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