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1/*
2 * mm/page-writeback.c
3 *
4 * Copyright (C) 2002, Linus Torvalds.
5 * Copyright (C) 2007 Red Hat, Inc., Peter Zijlstra
6 *
7 * Contains functions related to writing back dirty pages at the
8 * address_space level.
9 *
10 * 10Apr2002 Andrew Morton
11 * Initial version
12 */
13
14#include <linux/kernel.h>
15#include <linux/export.h>
16#include <linux/spinlock.h>
17#include <linux/fs.h>
18#include <linux/mm.h>
19#include <linux/swap.h>
20#include <linux/slab.h>
21#include <linux/pagemap.h>
22#include <linux/writeback.h>
23#include <linux/init.h>
24#include <linux/backing-dev.h>
25#include <linux/task_io_accounting_ops.h>
26#include <linux/blkdev.h>
27#include <linux/mpage.h>
28#include <linux/rmap.h>
29#include <linux/percpu.h>
30#include <linux/notifier.h>
31#include <linux/smp.h>
32#include <linux/sysctl.h>
33#include <linux/cpu.h>
34#include <linux/syscalls.h>
35#include <linux/buffer_head.h> /* __set_page_dirty_buffers */
36#include <linux/pagevec.h>
37#include <linux/timer.h>
38#include <linux/sched/rt.h>
39#include <linux/mm_inline.h>
40#include <trace/events/writeback.h>
41
42#include "internal.h"
43
44/*
45 * Sleep at most 200ms at a time in balance_dirty_pages().
46 */
47#define MAX_PAUSE max(HZ/5, 1)
48
49/*
50 * Try to keep balance_dirty_pages() call intervals higher than this many pages
51 * by raising pause time to max_pause when falls below it.
52 */
53#define DIRTY_POLL_THRESH (128 >> (PAGE_SHIFT - 10))
54
55/*
56 * Estimate write bandwidth at 200ms intervals.
57 */
58#define BANDWIDTH_INTERVAL max(HZ/5, 1)
59
60#define RATELIMIT_CALC_SHIFT 10
61
62/*
63 * After a CPU has dirtied this many pages, balance_dirty_pages_ratelimited
64 * will look to see if it needs to force writeback or throttling.
65 */
66static long ratelimit_pages = 32;
67
68/* The following parameters are exported via /proc/sys/vm */
69
70/*
71 * Start background writeback (via writeback threads) at this percentage
72 */
73int dirty_background_ratio = 10;
74
75/*
76 * dirty_background_bytes starts at 0 (disabled) so that it is a function of
77 * dirty_background_ratio * the amount of dirtyable memory
78 */
79unsigned long dirty_background_bytes;
80
81/*
82 * free highmem will not be subtracted from the total free memory
83 * for calculating free ratios if vm_highmem_is_dirtyable is true
84 */
85int vm_highmem_is_dirtyable;
86
87/*
88 * The generator of dirty data starts writeback at this percentage
89 */
90int vm_dirty_ratio = 20;
91
92/*
93 * vm_dirty_bytes starts at 0 (disabled) so that it is a function of
94 * vm_dirty_ratio * the amount of dirtyable memory
95 */
96unsigned long vm_dirty_bytes;
97
98/*
99 * The interval between `kupdate'-style writebacks
100 */
101unsigned int dirty_writeback_interval = 5 * 100; /* centiseconds */
102
103EXPORT_SYMBOL_GPL(dirty_writeback_interval);
104
105/*
106 * The longest time for which data is allowed to remain dirty
107 */
108unsigned int dirty_expire_interval = 30 * 100; /* centiseconds */
109
110/*
111 * Flag that makes the machine dump writes/reads and block dirtyings.
112 */
113int block_dump;
114
115/*
116 * Flag that puts the machine in "laptop mode". Doubles as a timeout in jiffies:
117 * a full sync is triggered after this time elapses without any disk activity.
118 */
119int laptop_mode;
120
121EXPORT_SYMBOL(laptop_mode);
122
123/* End of sysctl-exported parameters */
124
125struct wb_domain global_wb_domain;
126
127/* consolidated parameters for balance_dirty_pages() and its subroutines */
128struct dirty_throttle_control {
129#ifdef CONFIG_CGROUP_WRITEBACK
130 struct wb_domain *dom;
131 struct dirty_throttle_control *gdtc; /* only set in memcg dtc's */
132#endif
133 struct bdi_writeback *wb;
134 struct fprop_local_percpu *wb_completions;
135
136 unsigned long avail; /* dirtyable */
137 unsigned long dirty; /* file_dirty + write + nfs */
138 unsigned long thresh; /* dirty threshold */
139 unsigned long bg_thresh; /* dirty background threshold */
140
141 unsigned long wb_dirty; /* per-wb counterparts */
142 unsigned long wb_thresh;
143 unsigned long wb_bg_thresh;
144
145 unsigned long pos_ratio;
146};
147
148/*
149 * Length of period for aging writeout fractions of bdis. This is an
150 * arbitrarily chosen number. The longer the period, the slower fractions will
151 * reflect changes in current writeout rate.
152 */
153#define VM_COMPLETIONS_PERIOD_LEN (3*HZ)
154
155#ifdef CONFIG_CGROUP_WRITEBACK
156
157#define GDTC_INIT(__wb) .wb = (__wb), \
158 .dom = &global_wb_domain, \
159 .wb_completions = &(__wb)->completions
160
161#define GDTC_INIT_NO_WB .dom = &global_wb_domain
162
163#define MDTC_INIT(__wb, __gdtc) .wb = (__wb), \
164 .dom = mem_cgroup_wb_domain(__wb), \
165 .wb_completions = &(__wb)->memcg_completions, \
166 .gdtc = __gdtc
167
168static bool mdtc_valid(struct dirty_throttle_control *dtc)
169{
170 return dtc->dom;
171}
172
173static struct wb_domain *dtc_dom(struct dirty_throttle_control *dtc)
174{
175 return dtc->dom;
176}
177
178static struct dirty_throttle_control *mdtc_gdtc(struct dirty_throttle_control *mdtc)
179{
180 return mdtc->gdtc;
181}
182
183static struct fprop_local_percpu *wb_memcg_completions(struct bdi_writeback *wb)
184{
185 return &wb->memcg_completions;
186}
187
188static void wb_min_max_ratio(struct bdi_writeback *wb,
189 unsigned long *minp, unsigned long *maxp)
190{
191 unsigned long this_bw = wb->avg_write_bandwidth;
192 unsigned long tot_bw = atomic_long_read(&wb->bdi->tot_write_bandwidth);
193 unsigned long long min = wb->bdi->min_ratio;
194 unsigned long long max = wb->bdi->max_ratio;
195
196 /*
197 * @wb may already be clean by the time control reaches here and
198 * the total may not include its bw.
199 */
200 if (this_bw < tot_bw) {
201 if (min) {
202 min *= this_bw;
203 do_div(min, tot_bw);
204 }
205 if (max < 100) {
206 max *= this_bw;
207 do_div(max, tot_bw);
208 }
209 }
210
211 *minp = min;
212 *maxp = max;
213}
214
215#else /* CONFIG_CGROUP_WRITEBACK */
216
217#define GDTC_INIT(__wb) .wb = (__wb), \
218 .wb_completions = &(__wb)->completions
219#define GDTC_INIT_NO_WB
220#define MDTC_INIT(__wb, __gdtc)
221
222static bool mdtc_valid(struct dirty_throttle_control *dtc)
223{
224 return false;
225}
226
227static struct wb_domain *dtc_dom(struct dirty_throttle_control *dtc)
228{
229 return &global_wb_domain;
230}
231
232static struct dirty_throttle_control *mdtc_gdtc(struct dirty_throttle_control *mdtc)
233{
234 return NULL;
235}
236
237static struct fprop_local_percpu *wb_memcg_completions(struct bdi_writeback *wb)
238{
239 return NULL;
240}
241
242static void wb_min_max_ratio(struct bdi_writeback *wb,
243 unsigned long *minp, unsigned long *maxp)
244{
245 *minp = wb->bdi->min_ratio;
246 *maxp = wb->bdi->max_ratio;
247}
248
249#endif /* CONFIG_CGROUP_WRITEBACK */
250
251/*
252 * In a memory zone, there is a certain amount of pages we consider
253 * available for the page cache, which is essentially the number of
254 * free and reclaimable pages, minus some zone reserves to protect
255 * lowmem and the ability to uphold the zone's watermarks without
256 * requiring writeback.
257 *
258 * This number of dirtyable pages is the base value of which the
259 * user-configurable dirty ratio is the effictive number of pages that
260 * are allowed to be actually dirtied. Per individual zone, or
261 * globally by using the sum of dirtyable pages over all zones.
262 *
263 * Because the user is allowed to specify the dirty limit globally as
264 * absolute number of bytes, calculating the per-zone dirty limit can
265 * require translating the configured limit into a percentage of
266 * global dirtyable memory first.
267 */
268
269/**
270 * zone_dirtyable_memory - number of dirtyable pages in a zone
271 * @zone: the zone
272 *
273 * Returns the zone's number of pages potentially available for dirty
274 * page cache. This is the base value for the per-zone dirty limits.
275 */
276static unsigned long zone_dirtyable_memory(struct zone *zone)
277{
278 unsigned long nr_pages;
279
280 nr_pages = zone_page_state(zone, NR_FREE_PAGES);
281 /*
282 * Pages reserved for the kernel should not be considered
283 * dirtyable, to prevent a situation where reclaim has to
284 * clean pages in order to balance the zones.
285 */
286 nr_pages -= min(nr_pages, zone->totalreserve_pages);
287
288 nr_pages += zone_page_state(zone, NR_INACTIVE_FILE);
289 nr_pages += zone_page_state(zone, NR_ACTIVE_FILE);
290
291 return nr_pages;
292}
293
294static unsigned long highmem_dirtyable_memory(unsigned long total)
295{
296#ifdef CONFIG_HIGHMEM
297 int node;
298 unsigned long x = 0;
299
300 for_each_node_state(node, N_HIGH_MEMORY) {
301 struct zone *z = &NODE_DATA(node)->node_zones[ZONE_HIGHMEM];
302
303 x += zone_dirtyable_memory(z);
304 }
305 /*
306 * Unreclaimable memory (kernel memory or anonymous memory
307 * without swap) can bring down the dirtyable pages below
308 * the zone's dirty balance reserve and the above calculation
309 * will underflow. However we still want to add in nodes
310 * which are below threshold (negative values) to get a more
311 * accurate calculation but make sure that the total never
312 * underflows.
313 */
314 if ((long)x < 0)
315 x = 0;
316
317 /*
318 * Make sure that the number of highmem pages is never larger
319 * than the number of the total dirtyable memory. This can only
320 * occur in very strange VM situations but we want to make sure
321 * that this does not occur.
322 */
323 return min(x, total);
324#else
325 return 0;
326#endif
327}
328
329/**
330 * global_dirtyable_memory - number of globally dirtyable pages
331 *
332 * Returns the global number of pages potentially available for dirty
333 * page cache. This is the base value for the global dirty limits.
334 */
335static unsigned long global_dirtyable_memory(void)
336{
337 unsigned long x;
338
339 x = global_page_state(NR_FREE_PAGES);
340 /*
341 * Pages reserved for the kernel should not be considered
342 * dirtyable, to prevent a situation where reclaim has to
343 * clean pages in order to balance the zones.
344 */
345 x -= min(x, totalreserve_pages);
346
347 x += global_page_state(NR_INACTIVE_FILE);
348 x += global_page_state(NR_ACTIVE_FILE);
349
350 if (!vm_highmem_is_dirtyable)
351 x -= highmem_dirtyable_memory(x);
352
353 return x + 1; /* Ensure that we never return 0 */
354}
355
356/**
357 * domain_dirty_limits - calculate thresh and bg_thresh for a wb_domain
358 * @dtc: dirty_throttle_control of interest
359 *
360 * Calculate @dtc->thresh and ->bg_thresh considering
361 * vm_dirty_{bytes|ratio} and dirty_background_{bytes|ratio}. The caller
362 * must ensure that @dtc->avail is set before calling this function. The
363 * dirty limits will be lifted by 1/4 for PF_LESS_THROTTLE (ie. nfsd) and
364 * real-time tasks.
365 */
366static void domain_dirty_limits(struct dirty_throttle_control *dtc)
367{
368 const unsigned long available_memory = dtc->avail;
369 struct dirty_throttle_control *gdtc = mdtc_gdtc(dtc);
370 unsigned long bytes = vm_dirty_bytes;
371 unsigned long bg_bytes = dirty_background_bytes;
372 unsigned long ratio = vm_dirty_ratio;
373 unsigned long bg_ratio = dirty_background_ratio;
374 unsigned long thresh;
375 unsigned long bg_thresh;
376 struct task_struct *tsk;
377
378 /* gdtc is !NULL iff @dtc is for memcg domain */
379 if (gdtc) {
380 unsigned long global_avail = gdtc->avail;
381
382 /*
383 * The byte settings can't be applied directly to memcg
384 * domains. Convert them to ratios by scaling against
385 * globally available memory.
386 */
387 if (bytes)
388 ratio = min(DIV_ROUND_UP(bytes, PAGE_SIZE) * 100 /
389 global_avail, 100UL);
390 if (bg_bytes)
391 bg_ratio = min(DIV_ROUND_UP(bg_bytes, PAGE_SIZE) * 100 /
392 global_avail, 100UL);
393 bytes = bg_bytes = 0;
394 }
395
396 if (bytes)
397 thresh = DIV_ROUND_UP(bytes, PAGE_SIZE);
398 else
399 thresh = (ratio * available_memory) / 100;
400
401 if (bg_bytes)
402 bg_thresh = DIV_ROUND_UP(bg_bytes, PAGE_SIZE);
403 else
404 bg_thresh = (bg_ratio * available_memory) / 100;
405
406 if (bg_thresh >= thresh)
407 bg_thresh = thresh / 2;
408 tsk = current;
409 if (tsk->flags & PF_LESS_THROTTLE || rt_task(tsk)) {
410 bg_thresh += bg_thresh / 4;
411 thresh += thresh / 4;
412 }
413 dtc->thresh = thresh;
414 dtc->bg_thresh = bg_thresh;
415
416 /* we should eventually report the domain in the TP */
417 if (!gdtc)
418 trace_global_dirty_state(bg_thresh, thresh);
419}
420
421/**
422 * global_dirty_limits - background-writeback and dirty-throttling thresholds
423 * @pbackground: out parameter for bg_thresh
424 * @pdirty: out parameter for thresh
425 *
426 * Calculate bg_thresh and thresh for global_wb_domain. See
427 * domain_dirty_limits() for details.
428 */
429void global_dirty_limits(unsigned long *pbackground, unsigned long *pdirty)
430{
431 struct dirty_throttle_control gdtc = { GDTC_INIT_NO_WB };
432
433 gdtc.avail = global_dirtyable_memory();
434 domain_dirty_limits(&gdtc);
435
436 *pbackground = gdtc.bg_thresh;
437 *pdirty = gdtc.thresh;
438}
439
440/**
441 * zone_dirty_limit - maximum number of dirty pages allowed in a zone
442 * @zone: the zone
443 *
444 * Returns the maximum number of dirty pages allowed in a zone, based
445 * on the zone's dirtyable memory.
446 */
447static unsigned long zone_dirty_limit(struct zone *zone)
448{
449 unsigned long zone_memory = zone_dirtyable_memory(zone);
450 struct task_struct *tsk = current;
451 unsigned long dirty;
452
453 if (vm_dirty_bytes)
454 dirty = DIV_ROUND_UP(vm_dirty_bytes, PAGE_SIZE) *
455 zone_memory / global_dirtyable_memory();
456 else
457 dirty = vm_dirty_ratio * zone_memory / 100;
458
459 if (tsk->flags & PF_LESS_THROTTLE || rt_task(tsk))
460 dirty += dirty / 4;
461
462 return dirty;
463}
464
465/**
466 * zone_dirty_ok - tells whether a zone is within its dirty limits
467 * @zone: the zone to check
468 *
469 * Returns %true when the dirty pages in @zone are within the zone's
470 * dirty limit, %false if the limit is exceeded.
471 */
472bool zone_dirty_ok(struct zone *zone)
473{
474 unsigned long limit = zone_dirty_limit(zone);
475
476 return zone_page_state(zone, NR_FILE_DIRTY) +
477 zone_page_state(zone, NR_UNSTABLE_NFS) +
478 zone_page_state(zone, NR_WRITEBACK) <= limit;
479}
480
481int dirty_background_ratio_handler(struct ctl_table *table, int write,
482 void __user *buffer, size_t *lenp,
483 loff_t *ppos)
484{
485 int ret;
486
487 ret = proc_dointvec_minmax(table, write, buffer, lenp, ppos);
488 if (ret == 0 && write)
489 dirty_background_bytes = 0;
490 return ret;
491}
492
493int dirty_background_bytes_handler(struct ctl_table *table, int write,
494 void __user *buffer, size_t *lenp,
495 loff_t *ppos)
496{
497 int ret;
498
499 ret = proc_doulongvec_minmax(table, write, buffer, lenp, ppos);
500 if (ret == 0 && write)
501 dirty_background_ratio = 0;
502 return ret;
503}
504
505int dirty_ratio_handler(struct ctl_table *table, int write,
506 void __user *buffer, size_t *lenp,
507 loff_t *ppos)
508{
509 int old_ratio = vm_dirty_ratio;
510 int ret;
511
512 ret = proc_dointvec_minmax(table, write, buffer, lenp, ppos);
513 if (ret == 0 && write && vm_dirty_ratio != old_ratio) {
514 writeback_set_ratelimit();
515 vm_dirty_bytes = 0;
516 }
517 return ret;
518}
519
520int dirty_bytes_handler(struct ctl_table *table, int write,
521 void __user *buffer, size_t *lenp,
522 loff_t *ppos)
523{
524 unsigned long old_bytes = vm_dirty_bytes;
525 int ret;
526
527 ret = proc_doulongvec_minmax(table, write, buffer, lenp, ppos);
528 if (ret == 0 && write && vm_dirty_bytes != old_bytes) {
529 writeback_set_ratelimit();
530 vm_dirty_ratio = 0;
531 }
532 return ret;
533}
534
535static unsigned long wp_next_time(unsigned long cur_time)
536{
537 cur_time += VM_COMPLETIONS_PERIOD_LEN;
538 /* 0 has a special meaning... */
539 if (!cur_time)
540 return 1;
541 return cur_time;
542}
543
544static void wb_domain_writeout_inc(struct wb_domain *dom,
545 struct fprop_local_percpu *completions,
546 unsigned int max_prop_frac)
547{
548 __fprop_inc_percpu_max(&dom->completions, completions,
549 max_prop_frac);
550 /* First event after period switching was turned off? */
551 if (!unlikely(dom->period_time)) {
552 /*
553 * We can race with other __bdi_writeout_inc calls here but
554 * it does not cause any harm since the resulting time when
555 * timer will fire and what is in writeout_period_time will be
556 * roughly the same.
557 */
558 dom->period_time = wp_next_time(jiffies);
559 mod_timer(&dom->period_timer, dom->period_time);
560 }
561}
562
563/*
564 * Increment @wb's writeout completion count and the global writeout
565 * completion count. Called from test_clear_page_writeback().
566 */
567static inline void __wb_writeout_inc(struct bdi_writeback *wb)
568{
569 struct wb_domain *cgdom;
570
571 __inc_wb_stat(wb, WB_WRITTEN);
572 wb_domain_writeout_inc(&global_wb_domain, &wb->completions,
573 wb->bdi->max_prop_frac);
574
575 cgdom = mem_cgroup_wb_domain(wb);
576 if (cgdom)
577 wb_domain_writeout_inc(cgdom, wb_memcg_completions(wb),
578 wb->bdi->max_prop_frac);
579}
580
581void wb_writeout_inc(struct bdi_writeback *wb)
582{
583 unsigned long flags;
584
585 local_irq_save(flags);
586 __wb_writeout_inc(wb);
587 local_irq_restore(flags);
588}
589EXPORT_SYMBOL_GPL(wb_writeout_inc);
590
591/*
592 * On idle system, we can be called long after we scheduled because we use
593 * deferred timers so count with missed periods.
594 */
595static void writeout_period(unsigned long t)
596{
597 struct wb_domain *dom = (void *)t;
598 int miss_periods = (jiffies - dom->period_time) /
599 VM_COMPLETIONS_PERIOD_LEN;
600
601 if (fprop_new_period(&dom->completions, miss_periods + 1)) {
602 dom->period_time = wp_next_time(dom->period_time +
603 miss_periods * VM_COMPLETIONS_PERIOD_LEN);
604 mod_timer(&dom->period_timer, dom->period_time);
605 } else {
606 /*
607 * Aging has zeroed all fractions. Stop wasting CPU on period
608 * updates.
609 */
610 dom->period_time = 0;
611 }
612}
613
614int wb_domain_init(struct wb_domain *dom, gfp_t gfp)
615{
616 memset(dom, 0, sizeof(*dom));
617
618 spin_lock_init(&dom->lock);
619
620 init_timer_deferrable(&dom->period_timer);
621 dom->period_timer.function = writeout_period;
622 dom->period_timer.data = (unsigned long)dom;
623
624 dom->dirty_limit_tstamp = jiffies;
625
626 return fprop_global_init(&dom->completions, gfp);
627}
628
629#ifdef CONFIG_CGROUP_WRITEBACK
630void wb_domain_exit(struct wb_domain *dom)
631{
632 del_timer_sync(&dom->period_timer);
633 fprop_global_destroy(&dom->completions);
634}
635#endif
636
637/*
638 * bdi_min_ratio keeps the sum of the minimum dirty shares of all
639 * registered backing devices, which, for obvious reasons, can not
640 * exceed 100%.
