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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 or update dirty limit 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 bool freerun;
143 bool dirty_exceeded;
144};
145
146/*
147 * Length of period for aging writeout fractions of bdis. This is an
148 * arbitrarily chosen number. The longer the period, the slower fractions will
149 * reflect changes in current writeout rate.
150 */
151#define VM_COMPLETIONS_PERIOD_LEN (3*HZ)
152
153#ifdef CONFIG_CGROUP_WRITEBACK
154
155#define GDTC_INIT(__wb) .wb = (__wb), \
156 .dom = &global_wb_domain, \
157 .wb_completions = &(__wb)->completions
158
159#define GDTC_INIT_NO_WB .dom = &global_wb_domain
160
161#define MDTC_INIT(__wb, __gdtc) .wb = (__wb), \
162 .dom = mem_cgroup_wb_domain(__wb), \
163 .wb_completions = &(__wb)->memcg_completions, \
164 .gdtc = __gdtc
165
166static bool mdtc_valid(struct dirty_throttle_control *dtc)
167{
168 return dtc->dom;
169}
170
171static struct wb_domain *dtc_dom(struct dirty_throttle_control *dtc)
172{
173 return dtc->dom;
174}
175
176static struct dirty_throttle_control *mdtc_gdtc(struct dirty_throttle_control *mdtc)
177{
178 return mdtc->gdtc;
179}
180
181static struct fprop_local_percpu *wb_memcg_completions(struct bdi_writeback *wb)
182{
183 return &wb->memcg_completions;
184}
185
186static void wb_min_max_ratio(struct bdi_writeback *wb,
187 unsigned long *minp, unsigned long *maxp)
188{
189 unsigned long this_bw = READ_ONCE(wb->avg_write_bandwidth);
190 unsigned long tot_bw = atomic_long_read(&wb->bdi->tot_write_bandwidth);
191 unsigned long long min = wb->bdi->min_ratio;
192 unsigned long long max = wb->bdi->max_ratio;
193
194 /*
195 * @wb may already be clean by the time control reaches here and
196 * the total may not include its bw.
197 */
198 if (this_bw < tot_bw) {
199 if (min) {
200 min *= this_bw;
201 min = div64_ul(min, tot_bw);
202 }
203 if (max < 100 * BDI_RATIO_SCALE) {
204 max *= this_bw;
205 max = div64_ul(max, tot_bw);
206 }
207 }
208
209 *minp = min;
210 *maxp = max;
211}
212
213#else /* CONFIG_CGROUP_WRITEBACK */
214
215#define GDTC_INIT(__wb) .wb = (__wb), \
216 .wb_completions = &(__wb)->completions
217#define GDTC_INIT_NO_WB
218#define MDTC_INIT(__wb, __gdtc)
219
220static bool mdtc_valid(struct dirty_throttle_control *dtc)
221{
222 return false;
223}
224
225static struct wb_domain *dtc_dom(struct dirty_throttle_control *dtc)
226{
227 return &global_wb_domain;
228}
229
230static struct dirty_throttle_control *mdtc_gdtc(struct dirty_throttle_control *mdtc)
231{
232 return NULL;
233}
234
235static struct fprop_local_percpu *wb_memcg_completions(struct bdi_writeback *wb)
236{
237 return NULL;
238}
239
240static void wb_min_max_ratio(struct bdi_writeback *wb,
241 unsigned long *minp, unsigned long *maxp)
242{
243 *minp = wb->bdi->min_ratio;
244 *maxp = wb->bdi->max_ratio;
245}
246
247#endif /* CONFIG_CGROUP_WRITEBACK */
248
249/*
250 * In a memory zone, there is a certain amount of pages we consider
251 * available for the page cache, which is essentially the number of
252 * free and reclaimable pages, minus some zone reserves to protect
253 * lowmem and the ability to uphold the zone's watermarks without
254 * requiring writeback.
255 *
256 * This number of dirtyable pages is the base value of which the
257 * user-configurable dirty ratio is the effective number of pages that
258 * are allowed to be actually dirtied. Per individual zone, or
259 * globally by using the sum of dirtyable pages over all zones.
260 *
261 * Because the user is allowed to specify the dirty limit globally as
262 * absolute number of bytes, calculating the per-zone dirty limit can
263 * require translating the configured limit into a percentage of
264 * global dirtyable memory first.
265 */
266
267/**
268 * node_dirtyable_memory - number of dirtyable pages in a node
269 * @pgdat: the node
270 *
271 * Return: the node's number of pages potentially available for dirty
272 * page cache. This is the base value for the per-node dirty limits.
273 */
274static unsigned long node_dirtyable_memory(struct pglist_data *pgdat)
275{
276 unsigned long nr_pages = 0;
277 int z;
278
279 for (z = 0; z < MAX_NR_ZONES; z++) {
280 struct zone *zone = pgdat->node_zones + z;
281
282 if (!populated_zone(zone))
283 continue;
284
285 nr_pages += zone_page_state(zone, NR_FREE_PAGES);
286 }
287
288 /*
289 * Pages reserved for the kernel should not be considered
290 * dirtyable, to prevent a situation where reclaim has to
291 * clean pages in order to balance the zones.
292 */
293 nr_pages -= min(nr_pages, pgdat->totalreserve_pages);
294
295 nr_pages += node_page_state(pgdat, NR_INACTIVE_FILE);
296 nr_pages += node_page_state(pgdat, NR_ACTIVE_FILE);
297
298 return nr_pages;
299}
300
301static unsigned long highmem_dirtyable_memory(unsigned long total)
302{
303#ifdef CONFIG_HIGHMEM
304 int node;
305 unsigned long x = 0;
306 int i;
307
308 for_each_node_state(node, N_HIGH_MEMORY) {
309 for (i = ZONE_NORMAL + 1; i < MAX_NR_ZONES; i++) {
310 struct zone *z;
311 unsigned long nr_pages;
312
313 if (!is_highmem_idx(i))
314 continue;
315
316 z = &NODE_DATA(node)->node_zones[i];
317 if (!populated_zone(z))
318 continue;
319
320 nr_pages = zone_page_state(z, NR_FREE_PAGES);
321 /* watch for underflows */
322 nr_pages -= min(nr_pages, high_wmark_pages(z));
323 nr_pages += zone_page_state(z, NR_ZONE_INACTIVE_FILE);
324 nr_pages += zone_page_state(z, NR_ZONE_ACTIVE_FILE);
325 x += nr_pages;
326 }
327 }
328
329 /*
330 * Make sure that the number of highmem pages is never larger
331 * than the number of the total dirtyable memory. This can only
332 * occur in very strange VM situations but we want to make sure
333 * that this does not occur.
334 */
335 return min(x, total);
336#else
337 return 0;
338#endif
339}
340
341/**
342 * global_dirtyable_memory - number of globally dirtyable pages
343 *
344 * Return: the global number of pages potentially available for dirty
345 * page cache. This is the base value for the global dirty limits.
346 */
347static unsigned long global_dirtyable_memory(void)
348{
349 unsigned long x;
350
351 x = global_zone_page_state(NR_FREE_PAGES);
352 /*
353 * Pages reserved for the kernel should not be considered
354 * dirtyable, to prevent a situation where reclaim has to
355 * clean pages in order to balance the zones.
356 */
357 x -= min(x, totalreserve_pages);
358
359 x += global_node_page_state(NR_INACTIVE_FILE);
360 x += global_node_page_state(NR_ACTIVE_FILE);
361
362 if (!vm_highmem_is_dirtyable)
363 x -= highmem_dirtyable_memory(x);
364
365 return x + 1; /* Ensure that we never return 0 */
366}
367
368/**
369 * domain_dirty_limits - calculate thresh and bg_thresh for a wb_domain
370 * @dtc: dirty_throttle_control of interest
371 *
372 * Calculate @dtc->thresh and ->bg_thresh considering
373 * vm_dirty_{bytes|ratio} and dirty_background_{bytes|ratio}. The caller
374 * must ensure that @dtc->avail is set before calling this function. The
375 * dirty limits will be lifted by 1/4 for real-time tasks.
376 */
377static void domain_dirty_limits(struct dirty_throttle_control *dtc)
378{
379 const unsigned long available_memory = dtc->avail;
380 struct dirty_throttle_control *gdtc = mdtc_gdtc(dtc);
381 unsigned long bytes = vm_dirty_bytes;
382 unsigned long bg_bytes = dirty_background_bytes;
383 /* convert ratios to per-PAGE_SIZE for higher precision */
384 unsigned long ratio = (vm_dirty_ratio * PAGE_SIZE) / 100;
385 unsigned long bg_ratio = (dirty_background_ratio * PAGE_SIZE) / 100;
386 unsigned long thresh;
387 unsigned long bg_thresh;
388 struct task_struct *tsk;
389
390 /* gdtc is !NULL iff @dtc is for memcg domain */
391 if (gdtc) {
392 unsigned long global_avail = gdtc->avail;
393
394 /*
395 * The byte settings can't be applied directly to memcg
396 * domains. Convert them to ratios by scaling against
397 * globally available memory. As the ratios are in
398 * per-PAGE_SIZE, they can be obtained by dividing bytes by
399 * number of pages.
400 */
401 if (bytes)
402 ratio = min(DIV_ROUND_UP(bytes, global_avail),
403 PAGE_SIZE);
404 if (bg_bytes)
405 bg_ratio = min(DIV_ROUND_UP(bg_bytes, global_avail),
406 PAGE_SIZE);
407 bytes = bg_bytes = 0;
408 }
409
410 if (bytes)
411 thresh = DIV_ROUND_UP(bytes, PAGE_SIZE);
412 else
413 thresh = (ratio * available_memory) / PAGE_SIZE;
414
415 if (bg_bytes)
416 bg_thresh = DIV_ROUND_UP(bg_bytes, PAGE_SIZE);
417 else
418 bg_thresh = (bg_ratio * available_memory) / PAGE_SIZE;
419
420 tsk = current;
421 if (rt_or_dl_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 /*
426 * Dirty throttling logic assumes the limits in page units fit into
427 * 32-bits. This gives 16TB dirty limits max which is hopefully enough.
428 */
429 if (thresh > UINT_MAX)
430 thresh = UINT_MAX;
431 /* This makes sure bg_thresh is within 32-bits as well */
432 if (bg_thresh >= thresh)
433 bg_thresh = thresh / 2;
434 dtc->thresh = thresh;
435 dtc->bg_thresh = bg_thresh;
436
437 /* we should eventually report the domain in the TP */
438 if (!gdtc)
439 trace_global_dirty_state(bg_thresh, thresh);
440}
441
442/**
443 * global_dirty_limits - background-writeback and dirty-throttling thresholds
444 * @pbackground: out parameter for bg_thresh
445 * @pdirty: out parameter for thresh
446 *
447 * Calculate bg_thresh and thresh for global_wb_domain. See
448 * domain_dirty_limits() for details.
449 */
450void global_dirty_limits(unsigned long *pbackground, unsigned long *pdirty)
451{
452 struct dirty_throttle_control gdtc = { GDTC_INIT_NO_WB };
453
454 gdtc.avail = global_dirtyable_memory();
455 domain_dirty_limits(&gdtc);
456
457 *pbackground = gdtc.bg_thresh;
458 *pdirty = gdtc.thresh;
459}
460
461/**
462 * node_dirty_limit - maximum number of dirty pages allowed in a node
463 * @pgdat: the node
464 *
465 * Return: the maximum number of dirty pages allowed in a node, based
466 * on the node's dirtyable memory.
467 */
468static unsigned long node_dirty_limit(struct pglist_data *pgdat)
469{
470 unsigned long node_memory = node_dirtyable_memory(pgdat);
471 struct task_struct *tsk = current;
472 unsigned long dirty;
473
474 if (vm_dirty_bytes)
475 dirty = DIV_ROUND_UP(vm_dirty_bytes, PAGE_SIZE) *
476 node_memory / global_dirtyable_memory();
477 else
478 dirty = vm_dirty_ratio * node_memory / 100;
479
480 if (rt_or_dl_task(tsk))
481 dirty += dirty / 4;
482
483 /*
484 * Dirty throttling logic assumes the limits in page units fit into
485 * 32-bits. This gives 16TB dirty limits max which is hopefully enough.
486 */
487 return min_t(unsigned long, dirty, UINT_MAX);
488}
489
490/**
491 * node_dirty_ok - tells whether a node is within its dirty limits
492 * @pgdat: the node to check
493 *
494 * Return: %true when the dirty pages in @pgdat are within the node's
495 * dirty limit, %false if the limit is exceeded.
496 */
497bool node_dirty_ok(struct pglist_data *pgdat)
498{
499 unsigned long limit = node_dirty_limit(pgdat);
500 unsigned long nr_pages = 0;
501
502 nr_pages += node_page_state(pgdat, NR_FILE_DIRTY);
503 nr_pages += node_page_state(pgdat, NR_WRITEBACK);
504
505 return nr_pages <= limit;
506}
507
508#ifdef CONFIG_SYSCTL
509static int dirty_background_ratio_handler(const struct ctl_table *table, int write,
510 void *buffer, size_t *lenp, loff_t *ppos)
511{
512 int ret;
513
514 ret = proc_dointvec_minmax(table, write, buffer, lenp, ppos);
515 if (ret == 0 && write)
516 dirty_background_bytes = 0;
517 return ret;
518}
519
520static int dirty_background_bytes_handler(const struct ctl_table *table, int write,
521 void *buffer, size_t *lenp, loff_t *ppos)
522{
523 int ret;
524 unsigned long old_bytes = dirty_background_bytes;
525
526 ret = proc_doulongvec_minmax(table, write, buffer, lenp, ppos);
527 if (ret == 0 && write) {
528 if (DIV_ROUND_UP(dirty_background_bytes, PAGE_SIZE) >
529 UINT_MAX) {
530 dirty_background_bytes = old_bytes;
531 return -ERANGE;
532 }
533 dirty_background_ratio = 0;
534 }
535 return ret;
536}
537
538static int dirty_ratio_handler(const struct ctl_table *table, int write, void *buffer,
539 size_t *lenp, loff_t *ppos)
540{
541 int old_ratio = vm_dirty_ratio;
542 int ret;
543
544 ret = proc_dointvec_minmax(table, write, buffer, lenp, ppos);
545 if (ret == 0 && write && vm_dirty_ratio != old_ratio) {
546 writeback_set_ratelimit();
547 vm_dirty_bytes = 0;
548 }
549 return ret;
550}
551
552static int dirty_bytes_handler(const struct ctl_table *table, int write,
553 void *buffer, size_t *lenp, loff_t *ppos)
554{
555 unsigned long old_bytes = vm_dirty_bytes;
556 int ret;
557
558 ret = proc_doulongvec_minmax(table, write, buffer, lenp, ppos);
559 if (ret == 0 && write && vm_dirty_bytes != old_bytes) {
560 if (DIV_ROUND_UP(vm_dirty_bytes, PAGE_SIZE) > UINT_MAX) {
561 vm_dirty_bytes = old_bytes;
562 return -ERANGE;
563 }
564 writeback_set_ratelimit();
565 vm_dirty_ratio = 0;
566 }
567 return ret;
568}
569#endif
570
571static unsigned long wp_next_time(unsigned long cur_time)
572{
573 cur_time += VM_COMPLETIONS_PERIOD_LEN;
574 /* 0 has a special meaning... */
575 if (!cur_time)
576 return 1;
577 return cur_time;
578}
579
580static void wb_domain_writeout_add(struct wb_domain *dom,
581 struct fprop_local_percpu *completions,
582 unsigned int max_prop_frac, long nr)
583{
584 __fprop_add_percpu_max(&dom->completions, completions,
585 max_prop_frac, nr);
586 /* First event after period switching was turned off? */
587 if (unlikely(!dom->period_time)) {
588 /*
589 * We can race with other wb_domain_writeout_add calls here but
590 * it does not cause any harm since the resulting time when
591 * timer will fire and what is in writeout_period_time will be
592 * roughly the same.
