : NULL;
1539 struct dirty_throttle_control *sdtc;
1540 unsigned long nr_reclaimable; /* = file_dirty + unstable_nfs */
1541 long period;
1542 long pause;
1543 long max_pause;
1544 long min_pause;
1545 int nr_dirtied_pause;
1546 bool dirty_exceeded = false;
1547 unsigned long task_ratelimit;
1548 unsigned long dirty_ratelimit;
1549 struct backing_dev_info *bdi = wb->bdi;
1550 bool strictlimit = bdi->capabilities & BDI_CAP_STRICTLIMIT;
1551 unsigned long start_time = jiffies;
1552
1553 for (;;) {
1554 unsigned long now = jiffies;
1555 unsigned long dirty, thresh, bg_thresh;
1556 unsigned long m_dirty = 0; /* stop bogus uninit warnings */
1557 unsigned long m_thresh = 0;
1558 unsigned long m_bg_thresh = 0;
1559
1560 /*
1561 * Unstable writes are a feature of certain networked
1562 * filesystems (i.e. NFS) in which data may have been
1563 * written to the server's write cache, but has not yet
1564 * been flushed to permanent storage.
1565 */
1566 nr_reclaimable = global_page_state(NR_FILE_DIRTY) +
1567 global_page_state(NR_UNSTABLE_NFS);
1568 gdtc->avail = global_dirtyable_memory();
1569 gdtc->dirty = nr_reclaimable + global_page_state(NR_WRITEBACK);
1570
1571 domain_dirty_limits(gdtc);
1572
1573 if (unlikely(strictlimit)) {
1574 wb_dirty_limits(gdtc);
1575
1576 dirty = gdtc->wb_dirty;
1577 thresh = gdtc->wb_thresh;
1578 bg_thresh = gdtc->wb_bg_thresh;
1579 } else {
1580 dirty = gdtc->dirty;
1581 thresh = gdtc->thresh;
1582 bg_thresh = gdtc->bg_thresh;
1583 }
1584
1585 if (mdtc) {
1586 unsigned long filepages, headroom, writeback;
1587
1588 /*
1589 * If @wb belongs to !root memcg, repeat the same
1590 * basic calculations for the memcg domain.
1591 */
1592 mem_cgroup_wb_stats(wb, &filepages, &headroom,
1593 &mdtc->dirty, &writeback);
1594 mdtc->dirty += writeback;
1595 mdtc_calc_avail(mdtc, filepages, headroom);
1596
1597 domain_dirty_limits(mdtc);
1598
1599 if (unlikely(strictlimit)) {
1600 wb_dirty_limits(mdtc);
1601 m_dirty = mdtc->wb_dirty;
1602 m_thresh = mdtc->wb_thresh;
1603 m_bg_thresh = mdtc->wb_bg_thresh;
1604 } else {
1605 m_dirty = mdtc->dirty;
1606 m_thresh = mdtc->thresh;
1607 m_bg_thresh = mdtc->bg_thresh;
1608 }
1609 }
1610
1611 /*
1612 * Throttle it only when the background writeback cannot
1613 * catch-up. This avoids (excessively) small writeouts
1614 * when the wb limits are ramping up in case of !strictlimit.
1615 *
1616 * In strictlimit case make decision based on the wb counters
1617 * and limits. Small writeouts when the wb limits are ramping
1618 * up are the price we consciously pay for strictlimit-ing.
1619 *
1620 * If memcg domain is in effect, @dirty should be under
1621 * both global and memcg freerun ceilings.
1622 */
1623 if (dirty <= dirty_freerun_ceiling(thresh, bg_thresh) &&
1624 (!mdtc ||
1625 m_dirty <= dirty_freerun_ceiling(m_thresh, m_bg_thresh))) {
1626 unsigned long intv = dirty_poll_interval(dirty, thresh);
1627 unsigned long m_intv = ULONG_MAX;
1628
1629 current->dirty_paused_when = now;
1630 current->nr_dirtied = 0;
1631 if (mdtc)
1632 m_intv = dirty_poll_interval(m_dirty, m_thresh);
1633 current->nr_dirtied_pause = min(intv, m_intv);
1634 break;
1635 }
1636
1637 if (unlikely(!writeback_in_progress(wb)))
1638 wb_start_background_writeback(wb);
1639
1640 /*
1641 * Calculate global domain's pos_ratio and select the
1642 * global dtc by default.
1643 */
1644 if (!strictlimit)
1645 wb_dirty_limits(gdtc);
1646
1647 dirty_exceeded = (gdtc->wb_dirty > gdtc->wb_thresh) &&
1648 ((gdtc->dirty > gdtc->thresh) || strictlimit);
1649
1650 wb_position_ratio(gdtc);
1651 sdtc = gdtc;
1652
1653 if (mdtc) {
1654 /*
1655 * If memcg domain is in effect, calculate its
1656 * pos_ratio. @wb should satisfy constraints from
1657 * both global and memcg domains. Choose the one
1658 * w/ lower pos_ratio.
1659 */
1660 if (!strictlimit)
1661 wb_dirty_limits(mdtc);
1662
1663 dirty_exceeded |= (mdtc->wb_dirty > mdtc->wb_thresh) &&
1664 ((mdtc->dirty > mdtc->thresh) || strictlimit);
1665
1666 wb_position_ratio(mdtc);
1667 if (mdtc->pos_ratio < gdtc->pos_ratio)
1668 sdtc = mdtc;
1669 }
1670
1671 if (dirty_exceeded && !wb->dirty_exceeded)
1672 wb->dirty_exceeded = 1;
1673
1674 if (time_is_before_jiffies(wb->bw_time_stamp +
1675 BANDWIDTH_INTERVAL)) {
1676 spin_lock(&wb->list_lock);
1677 __wb_update_bandwidth(gdtc, mdtc, start_time, true);
1678 spin_unlock(&wb->list_lock);
1679 }
1680
1681 /* throttle according to the chosen dtc */
1682 dirty_ratelimit = wb->dirty_ratelimit;
1683 task_ratelimit = ((u64)dirty_ratelimit * sdtc->pos_ratio) >>
1684 RATELIMIT_CALC_SHIFT;
1685 max_pause = wb_max_pause(wb, sdtc->wb_dirty);
1686 min_pause = wb_min_pause(wb, max_pause,
1687 task_ratelimit, dirty_ratelimit,
1688 &nr_dirtied_pause);
1689
1690 if (unlikely(task_ratelimit == 0)) {
1691 period = max_pause;
1692 pause = max_pause;
1693 goto pause;
1694 }
1695 period = HZ * pages_dirtied / task_ratelimit;
1696 pause = period;
1697 if (current->dirty_paused_when)
1698 pause -= now - current->dirty_paused_when;
1699 /*
1700 * For less than 1s think time (ext3/4 may block the dirtier
1701 * for up to 800ms from time to time on 1-HDD; so does xfs,
1702 * however at much less frequency), try to compensate it in
1703 * future periods by updating the virtual time; otherwise just
1704 * do a reset, as it may be a light dirtier.
1705 */
1706 if (pause < min_pause) {
1707 trace_balance_dirty_pages(wb,
1708 sdtc->thresh,
1709 sdtc->bg_thresh,
1710 sdtc->dirty,
1711 sdtc->wb_thresh,
1712 sdtc->wb_dirty,
1713 dirty_ratelimit,
1714 task_ratelimit,
1715 pages_dirtied,
1716 period,
1717 min(pause, 0L),
1718 start_time);
1719 if (pause < -HZ) {
1720 current->dirty_paused_when = now;
1721 current->nr_dirtied = 0;
1722 } else if (period) {
1723 current->dirty_paused_when += period;
1724 current->nr_dirtied = 0;
1725 } else if (current->nr_dirtied_pause <= pages_dirtied)
1726 current->nr_dirtied_pause += pages_dirtied;
1727 break;
1728 }
1729 if (unlikely(pause > max_pause)) {
1730 /* for occasional dropped task_ratelimit */
1731 now += min(pause - max_pause, max_pause);
1732 pause = max_pause;
1733 }
1734
1735pause:
1736 trace_balance_dirty_pages(wb,
1737 sdtc->thresh,
1738 sdtc->bg_thresh,
1739 sdtc->dirty,
1740 sdtc->wb_thresh,
1741 sdtc->wb_dirty,
1742 dirty_ratelimit,
1743 task_ratelimit,
1744 pages_dirtied,
1745 period,
1746 pause,
1747 start_time);
1748 __set_current_state(TASK_KILLABLE);
1749 io_schedule_timeout(pause);
1750
1751 current->dirty_paused_when = now + pause;
1752 current->nr_dirtied = 0;
1753 current->nr_dirtied_pause = nr_dirtied_pause;
1754
1755 /*
1756 * This is typically equal to (dirty < thresh) and can also
1757 * keep "1000+ dd on a slow USB stick" under control.
1758 */
1759 if (task_ratelimit)
1760 break;
1761
1762 /*
1763 * In the case of an unresponding NFS server and the NFS dirty
1764 * pages exceeds dirty_thresh, give the other good wb's a pipe
1765 * to go through, so that tasks on them still remain responsive.
1766 *
1767 * In theory 1 page is enough to keep the comsumer-producer
1768 * pipe going: the flusher cleans 1 page => the task dirties 1
1769 * more page. However wb_dirty has accounting errors. So use
1770 * the larger and more IO friendly wb_stat_error.
1771 */
1772 if (sdtc->wb_dirty <= wb_stat_error(wb))
1773 break;
1774
1775 if (fatal_signal_pending(current))
1776 break;
1777 }
1778
1779 if (!dirty_exceeded && wb->dirty_exceeded)
1780 wb->dirty_exceeded = 0;
1781
1782 if (writeback_in_progress(wb))
1783 return;
1784
1785 /*
1786 * In laptop mode, we wait until hitting the higher threshold before
1787 * starting background writeout, and then write out all the way down
1788 * to the lower threshold. So slow writers cause minimal disk activity.
1789 *
1790 * In normal mode, we start background writeout at the lower
1791 * background_thresh, to keep the amount of dirty memory low.
1792 */
1793 if (laptop_mode)
1794 return;
1795
1796 if (nr_reclaimable > gdtc->bg_thresh)
1797 wb_start_background_writeback(wb);
1798}
1799
1800static DEFINE_PER_CPU(int, bdp_ratelimits);
1801
1802/*
1803 * Normal tasks are throttled by
1804 * loop {
1805 * dirty tsk->nr_dirtied_pause pages;
1806 * take a snap in balance_dirty_pages();
1807 * }
1808 * However there is a worst case. If every task exit immediately when dirtied
1809 * (tsk->nr_dirtied_pause - 1) pages, balance_dirty_pages() will never be
1810 * called to throttle the page dirties. The solution is to save the not yet
1811 * throttled page dirties in dirty_throttle_leaks on task exit and charge them
1812 * randomly into the running tasks. This works well for the above worst case,
1813 * as the new task will pick up and accumulate the old task's leaked dirty
1814 * count and eventually get throttled.
1815 */
1816DEFINE_PER_CPU(int, dirty_throttle_leaks) = 0;
1817
1818/**
1819 * balance_dirty_pages_ratelimited - balance dirty memory state
1820 * @mapping: address_space which was dirtied
1821 *
1822 * Processes which are dirtying memory should call in here once for each page
1823 * which was newly dirtied. The function will periodically check the system's
1824 * dirty state and will initiate writeback if needed.
1825 *
1826 * On really big machines, get_writeback_state is expensive, so try to avoid
1827 * calling it too often (ratelimiting). But once we're over the dirty memory
1828 * limit we decrease the ratelimiting by a lot, to prevent individual processes
1829 * from overshooting the limit by (ratelimit_pages) each.
1830 */
1831void balance_dirty_pages_ratelimited(struct address_space *mapping)
1832{
1833 struct inode *inode = mapping->host;
1834 struct backing_dev_info *bdi = inode_to_bdi(inode);
1835 struct bdi_writeback *wb = NULL;
1836 int ratelimit;
1837 int *p;
1838
1839 if (!bdi_cap_account_dirty(bdi))
1840 return;
1841
1842 if (inode_cgwb_enabled(inode))
1843 wb = wb_get_create_current(bdi, GFP_KERNEL);
1844 if (!wb)
1845 wb = &bdi->wb;
1846
1847 ratelimit = current->nr_dirtied_pause;
1848 if (wb->dirty_exceeded)
1849 ratelimit = min(ratelimit, 32 >> (PAGE_SHIFT - 10));
1850
1851 preempt_disable();
1852 /*
1853 * This prevents one CPU to accumulate too many dirtied pages without
1854 * calling into balance_dirty_pages(), which can happen when there are
1855 * 1000+ tasks, all of them start dirtying pages at exactly the same
1856 * time, hence all honoured too large initial task->nr_dirtied_pause.
1857 */
1858 p = this_cpu_ptr(&bdp_ratelimits);
1859 if (unlikely(current->nr_dirtied >= ratelimit))
1860 *p = 0;
1861 else if (unlikely(*p >= ratelimit_pages)) {
1862 *p = 0;
1863 ratelimit = 0;
1864 }
1865 /*
1866 * Pick up the dirtied pages by the exited tasks. This avoids lots of
1867 * short-lived tasks (eg. gcc invocations in a kernel build) escaping
1868 * the dirty throttling and livelock other long-run dirtiers.
1869 */
1870 p = this_cpu_ptr(&dirty_throttle_leaks);
1871 if (*p > 0 && current->nr_dirtied < ratelimit) {
1872 unsigned long nr_pages_dirtied;
1873 nr_pages_dirtied = min(*p, ratelimit - current->nr_dirtied);
1874 *p -= nr_pages_dirtied;
1875 current->nr_dirtied += nr_pages_dirtied;
1876 }
1877 preempt_enable();
1878
1879 if (unlikely(current->nr_dirtied >= ratelimit))
1880 balance_dirty_pages(mapping, wb, current->nr_dirtied);
1881
1882 wb_put(wb);
1883}
1884EXPORT_SYMBOL(balance_dirty_pages_ratelimited);
1885
1886/**
1887 * wb_over_bg_thresh - does @wb need to be written back?
1888 * @wb: bdi_writeback of interest
1889 *
1890 * Determines whether background writeback should keep writing @wb or it's
1891 * clean enough. Returns %true if writeback should continue.
1892 */
1893bool wb_over_bg_thresh(struct bdi_writeback *wb)
1894{
1895 struct dirty_throttle_control gdtc_stor = { GDTC_INIT(wb) };
1896 struct dirty_throttle_control mdtc_stor = { MDTC_INIT(wb, &gdtc_stor) };
1897 struct dirty_throttle_control * const gdtc = &gdtc_stor;
1898 struct dirty_throttle_control * const mdtc = mdtc_valid(&mdtc_stor) ?
1899 &mdtc_stor : NULL;
1900
1901 /*
1902 * Similar to balance_dirty_pages() but ignores pages being written
1903 * as we're trying to decide whether to put more under writeback.