641 */
642static unsigned int bdi_min_ratio;
643
644int bdi_set_min_ratio(struct backing_dev_info *bdi, unsigned int min_ratio)
645{
646 int ret = 0;
647
648 spin_lock_bh(&bdi_lock);
649 if (min_ratio > bdi->max_ratio) {
650 ret = -EINVAL;
651 } else {
652 min_ratio -= bdi->min_ratio;
653 if (bdi_min_ratio + min_ratio < 100) {
654 bdi_min_ratio += min_ratio;
655 bdi->min_ratio += min_ratio;
656 } else {
657 ret = -EINVAL;
658 }
659 }
660 spin_unlock_bh(&bdi_lock);
661
662 return ret;
663}
664
665int bdi_set_max_ratio(struct backing_dev_info *bdi, unsigned max_ratio)
666{
667 int ret = 0;
668
669 if (max_ratio > 100)
670 return -EINVAL;
671
672 spin_lock_bh(&bdi_lock);
673 if (bdi->min_ratio > max_ratio) {
674 ret = -EINVAL;
675 } else {
676 bdi->max_ratio = max_ratio;
677 bdi->max_prop_frac = (FPROP_FRAC_BASE * max_ratio) / 100;
678 }
679 spin_unlock_bh(&bdi_lock);
680
681 return ret;
682}
683EXPORT_SYMBOL(bdi_set_max_ratio);
684
685static unsigned long dirty_freerun_ceiling(unsigned long thresh,
686 unsigned long bg_thresh)
687{
688 return (thresh + bg_thresh) / 2;
689}
690
691static unsigned long hard_dirty_limit(struct wb_domain *dom,
692 unsigned long thresh)
693{
694 return max(thresh, dom->dirty_limit);
695}
696
697/*
698 * Memory which can be further allocated to a memcg domain is capped by
699 * system-wide clean memory excluding the amount being used in the domain.
700 */
701static void mdtc_calc_avail(struct dirty_throttle_control *mdtc,
702 unsigned long filepages, unsigned long headroom)
703{
704 struct dirty_throttle_control *gdtc = mdtc_gdtc(mdtc);
705 unsigned long clean = filepages - min(filepages, mdtc->dirty);
706 unsigned long global_clean = gdtc->avail - min(gdtc->avail, gdtc->dirty);
707 unsigned long other_clean = global_clean - min(global_clean, clean);
708
709 mdtc->avail = filepages + min(headroom, other_clean);
710}
711
712/**
713 * __wb_calc_thresh - @wb's share of dirty throttling threshold
714 * @dtc: dirty_throttle_context of interest
715 *
716 * Returns @wb's dirty limit in pages. The term "dirty" in the context of
717 * dirty balancing includes all PG_dirty, PG_writeback and NFS unstable pages.
718 *
719 * Note that balance_dirty_pages() will only seriously take it as a hard limit
720 * when sleeping max_pause per page is not enough to keep the dirty pages under
721 * control. For example, when the device is completely stalled due to some error
722 * conditions, or when there are 1000 dd tasks writing to a slow 10MB/s USB key.
723 * In the other normal situations, it acts more gently by throttling the tasks
724 * more (rather than completely block them) when the wb dirty pages go high.
725 *
726 * It allocates high/low dirty limits to fast/slow devices, in order to prevent
727 * - starving fast devices
728 * - piling up dirty pages (that will take long time to sync) on slow devices
729 *
730 * The wb's share of dirty limit will be adapting to its throughput and
731 * bounded by the bdi->min_ratio and/or bdi->max_ratio parameters, if set.
732 */
733static unsigned long __wb_calc_thresh(struct dirty_throttle_control *dtc)
734{
735 struct wb_domain *dom = dtc_dom(dtc);
736 unsigned long thresh = dtc->thresh;
737 u64 wb_thresh;
738 long numerator, denominator;
739 unsigned long wb_min_ratio, wb_max_ratio;
740
741 /*
742 * Calculate this BDI's share of the thresh ratio.
743 */
744 fprop_fraction_percpu(&dom->completions, dtc->wb_completions,
745 &numerator, &denominator);
746
747 wb_thresh = (thresh * (100 - bdi_min_ratio)) / 100;
748 wb_thresh *= numerator;
749 do_div(wb_thresh, denominator);
750
751 wb_min_max_ratio(dtc->wb, &wb_min_ratio, &wb_max_ratio);
752
753 wb_thresh += (thresh * wb_min_ratio) / 100;
754 if (wb_thresh > (thresh * wb_max_ratio) / 100)
755 wb_thresh = thresh * wb_max_ratio / 100;
756
757 return wb_thresh;
758}
759
760unsigned long wb_calc_thresh(struct bdi_writeback *wb, unsigned long thresh)
761{
762 struct dirty_throttle_control gdtc = { GDTC_INIT(wb),
763 .thresh = thresh };
764 return __wb_calc_thresh(&gdtc);
765}
766
767/*
768 * setpoint - dirty 3
769 * f(dirty) := 1.0 + (----------------)
770 * limit - setpoint
771 *
772 * it's a 3rd order polynomial that subjects to
773 *
774 * (1) f(freerun) = 2.0 => rampup dirty_ratelimit reasonably fast
775 * (2) f(setpoint) = 1.0 => the balance point
776 * (3) f(limit) = 0 => the hard limit
777 * (4) df/dx <= 0 => negative feedback control
778 * (5) the closer to setpoint, the smaller |df/dx| (and the reverse)
779 * => fast response on large errors; small oscillation near setpoint
780 */
781static long long pos_ratio_polynom(unsigned long setpoint,
782 unsigned long dirty,
783 unsigned long limit)
784{
785 long long pos_ratio;
786 long x;
787
788 x = div64_s64(((s64)setpoint - (s64)dirty) << RATELIMIT_CALC_SHIFT,
789 (limit - setpoint) | 1);
790 pos_ratio = x;
791 pos_ratio = pos_ratio * x >> RATELIMIT_CALC_SHIFT;
792 pos_ratio = pos_ratio * x >> RATELIMIT_CALC_SHIFT;
793 pos_ratio += 1 << RATELIMIT_CALC_SHIFT;
794
795 return clamp(pos_ratio, 0LL, 2LL << RATELIMIT_CALC_SHIFT);
796}
797
798/*
799 * Dirty position control.
800 *
801 * (o) global/bdi setpoints
802 *
803 * We want the dirty pages be balanced around the global/wb setpoints.
804 * When the number of dirty pages is higher/lower than the setpoint, the
805 * dirty position control ratio (and hence task dirty ratelimit) will be
806 * decreased/increased to bring the dirty pages back to the setpoint.
807 *
808 * pos_ratio = 1 << RATELIMIT_CALC_SHIFT
809 *
810 * if (dirty < setpoint) scale up pos_ratio
811 * if (dirty > setpoint) scale down pos_ratio
812 *
813 * if (wb_dirty < wb_setpoint) scale up pos_ratio
814 * if (wb_dirty > wb_setpoint) scale down pos_ratio
815 *
816 * task_ratelimit = dirty_ratelimit * pos_ratio >> RATELIMIT_CALC_SHIFT
817 *
818 * (o) global control line
819 *
820 * ^ pos_ratio
821 * |
822 * | |<===== global dirty control scope ======>|
823 * 2.0 .............*
824 * | .*
825 * | . *
826 * | . *
827 * | . *
828 * | . *
829 * | . *
830 * 1.0 ................................*
831 * | . . *
832 * | . . *
833 * | . . *
834 * | . . *
835 * | . . *
836 * 0 +------------.------------------.----------------------*------------->
837 * freerun^ setpoint^ limit^ dirty pages
838 *
839 * (o) wb control line
840 *
841 * ^ pos_ratio
842 * |
843 * | *
844 * | *
845 * | *
846 * | *
847 * | * |<=========== span ============>|
848 * 1.0 .......................*
849 * | . *
850 * | . *
851 * | . *
852 * | . *
853 * | . *
854 * | . *
855 * | . *
856 * | . *
857 * | . *
858 * | . *
859 * | . *
860 * 1/4 ...............................................* * * * * * * * * * * *
861 * | . .
862 * | . .
863 * | . .
864 * 0 +----------------------.-------------------------------.------------->
865 * wb_setpoint^ x_intercept^
866 *
867 * The wb control line won't drop below pos_ratio=1/4, so that wb_dirty can
868 * be smoothly throttled down to normal if it starts high in situations like
869 * - start writing to a slow SD card and a fast disk at the same time. The SD
870 * card's wb_dirty may rush to many times higher than wb_setpoint.
871 * - the wb dirty thresh drops quickly due to change of JBOD workload
872 */
873static void wb_position_ratio(struct dirty_throttle_control *dtc)
874{
875 struct bdi_writeback *wb = dtc->wb;
876 unsigned long write_bw = wb->avg_write_bandwidth;
877 unsigned long freerun = dirty_freerun_ceiling(dtc->thresh, dtc->bg_thresh);
878 unsigned long limit = hard_dirty_limit(dtc_dom(dtc), dtc->thresh);
879 unsigned long wb_thresh = dtc->wb_thresh;
880 unsigned long x_intercept;
881 unsigned long setpoint; /* dirty pages' target balance point */
882 unsigned long wb_setpoint;
883 unsigned long span;
884 long long pos_ratio; /* for scaling up/down the rate limit */
885 long x;
886
887 dtc->pos_ratio = 0;
888
889 if (unlikely(dtc->dirty >= limit))
890 return;
891
892 /*
893 * global setpoint
894 *
895 * See comment for pos_ratio_polynom().
896 */
897 setpoint = (freerun + limit) / 2;
898 pos_ratio = pos_ratio_polynom(setpoint, dtc->dirty, limit);
899
900 /*
901 * The strictlimit feature is a tool preventing mistrusted filesystems
902 * from growing a large number of dirty pages before throttling. For
903 * such filesystems balance_dirty_pages always checks wb counters
904 * against wb limits. Even if global "nr_dirty" is under "freerun".
905 * This is especially important for fuse which sets bdi->max_ratio to
906 * 1% by default. Without strictlimit feature, fuse writeback may
907 * consume arbitrary amount of RAM because it is accounted in
908 * NR_WRITEBACK_TEMP which is not involved in calculating "nr_dirty".
909 *
910 * Here, in wb_position_ratio(), we calculate pos_ratio based on
911 * two values: wb_dirty and wb_thresh. Let's consider an example:
912 * total amount of RAM is 16GB, bdi->max_ratio is equal to 1%, global
913 * limits are set by default to 10% and 20% (background and throttle).
914 * Then wb_thresh is 1% of 20% of 16GB. This amounts to ~8K pages.
915 * wb_calc_thresh(wb, bg_thresh) is about ~4K pages. wb_setpoint is
916 * about ~6K pages (as the average of background and throttle wb
917 * limits). The 3rd order polynomial will provide positive feedback if
918 * wb_dirty is under wb_setpoint and vice versa.
919 *
920 * Note, that we cannot use global counters in these calculations
921 * because we want to throttle process writing to a strictlimit wb
922 * much earlier than global "freerun" is reached (~23MB vs. ~2.3GB
923 * in the example above).
924 */
925 if (unlikely(wb->bdi->capabilities & BDI_CAP_STRICTLIMIT)) {
926 long long wb_pos_ratio;
927
928 if (dtc->wb_dirty < 8) {
929 dtc->pos_ratio = min_t(long long, pos_ratio * 2,
930 2 << RATELIMIT_CALC_SHIFT);
931 return;
932 }
933
934 if (dtc->wb_dirty >= wb_thresh)
935 return;
936
937 wb_setpoint = dirty_freerun_ceiling(wb_thresh,
938 dtc->wb_bg_thresh);
939
940 if (wb_setpoint == 0 || wb_setpoint == wb_thresh)
941 return;
942
943 wb_pos_ratio = pos_ratio_polynom(wb_setpoint, dtc->wb_dirty,
944 wb_thresh);
945
946 /*
947 * Typically, for strictlimit case, wb_setpoint << setpoint
948 * and pos_ratio >> wb_pos_ratio. In the other words global
949 * state ("dirty") is not limiting factor and we have to
950 * make decision based on wb counters. But there is an
951 * important case when global pos_ratio should get precedence:
952 * global limits are exceeded (e.g. due to activities on other
953 * wb's) while given strictlimit wb is below limit.
954 *
955 * "pos_ratio * wb_pos_ratio" would work for the case above,
956 * but it would look too non-natural for the case of all
957 * activity in the system coming from a single strictlimit wb
958 * with bdi->max_ratio == 100%.
959 *
960 * Note that min() below somewhat changes the dynamics of the
961 * control system. Normally, pos_ratio value can be well over 3
962 * (when globally we are at freerun and wb is well below wb
963 * setpoint). Now the maximum pos_ratio in the same situation
964 * is 2. We might want to tweak this if we observe the control
965 * system is too slow to adapt.
966 */
967 dtc->pos_ratio = min(pos_ratio, wb_pos_ratio);
968 return;
969 }
970
971 /*
972 * We have computed basic pos_ratio above based on global situation. If
973 * the wb is over/under its share of dirty pages, we want to scale
974 * pos_ratio further down/up. That is done by the following mechanism.
975 */
976
977 /*
978 * wb setpoint
979 *
980 * f(wb_dirty) := 1.0 + k * (wb_dirty - wb_setpoint)
981 *
982 * x_intercept - wb_dirty
983 * := --------------------------
984 * x_intercept - wb_setpoint
985 *
986 * The main wb control line is a linear function that subjects to
987 *
988 * (1) f(wb_setpoint) = 1.0
989 * (2) k = - 1 / (8 * write_bw) (in single wb case)
990 * or equally: x_intercept = wb_setpoint + 8 * write_bw
991 *
992 * For single wb case, the dirty pages are observed to fluctuate
993 * regularly within range
994 * [wb_setpoint - write_bw/2, wb_setpoint + write_bw/2]
995 * for various filesystems, where (2) can yield in a reasonable 12.5%
996 * fluctuation range for pos_ratio.
997 *
998 * For JBOD case, wb_thresh (not wb_dirty!) could fluctuate up to its
999 * own size, so move the slope over accordingly and choose a slope that
1000 * yields 100% pos_ratio fluctuation on suddenly doubled wb_thresh.
1001 */
1002 if (unlikely(wb_thresh > dtc->thresh))
1003 wb_thresh = dtc->thresh;
1004 /*
1005 * It's very possible that wb_thresh is close to 0 not because the
1006 * device is slow, but that it has remained inactive for long time.
1007 * Honour such devices a reasonable good (hopefully IO efficient)
1008 * threshold, so that the occasional writes won't be blocked and active
1009 * writes can rampup the threshold quickly.
1010 */
1011 wb_thresh = max(wb_thresh, (limit - dtc->dirty) / 8);
1012 /*
1013 * scale global setpoint to wb's:
1014 * wb_setpoint = setpoint * wb_thresh / thresh
1015 */
1016 x = div_u64((u64)wb_thresh << 16, dtc->thresh | 1);
1017 wb_setpoint = setpoint * (u64)x >> 16;
1018 /*
1019 * Use span=(8*write_bw) in single wb case as indicated by
1020 * (thresh - wb_thresh ~= 0) and transit to wb_thresh in JBOD case.
1021 *
1022 * wb_thresh thresh - wb_thresh
1023 * span = --------- * (8 * write_bw) + ------------------ * wb_thresh
1024 * thresh thresh
1025 */
1026 span = (dtc->thresh - wb_thresh + 8 * write_bw) * (u64)x >> 16;
1027 x_intercept = wb_setpoint + span;
1028
1029 if (dtc->wb_dirty < x_intercept - span / 4) {
1030 pos_ratio = div64_u64(pos_ratio * (x_intercept - dtc->wb_dirty),
1031 (x_intercept - wb_setpoint) | 1);
1032 } else
1033 pos_ratio /= 4;
1034
1035 /*
1036 * wb reserve area, safeguard against dirty pool underrun and disk idle
1037 * It may push the desired control point of global dirty pages higher
1038 * than setpoint.
1039 */
1040 x_intercept = wb_thresh / 2;
1041 if (dtc->wb_dirty < x_intercept) {
1042 if (dtc->wb_dirty > x_intercept / 8)
1043 pos_ratio = div_u64(pos_ratio * x_intercept,
1044 dtc->wb_dirty);
1045 else
1046 pos_ratio *= 8;
1047 }
1048
1049 dtc->pos_ratio = pos_ratio;
1050}
1051
1052static void wb_update_write_bandwidth(struct bdi_writeback *wb,
1053 unsigned long elapsed,
1054 unsigned long written)
1055{
1056 const unsigned long period = roundup_pow_of_two(3 * HZ);
1057 unsigned long avg = wb->avg_write_bandwidth;
1058 unsigned long old = wb->write_bandwidth;
1059 u64 bw;
1060
1061 /*
1062 * bw = written * HZ / elapsed
1063 *
1064 * bw * elapsed + write_bandwidth * (period - elapsed)
1065 * write_bandwidth = ---------------------------------------------------
1066 * period
1067 *
1068 * @written may have decreased due to account_page_redirty().
1069 * Avoid underflowing @bw calculation.
1070 */
1071 bw = written - min(written, wb->written_stamp);
1072 bw *= HZ;
1073 if (unlikely(elapsed > period)) {
1074 do_div(bw, elapsed);
1075 avg = bw;
1076 goto out;
1077 }
1078 bw += (u64)wb->write_bandwidth * (period - elapsed);
1079 bw >>= ilog2(period);
1080
1081 /*
1082 * one more level of smoothing, for filtering out sudden spikes
1083 */
1084 if (avg > old && old >= (unsigned long)bw)
1085 avg -= (avg - old) >> 3;
1086
1087 if (avg < old && old <= (unsigned long)bw)
1088 avg += (old - avg) >> 3;
1089
1090out:
1091 /* keep avg > 0 to guarantee that tot > 0 if there are dirty wbs */
1092 avg = max(avg, 1LU);
1093 if (wb_has_dirty_io(wb)) {
1094 long delta = avg - wb->avg_write_bandwidth;
1095 WARN_ON_ONCE(atomic_long_add_return(delta,
1096 &wb->bdi->tot_write_bandwidth) <= 0);
1097 }
1098 wb->write_bandwidth = bw;
1099 wb->avg_write_bandwidth = avg;
1100}
1101
1102static void update_dirty_limit(struct dirty_throttle_control *dtc)
1103{
1104 struct wb_domain *dom = dtc_dom(dtc);
1105 unsigned long thresh = dtc->thresh;
1106 unsigned long limit = dom->dirty_limit;
1107
1108 /*
1109 * Follow up in one step.
1110 */
1111 if (limit < thresh) {
1112 limit = thresh;
1113 goto update;
1114 }
1115
1116 /*
1117 * Follow down slowly. Use the higher one as the target, because thresh
1118 * may drop below dirty. This is exactly the reason to introduce
1119 * dom->dirty_limit which is guaranteed to lie above the dirty pages.
1120 */
1121 thresh = max(thresh, dtc->dirty);
1122 if (limit > thresh) {
1123 limit -= (limit - thresh) >> 5;
1124 goto update;
1125 }
1126 return;
1127update:
1128 dom->dirty_limit = limit;
1129}
1130
1131static void domain_update_bandwidth(struct dirty_throttle_control *dtc,
1132 unsigned long now)
1133{
1134 struct wb_domain *dom = dtc_dom(dtc);
1135
1136 /*
1137 * check locklessly first to optimize away locking for the most time
1138 */
1139 if (time_before(now, dom->dirty_limit_tstamp + BANDWIDTH_INTERVAL))
1140 return;
1141
1142 spin_lock(&dom->lock);
1143 if (time_after_eq(now, dom->dirty_limit_tstamp + BANDWIDTH_INTERVAL)) {
1144 update_dirty_limit(dtc);
1145 dom->dirty_limit_tstamp = now;
1146 }
1147 spin_unlock(&dom->lock);
1148}
1149
1150/*
1151 * Maintain wb->dirty_ratelimit, the base dirty throttle rate.
1152 *
1153 * Normal wb tasks will be curbed at or below it in long term.
1154 * Obviously it should be around (write_bw / N) when there are N dd tasks.
1155 */
1156static void wb_update_dirty_ratelimit(struct dirty_throttle_control *dtc,
1157 unsigned long dirtied,
1158 unsigned long elapsed)
1159{
1160 struct bdi_writeback *wb = dtc->wb;
1161 unsigned long dirty = dtc->dirty;
1162 unsigned long freerun = dirty_freerun_ceiling(dtc->thresh, dtc->bg_thresh);
1163 unsigned long limit = hard_dirty_limit(dtc_dom(dtc), dtc->thresh);
1164 unsigned long setpoint = (freerun + limit) / 2;
1165 unsigned long write_bw = wb->avg_write_bandwidth;
1166 unsigned long dirty_ratelimit = wb->dirty_ratelimit;
1167 unsigned long dirty_rate;
1168 unsigned long task_ratelimit;
1169 unsigned long balanced_dirty_ratelimit;
1170 unsigned long step;
1171 unsigned long x;
1172 unsigned long shift;
1173
1174 /*
1175 * The dirty rate will match the writeout rate in long term, except
1176 * when dirty pages are truncated by userspace or re-dirtied by FS.
1177 */
1178 dirty_rate = (dirtied - wb->dirtied_stamp) * HZ / elapsed;
1179
1180 /*
1181 * task_ratelimit reflects each dd's dirty rate for the past 200ms.
1182 */
1183 task_ratelimit = (u64)dirty_ratelimit *
1184 dtc->pos_ratio >> RATELIMIT_CALC_SHIFT;
1185 task_ratelimit++; /* it helps rampup dirty_ratelimit from tiny values */
1186
1187 /*
1188 * A linear estimation of the "balanced" throttle rate. The theory is,
1189 * if there are N dd tasks, each throttled at task_ratelimit, the wb's
1190 * dirty_rate will be measured to be (N * task_ratelimit). So the below
1191 * formula will yield the balanced rate limit (write_bw / N).