593 */
594 dom->period_time = wp_next_time(jiffies);
595 mod_timer(&dom->period_timer, dom->period_time);
596 }
597}
598
599/*
600 * Increment @wb's writeout completion count and the global writeout
601 * completion count. Called from __folio_end_writeback().
602 */
603static inline void __wb_writeout_add(struct bdi_writeback *wb, long nr)
604{
605 struct wb_domain *cgdom;
606
607 wb_stat_mod(wb, WB_WRITTEN, nr);
608 wb_domain_writeout_add(&global_wb_domain, &wb->completions,
609 wb->bdi->max_prop_frac, nr);
610
611 cgdom = mem_cgroup_wb_domain(wb);
612 if (cgdom)
613 wb_domain_writeout_add(cgdom, wb_memcg_completions(wb),
614 wb->bdi->max_prop_frac, nr);
615}
616
617void wb_writeout_inc(struct bdi_writeback *wb)
618{
619 unsigned long flags;
620
621 local_irq_save(flags);
622 __wb_writeout_add(wb, 1);
623 local_irq_restore(flags);
624}
625EXPORT_SYMBOL_GPL(wb_writeout_inc);
626
627/*
628 * On idle system, we can be called long after we scheduled because we use
629 * deferred timers so count with missed periods.
630 */
631static void writeout_period(struct timer_list *t)
632{
633 struct wb_domain *dom = from_timer(dom, t, period_timer);
634 int miss_periods = (jiffies - dom->period_time) /
635 VM_COMPLETIONS_PERIOD_LEN;
636
637 if (fprop_new_period(&dom->completions, miss_periods + 1)) {
638 dom->period_time = wp_next_time(dom->period_time +
639 miss_periods * VM_COMPLETIONS_PERIOD_LEN);
640 mod_timer(&dom->period_timer, dom->period_time);
641 } else {
642 /*
643 * Aging has zeroed all fractions. Stop wasting CPU on period
644 * updates.
645 */
646 dom->period_time = 0;
647 }
648}
649
650int wb_domain_init(struct wb_domain *dom, gfp_t gfp)
651{
652 memset(dom, 0, sizeof(*dom));
653
654 spin_lock_init(&dom->lock);
655
656 timer_setup(&dom->period_timer, writeout_period, TIMER_DEFERRABLE);
657
658 dom->dirty_limit_tstamp = jiffies;
659
660 return fprop_global_init(&dom->completions, gfp);
661}
662
663#ifdef CONFIG_CGROUP_WRITEBACK
664void wb_domain_exit(struct wb_domain *dom)
665{
666 del_timer_sync(&dom->period_timer);
667 fprop_global_destroy(&dom->completions);
668}
669#endif
670
671/*
672 * bdi_min_ratio keeps the sum of the minimum dirty shares of all
673 * registered backing devices, which, for obvious reasons, can not
674 * exceed 100%.
675 */
676static unsigned int bdi_min_ratio;
677
678static int bdi_check_pages_limit(unsigned long pages)
679{
680 unsigned long max_dirty_pages = global_dirtyable_memory();
681
682 if (pages > max_dirty_pages)
683 return -EINVAL;
684
685 return 0;
686}
687
688static unsigned long bdi_ratio_from_pages(unsigned long pages)
689{
690 unsigned long background_thresh;
691 unsigned long dirty_thresh;
692 unsigned long ratio;
693
694 global_dirty_limits(&background_thresh, &dirty_thresh);
695 if (!dirty_thresh)
696 return -EINVAL;
697 ratio = div64_u64(pages * 100ULL * BDI_RATIO_SCALE, dirty_thresh);
698
699 return ratio;
700}
701
702static u64 bdi_get_bytes(unsigned int ratio)
703{
704 unsigned long background_thresh;
705 unsigned long dirty_thresh;
706 u64 bytes;
707
708 global_dirty_limits(&background_thresh, &dirty_thresh);
709 bytes = (dirty_thresh * PAGE_SIZE * ratio) / BDI_RATIO_SCALE / 100;
710
711 return bytes;
712}
713
714static int __bdi_set_min_ratio(struct backing_dev_info *bdi, unsigned int min_ratio)
715{
716 unsigned int delta;
717 int ret = 0;
718
719 if (min_ratio > 100 * BDI_RATIO_SCALE)
720 return -EINVAL;
721
722 spin_lock_bh(&bdi_lock);
723 if (min_ratio > bdi->max_ratio) {
724 ret = -EINVAL;
725 } else {
726 if (min_ratio < bdi->min_ratio) {
727 delta = bdi->min_ratio - min_ratio;
728 bdi_min_ratio -= delta;
729 bdi->min_ratio = min_ratio;
730 } else {
731 delta = min_ratio - bdi->min_ratio;
732 if (bdi_min_ratio + delta < 100 * BDI_RATIO_SCALE) {
733 bdi_min_ratio += delta;
734 bdi->min_ratio = min_ratio;
735 } else {
736 ret = -EINVAL;
737 }
738 }
739 }
740 spin_unlock_bh(&bdi_lock);
741
742 return ret;
743}
744
745static int __bdi_set_max_ratio(struct backing_dev_info *bdi, unsigned int max_ratio)
746{
747 int ret = 0;
748
749 if (max_ratio > 100 * BDI_RATIO_SCALE)
750 return -EINVAL;
751
752 spin_lock_bh(&bdi_lock);
753 if (bdi->min_ratio > max_ratio) {
754 ret = -EINVAL;
755 } else {
756 bdi->max_ratio = max_ratio;
757 bdi->max_prop_frac = (FPROP_FRAC_BASE * max_ratio) /
758 (100 * BDI_RATIO_SCALE);
759 }
760 spin_unlock_bh(&bdi_lock);
761
762 return ret;
763}
764
765int bdi_set_min_ratio_no_scale(struct backing_dev_info *bdi, unsigned int min_ratio)
766{
767 return __bdi_set_min_ratio(bdi, min_ratio);
768}
769
770int bdi_set_max_ratio_no_scale(struct backing_dev_info *bdi, unsigned int max_ratio)
771{
772 return __bdi_set_max_ratio(bdi, max_ratio);
773}
774
775int bdi_set_min_ratio(struct backing_dev_info *bdi, unsigned int min_ratio)
776{
777 return __bdi_set_min_ratio(bdi, min_ratio * BDI_RATIO_SCALE);
778}
779
780int bdi_set_max_ratio(struct backing_dev_info *bdi, unsigned int max_ratio)
781{
782 return __bdi_set_max_ratio(bdi, max_ratio * BDI_RATIO_SCALE);
783}
784EXPORT_SYMBOL(bdi_set_max_ratio);
785
786u64 bdi_get_min_bytes(struct backing_dev_info *bdi)
787{
788 return bdi_get_bytes(bdi->min_ratio);
789}
790
791int bdi_set_min_bytes(struct backing_dev_info *bdi, u64 min_bytes)
792{
793 int ret;
794 unsigned long pages = min_bytes >> PAGE_SHIFT;
795 long min_ratio;
796
797 ret = bdi_check_pages_limit(pages);
798 if (ret)
799 return ret;
800
801 min_ratio = bdi_ratio_from_pages(pages);
802 if (min_ratio < 0)
803 return min_ratio;
804 return __bdi_set_min_ratio(bdi, min_ratio);
805}
806
807u64 bdi_get_max_bytes(struct backing_dev_info *bdi)
808{
809 return bdi_get_bytes(bdi->max_ratio);
810}
811
812int bdi_set_max_bytes(struct backing_dev_info *bdi, u64 max_bytes)
813{
814 int ret;
815 unsigned long pages = max_bytes >> PAGE_SHIFT;
816 long max_ratio;
817
818 ret = bdi_check_pages_limit(pages);
819 if (ret)
820 return ret;
821
822 max_ratio = bdi_ratio_from_pages(pages);
823 if (max_ratio < 0)
824 return max_ratio;
825 return __bdi_set_max_ratio(bdi, max_ratio);
826}
827
828int bdi_set_strict_limit(struct backing_dev_info *bdi, unsigned int strict_limit)
829{
830 if (strict_limit > 1)
831 return -EINVAL;
832
833 spin_lock_bh(&bdi_lock);
834 if (strict_limit)
835 bdi->capabilities |= BDI_CAP_STRICTLIMIT;
836 else
837 bdi->capabilities &= ~BDI_CAP_STRICTLIMIT;
838 spin_unlock_bh(&bdi_lock);
839
840 return 0;
841}
842
843static unsigned long dirty_freerun_ceiling(unsigned long thresh,
844 unsigned long bg_thresh)
845{
846 return (thresh + bg_thresh) / 2;
847}
848
849static unsigned long hard_dirty_limit(struct wb_domain *dom,
850 unsigned long thresh)
851{
852 return max(thresh, dom->dirty_limit);
853}
854
855/*
856 * Memory which can be further allocated to a memcg domain is capped by
857 * system-wide clean memory excluding the amount being used in the domain.
858 */
859static void mdtc_calc_avail(struct dirty_throttle_control *mdtc,
860 unsigned long filepages, unsigned long headroom)
861{
862 struct dirty_throttle_control *gdtc = mdtc_gdtc(mdtc);
863 unsigned long clean = filepages - min(filepages, mdtc->dirty);
864 unsigned long global_clean = gdtc->avail - min(gdtc->avail, gdtc->dirty);
865 unsigned long other_clean = global_clean - min(global_clean, clean);
866
867 mdtc->avail = filepages + min(headroom, other_clean);
868}
869
870static inline bool dtc_is_global(struct dirty_throttle_control *dtc)
871{
872 return mdtc_gdtc(dtc) == NULL;
873}
874
875/*
876 * Dirty background will ignore pages being written as we're trying to
877 * decide whether to put more under writeback.
878 */
879static void domain_dirty_avail(struct dirty_throttle_control *dtc,
880 bool include_writeback)
881{
882 if (dtc_is_global(dtc)) {
883 dtc->avail = global_dirtyable_memory();
884 dtc->dirty = global_node_page_state(NR_FILE_DIRTY);
885 if (include_writeback)
886 dtc->dirty += global_node_page_state(NR_WRITEBACK);
887 } else {
888 unsigned long filepages = 0, headroom = 0, writeback = 0;
889
890 mem_cgroup_wb_stats(dtc->wb, &filepages, &headroom, &dtc->dirty,
891 &writeback);
892 if (include_writeback)
893 dtc->dirty += writeback;
894 mdtc_calc_avail(dtc, filepages, headroom);
895 }
896}
897
898/**
899 * __wb_calc_thresh - @wb's share of dirty threshold
900 * @dtc: dirty_throttle_context of interest
901 * @thresh: dirty throttling or dirty background threshold of wb_domain in @dtc
902 *
903 * Note that balance_dirty_pages() will only seriously take dirty throttling
904 * threshold as a hard limit when sleeping max_pause per page is not enough
905 * to keep the dirty pages under control. For example, when the device is
906 * completely stalled due to some error conditions, or when there are 1000
907 * dd tasks writing to a slow 10MB/s USB key.
908 * In the other normal situations, it acts more gently by throttling the tasks
909 * more (rather than completely block them) when the wb dirty pages go high.
910 *
911 * It allocates high/low dirty limits to fast/slow devices, in order to prevent
912 * - starving fast devices
913 * - piling up dirty pages (that will take long time to sync) on slow devices
914 *
915 * The wb's share of dirty limit will be adapting to its throughput and
916 * bounded by the bdi->min_ratio and/or bdi->max_ratio parameters, if set.
917 *
918 * Return: @wb's dirty limit in pages. For dirty throttling limit, the term
919 * "dirty" in the context of dirty balancing includes all PG_dirty and
920 * PG_writeback pages.
921 */
922static unsigned long __wb_calc_thresh(struct dirty_throttle_control *dtc,
923 unsigned long thresh)
924{
925 struct wb_domain *dom = dtc_dom(dtc);
926 struct bdi_writeback *wb = dtc->wb;
927 u64 wb_thresh;
928 u64 wb_max_thresh;
929 unsigned long numerator, denominator;
930 unsigned long wb_min_ratio, wb_max_ratio;
931
932 /*
933 * Calculate this wb's share of the thresh ratio.
934 */
935 fprop_fraction_percpu(&dom->completions, dtc->wb_completions,
936 &numerator, &denominator);
937
938 wb_thresh = (thresh * (100 * BDI_RATIO_SCALE - bdi_min_ratio)) / (100 * BDI_RATIO_SCALE);
939 wb_thresh *= numerator;
940 wb_thresh = div64_ul(wb_thresh, denominator);
941
942 wb_min_max_ratio(wb, &wb_min_ratio, &wb_max_ratio);
943
944 wb_thresh += (thresh * wb_min_ratio) / (100 * BDI_RATIO_SCALE);
945 wb_max_thresh = thresh * wb_max_ratio / (100 * BDI_RATIO_SCALE);
946 if (wb_thresh > wb_max_thresh)
947 wb_thresh = wb_max_thresh;
948
949 /*
950 * With strictlimit flag, the wb_thresh is treated as
951 * a hard limit in balance_dirty_pages() and wb_position_ratio().
952 * It's possible that wb_thresh is close to zero, not because
953 * the device is slow, but because it has been inactive.
954 * To prevent occasional writes from being blocked, we raise wb_thresh.
955 */
956 if (unlikely(wb->bdi->capabilities & BDI_CAP_STRICTLIMIT)) {
957 unsigned long limit = hard_dirty_limit(dom, dtc->thresh);
958 u64 wb_scale_thresh = 0;
959
960 if (limit > dtc->dirty)
961 wb_scale_thresh = (limit - dtc->dirty) / 100;
962 wb_thresh = max(wb_thresh, min(wb_scale_thresh, wb_max_thresh / 4));
963 }
964
965 return wb_thresh;
966}
967
968unsigned long wb_calc_thresh(struct bdi_writeback *wb, unsigned long thresh)
969{
970 struct dirty_throttle_control gdtc = { GDTC_INIT(wb) };
971
972 return __wb_calc_thresh(&gdtc, thresh);
973}
974
975unsigned long cgwb_calc_thresh(struct bdi_writeback *wb)
976{
977 struct dirty_throttle_control gdtc = { GDTC_INIT_NO_WB };
978 struct dirty_throttle_control mdtc = { MDTC_INIT(wb, &gdtc) };
979
980 domain_dirty_avail(&gdtc, true);
981 domain_dirty_avail(&mdtc, true);
982 domain_dirty_limits(&mdtc);
983
984 return __wb_calc_thresh(&mdtc, mdtc.thresh);
985}
986
987/*
988 * setpoint - dirty 3
989 * f(dirty) := 1.0 + (----------------)
990 * limit - setpoint
991 *
992 * it's a 3rd order polynomial that subjects to
993 *
994 * (1) f(freerun) = 2.0 => rampup dirty_ratelimit reasonably fast
995 * (2) f(setpoint) = 1.0 => the balance point
996 * (3) f(limit) = 0 => the hard limit
997 * (4) df/dx <= 0 => negative feedback control
998 * (5) the closer to setpoint, the smaller |df/dx| (and the reverse)
999 * => fast response on large errors; small oscillation near setpoint
1000 */
1001static long long pos_ratio_polynom(unsigned long setpoint,
1002 unsigned long dirty,
1003 unsigned long limit)
1004{
1005 long long pos_ratio;
1006 long x;
1007
1008 x = div64_s64(((s64)setpoint - (s64)dirty) << RATELIMIT_CALC_SHIFT,
1009 (limit - setpoint) | 1);
1010 pos_ratio = x;
1011 pos_ratio = pos_ratio * x >> RATELIMIT_CALC_SHIFT;
1012 pos_ratio = pos_ratio * x >> RATELIMIT_CALC_SHIFT;
1013 pos_ratio += 1 << RATELIMIT_CALC_SHIFT;
1014
1015 return clamp(pos_ratio, 0LL, 2LL << RATELIMIT_CALC_SHIFT);
1016}
1017
1018/*
1019 * Dirty position control.