1904 */
1905 gdtc->avail = global_dirtyable_memory();
1906 gdtc->dirty = global_page_state(NR_FILE_DIRTY) +
1907 global_page_state(NR_UNSTABLE_NFS);
1908 domain_dirty_limits(gdtc);
1909
1910 if (gdtc->dirty > gdtc->bg_thresh)
1911 return true;
1912
1913 if (wb_stat(wb, WB_RECLAIMABLE) >
1914 wb_calc_thresh(gdtc->wb, gdtc->bg_thresh))
1915 return true;
1916
1917 if (mdtc) {
1918 unsigned long filepages, headroom, writeback;
1919
1920 mem_cgroup_wb_stats(wb, &filepages, &headroom, &mdtc->dirty,
1921 &writeback);
1922 mdtc_calc_avail(mdtc, filepages, headroom);
1923 domain_dirty_limits(mdtc); /* ditto, ignore writeback */
1924
1925 if (mdtc->dirty > mdtc->bg_thresh)
1926 return true;
1927
1928 if (wb_stat(wb, WB_RECLAIMABLE) >
1929 wb_calc_thresh(mdtc->wb, mdtc->bg_thresh))
1930 return true;
1931 }
1932
1933 return false;
1934}
1935
1936void throttle_vm_writeout(gfp_t gfp_mask)
1937{
1938 unsigned long background_thresh;
1939 unsigned long dirty_thresh;
1940
1941 for ( ; ; ) {
1942 global_dirty_limits(&background_thresh, &dirty_thresh);
1943 dirty_thresh = hard_dirty_limit(&global_wb_domain, dirty_thresh);
1944
1945 /*
1946 * Boost the allowable dirty threshold a bit for page
1947 * allocators so they don't get DoS'ed by heavy writers
1948 */
1949 dirty_thresh += dirty_thresh / 10; /* wheeee... */
1950
1951 if (global_page_state(NR_UNSTABLE_NFS) +
1952 global_page_state(NR_WRITEBACK) <= dirty_thresh)
1953 break;
1954 congestion_wait(BLK_RW_ASYNC, HZ/10);
1955
1956 /*
1957 * The caller might hold locks which can prevent IO completion
1958 * or progress in the filesystem. So we cannot just sit here
1959 * waiting for IO to complete.
1960 */
1961 if ((gfp_mask & (__GFP_FS|__GFP_IO)) != (__GFP_FS|__GFP_IO))
1962 break;
1963 }
1964}
1965
1966/*
1967 * sysctl handler for /proc/sys/vm/dirty_writeback_centisecs
1968 */
1969int dirty_writeback_centisecs_handler(struct ctl_table *table, int write,
1970 void __user *buffer, size_t *length, loff_t *ppos)
1971{
1972 proc_dointvec(table, write, buffer, length, ppos);
1973 return 0;
1974}
1975
1976#ifdef CONFIG_BLOCK
1977void laptop_mode_timer_fn(unsigned long data)
1978{
1979 struct request_queue *q = (struct request_queue *)data;
1980 int nr_pages = global_page_state(NR_FILE_DIRTY) +
1981 global_page_state(NR_UNSTABLE_NFS);
1982 struct bdi_writeback *wb;
1983
1984 /*
1985 * We want to write everything out, not just down to the dirty
1986 * threshold
1987 */
1988 if (!bdi_has_dirty_io(&q->backing_dev_info))
1989 return;
1990
1991 rcu_read_lock();
1992 list_for_each_entry_rcu(wb, &q->backing_dev_info.wb_list, bdi_node)
1993 if (wb_has_dirty_io(wb))
1994 wb_start_writeback(wb, nr_pages, true,
1995 WB_REASON_LAPTOP_TIMER);
1996 rcu_read_unlock();
1997}
1998
1999/*
2000 * We've spun up the disk and we're in laptop mode: schedule writeback
2001 * of all dirty data a few seconds from now. If the flush is already scheduled
2002 * then push it back - the user is still using the disk.
2003 */
2004void laptop_io_completion(struct backing_dev_info *info)
2005{
2006 mod_timer(&info->laptop_mode_wb_timer, jiffies + laptop_mode);
2007}
2008
2009/*
2010 * We're in laptop mode and we've just synced. The sync's writes will have
2011 * caused another writeback to be scheduled by laptop_io_completion.
2012 * Nothing needs to be written back anymore, so we unschedule the writeback.
2013 */
2014void laptop_sync_completion(void)
2015{
2016 struct backing_dev_info *bdi;
2017
2018 rcu_read_lock();
2019
2020 list_for_each_entry_rcu(bdi, &bdi_list, bdi_list)
2021 del_timer(&bdi->laptop_mode_wb_timer);
2022
2023 rcu_read_unlock();
2024}
2025#endif
2026
2027/*
2028 * If ratelimit_pages is too high then we can get into dirty-data overload
2029 * if a large number of processes all perform writes at the same time.
2030 * If it is too low then SMP machines will call the (expensive)
2031 * get_writeback_state too often.
2032 *
2033 * Here we set ratelimit_pages to a level which ensures that when all CPUs are
2034 * dirtying in parallel, we cannot go more than 3% (1/32) over the dirty memory
2035 * thresholds.
2036 */
2037
2038void writeback_set_ratelimit(void)
2039{
2040 struct wb_domain *dom = &global_wb_domain;
2041 unsigned long background_thresh;
2042 unsigned long dirty_thresh;
2043
2044 global_dirty_limits(&background_thresh, &dirty_thresh);
2045 dom->dirty_limit = dirty_thresh;
2046 ratelimit_pages = dirty_thresh / (num_online_cpus() * 32);
2047 if (ratelimit_pages < 16)
2048 ratelimit_pages = 16;
2049}
2050
2051static int
2052ratelimit_handler(struct notifier_block *self, unsigned long action,
2053 void *hcpu)
2054{
2055
2056 switch (action & ~CPU_TASKS_FROZEN) {
2057 case CPU_ONLINE:
2058 case CPU_DEAD:
2059 writeback_set_ratelimit();
2060 return NOTIFY_OK;
2061 default:
2062 return NOTIFY_DONE;
2063 }
2064}
2065
2066static struct notifier_block ratelimit_nb = {
2067 .notifier_call = ratelimit_handler,
2068 .next = NULL,
2069};
2070
2071/*
2072 * Called early on to tune the page writeback dirty limits.
2073 *
2074 * We used to scale dirty pages according to how total memory
2075 * related to pages that could be allocated for buffers (by
2076 * comparing nr_free_buffer_pages() to vm_total_pages.
2077 *
2078 * However, that was when we used "dirty_ratio" to scale with
2079 * all memory, and we don't do that any more. "dirty_ratio"
2080 * is now applied to total non-HIGHPAGE memory (by subtracting
2081 * totalhigh_pages from vm_total_pages), and as such we can't
2082 * get into the old insane situation any more where we had
2083 * large amounts of dirty pages compared to a small amount of
2084 * non-HIGHMEM memory.
2085 *
2086 * But we might still want to scale the dirty_ratio by how
2087 * much memory the box has..
2088 */
2089void __init page_writeback_init(void)
2090{
2091 BUG_ON(wb_domain_init(&global_wb_domain, GFP_KERNEL));
2092
2093 writeback_set_ratelimit();
2094 register_cpu_notifier(&ratelimit_nb);
2095}
2096
2097/**
2098 * tag_pages_for_writeback - tag pages to be written by write_cache_pages
2099 * @mapping: address space structure to write
2100 * @start: starting page index
2101 * @end: ending page index (inclusive)
2102 *
2103 * This function scans the page range from @start to @end (inclusive) and tags
2104 * all pages that have DIRTY tag set with a special TOWRITE tag. The idea is
2105 * that write_cache_pages (or whoever calls this function) will then use
2106 * TOWRITE tag to identify pages eligible for writeback. This mechanism is
2107 * used to avoid livelocking of writeback by a process steadily creating new
2108 * dirty pages in the file (thus it is important for this function to be quick
2109 * so that it can tag pages faster than a dirtying process can create them).
2110 */
2111/*
2112 * We tag pages in batches of WRITEBACK_TAG_BATCH to reduce tree_lock latency.
2113 */
2114void tag_pages_for_writeback(struct address_space *mapping,
2115 pgoff_t start, pgoff_t end)
2116{
2117#define WRITEBACK_TAG_BATCH 4096
2118 unsigned long tagged;
2119
2120 do {
2121 spin_lock_irq(&mapping->tree_lock);
2122 tagged = radix_tree_range_tag_if_tagged(&mapping->page_tree,
2123 &start, end, WRITEBACK_TAG_BATCH,
2124 PAGECACHE_TAG_DIRTY, PAGECACHE_TAG_TOWRITE);
2125 spin_unlock_irq(&mapping->tree_lock);
2126 WARN_ON_ONCE(tagged > WRITEBACK_TAG_BATCH);
2127 cond_resched();
2128 /* We check 'start' to handle wrapping when end == ~0UL */
2129 } while (tagged >= WRITEBACK_TAG_BATCH && start);
2130}
2131EXPORT_SYMBOL(tag_pages_for_writeback);
2132
2133/**
2134 * write_cache_pages - walk the list of dirty pages of the given address space and write all of them.
2135 * @mapping: address space structure to write
2136 * @wbc: subtract the number of written pages from *@wbc->nr_to_write
2137 * @writepage: function called for each page
2138 * @data: data passed to writepage function
2139 *
2140 * If a page is already under I/O, write_cache_pages() skips it, even
2141 * if it's dirty. This is desirable behaviour for memory-cleaning writeback,
2142 * but it is INCORRECT for data-integrity system calls such as fsync(). fsync()
2143 * and msync() need to guarantee that all the data which was dirty at the time
2144 * the call was made get new I/O started against them. If wbc->sync_mode is
2145 * WB_SYNC_ALL then we were called for data integrity and we must wait for
2146 * existing IO to complete.
2147 *
2148 * To avoid livelocks (when other process dirties new pages), we first tag
2149 * pages which should be written back with TOWRITE tag and only then start
2150 * writing them. For data-integrity sync we have to be careful so that we do
2151 * not miss some pages (e.g., because some other process has cleared TOWRITE
2152 * tag we set). The rule we follow is that TOWRITE tag can be cleared only
2153 * by the process clearing the DIRTY tag (and submitting the page for IO).
2154 */
2155int write_cache_pages(struct address_space *mapping,
2156 struct writeback_control *wbc, writepage_t writepage,
2157 void *data)
2158{
2159 int ret = 0;
2160 int done = 0;
2161 struct pagevec pvec;
2162 int nr_pages;
2163 pgoff_t uninitialized_var(writeback_index);
2164 pgoff_t index;
2165 pgoff_t end; /* Inclusive */
2166 pgoff_t done_index;
2167 int cycled;
2168 int range_whole = 0;
2169 int tag;
2170
2171 pagevec_init(&pvec, 0);
2172 if (wbc->range_cyclic) {
2173 writeback_index = mapping->writeback_index; /* prev offset */
2174 index = writeback_index;
2175 if (index == 0)
2176 cycled = 1;
2177 else
2178 cycled = 0;
2179 end = -1;
2180 } else {
2181 index = wbc->range_start >> PAGE_SHIFT;
2182 end = wbc->range_end >> PAGE_SHIFT;
2183 if (wbc->range_start == 0 && wbc->range_end == LLONG_MAX)
2184 range_whole = 1;
2185 cycled = 1; /* ignore range_cyclic tests */
2186 }
2187 if (wbc->sync_mode == WB_SYNC_ALL || wbc->tagged_writepages)
2188 tag = PAGECACHE_TAG_TOWRITE;
2189 else
2190 tag = PAGECACHE_TAG_DIRTY;
2191retry:
2192 if (wbc->sync_mode == WB_SYNC_ALL || wbc->tagged_writepages)
2193 tag_pages_for_writeback(mapping, index, end);
2194 done_index = index;
2195 while (!done && (index <= end)) {
2196 int i;
2197
2198 nr_pages = pagevec_lookup_tag(&pvec, mapping, &index, tag,
2199 min(end - index, (pgoff_t)PAGEVEC_SIZE-1) + 1);
2200 if (nr_pages == 0)
2201 break;
2202
2203 for (i = 0; i < nr_pages; i++) {
2204 struct page *page = pvec.pages[i];
2205
2206 /*
2207 * At this point, the page may be truncated or
2208 * invalidated (changing page->mapping to NULL), or
2209 * even swizzled back from swapper_space to tmpfs file
2210 * mapping. However, page->index will not change
2211 * because we have a reference on the page.
2212 */
2213 if (page->index > end) {
2214 /*
2215 * can't be range_cyclic (1st pass) because
2216 * end == -1 in that case.
2217 */
2218 done = 1;
2219 break;
2220 }
2221
2222 done_index = page->index;
2223
2224 lock_page(page);
2225
2226 /*
2227 * Page truncated or invalidated. We can freely skip it
2228 * then, even for data integrity operations: the page
2229 * has disappeared concurrently, so there could be no
2230 * real expectation of this data interity operation
2231 * even if there is now a new, dirty page at the same
2232 * pagecache address.
2233 */
2234 if (unlikely(page->mapping != mapping)) {
2235continue_unlock:
2236 unlock_page(page);
2237 continue;
2238 }
2239
2240 if (!PageDirty(page)) {
2241 /* someone wrote it for us */
2242 goto continue_unlock;
2243 }
2244
2245 if (PageWriteback(page)) {
2246 if (wbc->sync_mode != WB_SYNC_NONE)
2247 wait_on_page_writeback(page);
2248 else
2249 goto continue_unlock;
2250 }
2251
2252 BUG_ON(PageWriteback(page));
2253 if (!clear_page_dirty_for_io(page))
2254 goto continue_unlock;
2255
2256 trace_wbc_writepage(wbc, inode_to_bdi(mapping->host));
2257 ret = (*writepage)(page, wbc, data);
2258 if (unlikely(ret)) {
2259 if (ret == AOP_WRITEPAGE_ACTIVATE) {
2260 unlock_page(page);
2261 ret = 0;
2262 } else {
2263 /*
2264 * done_index is set past this page,
2265 * so media errors will not choke
2266 * background writeout for the entire
2267 * file. This has consequences for
2268 * range_cyclic semantics (ie. it may
2269 * not be suitable for data integrity
2270 * writeout).
2271 */
2272 done_index = page->index + 1;
2273 done = 1;
2274 break;
2275 }
2276 }
2277
2278 /*
2279 * We stop writing back only if we are not doing
2280 * integrity sync. In case of integrity sync we have to
2281 * keep going until we have written all the pages
2282 * we tagged for writeback prior to entering this loop.
2283 */
2284 if (--wbc->nr_to_write <= 0 &&
2285 wbc->sync_mode == WB_SYNC_NONE) {
2286 done = 1;
2287 break;
2288 }
2289 }
2290 pagevec_release(&pvec);
2291 cond_resched();
2292 }
2293 if (!cycled && !done) {
2294 /*
2295 * range_cyclic:
2296 * We hit the last page and there is more work to be done: wrap
2297 * back to the start of the file
2298 */
2299 cycled = 1;
2300 index = 0;
2301 end = writeback_index - 1;
2302 goto retry;
2303 }
2304 if (wbc->range_cyclic || (range_whole && wbc->nr_to_write > 0))
2305 mapping->writeback_index = done_index;
2306
2307 return ret;
2308}
2309EXPORT_SYMBOL(write_cache_pages);
2310
2311/*
2312 * Function used by generic_writepages to call the real writepage
2313 * function and set the mapping flags on error
2314 */
2315static int __writepage(struct page *page, struct writeback_control *wbc,
2316 void *data)
2317{
2318 struct address_space *mapping = data;
2319 int ret = mapping->a_ops->writepage(page, wbc);
2320 mapping_set_error(mapping, ret);
2321 return ret;
2322}
2323
2324/**
2325 * generic_writepages - walk the list of dirty pages of the given address space and writepage() all of them.
2326 * @mapping: address space structure to write
2327 * @wbc: subtract the number of written pages from *@wbc->nr_to_write
2328 *
2329 * This is a library function, which implements the writepages()
2330 * address_space_operation.