1192 *
1193 * Note that the expanded form is not a pure rate feedback:
1194 * rate_(i+1) = rate_(i) * (write_bw / dirty_rate) (1)
1195 * but also takes pos_ratio into account:
1196 * rate_(i+1) = rate_(i) * (write_bw / dirty_rate) * pos_ratio (2)
1197 *
1198 * (1) is not realistic because pos_ratio also takes part in balancing
1199 * the dirty rate. Consider the state
1200 * pos_ratio = 0.5 (3)
1201 * rate = 2 * (write_bw / N) (4)
1202 * If (1) is used, it will stuck in that state! Because each dd will
1203 * be throttled at
1204 * task_ratelimit = pos_ratio * rate = (write_bw / N) (5)
1205 * yielding
1206 * dirty_rate = N * task_ratelimit = write_bw (6)
1207 * put (6) into (1) we get
1208 * rate_(i+1) = rate_(i) (7)
1209 *
1210 * So we end up using (2) to always keep
1211 * rate_(i+1) ~= (write_bw / N) (8)
1212 * regardless of the value of pos_ratio. As long as (8) is satisfied,
1213 * pos_ratio is able to drive itself to 1.0, which is not only where
1214 * the dirty count meet the setpoint, but also where the slope of
1215 * pos_ratio is most flat and hence task_ratelimit is least fluctuated.
1216 */
1217 balanced_dirty_ratelimit = div_u64((u64)task_ratelimit * write_bw,
1218 dirty_rate | 1);
1219 /*
1220 * balanced_dirty_ratelimit ~= (write_bw / N) <= write_bw
1221 */
1222 if (unlikely(balanced_dirty_ratelimit > write_bw))
1223 balanced_dirty_ratelimit = write_bw;
1224
1225 /*
1226 * We could safely do this and return immediately:
1227 *
1228 * wb->dirty_ratelimit = balanced_dirty_ratelimit;
1229 *
1230 * However to get a more stable dirty_ratelimit, the below elaborated
1231 * code makes use of task_ratelimit to filter out singular points and
1232 * limit the step size.
1233 *
1234 * The below code essentially only uses the relative value of
1235 *
1236 * task_ratelimit - dirty_ratelimit
1237 * = (pos_ratio - 1) * dirty_ratelimit
1238 *
1239 * which reflects the direction and size of dirty position error.
1240 */
1241
1242 /*
1243 * dirty_ratelimit will follow balanced_dirty_ratelimit iff
1244 * task_ratelimit is on the same side of dirty_ratelimit, too.
1245 * For example, when
1246 * - dirty_ratelimit > balanced_dirty_ratelimit
1247 * - dirty_ratelimit > task_ratelimit (dirty pages are above setpoint)
1248 * lowering dirty_ratelimit will help meet both the position and rate
1249 * control targets. Otherwise, don't update dirty_ratelimit if it will
1250 * only help meet the rate target. After all, what the users ultimately
1251 * feel and care are stable dirty rate and small position error.
1252 *
1253 * |task_ratelimit - dirty_ratelimit| is used to limit the step size
1254 * and filter out the singular points of balanced_dirty_ratelimit. Which
1255 * keeps jumping around randomly and can even leap far away at times
1256 * due to the small 200ms estimation period of dirty_rate (we want to
1257 * keep that period small to reduce time lags).
1258 */
1259 step = 0;
1260
1261 /*
1262 * For strictlimit case, calculations above were based on wb counters
1263 * and limits (starting from pos_ratio = wb_position_ratio() and up to
1264 * balanced_dirty_ratelimit = task_ratelimit * write_bw / dirty_rate).
1265 * Hence, to calculate "step" properly, we have to use wb_dirty as
1266 * "dirty" and wb_setpoint as "setpoint".
1267 *
1268 * We rampup dirty_ratelimit forcibly if wb_dirty is low because
1269 * it's possible that wb_thresh is close to zero due to inactivity
1270 * of backing device.
1271 */
1272 if (unlikely(wb->bdi->capabilities & BDI_CAP_STRICTLIMIT)) {
1273 dirty = dtc->wb_dirty;
1274 if (dtc->wb_dirty < 8)
1275 setpoint = dtc->wb_dirty + 1;
1276 else
1277 setpoint = (dtc->wb_thresh + dtc->wb_bg_thresh) / 2;
1278 }
1279
1280 if (dirty < setpoint) {
1281 x = min3(wb->balanced_dirty_ratelimit,
1282 balanced_dirty_ratelimit, task_ratelimit);
1283 if (dirty_ratelimit < x)
1284 step = x - dirty_ratelimit;
1285 } else {
1286 x = max3(wb->balanced_dirty_ratelimit,
1287 balanced_dirty_ratelimit, task_ratelimit);
1288 if (dirty_ratelimit > x)
1289 step = dirty_ratelimit - x;
1290 }
1291
1292 /*
1293 * Don't pursue 100% rate matching. It's impossible since the balanced
1294 * rate itself is constantly fluctuating. So decrease the track speed
1295 * when it gets close to the target. Helps eliminate pointless tremors.
1296 */
1297 shift = dirty_ratelimit / (2 * step + 1);
1298 if (shift < BITS_PER_LONG)
1299 step = DIV_ROUND_UP(step >> shift, 8);
1300 else
1301 step = 0;
1302
1303 if (dirty_ratelimit < balanced_dirty_ratelimit)
1304 dirty_ratelimit += step;
1305 else
1306 dirty_ratelimit -= step;
1307
1308 wb->dirty_ratelimit = max(dirty_ratelimit, 1UL);
1309 wb->balanced_dirty_ratelimit = balanced_dirty_ratelimit;
1310
1311 trace_bdi_dirty_ratelimit(wb, dirty_rate, task_ratelimit);
1312}
1313
1314static void __wb_update_bandwidth(struct dirty_throttle_control *gdtc,
1315 struct dirty_throttle_control *mdtc,
1316 unsigned long start_time,
1317 bool update_ratelimit)
1318{
1319 struct bdi_writeback *wb = gdtc->wb;
1320 unsigned long now = jiffies;
1321 unsigned long elapsed = now - wb->bw_time_stamp;
1322 unsigned long dirtied;
1323 unsigned long written;
1324
1325 lockdep_assert_held(&wb->list_lock);
1326
1327 /*
1328 * rate-limit, only update once every 200ms.
1329 */
1330 if (elapsed < BANDWIDTH_INTERVAL)
1331 return;
1332
1333 dirtied = percpu_counter_read(&wb->stat[WB_DIRTIED]);
1334 written = percpu_counter_read(&wb->stat[WB_WRITTEN]);
1335
1336 /*
1337 * Skip quiet periods when disk bandwidth is under-utilized.
1338 * (at least 1s idle time between two flusher runs)
1339 */
1340 if (elapsed > HZ && time_before(wb->bw_time_stamp, start_time))
1341 goto snapshot;
1342
1343 if (update_ratelimit) {
1344 domain_update_bandwidth(gdtc, now);
1345 wb_update_dirty_ratelimit(gdtc, dirtied, elapsed);
1346
1347 /*
1348 * @mdtc is always NULL if !CGROUP_WRITEBACK but the
1349 * compiler has no way to figure that out. Help it.
1350 */
1351 if (IS_ENABLED(CONFIG_CGROUP_WRITEBACK) && mdtc) {
1352 domain_update_bandwidth(mdtc, now);
1353 wb_update_dirty_ratelimit(mdtc, dirtied, elapsed);
1354 }
1355 }
1356 wb_update_write_bandwidth(wb, elapsed, written);
1357
1358snapshot:
1359 wb->dirtied_stamp = dirtied;
1360 wb->written_stamp = written;
1361 wb->bw_time_stamp = now;
1362}
1363
1364void wb_update_bandwidth(struct bdi_writeback *wb, unsigned long start_time)
1365{
1366 struct dirty_throttle_control gdtc = { GDTC_INIT(wb) };
1367
1368 __wb_update_bandwidth(&gdtc, NULL, start_time, false);
1369}
1370
1371/*
1372 * After a task dirtied this many pages, balance_dirty_pages_ratelimited()
1373 * will look to see if it needs to start dirty throttling.
1374 *
1375 * If dirty_poll_interval is too low, big NUMA machines will call the expensive
1376 * global_page_state() too often. So scale it near-sqrt to the safety margin
1377 * (the number of pages we may dirty without exceeding the dirty limits).
1378 */
1379static unsigned long dirty_poll_interval(unsigned long dirty,
1380 unsigned long thresh)
1381{
1382 if (thresh > dirty)
1383 return 1UL << (ilog2(thresh - dirty) >> 1);
1384
1385 return 1;
1386}
1387
1388static unsigned long wb_max_pause(struct bdi_writeback *wb,
1389 unsigned long wb_dirty)
1390{
1391 unsigned long bw = wb->avg_write_bandwidth;
1392 unsigned long t;
1393
1394 /*
1395 * Limit pause time for small memory systems. If sleeping for too long
1396 * time, a small pool of dirty/writeback pages may go empty and disk go
1397 * idle.
1398 *
1399 * 8 serves as the safety ratio.
1400 */
1401 t = wb_dirty / (1 + bw / roundup_pow_of_two(1 + HZ / 8));
1402 t++;
1403
1404 return min_t(unsigned long, t, MAX_PAUSE);
1405}
1406
1407static long wb_min_pause(struct bdi_writeback *wb,
1408 long max_pause,
1409 unsigned long task_ratelimit,
1410 unsigned long dirty_ratelimit,
1411 int *nr_dirtied_pause)
1412{
1413 long hi = ilog2(wb->avg_write_bandwidth);
1414 long lo = ilog2(wb->dirty_ratelimit);
1415 long t; /* target pause */
1416 long pause; /* estimated next pause */
1417 int pages; /* target nr_dirtied_pause */
1418
1419 /* target for 10ms pause on 1-dd case */
1420 t = max(1, HZ / 100);
1421
1422 /*
1423 * Scale up pause time for concurrent dirtiers in order to reduce CPU
1424 * overheads.
1425 *
1426 * (N * 10ms) on 2^N concurrent tasks.
1427 */
1428 if (hi > lo)
1429 t += (hi - lo) * (10 * HZ) / 1024;
1430
1431 /*
1432 * This is a bit convoluted. We try to base the next nr_dirtied_pause
1433 * on the much more stable dirty_ratelimit. However the next pause time
1434 * will be computed based on task_ratelimit and the two rate limits may
1435 * depart considerably at some time. Especially if task_ratelimit goes
1436 * below dirty_ratelimit/2 and the target pause is max_pause, the next
1437 * pause time will be max_pause*2 _trimmed down_ to max_pause. As a
1438 * result task_ratelimit won't be executed faithfully, which could
1439 * eventually bring down dirty_ratelimit.
1440 *
1441 * We apply two rules to fix it up:
1442 * 1) try to estimate the next pause time and if necessary, use a lower
1443 * nr_dirtied_pause so as not to exceed max_pause. When this happens,
1444 * nr_dirtied_pause will be "dancing" with task_ratelimit.
1445 * 2) limit the target pause time to max_pause/2, so that the normal
1446 * small fluctuations of task_ratelimit won't trigger rule (1) and
1447 * nr_dirtied_pause will remain as stable as dirty_ratelimit.
1448 */
1449 t = min(t, 1 + max_pause / 2);
1450 pages = dirty_ratelimit * t / roundup_pow_of_two(HZ);
1451
1452 /*
1453 * Tiny nr_dirtied_pause is found to hurt I/O performance in the test
1454 * case fio-mmap-randwrite-64k, which does 16*{sync read, async write}.
1455 * When the 16 consecutive reads are often interrupted by some dirty
1456 * throttling pause during the async writes, cfq will go into idles
1457 * (deadline is fine). So push nr_dirtied_pause as high as possible
1458 * until reaches DIRTY_POLL_THRESH=32 pages.
1459 */
1460 if (pages < DIRTY_POLL_THRESH) {
1461 t = max_pause;
1462 pages = dirty_ratelimit * t / roundup_pow_of_two(HZ);
1463 if (pages > DIRTY_POLL_THRESH) {
1464 pages = DIRTY_POLL_THRESH;
1465 t = HZ * DIRTY_POLL_THRESH / dirty_ratelimit;
1466 }
1467 }
1468
1469 pause = HZ * pages / (task_ratelimit + 1);
1470 if (pause > max_pause) {
1471 t = max_pause;
1472 pages = task_ratelimit * t / roundup_pow_of_two(HZ);
1473 }
1474
1475 *nr_dirtied_pause = pages;
1476 /*
1477 * The minimal pause time will normally be half the target pause time.
1478 */
1479 return pages >= DIRTY_POLL_THRESH ? 1 + t / 2 : t;
1480}
1481
1482static inline void wb_dirty_limits(struct dirty_throttle_control *dtc)
1483{
1484 struct bdi_writeback *wb = dtc->wb;
1485 unsigned long wb_reclaimable;
1486
1487 /*
1488 * wb_thresh is not treated as some limiting factor as
1489 * dirty_thresh, due to reasons
1490 * - in JBOD setup, wb_thresh can fluctuate a lot
1491 * - in a system with HDD and USB key, the USB key may somehow
1492 * go into state (wb_dirty >> wb_thresh) either because
1493 * wb_dirty starts high, or because wb_thresh drops low.
1494 * In this case we don't want to hard throttle the USB key
1495 * dirtiers for 100 seconds until wb_dirty drops under
1496 * wb_thresh. Instead the auxiliary wb control line in
1497 * wb_position_ratio() will let the dirtier task progress
1498 * at some rate <= (write_bw / 2) for bringing down wb_dirty.
1499 */
1500 dtc->wb_thresh = __wb_calc_thresh(dtc);
1501 dtc->wb_bg_thresh = dtc->thresh ?
1502 div_u64((u64)dtc->wb_thresh * dtc->bg_thresh, dtc->thresh) : 0;
1503
1504 /*
1505 * In order to avoid the stacked BDI deadlock we need
1506 * to ensure we accurately count the 'dirty' pages when
1507 * the threshold is low.
1508 *
1509 * Otherwise it would be possible to get thresh+n pages
1510 * reported dirty, even though there are thresh-m pages
1511 * actually dirty; with m+n sitting in the percpu
1512 * deltas.
1513 */
1514 if (dtc->wb_thresh < 2 * wb_stat_error(wb)) {
1515 wb_reclaimable = wb_stat_sum(wb, WB_RECLAIMABLE);
1516 dtc->wb_dirty = wb_reclaimable + wb_stat_sum(wb, WB_WRITEBACK);
1517 } else {
1518 wb_reclaimable = wb_stat(wb, WB_RECLAIMABLE);
1519 dtc->wb_dirty = wb_reclaimable + wb_stat(wb, WB_WRITEBACK);
1520 }
1521}
1522
1523/*
1524 * balance_dirty_pages() must be called by processes which are generating dirty
1525 * data. It looks at the number of dirty pages in the machine and will force
1526 * the caller to wait once crossing the (background_thresh + dirty_thresh) / 2.
1527 * If we're over `background_thresh' then the writeback threads are woken to
1528 * perform some writeout.
1529 */
1530static void balance_dirty_pages(struct address_space *mapping,
1531 struct bdi_writeback *wb,
1532 unsigned long pages_dirtied)
1533{
1534 struct dirty_throttle_control gdtc_stor = { GDTC_INIT(wb) };
1535 struct dirty_throttle_control mdtc_stor = { MDTC_INIT(wb, &gdtc_stor) };
1536 struct dirty_throttle_control * const gdtc = &gdtc_stor;
1537 struct dirty_throttle_control * const mdtc = mdtc_valid(&mdtc_stor) ?
1538 &mdtc_stor : NULL;
1539 struct dirty_throttle_control *sdtc;
1540 unsigned long nr_reclaimable; /* = file_dirty + unstable_nfs */
1541 long period;
1542 long pause;
1543 long max_pause;
1544 long min_pause;
1545 int nr_dirtied_pause;
1546 bool dirty_exceeded = false;
1547 unsigned long task_ratelimit;
1548 unsigned long dirty_ratelimit;
1549 struct backing_dev_info *bdi = wb->bdi;
1550 bool strictlimit = bdi->capabilities & BDI_CAP_STRICTLIMIT;
1551 unsigned long start_time = jiffies;
1552
1553 for (;;) {
1554 unsigned long now = jiffies;
1555 unsigned long dirty, thresh, bg_thresh;
1556 unsigned long m_dirty = 0; /* stop bogus uninit warnings */
1557 unsigned long m_thresh = 0;
1558 unsigned long m_bg_thresh = 0;
1559
1560 /*
1561 * Unstable writes are a feature of certain networked
1562 * filesystems (i.e. NFS) in which data may have been
1563 * written to the server's write cache, but has not yet
1564 * been flushed to permanent storage.
1565 */
1566 nr_reclaimable = global_page_state(NR_FILE_DIRTY) +
1567 global_page_state(NR_UNSTABLE_NFS);
1568 gdtc->avail = global_dirtyable_memory();
1569 gdtc->dirty = nr_reclaimable + global_page_state(NR_WRITEBACK);
1570
1571 domain_dirty_limits(gdtc);
1572
1573 if (unlikely(strictlimit)) {
1574 wb_dirty_limits(gdtc);
1575
1576 dirty = gdtc->wb_dirty;
1577 thresh = gdtc->wb_thresh;
1578 bg_thresh = gdtc->wb_bg_thresh;
1579 } else {
1580 dirty = gdtc->dirty;
1581 thresh = gdtc->thresh;
1582 bg_thresh = gdtc->bg_thresh;
1583 }
1584
1585 if (mdtc) {
1586 unsigned long filepages, headroom, writeback;
1587
1588 /*
1589 * If @wb belongs to !root memcg, repeat the same
1590 * basic calculations for the memcg domain.
1591 */
1592 mem_cgroup_wb_stats(wb, &filepages, &headroom,
1593 &mdtc->dirty, &writeback);
1594 mdtc->dirty += writeback;
1595 mdtc_calc_avail(mdtc, filepages, headroom);
1596
1597 domain_dirty_limits(mdtc);
1598
1599 if (unlikely(strictlimit)) {
1600 wb_dirty_limits(mdtc);
1601 m_dirty = mdtc->wb_dirty;
1602 m_thresh = mdtc->wb_thresh;
1603 m_bg_thresh = mdtc->wb_bg_thresh;
1604 } else {
1605 m_dirty = mdtc->dirty;
1606 m_thresh = mdtc->thresh;
1607 m_bg_thresh = mdtc->bg_thresh;
1608 }
1609 }
1610
1611 /*
1612 * Throttle it only when the background writeback cannot
1613 * catch-up. This avoids (excessively) small writeouts
1614 * when the wb limits are ramping up in case of !strictlimit.
1615 *
1616 * In strictlimit case make decision based on the wb counters
1617 * and limits. Small writeouts when the wb limits are ramping
1618 * up are the price we consciously pay for strictlimit-ing.
1619 *
1620 * If memcg domain is in effect, @dirty should be under
1621 * both global and memcg freerun ceilings.
1622 */
1623 if (dirty <= dirty_freerun_ceiling(thresh, bg_thresh) &&
1624 (!mdtc ||
1625 m_dirty <= dirty_freerun_ceiling(m_thresh, m_bg_thresh))) {
1626 unsigned long intv = dirty_poll_interval(dirty, thresh);
1627 unsigned long m_intv = ULONG_MAX;
1628
1629 current->dirty_paused_when = now;
1630 current->nr_dirtied = 0;
1631 if (mdtc)
1632 m_intv = dirty_poll_interval(m_dirty, m_thresh);
1633 current->nr_dirtied_pause = min(intv, m_intv);
1634 break;
1635 }
1636
1637 if (unlikely(!writeback_in_progress(wb)))
1638 wb_start_background_writeback(wb);
1639
1640 /*
1641 * Calculate global domain's pos_ratio and select the
1642 * global dtc by default.
1643 */
1644 if (!strictlimit)
1645 wb_dirty_limits(gdtc);
1646
1647 dirty_exceeded = (gdtc->wb_dirty > gdtc->wb_thresh) &&
1648 ((gdtc->dirty > gdtc->thresh) || strictlimit);
1649
1650 wb_position_ratio(gdtc);
1651 sdtc = gdtc;
1652
1653 if (mdtc) {
1654 /*
1655 * If memcg domain is in effect, calculate its
1656 * pos_ratio. @wb should satisfy constraints from
1657 * both global and memcg domains. Choose the one
1658 * w/ lower pos_ratio.
1659 */
1660 if (!strictlimit)
1661 wb_dirty_limits(mdtc);
1662
1663 dirty_exceeded |= (mdtc->wb_dirty > mdtc->wb_thresh) &&
1664 ((mdtc->dirty > mdtc->thresh) || strictlimit);
1665
1666 wb_position_ratio(mdtc);
1667 if (mdtc->pos_ratio < gdtc->pos_ratio)
1668 sdtc = mdtc;
1669 }
1670
1671 if (dirty_exceeded && !wb->dirty_exceeded)
1672 wb->dirty_exceeded = 1;
1673
1674 if (time_is_before_jiffies(wb->bw_time_stamp +
1675 BANDWIDTH_INTERVAL)) {
1676 spin_lock(&wb->list_lock);
1677 __wb_update_bandwidth(gdtc, mdtc, start_time, true);
1678 spin_unlock(&wb->list_lock);
1679 }
1680
1681 /* throttle according to the chosen dtc */
1682 dirty_ratelimit = wb->dirty_ratelimit;
1683 task_ratelimit = ((u64)dirty_ratelimit * sdtc->pos_ratio) >>
1684 RATELIMIT_CALC_SHIFT;
1685 max_pause = wb_max_pause(wb, sdtc->wb_dirty);
1686 min_pause = wb_min_pause(wb, max_pause,
1687 task_ratelimit, dirty_ratelimit,
1688 &nr_dirtied_pause);
1689
1690 if (unlikely(task_ratelimit == 0)) {
1691 period = max_pause;
1692 pause = max_pause;
1693 goto pause;
1694 }
1695 period = HZ * pages_dirtied / task_ratelimit;
1696 pause = period;
1697 if (current->dirty_paused_when)
1698 pause -= now - current->dirty_paused_when;
1699 /*
1700 * For less than 1s think time (ext3/4 may block the dirtier
1701 * for up to 800ms from time to time on 1-HDD; so does xfs,
1702 * however at much less frequency), try to compensate it in
1703 * future periods by updating the virtual time; otherwise just
1704 * do a reset, as it may be a light dirtier.