1020 *
1021 * (o) global/bdi setpoints
1022 *
1023 * We want the dirty pages be balanced around the global/wb setpoints.
1024 * When the number of dirty pages is higher/lower than the setpoint, the
1025 * dirty position control ratio (and hence task dirty ratelimit) will be
1026 * decreased/increased to bring the dirty pages back to the setpoint.
1027 *
1028 * pos_ratio = 1 << RATELIMIT_CALC_SHIFT
1029 *
1030 * if (dirty < setpoint) scale up pos_ratio
1031 * if (dirty > setpoint) scale down pos_ratio
1032 *
1033 * if (wb_dirty < wb_setpoint) scale up pos_ratio
1034 * if (wb_dirty > wb_setpoint) scale down pos_ratio
1035 *
1036 * task_ratelimit = dirty_ratelimit * pos_ratio >> RATELIMIT_CALC_SHIFT
1037 *
1038 * (o) global control line
1039 *
1040 * ^ pos_ratio
1041 * |
1042 * | |<===== global dirty control scope ======>|
1043 * 2.0 * * * * * * *
1044 * | .*
1045 * | . *
1046 * | . *
1047 * | . *
1048 * | . *
1049 * | . *
1050 * 1.0 ................................*
1051 * | . . *
1052 * | . . *
1053 * | . . *
1054 * | . . *
1055 * | . . *
1056 * 0 +------------.------------------.----------------------*------------->
1057 * freerun^ setpoint^ limit^ dirty pages
1058 *
1059 * (o) wb control line
1060 *
1061 * ^ pos_ratio
1062 * |
1063 * | *
1064 * | *
1065 * | *
1066 * | *
1067 * | * |<=========== span ============>|
1068 * 1.0 .......................*
1069 * | . *
1070 * | . *
1071 * | . *
1072 * | . *
1073 * | . *
1074 * | . *
1075 * | . *
1076 * | . *
1077 * | . *
1078 * | . *
1079 * | . *
1080 * 1/4 ...............................................* * * * * * * * * * * *
1081 * | . .
1082 * | . .
1083 * | . .
1084 * 0 +----------------------.-------------------------------.------------->
1085 * wb_setpoint^ x_intercept^
1086 *
1087 * The wb control line won't drop below pos_ratio=1/4, so that wb_dirty can
1088 * be smoothly throttled down to normal if it starts high in situations like
1089 * - start writing to a slow SD card and a fast disk at the same time. The SD
1090 * card's wb_dirty may rush to many times higher than wb_setpoint.
1091 * - the wb dirty thresh drops quickly due to change of JBOD workload
1092 */
1093static void wb_position_ratio(struct dirty_throttle_control *dtc)
1094{
1095 struct bdi_writeback *wb = dtc->wb;
1096 unsigned long write_bw = READ_ONCE(wb->avg_write_bandwidth);
1097 unsigned long freerun = dirty_freerun_ceiling(dtc->thresh, dtc->bg_thresh);
1098 unsigned long limit = hard_dirty_limit(dtc_dom(dtc), dtc->thresh);
1099 unsigned long wb_thresh = dtc->wb_thresh;
1100 unsigned long x_intercept;
1101 unsigned long setpoint; /* dirty pages' target balance point */
1102 unsigned long wb_setpoint;
1103 unsigned long span;
1104 long long pos_ratio; /* for scaling up/down the rate limit */
1105 long x;
1106
1107 dtc->pos_ratio = 0;
1108
1109 if (unlikely(dtc->dirty >= limit))
1110 return;
1111
1112 /*
1113 * global setpoint
1114 *
1115 * See comment for pos_ratio_polynom().
1116 */
1117 setpoint = (freerun + limit) / 2;
1118 pos_ratio = pos_ratio_polynom(setpoint, dtc->dirty, limit);
1119
1120 /*
1121 * The strictlimit feature is a tool preventing mistrusted filesystems
1122 * from growing a large number of dirty pages before throttling. For
1123 * such filesystems balance_dirty_pages always checks wb counters
1124 * against wb limits. Even if global "nr_dirty" is under "freerun".
1125 * This is especially important for fuse which sets bdi->max_ratio to
1126 * 1% by default. Without strictlimit feature, fuse writeback may
1127 * consume arbitrary amount of RAM because it is accounted in
1128 * NR_WRITEBACK_TEMP which is not involved in calculating "nr_dirty".
1129 *
1130 * Here, in wb_position_ratio(), we calculate pos_ratio based on
1131 * two values: wb_dirty and wb_thresh. Let's consider an example:
1132 * total amount of RAM is 16GB, bdi->max_ratio is equal to 1%, global
1133 * limits are set by default to 10% and 20% (background and throttle).
1134 * Then wb_thresh is 1% of 20% of 16GB. This amounts to ~8K pages.
1135 * wb_calc_thresh(wb, bg_thresh) is about ~4K pages. wb_setpoint is
1136 * about ~6K pages (as the average of background and throttle wb
1137 * limits). The 3rd order polynomial will provide positive feedback if
1138 * wb_dirty is under wb_setpoint and vice versa.
1139 *
1140 * Note, that we cannot use global counters in these calculations
1141 * because we want to throttle process writing to a strictlimit wb
1142 * much earlier than global "freerun" is reached (~23MB vs. ~2.3GB
1143 * in the example above).
1144 */
1145 if (unlikely(wb->bdi->capabilities & BDI_CAP_STRICTLIMIT)) {
1146 long long wb_pos_ratio;
1147
1148 if (dtc->wb_dirty < 8) {
1149 dtc->pos_ratio = min_t(long long, pos_ratio * 2,
1150 2 << RATELIMIT_CALC_SHIFT);
1151 return;
1152 }
1153
1154 if (dtc->wb_dirty >= wb_thresh)
1155 return;
1156
1157 wb_setpoint = dirty_freerun_ceiling(wb_thresh,
1158 dtc->wb_bg_thresh);
1159
1160 if (wb_setpoint == 0 || wb_setpoint == wb_thresh)
1161 return;
1162
1163 wb_pos_ratio = pos_ratio_polynom(wb_setpoint, dtc->wb_dirty,
1164 wb_thresh);
1165
1166 /*
1167 * Typically, for strictlimit case, wb_setpoint << setpoint
1168 * and pos_ratio >> wb_pos_ratio. In the other words global
1169 * state ("dirty") is not limiting factor and we have to
1170 * make decision based on wb counters. But there is an
1171 * important case when global pos_ratio should get precedence:
1172 * global limits are exceeded (e.g. due to activities on other
1173 * wb's) while given strictlimit wb is below limit.
1174 *
1175 * "pos_ratio * wb_pos_ratio" would work for the case above,
1176 * but it would look too non-natural for the case of all
1177 * activity in the system coming from a single strictlimit wb
1178 * with bdi->max_ratio == 100%.
1179 *
1180 * Note that min() below somewhat changes the dynamics of the
1181 * control system. Normally, pos_ratio value can be well over 3
1182 * (when globally we are at freerun and wb is well below wb
1183 * setpoint). Now the maximum pos_ratio in the same situation
1184 * is 2. We might want to tweak this if we observe the control
1185 * system is too slow to adapt.
1186 */
1187 dtc->pos_ratio = min(pos_ratio, wb_pos_ratio);
1188 return;
1189 }
1190
1191 /*
1192 * We have computed basic pos_ratio above based on global situation. If
1193 * the wb is over/under its share of dirty pages, we want to scale
1194 * pos_ratio further down/up. That is done by the following mechanism.
1195 */
1196
1197 /*
1198 * wb setpoint
1199 *
1200 * f(wb_dirty) := 1.0 + k * (wb_dirty - wb_setpoint)
1201 *
1202 * x_intercept - wb_dirty
1203 * := --------------------------
1204 * x_intercept - wb_setpoint
1205 *
1206 * The main wb control line is a linear function that subjects to
1207 *
1208 * (1) f(wb_setpoint) = 1.0
1209 * (2) k = - 1 / (8 * write_bw) (in single wb case)
1210 * or equally: x_intercept = wb_setpoint + 8 * write_bw
1211 *
1212 * For single wb case, the dirty pages are observed to fluctuate
1213 * regularly within range
1214 * [wb_setpoint - write_bw/2, wb_setpoint + write_bw/2]
1215 * for various filesystems, where (2) can yield in a reasonable 12.5%
1216 * fluctuation range for pos_ratio.
1217 *
1218 * For JBOD case, wb_thresh (not wb_dirty!) could fluctuate up to its
1219 * own size, so move the slope over accordingly and choose a slope that
1220 * yields 100% pos_ratio fluctuation on suddenly doubled wb_thresh.
1221 */
1222 if (unlikely(wb_thresh > dtc->thresh))
1223 wb_thresh = dtc->thresh;
1224 /*
1225 * It's very possible that wb_thresh is close to 0 not because the
1226 * device is slow, but that it has remained inactive for long time.
1227 * Honour such devices a reasonable good (hopefully IO efficient)
1228 * threshold, so that the occasional writes won't be blocked and active
1229 * writes can rampup the threshold quickly.
1230 */
1231 wb_thresh = max(wb_thresh, (limit - dtc->dirty) / 8);
1232 /*
1233 * scale global setpoint to wb's:
1234 * wb_setpoint = setpoint * wb_thresh / thresh
1235 */
1236 x = div_u64((u64)wb_thresh << 16, dtc->thresh | 1);
1237 wb_setpoint = setpoint * (u64)x >> 16;
1238 /*
1239 * Use span=(8*write_bw) in single wb case as indicated by
1240 * (thresh - wb_thresh ~= 0) and transit to wb_thresh in JBOD case.
1241 *
1242 * wb_thresh thresh - wb_thresh
1243 * span = --------- * (8 * write_bw) + ------------------ * wb_thresh
1244 * thresh thresh
1245 */
1246 span = (dtc->thresh - wb_thresh + 8 * write_bw) * (u64)x >> 16;
1247 x_intercept = wb_setpoint + span;
1248
1249 if (dtc->wb_dirty < x_intercept - span / 4) {
1250 pos_ratio = div64_u64(pos_ratio * (x_intercept - dtc->wb_dirty),
1251 (x_intercept - wb_setpoint) | 1);
1252 } else
1253 pos_ratio /= 4;
1254
1255 /*
1256 * wb reserve area, safeguard against dirty pool underrun and disk idle
1257 * It may push the desired control point of global dirty pages higher
1258 * than setpoint.
1259 */
1260 x_intercept = wb_thresh / 2;
1261 if (dtc->wb_dirty < x_intercept) {
1262 if (dtc->wb_dirty > x_intercept / 8)
1263 pos_ratio = div_u64(pos_ratio * x_intercept,
1264 dtc->wb_dirty);
1265 else
1266 pos_ratio *= 8;
1267 }
1268
1269 dtc->pos_ratio = pos_ratio;
1270}
1271
1272static void wb_update_write_bandwidth(struct bdi_writeback *wb,
1273 unsigned long elapsed,
1274 unsigned long written)
1275{
1276 const unsigned long period = roundup_pow_of_two(3 * HZ);
1277 unsigned long avg = wb->avg_write_bandwidth;
1278 unsigned long old = wb->write_bandwidth;
1279 u64 bw;
1280
1281 /*
1282 * bw = written * HZ / elapsed
1283 *
1284 * bw * elapsed + write_bandwidth * (period - elapsed)
1285 * write_bandwidth = ---------------------------------------------------
1286 * period
1287 *
1288 * @written may have decreased due to folio_redirty_for_writepage().
1289 * Avoid underflowing @bw calculation.
1290 */
1291 bw = written - min(written, wb->written_stamp);
1292 bw *= HZ;
1293 if (unlikely(elapsed > period)) {
1294 bw = div64_ul(bw, elapsed);
1295 avg = bw;
1296 goto out;
1297 }
1298 bw += (u64)wb->write_bandwidth * (period - elapsed);
1299 bw >>= ilog2(period);
1300
1301 /*
1302 * one more level of smoothing, for filtering out sudden spikes
1303 */
1304 if (avg > old && old >= (unsigned long)bw)
1305 avg -= (avg - old) >> 3;
1306
1307 if (avg < old && old <= (unsigned long)bw)
1308 avg += (old - avg) >> 3;
1309
1310out:
1311 /* keep avg > 0 to guarantee that tot > 0 if there are dirty wbs */
1312 avg = max(avg, 1LU);
1313 if (wb_has_dirty_io(wb)) {
1314 long delta = avg - wb->avg_write_bandwidth;
1315 WARN_ON_ONCE(atomic_long_add_return(delta,
1316 &wb->bdi->tot_write_bandwidth) <= 0);
1317 }
1318 wb->write_bandwidth = bw;
1319 WRITE_ONCE(wb->avg_write_bandwidth, avg);
1320}
1321
1322static void update_dirty_limit(struct dirty_throttle_control *dtc)
1323{
1324 struct wb_domain *dom = dtc_dom(dtc);
1325 unsigned long thresh = dtc->thresh;
1326 unsigned long limit = dom->dirty_limit;
1327
1328 /*
1329 * Follow up in one step.
1330 */
1331 if (limit < thresh) {
1332 limit = thresh;
1333 goto update;
1334 }
1335
1336 /*
1337 * Follow down slowly. Use the higher one as the target, because thresh
1338 * may drop below dirty. This is exactly the reason to introduce
1339 * dom->dirty_limit which is guaranteed to lie above the dirty pages.
1340 */
1341 thresh = max(thresh, dtc->dirty);
1342 if (limit > thresh) {
1343 limit -= (limit - thresh) >> 5;
1344 goto update;
1345 }
1346 return;
1347update:
1348 dom->dirty_limit = limit;
1349}
1350
1351static void domain_update_dirty_limit(struct dirty_throttle_control *dtc,
1352 unsigned long now)
1353{
1354 struct wb_domain *dom = dtc_dom(dtc);
1355
1356 /*
1357 * check locklessly first to optimize away locking for the most time
1358 */
1359 if (time_before(now, dom->dirty_limit_tstamp + BANDWIDTH_INTERVAL))
1360 return;
1361
1362 spin_lock(&dom->lock);
1363 if (time_after_eq(now, dom->dirty_limit_tstamp + BANDWIDTH_INTERVAL)) {
1364 update_dirty_limit(dtc);
1365 dom->dirty_limit_tstamp = now;
1366 }
1367 spin_unlock(&dom->lock);
1368}
1369
1370/*
1371 * Maintain wb->dirty_ratelimit, the base dirty throttle rate.