2331 */
2332int generic_writepages(struct address_space *mapping,
2333 struct writeback_control *wbc)
2334{
2335 struct blk_plug plug;
2336 int ret;
2337
2338 /* deal with chardevs and other special file */
2339 if (!mapping->a_ops->writepage)
2340 return 0;
2341
2342 blk_start_plug(&plug);
2343 ret = write_cache_pages(mapping, wbc, __writepage, mapping);
2344 blk_finish_plug(&plug);
2345 return ret;
2346}
2347
2348EXPORT_SYMBOL(generic_writepages);
2349
2350int do_writepages(struct address_space *mapping, struct writeback_control *wbc)
2351{
2352 int ret;
2353
2354 if (wbc->nr_to_write <= 0)
2355 return 0;
2356 if (mapping->a_ops->writepages)
2357 ret = mapping->a_ops->writepages(mapping, wbc);
2358 else
2359 ret = generic_writepages(mapping, wbc);
2360 return ret;
2361}
2362
2363/**
2364 * write_one_page - write out a single page and optionally wait on I/O
2365 * @page: the page to write
2366 * @wait: if true, wait on writeout
2367 *
2368 * The page must be locked by the caller and will be unlocked upon return.
2369 *
2370 * write_one_page() returns a negative error code if I/O failed.
2371 */
2372int write_one_page(struct page *page, int wait)
2373{
2374 struct address_space *mapping = page->mapping;
2375 int ret = 0;
2376 struct writeback_control wbc = {
2377 .sync_mode = WB_SYNC_ALL,
2378 .nr_to_write = 1,
2379 };
2380
2381 BUG_ON(!PageLocked(page));
2382
2383 if (wait)
2384 wait_on_page_writeback(page);
2385
2386 if (clear_page_dirty_for_io(page)) {
2387 get_page(page);
2388 ret = mapping->a_ops->writepage(page, &wbc);
2389 if (ret == 0 && wait) {
2390 wait_on_page_writeback(page);
2391 if (PageError(page))
2392 ret = -EIO;
2393 }
2394 put_page(page);
2395 } else {
2396 unlock_page(page);
2397 }
2398 return ret;
2399}
2400EXPORT_SYMBOL(write_one_page);
2401
2402/*
2403 * For address_spaces which do not use buffers nor write back.
2404 */
2405int __set_page_dirty_no_writeback(struct page *page)
2406{
2407 if (!PageDirty(page))
2408 return !TestSetPageDirty(page);
2409 return 0;
2410}
2411
2412/*
2413 * Helper function for set_page_dirty family.
2414 *
2415 * Caller must hold lock_page_memcg().
2416 *
2417 * NOTE: This relies on being atomic wrt interrupts.
2418 */
2419void account_page_dirtied(struct page *page, struct address_space *mapping)
2420{
2421 struct inode *inode = mapping->host;
2422
2423 trace_writeback_dirty_page(page, mapping);
2424
2425 if (mapping_cap_account_dirty(mapping)) {
2426 struct bdi_writeback *wb;
2427
2428 inode_attach_wb(inode, page);
2429 wb = inode_to_wb(inode);
2430
2431 mem_cgroup_inc_page_stat(page, MEM_CGROUP_STAT_DIRTY);
2432 __inc_zone_page_state(page, NR_FILE_DIRTY);
2433 __inc_zone_page_state(page, NR_DIRTIED);
2434 __inc_wb_stat(wb, WB_RECLAIMABLE);
2435 __inc_wb_stat(wb, WB_DIRTIED);
2436 task_io_account_write(PAGE_SIZE);
2437 current->nr_dirtied++;
2438 this_cpu_inc(bdp_ratelimits);
2439 }
2440}
2441EXPORT_SYMBOL(account_page_dirtied);
2442
2443/*
2444 * Helper function for deaccounting dirty page without writeback.
2445 *
2446 * Caller must hold lock_page_memcg().
2447 */
2448void account_page_cleaned(struct page *page, struct address_space *mapping,
2449 struct bdi_writeback *wb)
2450{
2451 if (mapping_cap_account_dirty(mapping)) {
2452 mem_cgroup_dec_page_stat(page, MEM_CGROUP_STAT_DIRTY);
2453 dec_zone_page_state(page, NR_FILE_DIRTY);
2454 dec_wb_stat(wb, WB_RECLAIMABLE);
2455 task_io_account_cancelled_write(PAGE_SIZE);
2456 }
2457}
2458
2459/*
2460 * For address_spaces which do not use buffers. Just tag the page as dirty in
2461 * its radix tree.
2462 *
2463 * This is also used when a single buffer is being dirtied: we want to set the
2464 * page dirty in that case, but not all the buffers. This is a "bottom-up"
2465 * dirtying, whereas __set_page_dirty_buffers() is a "top-down" dirtying.
2466 *
2467 * The caller must ensure this doesn't race with truncation. Most will simply
2468 * hold the page lock, but e.g. zap_pte_range() calls with the page mapped and
2469 * the pte lock held, which also locks out truncation.
2470 */
2471int __set_page_dirty_nobuffers(struct page *page)
2472{
2473 lock_page_memcg(page);
2474 if (!TestSetPageDirty(page)) {
2475 struct address_space *mapping = page_mapping(page);
2476 unsigned long flags;
2477
2478 if (!mapping) {
2479 unlock_page_memcg(page);
2480 return 1;
2481 }
2482
2483 spin_lock_irqsave(&mapping->tree_lock, flags);
2484 BUG_ON(page_mapping(page) != mapping);
2485 WARN_ON_ONCE(!PagePrivate(page) && !PageUptodate(page));
2486 account_page_dirtied(page, mapping);
2487 radix_tree_tag_set(&mapping->page_tree, page_index(page),
2488 PAGECACHE_TAG_DIRTY);
2489 spin_unlock_irqrestore(&mapping->tree_lock, flags);
2490 unlock_page_memcg(page);
2491
2492 if (mapping->host) {
2493 /* !PageAnon && !swapper_space */
2494 __mark_inode_dirty(mapping->host, I_DIRTY_PAGES);
2495 }
2496 return 1;
2497 }
2498 unlock_page_memcg(page);
2499 return 0;
2500}
2501EXPORT_SYMBOL(__set_page_dirty_nobuffers);
2502
2503/*
2504 * Call this whenever redirtying a page, to de-account the dirty counters
2505 * (NR_DIRTIED, BDI_DIRTIED, tsk->nr_dirtied), so that they match the written
2506 * counters (NR_WRITTEN, BDI_WRITTEN) in long term. The mismatches will lead to
2507 * systematic errors in balanced_dirty_ratelimit and the dirty pages position
2508 * control.
2509 */
2510void account_page_redirty(struct page *page)
2511{
2512 struct address_space *mapping = page->mapping;
2513
2514 if (mapping && mapping_cap_account_dirty(mapping)) {
2515 struct inode *inode = mapping->host;
2516 struct bdi_writeback *wb;
2517 bool locked;
2518
2519 wb = unlocked_inode_to_wb_begin(inode, &locked);
2520 current->nr_dirtied--;
2521 dec_zone_page_state(page, NR_DIRTIED);
2522 dec_wb_stat(wb, WB_DIRTIED);
2523 unlocked_inode_to_wb_end(inode, locked);
2524 }
2525}
2526EXPORT_SYMBOL(account_page_redirty);
2527
2528/*
2529 * When a writepage implementation decides that it doesn't want to write this
2530 * page for some reason, it should redirty the locked page via
2531 * redirty_page_for_writepage() and it should then unlock the page and return 0
2532 */
2533int redirty_page_for_writepage(struct writeback_control *wbc, struct page *page)
2534{
2535 int ret;
2536
2537 wbc->pages_skipped++;
2538 ret = __set_page_dirty_nobuffers(page);
2539 account_page_redirty(page);
2540 return ret;
2541}
2542EXPORT_SYMBOL(redirty_page_for_writepage);
2543
2544/*
2545 * Dirty a page.
2546 *
2547 * For pages with a mapping this should be done under the page lock
2548 * for the benefit of asynchronous memory errors who prefer a consistent
2549 * dirty state. This rule can be broken in some special cases,
2550 * but should be better not to.
2551 *
2552 * If the mapping doesn't provide a set_page_dirty a_op, then
2553 * just fall through and assume that it wants buffer_heads.
2554 */
2555int set_page_dirty(struct page *page)
2556{
2557 struct address_space *mapping = page_mapping(page);
2558
2559 if (likely(mapping)) {
2560 int (*spd)(struct page *) = mapping->a_ops->set_page_dirty;
2561 /*
2562 * readahead/lru_deactivate_page could remain
2563 * PG_readahead/PG_reclaim due to race with end_page_writeback
2564 * About readahead, if the page is written, the flags would be
2565 * reset. So no problem.
2566 * About lru_deactivate_page, if the page is redirty, the flag
2567 * will be reset. So no problem. but if the page is used by readahead
2568 * it will confuse readahead and make it restart the size rampup
2569 * process. But it's a trivial problem.
2570 */
2571 if (PageReclaim(page))
2572 ClearPageReclaim(page);
2573#ifdef CONFIG_BLOCK
2574 if (!spd)
2575 spd = __set_page_dirty_buffers;
2576#endif
2577 return (*spd)(page);
2578 }
2579 if (!PageDirty(page)) {
2580 if (!TestSetPageDirty(page))
2581 return 1;
2582 }
2583 return 0;
2584}
2585EXPORT_SYMBOL(set_page_dirty);
2586
2587/*
2588 * set_page_dirty() is racy if the caller has no reference against
2589 * page->mapping->host, and if the page is unlocked. This is because another
2590 * CPU could truncate the page off the mapping and then free the mapping.
2591 *
2592 * Usually, the page _is_ locked, or the caller is a user-space process which
2593 * holds a reference on the inode by having an open file.
2594 *
2595 * In other cases, the page should be locked before running set_page_dirty().
2596 */
2597int set_page_dirty_lock(struct page *page)
2598{
2599 int ret;
2600
2601 lock_page(page);
2602 ret = set_page_dirty(page);
2603 unlock_page(page);
2604 return ret;
2605}
2606EXPORT_SYMBOL(set_page_dirty_lock);
2607
2608/*
2609 * This cancels just the dirty bit on the kernel page itself, it does NOT
2610 * actually remove dirty bits on any mmap's that may be around. It also
2611 * leaves the page tagged dirty, so any sync activity will still find it on
2612 * the dirty lists, and in particular, clear_page_dirty_for_io() will still
2613 * look at the dirty bits in the VM.
2614 *
2615 * Doing this should *normally* only ever be done when a page is truncated,
2616 * and is not actually mapped anywhere at all. However, fs/buffer.c does
2617 * this when it notices that somebody has cleaned out all the buffers on a
2618 * page without actually doing it through the VM. Can you say "ext3 is
2619 * horribly ugly"? Thought you could.
2620 */
2621void cancel_dirty_page(struct page *page)
2622{
2623 struct address_space *mapping = page_mapping(page);
2624
2625 if (mapping_cap_account_dirty(mapping)) {
2626 struct inode *inode = mapping->host;
2627 struct bdi_writeback *wb;
2628 bool locked;
2629
2630 lock_page_memcg(page);
2631 wb = unlocked_inode_to_wb_begin(inode, &locked);
2632
2633 if (TestClearPageDirty(page))
2634 account_page_cleaned(page, mapping, wb);
2635
2636 unlocked_inode_to_wb_end(inode, locked);
2637 unlock_page_memcg(page);
2638 } else {
2639 ClearPageDirty(page);
2640 }
2641}
2642EXPORT_SYMBOL(cancel_dirty_page);
2643
2644/*
2645 * Clear a page's dirty flag, while caring for dirty memory accounting.
2646 * Returns true if the page was previously dirty.
2647 *
2648 * This is for preparing to put the page under writeout. We leave the page
2649 * tagged as dirty in the radix tree so that a concurrent write-for-sync
2650 * can discover it via a PAGECACHE_TAG_DIRTY walk. The ->writepage
2651 * implementation will run either set_page_writeback() or set_page_dirty(),
2652 * at which stage we bring the page's dirty flag and radix-tree dirty tag
2653 * back into sync.
2654 *
2655 * This incoherency between the page's dirty flag and radix-tree tag is
2656 * unfortunate, but it only exists while the page is locked.
2657 */
2658int clear_page_dirty_for_io(struct page *page)
2659{
2660 struct address_space *mapping = page_mapping(page);
2661 int ret = 0;
2662
2663 BUG_ON(!PageLocked(page));
2664
2665 if (mapping && mapping_cap_account_dirty(mapping)) {
2666 struct inode *inode = mapping->host;
2667 struct bdi_writeback *wb;
2668 bool locked;
2669
2670 /*
2671 * Yes, Virginia, this is indeed insane.
2672 *
2673 * We use this sequence to make sure that
2674 * (a) we account for dirty stats properly
2675 * (b) we tell the low-level filesystem to
2676 * mark the whole page dirty if it was
2677 * dirty in a pagetable. Only to then
2678 * (c) clean the page again and return 1 to
2679 * cause the writeback.
2680 *
2681 * This way we avoid all nasty races with the
2682 * dirty bit in multiple places and clearing
2683 * them concurrently from different threads.
2684 *
2685 * Note! Normally the "set_page_dirty(page)"
2686 * has no effect on the actual dirty bit - since
2687 * that will already usually be set. But we
2688 * need the side effects, and it can help us
2689 * avoid races.
2690 *
2691 * We basically use the page "master dirty bit"
2692 * as a serialization point for all the different
2693 * threads doing their things.
2694 */
2695 if (page_mkclean(page))
2696 set_page_dirty(page);
2697 /*
2698 * We carefully synchronise fault handlers against
2699 * installing a dirty pte and marking the page dirty
2700 * at this point. We do this by having them hold the
2701 * page lock while dirtying the page, and pages are
2702 * always locked coming in here, so we get the desired
2703 * exclusion.
2704 */
2705 wb = unlocked_inode_to_wb_begin(inode, &locked);
2706 if (TestClearPageDirty(page)) {
2707 mem_cgroup_dec_page_stat(page, MEM_CGROUP_STAT_DIRTY);
2708 dec_zone_page_state(page, NR_FILE_DIRTY);
2709 dec_wb_stat(wb, WB_RECLAIMABLE);
2710 ret = 1;
2711 }
2712 unlocked_inode_to_wb_end(inode, locked);
2713 return ret;
2714 }
2715 return TestClearPageDirty(page);
2716}
2717EXPORT_SYMBOL(clear_page_dirty_for_io);
2718
2719int test_clear_page_writeback(struct page *page)
2720{
2721 struct address_space *mapping = page_mapping(page);
2722 int ret;
2723
2724 lock_page_memcg(page);
2725 if (mapping) {
2726 struct inode *inode = mapping->host;
2727 struct backing_dev_info *bdi = inode_to_bdi(inode);
2728 unsigned long flags;
2729
2730 spin_lock_irqsave(&mapping->tree_lock, flags);
2731 ret = TestClearPageWriteback(page);
2732 if (ret) {
2733 radix_tree_tag_clear(&mapping->page_tree,
2734 page_index(page),
2735 PAGECACHE_TAG_WRITEBACK);
2736 if (bdi_cap_account_writeback(bdi)) {
2737 struct bdi_writeback *wb = inode_to_wb(inode);
2738
2739 __dec_wb_stat(wb, WB_WRITEBACK);
2740 __wb_writeout_inc(wb);
2741 }
2742 }
2743 spin_unlock_irqrestore(&mapping->tree_lock, flags);
2744 } else {
2745 ret = TestClearPageWriteback(page);
2746 }
2747 if (ret) {
2748 mem_cgroup_dec_page_stat(page, MEM_CGROUP_STAT_WRITEBACK);
2749 dec_zone_page_state(page, NR_WRITEBACK);
2750 inc_zone_page_state(page, NR_WRITTEN);
2751 }
2752 unlock_page_memcg(page);
2753 return ret;
2754}
2755
2756int __test_set_page_writeback(struct page *page, bool keep_write)
2757{
2758 struct address_space *mapping = page_mapping(page);
2759 int ret;
2760
2761 lock_page_memcg(page);
2762 if (mapping) {
2763 struct inode *inode = mapping->host;
2764 struct backing_dev_info *bdi = inode_to_bdi(inode);
2765 unsigned long flags;
2766
2767 spin_lock_irqsave(&mapping->tree_lock, flags);
2768 ret = TestSetPageWriteback(page);
2769 if (!ret) {
2770 radix_tree_tag_set(&mapping->page_tree,
2771 page_index(page),
2772 PAGECACHE_TAG_WRITEBACK);
2773 if (bdi_cap_account_writeback(bdi))
2774 __inc_wb_stat(inode_to_wb(inode), WB_WRITEBACK);
2775 }
2776 if (!PageDirty(page))
2777 radix_tree_tag_clear(&mapping->page_tree,
2778 page_index(page),
2779 PAGECACHE_TAG_DIRTY);
2780 if (!keep_write)
2781 radix_tree_tag_clear(&mapping->page_tree,
2782 page_index(page),
2783 PAGECACHE_TAG_TOWRITE);
2784 spin_unlock_irqrestore(&mapping->tree_lock, flags);
2785 } else {
2786 ret = TestSetPageWriteback(page);
2787 }
2788 if (!ret) {
2789 mem_cgroup_inc_page_stat(page, MEM_CGROUP_STAT_WRITEBACK);
2790 inc_zone_page_state(page, NR_WRITEBACK);
2791 }
2792 unlock_page_memcg(page);
2793 return ret;
2794
2795}
2796EXPORT_SYMBOL(__test_set_page_writeback);
2797
2798/*
2799 * Return true if any of the pages in the mapping are marked with the
2800 * passed tag.