1705 */
1706 if (pause < min_pause) {
1707 trace_balance_dirty_pages(wb,
1708 sdtc->thresh,
1709 sdtc->bg_thresh,
1710 sdtc->dirty,
1711 sdtc->wb_thresh,
1712 sdtc->wb_dirty,
1713 dirty_ratelimit,
1714 task_ratelimit,
1715 pages_dirtied,
1716 period,
1717 min(pause, 0L),
1718 start_time);
1719 if (pause < -HZ) {
1720 current->dirty_paused_when = now;
1721 current->nr_dirtied = 0;
1722 } else if (period) {
1723 current->dirty_paused_when += period;
1724 current->nr_dirtied = 0;
1725 } else if (current->nr_dirtied_pause <= pages_dirtied)
1726 current->nr_dirtied_pause += pages_dirtied;
1727 break;
1728 }
1729 if (unlikely(pause > max_pause)) {
1730 /* for occasional dropped task_ratelimit */
1731 now += min(pause - max_pause, max_pause);
1732 pause = max_pause;
1733 }
1734
1735pause:
1736 trace_balance_dirty_pages(wb,
1737 sdtc->thresh,
1738 sdtc->bg_thresh,
1739 sdtc->dirty,
1740 sdtc->wb_thresh,
1741 sdtc->wb_dirty,
1742 dirty_ratelimit,
1743 task_ratelimit,
1744 pages_dirtied,
1745 period,
1746 pause,
1747 start_time);
1748 __set_current_state(TASK_KILLABLE);
1749 io_schedule_timeout(pause);
1750
1751 current->dirty_paused_when = now + pause;
1752 current->nr_dirtied = 0;
1753 current->nr_dirtied_pause = nr_dirtied_pause;
1754
1755 /*
1756 * This is typically equal to (dirty < thresh) and can also
1757 * keep "1000+ dd on a slow USB stick" under control.
1758 */
1759 if (task_ratelimit)
1760 break;
1761
1762 /*
1763 * In the case of an unresponding NFS server and the NFS dirty
1764 * pages exceeds dirty_thresh, give the other good wb's a pipe
1765 * to go through, so that tasks on them still remain responsive.
1766 *
1767 * In theory 1 page is enough to keep the comsumer-producer
1768 * pipe going: the flusher cleans 1 page => the task dirties 1
1769 * more page. However wb_dirty has accounting errors. So use
1770 * the larger and more IO friendly wb_stat_error.
1771 */
1772 if (sdtc->wb_dirty <= wb_stat_error(wb))
1773 break;
1774
1775 if (fatal_signal_pending(current))
1776 break;
1777 }
1778
1779 if (!dirty_exceeded && wb->dirty_exceeded)
1780 wb->dirty_exceeded = 0;
1781
1782 if (writeback_in_progress(wb))
1783 return;
1784
1785 /*
1786 * In laptop mode, we wait until hitting the higher threshold before
1787 * starting background writeout, and then write out all the way down
1788 * to the lower threshold. So slow writers cause minimal disk activity.
1789 *
1790 * In normal mode, we start background writeout at the lower
1791 * background_thresh, to keep the amount of dirty memory low.
1792 */
1793 if (laptop_mode)
1794 return;
1795
1796 if (nr_reclaimable > gdtc->bg_thresh)
1797 wb_start_background_writeback(wb);
1798}
1799
1800static DEFINE_PER_CPU(int, bdp_ratelimits);
1801
1802/*
1803 * Normal tasks are throttled by
1804 * loop {
1805 * dirty tsk->nr_dirtied_pause pages;
1806 * take a snap in balance_dirty_pages();
1807 * }
1808 * However there is a worst case. If every task exit immediately when dirtied
1809 * (tsk->nr_dirtied_pause - 1) pages, balance_dirty_pages() will never be
1810 * called to throttle the page dirties. The solution is to save the not yet
1811 * throttled page dirties in dirty_throttle_leaks on task exit and charge them
1812 * randomly into the running tasks. This works well for the above worst case,
1813 * as the new task will pick up and accumulate the old task's leaked dirty
1814 * count and eventually get throttled.
1815 */
1816DEFINE_PER_CPU(int, dirty_throttle_leaks) = 0;
1817
1818/**
1819 * balance_dirty_pages_ratelimited - balance dirty memory state
1820 * @mapping: address_space which was dirtied
1821 *
1822 * Processes which are dirtying memory should call in here once for each page
1823 * which was newly dirtied. The function will periodically check the system's
1824 * dirty state and will initiate writeback if needed.
1825 *
1826 * On really big machines, get_writeback_state is expensive, so try to avoid
1827 * calling it too often (ratelimiting). But once we're over the dirty memory
1828 * limit we decrease the ratelimiting by a lot, to prevent individual processes
1829 * from overshooting the limit by (ratelimit_pages) each.
1830 */
1831void balance_dirty_pages_ratelimited(struct address_space *mapping)
1832{
1833 struct inode *inode = mapping->host;
1834 struct backing_dev_info *bdi = inode_to_bdi(inode);
1835 struct bdi_writeback *wb = NULL;
1836 int ratelimit;
1837 int *p;
1838
1839 if (!bdi_cap_account_dirty(bdi))
1840 return;
1841
1842 if (inode_cgwb_enabled(inode))
1843 wb = wb_get_create_current(bdi, GFP_KERNEL);
1844 if (!wb)
1845 wb = &bdi->wb;
1846
1847 ratelimit = current->nr_dirtied_pause;
1848 if (wb->dirty_exceeded)
1849 ratelimit = min(ratelimit, 32 >> (PAGE_SHIFT - 10));
1850
1851 preempt_disable();
1852 /*
1853 * This prevents one CPU to accumulate too many dirtied pages without
1854 * calling into balance_dirty_pages(), which can happen when there are
1855 * 1000+ tasks, all of them start dirtying pages at exactly the same
1856 * time, hence all honoured too large initial task->nr_dirtied_pause.
1857 */
1858 p = this_cpu_ptr(&bdp_ratelimits);
1859 if (unlikely(current->nr_dirtied >= ratelimit))
1860 *p = 0;
1861 else if (unlikely(*p >= ratelimit_pages)) {
1862 *p = 0;
1863 ratelimit = 0;
1864 }
1865 /*
1866 * Pick up the dirtied pages by the exited tasks. This avoids lots of
1867 * short-lived tasks (eg. gcc invocations in a kernel build) escaping
1868 * the dirty throttling and livelock other long-run dirtiers.
1869 */
1870 p = this_cpu_ptr(&dirty_throttle_leaks);
1871 if (*p > 0 && current->nr_dirtied < ratelimit) {
1872 unsigned long nr_pages_dirtied;
1873 nr_pages_dirtied = min(*p, ratelimit - current->nr_dirtied);
1874 *p -= nr_pages_dirtied;
1875 current->nr_dirtied += nr_pages_dirtied;
1876 }
1877 preempt_enable();
1878
1879 if (unlikely(current->nr_dirtied >= ratelimit))
1880 balance_dirty_pages(mapping, wb, current->nr_dirtied);
1881
1882 wb_put(wb);
1883}
1884EXPORT_SYMBOL(balance_dirty_pages_ratelimited);
1885
1886/**
1887 * wb_over_bg_thresh - does @wb need to be written back?
1888 * @wb: bdi_writeback of interest
1889 *
1890 * Determines whether background writeback should keep writing @wb or it's
1891 * clean enough. Returns %true if writeback should continue.
1892 */
1893bool wb_over_bg_thresh(struct bdi_writeback *wb)
1894{
1895 struct dirty_throttle_control gdtc_stor = { GDTC_INIT(wb) };
1896 struct dirty_throttle_control mdtc_stor = { MDTC_INIT(wb, &gdtc_stor) };
1897 struct dirty_throttle_control * const gdtc = &gdtc_stor;
1898 struct dirty_throttle_control * const mdtc = mdtc_valid(&mdtc_stor) ?
1899 &mdtc_stor : NULL;
1900
1901 /*
1902 * Similar to balance_dirty_pages() but ignores pages being written
1903 * as we're trying to decide whether to put more under writeback.
1904 */
1905 gdtc->avail = global_dirtyable_memory();
1906 gdtc->dirty = global_page_state(NR_FILE_DIRTY) +
1907 global_page_state(NR_UNSTABLE_NFS);
1908 domain_dirty_limits(gdtc);
1909
1910 if (gdtc->dirty > gdtc->bg_thresh)
1911 return true;
1912
1913 if (wb_stat(wb, WB_RECLAIMABLE) >
1914 wb_calc_thresh(gdtc->wb, gdtc->bg_thresh))
1915 return true;
1916
1917 if (mdtc) {
1918 unsigned long filepages, headroom, writeback;
1919
1920 mem_cgroup_wb_stats(wb, &filepages, &headroom, &mdtc->dirty,
1921 &writeback);
1922 mdtc_calc_avail(mdtc, filepages, headroom);
1923 domain_dirty_limits(mdtc); /* ditto, ignore writeback */
1924
1925 if (mdtc->dirty > mdtc->bg_thresh)
1926 return true;
1927
1928 if (wb_stat(wb, WB_RECLAIMABLE) >
1929 wb_calc_thresh(mdtc->wb, mdtc->bg_thresh))
1930 return true;
1931 }
1932
1933 return false;
1934}
1935
1936void throttle_vm_writeout(gfp_t gfp_mask)
1937{
1938 unsigned long background_thresh;
1939 unsigned long dirty_thresh;
1940
1941 for ( ; ; ) {
1942 global_dirty_limits(&background_thresh, &dirty_thresh);
1943 dirty_thresh = hard_dirty_limit(&global_wb_domain, dirty_thresh);
1944
1945 /*
1946 * Boost the allowable dirty threshold a bit for page
1947 * allocators so they don't get DoS'ed by heavy writers
1948 */
1949 dirty_thresh += dirty_thresh / 10; /* wheeee... */
1950
1951 if (global_page_state(NR_UNSTABLE_NFS) +
1952 global_page_state(NR_WRITEBACK) <= dirty_thresh)
1953 break;
1954 congestion_wait(BLK_RW_ASYNC, HZ/10);
1955
1956 /*
1957 * The caller might hold locks which can prevent IO completion
1958 * or progress in the filesystem. So we cannot just sit here
1959 * waiting for IO to complete.
1960 */
1961 if ((gfp_mask & (__GFP_FS|__GFP_IO)) != (__GFP_FS|__GFP_IO))
1962 break;
1963 }
1964}
1965
1966/*
1967 * sysctl handler for /proc/sys/vm/dirty_writeback_centisecs
1968 */
1969int dirty_writeback_centisecs_handler(struct ctl_table *table, int write,
1970 void __user *buffer, size_t *length, loff_t *ppos)
1971{
1972 proc_dointvec(table, write, buffer, length, ppos);
1973 return 0;
1974}
1975
1976#ifdef CONFIG_BLOCK
1977void laptop_mode_timer_fn(unsigned long data)
1978{
1979 struct request_queue *q = (struct request_queue *)data;
1980 int nr_pages = global_page_state(NR_FILE_DIRTY) +
1981 global_page_state(NR_UNSTABLE_NFS);
1982 struct bdi_writeback *wb;
1983
1984 /*
1985 * We want to write everything out, not just down to the dirty
1986 * threshold
1987 */
1988 if (!bdi_has_dirty_io(&q->backing_dev_info))
1989 return;
1990
1991 rcu_read_lock();
1992 list_for_each_entry_rcu(wb, &q->backing_dev_info.wb_list, bdi_node)
1993 if (wb_has_dirty_io(wb))
1994 wb_start_writeback(wb, nr_pages, true,
1995 WB_REASON_LAPTOP_TIMER);
1996 rcu_read_unlock();
1997}
1998
1999/*
2000 * We've spun up the disk and we're in laptop mode: schedule writeback
2001 * of all dirty data a few seconds from now. If the flush is already scheduled
2002 * then push it back - the user is still using the disk.
2003 */
2004void laptop_io_completion(struct backing_dev_info *info)
2005{
2006 mod_timer(&info->laptop_mode_wb_timer, jiffies + laptop_mode);
2007}
2008
2009/*
2010 * We're in laptop mode and we've just synced. The sync's writes will have
2011 * caused another writeback to be scheduled by laptop_io_completion.
2012 * Nothing needs to be written back anymore, so we unschedule the writeback.
2013 */
2014void laptop_sync_completion(void)
2015{
2016 struct backing_dev_info *bdi;
2017
2018 rcu_read_lock();
2019
2020 list_for_each_entry_rcu(bdi, &bdi_list, bdi_list)
2021 del_timer(&bdi->laptop_mode_wb_timer);
2022
2023 rcu_read_unlock();
2024}
2025#endif
2026
2027/*
2028 * If ratelimit_pages is too high then we can get into dirty-data overload
2029 * if a large number of processes all perform writes at the same time.
2030 * If it is too low then SMP machines will call the (expensive)
2031 * get_writeback_state too often.
2032 *
2033 * Here we set ratelimit_pages to a level which ensures that when all CPUs are
2034 * dirtying in parallel, we cannot go more than 3% (1/32) over the dirty memory
2035 * thresholds.
2036 */
2037
2038void writeback_set_ratelimit(void)
2039{
2040 struct wb_domain *dom = &global_wb_domain;
2041 unsigned long background_thresh;
2042 unsigned long dirty_thresh;
2043
2044 global_dirty_limits(&background_thresh, &dirty_thresh);
2045 dom->dirty_limit = dirty_thresh;
2046 ratelimit_pages = dirty_thresh / (num_online_cpus() * 32);
2047 if (ratelimit_pages < 16)
2048 ratelimit_pages = 16;
2049}
2050
2051static int
2052ratelimit_handler(struct notifier_block *self, unsigned long action,
2053 void *hcpu)
2054{
2055
2056 switch (action & ~CPU_TASKS_FROZEN) {
2057 case CPU_ONLINE:
2058 case CPU_DEAD:
2059 writeback_set_ratelimit();
2060 return NOTIFY_OK;
2061 default:
2062 return NOTIFY_DONE;
2063 }
2064}
2065
2066static struct notifier_block ratelimit_nb = {
2067 .notifier_call = ratelimit_handler,
2068 .next = NULL,
2069};
2070
2071/*
2072 * Called early on to tune the page writeback dirty limits.
2073 *
2074 * We used to scale dirty pages according to how total memory
2075 * related to pages that could be allocated for buffers (by
2076 * comparing nr_free_buffer_pages() to vm_total_pages.
2077 *
2078 * However, that was when we used "dirty_ratio" to scale with
2079 * all memory, and we don't do that any more. "dirty_ratio"
2080 * is now applied to total non-HIGHPAGE memory (by subtracting
2081 * totalhigh_pages from vm_total_pages), and as such we can't
2082 * get into the old insane situation any more where we had
2083 * large amounts of dirty pages compared to a small amount of
2084 * non-HIGHMEM memory.
2085 *
2086 * But we might still want to scale the dirty_ratio by how
2087 * much memory the box has..
2088 */
2089void __init page_writeback_init(void)
2090{
2091 BUG_ON(wb_domain_init(&global_wb_domain, GFP_KERNEL));
2092
2093 writeback_set_ratelimit();
2094 register_cpu_notifier(&ratelimit_nb);
2095}
2096
2097/**
2098 * tag_pages_for_writeback - tag pages to be written by write_cache_pages
2099 * @mapping: address space structure to write
2100 * @start: starting page index
2101 * @end: ending page index (inclusive)
2102 *
2103 * This function scans the page range from @start to @end (inclusive) and tags
2104 * all pages that have DIRTY tag set with a special TOWRITE tag. The idea is
2105 * that write_cache_pages (or whoever calls this function) will then use
2106 * TOWRITE tag to identify pages eligible for writeback. This mechanism is
2107 * used to avoid livelocking of writeback by a process steadily creating new
2108 * dirty pages in the file (thus it is important for this function to be quick
2109 * so that it can tag pages faster than a dirtying process can create them).
2110 */
2111/*
2112 * We tag pages in batches of WRITEBACK_TAG_BATCH to reduce tree_lock latency.
2113 */
2114void tag_pages_for_writeback(struct address_space *mapping,
2115 pgoff_t start, pgoff_t end)
2116{
2117#define WRITEBACK_TAG_BATCH 4096
2118 unsigned long tagged;
2119
2120 do {
2121 spin_lock_irq(&mapping->tree_lock);
2122 tagged = radix_tree_range_tag_if_tagged(&mapping->page_tree,
2123 &start, end, WRITEBACK_TAG_BATCH,
2124 PAGECACHE_TAG_DIRTY, PAGECACHE_TAG_TOWRITE);
2125 spin_unlock_irq(&mapping->tree_lock);
2126 WARN_ON_ONCE(tagged > WRITEBACK_TAG_BATCH);
2127 cond_resched();
2128 /* We check 'start' to handle wrapping when end == ~0UL */
2129 } while (tagged >= WRITEBACK_TAG_BATCH && start);
2130}
2131EXPORT_SYMBOL(tag_pages_for_writeback);
2132
2133/**
2134 * write_cache_pages - walk the list of dirty pages of the given address space and write all of them.
2135 * @mapping: address space structure to write
2136 * @wbc: subtract the number of written pages from *@wbc->nr_to_write
2137 * @writepage: function called for each page
2138 * @data: data passed to writepage function
2139 *
2140 * If a page is already under I/O, write_cache_pages() skips it, even
2141 * if it's dirty. This is desirable behaviour for memory-cleaning writeback,
2142 * but it is INCORRECT for data-integrity system calls such as fsync(). fsync()
2143 * and msync() need to guarantee that all the data which was dirty at the time
2144 * the call was made get new I/O started against them. If wbc->sync_mode is
2145 * WB_SYNC_ALL then we were called for data integrity and we must wait for
2146 * existing IO to complete.
2147 *
2148 * To avoid livelocks (when other process dirties new pages), we first tag
2149 * pages which should be written back with TOWRITE tag and only then start
2150 * writing them. For data-integrity sync we have to be careful so that we do
2151 * not miss some pages (e.g., because some other process has cleared TOWRITE
2152 * tag we set). The rule we follow is that TOWRITE tag can be cleared only
2153 * by the process clearing the DIRTY tag (and submitting the page for IO).
2154 */
2155int write_cache_pages(struct address_space *mapping,
2156 struct writeback_control *wbc, writepage_t writepage,
2157 void *data)
2158{
2159 int ret = 0;
2160 int done = 0;
2161 struct pagevec pvec;
2162 int nr_pages;
2163 pgoff_t uninitialized_var(writeback_index);
2164 pgoff_t index;
2165 pgoff_t end; /* Inclusive */
2166 pgoff_t done_index;
2167 int cycled;
2168 int range_whole = 0;
2169 int tag;
2170
2171 pagevec_init(&pvec, 0);
2172 if (wbc->range_cyclic) {
2173 writeback_index = mapping->writeback_index; /* prev offset */
2174 index = writeback_index;
2175 if (index == 0)
2176 cycled = 1;
2177 else
2178 cycled = 0;
2179 end = -1;
2180 } else {
2181 index = wbc->range_start >> PAGE_SHIFT;
2182 end = wbc->range_end >> PAGE_SHIFT;
2183 if (wbc->range_start == 0 && wbc->range_end == LLONG_MAX)
2184 range_whole = 1;
2185 cycled = 1; /* ignore range_cyclic tests */
2186 }
2187 if (wbc->sync_mode == WB_SYNC_ALL || wbc->tagged_writepages)
2188 tag = PAGECACHE_TAG_TOWRITE;
2189 else
2190 tag = PAGECACHE_TAG_DIRTY;
2191retry:
2192 if (wbc->sync_mode == WB_SYNC_ALL || wbc->tagged_writepages)
2193 tag_pages_for_writeback(mapping, index, end);
2194 done_index = index;
2195 while (!done && (index <= end)) {
2196 int i;
2197
2198 nr_pages = pagevec_lookup_tag(&pvec, mapping, &index, tag,
2199 min(end - index, (pgoff_t)PAGEVEC_SIZE-1) + 1);
2200 if (nr_pages == 0)
2201 break;
2202
2203 for (i = 0; i < nr_pages; i++) {
2204 struct page *page = pvec.pages[i];
2205
2206 /*
2207 * At this point, the page may be truncated or
2208 * invalidated (changing page->mapping to NULL), or
2209 * even swizzled back from swapper_space to tmpfs file
2210 * mapping. However, page->index will not change
2211 * because we have a reference on the page.
2212 */
2213 if (page->index > end) {
2214 /*
2215 * can't be range_cyclic (1st pass) because
2216 * end == -1 in that case.
2217 */
2218 done = 1;
2219 break;
2220 }
2221
2222 done_index = page->index;
2223
2224 lock_page(page);
2225
2226 /*
2227 * Page truncated or invalidated. We can freely skip it
2228 * then, even for data integrity operations: the page
2229 * has disappeared concurrently, so there could be no
2230 * real expectation of this data interity operation
2231 * even if there is now a new, dirty page at the same
2232 * pagecache address.
2233 */
2234 if (unlikely(page->mapping != mapping)) {
2235continue_unlock:
2236 unlock_page(page);
2237 continue;
2238 }
2239
2240 if (!PageDirty(page)) {
2241 /* someone wrote it for us */
2242 goto continue_unlock;
2243 }
2244
2245 if (PageWriteback(page)) {
2246 if (wbc->sync_mode != WB_SYNC_NONE)
2247 wait_on_page_writeback(page);
2248 else
2249 goto continue_unlock;
2250 }
2251
2252 BUG_ON(PageWriteback(page));
2253 if (!clear_page_dirty_for_io(page))
2254 goto continue_unlock;
2255
2256 trace_wbc_writepage(wbc, inode_to_bdi(mapping->host));
2257 ret = (*writepage)(page, wbc, data);
2258 if (unlikely(ret)) {
2259 if (ret == AOP_WRITEPAGE_ACTIVATE) {
2260 unlock_page(page);
2261 ret = 0;
2262 } else {
2263 /*
2264 * done_index is set past this page,
2265 * so media errors will not choke
2266 * background writeout for the entire
2267 * file. This has consequences for
2268 * range_cyclic semantics (ie. it may
2269 * not be suitable for data integrity
2270 * writeout).