1372 *
1373 * Normal wb tasks will be curbed at or below it in long term.
1374 * Obviously it should be around (write_bw / N) when there are N dd tasks.
1375 */
1376static void wb_update_dirty_ratelimit(struct dirty_throttle_control *dtc,
1377 unsigned long dirtied,
1378 unsigned long elapsed)
1379{
1380 struct bdi_writeback *wb = dtc->wb;
1381 unsigned long dirty = dtc->dirty;
1382 unsigned long freerun = dirty_freerun_ceiling(dtc->thresh, dtc->bg_thresh);
1383 unsigned long limit = hard_dirty_limit(dtc_dom(dtc), dtc->thresh);
1384 unsigned long setpoint = (freerun + limit) / 2;
1385 unsigned long write_bw = wb->avg_write_bandwidth;
1386 unsigned long dirty_ratelimit = wb->dirty_ratelimit;
1387 unsigned long dirty_rate;
1388 unsigned long task_ratelimit;
1389 unsigned long balanced_dirty_ratelimit;
1390 unsigned long step;
1391 unsigned long x;
1392 unsigned long shift;
1393
1394 /*
1395 * The dirty rate will match the writeout rate in long term, except
1396 * when dirty pages are truncated by userspace or re-dirtied by FS.
1397 */
1398 dirty_rate = (dirtied - wb->dirtied_stamp) * HZ / elapsed;
1399
1400 /*
1401 * task_ratelimit reflects each dd's dirty rate for the past 200ms.
1402 */
1403 task_ratelimit = (u64)dirty_ratelimit *
1404 dtc->pos_ratio >> RATELIMIT_CALC_SHIFT;
1405 task_ratelimit++; /* it helps rampup dirty_ratelimit from tiny values */
1406
1407 /*
1408 * A linear estimation of the "balanced" throttle rate. The theory is,
1409 * if there are N dd tasks, each throttled at task_ratelimit, the wb's
1410 * dirty_rate will be measured to be (N * task_ratelimit). So the below
1411 * formula will yield the balanced rate limit (write_bw / N).
1412 *
1413 * Note that the expanded form is not a pure rate feedback:
1414 * rate_(i+1) = rate_(i) * (write_bw / dirty_rate) (1)
1415 * but also takes pos_ratio into account:
1416 * rate_(i+1) = rate_(i) * (write_bw / dirty_rate) * pos_ratio (2)
1417 *
1418 * (1) is not realistic because pos_ratio also takes part in balancing
1419 * the dirty rate. Consider the state
1420 * pos_ratio = 0.5 (3)
1421 * rate = 2 * (write_bw / N) (4)
1422 * If (1) is used, it will stuck in that state! Because each dd will
1423 * be throttled at
1424 * task_ratelimit = pos_ratio * rate = (write_bw / N) (5)
1425 * yielding
1426 * dirty_rate = N * task_ratelimit = write_bw (6)
1427 * put (6) into (1) we get
1428 * rate_(i+1) = rate_(i) (7)
1429 *
1430 * So we end up using (2) to always keep
1431 * rate_(i+1) ~= (write_bw / N) (8)
1432 * regardless of the value of pos_ratio. As long as (8) is satisfied,
1433 * pos_ratio is able to drive itself to 1.0, which is not only where
1434 * the dirty count meet the setpoint, but also where the slope of
1435 * pos_ratio is most flat and hence task_ratelimit is least fluctuated.
1436 */
1437 balanced_dirty_ratelimit = div_u64((u64)task_ratelimit * write_bw,
1438 dirty_rate | 1);
1439 /*
1440 * balanced_dirty_ratelimit ~= (write_bw / N) <= write_bw
1441 */
1442 if (unlikely(balanced_dirty_ratelimit > write_bw))
1443 balanced_dirty_ratelimit = write_bw;
1444
1445 /*
1446 * We could safely do this and return immediately:
1447 *
1448 * wb->dirty_ratelimit = balanced_dirty_ratelimit;
1449 *
1450 * However to get a more stable dirty_ratelimit, the below elaborated
1451 * code makes use of task_ratelimit to filter out singular points and
1452 * limit the step size.
1453 *
1454 * The below code essentially only uses the relative value of
1455 *
1456 * task_ratelimit - dirty_ratelimit
1457 * = (pos_ratio - 1) * dirty_ratelimit
1458 *
1459 * which reflects the direction and size of dirty position error.
1460 */
1461
1462 /*
1463 * dirty_ratelimit will follow balanced_dirty_ratelimit iff
1464 * task_ratelimit is on the same side of dirty_ratelimit, too.
1465 * For example, when
1466 * - dirty_ratelimit > balanced_dirty_ratelimit
1467 * - dirty_ratelimit > task_ratelimit (dirty pages are above setpoint)
1468 * lowering dirty_ratelimit will help meet both the position and rate
1469 * control targets. Otherwise, don't update dirty_ratelimit if it will
1470 * only help meet the rate target. After all, what the users ultimately
1471 * feel and care are stable dirty rate and small position error.
1472 *
1473 * |task_ratelimit - dirty_ratelimit| is used to limit the step size
1474 * and filter out the singular points of balanced_dirty_ratelimit. Which
1475 * keeps jumping around randomly and can even leap far away at times
1476 * due to the small 200ms estimation period of dirty_rate (we want to
1477 * keep that period small to reduce time lags).
1478 */
1479 step = 0;
1480
1481 /*
1482 * For strictlimit case, calculations above were based on wb counters
1483 * and limits (starting from pos_ratio = wb_position_ratio() and up to
1484 * balanced_dirty_ratelimit = task_ratelimit * write_bw / dirty_rate).
1485 * Hence, to calculate "step" properly, we have to use wb_dirty as
1486 * "dirty" and wb_setpoint as "setpoint".
1487 *
1488 * We rampup dirty_ratelimit forcibly if wb_dirty is low because
1489 * it's possible that wb_thresh is close to zero due to inactivity
1490 * of backing device.
1491 */
1492 if (unlikely(wb->bdi->capabilities & BDI_CAP_STRICTLIMIT)) {
1493 dirty = dtc->wb_dirty;
1494 if (dtc->wb_dirty < 8)
1495 setpoint = dtc->wb_dirty + 1;
1496 else
1497 setpoint = (dtc->wb_thresh + dtc->wb_bg_thresh) / 2;
1498 }
1499
1500 if (dirty < setpoint) {
1501 x = min3(wb->balanced_dirty_ratelimit,
1502 balanced_dirty_ratelimit, task_ratelimit);
1503 if (dirty_ratelimit < x)
1504 step = x - dirty_ratelimit;
1505 } else {
1506 x = max3(wb->balanced_dirty_ratelimit,
1507 balanced_dirty_ratelimit, task_ratelimit);
1508 if (dirty_ratelimit > x)
1509 step = dirty_ratelimit - x;
1510 }
1511
1512 /*
1513 * Don't pursue 100% rate matching. It's impossible since the balanced
1514 * rate itself is constantly fluctuating. So decrease the track speed
1515 * when it gets close to the target. Helps eliminate pointless tremors.
1516 */
1517 shift = dirty_ratelimit / (2 * step + 1);
1518 if (shift < BITS_PER_LONG)
1519 step = DIV_ROUND_UP(step >> shift, 8);
1520 else
1521 step = 0;
1522
1523 if (dirty_ratelimit < balanced_dirty_ratelimit)
1524 dirty_ratelimit += step;
1525 else
1526 dirty_ratelimit -= step;
1527
1528 WRITE_ONCE(wb->dirty_ratelimit, max(dirty_ratelimit, 1UL));
1529 wb->balanced_dirty_ratelimit = balanced_dirty_ratelimit;
1530
1531 trace_bdi_dirty_ratelimit(wb, dirty_rate, task_ratelimit);
1532}
1533
1534static void __wb_update_bandwidth(struct dirty_throttle_control *gdtc,
1535 struct dirty_throttle_control *mdtc,
1536 bool update_ratelimit)
1537{
1538 struct bdi_writeback *wb = gdtc->wb;
1539 unsigned long now = jiffies;
1540 unsigned long elapsed;
1541 unsigned long dirtied;
1542 unsigned long written;
1543
1544 spin_lock(&wb->list_lock);
1545
1546 /*
1547 * Lockless checks for elapsed time are racy and delayed update after
1548 * IO completion doesn't do it at all (to make sure written pages are
1549 * accounted reasonably quickly). Make sure elapsed >= 1 to avoid
1550 * division errors.
1551 */
1552 elapsed = max(now - wb->bw_time_stamp, 1UL);
1553 dirtied = percpu_counter_read(&wb->stat[WB_DIRTIED]);
1554 written = percpu_counter_read(&wb->stat[WB_WRITTEN]);
1555
1556 if (update_ratelimit) {
1557 domain_update_dirty_limit(gdtc, now);
1558 wb_update_dirty_ratelimit(gdtc, dirtied, elapsed);
1559
1560 /*
1561 * @mdtc is always NULL if !CGROUP_WRITEBACK but the
1562 * compiler has no way to figure that out. Help it.
1563 */
1564 if (IS_ENABLED(CONFIG_CGROUP_WRITEBACK) && mdtc) {
1565 domain_update_dirty_limit(mdtc, now);
1566 wb_update_dirty_ratelimit(mdtc, dirtied, elapsed);
1567 }
1568 }
1569 wb_update_write_bandwidth(wb, elapsed, written);
1570
1571 wb->dirtied_stamp = dirtied;
1572 wb->written_stamp = written;
1573 WRITE_ONCE(wb->bw_time_stamp, now);
1574 spin_unlock(&wb->list_lock);
1575}
1576
1577void wb_update_bandwidth(struct bdi_writeback *wb)
1578{
1579 struct dirty_throttle_control gdtc = { GDTC_INIT(wb) };
1580
1581 __wb_update_bandwidth(&gdtc, NULL, false);
1582}
1583
1584/* Interval after which we consider wb idle and don't estimate bandwidth */
1585#define WB_BANDWIDTH_IDLE_JIF (HZ)
1586
1587static void wb_bandwidth_estimate_start(struct bdi_writeback *wb)
1588{
1589 unsigned long now = jiffies;
1590 unsigned long elapsed = now - READ_ONCE(wb->bw_time_stamp);
1591
1592 if (elapsed > WB_BANDWIDTH_IDLE_JIF &&
1593 !atomic_read(&wb->writeback_inodes)) {
1594 spin_lock(&wb->list_lock);
1595 wb->dirtied_stamp = wb_stat(wb, WB_DIRTIED);
1596 wb->written_stamp = wb_stat(wb, WB_WRITTEN);
1597 WRITE_ONCE(wb->bw_time_stamp, now);
1598 spin_unlock(&wb->list_lock);
1599 }
1600}
1601
1602/*
1603 * After a task dirtied this many pages, balance_dirty_pages_ratelimited()
1604 * will look to see if it needs to start dirty throttling.
1605 *
1606 * If dirty_poll_interval is too low, big NUMA machines will call the expensive
1607 * global_zone_page_state() too often. So scale it near-sqrt to the safety margin
1608 * (the number of pages we may dirty without exceeding the dirty limits).
1609 */
1610static unsigned long dirty_poll_interval(unsigned long dirty,
1611 unsigned long thresh)
1612{
1613 if (thresh > dirty)
1614 return 1UL << (ilog2(thresh - dirty) >> 1);
1615
1616 return 1;
1617}
1618
1619static unsigned long wb_max_pause(struct bdi_writeback *wb,
1620 unsigned long wb_dirty)
1621{
1622 unsigned long bw = READ_ONCE(wb->avg_write_bandwidth);
1623 unsigned long t;
1624
1625 /*
1626 * Limit pause time for small memory systems. If sleeping for too long
1627 * time, a small pool of dirty/writeback pages may go empty and disk go
1628 * idle.
1629 *
1630 * 8 serves as the safety ratio.
1631 */
1632 t = wb_dirty / (1 + bw / roundup_pow_of_two(1 + HZ / 8));
1633 t++;
1634
1635 return min_t(unsigned long, t, MAX_PAUSE);
1636}
1637
1638static long wb_min_pause(struct bdi_writeback *wb,
1639 long max_pause,
1640 unsigned long task_ratelimit,
1641 unsigned long dirty_ratelimit,
1642 int *nr_dirtied_pause)
1643{
1644 long hi = ilog2(READ_ONCE(wb->avg_write_bandwidth));
1645 long lo = ilog2(READ_ONCE(wb->dirty_ratelimit));
1646 long t; /* target pause */
1647 long pause; /* estimated next pause */
1648 int pages; /* target nr_dirtied_pause */
1649
1650 /* target for 10ms pause on 1-dd case */
1651 t = max(1, HZ / 100);
1652
1653 /*
1654 * Scale up pause time for concurrent dirtiers in order to reduce CPU
1655 * overheads.
1656 *
1657 * (N * 10ms) on 2^N concurrent tasks.
1658 */
1659 if (hi > lo)
1660 t += (hi - lo) * (10 * HZ) / 1024;
1661
1662 /*
1663 * This is a bit convoluted. We try to base the next nr_dirtied_pause
1664 * on the much more stable dirty_ratelimit. However the next pause time
1665 * will be computed based on task_ratelimit and the two rate limits may
1666 * depart considerably at some time. Especially if task_ratelimit goes
1667 * below dirty_ratelimit/2 and the target pause is max_pause, the next
1668 * pause time will be max_pause*2 _trimmed down_ to max_pause. As a
1669 * result task_ratelimit won't be executed faithfully, which could
1670 * eventually bring down dirty_ratelimit.
1671 *
1672 * We apply two rules to fix it up:
1673 * 1) try to estimate the next pause time and if necessary, use a lower
1674 * nr_dirtied_pause so as not to exceed max_pause. When this happens,
1675 * nr_dirtied_pause will be "dancing" with task_ratelimit.
1676 * 2) limit the target pause time to max_pause/2, so that the normal
1677 * small fluctuations of task_ratelimit won't trigger rule (1) and
1678 * nr_dirtied_pause will remain as stable as dirty_ratelimit.
1679 */
1680 t = min(t, 1 + max_pause / 2);
1681 pages = dirty_ratelimit * t / roundup_pow_of_two(HZ);
1682
1683 /*
1684 * Tiny nr_dirtied_pause is found to hurt I/O performance in the test
1685 * case fio-mmap-randwrite-64k, which does 16*{sync read, async write}.
1686 * When the 16 consecutive reads are often interrupted by some dirty
1687 * throttling pause during the async writes, cfq will go into idles
1688 * (deadline is fine). So push nr_dirtied_pause as high as possible
1689 * until reaches DIRTY_POLL_THRESH=32 pages.
1690 */
1691 if (pages < DIRTY_POLL_THRESH) {
1692 t = max_pause;
1693 pages = dirty_ratelimit * t / roundup_pow_of_two(HZ);
1694 if (pages > DIRTY_POLL_THRESH) {
1695 pages = DIRTY_POLL_THRESH;
1696 t = HZ * DIRTY_POLL_THRESH / dirty_ratelimit;
1697 }
1698 }
1699
1700 pause = HZ * pages / (task_ratelimit + 1);
1701 if (pause > max_pause) {
1702 t = max_pause;
1703 pages = task_ratelimit * t / roundup_pow_of_two(HZ);
1704 }
1705
1706 *nr_dirtied_pause = pages;
1707 /*
1708 * The minimal pause time will normally be half the target pause time.