2801 */
2802int mapping_tagged(struct address_space *mapping, int tag)
2803{
2804 return radix_tree_tagged(&mapping->page_tree, tag);
2805}
2806EXPORT_SYMBOL(mapping_tagged);
2807
2808/**
2809 * wait_for_stable_page() - wait for writeback to finish, if necessary.
2810 * @page: The page to wait on.
2811 *
2812 * This function determines if the given page is related to a backing device
2813 * that requires page contents to be held stable during writeback. If so, then
2814 * it will wait for any pending writeback to complete.
2815 */
2816void wait_for_stable_page(struct page *page)
2817{
2818 if (bdi_cap_stable_pages_required(inode_to_bdi(page->mapping->host)))
2819 wait_on_page_writeback(page);
2820}
2821EXPORT_SYMBOL_GPL(wait_for_stable_page);
1// SPDX-License-Identifier: GPL-2.0-only
2/*
3 * mm/page-writeback.c
4 *
5 * Copyright (C) 2002, Linus Torvalds.
6 * Copyright (C) 2007 Red Hat, Inc., Peter Zijlstra
7 *
8 * Contains functions related to writing back dirty pages at the
9 * address_space level.
10 *
11 * 10Apr2002 Andrew Morton
12 * Initial version
13 */
14
15#include <linux/kernel.h>
16#include <linux/math64.h>
17#include <linux/export.h>
18#include <linux/spinlock.h>
19#include <linux/fs.h>
20#include <linux/mm.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>
42
43#include "internal.h"
44
45/*
46 * Sleep at most 200ms at a time in balance_dirty_pages().
47 */
48#define MAX_PAUSE max(HZ/5, 1)
49
50/*
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.
53 */
54#define DIRTY_POLL_THRESH (128 >> (PAGE_SHIFT - 10))
55
56/*
57 * Estimate write bandwidth at 200ms intervals.
58 */
59#define BANDWIDTH_INTERVAL max(HZ/5, 1)
60
61#define RATELIMIT_CALC_SHIFT 10
62
63/*
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.
66 */
67static long ratelimit_pages = 32;
68
69/* The following parameters are exported via /proc/sys/vm */
70
71/*
72 * Start background writeback (via writeback threads) at this percentage
73 */
74static int dirty_background_ratio = 10;
75
76/*
77 * dirty_background_bytes starts at 0 (disabled) so that it is a function of
78 * dirty_background_ratio * the amount of dirtyable memory
79 */
80static unsigned long dirty_background_bytes;
81
82/*
83 * free highmem will not be subtracted from the total free memory
84 * for calculating free ratios if vm_highmem_is_dirtyable is true
85 */
86static int vm_highmem_is_dirtyable;
87
88/*
89 * The generator of dirty data starts writeback at this percentage
90 */
91static int vm_dirty_ratio = 20;
92
93/*
94 * vm_dirty_bytes starts at 0 (disabled) so that it is a function of
95 * vm_dirty_ratio * the amount of dirtyable memory
96 */
97static unsigned long vm_dirty_bytes;
98
99/*
100 * The interval between `kupdate'-style writebacks
101 */
102unsigned int dirty_writeback_interval = 5 * 100; /* centiseconds */
103
104EXPORT_SYMBOL_GPL(dirty_writeback_interval);
105
106/*
107 * The longest time for which data is allowed to remain dirty
108 */
109unsigned int dirty_expire_interval = 30 * 100; /* centiseconds */
110
111/*
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.
114 */
115int laptop_mode;
116
117EXPORT_SYMBOL(laptop_mode);
118
119/* End of sysctl-exported parameters */
120
121struct wb_domain global_wb_domain;
122
123/* consolidated parameters for balance_dirty_pages() and its subroutines */
124struct 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 */
128#endif
129 struct bdi_writeback *wb;
130 struct fprop_local_percpu *wb_completions;
131
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 */
136
137 unsigned long wb_dirty; /* per-wb counterparts */
138 unsigned long wb_thresh;
139 unsigned long wb_bg_thresh;
140
141 unsigned long pos_ratio;
142};
143
144/*
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.
148 */
149#define VM_COMPLETIONS_PERIOD_LEN (3*HZ)
150
151#ifdef CONFIG_CGROUP_WRITEBACK
152
153#define GDTC_INIT(__wb) .wb = (__wb), \
154 .dom = &global_wb_domain, \
155 .wb_completions = &(__wb)->completions
156
157#define GDTC_INIT_NO_WB .dom = &global_wb_domain
158
159#define MDTC_INIT(__wb, __gdtc) .wb = (__wb), \
160 .dom = mem_cgroup_wb_domain(__wb), \
161 .wb_completions = &(__wb)->memcg_completions, \
162 .gdtc = __gdtc
163
164static bool mdtc_valid(struct dirty_throttle_control *dtc)
165{
166 return dtc->dom;
167}
168
169static struct wb_domain *dtc_dom(struct dirty_throttle_control *dtc)
170{
171 return dtc->dom;
172}
173
174static struct dirty_throttle_control *mdtc_gdtc(struct dirty_throttle_control *mdtc)
175{
176 return mdtc->gdtc;
177}
178
179static struct fprop_local_percpu *wb_memcg_completions(struct bdi_writeback *wb)
180{
181 return &wb->memcg_completions;
182}
183
184static void wb_min_max_ratio(struct bdi_writeback *wb,
185 unsigned long *minp, unsigned long *maxp)
186{
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;
191
192 /*
193 * @wb may already be clean by the time control reaches here and
194 * the total may not include its bw.
195 */
196 if (this_bw < tot_bw) {
197 if (min) {
198 min *= this_bw;
199 min = div64_ul(min, tot_bw);
200 }
201 if (max < 100 * BDI_RATIO_SCALE) {
202 max *= this_bw;
203 max = div64_ul(max, tot_bw);
204 }
205 }
206
207 *minp = min;
208 *maxp = max;
209}
210
211#else /* CONFIG_CGROUP_WRITEBACK */
212
213#define GDTC_INIT(__wb) .wb = (__wb), \
214 .wb_completions = &(__wb)->completions
215#define GDTC_INIT_NO_WB
216#define MDTC_INIT(__wb, __gdtc)
217
218static bool mdtc_valid(struct dirty_throttle_control *dtc)
219{
220 return false;
221}
222
223static struct wb_domain *dtc_dom(struct dirty_throttle_control *dtc)
224{
225 return &global_wb_domain;
226}
227
228static struct dirty_throttle_control *mdtc_gdtc(struct dirty_throttle_control *mdtc)
229{
230 return NULL;
231}
232
233static struct fprop_local_percpu *wb_memcg_completions(struct bdi_writeback *wb)
234{
235 return NULL;
236}
237
238static void wb_min_max_ratio(struct bdi_writeback *wb,
239 unsigned long *minp, unsigned long *maxp)
240{
241 *minp = wb->bdi->min_ratio;
242 *maxp = wb->bdi->max_ratio;
243}
244
245#endif /* CONFIG_CGROUP_WRITEBACK */
246
247/*
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.
253 *
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.
258 *
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.
263 */
264
265/**
266 * node_dirtyable_memory - number of dirtyable pages in a node
267 * @pgdat: the node
268 *
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.
271 */
272static unsigned long node_dirtyable_memory(struct pglist_data *pgdat)
273{
274 unsigned long nr_pages = 0;
275 int z;
276
277 for (z = 0; z < MAX_NR_ZONES; z++) {
278 struct zone *zone = pgdat->node_zones + z;
279
280 if (!populated_zone(zone))
281 continue;
282
283 nr_pages += zone_page_state(zone, NR_FREE_PAGES);
284 }
285
286 /*
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.
290 */
291 nr_pages -= min(nr_pages, pgdat->totalreserve_pages);
292
293 nr_pages += node_page_state(pgdat, NR_INACTIVE_FILE);
294 nr_pages += node_page_state(pgdat, NR_ACTIVE_FILE);
295
296 return nr_pages;
297}
298
299static unsigned long highmem_dirtyable_memory(unsigned long total)
300{
301#ifdef CONFIG_HIGHMEM
302 int node;
303 unsigned long x = 0;
304 int i;
305
306 for_each_node_state(node, N_HIGH_MEMORY) {
307 for (i = ZONE_NORMAL + 1; i < MAX_NR_ZONES; i++) {
308 struct zone *z;
309 unsigned long nr_pages;
310
311 if (!is_highmem_idx(i))
312 continue;
313
314 z = &NODE_DATA(node)->node_zones[i];
315 if (!populated_zone(z))
316 continue;
317
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);
323 x += nr_pages;
324 }
325 }
326
327 /*
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.
332 */
333 return min(x, total);
334#else
335 return 0;
336#endif
337}
338
339/**
340 * global_dirtyable_memory - number of globally dirtyable pages
341 *
342 * Return: the global number of pages potentially available for dirty
343 * page cache. This is the base value for the global dirty limits.
344 */
345static unsigned long global_dirtyable_memory(void)
346{
347 unsigned long x;
348
349 x = global_zone_page_state(NR_FREE_PAGES);
350 /*
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.
354 */
355 x -= min(x, totalreserve_pages);
356
357 x += global_node_page_state(NR_INACTIVE_FILE);
358 x += global_node_page_state(NR_ACTIVE_FILE);
359
360 if (!vm_highmem_is_dirtyable)
361 x -= highmem_dirtyable_memory(x);
362
363 return x + 1; /* Ensure that we never return 0 */
364}
365
366/**
367 * domain_dirty_limits - calculate thresh and bg_thresh for a wb_domain
368 * @dtc: dirty_throttle_control of interest
369 *
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.
374 */
375static void domain_dirty_limits(struct dirty_throttle_control *dtc)
376{
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;
387
388 /* gdtc is !NULL iff @dtc is for memcg domain */
389 if (gdtc) {
390 unsigned long global_avail = gdtc->avail;
391
392 /*
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
397 * number of pages.
398 */
399 if (bytes)
400 ratio = min(DIV_ROUND_UP(bytes, global_avail),
401 PAGE_SIZE);
402 if (bg_bytes)
403 bg_ratio = min(DIV_ROUND_UP(bg_bytes, global_avail),
404 PAGE_SIZE);
405 bytes = bg_bytes = 0;
406 }
407
408 if (bytes)
409 thresh = DIV_ROUND_UP(bytes, PAGE_SIZE);
410 else
411 thresh = (ratio * available_memory) / PAGE_SIZE;
412
413 if (bg_bytes)
414 bg_thresh = DIV_ROUND_UP(bg_bytes, PAGE_SIZE);
415 else
416 bg_thresh = (bg_ratio * available_memory) / PAGE_SIZE;
417
418 if (bg_thresh >= thresh)
419 bg_thresh = thresh / 2;
420 tsk = current;
421 if (rt_task(tsk)) {
422 bg_thresh += bg_thresh / 4 + global_wb_domain.dirty_limit / 32;
423 thresh += thresh / 4 + global_wb_domain.dirty_limit / 32;
424 }
425 dtc->thresh = thresh;
426 dtc->bg_thresh = bg_thresh;
427
428 /* we should eventually report the domain in the TP */
429 if (!gdtc)
430 trace_global_dirty_state(bg_thresh, thresh);
431}
432
433/**
434 * global_dirty_limits - background-writeback and dirty-throttling thresholds
435 * @pbackground: out parameter for bg_thresh
436 * @pdirty: out parameter for thresh
437 *
438 * Calculate bg_thresh and thresh for global_wb_domain. See
439 * domain_dirty_limits() for details.
440 */
441void global_dirty_limits(unsigned long *pbackground, unsigned long *pdirty)
442{
443 struct dirty_throttle_control gdtc = { GDTC_INIT_NO_WB };
444
445 gdtc.avail = global_dirtyable_memory();
446 domain_dirty_limits(&gdtc);
447
448 *pbackground = gdtc.bg_thresh;
449 *pdirty = gdtc.thresh;
450}
451
452/**
453 * node_dirty_limit - maximum number of dirty pages allowed in a node
454 * @pgdat: the node
455 *
456 * Return: the maximum number of dirty pages allowed in a node, based
457 * on the node's dirtyable memory.
458 */
459static unsigned long node_dirty_limit(struct pglist_data *pgdat)
460{
461 unsigned long node_memory = node_dirtyable_memory(pgdat);
462 struct task_struct *tsk = current;
463 unsigned long dirty;
464
465 if (vm_dirty_bytes)
466 dirty = DIV_ROUND_UP(vm_dirty_bytes, PAGE_SIZE) *
467 node_memory / global_dirtyable_memory();
468 else
469 dirty = vm_dirty_ratio * node_memory / 100;
470
471 if (rt_task(tsk))
472 dirty += dirty / 4;
473
474 return dirty;
475}
476
477/**
478 * node_dirty_ok - tells whether a node is within its dirty limits
479 * @pgdat: the node to check
480 *
481 * Return: %true when the dirty pages in @pgdat are within the node's
482 * dirty limit, %false if the limit is exceeded.