2271 */
2272 done_index = page->index + 1;
2273 done = 1;
2274 break;
2275 }
2276 }
2277
2278 /*
2279 * We stop writing back only if we are not doing
2280 * integrity sync. In case of integrity sync we have to
2281 * keep going until we have written all the pages
2282 * we tagged for writeback prior to entering this loop.
2283 */
2284 if (--wbc->nr_to_write <= 0 &&
2285 wbc->sync_mode == WB_SYNC_NONE) {
2286 done = 1;
2287 break;
2288 }
2289 }
2290 pagevec_release(&pvec);
2291 cond_resched();
2292 }
2293 if (!cycled && !done) {
2294 /*
2295 * range_cyclic:
2296 * We hit the last page and there is more work to be done: wrap
2297 * back to the start of the file
2298 */
2299 cycled = 1;
2300 index = 0;
2301 end = writeback_index - 1;
2302 goto retry;
2303 }
2304 if (wbc->range_cyclic || (range_whole && wbc->nr_to_write > 0))
2305 mapping->writeback_index = done_index;
2306
2307 return ret;
2308}
2309EXPORT_SYMBOL(write_cache_pages);
2310
2311/*
2312 * Function used by generic_writepages to call the real writepage
2313 * function and set the mapping flags on error
2314 */
2315static int __writepage(struct page *page, struct writeback_control *wbc,
2316 void *data)
2317{
2318 struct address_space *mapping = data;
2319 int ret = mapping->a_ops->writepage(page, wbc);
2320 mapping_set_error(mapping, ret);
2321 return ret;
2322}
2323
2324/**
2325 * generic_writepages - walk the list of dirty pages of the given address space and writepage() all of them.
2326 * @mapping: address space structure to write
2327 * @wbc: subtract the number of written pages from *@wbc->nr_to_write
2328 *
2329 * This is a library function, which implements the writepages()
2330 * address_space_operation.
2331 */
2332int generic_writepages(struct address_space *mapping,
2333 struct writeback_control *wbc)
2334{
2335 struct blk_plug plug;
2336 int ret;
2337
2338 /* deal with chardevs and other special file */
2339 if (!mapping->a_ops->writepage)
2340 return 0;
2341
2342 blk_start_plug(&plug);
2343 ret = write_cache_pages(mapping, wbc, __writepage, mapping);
2344 blk_finish_plug(&plug);
2345 return ret;
2346}
2347
2348EXPORT_SYMBOL(generic_writepages);
2349
2350int do_writepages(struct address_space *mapping, struct writeback_control *wbc)
2351{
2352 int ret;
2353
2354 if (wbc->nr_to_write <= 0)
2355 return 0;
2356 if (mapping->a_ops->writepages)
2357 ret = mapping->a_ops->writepages(mapping, wbc);
2358 else
2359 ret = generic_writepages(mapping, wbc);
2360 return ret;
2361}
2362
2363/**
2364 * write_one_page - write out a single page and optionally wait on I/O
2365 * @page: the page to write
2366 * @wait: if true, wait on writeout
2367 *
2368 * The page must be locked by the caller and will be unlocked upon return.
2369 *
2370 * write_one_page() returns a negative error code if I/O failed.
2371 */
2372int write_one_page(struct page *page, int wait)
2373{
2374 struct address_space *mapping = page->mapping;
2375 int ret = 0;
2376 struct writeback_control wbc = {
2377 .sync_mode = WB_SYNC_ALL,
2378 .nr_to_write = 1,
2379 };
2380
2381 BUG_ON(!PageLocked(page));
2382
2383 if (wait)
2384 wait_on_page_writeback(page);
2385
2386 if (clear_page_dirty_for_io(page)) {
2387 get_page(page);
2388 ret = mapping->a_ops->writepage(page, &wbc);
2389 if (ret == 0 && wait) {
2390 wait_on_page_writeback(page);
2391 if (PageError(page))
2392 ret = -EIO;
2393 }
2394 put_page(page);
2395 } else {
2396 unlock_page(page);
2397 }
2398 return ret;
2399}
2400EXPORT_SYMBOL(write_one_page);
2401
2402/*
2403 * For address_spaces which do not use buffers nor write back.
2404 */
2405int __set_page_dirty_no_writeback(struct page *page)
2406{
2407 if (!PageDirty(page))
2408 return !TestSetPageDirty(page);
2409 return 0;
2410}
2411
2412/*
2413 * Helper function for set_page_dirty family.
2414 *
2415 * Caller must hold lock_page_memcg().
2416 *
2417 * NOTE: This relies on being atomic wrt interrupts.
2418 */
2419void account_page_dirtied(struct page *page, struct address_space *mapping)
2420{
2421 struct inode *inode = mapping->host;
2422
2423 trace_writeback_dirty_page(page, mapping);
2424
2425 if (mapping_cap_account_dirty(mapping)) {
2426 struct bdi_writeback *wb;
2427
2428 inode_attach_wb(inode, page);
2429 wb = inode_to_wb(inode);
2430
2431 mem_cgroup_inc_page_stat(page, MEM_CGROUP_STAT_DIRTY);
2432 __inc_zone_page_state(page, NR_FILE_DIRTY);
2433 __inc_zone_page_state(page, NR_DIRTIED);
2434 __inc_wb_stat(wb, WB_RECLAIMABLE);
2435 __inc_wb_stat(wb, WB_DIRTIED);
2436 task_io_account_write(PAGE_SIZE);
2437 current->nr_dirtied++;
2438 this_cpu_inc(bdp_ratelimits);
2439 }
2440}
2441EXPORT_SYMBOL(account_page_dirtied);
2442
2443/*
2444 * Helper function for deaccounting dirty page without writeback.
2445 *
2446 * Caller must hold lock_page_memcg().
2447 */
2448void account_page_cleaned(struct page *page, struct address_space *mapping,
2449 struct bdi_writeback *wb)
2450{
2451 if (mapping_cap_account_dirty(mapping)) {
2452 mem_cgroup_dec_page_stat(page, MEM_CGROUP_STAT_DIRTY);
2453 dec_zone_page_state(page, NR_FILE_DIRTY);
2454 dec_wb_stat(wb, WB_RECLAIMABLE);
2455 task_io_account_cancelled_write(PAGE_SIZE);
2456 }
2457}
2458
2459/*
2460 * For address_spaces which do not use buffers. Just tag the page as dirty in
2461 * its radix tree.
2462 *
2463 * This is also used when a single buffer is being dirtied: we want to set the
2464 * page dirty in that case, but not all the buffers. This is a "bottom-up"
2465 * dirtying, whereas __set_page_dirty_buffers() is a "top-down" dirtying.
2466 *
2467 * The caller must ensure this doesn't race with truncation. Most will simply
2468 * hold the page lock, but e.g. zap_pte_range() calls with the page mapped and
2469 * the pte lock held, which also locks out truncation.
2470 */
2471int __set_page_dirty_nobuffers(struct page *page)
2472{
2473 lock_page_memcg(page);
2474 if (!TestSetPageDirty(page)) {
2475 struct address_space *mapping = page_mapping(page);
2476 unsigned long flags;
2477
2478 if (!mapping) {
2479 unlock_page_memcg(page);
2480 return 1;
2481 }
2482
2483 spin_lock_irqsave(&mapping->tree_lock, flags);
2484 BUG_ON(page_mapping(page) != mapping);
2485 WARN_ON_ONCE(!PagePrivate(page) && !PageUptodate(page));
2486 account_page_dirtied(page, mapping);
2487 radix_tree_tag_set(&mapping->page_tree, page_index(page),
2488 PAGECACHE_TAG_DIRTY);
2489 spin_unlock_irqrestore(&mapping->tree_lock, flags);
2490 unlock_page_memcg(page);
2491
2492 if (mapping->host) {
2493 /* !PageAnon && !swapper_space */
2494 __mark_inode_dirty(mapping->host, I_DIRTY_PAGES);
2495 }
2496 return 1;
2497 }
2498 unlock_page_memcg(page);
2499 return 0;
2500}
2501EXPORT_SYMBOL(__set_page_dirty_nobuffers);
2502
2503/*
2504 * Call this whenever redirtying a page, to de-account the dirty counters
2505 * (NR_DIRTIED, BDI_DIRTIED, tsk->nr_dirtied), so that they match the written
2506 * counters (NR_WRITTEN, BDI_WRITTEN) in long term. The mismatches will lead to
2507 * systematic errors in balanced_dirty_ratelimit and the dirty pages position
2508 * control.
2509 */
2510void account_page_redirty(struct page *page)
2511{
2512 struct address_space *mapping = page->mapping;
2513
2514 if (mapping && mapping_cap_account_dirty(mapping)) {
2515 struct inode *inode = mapping->host;
2516 struct bdi_writeback *wb;
2517 bool locked;
2518
2519 wb = unlocked_inode_to_wb_begin(inode, &locked);
2520 current->nr_dirtied--;
2521 dec_zone_page_state(page, NR_DIRTIED);
2522 dec_wb_stat(wb, WB_DIRTIED);
2523 unlocked_inode_to_wb_end(inode, locked);
2524 }
2525}
2526EXPORT_SYMBOL(account_page_redirty);
2527
2528/*
2529 * When a writepage implementation decides that it doesn't want to write this
2530 * page for some reason, it should redirty the locked page via
2531 * redirty_page_for_writepage() and it should then unlock the page and return 0
2532 */
2533int redirty_page_for_writepage(struct writeback_control *wbc, struct page *page)
2534{
2535 int ret;
2536
2537 wbc->pages_skipped++;
2538 ret = __set_page_dirty_nobuffers(page);
2539 account_page_redirty(page);
2540 return ret;
2541}
2542EXPORT_SYMBOL(redirty_page_for_writepage);
2543
2544/*
2545 * Dirty a page.
2546 *
2547 * For pages with a mapping this should be done under the page lock
2548 * for the benefit of asynchronous memory errors who prefer a consistent
2549 * dirty state. This rule can be broken in some special cases,
2550 * but should be better not to.
2551 *
2552 * If the mapping doesn't provide a set_page_dirty a_op, then
2553 * just fall through and assume that it wants buffer_heads.
2554 */
2555int set_page_dirty(struct page *page)
2556{
2557 struct address_space *mapping = page_mapping(page);
2558
2559 if (likely(mapping)) {
2560 int (*spd)(struct page *) = mapping->a_ops->set_page_dirty;
2561 /*
2562 * readahead/lru_deactivate_page could remain
2563 * PG_readahead/PG_reclaim due to race with end_page_writeback
2564 * About readahead, if the page is written, the flags would be
2565 * reset. So no problem.
2566 * About lru_deactivate_page, if the page is redirty, the flag
2567 * will be reset. So no problem. but if the page is used by readahead
2568 * it will confuse readahead and make it restart the size rampup
2569 * process. But it's a trivial problem.
2570 */
2571 if (PageReclaim(page))
2572 ClearPageReclaim(page);
2573#ifdef CONFIG_BLOCK
2574 if (!spd)
2575 spd = __set_page_dirty_buffers;
2576#endif
2577 return (*spd)(page);
2578 }
2579 if (!PageDirty(page)) {
2580 if (!TestSetPageDirty(page))
2581 return 1;
2582 }
2583 return 0;
2584}
2585EXPORT_SYMBOL(set_page_dirty);
2586
2587/*
2588 * set_page_dirty() is racy if the caller has no reference against
2589 * page->mapping->host, and if the page is unlocked. This is because another
2590 * CPU could truncate the page off the mapping and then free the mapping.
2591 *
2592 * Usually, the page _is_ locked, or the caller is a user-space process which
2593 * holds a reference on the inode by having an open file.
2594 *
2595 * In other cases, the page should be locked before running set_page_dirty().
2596 */
2597int set_page_dirty_lock(struct page *page)
2598{
2599 int ret;
2600
2601 lock_page(page);
2602 ret = set_page_dirty(page);
2603 unlock_page(page);
2604 return ret;
2605}
2606EXPORT_SYMBOL(set_page_dirty_lock);
2607
2608/*
2609 * This cancels just the dirty bit on the kernel page itself, it does NOT
2610 * actually remove dirty bits on any mmap's that may be around. It also
2611 * leaves the page tagged dirty, so any sync activity will still find it on
2612 * the dirty lists, and in particular, clear_page_dirty_for_io() will still
2613 * look at the dirty bits in the VM.
2614 *
2615 * Doing this should *normally* only ever be done when a page is truncated,
2616 * and is not actually mapped anywhere at all. However, fs/buffer.c does
2617 * this when it notices that somebody has cleaned out all the buffers on a
2618 * page without actually doing it through the VM. Can you say "ext3 is
2619 * horribly ugly"? Thought you could.
2620 */
2621void cancel_dirty_page(struct page *page)
2622{
2623 struct address_space *mapping = page_mapping(page);
2624
2625 if (mapping_cap_account_dirty(mapping)) {
2626 struct inode *inode = mapping->host;
2627 struct bdi_writeback *wb;
2628 bool locked;
2629
2630 lock_page_memcg(page);
2631 wb = unlocked_inode_to_wb_begin(inode, &locked);
2632
2633 if (TestClearPageDirty(page))
2634 account_page_cleaned(page, mapping, wb);
2635
2636 unlocked_inode_to_wb_end(inode, locked);
2637 unlock_page_memcg(page);
2638 } else {
2639 ClearPageDirty(page);
2640 }
2641}
2642EXPORT_SYMBOL(cancel_dirty_page);
2643
2644/*
2645 * Clear a page's dirty flag, while caring for dirty memory accounting.
2646 * Returns true if the page was previously dirty.
2647 *
2648 * This is for preparing to put the page under writeout. We leave the page
2649 * tagged as dirty in the radix tree so that a concurrent write-for-sync
2650 * can discover it via a PAGECACHE_TAG_DIRTY walk. The ->writepage
2651 * implementation will run either set_page_writeback() or set_page_dirty(),
2652 * at which stage we bring the page's dirty flag and radix-tree dirty tag
2653 * back into sync.
2654 *
2655 * This incoherency between the page's dirty flag and radix-tree tag is
2656 * unfortunate, but it only exists while the page is locked.
2657 */
2658int clear_page_dirty_for_io(struct page *page)
2659{
2660 struct address_space *mapping = page_mapping(page);
2661 int ret = 0;
2662
2663 BUG_ON(!PageLocked(page));
2664
2665 if (mapping && mapping_cap_account_dirty(mapping)) {
2666 struct inode *inode = mapping->host;
2667 struct bdi_writeback *wb;
2668 bool locked;
2669
2670 /*
2671 * Yes, Virginia, this is indeed insane.
2672 *
2673 * We use this sequence to make sure that
2674 * (a) we account for dirty stats properly
2675 * (b) we tell the low-level filesystem to
2676 * mark the whole page dirty if it was
2677 * dirty in a pagetable. Only to then
2678 * (c) clean the page again and return 1 to
2679 * cause the writeback.
2680 *
2681 * This way we avoid all nasty races with the
2682 * dirty bit in multiple places and clearing
2683 * them concurrently from different threads.
2684 *
2685 * Note! Normally the "set_page_dirty(page)"
2686 * has no effect on the actual dirty bit - since
2687 * that will already usually be set. But we
2688 * need the side effects, and it can help us
2689 * avoid races.
2690 *
2691 * We basically use the page "master dirty bit"
2692 * as a serialization point for all the different
2693 * threads doing their things.
2694 */
2695 if (page_mkclean(page))
2696 set_page_dirty(page);
2697 /*
2698 * We carefully synchronise fault handlers against
2699 * installing a dirty pte and marking the page dirty
2700 * at this point. We do this by having them hold the
2701 * page lock while dirtying the page, and pages are
2702 * always locked coming in here, so we get the desired
2703 * exclusion.
2704 */
2705 wb = unlocked_inode_to_wb_begin(inode, &locked);
2706 if (TestClearPageDirty(page)) {
2707 mem_cgroup_dec_page_stat(page, MEM_CGROUP_STAT_DIRTY);
2708 dec_zone_page_state(page, NR_FILE_DIRTY);
2709 dec_wb_stat(wb, WB_RECLAIMABLE);
2710 ret = 1;
2711 }
2712 unlocked_inode_to_wb_end(inode, locked);
2713 return ret;
2714 }
2715 return TestClearPageDirty(page);
2716}
2717EXPORT_SYMBOL(clear_page_dirty_for_io);
2718
2719int test_clear_page_writeback(struct page *page)
2720{
2721 struct address_space *mapping = page_mapping(page);
2722 int ret;
2723
2724 lock_page_memcg(page);
2725 if (mapping) {
2726 struct inode *inode = mapping->host;
2727 struct backing_dev_info *bdi = inode_to_bdi(inode);
2728 unsigned long flags;
2729
2730 spin_lock_irqsave(&mapping->tree_lock, flags);
2731 ret = TestClearPageWriteback(page);
2732 if (ret) {
2733 radix_tree_tag_clear(&mapping->page_tree,
2734 page_index(page),
2735 PAGECACHE_TAG_WRITEBACK);
2736 if (bdi_cap_account_writeback(bdi)) {
2737 struct bdi_writeback *wb = inode_to_wb(inode);
2738
2739 __dec_wb_stat(wb, WB_WRITEBACK);
2740 __wb_writeout_inc(wb);
2741 }
2742 }
2743 spin_unlock_irqrestore(&mapping->tree_lock, flags);
2744 } else {
2745 ret = TestClearPageWriteback(page);
2746 }
2747 if (ret) {
2748 mem_cgroup_dec_page_stat(page, MEM_CGROUP_STAT_WRITEBACK);
2749 dec_zone_page_state(page, NR_WRITEBACK);
2750 inc_zone_page_state(page, NR_WRITTEN);
2751 }
2752 unlock_page_memcg(page);
2753 return ret;
2754}
2755
2756int __test_set_page_writeback(struct page *page, bool keep_write)
2757{
2758 struct address_space *mapping = page_mapping(page);
2759 int ret;
2760
2761 lock_page_memcg(page);
2762 if (mapping) {
2763 struct inode *inode = mapping->host;
2764 struct backing_dev_info *bdi = inode_to_bdi(inode);
2765 unsigned long flags;
2766
2767 spin_lock_irqsave(&mapping->tree_lock, flags);
2768 ret = TestSetPageWriteback(page);
2769 if (!ret) {
2770 radix_tree_tag_set(&mapping->page_tree,
2771 page_index(page),
2772 PAGECACHE_TAG_WRITEBACK);
2773 if (bdi_cap_account_writeback(bdi))
2774 __inc_wb_stat(inode_to_wb(inode), WB_WRITEBACK);
2775 }
2776 if (!PageDirty(page))
2777 radix_tree_tag_clear(&mapping->page_tree,
2778 page_index(page),
2779 PAGECACHE_TAG_DIRTY);
2780 if (!keep_write)
2781 radix_tree_tag_clear(&mapping->page_tree,
2782 page_index(page),
2783 PAGECACHE_TAG_TOWRITE);
2784 spin_unlock_irqrestore(&mapping->tree_lock, flags);
2785 } else {
2786 ret = TestSetPageWriteback(page);
2787 }
2788 if (!ret) {
2789 mem_cgroup_inc_page_stat(page, MEM_CGROUP_STAT_WRITEBACK);
2790 inc_zone_page_state(page, NR_WRITEBACK);
2791 }
2792 unlock_page_memcg(page);
2793 return ret;
2794
2795}
2796EXPORT_SYMBOL(__test_set_page_writeback);
2797
2798/*
2799 * Return true if any of the pages in the mapping are marked with the
2800 * passed tag.
2801 */
2802int mapping_tagged(struct address_space *mapping, int tag)
2803{
2804 return radix_tree_tagged(&mapping->page_tree, tag);
2805}
2806EXPORT_SYMBOL(mapping_tagged);
2807
2808/**
2809 * wait_for_stable_page() - wait for writeback to finish, if necessary.
2810 * @page: The page to wait on.
2811 *
2812 * This function determines if the given page is related to a backing device
2813 * that requires page contents to be held stable during writeback. If so, then
2814 * it will wait for any pending writeback to complete.
2815 */
2816void wait_for_stable_page(struct page *page)
2817{
2818 if (bdi_cap_stable_pages_required(inode_to_bdi(page->mapping->host)))
2819 wait_on_page_writeback(page);
2820}
2821EXPORT_SYMBOL_GPL(wait_for_stable_page);
1/*
2 * mm/page-writeback.c
3 *
4 * Copyright (C) 2002, Linus Torvalds.
5 * Copyright (C) 2007 Red Hat, Inc., Peter Zijlstra <pzijlstr@redhat.com>
6 *
7 * Contains functions related to writing back dirty pages at the
8 * address_space level.
9 *
10 * 10Apr2002 Andrew Morton
11 * Initial version
12 */
13
14#include <linux/kernel.h>
15#include <linux/export.h>
16#include <linux/spinlock.h>
17#include <linux/fs.h>
18#include <linux/mm.h>
19#include <linux/swap.h>
20#include <linux/slab.h>
21#include <linux/pagemap.h>
22#include <linux/writeback.h>
23#include <linux/init.h>
24#include <linux/backing-dev.h>
25#include <linux/task_io_accounting_ops.h>
26#include <linux/blkdev.h>
27#include <linux/mpage.h>
28#include <linux/rmap.h>
29#include <linux/percpu.h>
30#include <linux/notifier.h>
31#include <linux/smp.h>
32#include <linux/sysctl.h>
33#include <linux/cpu.h>
34#include <linux/syscalls.h>
35#include <linux/buffer_head.h> /* __set_page_dirty_buffers */
36#include <linux/pagevec.h>
37#include <linux/timer.h>
38#include <linux/sched/rt.h>
39#include <linux/mm_inline.h>
40#include <trace/events/writeback.h>
41
42#include "internal.h"
43
44/*
45 * Sleep at most 200ms at a time in balance_dirty_pages().