1709 */
1710 return pages >= DIRTY_POLL_THRESH ? 1 + t / 2 : t;
1711}
1712
1713static inline void wb_dirty_limits(struct dirty_throttle_control *dtc)
1714{
1715 struct bdi_writeback *wb = dtc->wb;
1716 unsigned long wb_reclaimable;
1717
1718 /*
1719 * wb_thresh is not treated as some limiting factor as
1720 * dirty_thresh, due to reasons
1721 * - in JBOD setup, wb_thresh can fluctuate a lot
1722 * - in a system with HDD and USB key, the USB key may somehow
1723 * go into state (wb_dirty >> wb_thresh) either because
1724 * wb_dirty starts high, or because wb_thresh drops low.
1725 * In this case we don't want to hard throttle the USB key
1726 * dirtiers for 100 seconds until wb_dirty drops under
1727 * wb_thresh. Instead the auxiliary wb control line in
1728 * wb_position_ratio() will let the dirtier task progress
1729 * at some rate <= (write_bw / 2) for bringing down wb_dirty.
1730 */
1731 dtc->wb_thresh = __wb_calc_thresh(dtc, dtc->thresh);
1732 dtc->wb_bg_thresh = dtc->thresh ?
1733 div_u64((u64)dtc->wb_thresh * dtc->bg_thresh, dtc->thresh) : 0;
1734
1735 /*
1736 * In order to avoid the stacked BDI deadlock we need
1737 * to ensure we accurately count the 'dirty' pages when
1738 * the threshold is low.
1739 *
1740 * Otherwise it would be possible to get thresh+n pages
1741 * reported dirty, even though there are thresh-m pages
1742 * actually dirty; with m+n sitting in the percpu
1743 * deltas.
1744 */
1745 if (dtc->wb_thresh < 2 * wb_stat_error()) {
1746 wb_reclaimable = wb_stat_sum(wb, WB_RECLAIMABLE);
1747 dtc->wb_dirty = wb_reclaimable + wb_stat_sum(wb, WB_WRITEBACK);
1748 } else {
1749 wb_reclaimable = wb_stat(wb, WB_RECLAIMABLE);
1750 dtc->wb_dirty = wb_reclaimable + wb_stat(wb, WB_WRITEBACK);
1751 }
1752}
1753
1754static unsigned long domain_poll_intv(struct dirty_throttle_control *dtc,
1755 bool strictlimit)
1756{
1757 unsigned long dirty, thresh;
1758
1759 if (strictlimit) {
1760 dirty = dtc->wb_dirty;
1761 thresh = dtc->wb_thresh;
1762 } else {
1763 dirty = dtc->dirty;
1764 thresh = dtc->thresh;
1765 }
1766
1767 return dirty_poll_interval(dirty, thresh);
1768}
1769
1770/*
1771 * Throttle it only when the background writeback cannot catch-up. This avoids
1772 * (excessively) small writeouts when the wb limits are ramping up in case of
1773 * !strictlimit.
1774 *
1775 * In strictlimit case make decision based on the wb counters and limits. Small
1776 * writeouts when the wb limits are ramping up are the price we consciously pay
1777 * for strictlimit-ing.
1778 */
1779static void domain_dirty_freerun(struct dirty_throttle_control *dtc,
1780 bool strictlimit)
1781{
1782 unsigned long dirty, thresh, bg_thresh;
1783
1784 if (unlikely(strictlimit)) {
1785 wb_dirty_limits(dtc);
1786 dirty = dtc->wb_dirty;
1787 thresh = dtc->wb_thresh;
1788 bg_thresh = dtc->wb_bg_thresh;
1789 } else {
1790 dirty = dtc->dirty;
1791 thresh = dtc->thresh;
1792 bg_thresh = dtc->bg_thresh;
1793 }
1794 dtc->freerun = dirty <= dirty_freerun_ceiling(thresh, bg_thresh);
1795}
1796
1797static void balance_domain_limits(struct dirty_throttle_control *dtc,
1798 bool strictlimit)
1799{
1800 domain_dirty_avail(dtc, true);
1801 domain_dirty_limits(dtc);
1802 domain_dirty_freerun(dtc, strictlimit);
1803}
1804
1805static void wb_dirty_freerun(struct dirty_throttle_control *dtc,
1806 bool strictlimit)
1807{
1808 dtc->freerun = false;
1809
1810 /* was already handled in domain_dirty_freerun */
1811 if (strictlimit)
1812 return;
1813
1814 wb_dirty_limits(dtc);
1815 /*
1816 * LOCAL_THROTTLE tasks must not be throttled when below the per-wb
1817 * freerun ceiling.
1818 */
1819 if (!(current->flags & PF_LOCAL_THROTTLE))
1820 return;
1821
1822 dtc->freerun = dtc->wb_dirty <
1823 dirty_freerun_ceiling(dtc->wb_thresh, dtc->wb_bg_thresh);
1824}
1825
1826static inline void wb_dirty_exceeded(struct dirty_throttle_control *dtc,
1827 bool strictlimit)
1828{
1829 dtc->dirty_exceeded = (dtc->wb_dirty > dtc->wb_thresh) &&
1830 ((dtc->dirty > dtc->thresh) || strictlimit);
1831}
1832
1833/*
1834 * The limits fields dirty_exceeded and pos_ratio won't be updated if wb is
1835 * in freerun state. Please don't use these invalid fields in freerun case.
1836 */
1837static void balance_wb_limits(struct dirty_throttle_control *dtc,
1838 bool strictlimit)
1839{
1840 wb_dirty_freerun(dtc, strictlimit);
1841 if (dtc->freerun)
1842 return;
1843
1844 wb_dirty_exceeded(dtc, strictlimit);
1845 wb_position_ratio(dtc);
1846}
1847
1848/*
1849 * balance_dirty_pages() must be called by processes which are generating dirty
1850 * data. It looks at the number of dirty pages in the machine and will force
1851 * the caller to wait once crossing the (background_thresh + dirty_thresh) / 2.
1852 * If we're over `background_thresh' then the writeback threads are woken to
1853 * perform some writeout.
1854 */
1855static int balance_dirty_pages(struct bdi_writeback *wb,
1856 unsigned long pages_dirtied, unsigned int flags)
1857{
1858 struct dirty_throttle_control gdtc_stor = { GDTC_INIT(wb) };
1859 struct dirty_throttle_control mdtc_stor = { MDTC_INIT(wb, &gdtc_stor) };
1860 struct dirty_throttle_control * const gdtc = &gdtc_stor;
1861 struct dirty_throttle_control * const mdtc = mdtc_valid(&mdtc_stor) ?
1862 &mdtc_stor : NULL;
1863 struct dirty_throttle_control *sdtc;
1864 unsigned long nr_dirty;
1865 long period;
1866 long pause;
1867 long max_pause;
1868 long min_pause;
1869 int nr_dirtied_pause;
1870 unsigned long task_ratelimit;
1871 unsigned long dirty_ratelimit;
1872 struct backing_dev_info *bdi = wb->bdi;
1873 bool strictlimit = bdi->capabilities & BDI_CAP_STRICTLIMIT;
1874 unsigned long start_time = jiffies;
1875 int ret = 0;
1876
1877 for (;;) {
1878 unsigned long now = jiffies;
1879
1880 nr_dirty = global_node_page_state(NR_FILE_DIRTY);
1881
1882 balance_domain_limits(gdtc, strictlimit);
1883 if (mdtc) {
1884 /*
1885 * If @wb belongs to !root memcg, repeat the same
1886 * basic calculations for the memcg domain.
1887 */
1888 balance_domain_limits(mdtc, strictlimit);
1889 }
1890
1891 /*
1892 * In laptop mode, we wait until hitting the higher threshold
1893 * before starting background writeout, and then write out all
1894 * the way down to the lower threshold. So slow writers cause
1895 * minimal disk activity.
1896 *
1897 * In normal mode, we start background writeout at the lower
1898 * background_thresh, to keep the amount of dirty memory low.
1899 */
1900 if (!laptop_mode && nr_dirty > gdtc->bg_thresh &&
1901 !writeback_in_progress(wb))
1902 wb_start_background_writeback(wb);
1903
1904 /*
1905 * If memcg domain is in effect, @dirty should be under
1906 * both global and memcg freerun ceilings.
1907 */
1908 if (gdtc->freerun && (!mdtc || mdtc->freerun)) {
1909 unsigned long intv;
1910 unsigned long m_intv;
1911
1912free_running:
1913 intv = domain_poll_intv(gdtc, strictlimit);
1914 m_intv = ULONG_MAX;
1915
1916 current->dirty_paused_when = now;
1917 current->nr_dirtied = 0;
1918 if (mdtc)
1919 m_intv = domain_poll_intv(mdtc, strictlimit);
1920 current->nr_dirtied_pause = min(intv, m_intv);
1921 break;
1922 }
1923
1924 /* Start writeback even when in laptop mode */
1925 if (unlikely(!writeback_in_progress(wb)))
1926 wb_start_background_writeback(wb);
1927
1928 mem_cgroup_flush_foreign(wb);
1929
1930 /*
1931 * Calculate global domain's pos_ratio and select the
1932 * global dtc by default.
1933 */
1934 balance_wb_limits(gdtc, strictlimit);
1935 if (gdtc->freerun)
1936 goto free_running;
1937 sdtc = gdtc;
1938
1939 if (mdtc) {
1940 /*
1941 * If memcg domain is in effect, calculate its
1942 * pos_ratio. @wb should satisfy constraints from
1943 * both global and memcg domains. Choose the one
1944 * w/ lower pos_ratio.
1945 */
1946 balance_wb_limits(mdtc, strictlimit);
1947 if (mdtc->freerun)
1948 goto free_running;
1949 if (mdtc->pos_ratio < gdtc->pos_ratio)
1950 sdtc = mdtc;
1951 }
1952
1953 wb->dirty_exceeded = gdtc->dirty_exceeded ||
1954 (mdtc && mdtc->dirty_exceeded);
1955 if (time_is_before_jiffies(READ_ONCE(wb->bw_time_stamp) +
1956 BANDWIDTH_INTERVAL))
1957 __wb_update_bandwidth(gdtc, mdtc, true);
1958
1959 /* throttle according to the chosen dtc */
1960 dirty_ratelimit = READ_ONCE(wb->dirty_ratelimit);
1961 task_ratelimit = ((u64)dirty_ratelimit * sdtc->pos_ratio) >>
1962 RATELIMIT_CALC_SHIFT;
1963 max_pause = wb_max_pause(wb, sdtc->wb_dirty);
1964 min_pause = wb_min_pause(wb, max_pause,
1965 task_ratelimit, dirty_ratelimit,
1966 &nr_dirtied_pause);
1967
1968 if (unlikely(task_ratelimit == 0)) {
1969 period = max_pause;
1970 pause = max_pause;
1971 goto pause;
1972 }
1973 period = HZ * pages_dirtied / task_ratelimit;
1974 pause = period;
1975 if (current->dirty_paused_when)
1976 pause -= now - current->dirty_paused_when;
1977 /*
1978 * For less than 1s think time (ext3/4 may block the dirtier
1979 * for up to 800ms from time to time on 1-HDD; so does xfs,
1980 * however at much less frequency), try to compensate it in
1981 * future periods by updating the virtual time; otherwise just
1982 * do a reset, as it may be a light dirtier.
1983 */
1984 if (pause < min_pause) {
1985 trace_balance_dirty_pages(wb,
1986 sdtc->thresh,
1987 sdtc->bg_thresh,
1988 sdtc->dirty,
1989 sdtc->wb_thresh,
1990 sdtc->wb_dirty,
1991 dirty_ratelimit,
1992 task_ratelimit,
1993 pages_dirtied,
1994 period,
1995 min(pause, 0L),
1996 start_time);
1997 if (pause < -HZ) {
1998 current->dirty_paused_when = now;
1999 current->nr_dirtied = 0;
2000 } else if (period) {
2001 current->dirty_paused_when += period;
2002 current->nr_dirtied = 0;
2003 } else if (current->nr_dirtied_pause <= pages_dirtied)
2004 current->nr_dirtied_pause += pages_dirtied;
2005 break;
2006 }
2007 if (unlikely(pause > max_pause)) {
2008 /* for occasional dropped task_ratelimit */
2009 now += min(pause - max_pause, max_pause);
2010 pause = max_pause;
2011 }
2012
2013pause:
2014 trace_balance_dirty_pages(wb,
2015 sdtc->thresh,
2016 sdtc->bg_thresh,
2017 sdtc->dirty,
2018 sdtc->wb_thresh,
2019 sdtc->wb_dirty,
2020 dirty_ratelimit,
2021 task_ratelimit,
2022 pages_dirtied,
2023 period,
2024 pause,
2025 start_time);
2026 if (flags & BDP_ASYNC) {
2027 ret = -EAGAIN;
2028 break;
2029 }
2030 __set_current_state(TASK_KILLABLE);
2031 bdi->last_bdp_sleep = jiffies;
2032 io_schedule_timeout(pause);
2033
2034 current->dirty_paused_when = now + pause;
2035 current->nr_dirtied = 0;
2036 current->nr_dirtied_pause = nr_dirtied_pause;
2037
2038 /*
2039 * This is typically equal to (dirty < thresh) and can also
2040 * keep "1000+ dd on a slow USB stick" under control.
2041 */
2042 if (task_ratelimit)
2043 break;
2044
2045 /*
2046 * In the case of an unresponsive NFS server and the NFS dirty
2047 * pages exceeds dirty_thresh, give the other good wb's a pipe
2048 * to go through, so that tasks on them still remain responsive.
2049 *
2050 * In theory 1 page is enough to keep the consumer-producer
2051 * pipe going: the flusher cleans 1 page => the task dirties 1
2052 * more page. However wb_dirty has accounting errors. So use
2053 * the larger and more IO friendly wb_stat_error.
2054 */
2055 if (sdtc->wb_dirty <= wb_stat_error())
2056 break;
2057
2058 if (fatal_signal_pending(current))
2059 break;
2060 }
2061 return ret;
2062}
2063
2064static DEFINE_PER_CPU(int, bdp_ratelimits);
2065
2066/*
2067 * Normal tasks are throttled by
2068 * loop {
2069 * dirty tsk->nr_dirtied_pause pages;
2070 * take a snap in balance_dirty_pages();
2071 * }
2072 * However there is a worst case. If every task exit immediately when dirtied
2073 * (tsk->nr_dirtied_pause - 1) pages, balance_dirty_pages() will never be
2074 * called to throttle the page dirties. The solution is to save the not yet
2075 * throttled page dirties in dirty_throttle_leaks on task exit and charge them
2076 * randomly into the running tasks. This works well for the above worst case,
2077 * as the new task will pick up and accumulate the old task's leaked dirty
2078 * count and eventually get throttled.
2079 */
2080DEFINE_PER_CPU(int, dirty_throttle_leaks) = 0;
2081
2082/**
2083 * balance_dirty_pages_ratelimited_flags - Balance dirty memory state.
2084 * @mapping: address_space which was dirtied.
2085 * @flags: BDP flags.
2086 *
2087 * Processes which are dirtying memory should call in here once for each page
2088 * which was newly dirtied. The function will periodically check the system's
2089 * dirty state and will initiate writeback if needed.
2090 *
2091 * See balance_dirty_pages_ratelimited() for details.