483 */
484bool node_dirty_ok(struct pglist_data *pgdat)
485{
486 unsigned long limit = node_dirty_limit(pgdat);
487 unsigned long nr_pages = 0;
488
489 nr_pages += node_page_state(pgdat, NR_FILE_DIRTY);
490 nr_pages += node_page_state(pgdat, NR_WRITEBACK);
491
492 return nr_pages <= limit;
493}
494
495#ifdef CONFIG_SYSCTL
496static int dirty_background_ratio_handler(struct ctl_table *table, int write,
497 void *buffer, size_t *lenp, loff_t *ppos)
498{
499 int ret;
500
501 ret = proc_dointvec_minmax(table, write, buffer, lenp, ppos);
502 if (ret == 0 && write)
503 dirty_background_bytes = 0;
504 return ret;
505}
506
507static int dirty_background_bytes_handler(struct ctl_table *table, int write,
508 void *buffer, size_t *lenp, loff_t *ppos)
509{
510 int ret;
511
512 ret = proc_doulongvec_minmax(table, write, buffer, lenp, ppos);
513 if (ret == 0 && write)
514 dirty_background_ratio = 0;
515 return ret;
516}
517
518static int dirty_ratio_handler(struct ctl_table *table, int write, void *buffer,
519 size_t *lenp, loff_t *ppos)
520{
521 int old_ratio = vm_dirty_ratio;
522 int ret;
523
524 ret = proc_dointvec_minmax(table, write, buffer, lenp, ppos);
525 if (ret == 0 && write && vm_dirty_ratio != old_ratio) {
526 writeback_set_ratelimit();
527 vm_dirty_bytes = 0;
528 }
529 return ret;
530}
531
532static int dirty_bytes_handler(struct ctl_table *table, int write,
533 void *buffer, size_t *lenp, loff_t *ppos)
534{
535 unsigned long old_bytes = vm_dirty_bytes;
536 int ret;
537
538 ret = proc_doulongvec_minmax(table, write, buffer, lenp, ppos);
539 if (ret == 0 && write && vm_dirty_bytes != old_bytes) {
540 writeback_set_ratelimit();
541 vm_dirty_ratio = 0;
542 }
543 return ret;
544}
545#endif
546
547static unsigned long wp_next_time(unsigned long cur_time)
548{
549 cur_time += VM_COMPLETIONS_PERIOD_LEN;
550 /* 0 has a special meaning... */
551 if (!cur_time)
552 return 1;
553 return cur_time;
554}
555
556static void wb_domain_writeout_add(struct wb_domain *dom,
557 struct fprop_local_percpu *completions,
558 unsigned int max_prop_frac, long nr)
559{
560 __fprop_add_percpu_max(&dom->completions, completions,
561 max_prop_frac, nr);
562 /* First event after period switching was turned off? */
563 if (unlikely(!dom->period_time)) {
564 /*
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
568 * roughly the same.
569 */
570 dom->period_time = wp_next_time(jiffies);
571 mod_timer(&dom->period_timer, dom->period_time);
572 }
573}
574
575/*
576 * Increment @wb's writeout completion count and the global writeout
577 * completion count. Called from __folio_end_writeback().
578 */
579static inline void __wb_writeout_add(struct bdi_writeback *wb, long nr)
580{
581 struct wb_domain *cgdom;
582
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);
586
587 cgdom = mem_cgroup_wb_domain(wb);
588 if (cgdom)
589 wb_domain_writeout_add(cgdom, wb_memcg_completions(wb),
590 wb->bdi->max_prop_frac, nr);
591}
592
593void wb_writeout_inc(struct bdi_writeback *wb)
594{
595 unsigned long flags;
596
597 local_irq_save(flags);
598 __wb_writeout_add(wb, 1);
599 local_irq_restore(flags);
600}
601EXPORT_SYMBOL_GPL(wb_writeout_inc);
602
603/*
604 * On idle system, we can be called long after we scheduled because we use
605 * deferred timers so count with missed periods.
606 */
607static void writeout_period(struct timer_list *t)
608{
609 struct wb_domain *dom = from_timer(dom, t, period_timer);
610 int miss_periods = (jiffies - dom->period_time) /
611 VM_COMPLETIONS_PERIOD_LEN;
612
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);
617 } else {
618 /*
619 * Aging has zeroed all fractions. Stop wasting CPU on period
620 * updates.
621 */
622 dom->period_time = 0;
623 }
624}
625
626int wb_domain_init(struct wb_domain *dom, gfp_t gfp)
627{
628 memset(dom, 0, sizeof(*dom));
629
630 spin_lock_init(&dom->lock);
631
632 timer_setup(&dom->period_timer, writeout_period, TIMER_DEFERRABLE);
633
634 dom->dirty_limit_tstamp = jiffies;
635
636 return fprop_global_init(&dom->completions, gfp);
637}
638
639#ifdef CONFIG_CGROUP_WRITEBACK
640void wb_domain_exit(struct wb_domain *dom)
641{
642 del_timer_sync(&dom->period_timer);
643 fprop_global_destroy(&dom->completions);
644}
645#endif
646
647/*
648 * bdi_min_ratio keeps the sum of the minimum dirty shares of all
649 * registered backing devices, which, for obvious reasons, can not
650 * exceed 100%.
651 */
652static unsigned int bdi_min_ratio;
653
654static int bdi_check_pages_limit(unsigned long pages)
655{
656 unsigned long max_dirty_pages = global_dirtyable_memory();
657
658 if (pages > max_dirty_pages)
659 return -EINVAL;
660
661 return 0;
662}
663
664static unsigned long bdi_ratio_from_pages(unsigned long pages)
665{
666 unsigned long background_thresh;
667 unsigned long dirty_thresh;
668 unsigned long ratio;
669
670 global_dirty_limits(&background_thresh, &dirty_thresh);
671 ratio = div64_u64(pages * 100ULL * BDI_RATIO_SCALE, dirty_thresh);
672
673 return ratio;
674}
675
676static u64 bdi_get_bytes(unsigned int ratio)
677{
678 unsigned long background_thresh;
679 unsigned long dirty_thresh;
680 u64 bytes;
681
682 global_dirty_limits(&background_thresh, &dirty_thresh);
683 bytes = (dirty_thresh * PAGE_SIZE * ratio) / BDI_RATIO_SCALE / 100;
684
685 return bytes;
686}
687
688static int __bdi_set_min_ratio(struct backing_dev_info *bdi, unsigned int min_ratio)
689{
690 unsigned int delta;
691 int ret = 0;
692
693 if (min_ratio > 100 * BDI_RATIO_SCALE)
694 return -EINVAL;
695
696 spin_lock_bh(&bdi_lock);
697 if (min_ratio > bdi->max_ratio) {
698 ret = -EINVAL;
699 } else {
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;
704 } else {
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;
709 } else {
710 ret = -EINVAL;
711 }
712 }
713 }
714 spin_unlock_bh(&bdi_lock);
715
716 return ret;
717}
718
719static int __bdi_set_max_ratio(struct backing_dev_info *bdi, unsigned int max_ratio)
720{
721 int ret = 0;
722
723 if (max_ratio > 100 * BDI_RATIO_SCALE)
724 return -EINVAL;
725
726 spin_lock_bh(&bdi_lock);
727 if (bdi->min_ratio > max_ratio) {
728 ret = -EINVAL;
729 } else {
730 bdi->max_ratio = max_ratio;
731 bdi->max_prop_frac = (FPROP_FRAC_BASE * max_ratio) /
732 (100 * BDI_RATIO_SCALE);
733 }
734 spin_unlock_bh(&bdi_lock);
735
736 return ret;
737}
738
739int bdi_set_min_ratio_no_scale(struct backing_dev_info *bdi, unsigned int min_ratio)
740{
741 return __bdi_set_min_ratio(bdi, min_ratio);
742}
743
744int bdi_set_max_ratio_no_scale(struct backing_dev_info *bdi, unsigned int max_ratio)
745{
746 return __bdi_set_max_ratio(bdi, max_ratio);
747}
748
749int bdi_set_min_ratio(struct backing_dev_info *bdi, unsigned int min_ratio)
750{
751 return __bdi_set_min_ratio(bdi, min_ratio * BDI_RATIO_SCALE);
752}
753
754int bdi_set_max_ratio(struct backing_dev_info *bdi, unsigned int max_ratio)
755{
756 return __bdi_set_max_ratio(bdi, max_ratio * BDI_RATIO_SCALE);
757}
758EXPORT_SYMBOL(bdi_set_max_ratio);
759
760u64 bdi_get_min_bytes(struct backing_dev_info *bdi)
761{
762 return bdi_get_bytes(bdi->min_ratio);
763}
764
765int bdi_set_min_bytes(struct backing_dev_info *bdi, u64 min_bytes)
766{
767 int ret;
768 unsigned long pages = min_bytes >> PAGE_SHIFT;
769 unsigned long min_ratio;
770
771 ret = bdi_check_pages_limit(pages);
772 if (ret)
773 return ret;
774
775 min_ratio = bdi_ratio_from_pages(pages);
776 return __bdi_set_min_ratio(bdi, min_ratio);
777}
778
779u64 bdi_get_max_bytes(struct backing_dev_info *bdi)
780{
781 return bdi_get_bytes(bdi->max_ratio);
782}
783
784int bdi_set_max_bytes(struct backing_dev_info *bdi, u64 max_bytes)
785{
786 int ret;
787 unsigned long pages = max_bytes >> PAGE_SHIFT;
788 unsigned long max_ratio;
789
790 ret = bdi_check_pages_limit(pages);
791 if (ret)
792 return ret;
793
794 max_ratio = bdi_ratio_from_pages(pages);
795 return __bdi_set_max_ratio(bdi, max_ratio);
796}
797
798int bdi_set_strict_limit(struct backing_dev_info *bdi, unsigned int strict_limit)
799{
800 if (strict_limit > 1)
801 return -EINVAL;
802
803 spin_lock_bh(&bdi_lock);
804 if (strict_limit)
805 bdi->capabilities |= BDI_CAP_STRICTLIMIT;
806 else
807 bdi->capabilities &= ~BDI_CAP_STRICTLIMIT;
808 spin_unlock_bh(&bdi_lock);
809
810 return 0;
811}
812
813static unsigned long dirty_freerun_ceiling(unsigned long thresh,
814 unsigned long bg_thresh)
815{
816 return (thresh + bg_thresh) / 2;
817}
818
819static unsigned long hard_dirty_limit(struct wb_domain *dom,
820 unsigned long thresh)
821{
822 return max(thresh, dom->dirty_limit);
823}
824
825/*
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.
828 */
829static void mdtc_calc_avail(struct dirty_throttle_control *mdtc,
830 unsigned long filepages, unsigned long headroom)
831{
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);
836
837 mdtc->avail = filepages + min(headroom, other_clean);
838}
839
840/**
841 * __wb_calc_thresh - @wb's share of dirty throttling threshold
842 * @dtc: dirty_throttle_context of interest
843 *
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.
850 *
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
854 *
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.
857 *
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.
860 */
861static unsigned long __wb_calc_thresh(struct dirty_throttle_control *dtc)
862{
863 struct wb_domain *dom = dtc_dom(dtc);
864 unsigned long thresh = dtc->thresh;
865 u64 wb_thresh;
866 unsigned long numerator, denominator;
867 unsigned long wb_min_ratio, wb_max_ratio;
868
869 /*
870 * Calculate this BDI's share of the thresh ratio.
871 */
872 fprop_fraction_percpu(&dom->completions, dtc->wb_completions,
873 &numerator, &denominator);
874
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);
878
879 wb_min_max_ratio(dtc->wb, &wb_min_ratio, &wb_max_ratio);
880
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);
884
885 return wb_thresh;
886}
887
888unsigned long wb_calc_thresh(struct bdi_writeback *wb, unsigned long thresh)
889{
890 struct dirty_throttle_control gdtc = { GDTC_INIT(wb),
891 .thresh = thresh };
892 return __wb_calc_thresh(&gdtc);
893}
894
895/*
896 * setpoint - dirty 3
897 * f(dirty) := 1.0 + (----------------)
898 * limit - setpoint
899 *
900 * it's a 3rd order polynomial that subjects to
901 *
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
908 */
909static long long pos_ratio_polynom(unsigned long setpoint,
910 unsigned long dirty,
911 unsigned long limit)
912{
913 long long pos_ratio;
914 long x;
915
916 x = div64_s64(((s64)setpoint - (s64)dirty) << RATELIMIT_CALC_SHIFT,
917 (limit - setpoint) | 1);
918 pos_ratio = x;
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;
922
923 return clamp(pos_ratio, 0LL, 2LL << RATELIMIT_CALC_SHIFT);
924}
925
926/*
927 * Dirty position control.
928 *
929 * (o) global/bdi setpoints
930 *
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.
935 *
936 * pos_ratio = 1 << RATELIMIT_CALC_SHIFT
937 *
938 * if (dirty < setpoint) scale up pos_ratio
939 * if (dirty > setpoint) scale down pos_ratio
940 *
941 * if (wb_dirty < wb_setpoint) scale up pos_ratio
942 * if (wb_dirty > wb_setpoint) scale down pos_ratio
943 *
944 * task_ratelimit = dirty_ratelimit * pos_ratio >> RATELIMIT_CALC_SHIFT
945 *
946 * (o) global control line
947 *
948 * ^ pos_ratio
949 * |
950 * | |<===== global dirty control scope ======>|
951 * 2.0 * * * * * * *
952 * | .*
953 * | . *
954 * | . *
955 * | . *
956 * | . *
957 * | . *
958 * 1.0 ................................*
959 * | . . *
960 * | . . *
961 * | . . *
962 * | . . *
963 * | . . *
964 * 0 +------------.------------------.----------------------*------------->
965 * freerun^ setpoint^ limit^ dirty pages
966 *
967 * (o) wb control line
968 *
969 * ^ pos_ratio
970 * |
971 * | *
972 * | *
973 * | *
974 * | *
975 * | * |<=========== span ============>|
976 * 1.0 .......................*
977 * | . *
978 * | . *
979 * | . *
980 * | . *
981 * | . *
982 * | . *
983 * | . *
984 * | . *
985 * | . *
986 * | . *
987 * | . *
988 * 1/4 ...............................................* * * * * * * * * * * *
989 * | . .
990 * | . .
991 * | . .
992 * 0 +----------------------.-------------------------------.------------->
993 * wb_setpoint^ x_intercept^
994 *
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
1000 */
1001static void wb_position_ratio(struct dirty_throttle_control *dtc)
1002{
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;
1011 unsigned long span;
1012 long long pos_ratio; /* for scaling up/down the rate limit */
1013 long x;
1014
1015 dtc->pos_ratio = 0;
1016
1017 if (unlikely(dtc->dirty >= limit))
1018 return;
1019
1020 /*
1021 * global setpoint
1022 *
1023 * See comment for pos_ratio_polynom().
1024 */
1025 setpoint = (freerun + limit) / 2;
1026 pos_ratio = pos_ratio_polynom(setpoint, dtc->dirty, limit);
1027
1028 /*
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".
1037 *
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.
1047 *
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).
1052 */
1053 if (unlikely(wb->bdi->capabilities & BDI_CAP_STRICTLIMIT)) {
1054 long long wb_pos_ratio;
1055
1056 if (dtc->wb_dirty < 8) {
1057 dtc->pos_ratio = min_t(long long, pos_ratio * 2,
1058 2 << RATELIMIT_CALC_SHIFT);
1059 return;
1060 }
1061
1062 if (dtc->wb_dirty >= wb_thresh)
1063 return;
1064
1065 wb_setpoint = dirty_freerun_ceiling(wb_thresh,
1066 dtc->wb_bg_thresh);
1067
1068 if (wb_setpoint == 0 || wb_setpoint == wb_thresh)
1069 return;
1070
1071 wb_pos_ratio = pos_ratio_polynom(wb_setpoint, dtc->wb_dirty,
1072 wb_thresh);
1073
1074 /*
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.
1082 *
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%.
1087 *
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.
1094 */
1095 dtc->pos_ratio = min(pos_ratio, wb_pos_ratio);
1096 return;
1097 }
1098
1099 /*
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.
1103 */
1104
1105 /*
1106 * wb setpoint
1107 *
1108 * f(wb_dirty) := 1.0 + k * (wb_dirty - wb_setpoint)
1109 *
1110 * x_intercept - wb_dirty
1111 * := --------------------------
1112 * x_intercept - wb_setpoint
1113 *
1114 * The main wb control line is a linear function that subjects to
1115 *
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
1119 *
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.
1125 *
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.
1129 */
1130 if (unlikely(wb_thresh > dtc->thresh))
1131 wb_thresh = dtc->thresh;
1132 /*
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.
1138 */
1139 wb_thresh = max(wb_thresh, (limit - dtc->dirty) / 8);
1140 /*
1141 * scale global setpoint to wb's:
1142 * wb_setpoint = setpoint * wb_thresh / thresh
1143 */
1144 x = div_u64((u64)wb_thresh << 16, dtc->thresh | 1);
1145 wb_setpoint = setpoint * (u64)x >> 16;
1146 /*
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.