46 */
47#define MAX_PAUSE max(HZ/5, 1)
48
49/*
50 * Try to keep balance_dirty_pages() call intervals higher than this many pages
51 * by raising pause time to max_pause when falls below it.
52 */
53#define DIRTY_POLL_THRESH (128 >> (PAGE_SHIFT - 10))
54
55/*
56 * Estimate write bandwidth at 200ms intervals.
57 */
58#define BANDWIDTH_INTERVAL max(HZ/5, 1)
59
60#define RATELIMIT_CALC_SHIFT 10
61
62/*
63 * After a CPU has dirtied this many pages, balance_dirty_pages_ratelimited
64 * will look to see if it needs to force writeback or throttling.
65 */
66static long ratelimit_pages = 32;
67
68/* The following parameters are exported via /proc/sys/vm */
69
70/*
71 * Start background writeback (via writeback threads) at this percentage
72 */
73int dirty_background_ratio = 10;
74
75/*
76 * dirty_background_bytes starts at 0 (disabled) so that it is a function of
77 * dirty_background_ratio * the amount of dirtyable memory
78 */
79unsigned long dirty_background_bytes;
80
81/*
82 * free highmem will not be subtracted from the total free memory
83 * for calculating free ratios if vm_highmem_is_dirtyable is true
84 */
85int vm_highmem_is_dirtyable;
86
87/*
88 * The generator of dirty data starts writeback at this percentage
89 */
90int vm_dirty_ratio = 20;
91
92/*
93 * vm_dirty_bytes starts at 0 (disabled) so that it is a function of
94 * vm_dirty_ratio * the amount of dirtyable memory
95 */
96unsigned long vm_dirty_bytes;
97
98/*
99 * The interval between `kupdate'-style writebacks
100 */
101unsigned int dirty_writeback_interval = 5 * 100; /* centiseconds */
102
103EXPORT_SYMBOL_GPL(dirty_writeback_interval);
104
105/*
106 * The longest time for which data is allowed to remain dirty
107 */
108unsigned int dirty_expire_interval = 30 * 100; /* centiseconds */
109
110/*
111 * Flag that makes the machine dump writes/reads and block dirtyings.
112 */
113int block_dump;
114
115/*
116 * Flag that puts the machine in "laptop mode". Doubles as a timeout in jiffies:
117 * a full sync is triggered after this time elapses without any disk activity.
118 */
119int laptop_mode;
120
121EXPORT_SYMBOL(laptop_mode);
122
123/* End of sysctl-exported parameters */
124
125unsigned long global_dirty_limit;
126
127/*
128 * Scale the writeback cache size proportional to the relative writeout speeds.
129 *
130 * We do this by keeping a floating proportion between BDIs, based on page
131 * writeback completions [end_page_writeback()]. Those devices that write out
132 * pages fastest will get the larger share, while the slower will get a smaller
133 * share.
134 *
135 * We use page writeout completions because we are interested in getting rid of
136 * dirty pages. Having them written out is the primary goal.
137 *
138 * We introduce a concept of time, a period over which we measure these events,
139 * because demand can/will vary over time. The length of this period itself is
140 * measured in page writeback completions.
141 *
142 */
143static struct fprop_global writeout_completions;
144
145static void writeout_period(unsigned long t);
146/* Timer for aging of writeout_completions */
147static struct timer_list writeout_period_timer =
148 TIMER_DEFERRED_INITIALIZER(writeout_period, 0, 0);
149static unsigned long writeout_period_time = 0;
150
151/*
152 * Length of period for aging writeout fractions of bdis. This is an
153 * arbitrarily chosen number. The longer the period, the slower fractions will
154 * reflect changes in current writeout rate.
155 */
156#define VM_COMPLETIONS_PERIOD_LEN (3*HZ)
157
158/*
159 * Work out the current dirty-memory clamping and background writeout
160 * thresholds.
161 *
162 * The main aim here is to lower them aggressively if there is a lot of mapped
163 * memory around. To avoid stressing page reclaim with lots of unreclaimable
164 * pages. It is better to clamp down on writers than to start swapping, and
165 * performing lots of scanning.
166 *
167 * We only allow 1/2 of the currently-unmapped memory to be dirtied.
168 *
169 * We don't permit the clamping level to fall below 5% - that is getting rather
170 * excessive.
171 *
172 * We make sure that the background writeout level is below the adjusted
173 * clamping level.
174 */
175
176/*
177 * In a memory zone, there is a certain amount of pages we consider
178 * available for the page cache, which is essentially the number of
179 * free and reclaimable pages, minus some zone reserves to protect
180 * lowmem and the ability to uphold the zone's watermarks without
181 * requiring writeback.
182 *
183 * This number of dirtyable pages is the base value of which the
184 * user-configurable dirty ratio is the effictive number of pages that
185 * are allowed to be actually dirtied. Per individual zone, or
186 * globally by using the sum of dirtyable pages over all zones.
187 *
188 * Because the user is allowed to specify the dirty limit globally as
189 * absolute number of bytes, calculating the per-zone dirty limit can
190 * require translating the configured limit into a percentage of
191 * global dirtyable memory first.
192 */
193
194/**
195 * zone_dirtyable_memory - number of dirtyable pages in a zone
196 * @zone: the zone
197 *
198 * Returns the zone's number of pages potentially available for dirty
199 * page cache. This is the base value for the per-zone dirty limits.
200 */
201static unsigned long zone_dirtyable_memory(struct zone *zone)
202{
203 unsigned long nr_pages;
204
205 nr_pages = zone_page_state(zone, NR_FREE_PAGES);
206 nr_pages -= min(nr_pages, zone->dirty_balance_reserve);
207
208 nr_pages += zone_page_state(zone, NR_INACTIVE_FILE);
209 nr_pages += zone_page_state(zone, NR_ACTIVE_FILE);
210
211 return nr_pages;
212}
213
214static unsigned long highmem_dirtyable_memory(unsigned long total)
215{
216#ifdef CONFIG_HIGHMEM
217 int node;
218 unsigned long x = 0;
219
220 for_each_node_state(node, N_HIGH_MEMORY) {
221 struct zone *z = &NODE_DATA(node)->node_zones[ZONE_HIGHMEM];
222
223 x += zone_dirtyable_memory(z);
224 }
225 /*
226 * Unreclaimable memory (kernel memory or anonymous memory
227 * without swap) can bring down the dirtyable pages below
228 * the zone's dirty balance reserve and the above calculation
229 * will underflow. However we still want to add in nodes
230 * which are below threshold (negative values) to get a more
231 * accurate calculation but make sure that the total never
232 * underflows.
233 */
234 if ((long)x < 0)
235 x = 0;
236
237 /*
238 * Make sure that the number of highmem pages is never larger
239 * than the number of the total dirtyable memory. This can only
240 * occur in very strange VM situations but we want to make sure
241 * that this does not occur.
242 */
243 return min(x, total);
244#else
245 return 0;
246#endif
247}
248
249/**
250 * global_dirtyable_memory - number of globally dirtyable pages
251 *
252 * Returns the global number of pages potentially available for dirty
253 * page cache. This is the base value for the global dirty limits.
254 */
255static unsigned long global_dirtyable_memory(void)
256{
257 unsigned long x;
258
259 x = global_page_state(NR_FREE_PAGES);
260 x -= min(x, dirty_balance_reserve);
261
262 x += global_page_state(NR_INACTIVE_FILE);
263 x += global_page_state(NR_ACTIVE_FILE);
264
265 if (!vm_highmem_is_dirtyable)
266 x -= highmem_dirtyable_memory(x);
267
268 return x + 1; /* Ensure that we never return 0 */
269}
270
271/*
272 * global_dirty_limits - background-writeback and dirty-throttling thresholds
273 *
274 * Calculate the dirty thresholds based on sysctl parameters
275 * - vm.dirty_background_ratio or vm.dirty_background_bytes
276 * - vm.dirty_ratio or vm.dirty_bytes
277 * The dirty limits will be lifted by 1/4 for PF_LESS_THROTTLE (ie. nfsd) and
278 * real-time tasks.
279 */
280void global_dirty_limits(unsigned long *pbackground, unsigned long *pdirty)
281{
282 unsigned long background;
283 unsigned long dirty;
284 unsigned long uninitialized_var(available_memory);
285 struct task_struct *tsk;
286
287 if (!vm_dirty_bytes || !dirty_background_bytes)
288 available_memory = global_dirtyable_memory();
289
290 if (vm_dirty_bytes)
291 dirty = DIV_ROUND_UP(vm_dirty_bytes, PAGE_SIZE);
292 else
293 dirty = (vm_dirty_ratio * available_memory) / 100;
294
295 if (dirty_background_bytes)
296 background = DIV_ROUND_UP(dirty_background_bytes, PAGE_SIZE);
297 else
298 background = (dirty_background_ratio * available_memory) / 100;
299
300 if (background >= dirty)
301 background = dirty / 2;
302 tsk = current;
303 if (tsk->flags & PF_LESS_THROTTLE || rt_task(tsk)) {
304 background += background / 4;
305 dirty += dirty / 4;
306 }
307 *pbackground = background;
308 *pdirty = dirty;
309 trace_global_dirty_state(background, dirty);
310}
311
312/**
313 * zone_dirty_limit - maximum number of dirty pages allowed in a zone
314 * @zone: the zone
315 *
316 * Returns the maximum number of dirty pages allowed in a zone, based
317 * on the zone's dirtyable memory.
318 */
319static unsigned long zone_dirty_limit(struct zone *zone)
320{
321 unsigned long zone_memory = zone_dirtyable_memory(zone);
322 struct task_struct *tsk = current;
323 unsigned long dirty;
324
325 if (vm_dirty_bytes)
326 dirty = DIV_ROUND_UP(vm_dirty_bytes, PAGE_SIZE) *
327 zone_memory / global_dirtyable_memory();
328 else
329 dirty = vm_dirty_ratio * zone_memory / 100;
330
331 if (tsk->flags & PF_LESS_THROTTLE || rt_task(tsk))
332 dirty += dirty / 4;
333
334 return dirty;
335}
336
337/**
338 * zone_dirty_ok - tells whether a zone is within its dirty limits
339 * @zone: the zone to check
340 *
341 * Returns %true when the dirty pages in @zone are within the zone's
342 * dirty limit, %false if the limit is exceeded.
343 */
344bool zone_dirty_ok(struct zone *zone)
345{
346 unsigned long limit = zone_dirty_limit(zone);
347
348 return zone_page_state(zone, NR_FILE_DIRTY) +
349 zone_page_state(zone, NR_UNSTABLE_NFS) +
350 zone_page_state(zone, NR_WRITEBACK) <= limit;
351}
352
353int dirty_background_ratio_handler(struct ctl_table *table, int write,
354 void __user *buffer, size_t *lenp,
355 loff_t *ppos)
356{
357 int ret;
358
359 ret = proc_dointvec_minmax(table, write, buffer, lenp, ppos);
360 if (ret == 0 && write)
361 dirty_background_bytes = 0;
362 return ret;
363}
364
365int dirty_background_bytes_handler(struct ctl_table *table, int write,
366 void __user *buffer, size_t *lenp,
367 loff_t *ppos)
368{
369 int ret;
370
371 ret = proc_doulongvec_minmax(table, write, buffer, lenp, ppos);
372 if (ret == 0 && write)
373 dirty_background_ratio = 0;
374 return ret;
375}
376
377int dirty_ratio_handler(struct ctl_table *table, int write,
378 void __user *buffer, size_t *lenp,
379 loff_t *ppos)
380{
381 int old_ratio = vm_dirty_ratio;
382 int ret;
383
384 ret = proc_dointvec_minmax(table, write, buffer, lenp, ppos);
385 if (ret == 0 && write && vm_dirty_ratio != old_ratio) {
386 writeback_set_ratelimit();
387 vm_dirty_bytes = 0;
388 }
389 return ret;
390}
391
392int dirty_bytes_handler(struct ctl_table *table, int write,
393 void __user *buffer, size_t *lenp,
394 loff_t *ppos)
395{
396 unsigned long old_bytes = vm_dirty_bytes;
397 int ret;
398
399 ret = proc_doulongvec_minmax(table, write, buffer, lenp, ppos);
400 if (ret == 0 && write && vm_dirty_bytes != old_bytes) {
401 writeback_set_ratelimit();
402 vm_dirty_ratio = 0;
403 }
404 return ret;
405}
406
407static unsigned long wp_next_time(unsigned long cur_time)
408{
409 cur_time += VM_COMPLETIONS_PERIOD_LEN;
410 /* 0 has a special meaning... */
411 if (!cur_time)
412 return 1;
413 return cur_time;
414}
415
416/*
417 * Increment the BDI's writeout completion count and the global writeout
418 * completion count. Called from test_clear_page_writeback().
419 */
420static inline void __bdi_writeout_inc(struct backing_dev_info *bdi)
421{
422 __inc_bdi_stat(bdi, BDI_WRITTEN);
423 __fprop_inc_percpu_max(&writeout_completions, &bdi->completions,
424 bdi->max_prop_frac);
425 /* First event after period switching was turned off? */
426 if (!unlikely(writeout_period_time)) {
427 /*
428 * We can race with other __bdi_writeout_inc calls here but
429 * it does not cause any harm since the resulting time when
430 * timer will fire and what is in writeout_period_time will be
431 * roughly the same.
432 */
433 writeout_period_time = wp_next_time(jiffies);
434 mod_timer(&writeout_period_timer, writeout_period_time);
435 }
436}
437
438void bdi_writeout_inc(struct backing_dev_info *bdi)
439{
440 unsigned long flags;
441
442 local_irq_save(flags);
443 __bdi_writeout_inc(bdi);
444 local_irq_restore(flags);
445}
446EXPORT_SYMBOL_GPL(bdi_writeout_inc);
447
448/*
449 * Obtain an accurate fraction of the BDI's portion.
450 */
451static void bdi_writeout_fraction(struct backing_dev_info *bdi,
452 long *numerator, long *denominator)
453{
454 fprop_fraction_percpu(&writeout_completions, &bdi->completions,
455 numerator, denominator);
456}
457
458/*
459 * On idle system, we can be called long after we scheduled because we use
460 * deferred timers so count with missed periods.
461 */
462static void writeout_period(unsigned long t)
463{
464 int miss_periods = (jiffies - writeout_period_time) /
465 VM_COMPLETIONS_PERIOD_LEN;
466
467 if (fprop_new_period(&writeout_completions, miss_periods + 1)) {
468 writeout_period_time = wp_next_time(writeout_period_time +
469 miss_periods * VM_COMPLETIONS_PERIOD_LEN);
470 mod_timer(&writeout_period_timer, writeout_period_time);
471 } else {
472 /*
473 * Aging has zeroed all fractions. Stop wasting CPU on period
474 * updates.
475 */
476 writeout_period_time = 0;
477 }
478}
479
480/*
481 * bdi_min_ratio keeps the sum of the minimum dirty shares of all
482 * registered backing devices, which, for obvious reasons, can not
483 * exceed 100%.
484 */
485static unsigned int bdi_min_ratio;
486
487int bdi_set_min_ratio(struct backing_dev_info *bdi, unsigned int min_ratio)
488{
489 int ret = 0;
490
491 spin_lock_bh(&bdi_lock);
492 if (min_ratio > bdi->max_ratio) {
493 ret = -EINVAL;
494 } else {
495 min_ratio -= bdi->min_ratio;
496 if (bdi_min_ratio + min_ratio < 100) {
497 bdi_min_ratio += min_ratio;
498 bdi->min_ratio += min_ratio;
499 } else {
500 ret = -EINVAL;
501 }
502 }
503 spin_unlock_bh(&bdi_lock);
504
505 return ret;
506}
507
508int bdi_set_max_ratio(struct backing_dev_info *bdi, unsigned max_ratio)
509{
510 int ret = 0;
511
512 if (max_ratio > 100)
513 return -EINVAL;
514
515 spin_lock_bh(&bdi_lock);
516 if (bdi->min_ratio > max_ratio) {
517 ret = -EINVAL;
518 } else {
519 bdi->max_ratio = max_ratio;
520 bdi->max_prop_frac = (FPROP_FRAC_BASE * max_ratio) / 100;
521 }
522 spin_unlock_bh(&bdi_lock);
523
524 return ret;
525}
526EXPORT_SYMBOL(bdi_set_max_ratio);
527
528static unsigned long dirty_freerun_ceiling(unsigned long thresh,
529 unsigned long bg_thresh)
530{
531 return (thresh + bg_thresh) / 2;
532}
533
534static unsigned long hard_dirty_limit(unsigned long thresh)
535{
536 return max(thresh, global_dirty_limit);
537}
538
539/**
540 * bdi_dirty_limit - @bdi's share of dirty throttling threshold
541 * @bdi: the backing_dev_info to query
542 * @dirty: global dirty limit in pages
543 *
544 * Returns @bdi's dirty limit in pages. The term "dirty" in the context of
545 * dirty balancing includes all PG_dirty, PG_writeback and NFS unstable pages.
546 *
547 * Note that balance_dirty_pages() will only seriously take it as a hard limit
548 * when sleeping max_pause per page is not enough to keep the dirty pages under
549 * control. For example, when the device is completely stalled due to some error
550 * conditions, or when there are 1000 dd tasks writing to a slow 10MB/s USB key.
551 * In the other normal situations, it acts more gently by throttling the tasks
552 * more (rather than completely block them) when the bdi dirty pages go high.
553 *
554 * It allocates high/low dirty limits to fast/slow devices, in order to prevent
555 * - starving fast devices
556 * - piling up dirty pages (that will take long time to sync) on slow devices
557 *
558 * The bdi's share of dirty limit will be adapting to its throughput and
559 * bounded by the bdi->min_ratio and/or bdi->max_ratio parameters, if set.
560 */
561unsigned long bdi_dirty_limit(struct backing_dev_info *bdi, unsigned long dirty)
562{
563 u64 bdi_dirty;
564 long numerator, denominator;
565
566 /*
567 * Calculate this BDI's share of the dirty ratio.
568 */
569 bdi_writeout_fraction(bdi, &numerator, &denominator);
570
571 bdi_dirty = (dirty * (100 - bdi_min_ratio)) / 100;
572 bdi_dirty *= numerator;
573 do_div(bdi_dirty, denominator);
574
575 bdi_dirty += (dirty * bdi->min_ratio) / 100;
576 if (bdi_dirty > (dirty * bdi->max_ratio) / 100)
577 bdi_dirty = dirty * bdi->max_ratio / 100;
578
579 return bdi_dirty;
580}
581
582/*
583 * setpoint - dirty 3
584 * f(dirty) := 1.0 + (----------------)
585 * limit - setpoint
586 *
587 * it's a 3rd order polynomial that subjects to
588 *
589 * (1) f(freerun) = 2.0 => rampup dirty_ratelimit reasonably fast
590 * (2) f(setpoint) = 1.0 => the balance point
591 * (3) f(limit) = 0 => the hard limit
592 * (4) df/dx <= 0 => negative feedback control
593 * (5) the closer to setpoint, the smaller |df/dx| (and the reverse)
594 * => fast response on large errors; small oscillation near setpoint
595 */
596static long long pos_ratio_polynom(unsigned long setpoint,
597 unsigned long dirty,
598 unsigned long limit)
599{
600 long long pos_ratio;
601 long x;
602
603 x = div64_s64(((s64)setpoint - (s64)dirty) << RATELIMIT_CALC_SHIFT,
604 limit - setpoint + 1);
605 pos_ratio = x;
606 pos_ratio = pos_ratio * x >> RATELIMIT_CALC_SHIFT;
607 pos_ratio = pos_ratio * x >> RATELIMIT_CALC_SHIFT;
608 pos_ratio += 1 << RATELIMIT_CALC_SHIFT;
609
610 return clamp(pos_ratio, 0LL, 2LL << RATELIMIT_CALC_SHIFT);
611}
612
613/*
614 * Dirty position control.
615 *
616 * (o) global/bdi setpoints
617 *
618 * We want the dirty pages be balanced around the global/bdi setpoints.
619 * When the number of dirty pages is higher/lower than the setpoint, the
620 * dirty position control ratio (and hence task dirty ratelimit) will be
621 * decreased/increased to bring the dirty pages back to the setpoint.
622 *
623 * pos_ratio = 1 << RATELIMIT_CALC_SHIFT
624 *
625 * if (dirty < setpoint) scale up pos_ratio
626 * if (dirty > setpoint) scale down pos_ratio
627 *
628 * if (bdi_dirty < bdi_setpoint) scale up pos_ratio
629 * if (bdi_dirty > bdi_setpoint) scale down pos_ratio
630 *
631 * task_ratelimit = dirty_ratelimit * pos_ratio >> RATELIMIT_CALC_SHIFT
632 *
633 * (o) global control line
634 *
635 * ^ pos_ratio
636 * |
637 * | |<===== global dirty control scope ======>|
638 * 2.0 .............*
639 * | .*
640 * | . *
641 * | . *
642 * | . *
643 * | . *
644 * | . *
645 * 1.0 ................................*
646 * | . . *
647 * | . . *
648 * | . . *
649 * | . . *
650 * | . . *
651 * 0 +------------.------------------.----------------------*------------->
652 * freerun^ setpoint^ limit^ dirty pages
653 *
654 * (o) bdi control line
655 *
656 * ^ pos_ratio
657 * |
658 * | *
659 * | *
660 * | *
661 * | *
662 * | * |<=========== span ============>|
663 * 1.0 .......................*
664 * | . *
665 * | . *
666 * | . *
667 * | . *
668 * | . *
669 * | . *
670 * | . *
671 * | . *
672 * | . *
673 * | . *
674 * | . *
675 * 1/4 ...............................................* * * * * * * * * * * *
676 * | . .