2092 *
2093 * Return: If @flags contains BDP_ASYNC, it may return -EAGAIN to
2094 * indicate that memory is out of balance and the caller must wait
2095 * for I/O to complete. Otherwise, it will return 0 to indicate
2096 * that either memory was already in balance, or it was able to sleep
2097 * until the amount of dirty memory returned to balance.
2098 */
2099int balance_dirty_pages_ratelimited_flags(struct address_space *mapping,
2100 unsigned int flags)
2101{
2102 struct inode *inode = mapping->host;
2103 struct backing_dev_info *bdi = inode_to_bdi(inode);
2104 struct bdi_writeback *wb = NULL;
2105 int ratelimit;
2106 int ret = 0;
2107 int *p;
2108
2109 if (!(bdi->capabilities & BDI_CAP_WRITEBACK))
2110 return ret;
2111
2112 if (inode_cgwb_enabled(inode))
2113 wb = wb_get_create_current(bdi, GFP_KERNEL);
2114 if (!wb)
2115 wb = &bdi->wb;
2116
2117 ratelimit = current->nr_dirtied_pause;
2118 if (wb->dirty_exceeded)
2119 ratelimit = min(ratelimit, 32 >> (PAGE_SHIFT - 10));
2120
2121 preempt_disable();
2122 /*
2123 * This prevents one CPU to accumulate too many dirtied pages without
2124 * calling into balance_dirty_pages(), which can happen when there are
2125 * 1000+ tasks, all of them start dirtying pages at exactly the same
2126 * time, hence all honoured too large initial task->nr_dirtied_pause.
2127 */
2128 p = this_cpu_ptr(&bdp_ratelimits);
2129 if (unlikely(current->nr_dirtied >= ratelimit))
2130 *p = 0;
2131 else if (unlikely(*p >= ratelimit_pages)) {
2132 *p = 0;
2133 ratelimit = 0;
2134 }
2135 /*
2136 * Pick up the dirtied pages by the exited tasks. This avoids lots of
2137 * short-lived tasks (eg. gcc invocations in a kernel build) escaping
2138 * the dirty throttling and livelock other long-run dirtiers.
2139 */
2140 p = this_cpu_ptr(&dirty_throttle_leaks);
2141 if (*p > 0 && current->nr_dirtied < ratelimit) {
2142 unsigned long nr_pages_dirtied;
2143 nr_pages_dirtied = min(*p, ratelimit - current->nr_dirtied);
2144 *p -= nr_pages_dirtied;
2145 current->nr_dirtied += nr_pages_dirtied;
2146 }
2147 preempt_enable();
2148
2149 if (unlikely(current->nr_dirtied >= ratelimit))
2150 ret = balance_dirty_pages(wb, current->nr_dirtied, flags);
2151
2152 wb_put(wb);
2153 return ret;
2154}
2155EXPORT_SYMBOL_GPL(balance_dirty_pages_ratelimited_flags);
2156
2157/**
2158 * balance_dirty_pages_ratelimited - balance dirty memory state.
2159 * @mapping: address_space which was dirtied.
2160 *
2161 * Processes which are dirtying memory should call in here once for each page
2162 * which was newly dirtied. The function will periodically check the system's
2163 * dirty state and will initiate writeback if needed.
2164 *
2165 * Once we're over the dirty memory limit we decrease the ratelimiting
2166 * by a lot, to prevent individual processes from overshooting the limit
2167 * by (ratelimit_pages) each.
2168 */
2169void balance_dirty_pages_ratelimited(struct address_space *mapping)
2170{
2171 balance_dirty_pages_ratelimited_flags(mapping, 0);
2172}
2173EXPORT_SYMBOL(balance_dirty_pages_ratelimited);
2174
2175/*
2176 * Similar to wb_dirty_limits, wb_bg_dirty_limits also calculates dirty
2177 * and thresh, but it's for background writeback.
2178 */
2179static void wb_bg_dirty_limits(struct dirty_throttle_control *dtc)
2180{
2181 struct bdi_writeback *wb = dtc->wb;
2182
2183 dtc->wb_bg_thresh = __wb_calc_thresh(dtc, dtc->bg_thresh);
2184 if (dtc->wb_bg_thresh < 2 * wb_stat_error())
2185 dtc->wb_dirty = wb_stat_sum(wb, WB_RECLAIMABLE);
2186 else
2187 dtc->wb_dirty = wb_stat(wb, WB_RECLAIMABLE);
2188}
2189
2190static bool domain_over_bg_thresh(struct dirty_throttle_control *dtc)
2191{
2192 domain_dirty_avail(dtc, false);
2193 domain_dirty_limits(dtc);
2194 if (dtc->dirty > dtc->bg_thresh)
2195 return true;
2196
2197 wb_bg_dirty_limits(dtc);
2198 if (dtc->wb_dirty > dtc->wb_bg_thresh)
2199 return true;
2200
2201 return false;
2202}
2203
2204/**
2205 * wb_over_bg_thresh - does @wb need to be written back?
2206 * @wb: bdi_writeback of interest
2207 *
2208 * Determines whether background writeback should keep writing @wb or it's
2209 * clean enough.
2210 *
2211 * Return: %true if writeback should continue.
2212 */
2213bool wb_over_bg_thresh(struct bdi_writeback *wb)
2214{
2215 struct dirty_throttle_control gdtc = { GDTC_INIT(wb) };
2216 struct dirty_throttle_control mdtc = { MDTC_INIT(wb, &gdtc) };
2217
2218 if (domain_over_bg_thresh(&gdtc))
2219 return true;
2220
2221 if (mdtc_valid(&mdtc))
2222 return domain_over_bg_thresh(&mdtc);
2223
2224 return false;
2225}
2226
2227#ifdef CONFIG_SYSCTL
2228/*
2229 * sysctl handler for /proc/sys/vm/dirty_writeback_centisecs
2230 */
2231static int dirty_writeback_centisecs_handler(const struct ctl_table *table, int write,
2232 void *buffer, size_t *length, loff_t *ppos)
2233{
2234 unsigned int old_interval = dirty_writeback_interval;
2235 int ret;
2236
2237 ret = proc_dointvec(table, write, buffer, length, ppos);
2238
2239 /*
2240 * Writing 0 to dirty_writeback_interval will disable periodic writeback
2241 * and a different non-zero value will wakeup the writeback threads.
2242 * wb_wakeup_delayed() would be more appropriate, but it's a pain to
2243 * iterate over all bdis and wbs.
2244 * The reason we do this is to make the change take effect immediately.
2245 */
2246 if (!ret && write && dirty_writeback_interval &&
2247 dirty_writeback_interval != old_interval)
2248 wakeup_flusher_threads(WB_REASON_PERIODIC);
2249
2250 return ret;
2251}
2252#endif
2253
2254void laptop_mode_timer_fn(struct timer_list *t)
2255{
2256 struct backing_dev_info *backing_dev_info =
2257 from_timer(backing_dev_info, t, laptop_mode_wb_timer);
2258
2259 wakeup_flusher_threads_bdi(backing_dev_info, WB_REASON_LAPTOP_TIMER);
2260}
2261
2262/*
2263 * We've spun up the disk and we're in laptop mode: schedule writeback
2264 * of all dirty data a few seconds from now. If the flush is already scheduled
2265 * then push it back - the user is still using the disk.
2266 */
2267void laptop_io_completion(struct backing_dev_info *info)
2268{
2269 mod_timer(&info->laptop_mode_wb_timer, jiffies + laptop_mode);
2270}
2271
2272/*
2273 * We're in laptop mode and we've just synced. The sync's writes will have
2274 * caused another writeback to be scheduled by laptop_io_completion.
2275 * Nothing needs to be written back anymore, so we unschedule the writeback.
2276 */
2277void laptop_sync_completion(void)
2278{
2279 struct backing_dev_info *bdi;
2280
2281 rcu_read_lock();
2282
2283 list_for_each_entry_rcu(bdi, &bdi_list, bdi_list)
2284 del_timer(&bdi->laptop_mode_wb_timer);
2285
2286 rcu_read_unlock();
2287}
2288
2289/*
2290 * If ratelimit_pages is too high then we can get into dirty-data overload
2291 * if a large number of processes all perform writes at the same time.
2292 *
2293 * Here we set ratelimit_pages to a level which ensures that when all CPUs are
2294 * dirtying in parallel, we cannot go more than 3% (1/32) over the dirty memory
2295 * thresholds.
2296 */
2297
2298void writeback_set_ratelimit(void)
2299{
2300 struct wb_domain *dom = &global_wb_domain;
2301 unsigned long background_thresh;
2302 unsigned long dirty_thresh;
2303
2304 global_dirty_limits(&background_thresh, &dirty_thresh);
2305 dom->dirty_limit = dirty_thresh;
2306 ratelimit_pages = dirty_thresh / (num_online_cpus() * 32);
2307 if (ratelimit_pages < 16)
2308 ratelimit_pages = 16;
2309}
2310
2311static int page_writeback_cpu_online(unsigned int cpu)
2312{
2313 writeback_set_ratelimit();
2314 return 0;
2315}
2316
2317#ifdef CONFIG_SYSCTL
2318
2319/* this is needed for the proc_doulongvec_minmax of vm_dirty_bytes */
2320static const unsigned long dirty_bytes_min = 2 * PAGE_SIZE;
2321
2322static struct ctl_table vm_page_writeback_sysctls[] = {
2323 {
2324 .procname = "dirty_background_ratio",
2325 .data = &dirty_background_ratio,
2326 .maxlen = sizeof(dirty_background_ratio),
2327 .mode = 0644,
2328 .proc_handler = dirty_background_ratio_handler,
2329 .extra1 = SYSCTL_ZERO,
2330 .extra2 = SYSCTL_ONE_HUNDRED,
2331 },
2332 {
2333 .procname = "dirty_background_bytes",
2334 .data = &dirty_background_bytes,
2335 .maxlen = sizeof(dirty_background_bytes),
2336 .mode = 0644,
2337 .proc_handler = dirty_background_bytes_handler,
2338 .extra1 = SYSCTL_LONG_ONE,
2339 },
2340 {
2341 .procname = "dirty_ratio",
2342 .data = &vm_dirty_ratio,
2343 .maxlen = sizeof(vm_dirty_ratio),
2344 .mode = 0644,
2345 .proc_handler = dirty_ratio_handler,
2346 .extra1 = SYSCTL_ZERO,
2347 .extra2 = SYSCTL_ONE_HUNDRED,
2348 },
2349 {
2350 .procname = "dirty_bytes",
2351 .data = &vm_dirty_bytes,
2352 .maxlen = sizeof(vm_dirty_bytes),
2353 .mode = 0644,
2354 .proc_handler = dirty_bytes_handler,
2355 .extra1 = (void *)&dirty_bytes_min,
2356 },
2357 {
2358 .procname = "dirty_writeback_centisecs",
2359 .data = &dirty_writeback_interval,
2360 .maxlen = sizeof(dirty_writeback_interval),
2361 .mode = 0644,
2362 .proc_handler = dirty_writeback_centisecs_handler,
2363 },
2364 {
2365 .procname = "dirty_expire_centisecs",
2366 .data = &dirty_expire_interval,
2367 .maxlen = sizeof(dirty_expire_interval),
2368 .mode = 0644,
2369 .proc_handler = proc_dointvec_minmax,
2370 .extra1 = SYSCTL_ZERO,
2371 },
2372#ifdef CONFIG_HIGHMEM
2373 {
2374 .procname = "highmem_is_dirtyable",
2375 .data = &vm_highmem_is_dirtyable,
2376 .maxlen = sizeof(vm_highmem_is_dirtyable),
2377 .mode = 0644,
2378 .proc_handler = proc_dointvec_minmax,
2379 .extra1 = SYSCTL_ZERO,
2380 .extra2 = SYSCTL_ONE,
2381 },
2382#endif
2383 {
2384 .procname = "laptop_mode",
2385 .data = &laptop_mode,
2386 .maxlen = sizeof(laptop_mode),
2387 .mode = 0644,
2388 .proc_handler = proc_dointvec_jiffies,
2389 },
2390};
2391#endif
2392
2393/*
2394 * Called early on to tune the page writeback dirty limits.
2395 *
2396 * We used to scale dirty pages according to how total memory
2397 * related to pages that could be allocated for buffers.
2398 *
2399 * However, that was when we used "dirty_ratio" to scale with
2400 * all memory, and we don't do that any more. "dirty_ratio"
2401 * is now applied to total non-HIGHPAGE memory, and as such we can't
2402 * get into the old insane situation any more where we had
2403 * large amounts of dirty pages compared to a small amount of
2404 * non-HIGHMEM memory.
2405 *
2406 * But we might still want to scale the dirty_ratio by how
2407 * much memory the box has..
2408 */
2409void __init page_writeback_init(void)
2410{
2411 BUG_ON(wb_domain_init(&global_wb_domain, GFP_KERNEL));
2412
2413 cpuhp_setup_state(CPUHP_AP_ONLINE_DYN, "mm/writeback:online",
2414 page_writeback_cpu_online, NULL);
2415 cpuhp_setup_state(CPUHP_MM_WRITEBACK_DEAD, "mm/writeback:dead", NULL,
2416 page_writeback_cpu_online);
2417#ifdef CONFIG_SYSCTL
2418 register_sysctl_init("vm", vm_page_writeback_sysctls);
2419#endif
2420}
2421
2422/**
2423 * tag_pages_for_writeback - tag pages to be written by writeback
2424 * @mapping: address space structure to write
2425 * @start: starting page index
2426 * @end: ending page index (inclusive)
2427 *
2428 * This function scans the page range from @start to @end (inclusive) and tags
2429 * all pages that have DIRTY tag set with a special TOWRITE tag. The caller
2430 * can then use the TOWRITE tag to identify pages eligible for writeback.
2431 * This mechanism is used to avoid livelocking of writeback by a process
2432 * steadily creating new dirty pages in the file (thus it is important for this
2433 * function to be quick so that it can tag pages faster than a dirtying process
2434 * can create them).
2435 */
2436void tag_pages_for_writeback(struct address_space *mapping,
2437 pgoff_t start, pgoff_t end)
2438{
2439 XA_STATE(xas, &mapping->i_pages, start);
2440 unsigned int tagged = 0;
2441 void *page;
2442
2443 xas_lock_irq(&xas);
2444 xas_for_each_marked(&xas, page, end, PAGECACHE_TAG_DIRTY) {
2445 xas_set_mark(&xas, PAGECACHE_TAG_TOWRITE);
2446 if (++tagged % XA_CHECK_SCHED)
2447 continue;
2448
2449 xas_pause(&xas);
2450 xas_unlock_irq(&xas);
2451 cond_resched();
2452 xas_lock_irq(&xas);
2453 }
2454 xas_unlock_irq(&xas);
2455}
2456EXPORT_SYMBOL(tag_pages_for_writeback);
2457
2458static bool folio_prepare_writeback(struct address_space *mapping,
2459 struct writeback_control *wbc, struct folio *folio)
2460{
2461 /*
2462 * Folio truncated or invalidated. We can freely skip it then,
2463 * even for data integrity operations: the folio has disappeared
2464 * concurrently, so there could be no real expectation of this
2465 * data integrity operation even if there is now a new, dirty
2466 * folio at the same pagecache index.
2467 */
2468 if (unlikely(folio->mapping != mapping))
2469 return false;
2470
2471 /*
2472 * Did somebody else write it for us?