1149 *
1150 * wb_thresh thresh - wb_thresh
1151 * span = --------- * (8 * write_bw) + ------------------ * wb_thresh
1152 * thresh thresh
1153 */
1154 span = (dtc->thresh - wb_thresh + 8 * write_bw) * (u64)x >> 16;
1155 x_intercept = wb_setpoint + span;
1156
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);
1160 } else
1161 pos_ratio /= 4;
1162
1163 /*
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
1166 * than setpoint.
1167 */
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,
1172 dtc->wb_dirty);
1173 else
1174 pos_ratio *= 8;
1175 }
1176
1177 dtc->pos_ratio = pos_ratio;
1178}
1179
1180static void wb_update_write_bandwidth(struct bdi_writeback *wb,
1181 unsigned long elapsed,
1182 unsigned long written)
1183{
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;
1187 u64 bw;
1188
1189 /*
1190 * bw = written * HZ / elapsed
1191 *
1192 * bw * elapsed + write_bandwidth * (period - elapsed)
1193 * write_bandwidth = ---------------------------------------------------
1194 * period
1195 *
1196 * @written may have decreased due to folio_redirty_for_writepage().
1197 * Avoid underflowing @bw calculation.
1198 */
1199 bw = written - min(written, wb->written_stamp);
1200 bw *= HZ;
1201 if (unlikely(elapsed > period)) {
1202 bw = div64_ul(bw, elapsed);
1203 avg = bw;
1204 goto out;
1205 }
1206 bw += (u64)wb->write_bandwidth * (period - elapsed);
1207 bw >>= ilog2(period);
1208
1209 /*
1210 * one more level of smoothing, for filtering out sudden spikes
1211 */
1212 if (avg > old && old >= (unsigned long)bw)
1213 avg -= (avg - old) >> 3;
1214
1215 if (avg < old && old <= (unsigned long)bw)
1216 avg += (old - avg) >> 3;
1217
1218out:
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);
1225 }
1226 wb->write_bandwidth = bw;
1227 WRITE_ONCE(wb->avg_write_bandwidth, avg);
1228}
1229
1230static void update_dirty_limit(struct dirty_throttle_control *dtc)
1231{
1232 struct wb_domain *dom = dtc_dom(dtc);
1233 unsigned long thresh = dtc->thresh;
1234 unsigned long limit = dom->dirty_limit;
1235
1236 /*
1237 * Follow up in one step.
1238 */
1239 if (limit < thresh) {
1240 limit = thresh;
1241 goto update;
1242 }
1243
1244 /*
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.
1248 */
1249 thresh = max(thresh, dtc->dirty);
1250 if (limit > thresh) {
1251 limit -= (limit - thresh) >> 5;
1252 goto update;
1253 }
1254 return;
1255update:
1256 dom->dirty_limit = limit;
1257}
1258
1259static void domain_update_dirty_limit(struct dirty_throttle_control *dtc,
1260 unsigned long now)
1261{
1262 struct wb_domain *dom = dtc_dom(dtc);
1263
1264 /*
1265 * check locklessly first to optimize away locking for the most time
1266 */
1267 if (time_before(now, dom->dirty_limit_tstamp + BANDWIDTH_INTERVAL))
1268 return;
1269
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;
1274 }
1275 spin_unlock(&dom->lock);
1276}
1277
1278/*
1279 * Maintain wb->dirty_ratelimit, the base dirty throttle rate.
1280 *
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.
1283 */
1284static void wb_update_dirty_ratelimit(struct dirty_throttle_control *dtc,
1285 unsigned long dirtied,
1286 unsigned long elapsed)
1287{
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;
1298 unsigned long step;
1299 unsigned long x;
1300 unsigned long shift;
1301
1302 /*
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.
1305 */
1306 dirty_rate = (dirtied - wb->dirtied_stamp) * HZ / elapsed;
1307
1308 /*
1309 * task_ratelimit reflects each dd's dirty rate for the past 200ms.
1310 */
1311 task_ratelimit = (u64)dirty_ratelimit *
1312 dtc->pos_ratio >> RATELIMIT_CALC_SHIFT;
1313 task_ratelimit++; /* it helps rampup dirty_ratelimit from tiny values */
1314
1315 /*
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).
1320 *
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)
1325 *
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
1331 * be throttled at
1332 * task_ratelimit = pos_ratio * rate = (write_bw / N) (5)
1333 * yielding
1334 * dirty_rate = N * task_ratelimit = write_bw (6)
1335 * put (6) into (1) we get
1336 * rate_(i+1) = rate_(i) (7)
1337 *
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.
1344 */
1345 balanced_dirty_ratelimit = div_u64((u64)task_ratelimit * write_bw,
1346 dirty_rate | 1);
1347 /*
1348 * balanced_dirty_ratelimit ~= (write_bw / N) <= write_bw
1349 */
1350 if (unlikely(balanced_dirty_ratelimit > write_bw))
1351 balanced_dirty_ratelimit = write_bw;
1352
1353 /*
1354 * We could safely do this and return immediately:
1355 *
1356 * wb->dirty_ratelimit = balanced_dirty_ratelimit;
1357 *
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.
1361 *
1362 * The below code essentially only uses the relative value of
1363 *
1364 * task_ratelimit - dirty_ratelimit
1365 * = (pos_ratio - 1) * dirty_ratelimit
1366 *
1367 * which reflects the direction and size of dirty position error.
1368 */
1369
1370 /*
1371 * dirty_ratelimit will follow balanced_dirty_ratelimit iff
1372 * task_ratelimit is on the same side of dirty_ratelimit, too.
1373 * For example, when
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.
1380 *
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).
1386 */
1387 step = 0;
1388
1389 /*
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".
1395 *
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.
1399 */
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;
1404 else
1405 setpoint = (dtc->wb_thresh + dtc->wb_bg_thresh) / 2;
1406 }
1407
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;
1413 } else {
1414 x = max3(wb->balanced_dirty_ratelimit,
1415 balanced_dirty_ratelimit, task_ratelimit);
1416 if (dirty_ratelimit > x)
1417 step = dirty_ratelimit - x;
1418 }
1419
1420 /*
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.
1424 */
1425 shift = dirty_ratelimit / (2 * step + 1);
1426 if (shift < BITS_PER_LONG)
1427 step = DIV_ROUND_UP(step >> shift, 8);
1428 else
1429 step = 0;
1430
1431 if (dirty_ratelimit < balanced_dirty_ratelimit)
1432 dirty_ratelimit += step;
1433 else
1434 dirty_ratelimit -= step;
1435
1436 WRITE_ONCE(wb->dirty_ratelimit, max(dirty_ratelimit, 1UL));
1437 wb->balanced_dirty_ratelimit = balanced_dirty_ratelimit;
1438
1439 trace_bdi_dirty_ratelimit(wb, dirty_rate, task_ratelimit);
1440}
1441
1442static void __wb_update_bandwidth(struct dirty_throttle_control *gdtc,
1443 struct dirty_throttle_control *mdtc,
1444 bool update_ratelimit)
1445{
1446 struct bdi_writeback *wb = gdtc->wb;
1447 unsigned long now = jiffies;
1448 unsigned long elapsed;
1449 unsigned long dirtied;
1450 unsigned long written;
1451
1452 spin_lock(&wb->list_lock);
1453
1454 /*
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
1458 * division errors.
1459 */
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]);
1463
1464 if (update_ratelimit) {
1465 domain_update_dirty_limit(gdtc, now);
1466 wb_update_dirty_ratelimit(gdtc, dirtied, elapsed);
1467
1468 /*
1469 * @mdtc is always NULL if !CGROUP_WRITEBACK but the
1470 * compiler has no way to figure that out. Help it.
1471 */
1472 if (IS_ENABLED(CONFIG_CGROUP_WRITEBACK) && mdtc) {
1473 domain_update_dirty_limit(mdtc, now);
1474 wb_update_dirty_ratelimit(mdtc, dirtied, elapsed);
1475 }
1476 }
1477 wb_update_write_bandwidth(wb, elapsed, written);
1478
1479 wb->dirtied_stamp = dirtied;
1480 wb->written_stamp = written;
1481 WRITE_ONCE(wb->bw_time_stamp, now);
1482 spin_unlock(&wb->list_lock);
1483}
1484
1485void wb_update_bandwidth(struct bdi_writeback *wb)
1486{
1487 struct dirty_throttle_control gdtc = { GDTC_INIT(wb) };
1488
1489 __wb_update_bandwidth(&gdtc, NULL, false);
1490}
1491
1492/* Interval after which we consider wb idle and don't estimate bandwidth */
1493#define WB_BANDWIDTH_IDLE_JIF (HZ)
1494
1495static void wb_bandwidth_estimate_start(struct bdi_writeback *wb)
1496{
1497 unsigned long now = jiffies;
1498 unsigned long elapsed = now - READ_ONCE(wb->bw_time_stamp);
1499
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);
1507 }
1508}
1509
1510/*
1511 * After a task dirtied this many pages, balance_dirty_pages_ratelimited()
1512 * will look to see if it needs to start dirty throttling.
1513 *
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).
1517 */
1518static unsigned long dirty_poll_interval(unsigned long dirty,
1519 unsigned long thresh)
1520{
1521 if (thresh > dirty)
1522 return 1UL << (ilog2(thresh - dirty) >> 1);
1523
1524 return 1;
1525}
1526
1527static unsigned long wb_max_pause(struct bdi_writeback *wb,
1528 unsigned long wb_dirty)
1529{
1530 unsigned long bw = READ_ONCE(wb->avg_write_bandwidth);
1531 unsigned long t;
1532
1533 /*
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
1536 * idle.
1537 *
1538 * 8 serves as the safety ratio.
1539 */
1540 t = wb_dirty / (1 + bw / roundup_pow_of_two(1 + HZ / 8));
1541 t++;
1542
1543 return min_t(unsigned long, t, MAX_PAUSE);
1544}
1545
1546static long wb_min_pause(struct bdi_writeback *wb,
1547 long max_pause,
1548 unsigned long task_ratelimit,
1549 unsigned long dirty_ratelimit,
1550 int *nr_dirtied_pause)
1551{
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 */
1557
1558 /* target for 10ms pause on 1-dd case */
1559 t = max(1, HZ / 100);
1560
1561 /*
1562 * Scale up pause time for concurrent dirtiers in order to reduce CPU
1563 * overheads.
1564 *
1565 * (N * 10ms) on 2^N concurrent tasks.
1566 */
1567 if (hi > lo)
1568 t += (hi - lo) * (10 * HZ) / 1024;
1569
1570 /*
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.
1579 *
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.
1587 */
1588 t = min(t, 1 + max_pause / 2);
1589 pages = dirty_ratelimit * t / roundup_pow_of_two(HZ);
1590
1591 /*
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.
1598 */
1599 if (pages < DIRTY_POLL_THRESH) {
1600 t = max_pause;
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;
1605 }
1606 }
1607
1608 pause = HZ * pages / (task_ratelimit + 1);
1609 if (pause > max_pause) {
1610 t = max_pause;
1611 pages = task_ratelimit * t / roundup_pow_of_two(HZ);
1612 }
1613
1614 *nr_dirtied_pause = pages;
1615 /*
1616 * The minimal pause time will normally be half the target pause time.
1617 */
1618 return pages >= DIRTY_POLL_THRESH ? 1 + t / 2 : t;
1619}
1620
1621static inline void wb_dirty_limits(struct dirty_throttle_control *dtc)
1622{
1623 struct bdi_writeback *wb = dtc->wb;
1624 unsigned long wb_reclaimable;
1625
1626 /*
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.
1638 */
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;
1642
1643 /*
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.
1647 *
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
1651 * deltas.
1652 */
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);
1656 } else {
1657 wb_reclaimable = wb_stat(wb, WB_RECLAIMABLE);
1658 dtc->wb_dirty = wb_reclaimable + wb_stat(wb, WB_WRITEBACK);
1659 }
1660}
1661
1662/*
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.
1668 */
1669static int balance_dirty_pages(struct bdi_writeback *wb,
1670 unsigned long pages_dirtied, unsigned int flags)
1671{
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) ?
1676 &mdtc_stor : NULL;
1677 struct dirty_throttle_control *sdtc;
1678 unsigned long nr_reclaimable; /* = file_dirty */
1679 long period;
1680 long pause;
1681 long max_pause;
1682 long min_pause;
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;
1690 int ret = 0;
1691
1692 for (;;) {
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;
1698
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);
1702
1703 domain_dirty_limits(gdtc);
1704
1705 if (unlikely(strictlimit)) {
1706 wb_dirty_limits(gdtc);
1707
1708 dirty = gdtc->wb_dirty;
1709 thresh = gdtc->wb_thresh;
1710 bg_thresh = gdtc->wb_bg_thresh;
1711 } else {
1712 dirty = gdtc->dirty;
1713 thresh = gdtc->thresh;
1714 bg_thresh = gdtc->bg_thresh;
1715 }
1716
1717 if (mdtc) {
1718 unsigned long filepages, headroom, writeback;
1719
1720 /*
1721 * If @wb belongs to !root memcg, repeat the same
1722 * basic calculations for the memcg domain.
1723 */
1724 mem_cgroup_wb_stats(wb, &filepages, &headroom,
1725 &mdtc->dirty, &writeback);
1726 mdtc->dirty += writeback;
1727 mdtc_calc_avail(mdtc, filepages, headroom);
1728
1729 domain_dirty_limits(mdtc);
1730
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;
1736 } else {
1737 m_dirty = mdtc->dirty;
1738 m_thresh = mdtc->thresh;
1739 m_bg_thresh = mdtc->bg_thresh;
1740 }
1741 }
1742
1743 /*
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.
1748 *
1749 * In normal mode, we start background writeout at the lower
1750 * background_thresh, to keep the amount of dirty memory low.
1751 */
1752 if (!laptop_mode && nr_reclaimable > gdtc->bg_thresh &&
1753 !writeback_in_progress(wb))
1754 wb_start_background_writeback(wb);
1755
1756 /*
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.
1760 *
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.
1764 *
1765 * If memcg domain is in effect, @dirty should be under
1766 * both global and memcg freerun ceilings.
1767 */
1768 if (dirty <= dirty_freerun_ceiling(thresh, bg_thresh) &&
1769 (!mdtc ||
1770 m_dirty <= dirty_freerun_ceiling(m_thresh, m_bg_thresh))) {
1771 unsigned long intv;
1772 unsigned long m_intv;
1773
1774free_running:
1775 intv = dirty_poll_interval(dirty, thresh);
1776 m_intv = ULONG_MAX;
1777
1778 current->dirty_paused_when = now;
1779 current->nr_dirtied = 0;
1780 if (mdtc)
1781 m_intv = dirty_poll_interval(m_dirty, m_thresh);
1782 current->nr_dirtied_pause = min(intv, m_intv);
1783 break;
1784 }
1785
1786 /* Start writeback even when in laptop mode */
1787 if (unlikely(!writeback_in_progress(wb)))
1788 wb_start_background_writeback(wb);
1789
1790 mem_cgroup_flush_foreign(wb);
1791
1792 /*
1793 * Calculate global domain's pos_ratio and select the
1794 * global dtc by default.
1795 */
1796 if (!strictlimit) {
1797 wb_dirty_limits(gdtc);
1798
1799 if ((current->flags & PF_LOCAL_THROTTLE) &&
1800 gdtc->wb_dirty <
1801 dirty_freerun_ceiling(gdtc->wb_thresh,
1802 gdtc->wb_bg_thresh))
1803 /*
1804 * LOCAL_THROTTLE tasks must not be throttled
1805 * when below the per-wb freerun ceiling.