677 * | . .
678 * | . .
679 * 0 +----------------------.-------------------------------.------------->
680 * bdi_setpoint^ x_intercept^
681 *
682 * The bdi control line won't drop below pos_ratio=1/4, so that bdi_dirty can
683 * be smoothly throttled down to normal if it starts high in situations like
684 * - start writing to a slow SD card and a fast disk at the same time. The SD
685 * card's bdi_dirty may rush to many times higher than bdi_setpoint.
686 * - the bdi dirty thresh drops quickly due to change of JBOD workload
687 */
688static unsigned long bdi_position_ratio(struct backing_dev_info *bdi,
689 unsigned long thresh,
690 unsigned long bg_thresh,
691 unsigned long dirty,
692 unsigned long bdi_thresh,
693 unsigned long bdi_dirty)
694{
695 unsigned long write_bw = bdi->avg_write_bandwidth;
696 unsigned long freerun = dirty_freerun_ceiling(thresh, bg_thresh);
697 unsigned long limit = hard_dirty_limit(thresh);
698 unsigned long x_intercept;
699 unsigned long setpoint; /* dirty pages' target balance point */
700 unsigned long bdi_setpoint;
701 unsigned long span;
702 long long pos_ratio; /* for scaling up/down the rate limit */
703 long x;
704
705 if (unlikely(dirty >= limit))
706 return 0;
707
708 /*
709 * global setpoint
710 *
711 * See comment for pos_ratio_polynom().
712 */
713 setpoint = (freerun + limit) / 2;
714 pos_ratio = pos_ratio_polynom(setpoint, dirty, limit);
715
716 /*
717 * The strictlimit feature is a tool preventing mistrusted filesystems
718 * from growing a large number of dirty pages before throttling. For
719 * such filesystems balance_dirty_pages always checks bdi counters
720 * against bdi limits. Even if global "nr_dirty" is under "freerun".
721 * This is especially important for fuse which sets bdi->max_ratio to
722 * 1% by default. Without strictlimit feature, fuse writeback may
723 * consume arbitrary amount of RAM because it is accounted in
724 * NR_WRITEBACK_TEMP which is not involved in calculating "nr_dirty".
725 *
726 * Here, in bdi_position_ratio(), we calculate pos_ratio based on
727 * two values: bdi_dirty and bdi_thresh. Let's consider an example:
728 * total amount of RAM is 16GB, bdi->max_ratio is equal to 1%, global
729 * limits are set by default to 10% and 20% (background and throttle).
730 * Then bdi_thresh is 1% of 20% of 16GB. This amounts to ~8K pages.
731 * bdi_dirty_limit(bdi, bg_thresh) is about ~4K pages. bdi_setpoint is
732 * about ~6K pages (as the average of background and throttle bdi
733 * limits). The 3rd order polynomial will provide positive feedback if
734 * bdi_dirty is under bdi_setpoint and vice versa.
735 *
736 * Note, that we cannot use global counters in these calculations
737 * because we want to throttle process writing to a strictlimit BDI
738 * much earlier than global "freerun" is reached (~23MB vs. ~2.3GB
739 * in the example above).
740 */
741 if (unlikely(bdi->capabilities & BDI_CAP_STRICTLIMIT)) {
742 long long bdi_pos_ratio;
743 unsigned long bdi_bg_thresh;
744
745 if (bdi_dirty < 8)
746 return min_t(long long, pos_ratio * 2,
747 2 << RATELIMIT_CALC_SHIFT);
748
749 if (bdi_dirty >= bdi_thresh)
750 return 0;
751
752 bdi_bg_thresh = div_u64((u64)bdi_thresh * bg_thresh, thresh);
753 bdi_setpoint = dirty_freerun_ceiling(bdi_thresh,
754 bdi_bg_thresh);
755
756 if (bdi_setpoint == 0 || bdi_setpoint == bdi_thresh)
757 return 0;
758
759 bdi_pos_ratio = pos_ratio_polynom(bdi_setpoint, bdi_dirty,
760 bdi_thresh);
761
762 /*
763 * Typically, for strictlimit case, bdi_setpoint << setpoint
764 * and pos_ratio >> bdi_pos_ratio. In the other words global
765 * state ("dirty") is not limiting factor and we have to
766 * make decision based on bdi counters. But there is an
767 * important case when global pos_ratio should get precedence:
768 * global limits are exceeded (e.g. due to activities on other
769 * BDIs) while given strictlimit BDI is below limit.
770 *
771 * "pos_ratio * bdi_pos_ratio" would work for the case above,
772 * but it would look too non-natural for the case of all
773 * activity in the system coming from a single strictlimit BDI
774 * with bdi->max_ratio == 100%.
775 *
776 * Note that min() below somewhat changes the dynamics of the
777 * control system. Normally, pos_ratio value can be well over 3
778 * (when globally we are at freerun and bdi is well below bdi
779 * setpoint). Now the maximum pos_ratio in the same situation
780 * is 2. We might want to tweak this if we observe the control
781 * system is too slow to adapt.
782 */
783 return min(pos_ratio, bdi_pos_ratio);
784 }
785
786 /*
787 * We have computed basic pos_ratio above based on global situation. If
788 * the bdi is over/under its share of dirty pages, we want to scale
789 * pos_ratio further down/up. That is done by the following mechanism.
790 */
791
792 /*
793 * bdi setpoint
794 *
795 * f(bdi_dirty) := 1.0 + k * (bdi_dirty - bdi_setpoint)
796 *
797 * x_intercept - bdi_dirty
798 * := --------------------------
799 * x_intercept - bdi_setpoint
800 *
801 * The main bdi control line is a linear function that subjects to
802 *
803 * (1) f(bdi_setpoint) = 1.0
804 * (2) k = - 1 / (8 * write_bw) (in single bdi case)
805 * or equally: x_intercept = bdi_setpoint + 8 * write_bw
806 *
807 * For single bdi case, the dirty pages are observed to fluctuate
808 * regularly within range
809 * [bdi_setpoint - write_bw/2, bdi_setpoint + write_bw/2]
810 * for various filesystems, where (2) can yield in a reasonable 12.5%
811 * fluctuation range for pos_ratio.
812 *
813 * For JBOD case, bdi_thresh (not bdi_dirty!) could fluctuate up to its
814 * own size, so move the slope over accordingly and choose a slope that
815 * yields 100% pos_ratio fluctuation on suddenly doubled bdi_thresh.
816 */
817 if (unlikely(bdi_thresh > thresh))
818 bdi_thresh = thresh;
819 /*
820 * It's very possible that bdi_thresh is close to 0 not because the
821 * device is slow, but that it has remained inactive for long time.
822 * Honour such devices a reasonable good (hopefully IO efficient)
823 * threshold, so that the occasional writes won't be blocked and active
824 * writes can rampup the threshold quickly.
825 */
826 bdi_thresh = max(bdi_thresh, (limit - dirty) / 8);
827 /*
828 * scale global setpoint to bdi's:
829 * bdi_setpoint = setpoint * bdi_thresh / thresh
830 */
831 x = div_u64((u64)bdi_thresh << 16, thresh + 1);
832 bdi_setpoint = setpoint * (u64)x >> 16;
833 /*
834 * Use span=(8*write_bw) in single bdi case as indicated by
835 * (thresh - bdi_thresh ~= 0) and transit to bdi_thresh in JBOD case.
836 *
837 * bdi_thresh thresh - bdi_thresh
838 * span = ---------- * (8 * write_bw) + ------------------- * bdi_thresh
839 * thresh thresh
840 */
841 span = (thresh - bdi_thresh + 8 * write_bw) * (u64)x >> 16;
842 x_intercept = bdi_setpoint + span;
843
844 if (bdi_dirty < x_intercept - span / 4) {
845 pos_ratio = div64_u64(pos_ratio * (x_intercept - bdi_dirty),
846 x_intercept - bdi_setpoint + 1);
847 } else
848 pos_ratio /= 4;
849
850 /*
851 * bdi reserve area, safeguard against dirty pool underrun and disk idle
852 * It may push the desired control point of global dirty pages higher
853 * than setpoint.
854 */
855 x_intercept = bdi_thresh / 2;
856 if (bdi_dirty < x_intercept) {
857 if (bdi_dirty > x_intercept / 8)
858 pos_ratio = div_u64(pos_ratio * x_intercept, bdi_dirty);
859 else
860 pos_ratio *= 8;
861 }
862
863 return pos_ratio;
864}
865
866static void bdi_update_write_bandwidth(struct backing_dev_info *bdi,
867 unsigned long elapsed,
868 unsigned long written)
869{
870 const unsigned long period = roundup_pow_of_two(3 * HZ);
871 unsigned long avg = bdi->avg_write_bandwidth;
872 unsigned long old = bdi->write_bandwidth;
873 u64 bw;
874
875 /*
876 * bw = written * HZ / elapsed
877 *
878 * bw * elapsed + write_bandwidth * (period - elapsed)
879 * write_bandwidth = ---------------------------------------------------
880 * period
881 */
882 bw = written - bdi->written_stamp;
883 bw *= HZ;
884 if (unlikely(elapsed > period)) {
885 do_div(bw, elapsed);
886 avg = bw;
887 goto out;
888 }
889 bw += (u64)bdi->write_bandwidth * (period - elapsed);
890 bw >>= ilog2(period);
891
892 /*
893 * one more level of smoothing, for filtering out sudden spikes
894 */
895 if (avg > old && old >= (unsigned long)bw)
896 avg -= (avg - old) >> 3;
897
898 if (avg < old && old <= (unsigned long)bw)
899 avg += (old - avg) >> 3;
900
901out:
902 bdi->write_bandwidth = bw;
903 bdi->avg_write_bandwidth = avg;
904}
905
906/*
907 * The global dirtyable memory and dirty threshold could be suddenly knocked
908 * down by a large amount (eg. on the startup of KVM in a swapless system).
909 * This may throw the system into deep dirty exceeded state and throttle
910 * heavy/light dirtiers alike. To retain good responsiveness, maintain
911 * global_dirty_limit for tracking slowly down to the knocked down dirty
912 * threshold.
913 */
914static void update_dirty_limit(unsigned long thresh, unsigned long dirty)
915{
916 unsigned long limit = global_dirty_limit;
917
918 /*
919 * Follow up in one step.
920 */
921 if (limit < thresh) {
922 limit = thresh;
923 goto update;
924 }
925
926 /*
927 * Follow down slowly. Use the higher one as the target, because thresh
928 * may drop below dirty. This is exactly the reason to introduce
929 * global_dirty_limit which is guaranteed to lie above the dirty pages.
930 */
931 thresh = max(thresh, dirty);
932 if (limit > thresh) {
933 limit -= (limit - thresh) >> 5;
934 goto update;
935 }
936 return;
937update:
938 global_dirty_limit = limit;
939}
940
941static void global_update_bandwidth(unsigned long thresh,
942 unsigned long dirty,
943 unsigned long now)
944{
945 static DEFINE_SPINLOCK(dirty_lock);
946 static unsigned long update_time;
947
948 /*
949 * check locklessly first to optimize away locking for the most time
950 */
951 if (time_before(now, update_time + BANDWIDTH_INTERVAL))
952 return;
953
954 spin_lock(&dirty_lock);
955 if (time_after_eq(now, update_time + BANDWIDTH_INTERVAL)) {
956 update_dirty_limit(thresh, dirty);
957 update_time = now;
958 }
959 spin_unlock(&dirty_lock);
960}
961
962/*
963 * Maintain bdi->dirty_ratelimit, the base dirty throttle rate.
964 *
965 * Normal bdi tasks will be curbed at or below it in long term.
966 * Obviously it should be around (write_bw / N) when there are N dd tasks.
967 */
968static void bdi_update_dirty_ratelimit(struct backing_dev_info *bdi,
969 unsigned long thresh,
970 unsigned long bg_thresh,
971 unsigned long dirty,
972 unsigned long bdi_thresh,
973 unsigned long bdi_dirty,
974 unsigned long dirtied,
975 unsigned long elapsed)
976{
977 unsigned long freerun = dirty_freerun_ceiling(thresh, bg_thresh);
978 unsigned long limit = hard_dirty_limit(thresh);
979 unsigned long setpoint = (freerun + limit) / 2;
980 unsigned long write_bw = bdi->avg_write_bandwidth;
981 unsigned long dirty_ratelimit = bdi->dirty_ratelimit;
982 unsigned long dirty_rate;
983 unsigned long task_ratelimit;
984 unsigned long balanced_dirty_ratelimit;
985 unsigned long pos_ratio;
986 unsigned long step;
987 unsigned long x;
988
989 /*
990 * The dirty rate will match the writeout rate in long term, except
991 * when dirty pages are truncated by userspace or re-dirtied by FS.
992 */
993 dirty_rate = (dirtied - bdi->dirtied_stamp) * HZ / elapsed;
994
995 pos_ratio = bdi_position_ratio(bdi, thresh, bg_thresh, dirty,
996 bdi_thresh, bdi_dirty);
997 /*
998 * task_ratelimit reflects each dd's dirty rate for the past 200ms.
999 */
1000 task_ratelimit = (u64)dirty_ratelimit *
1001 pos_ratio >> RATELIMIT_CALC_SHIFT;
1002 task_ratelimit++; /* it helps rampup dirty_ratelimit from tiny values */
1003
1004 /*
1005 * A linear estimation of the "balanced" throttle rate. The theory is,
1006 * if there are N dd tasks, each throttled at task_ratelimit, the bdi's
1007 * dirty_rate will be measured to be (N * task_ratelimit). So the below
1008 * formula will yield the balanced rate limit (write_bw / N).
1009 *
1010 * Note that the expanded form is not a pure rate feedback:
1011 * rate_(i+1) = rate_(i) * (write_bw / dirty_rate) (1)
1012 * but also takes pos_ratio into account:
1013 * rate_(i+1) = rate_(i) * (write_bw / dirty_rate) * pos_ratio (2)
1014 *
1015 * (1) is not realistic because pos_ratio also takes part in balancing
1016 * the dirty rate. Consider the state
1017 * pos_ratio = 0.5 (3)
1018 * rate = 2 * (write_bw / N) (4)
1019 * If (1) is used, it will stuck in that state! Because each dd will
1020 * be throttled at
1021 * task_ratelimit = pos_ratio * rate = (write_bw / N) (5)
1022 * yielding
1023 * dirty_rate = N * task_ratelimit = write_bw (6)
1024 * put (6) into (1) we get
1025 * rate_(i+1) = rate_(i) (7)
1026 *
1027 * So we end up using (2) to always keep
1028 * rate_(i+1) ~= (write_bw / N) (8)
1029 * regardless of the value of pos_ratio. As long as (8) is satisfied,
1030 * pos_ratio is able to drive itself to 1.0, which is not only where
1031 * the dirty count meet the setpoint, but also where the slope of
1032 * pos_ratio is most flat and hence task_ratelimit is least fluctuated.
1033 */
1034 balanced_dirty_ratelimit = div_u64((u64)task_ratelimit * write_bw,
1035 dirty_rate | 1);
1036 /*
1037 * balanced_dirty_ratelimit ~= (write_bw / N) <= write_bw
1038 */
1039 if (unlikely(balanced_dirty_ratelimit > write_bw))
1040 balanced_dirty_ratelimit = write_bw;
1041
1042 /*
1043 * We could safely do this and return immediately:
1044 *
1045 * bdi->dirty_ratelimit = balanced_dirty_ratelimit;
1046 *
1047 * However to get a more stable dirty_ratelimit, the below elaborated
1048 * code makes use of task_ratelimit to filter out singular points and
1049 * limit the step size.
1050 *
1051 * The below code essentially only uses the relative value of
1052 *
1053 * task_ratelimit - dirty_ratelimit
1054 * = (pos_ratio - 1) * dirty_ratelimit
1055 *
1056 * which reflects the direction and size of dirty position error.
1057 */
1058
1059 /*
1060 * dirty_ratelimit will follow balanced_dirty_ratelimit iff
1061 * task_ratelimit is on the same side of dirty_ratelimit, too.
1062 * For example, when
1063 * - dirty_ratelimit > balanced_dirty_ratelimit
1064 * - dirty_ratelimit > task_ratelimit (dirty pages are above setpoint)
1065 * lowering dirty_ratelimit will help meet both the position and rate
1066 * control targets. Otherwise, don't update dirty_ratelimit if it will
1067 * only help meet the rate target. After all, what the users ultimately
1068 * feel and care are stable dirty rate and small position error.
1069 *
1070 * |task_ratelimit - dirty_ratelimit| is used to limit the step size
1071 * and filter out the singular points of balanced_dirty_ratelimit. Which
1072 * keeps jumping around randomly and can even leap far away at times
1073 * due to the small 200ms estimation period of dirty_rate (we want to
1074 * keep that period small to reduce time lags).
1075 */
1076 step = 0;
1077
1078 /*
1079 * For strictlimit case, calculations above were based on bdi counters
1080 * and limits (starting from pos_ratio = bdi_position_ratio() and up to
1081 * balanced_dirty_ratelimit = task_ratelimit * write_bw / dirty_rate).
1082 * Hence, to calculate "step" properly, we have to use bdi_dirty as
1083 * "dirty" and bdi_setpoint as "setpoint".
1084 *
1085 * We rampup dirty_ratelimit forcibly if bdi_dirty is low because
1086 * it's possible that bdi_thresh is close to zero due to inactivity
1087 * of backing device (see the implementation of bdi_dirty_limit()).
1088 */
1089 if (unlikely(bdi->capabilities & BDI_CAP_STRICTLIMIT)) {
1090 dirty = bdi_dirty;
1091 if (bdi_dirty < 8)
1092 setpoint = bdi_dirty + 1;
1093 else
1094 setpoint = (bdi_thresh +
1095 bdi_dirty_limit(bdi, bg_thresh)) / 2;
1096 }
1097
1098 if (dirty < setpoint) {
1099 x = min(bdi->balanced_dirty_ratelimit,
1100 min(balanced_dirty_ratelimit, task_ratelimit));
1101 if (dirty_ratelimit < x)
1102 step = x - dirty_ratelimit;
1103 } else {
1104 x = max(bdi->balanced_dirty_ratelimit,
1105 max(balanced_dirty_ratelimit, task_ratelimit));
1106 if (dirty_ratelimit > x)
1107 step = dirty_ratelimit - x;
1108 }
1109
1110 /*
1111 * Don't pursue 100% rate matching. It's impossible since the balanced
1112 * rate itself is constantly fluctuating. So decrease the track speed
1113 * when it gets close to the target. Helps eliminate pointless tremors.
1114 */
1115 step >>= dirty_ratelimit / (2 * step + 1);
1116 /*
1117 * Limit the tracking speed to avoid overshooting.
1118 */
1119 step = (step + 7) / 8;
1120
1121 if (dirty_ratelimit < balanced_dirty_ratelimit)
1122 dirty_ratelimit += step;
1123 else
1124 dirty_ratelimit -= step;
1125
1126 bdi->dirty_ratelimit = max(dirty_ratelimit, 1UL);
1127 bdi->balanced_dirty_ratelimit = balanced_dirty_ratelimit;
1128
1129 trace_bdi_dirty_ratelimit(bdi, dirty_rate, task_ratelimit);
1130}
1131
1132void __bdi_update_bandwidth(struct backing_dev_info *bdi,
1133 unsigned long thresh,
1134 unsigned long bg_thresh,
1135 unsigned long dirty,
1136 unsigned long bdi_thresh,
1137 unsigned long bdi_dirty,
1138 unsigned long start_time)
1139{
1140 unsigned long now = jiffies;
1141 unsigned long elapsed = now - bdi->bw_time_stamp;
1142 unsigned long dirtied;
1143 unsigned long written;
1144
1145 /*
1146 * rate-limit, only update once every 200ms.
1147 */
1148 if (elapsed < BANDWIDTH_INTERVAL)
1149 return;
1150
1151 dirtied = percpu_counter_read(&bdi->bdi_stat[BDI_DIRTIED]);
1152 written = percpu_counter_read(&bdi->bdi_stat[BDI_WRITTEN]);
1153
1154 /*
1155 * Skip quiet periods when disk bandwidth is under-utilized.
1156 * (at least 1s idle time between two flusher runs)
1157 */
1158 if (elapsed > HZ && time_before(bdi->bw_time_stamp, start_time))
1159 goto snapshot;
1160
1161 if (thresh) {
1162 global_update_bandwidth(thresh, dirty, now);
1163 bdi_update_dirty_ratelimit(bdi, thresh, bg_thresh, dirty,
1164 bdi_thresh, bdi_dirty,
1165 dirtied, elapsed);
1166 }
1167 bdi_update_write_bandwidth(bdi, elapsed, written);
1168
1169snapshot:
1170 bdi->dirtied_stamp = dirtied;
1171 bdi->written_stamp = written;
1172 bdi->bw_time_stamp = now;
1173}
1174
1175static void bdi_update_bandwidth(struct backing_dev_info *bdi,
1176 unsigned long thresh,
1177 unsigned long bg_thresh,
1178 unsigned long dirty,
1179 unsigned long bdi_thresh,
1180 unsigned long bdi_dirty,
1181 unsigned long start_time)
1182{
1183 if (time_is_after_eq_jiffies(bdi->bw_time_stamp + BANDWIDTH_INTERVAL))
1184 return;
1185 spin_lock(&bdi->wb.list_lock);
1186 __bdi_update_bandwidth(bdi, thresh, bg_thresh, dirty,
1187 bdi_thresh, bdi_dirty, start_time);
1188 spin_unlock(&bdi->wb.list_lock);
1189}
1190
1191/*
1192 * After a task dirtied this many pages, balance_dirty_pages_ratelimited()
1193 * will look to see if it needs to start dirty throttling.
1194 *
1195 * If dirty_poll_interval is too low, big NUMA machines will call the expensive
1196 * global_page_state() too often. So scale it near-sqrt to the safety margin
1197 * (the number of pages we may dirty without exceeding the dirty limits).