2473 */
2474 if (!folio_test_dirty(folio))
2475 return false;
2476
2477 if (folio_test_writeback(folio)) {
2478 if (wbc->sync_mode == WB_SYNC_NONE)
2479 return false;
2480 folio_wait_writeback(folio);
2481 }
2482 BUG_ON(folio_test_writeback(folio));
2483
2484 if (!folio_clear_dirty_for_io(folio))
2485 return false;
2486
2487 return true;
2488}
2489
2490static xa_mark_t wbc_to_tag(struct writeback_control *wbc)
2491{
2492 if (wbc->sync_mode == WB_SYNC_ALL || wbc->tagged_writepages)
2493 return PAGECACHE_TAG_TOWRITE;
2494 return PAGECACHE_TAG_DIRTY;
2495}
2496
2497static pgoff_t wbc_end(struct writeback_control *wbc)
2498{
2499 if (wbc->range_cyclic)
2500 return -1;
2501 return wbc->range_end >> PAGE_SHIFT;
2502}
2503
2504static struct folio *writeback_get_folio(struct address_space *mapping,
2505 struct writeback_control *wbc)
2506{
2507 struct folio *folio;
2508
2509retry:
2510 folio = folio_batch_next(&wbc->fbatch);
2511 if (!folio) {
2512 folio_batch_release(&wbc->fbatch);
2513 cond_resched();
2514 filemap_get_folios_tag(mapping, &wbc->index, wbc_end(wbc),
2515 wbc_to_tag(wbc), &wbc->fbatch);
2516 folio = folio_batch_next(&wbc->fbatch);
2517 if (!folio)
2518 return NULL;
2519 }
2520
2521 folio_lock(folio);
2522 if (unlikely(!folio_prepare_writeback(mapping, wbc, folio))) {
2523 folio_unlock(folio);
2524 goto retry;
2525 }
2526
2527 trace_wbc_writepage(wbc, inode_to_bdi(mapping->host));
2528 return folio;
2529}
2530
2531/**
2532 * writeback_iter - iterate folio of a mapping for writeback
2533 * @mapping: address space structure to write
2534 * @wbc: writeback context
2535 * @folio: previously iterated folio (%NULL to start)
2536 * @error: in-out pointer for writeback errors (see below)
2537 *
2538 * This function returns the next folio for the writeback operation described by
2539 * @wbc on @mapping and should be called in a while loop in the ->writepages
2540 * implementation.
2541 *
2542 * To start the writeback operation, %NULL is passed in the @folio argument, and
2543 * for every subsequent iteration the folio returned previously should be passed
2544 * back in.
2545 *
2546 * If there was an error in the per-folio writeback inside the writeback_iter()
2547 * loop, @error should be set to the error value.
2548 *
2549 * Once the writeback described in @wbc has finished, this function will return
2550 * %NULL and if there was an error in any iteration restore it to @error.
2551 *
2552 * Note: callers should not manually break out of the loop using break or goto
2553 * but must keep calling writeback_iter() until it returns %NULL.
2554 *
2555 * Return: the folio to write or %NULL if the loop is done.
2556 */
2557struct folio *writeback_iter(struct address_space *mapping,
2558 struct writeback_control *wbc, struct folio *folio, int *error)
2559{
2560 if (!folio) {
2561 folio_batch_init(&wbc->fbatch);
2562 wbc->saved_err = *error = 0;
2563
2564 /*
2565 * For range cyclic writeback we remember where we stopped so
2566 * that we can continue where we stopped.
2567 *
2568 * For non-cyclic writeback we always start at the beginning of
2569 * the passed in range.
2570 */
2571 if (wbc->range_cyclic)
2572 wbc->index = mapping->writeback_index;
2573 else
2574 wbc->index = wbc->range_start >> PAGE_SHIFT;
2575
2576 /*
2577 * To avoid livelocks when other processes dirty new pages, we
2578 * first tag pages which should be written back and only then
2579 * start writing them.
2580 *
2581 * For data-integrity writeback we have to be careful so that we
2582 * do not miss some pages (e.g., because some other process has
2583 * cleared the TOWRITE tag we set). The rule we follow is that
2584 * TOWRITE tag can be cleared only by the process clearing the
2585 * DIRTY tag (and submitting the page for I/O).
2586 */
2587 if (wbc->sync_mode == WB_SYNC_ALL || wbc->tagged_writepages)
2588 tag_pages_for_writeback(mapping, wbc->index,
2589 wbc_end(wbc));
2590 } else {
2591 wbc->nr_to_write -= folio_nr_pages(folio);
2592
2593 WARN_ON_ONCE(*error > 0);
2594
2595 /*
2596 * For integrity writeback we have to keep going until we have
2597 * written all the folios we tagged for writeback above, even if
2598 * we run past wbc->nr_to_write or encounter errors.
2599 * We stash away the first error we encounter in wbc->saved_err
2600 * so that it can be retrieved when we're done. This is because
2601 * the file system may still have state to clear for each folio.
2602 *
2603 * For background writeback we exit as soon as we run past
2604 * wbc->nr_to_write or encounter the first error.
2605 */
2606 if (wbc->sync_mode == WB_SYNC_ALL) {
2607 if (*error && !wbc->saved_err)
2608 wbc->saved_err = *error;
2609 } else {
2610 if (*error || wbc->nr_to_write <= 0)
2611 goto done;
2612 }
2613 }
2614
2615 folio = writeback_get_folio(mapping, wbc);
2616 if (!folio) {
2617 /*
2618 * To avoid deadlocks between range_cyclic writeback and callers
2619 * that hold pages in PageWriteback to aggregate I/O until
2620 * the writeback iteration finishes, we do not loop back to the
2621 * start of the file. Doing so causes a page lock/page
2622 * writeback access order inversion - we should only ever lock
2623 * multiple pages in ascending page->index order, and looping
2624 * back to the start of the file violates that rule and causes
2625 * deadlocks.
2626 */
2627 if (wbc->range_cyclic)
2628 mapping->writeback_index = 0;
2629
2630 /*
2631 * Return the first error we encountered (if there was any) to
2632 * the caller.
2633 */
2634 *error = wbc->saved_err;
2635 }
2636 return folio;
2637
2638done:
2639 if (wbc->range_cyclic)
2640 mapping->writeback_index = folio_next_index(folio);
2641 folio_batch_release(&wbc->fbatch);
2642 return NULL;
2643}
2644EXPORT_SYMBOL_GPL(writeback_iter);
2645
2646/**
2647 * write_cache_pages - walk the list of dirty pages of the given address space and write all of them.
2648 * @mapping: address space structure to write
2649 * @wbc: subtract the number of written pages from *@wbc->nr_to_write
2650 * @writepage: function called for each page
2651 * @data: data passed to writepage function
2652 *
2653 * Return: %0 on success, negative error code otherwise
2654 *
2655 * Note: please use writeback_iter() instead.
2656 */
2657int write_cache_pages(struct address_space *mapping,
2658 struct writeback_control *wbc, writepage_t writepage,
2659 void *data)
2660{
2661 struct folio *folio = NULL;
2662 int error;
2663
2664 while ((folio = writeback_iter(mapping, wbc, folio, &error))) {
2665 error = writepage(folio, wbc, data);
2666 if (error == AOP_WRITEPAGE_ACTIVATE) {
2667 folio_unlock(folio);
2668 error = 0;
2669 }
2670 }
2671
2672 return error;
2673}
2674EXPORT_SYMBOL(write_cache_pages);
2675
2676static int writeback_use_writepage(struct address_space *mapping,
2677 struct writeback_control *wbc)
2678{
2679 struct folio *folio = NULL;
2680 struct blk_plug plug;
2681 int err;
2682
2683 blk_start_plug(&plug);
2684 while ((folio = writeback_iter(mapping, wbc, folio, &err))) {
2685 err = mapping->a_ops->writepage(&folio->page, wbc);
2686 if (err == AOP_WRITEPAGE_ACTIVATE) {
2687 folio_unlock(folio);
2688 err = 0;
2689 }
2690 mapping_set_error(mapping, err);
2691 }
2692 blk_finish_plug(&plug);
2693
2694 return err;
2695}
2696
2697int do_writepages(struct address_space *mapping, struct writeback_control *wbc)
2698{
2699 int ret;
2700 struct bdi_writeback *wb;
2701
2702 if (wbc->nr_to_write <= 0)
2703 return 0;
2704 wb = inode_to_wb_wbc(mapping->host, wbc);
2705 wb_bandwidth_estimate_start(wb);
2706 while (1) {
2707 if (mapping->a_ops->writepages) {
2708 ret = mapping->a_ops->writepages(mapping, wbc);
2709 } else if (mapping->a_ops->writepage) {
2710 ret = writeback_use_writepage(mapping, wbc);
2711 } else {
2712 /* deal with chardevs and other special files */
2713 ret = 0;
2714 }
2715 if (ret != -ENOMEM || wbc->sync_mode != WB_SYNC_ALL)
2716 break;
2717
2718 /*
2719 * Lacking an allocation context or the locality or writeback
2720 * state of any of the inode's pages, throttle based on
2721 * writeback activity on the local node. It's as good a
2722 * guess as any.
2723 */
2724 reclaim_throttle(NODE_DATA(numa_node_id()),
2725 VMSCAN_THROTTLE_WRITEBACK);
2726 }
2727 /*
2728 * Usually few pages are written by now from those we've just submitted
2729 * but if there's constant writeback being submitted, this makes sure
2730 * writeback bandwidth is updated once in a while.
2731 */
2732 if (time_is_before_jiffies(READ_ONCE(wb->bw_time_stamp) +
2733 BANDWIDTH_INTERVAL))
2734 wb_update_bandwidth(wb);
2735 return ret;
2736}
2737
2738/*
2739 * For address_spaces which do not use buffers nor write back.
2740 */
2741bool noop_dirty_folio(struct address_space *mapping, struct folio *folio)
2742{
2743 if (!folio_test_dirty(folio))
2744 return !folio_test_set_dirty(folio);
2745 return false;
2746}
2747EXPORT_SYMBOL(noop_dirty_folio);
2748
2749/*
2750 * Helper function for set_page_dirty family.
2751 *
2752 * NOTE: This relies on being atomic wrt interrupts.
2753 */
2754static void folio_account_dirtied(struct folio *folio,
2755 struct address_space *mapping)
2756{
2757 struct inode *inode = mapping->host;
2758
2759 trace_writeback_dirty_folio(folio, mapping);
2760
2761 if (mapping_can_writeback(mapping)) {
2762 struct bdi_writeback *wb;
2763 long nr = folio_nr_pages(folio);
2764
2765 inode_attach_wb(inode, folio);
2766 wb = inode_to_wb(inode);
2767
2768 __lruvec_stat_mod_folio(folio, NR_FILE_DIRTY, nr);
2769 __zone_stat_mod_folio(folio, NR_ZONE_WRITE_PENDING, nr);
2770 __node_stat_mod_folio(folio, NR_DIRTIED, nr);
2771 wb_stat_mod(wb, WB_RECLAIMABLE, nr);
2772 wb_stat_mod(wb, WB_DIRTIED, nr);
2773 task_io_account_write(nr * PAGE_SIZE);
2774 current->nr_dirtied += nr;
2775 __this_cpu_add(bdp_ratelimits, nr);
2776
2777 mem_cgroup_track_foreign_dirty(folio, wb);
2778 }
2779}
2780
2781/*
2782 * Helper function for deaccounting dirty page without writeback.
2783 *
2784 */
2785void folio_account_cleaned(struct folio *folio, struct bdi_writeback *wb)
2786{
2787 long nr = folio_nr_pages(folio);
2788
2789 lruvec_stat_mod_folio(folio, NR_FILE_DIRTY, -nr);
2790 zone_stat_mod_folio(folio, NR_ZONE_WRITE_PENDING, -nr);
2791 wb_stat_mod(wb, WB_RECLAIMABLE, -nr);
2792 task_io_account_cancelled_write(nr * PAGE_SIZE);
2793}
2794
2795/*
2796 * Mark the folio dirty, and set it dirty in the page cache.
2797 *
2798 * If warn is true, then emit a warning if the folio is not uptodate and has
2799 * not been truncated.
2800 *
2801 * It is the caller's responsibility to prevent the folio from being truncated
2802 * while this function is in progress, although it may have been truncated
2803 * before this function is called. Most callers have the folio locked.
2804 * A few have the folio blocked from truncation through other means (e.g.
2805 * zap_vma_pages() has it mapped and is holding the page table lock).
2806 * When called from mark_buffer_dirty(), the filesystem should hold a
2807 * reference to the buffer_head that is being marked dirty, which causes
2808 * try_to_free_buffers() to fail.
2809 */
2810void __folio_mark_dirty(struct folio *folio, struct address_space *mapping,
2811 int warn)
2812{
2813 unsigned long flags;
2814
2815 xa_lock_irqsave(&mapping->i_pages, flags);
2816 if (folio->mapping) { /* Race with truncate? */
2817 WARN_ON_ONCE(warn && !folio_test_uptodate(folio));
2818 folio_account_dirtied(folio, mapping);
2819 __xa_set_mark(&mapping->i_pages, folio_index(folio),
2820 PAGECACHE_TAG_DIRTY);
2821 }
2822 xa_unlock_irqrestore(&mapping->i_pages, flags);
2823}
2824
2825/**
2826 * filemap_dirty_folio - Mark a folio dirty for filesystems which do not use buffer_heads.
2827 * @mapping: Address space this folio belongs to.
2828 * @folio: Folio to be marked as dirty.
2829 *
2830 * Filesystems which do not use buffer heads should call this function
2831 * from their dirty_folio address space operation. It ignores the
2832 * contents of folio_get_private(), so if the filesystem marks individual
2833 * blocks as dirty, the filesystem should handle that itself.
2834 *
2835 * This is also sometimes used by filesystems which use buffer_heads when
2836 * a single buffer is being dirtied: we want to set the folio dirty in
2837 * that case, but not all the buffers. This is a "bottom-up" dirtying,
2838 * whereas block_dirty_folio() is a "top-down" dirtying.
2839 *
2840 * The caller must ensure this doesn't race with truncation. Most will
2841 * simply hold the folio lock, but e.g. zap_pte_range() calls with the
2842 * folio mapped and the pte lock held, which also locks out truncation.
2843 */
2844bool filemap_dirty_folio(struct address_space *mapping, struct folio *folio)
2845{
2846 if (folio_test_set_dirty(folio))
2847 return false;
2848
2849 __folio_mark_dirty(folio, mapping, !folio_test_private(folio));
2850
2851 if (mapping->host) {
2852 /* !PageAnon && !swapper_space */
2853 __mark_inode_dirty(mapping->host, I_DIRTY_PAGES);
2854 }
2855 return true;
2856}
2857EXPORT_SYMBOL(filemap_dirty_folio);
2858
2859/**
2860 * folio_redirty_for_writepage - Decline to write a dirty folio.
2861 * @wbc: The writeback control.
2862 * @folio: The folio.
2863 *
2864 * When a writepage implementation decides that it doesn't want to write
2865 * @folio for some reason, it should call this function, unlock @folio and
2866 * return 0.
2867 *
2868 * Return: True if we redirtied the folio. False if someone else dirtied
2869 * it first.