1806 */
1807 goto free_running;
1808 }
1809
1810 dirty_exceeded = (gdtc->wb_dirty > gdtc->wb_thresh) &&
1811 ((gdtc->dirty > gdtc->thresh) || strictlimit);
1812
1813 wb_position_ratio(gdtc);
1814 sdtc = gdtc;
1815
1816 if (mdtc) {
1817 /*
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.
1822 */
1823 if (!strictlimit) {
1824 wb_dirty_limits(mdtc);
1825
1826 if ((current->flags & PF_LOCAL_THROTTLE) &&
1827 mdtc->wb_dirty <
1828 dirty_freerun_ceiling(mdtc->wb_thresh,
1829 mdtc->wb_bg_thresh))
1830 /*
1831 * LOCAL_THROTTLE tasks must not be
1832 * throttled when below the per-wb
1833 * freerun ceiling.
1834 */
1835 goto free_running;
1836 }
1837 dirty_exceeded |= (mdtc->wb_dirty > mdtc->wb_thresh) &&
1838 ((mdtc->dirty > mdtc->thresh) || strictlimit);
1839
1840 wb_position_ratio(mdtc);
1841 if (mdtc->pos_ratio < gdtc->pos_ratio)
1842 sdtc = mdtc;
1843 }
1844
1845 if (dirty_exceeded != wb->dirty_exceeded)
1846 wb->dirty_exceeded = dirty_exceeded;
1847
1848 if (time_is_before_jiffies(READ_ONCE(wb->bw_time_stamp) +
1849 BANDWIDTH_INTERVAL))
1850 __wb_update_bandwidth(gdtc, mdtc, true);
1851
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,
1859 &nr_dirtied_pause);
1860
1861 if (unlikely(task_ratelimit == 0)) {
1862 period = max_pause;
1863 pause = max_pause;
1864 goto pause;
1865 }
1866 period = HZ * pages_dirtied / task_ratelimit;
1867 pause = period;
1868 if (current->dirty_paused_when)
1869 pause -= now - current->dirty_paused_when;
1870 /*
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.
1876 */
1877 if (pause < min_pause) {
1878 trace_balance_dirty_pages(wb,
1879 sdtc->thresh,
1880 sdtc->bg_thresh,
1881 sdtc->dirty,
1882 sdtc->wb_thresh,
1883 sdtc->wb_dirty,
1884 dirty_ratelimit,
1885 task_ratelimit,
1886 pages_dirtied,
1887 period,
1888 min(pause, 0L),
1889 start_time);
1890 if (pause < -HZ) {
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;
1898 break;
1899 }
1900 if (unlikely(pause > max_pause)) {
1901 /* for occasional dropped task_ratelimit */
1902 now += min(pause - max_pause, max_pause);
1903 pause = max_pause;
1904 }
1905
1906pause:
1907 trace_balance_dirty_pages(wb,
1908 sdtc->thresh,
1909 sdtc->bg_thresh,
1910 sdtc->dirty,
1911 sdtc->wb_thresh,
1912 sdtc->wb_dirty,
1913 dirty_ratelimit,
1914 task_ratelimit,
1915 pages_dirtied,
1916 period,
1917 pause,
1918 start_time);
1919 if (flags & BDP_ASYNC) {
1920 ret = -EAGAIN;
1921 break;
1922 }
1923 __set_current_state(TASK_KILLABLE);
1924 bdi->last_bdp_sleep = jiffies;
1925 io_schedule_timeout(pause);
1926
1927 current->dirty_paused_when = now + pause;
1928 current->nr_dirtied = 0;
1929 current->nr_dirtied_pause = nr_dirtied_pause;
1930
1931 /*
1932 * This is typically equal to (dirty < thresh) and can also
1933 * keep "1000+ dd on a slow USB stick" under control.
1934 */
1935 if (task_ratelimit)
1936 break;
1937
1938 /*
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.
1942 *
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.
1947 */
1948 if (sdtc->wb_dirty <= wb_stat_error())
1949 break;
1950
1951 if (fatal_signal_pending(current))
1952 break;
1953 }
1954 return ret;
1955}
1956
1957static DEFINE_PER_CPU(int, bdp_ratelimits);
1958
1959/*
1960 * Normal tasks are throttled by
1961 * loop {
1962 * dirty tsk->nr_dirtied_pause pages;
1963 * take a snap in balance_dirty_pages();
1964 * }
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.
1972 */
1973DEFINE_PER_CPU(int, dirty_throttle_leaks) = 0;
1974
1975/**
1976 * balance_dirty_pages_ratelimited_flags - Balance dirty memory state.
1977 * @mapping: address_space which was dirtied.
1978 * @flags: BDP flags.
1979 *
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.
1983 *
1984 * See balance_dirty_pages_ratelimited() for details.
1985 *
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.
1991 */
1992int balance_dirty_pages_ratelimited_flags(struct address_space *mapping,
1993 unsigned int flags)
1994{
1995 struct inode *inode = mapping->host;
1996 struct backing_dev_info *bdi = inode_to_bdi(inode);
1997 struct bdi_writeback *wb = NULL;
1998 int ratelimit;
1999 int ret = 0;
2000 int *p;
2001
2002 if (!(bdi->capabilities & BDI_CAP_WRITEBACK))
2003 return ret;
2004
2005 if (inode_cgwb_enabled(inode))
2006 wb = wb_get_create_current(bdi, GFP_KERNEL);
2007 if (!wb)
2008 wb = &bdi->wb;
2009
2010 ratelimit = current->nr_dirtied_pause;
2011 if (wb->dirty_exceeded)
2012 ratelimit = min(ratelimit, 32 >> (PAGE_SHIFT - 10));
2013
2014 preempt_disable();
2015 /*
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.
2020 */
2021 p = this_cpu_ptr(&bdp_ratelimits);
2022 if (unlikely(current->nr_dirtied >= ratelimit))
2023 *p = 0;
2024 else if (unlikely(*p >= ratelimit_pages)) {
2025 *p = 0;
2026 ratelimit = 0;
2027 }
2028 /*
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.
2032 */
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;
2039 }
2040 preempt_enable();
2041
2042 if (unlikely(current->nr_dirtied >= ratelimit))
2043 ret = balance_dirty_pages(wb, current->nr_dirtied, flags);
2044
2045 wb_put(wb);
2046 return ret;
2047}
2048EXPORT_SYMBOL_GPL(balance_dirty_pages_ratelimited_flags);
2049
2050/**
2051 * balance_dirty_pages_ratelimited - balance dirty memory state.
2052 * @mapping: address_space which was dirtied.
2053 *
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.
2057 *
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.
2061 */
2062void balance_dirty_pages_ratelimited(struct address_space *mapping)
2063{
2064 balance_dirty_pages_ratelimited_flags(mapping, 0);
2065}
2066EXPORT_SYMBOL(balance_dirty_pages_ratelimited);
2067
2068/**
2069 * wb_over_bg_thresh - does @wb need to be written back?
2070 * @wb: bdi_writeback of interest
2071 *
2072 * Determines whether background writeback should keep writing @wb or it's
2073 * clean enough.
2074 *
2075 * Return: %true if writeback should continue.
2076 */
2077bool wb_over_bg_thresh(struct bdi_writeback *wb)
2078{
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) ?
2083 &mdtc_stor : NULL;
2084 unsigned long reclaimable;
2085 unsigned long thresh;
2086
2087 /*
2088 * Similar to balance_dirty_pages() but ignores pages being written
2089 * as we're trying to decide whether to put more under writeback.
2090 */
2091 gdtc->avail = global_dirtyable_memory();
2092 gdtc->dirty = global_node_page_state(NR_FILE_DIRTY);
2093 domain_dirty_limits(gdtc);
2094
2095 if (gdtc->dirty > gdtc->bg_thresh)
2096 return true;
2097
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);
2101 else
2102 reclaimable = wb_stat(wb, WB_RECLAIMABLE);
2103
2104 if (reclaimable > thresh)
2105 return true;
2106
2107 if (mdtc) {
2108 unsigned long filepages, headroom, writeback;
2109
2110 mem_cgroup_wb_stats(wb, &filepages, &headroom, &mdtc->dirty,
2111 &writeback);
2112 mdtc_calc_avail(mdtc, filepages, headroom);
2113 domain_dirty_limits(mdtc); /* ditto, ignore writeback */
2114
2115 if (mdtc->dirty > mdtc->bg_thresh)
2116 return true;
2117
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);
2121 else
2122 reclaimable = wb_stat(wb, WB_RECLAIMABLE);
2123
2124 if (reclaimable > thresh)
2125 return true;
2126 }
2127
2128 return false;
2129}
2130
2131#ifdef CONFIG_SYSCTL
2132/*
2133 * sysctl handler for /proc/sys/vm/dirty_writeback_centisecs
2134 */
2135static int dirty_writeback_centisecs_handler(struct ctl_table *table, int write,
2136 void *buffer, size_t *length, loff_t *ppos)
2137{
2138 unsigned int old_interval = dirty_writeback_interval;
2139 int ret;
2140
2141 ret = proc_dointvec(table, write, buffer, length, ppos);
2142
2143 /*
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.
2149 */
2150 if (!ret && write && dirty_writeback_interval &&
2151 dirty_writeback_interval != old_interval)
2152 wakeup_flusher_threads(WB_REASON_PERIODIC);
2153
2154 return ret;
2155}
2156#endif
2157
2158void laptop_mode_timer_fn(struct timer_list *t)
2159{
2160 struct backing_dev_info *backing_dev_info =
2161 from_timer(backing_dev_info, t, laptop_mode_wb_timer);
2162
2163 wakeup_flusher_threads_bdi(backing_dev_info, WB_REASON_LAPTOP_TIMER);
2164}
2165
2166/*
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.
2170 */
2171void laptop_io_completion(struct backing_dev_info *info)
2172{
2173 mod_timer(&info->laptop_mode_wb_timer, jiffies + laptop_mode);
2174}
2175
2176/*
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.
2180 */
2181void laptop_sync_completion(void)
2182{
2183 struct backing_dev_info *bdi;
2184
2185 rcu_read_lock();
2186
2187 list_for_each_entry_rcu(bdi, &bdi_list, bdi_list)
2188 del_timer(&bdi->laptop_mode_wb_timer);
2189
2190 rcu_read_unlock();
2191}
2192
2193/*
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.
2196 *
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
2199 * thresholds.
2200 */
2201
2202void writeback_set_ratelimit(void)
2203{
2204 struct wb_domain *dom = &global_wb_domain;
2205 unsigned long background_thresh;
2206 unsigned long dirty_thresh;
2207
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;
2213}
2214
2215static int page_writeback_cpu_online(unsigned int cpu)
2216{
2217 writeback_set_ratelimit();
2218 return 0;
2219}
2220
2221#ifdef CONFIG_SYSCTL
2222
2223/* this is needed for the proc_doulongvec_minmax of vm_dirty_bytes */
2224static const unsigned long dirty_bytes_min = 2 * PAGE_SIZE;
2225
2226static struct ctl_table vm_page_writeback_sysctls[] = {
2227 {
2228 .procname = "dirty_background_ratio",
2229 .data = &dirty_background_ratio,
2230 .maxlen = sizeof(dirty_background_ratio),
2231 .mode = 0644,
2232 .proc_handler = dirty_background_ratio_handler,
2233 .extra1 = SYSCTL_ZERO,
2234 .extra2 = SYSCTL_ONE_HUNDRED,
2235 },
2236 {
2237 .procname = "dirty_background_bytes",
2238 .data = &dirty_background_bytes,
2239 .maxlen = sizeof(dirty_background_bytes),
2240 .mode = 0644,
2241 .proc_handler = dirty_background_bytes_handler,
2242 .extra1 = SYSCTL_LONG_ONE,
2243 },
2244 {
2245 .procname = "dirty_ratio",
2246 .data = &vm_dirty_ratio,
2247 .maxlen = sizeof(vm_dirty_ratio),
2248 .mode = 0644,
2249 .proc_handler = dirty_ratio_handler,
2250 .extra1 = SYSCTL_ZERO,
2251 .extra2 = SYSCTL_ONE_HUNDRED,
2252 },
2253 {
2254 .procname = "dirty_bytes",
2255 .data = &vm_dirty_bytes,
2256 .maxlen = sizeof(vm_dirty_bytes),
2257 .mode = 0644,
2258 .proc_handler = dirty_bytes_handler,
2259 .extra1 = (void *)&dirty_bytes_min,
2260 },
2261 {
2262 .procname = "dirty_writeback_centisecs",
2263 .data = &dirty_writeback_interval,
2264 .maxlen = sizeof(dirty_writeback_interval),
2265 .mode = 0644,
2266 .proc_handler = dirty_writeback_centisecs_handler,
2267 },
2268 {
2269 .procname = "dirty_expire_centisecs",
2270 .data = &dirty_expire_interval,
2271 .maxlen = sizeof(dirty_expire_interval),
2272 .mode = 0644,
2273 .proc_handler = proc_dointvec_minmax,
2274 .extra1 = SYSCTL_ZERO,
2275 },
2276#ifdef CONFIG_HIGHMEM
2277 {
2278 .procname = "highmem_is_dirtyable",
2279 .data = &vm_highmem_is_dirtyable,
2280 .maxlen = sizeof(vm_highmem_is_dirtyable),
2281 .mode = 0644,
2282 .proc_handler = proc_dointvec_minmax,
2283 .extra1 = SYSCTL_ZERO,
2284 .extra2 = SYSCTL_ONE,
2285 },
2286#endif
2287 {
2288 .procname = "laptop_mode",
2289 .data = &laptop_mode,
2290 .maxlen = sizeof(laptop_mode),
2291 .mode = 0644,
2292 .proc_handler = proc_dointvec_jiffies,
2293 },
2294 {}
2295};
2296#endif
2297
2298/*
2299 * Called early on to tune the page writeback dirty limits.
2300 *
2301 * We used to scale dirty pages according to how total memory
2302 * related to pages that could be allocated for buffers.
2303 *
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.
2310 *
2311 * But we might still want to scale the dirty_ratio by how
2312 * much memory the box has..
2313 */
2314void __init page_writeback_init(void)
2315{
2316 BUG_ON(wb_domain_init(&global_wb_domain, GFP_KERNEL));
2317
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);
2324#endif
2325}
2326
2327/**
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)
2332 *
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).
2340 */
2341void tag_pages_for_writeback(struct address_space *mapping,
2342 pgoff_t start, pgoff_t end)
2343{
2344 XA_STATE(xas, &mapping->i_pages, start);
2345 unsigned int tagged = 0;
2346 void *page;
2347
2348 xas_lock_irq(&xas);
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)
2352 continue;
2353
2354 xas_pause(&xas);
2355 xas_unlock_irq(&xas);
2356 cond_resched();
2357 xas_lock_irq(&xas);
2358 }
2359 xas_unlock_irq(&xas);
2360}
2361EXPORT_SYMBOL(tag_pages_for_writeback);
2362
2363/**
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
2369 *
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.
2377 *
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).
2384 *
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.