2870 */
2871bool folio_redirty_for_writepage(struct writeback_control *wbc,
2872 struct folio *folio)
2873{
2874 struct address_space *mapping = folio->mapping;
2875 long nr = folio_nr_pages(folio);
2876 bool ret;
2877
2878 wbc->pages_skipped += nr;
2879 ret = filemap_dirty_folio(mapping, folio);
2880 if (mapping && mapping_can_writeback(mapping)) {
2881 struct inode *inode = mapping->host;
2882 struct bdi_writeback *wb;
2883 struct wb_lock_cookie cookie = {};
2884
2885 wb = unlocked_inode_to_wb_begin(inode, &cookie);
2886 current->nr_dirtied -= nr;
2887 node_stat_mod_folio(folio, NR_DIRTIED, -nr);
2888 wb_stat_mod(wb, WB_DIRTIED, -nr);
2889 unlocked_inode_to_wb_end(inode, &cookie);
2890 }
2891 return ret;
2892}
2893EXPORT_SYMBOL(folio_redirty_for_writepage);
2894
2895/**
2896 * folio_mark_dirty - Mark a folio as being modified.
2897 * @folio: The folio.
2898 *
2899 * The folio may not be truncated while this function is running.
2900 * Holding the folio lock is sufficient to prevent truncation, but some
2901 * callers cannot acquire a sleeping lock. These callers instead hold
2902 * the page table lock for a page table which contains at least one page
2903 * in this folio. Truncation will block on the page table lock as it
2904 * unmaps pages before removing the folio from its mapping.
2905 *
2906 * Return: True if the folio was newly dirtied, false if it was already dirty.
2907 */
2908bool folio_mark_dirty(struct folio *folio)
2909{
2910 struct address_space *mapping = folio_mapping(folio);
2911
2912 if (likely(mapping)) {
2913 /*
2914 * readahead/folio_deactivate could remain
2915 * PG_readahead/PG_reclaim due to race with folio_end_writeback
2916 * About readahead, if the folio is written, the flags would be
2917 * reset. So no problem.
2918 * About folio_deactivate, if the folio is redirtied,
2919 * the flag will be reset. So no problem. but if the
2920 * folio is used by readahead it will confuse readahead
2921 * and make it restart the size rampup process. But it's
2922 * a trivial problem.
2923 */
2924 if (folio_test_reclaim(folio))
2925 folio_clear_reclaim(folio);
2926 return mapping->a_ops->dirty_folio(mapping, folio);
2927 }
2928
2929 return noop_dirty_folio(mapping, folio);
2930}
2931EXPORT_SYMBOL(folio_mark_dirty);
2932
2933/*
2934 * folio_mark_dirty() is racy if the caller has no reference against
2935 * folio->mapping->host, and if the folio is unlocked. This is because another
2936 * CPU could truncate the folio off the mapping and then free the mapping.
2937 *
2938 * Usually, the folio _is_ locked, or the caller is a user-space process which
2939 * holds a reference on the inode by having an open file.
2940 *
2941 * In other cases, the folio should be locked before running folio_mark_dirty().
2942 */
2943bool folio_mark_dirty_lock(struct folio *folio)
2944{
2945 bool ret;
2946
2947 folio_lock(folio);
2948 ret = folio_mark_dirty(folio);
2949 folio_unlock(folio);
2950 return ret;
2951}
2952EXPORT_SYMBOL(folio_mark_dirty_lock);
2953
2954/*
2955 * This cancels just the dirty bit on the kernel page itself, it does NOT
2956 * actually remove dirty bits on any mmap's that may be around. It also
2957 * leaves the page tagged dirty, so any sync activity will still find it on
2958 * the dirty lists, and in particular, clear_page_dirty_for_io() will still
2959 * look at the dirty bits in the VM.
2960 *
2961 * Doing this should *normally* only ever be done when a page is truncated,
2962 * and is not actually mapped anywhere at all. However, fs/buffer.c does
2963 * this when it notices that somebody has cleaned out all the buffers on a
2964 * page without actually doing it through the VM. Can you say "ext3 is
2965 * horribly ugly"? Thought you could.
2966 */
2967void __folio_cancel_dirty(struct folio *folio)
2968{
2969 struct address_space *mapping = folio_mapping(folio);
2970
2971 if (mapping_can_writeback(mapping)) {
2972 struct inode *inode = mapping->host;
2973 struct bdi_writeback *wb;
2974 struct wb_lock_cookie cookie = {};
2975
2976 wb = unlocked_inode_to_wb_begin(inode, &cookie);
2977
2978 if (folio_test_clear_dirty(folio))
2979 folio_account_cleaned(folio, wb);
2980
2981 unlocked_inode_to_wb_end(inode, &cookie);
2982 } else {
2983 folio_clear_dirty(folio);
2984 }
2985}
2986EXPORT_SYMBOL(__folio_cancel_dirty);
2987
2988/*
2989 * Clear a folio's dirty flag, while caring for dirty memory accounting.
2990 * Returns true if the folio was previously dirty.
2991 *
2992 * This is for preparing to put the folio under writeout. We leave
2993 * the folio tagged as dirty in the xarray so that a concurrent
2994 * write-for-sync can discover it via a PAGECACHE_TAG_DIRTY walk.
2995 * The ->writepage implementation will run either folio_start_writeback()
2996 * or folio_mark_dirty(), at which stage we bring the folio's dirty flag
2997 * and xarray dirty tag back into sync.
2998 *
2999 * This incoherency between the folio's dirty flag and xarray tag is
3000 * unfortunate, but it only exists while the folio is locked.
3001 */
3002bool folio_clear_dirty_for_io(struct folio *folio)
3003{
3004 struct address_space *mapping = folio_mapping(folio);
3005 bool ret = false;
3006
3007 VM_BUG_ON_FOLIO(!folio_test_locked(folio), folio);
3008
3009 if (mapping && mapping_can_writeback(mapping)) {
3010 struct inode *inode = mapping->host;
3011 struct bdi_writeback *wb;
3012 struct wb_lock_cookie cookie = {};
3013
3014 /*
3015 * Yes, Virginia, this is indeed insane.
3016 *
3017 * We use this sequence to make sure that
3018 * (a) we account for dirty stats properly
3019 * (b) we tell the low-level filesystem to
3020 * mark the whole folio dirty if it was
3021 * dirty in a pagetable. Only to then
3022 * (c) clean the folio again and return 1 to
3023 * cause the writeback.
3024 *
3025 * This way we avoid all nasty races with the
3026 * dirty bit in multiple places and clearing
3027 * them concurrently from different threads.
3028 *
3029 * Note! Normally the "folio_mark_dirty(folio)"
3030 * has no effect on the actual dirty bit - since
3031 * that will already usually be set. But we
3032 * need the side effects, and it can help us
3033 * avoid races.
3034 *
3035 * We basically use the folio "master dirty bit"
3036 * as a serialization point for all the different
3037 * threads doing their things.
3038 */
3039 if (folio_mkclean(folio))
3040 folio_mark_dirty(folio);
3041 /*
3042 * We carefully synchronise fault handlers against
3043 * installing a dirty pte and marking the folio dirty
3044 * at this point. We do this by having them hold the
3045 * page lock while dirtying the folio, and folios are
3046 * always locked coming in here, so we get the desired
3047 * exclusion.
3048 */
3049 wb = unlocked_inode_to_wb_begin(inode, &cookie);
3050 if (folio_test_clear_dirty(folio)) {
3051 long nr = folio_nr_pages(folio);
3052 lruvec_stat_mod_folio(folio, NR_FILE_DIRTY, -nr);
3053 zone_stat_mod_folio(folio, NR_ZONE_WRITE_PENDING, -nr);
3054 wb_stat_mod(wb, WB_RECLAIMABLE, -nr);
3055 ret = true;
3056 }
3057 unlocked_inode_to_wb_end(inode, &cookie);
3058 return ret;
3059 }
3060 return folio_test_clear_dirty(folio);
3061}
3062EXPORT_SYMBOL(folio_clear_dirty_for_io);
3063
3064static void wb_inode_writeback_start(struct bdi_writeback *wb)
3065{
3066 atomic_inc(&wb->writeback_inodes);
3067}
3068
3069static void wb_inode_writeback_end(struct bdi_writeback *wb)
3070{
3071 unsigned long flags;
3072 atomic_dec(&wb->writeback_inodes);
3073 /*
3074 * Make sure estimate of writeback throughput gets updated after
3075 * writeback completed. We delay the update by BANDWIDTH_INTERVAL
3076 * (which is the interval other bandwidth updates use for batching) so
3077 * that if multiple inodes end writeback at a similar time, they get
3078 * batched into one bandwidth update.
3079 */
3080 spin_lock_irqsave(&wb->work_lock, flags);
3081 if (test_bit(WB_registered, &wb->state))
3082 queue_delayed_work(bdi_wq, &wb->bw_dwork, BANDWIDTH_INTERVAL);
3083 spin_unlock_irqrestore(&wb->work_lock, flags);
3084}
3085
3086bool __folio_end_writeback(struct folio *folio)
3087{
3088 long nr = folio_nr_pages(folio);
3089 struct address_space *mapping = folio_mapping(folio);
3090 bool ret;
3091
3092 if (mapping && mapping_use_writeback_tags(mapping)) {
3093 struct inode *inode = mapping->host;
3094 struct backing_dev_info *bdi = inode_to_bdi(inode);
3095 unsigned long flags;
3096
3097 xa_lock_irqsave(&mapping->i_pages, flags);
3098 ret = folio_xor_flags_has_waiters(folio, 1 << PG_writeback);
3099 __xa_clear_mark(&mapping->i_pages, folio_index(folio),
3100 PAGECACHE_TAG_WRITEBACK);
3101 if (bdi->capabilities & BDI_CAP_WRITEBACK_ACCT) {
3102 struct bdi_writeback *wb = inode_to_wb(inode);
3103
3104 wb_stat_mod(wb, WB_WRITEBACK, -nr);
3105 __wb_writeout_add(wb, nr);
3106 if (!mapping_tagged(mapping, PAGECACHE_TAG_WRITEBACK))
3107 wb_inode_writeback_end(wb);
3108 }
3109
3110 if (mapping->host && !mapping_tagged(mapping,
3111 PAGECACHE_TAG_WRITEBACK))
3112 sb_clear_inode_writeback(mapping->host);
3113
3114 xa_unlock_irqrestore(&mapping->i_pages, flags);
3115 } else {
3116 ret = folio_xor_flags_has_waiters(folio, 1 << PG_writeback);
3117 }
3118
3119 lruvec_stat_mod_folio(folio, NR_WRITEBACK, -nr);
3120 zone_stat_mod_folio(folio, NR_ZONE_WRITE_PENDING, -nr);
3121 node_stat_mod_folio(folio, NR_WRITTEN, nr);
3122
3123 return ret;
3124}
3125
3126void __folio_start_writeback(struct folio *folio, bool keep_write)
3127{
3128 long nr = folio_nr_pages(folio);
3129 struct address_space *mapping = folio_mapping(folio);
3130 int access_ret;
3131
3132 VM_BUG_ON_FOLIO(folio_test_writeback(folio), folio);
3133
3134 if (mapping && mapping_use_writeback_tags(mapping)) {
3135 XA_STATE(xas, &mapping->i_pages, folio_index(folio));
3136 struct inode *inode = mapping->host;
3137 struct backing_dev_info *bdi = inode_to_bdi(inode);
3138 unsigned long flags;
3139 bool on_wblist;
3140
3141 xas_lock_irqsave(&xas, flags);
3142 xas_load(&xas);
3143 folio_test_set_writeback(folio);
3144
3145 on_wblist = mapping_tagged(mapping, PAGECACHE_TAG_WRITEBACK);
3146
3147 xas_set_mark(&xas, PAGECACHE_TAG_WRITEBACK);
3148 if (bdi->capabilities & BDI_CAP_WRITEBACK_ACCT) {
3149 struct bdi_writeback *wb = inode_to_wb(inode);
3150
3151 wb_stat_mod(wb, WB_WRITEBACK, nr);
3152 if (!on_wblist)
3153 wb_inode_writeback_start(wb);
3154 }
3155
3156 /*
3157 * We can come through here when swapping anonymous
3158 * folios, so we don't necessarily have an inode to
3159 * track for sync.
3160 */
3161 if (mapping->host && !on_wblist)
3162 sb_mark_inode_writeback(mapping->host);
3163 if (!folio_test_dirty(folio))
3164 xas_clear_mark(&xas, PAGECACHE_TAG_DIRTY);
3165 if (!keep_write)
3166 xas_clear_mark(&xas, PAGECACHE_TAG_TOWRITE);
3167 xas_unlock_irqrestore(&xas, flags);
3168 } else {
3169 folio_test_set_writeback(folio);
3170 }
3171
3172 lruvec_stat_mod_folio(folio, NR_WRITEBACK, nr);
3173 zone_stat_mod_folio(folio, NR_ZONE_WRITE_PENDING, nr);
3174
3175 access_ret = arch_make_folio_accessible(folio);
3176 /*
3177 * If writeback has been triggered on a page that cannot be made
3178 * accessible, it is too late to recover here.
3179 */
3180 VM_BUG_ON_FOLIO(access_ret != 0, folio);
3181}
3182EXPORT_SYMBOL(__folio_start_writeback);
3183
3184/**
3185 * folio_wait_writeback - Wait for a folio to finish writeback.
3186 * @folio: The folio to wait for.
3187 *
3188 * If the folio is currently being written back to storage, wait for the
3189 * I/O to complete.
3190 *
3191 * Context: Sleeps. Must be called in process context and with
3192 * no spinlocks held. Caller should hold a reference on the folio.
3193 * If the folio is not locked, writeback may start again after writeback
3194 * has finished.
3195 */
3196void folio_wait_writeback(struct folio *folio)
3197{
3198 while (folio_test_writeback(folio)) {
3199 trace_folio_wait_writeback(folio, folio_mapping(folio));
3200 folio_wait_bit(folio, PG_writeback);
3201 }
3202}
3203EXPORT_SYMBOL_GPL(folio_wait_writeback);
3204
3205/**
3206 * folio_wait_writeback_killable - Wait for a folio to finish writeback.
3207 * @folio: The folio to wait for.
3208 *
3209 * If the folio is currently being written back to storage, wait for the
3210 * I/O to complete or a fatal signal to arrive.
3211 *
3212 * Context: Sleeps. Must be called in process context and with
3213 * no spinlocks held. Caller should hold a reference on the folio.
3214 * If the folio is not locked, writeback may start again after writeback
3215 * has finished.
3216 * Return: 0 on success, -EINTR if we get a fatal signal while waiting.
3217 */
3218int folio_wait_writeback_killable(struct folio *folio)
3219{
3220 while (folio_test_writeback(folio)) {
3221 trace_folio_wait_writeback(folio, folio_mapping(folio));
3222 if (folio_wait_bit_killable(folio, PG_writeback))
3223 return -EINTR;
3224 }
3225
3226 return 0;
3227}
3228EXPORT_SYMBOL_GPL(folio_wait_writeback_killable);
3229
3230/**
3231 * folio_wait_stable() - wait for writeback to finish, if necessary.
3232 * @folio: The folio to wait on.
3233 *
3234 * This function determines if the given folio is related to a backing
3235 * device that requires folio contents to be held stable during writeback.
3236 * If so, then it will wait for any pending writeback to complete.
3237 *
3238 * Context: Sleeps. Must be called in process context and with
3239 * no spinlocks held. Caller should hold a reference on the folio.
3240 * If the folio is not locked, writeback may start again after writeback
3241 * has finished.
3242 */
3243void folio_wait_stable(struct folio *folio)
3244{
3245 if (mapping_stable_writes(folio_mapping(folio)))
3246 folio_wait_writeback(folio);
3247}
3248EXPORT_SYMBOL_GPL(folio_wait_stable);