2391 *
2392 * Return: %0 on success, negative error code otherwise
2393 */
2394int write_cache_pages(struct address_space *mapping,
2395 struct writeback_control *wbc, writepage_t writepage,
2396 void *data)
2397{
2398 int ret = 0;
2399 int done = 0;
2400 int error;
2401 struct folio_batch fbatch;
2402 int nr_folios;
2403 pgoff_t index;
2404 pgoff_t end; /* Inclusive */
2405 pgoff_t done_index;
2406 int range_whole = 0;
2407 xa_mark_t tag;
2408
2409 folio_batch_init(&fbatch);
2410 if (wbc->range_cyclic) {
2411 index = mapping->writeback_index; /* prev offset */
2412 end = -1;
2413 } else {
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)
2417 range_whole = 1;
2418 }
2419 if (wbc->sync_mode == WB_SYNC_ALL || wbc->tagged_writepages) {
2420 tag_pages_for_writeback(mapping, index, end);
2421 tag = PAGECACHE_TAG_TOWRITE;
2422 } else {
2423 tag = PAGECACHE_TAG_DIRTY;
2424 }
2425 done_index = index;
2426 while (!done && (index <= end)) {
2427 int i;
2428
2429 nr_folios = filemap_get_folios_tag(mapping, &index, end,
2430 tag, &fbatch);
2431
2432 if (nr_folios == 0)
2433 break;
2434
2435 for (i = 0; i < nr_folios; i++) {
2436 struct folio *folio = fbatch.folios[i];
2437 unsigned long nr;
2438
2439 done_index = folio->index;
2440
2441 folio_lock(folio);
2442
2443 /*
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.
2450 */
2451 if (unlikely(folio->mapping != mapping)) {
2452continue_unlock:
2453 folio_unlock(folio);
2454 continue;
2455 }
2456
2457 if (!folio_test_dirty(folio)) {
2458 /* someone wrote it for us */
2459 goto continue_unlock;
2460 }
2461
2462 if (folio_test_writeback(folio)) {
2463 if (wbc->sync_mode != WB_SYNC_NONE)
2464 folio_wait_writeback(folio);
2465 else
2466 goto continue_unlock;
2467 }
2468
2469 BUG_ON(folio_test_writeback(folio));
2470 if (!folio_clear_dirty_for_io(folio))
2471 goto continue_unlock;
2472
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)) {
2477 /*
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
2487 * the first error.
2488 */
2489 if (error == AOP_WRITEPAGE_ACTIVATE) {
2490 folio_unlock(folio);
2491 error = 0;
2492 } else if (wbc->sync_mode != WB_SYNC_ALL) {
2493 ret = error;
2494 done_index = folio->index + nr;
2495 done = 1;
2496 break;
2497 }
2498 if (!ret)
2499 ret = error;
2500 }
2501
2502 /*
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.
2507 */
2508 wbc->nr_to_write -= nr;
2509 if (wbc->nr_to_write <= 0 &&
2510 wbc->sync_mode == WB_SYNC_NONE) {
2511 done = 1;
2512 break;
2513 }
2514 }
2515 folio_batch_release(&fbatch);
2516 cond_resched();
2517 }
2518
2519 /*
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.
2523 */
2524 if (wbc->range_cyclic && !done)
2525 done_index = 0;
2526 if (wbc->range_cyclic || (range_whole && wbc->nr_to_write > 0))
2527 mapping->writeback_index = done_index;
2528
2529 return ret;
2530}
2531EXPORT_SYMBOL(write_cache_pages);
2532
2533static int writepage_cb(struct folio *folio, struct writeback_control *wbc,
2534 void *data)
2535{
2536 struct address_space *mapping = data;
2537 int ret = mapping->a_ops->writepage(&folio->page, wbc);
2538 mapping_set_error(mapping, ret);
2539 return ret;
2540}
2541
2542int do_writepages(struct address_space *mapping, struct writeback_control *wbc)
2543{
2544 int ret;
2545 struct bdi_writeback *wb;
2546
2547 if (wbc->nr_to_write <= 0)
2548 return 0;
2549 wb = inode_to_wb_wbc(mapping->host, wbc);
2550 wb_bandwidth_estimate_start(wb);
2551 while (1) {
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;
2556
2557 blk_start_plug(&plug);
2558 ret = write_cache_pages(mapping, wbc, writepage_cb,
2559 mapping);
2560 blk_finish_plug(&plug);
2561 } else {
2562 /* deal with chardevs and other special files */
2563 ret = 0;
2564 }
2565 if (ret != -ENOMEM || wbc->sync_mode != WB_SYNC_ALL)
2566 break;
2567
2568 /*
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
2572 * guess as any.
2573 */
2574 reclaim_throttle(NODE_DATA(numa_node_id()),
2575 VMSCAN_THROTTLE_WRITEBACK);
2576 }
2577 /*
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.
2581 */
2582 if (time_is_before_jiffies(READ_ONCE(wb->bw_time_stamp) +
2583 BANDWIDTH_INTERVAL))
2584 wb_update_bandwidth(wb);
2585 return ret;
2586}
2587
2588/*
2589 * For address_spaces which do not use buffers nor write back.
2590 */
2591bool noop_dirty_folio(struct address_space *mapping, struct folio *folio)
2592{
2593 if (!folio_test_dirty(folio))
2594 return !folio_test_set_dirty(folio);
2595 return false;
2596}
2597EXPORT_SYMBOL(noop_dirty_folio);
2598
2599/*
2600 * Helper function for set_page_dirty family.
2601 *
2602 * Caller must hold folio_memcg_lock().
2603 *
2604 * NOTE: This relies on being atomic wrt interrupts.
2605 */
2606static void folio_account_dirtied(struct folio *folio,
2607 struct address_space *mapping)
2608{
2609 struct inode *inode = mapping->host;
2610
2611 trace_writeback_dirty_folio(folio, mapping);
2612
2613 if (mapping_can_writeback(mapping)) {
2614 struct bdi_writeback *wb;
2615 long nr = folio_nr_pages(folio);
2616
2617 inode_attach_wb(inode, folio);
2618 wb = inode_to_wb(inode);
2619
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);
2628
2629 mem_cgroup_track_foreign_dirty(folio, wb);
2630 }
2631}
2632
2633/*
2634 * Helper function for deaccounting dirty page without writeback.
2635 *
2636 * Caller must hold folio_memcg_lock().
2637 */
2638void folio_account_cleaned(struct folio *folio, struct bdi_writeback *wb)
2639{
2640 long nr = folio_nr_pages(folio);
2641
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);
2646}
2647
2648/*
2649 * Mark the folio dirty, and set it dirty in the page cache, and mark
2650 * the inode dirty.
2651 *
2652 * If warn is true, then emit a warning if the folio is not uptodate and has
2653 * not been truncated.
2654 *
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.
2660 */
2661void __folio_mark_dirty(struct folio *folio, struct address_space *mapping,
2662 int warn)
2663{
2664 unsigned long flags;
2665
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);
2672 }
2673 xa_unlock_irqrestore(&mapping->i_pages, flags);
2674}
2675
2676/**
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.
2680 *
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.
2685 *
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.
2690 *
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.
2694 */
2695bool filemap_dirty_folio(struct address_space *mapping, struct folio *folio)
2696{
2697 folio_memcg_lock(folio);
2698 if (folio_test_set_dirty(folio)) {
2699 folio_memcg_unlock(folio);
2700 return false;
2701 }
2702
2703 __folio_mark_dirty(folio, mapping, !folio_test_private(folio));
2704 folio_memcg_unlock(folio);
2705
2706 if (mapping->host) {
2707 /* !PageAnon && !swapper_space */
2708 __mark_inode_dirty(mapping->host, I_DIRTY_PAGES);
2709 }
2710 return true;
2711}
2712EXPORT_SYMBOL(filemap_dirty_folio);
2713
2714/**
2715 * folio_redirty_for_writepage - Decline to write a dirty folio.
2716 * @wbc: The writeback control.
2717 * @folio: The folio.
2718 *
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
2721 * return 0.
2722 *
2723 * Return: True if we redirtied the folio. False if someone else dirtied
2724 * it first.
2725 */
2726bool folio_redirty_for_writepage(struct writeback_control *wbc,
2727 struct folio *folio)
2728{
2729 struct address_space *mapping = folio->mapping;
2730 long nr = folio_nr_pages(folio);
2731 bool ret;
2732
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 = {};
2739
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);
2745 }
2746 return ret;
2747}
2748EXPORT_SYMBOL(folio_redirty_for_writepage);
2749
2750/**
2751 * folio_mark_dirty - Mark a folio as being modified.
2752 * @folio: The folio.
2753 *
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.
2760 *
2761 * Return: True if the folio was newly dirtied, false if it was already dirty.
2762 */
2763bool folio_mark_dirty(struct folio *folio)
2764{
2765 struct address_space *mapping = folio_mapping(folio);
2766
2767 if (likely(mapping)) {
2768 /*
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.
2778 */
2779 if (folio_test_reclaim(folio))
2780 folio_clear_reclaim(folio);
2781 return mapping->a_ops->dirty_folio(mapping, folio);
2782 }
2783
2784 return noop_dirty_folio(mapping, folio);
2785}
2786EXPORT_SYMBOL(folio_mark_dirty);
2787
2788/*
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.
2792 *
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.
2795 *
2796 * In other cases, the page should be locked before running set_page_dirty().
2797 */
2798int set_page_dirty_lock(struct page *page)
2799{
2800 int ret;
2801
2802 lock_page(page);
2803 ret = set_page_dirty(page);
2804 unlock_page(page);
2805 return ret;
2806}
2807EXPORT_SYMBOL(set_page_dirty_lock);
2808
2809/*
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.
2815 *
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.
2821 */
2822void __folio_cancel_dirty(struct folio *folio)
2823{
2824 struct address_space *mapping = folio_mapping(folio);
2825
2826 if (mapping_can_writeback(mapping)) {
2827 struct inode *inode = mapping->host;
2828 struct bdi_writeback *wb;
2829 struct wb_lock_cookie cookie = {};
2830
2831 folio_memcg_lock(folio);
2832 wb = unlocked_inode_to_wb_begin(inode, &cookie);
2833
2834 if (folio_test_clear_dirty(folio))
2835 folio_account_cleaned(folio, wb);
2836
2837 unlocked_inode_to_wb_end(inode, &cookie);
2838 folio_memcg_unlock(folio);
2839 } else {
2840 folio_clear_dirty(folio);
2841 }
2842}
2843EXPORT_SYMBOL(__folio_cancel_dirty);
2844
2845/*
2846 * Clear a folio's dirty flag, while caring for dirty memory accounting.
2847 * Returns true if the folio was previously dirty.
2848 *
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.
2855 *
2856 * This incoherency between the folio's dirty flag and xarray tag is
2857 * unfortunate, but it only exists while the folio is locked.
2858 */
2859bool folio_clear_dirty_for_io(struct folio *folio)
2860{
2861 struct address_space *mapping = folio_mapping(folio);
2862 bool ret = false;
2863
2864 VM_BUG_ON_FOLIO(!folio_test_locked(folio), folio);
2865
2866 if (mapping && mapping_can_writeback(mapping)) {
2867 struct inode *inode = mapping->host;
2868 struct bdi_writeback *wb;
2869 struct wb_lock_cookie cookie = {};
2870
2871 /*
2872 * Yes, Virginia, this is indeed insane.
2873 *
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.
2881 *
2882 * This way we avoid all nasty races with the
2883 * dirty bit in multiple places and clearing
2884 * them concurrently from different threads.
2885 *
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
2890 * avoid races.
2891 *
2892 * We basically use the folio "master dirty bit"
2893 * as a serialization point for all the different
2894 * threads doing their things.
2895 */
2896 if (folio_mkclean(folio))
2897 folio_mark_dirty(folio);
2898 /*
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
2904 * exclusion.
2905 */
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);
2912 ret = true;
2913 }
2914 unlocked_inode_to_wb_end(inode, &cookie);
2915 return ret;
2916 }
2917 return folio_test_clear_dirty(folio);
2918}
2919EXPORT_SYMBOL(folio_clear_dirty_for_io);
2920
2921static void wb_inode_writeback_start(struct bdi_writeback *wb)
2922{
2923 atomic_inc(&wb->writeback_inodes);
2924}
2925
2926static void wb_inode_writeback_end(struct bdi_writeback *wb)
2927{
2928 unsigned long flags;
2929 atomic_dec(&wb->writeback_inodes);
2930 /*
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.
2936 */
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);
2941}
2942
2943bool __folio_end_writeback(struct folio *folio)
2944{
2945 long nr = folio_nr_pages(folio);
2946 struct address_space *mapping = folio_mapping(folio);
2947 bool ret;
2948
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;
2954
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);
2961
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);
2966 }
2967
2968 if (mapping->host && !mapping_tagged(mapping,
2969 PAGECACHE_TAG_WRITEBACK))
2970 sb_clear_inode_writeback(mapping->host);
2971
2972 xa_unlock_irqrestore(&mapping->i_pages, flags);
2973 } else {
2974 ret = folio_xor_flags_has_waiters(folio, 1 << PG_writeback);
2975 }
2976
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);
2981
2982 return ret;
2983}
2984
2985void __folio_start_writeback(struct folio *folio, bool keep_write)
2986{
2987 long nr = folio_nr_pages(folio);
2988 struct address_space *mapping = folio_mapping(folio);
2989 int access_ret;
2990
2991 VM_BUG_ON_FOLIO(folio_test_writeback(folio), folio);
2992
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;
2999 bool on_wblist;
3000
3001 xas_lock_irqsave(&xas, flags);
3002 xas_load(&xas);
3003 folio_test_set_writeback(folio);
3004
3005 on_wblist = mapping_tagged(mapping, PAGECACHE_TAG_WRITEBACK);
3006
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);
3010
3011 wb_stat_mod(wb, WB_WRITEBACK, nr);
3012 if (!on_wblist)
3013 wb_inode_writeback_start(wb);
3014 }
3015
3016 /*
3017 * We can come through here when swapping anonymous
3018 * folios, so we don't necessarily have an inode to
3019 * track for sync.
3020 */
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);
3025 if (!keep_write)
3026 xas_clear_mark(&xas, PAGECACHE_TAG_TOWRITE);
3027 xas_unlock_irqrestore(&xas, flags);
3028 } else {
3029 folio_test_set_writeback(folio);
3030 }
3031
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);
3035
3036 access_ret = arch_make_folio_accessible(folio);
3037 /*
3038 * If writeback has been triggered on a page that cannot be made
3039 * accessible, it is too late to recover here.
3040 */
3041 VM_BUG_ON_FOLIO(access_ret != 0, folio);
3042}
3043EXPORT_SYMBOL(__folio_start_writeback);
3044
3045/**
3046 * folio_wait_writeback - Wait for a folio to finish writeback.
3047 * @folio: The folio to wait for.
3048 *
3049 * If the folio is currently being written back to storage, wait for the
3050 * I/O to complete.
3051 *
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
3055 * has finished.
3056 */
3057void folio_wait_writeback(struct folio *folio)
3058{
3059 while (folio_test_writeback(folio)) {
3060 trace_folio_wait_writeback(folio, folio_mapping(folio));
3061 folio_wait_bit(folio, PG_writeback);
3062 }
3063}
3064EXPORT_SYMBOL_GPL(folio_wait_writeback);
3065
3066/**
3067 * folio_wait_writeback_killable - Wait for a folio to finish writeback.
3068 * @folio: The folio to wait for.
3069 *
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.
3072 *
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
3076 * has finished.
3077 * Return: 0 on success, -EINTR if we get a fatal signal while waiting.
3078 */
3079int folio_wait_writeback_killable(struct folio *folio)
3080{
3081 while (folio_test_writeback(folio)) {
3082 trace_folio_wait_writeback(folio, folio_mapping(folio));
3083 if (folio_wait_bit_killable(folio, PG_writeback))
3084 return -EINTR;
3085 }
3086
3087 return 0;
3088}
3089EXPORT_SYMBOL_GPL(folio_wait_writeback_killable);
3090
3091/**
3092 * folio_wait_stable() - wait for writeback to finish, if necessary.
3093 * @folio: The folio to wait on.
3094 *
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.
3098 *
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
3102 * has finished.
3103 */
3104void folio_wait_stable(struct folio *folio)
3105{
3106 if (mapping_stable_writes(folio_mapping(folio)))
3107 folio_wait_writeback(folio);
3108}
3109EXPORT_SYMBOL_GPL(folio_wait_stable);