1198 */
1199static unsigned long dirty_poll_interval(unsigned long dirty,
1200 unsigned long thresh)
1201{
1202 if (thresh > dirty)
1203 return 1UL << (ilog2(thresh - dirty) >> 1);
1204
1205 return 1;
1206}
1207
1208static unsigned long bdi_max_pause(struct backing_dev_info *bdi,
1209 unsigned long bdi_dirty)
1210{
1211 unsigned long bw = bdi->avg_write_bandwidth;
1212 unsigned long t;
1213
1214 /*
1215 * Limit pause time for small memory systems. If sleeping for too long
1216 * time, a small pool of dirty/writeback pages may go empty and disk go
1217 * idle.
1218 *
1219 * 8 serves as the safety ratio.
1220 */
1221 t = bdi_dirty / (1 + bw / roundup_pow_of_two(1 + HZ / 8));
1222 t++;
1223
1224 return min_t(unsigned long, t, MAX_PAUSE);
1225}
1226
1227static long bdi_min_pause(struct backing_dev_info *bdi,
1228 long max_pause,
1229 unsigned long task_ratelimit,
1230 unsigned long dirty_ratelimit,
1231 int *nr_dirtied_pause)
1232{
1233 long hi = ilog2(bdi->avg_write_bandwidth);
1234 long lo = ilog2(bdi->dirty_ratelimit);
1235 long t; /* target pause */
1236 long pause; /* estimated next pause */
1237 int pages; /* target nr_dirtied_pause */
1238
1239 /* target for 10ms pause on 1-dd case */
1240 t = max(1, HZ / 100);
1241
1242 /*
1243 * Scale up pause time for concurrent dirtiers in order to reduce CPU
1244 * overheads.
1245 *
1246 * (N * 10ms) on 2^N concurrent tasks.
1247 */
1248 if (hi > lo)
1249 t += (hi - lo) * (10 * HZ) / 1024;
1250
1251 /*
1252 * This is a bit convoluted. We try to base the next nr_dirtied_pause
1253 * on the much more stable dirty_ratelimit. However the next pause time
1254 * will be computed based on task_ratelimit and the two rate limits may
1255 * depart considerably at some time. Especially if task_ratelimit goes
1256 * below dirty_ratelimit/2 and the target pause is max_pause, the next
1257 * pause time will be max_pause*2 _trimmed down_ to max_pause. As a
1258 * result task_ratelimit won't be executed faithfully, which could
1259 * eventually bring down dirty_ratelimit.
1260 *
1261 * We apply two rules to fix it up:
1262 * 1) try to estimate the next pause time and if necessary, use a lower
1263 * nr_dirtied_pause so as not to exceed max_pause. When this happens,
1264 * nr_dirtied_pause will be "dancing" with task_ratelimit.
1265 * 2) limit the target pause time to max_pause/2, so that the normal
1266 * small fluctuations of task_ratelimit won't trigger rule (1) and
1267 * nr_dirtied_pause will remain as stable as dirty_ratelimit.
1268 */
1269 t = min(t, 1 + max_pause / 2);
1270 pages = dirty_ratelimit * t / roundup_pow_of_two(HZ);
1271
1272 /*
1273 * Tiny nr_dirtied_pause is found to hurt I/O performance in the test
1274 * case fio-mmap-randwrite-64k, which does 16*{sync read, async write}.
1275 * When the 16 consecutive reads are often interrupted by some dirty
1276 * throttling pause during the async writes, cfq will go into idles
1277 * (deadline is fine). So push nr_dirtied_pause as high as possible
1278 * until reaches DIRTY_POLL_THRESH=32 pages.
1279 */
1280 if (pages < DIRTY_POLL_THRESH) {
1281 t = max_pause;
1282 pages = dirty_ratelimit * t / roundup_pow_of_two(HZ);
1283 if (pages > DIRTY_POLL_THRESH) {
1284 pages = DIRTY_POLL_THRESH;
1285 t = HZ * DIRTY_POLL_THRESH / dirty_ratelimit;
1286 }
1287 }
1288
1289 pause = HZ * pages / (task_ratelimit + 1);
1290 if (pause > max_pause) {
1291 t = max_pause;
1292 pages = task_ratelimit * t / roundup_pow_of_two(HZ);
1293 }
1294
1295 *nr_dirtied_pause = pages;
1296 /*
1297 * The minimal pause time will normally be half the target pause time.
1298 */
1299 return pages >= DIRTY_POLL_THRESH ? 1 + t / 2 : t;
1300}
1301
1302static inline void bdi_dirty_limits(struct backing_dev_info *bdi,
1303 unsigned long dirty_thresh,
1304 unsigned long background_thresh,
1305 unsigned long *bdi_dirty,
1306 unsigned long *bdi_thresh,
1307 unsigned long *bdi_bg_thresh)
1308{
1309 unsigned long bdi_reclaimable;
1310
1311 /*
1312 * bdi_thresh is not treated as some limiting factor as
1313 * dirty_thresh, due to reasons
1314 * - in JBOD setup, bdi_thresh can fluctuate a lot
1315 * - in a system with HDD and USB key, the USB key may somehow
1316 * go into state (bdi_dirty >> bdi_thresh) either because
1317 * bdi_dirty starts high, or because bdi_thresh drops low.
1318 * In this case we don't want to hard throttle the USB key
1319 * dirtiers for 100 seconds until bdi_dirty drops under
1320 * bdi_thresh. Instead the auxiliary bdi control line in
1321 * bdi_position_ratio() will let the dirtier task progress
1322 * at some rate <= (write_bw / 2) for bringing down bdi_dirty.
1323 */
1324 *bdi_thresh = bdi_dirty_limit(bdi, dirty_thresh);
1325
1326 if (bdi_bg_thresh)
1327 *bdi_bg_thresh = div_u64((u64)*bdi_thresh *
1328 background_thresh,
1329 dirty_thresh);
1330
1331 /*
1332 * In order to avoid the stacked BDI deadlock we need
1333 * to ensure we accurately count the 'dirty' pages when
1334 * the threshold is low.
1335 *
1336 * Otherwise it would be possible to get thresh+n pages
1337 * reported dirty, even though there are thresh-m pages
1338 * actually dirty; with m+n sitting in the percpu
1339 * deltas.
1340 */
1341 if (*bdi_thresh < 2 * bdi_stat_error(bdi)) {
1342 bdi_reclaimable = bdi_stat_sum(bdi, BDI_RECLAIMABLE);
1343 *bdi_dirty = bdi_reclaimable +
1344 bdi_stat_sum(bdi, BDI_WRITEBACK);
1345 } else {
1346 bdi_reclaimable = bdi_stat(bdi, BDI_RECLAIMABLE);
1347 *bdi_dirty = bdi_reclaimable +
1348 bdi_stat(bdi, BDI_WRITEBACK);
1349 }
1350}
1351
1352/*
1353 * balance_dirty_pages() must be called by processes which are generating dirty
1354 * data. It looks at the number of dirty pages in the machine and will force
1355 * the caller to wait once crossing the (background_thresh + dirty_thresh) / 2.
1356 * If we're over `background_thresh' then the writeback threads are woken to
1357 * perform some writeout.
1358 */
1359static void balance_dirty_pages(struct address_space *mapping,
1360 unsigned long pages_dirtied)
1361{
1362 unsigned long nr_reclaimable; /* = file_dirty + unstable_nfs */
1363 unsigned long nr_dirty; /* = file_dirty + writeback + unstable_nfs */
1364 unsigned long background_thresh;
1365 unsigned long dirty_thresh;
1366 long period;
1367 long pause;
1368 long max_pause;
1369 long min_pause;
1370 int nr_dirtied_pause;
1371 bool dirty_exceeded = false;
1372 unsigned long task_ratelimit;
1373 unsigned long dirty_ratelimit;
1374 unsigned long pos_ratio;
1375 struct backing_dev_info *bdi = mapping->backing_dev_info;
1376 bool strictlimit = bdi->capabilities & BDI_CAP_STRICTLIMIT;
1377 unsigned long start_time = jiffies;
1378
1379 for (;;) {
1380 unsigned long now = jiffies;
1381 unsigned long uninitialized_var(bdi_thresh);
1382 unsigned long thresh;
1383 unsigned long uninitialized_var(bdi_dirty);
1384 unsigned long dirty;
1385 unsigned long bg_thresh;
1386
1387 /*
1388 * Unstable writes are a feature of certain networked
1389 * filesystems (i.e. NFS) in which data may have been
1390 * written to the server's write cache, but has not yet
1391 * been flushed to permanent storage.
1392 */
1393 nr_reclaimable = global_page_state(NR_FILE_DIRTY) +
1394 global_page_state(NR_UNSTABLE_NFS);
1395 nr_dirty = nr_reclaimable + global_page_state(NR_WRITEBACK);
1396
1397 global_dirty_limits(&background_thresh, &dirty_thresh);
1398
1399 if (unlikely(strictlimit)) {
1400 bdi_dirty_limits(bdi, dirty_thresh, background_thresh,
1401 &bdi_dirty, &bdi_thresh, &bg_thresh);
1402
1403 dirty = bdi_dirty;
1404 thresh = bdi_thresh;
1405 } else {
1406 dirty = nr_dirty;
1407 thresh = dirty_thresh;
1408 bg_thresh = background_thresh;
1409 }
1410
1411 /*
1412 * Throttle it only when the background writeback cannot
1413 * catch-up. This avoids (excessively) small writeouts
1414 * when the bdi limits are ramping up in case of !strictlimit.
1415 *
1416 * In strictlimit case make decision based on the bdi counters
1417 * and limits. Small writeouts when the bdi limits are ramping
1418 * up are the price we consciously pay for strictlimit-ing.
1419 */
1420 if (dirty <= dirty_freerun_ceiling(thresh, bg_thresh)) {
1421 current->dirty_paused_when = now;
1422 current->nr_dirtied = 0;
1423 current->nr_dirtied_pause =
1424 dirty_poll_interval(dirty, thresh);
1425 break;
1426 }
1427
1428 if (unlikely(!writeback_in_progress(bdi)))
1429 bdi_start_background_writeback(bdi);
1430
1431 if (!strictlimit)
1432 bdi_dirty_limits(bdi, dirty_thresh, background_thresh,
1433 &bdi_dirty, &bdi_thresh, NULL);
1434
1435 dirty_exceeded = (bdi_dirty > bdi_thresh) &&
1436 ((nr_dirty > dirty_thresh) || strictlimit);
1437 if (dirty_exceeded && !bdi->dirty_exceeded)
1438 bdi->dirty_exceeded = 1;
1439
1440 bdi_update_bandwidth(bdi, dirty_thresh, background_thresh,
1441 nr_dirty, bdi_thresh, bdi_dirty,
1442 start_time);
1443
1444 dirty_ratelimit = bdi->dirty_ratelimit;
1445 pos_ratio = bdi_position_ratio(bdi, dirty_thresh,
1446 background_thresh, nr_dirty,
1447 bdi_thresh, bdi_dirty);
1448 task_ratelimit = ((u64)dirty_ratelimit * pos_ratio) >>
1449 RATELIMIT_CALC_SHIFT;
1450 max_pause = bdi_max_pause(bdi, bdi_dirty);
1451 min_pause = bdi_min_pause(bdi, max_pause,
1452 task_ratelimit, dirty_ratelimit,
1453 &nr_dirtied_pause);
1454
1455 if (unlikely(task_ratelimit == 0)) {
1456 period = max_pause;
1457 pause = max_pause;
1458 goto pause;
1459 }
1460 period = HZ * pages_dirtied / task_ratelimit;
1461 pause = period;
1462 if (current->dirty_paused_when)
1463 pause -= now - current->dirty_paused_when;
1464 /*
1465 * For less than 1s think time (ext3/4 may block the dirtier
1466 * for up to 800ms from time to time on 1-HDD; so does xfs,
1467 * however at much less frequency), try to compensate it in
1468 * future periods by updating the virtual time; otherwise just
1469 * do a reset, as it may be a light dirtier.
1470 */
1471 if (pause < min_pause) {
1472 trace_balance_dirty_pages(bdi,
1473 dirty_thresh,
1474 background_thresh,
1475 nr_dirty,
1476 bdi_thresh,
1477 bdi_dirty,
1478 dirty_ratelimit,
1479 task_ratelimit,
1480 pages_dirtied,
1481 period,
1482 min(pause, 0L),
1483 start_time);
1484 if (pause < -HZ) {
1485 current->dirty_paused_when = now;
1486 current->nr_dirtied = 0;
1487 } else if (period) {
1488 current->dirty_paused_when += period;
1489 current->nr_dirtied = 0;
1490 } else if (current->nr_dirtied_pause <= pages_dirtied)
1491 current->nr_dirtied_pause += pages_dirtied;
1492 break;
1493 }
1494 if (unlikely(pause > max_pause)) {
1495 /* for occasional dropped task_ratelimit */
1496 now += min(pause - max_pause, max_pause);
1497 pause = max_pause;
1498 }
1499
1500pause:
1501 trace_balance_dirty_pages(bdi,
1502 dirty_thresh,
1503 background_thresh,
1504 nr_dirty,
1505 bdi_thresh,
1506 bdi_dirty,
1507 dirty_ratelimit,
1508 task_ratelimit,
1509 pages_dirtied,
1510 period,
1511 pause,
1512 start_time);
1513 __set_current_state(TASK_KILLABLE);
1514 io_schedule_timeout(pause);
1515
1516 current->dirty_paused_when = now + pause;
1517 current->nr_dirtied = 0;
1518 current->nr_dirtied_pause = nr_dirtied_pause;
1519
1520 /*
1521 * This is typically equal to (nr_dirty < dirty_thresh) and can
1522 * also keep "1000+ dd on a slow USB stick" under control.
1523 */
1524 if (task_ratelimit)
1525 break;
1526
1527 /*
1528 * In the case of an unresponding NFS server and the NFS dirty
1529 * pages exceeds dirty_thresh, give the other good bdi's a pipe
1530 * to go through, so that tasks on them still remain responsive.
1531 *
1532 * In theory 1 page is enough to keep the comsumer-producer
1533 * pipe going: the flusher cleans 1 page => the task dirties 1
1534 * more page. However bdi_dirty has accounting errors. So use
1535 * the larger and more IO friendly bdi_stat_error.
1536 */
1537 if (bdi_dirty <= bdi_stat_error(bdi))
1538 break;
1539
1540 if (fatal_signal_pending(current))
1541 break;
1542 }
1543
1544 if (!dirty_exceeded && bdi->dirty_exceeded)
1545 bdi->dirty_exceeded = 0;
1546
1547 if (writeback_in_progress(bdi))
1548 return;
1549
1550 /*
1551 * In laptop mode, we wait until hitting the higher threshold before
1552 * starting background writeout, and then write out all the way down
1553 * to the lower threshold. So slow writers cause minimal disk activity.
1554 *
1555 * In normal mode, we start background writeout at the lower
1556 * background_thresh, to keep the amount of dirty memory low.
1557 */
1558 if (laptop_mode)
1559 return;
1560
1561 if (nr_reclaimable > background_thresh)
1562 bdi_start_background_writeback(bdi);
1563}
1564
1565void set_page_dirty_balance(struct page *page)
1566{
1567 if (set_page_dirty(page)) {
1568 struct address_space *mapping = page_mapping(page);
1569
1570 if (mapping)
1571 balance_dirty_pages_ratelimited(mapping);
1572 }
1573}
1574
1575static DEFINE_PER_CPU(int, bdp_ratelimits);
1576
1577/*
1578 * Normal tasks are throttled by
1579 * loop {
1580 * dirty tsk->nr_dirtied_pause pages;
1581 * take a snap in balance_dirty_pages();
1582 * }
1583 * However there is a worst case. If every task exit immediately when dirtied
1584 * (tsk->nr_dirtied_pause - 1) pages, balance_dirty_pages() will never be
1585 * called to throttle the page dirties. The solution is to save the not yet
1586 * throttled page dirties in dirty_throttle_leaks on task exit and charge them
1587 * randomly into the running tasks. This works well for the above worst case,
1588 * as the new task will pick up and accumulate the old task's leaked dirty
1589 * count and eventually get throttled.
1590 */
1591DEFINE_PER_CPU(int, dirty_throttle_leaks) = 0;
1592
1593/**
1594 * balance_dirty_pages_ratelimited - balance dirty memory state
1595 * @mapping: address_space which was dirtied
1596 *
1597 * Processes which are dirtying memory should call in here once for each page
1598 * which was newly dirtied. The function will periodically check the system's
1599 * dirty state and will initiate writeback if needed.
1600 *
1601 * On really big machines, get_writeback_state is expensive, so try to avoid
1602 * calling it too often (ratelimiting). But once we're over the dirty memory
1603 * limit we decrease the ratelimiting by a lot, to prevent individual processes
1604 * from overshooting the limit by (ratelimit_pages) each.
1605 */
1606void balance_dirty_pages_ratelimited(struct address_space *mapping)
1607{
1608 struct backing_dev_info *bdi = mapping->backing_dev_info;
1609 int ratelimit;
1610 int *p;
1611
1612 if (!bdi_cap_account_dirty(bdi))
1613 return;
1614
1615 ratelimit = current->nr_dirtied_pause;
1616 if (bdi->dirty_exceeded)
1617 ratelimit = min(ratelimit, 32 >> (PAGE_SHIFT - 10));
1618
1619 preempt_disable();
1620 /*
1621 * This prevents one CPU to accumulate too many dirtied pages without
1622 * calling into balance_dirty_pages(), which can happen when there are
1623 * 1000+ tasks, all of them start dirtying pages at exactly the same
1624 * time, hence all honoured too large initial task->nr_dirtied_pause.
1625 */
1626 p = &__get_cpu_var(bdp_ratelimits);
1627 if (unlikely(current->nr_dirtied >= ratelimit))
1628 *p = 0;
1629 else if (unlikely(*p >= ratelimit_pages)) {
1630 *p = 0;
1631 ratelimit = 0;
1632 }
1633 /*
1634 * Pick up the dirtied pages by the exited tasks. This avoids lots of
1635 * short-lived tasks (eg. gcc invocations in a kernel build) escaping
1636 * the dirty throttling and livelock other long-run dirtiers.
1637 */
1638 p = &__get_cpu_var(dirty_throttle_leaks);
1639 if (*p > 0 && current->nr_dirtied < ratelimit) {
1640 unsigned long nr_pages_dirtied;
1641 nr_pages_dirtied = min(*p, ratelimit - current->nr_dirtied);
1642 *p -= nr_pages_dirtied;
1643 current->nr_dirtied += nr_pages_dirtied;
1644 }
1645 preempt_enable();
1646
1647 if (unlikely(current->nr_dirtied >= ratelimit))
1648 balance_dirty_pages(mapping, current->nr_dirtied);
1649}
1650EXPORT_SYMBOL(balance_dirty_pages_ratelimited);
1651
1652void throttle_vm_writeout(gfp_t gfp_mask)
1653{
1654 unsigned long background_thresh;
1655 unsigned long dirty_thresh;
1656
1657 for ( ; ; ) {
1658 global_dirty_limits(&background_thresh, &dirty_thresh);
1659 dirty_thresh = hard_dirty_limit(dirty_thresh);
1660
1661 /*
1662 * Boost the allowable dirty threshold a bit for page
1663 * allocators so they don't get DoS'ed by heavy writers
1664 */
1665 dirty_thresh += dirty_thresh / 10; /* wheeee... */
1666
1667 if (global_page_state(NR_UNSTABLE_NFS) +
1668 global_page_state(NR_WRITEBACK) <= dirty_thresh)
1669 break;
1670 congestion_wait(BLK_RW_ASYNC, HZ/10);
1671
1672 /*
1673 * The caller might hold locks which can prevent IO completion
1674 * or progress in the filesystem. So we cannot just sit here
1675 * waiting for IO to complete.
1676 */
1677 if ((gfp_mask & (__GFP_FS|__GFP_IO)) != (__GFP_FS|__GFP_IO))
1678 break;
1679 }
1680}
1681
1682/*
1683 * sysctl handler for /proc/sys/vm/dirty_writeback_centisecs
1684 */
1685int dirty_writeback_centisecs_handler(ctl_table *table, int write,
1686 void __user *buffer, size_t *length, loff_t *ppos)
1687{
1688 proc_dointvec(table, write, buffer, length, ppos);
1689 return 0;
1690}
1691
1692#ifdef CONFIG_BLOCK
1693void laptop_mode_timer_fn(unsigned long data)
1694{
1695 struct request_queue *q = (struct request_queue *)data;
1696 int nr_pages = global_page_state(NR_FILE_DIRTY) +
1697 global_page_state(NR_UNSTABLE_NFS);
1698
1699 /*
1700 * We want to write everything out, not just down to the dirty
1701 * threshold
1702 */
1703 if (bdi_has_dirty_io(&q->backing_dev_info))
1704 bdi_start_writeback(&q->backing_dev_info, nr_pages,
1705 WB_REASON_LAPTOP_TIMER);
1706}
1707
1708/*
1709 * We've spun up the disk and we're in laptop mode: schedule writeback
1710 * of all dirty data a few seconds from now. If the flush is already scheduled
1711 * then push it back - the user is still using the disk.
1712 */
1713void laptop_io_completion(struct backing_dev_info *info)
1714{
1715 mod_timer(&info->laptop_mode_wb_timer, jiffies + laptop_mode);
1716}
1717
1718/*
1719 * We're in laptop mode and we've just synced. The sync's writes will have
1720 * caused another writeback to be scheduled by laptop_io_completion.
1721 * Nothing needs to be written back anymore, so we unschedule the writeback.
1722 */
1723void laptop_sync_completion(void)
1724{
1725 struct backing_dev_info *bdi;
1726
1727 rcu_read_lock();
1728
1729 list_for_each_entry_rcu(bdi, &bdi_list, bdi_list)
1730 del_timer(&bdi->laptop_mode_wb_timer);
1731
1732 rcu_read_unlock();
1733}
1734#endif
1735
1736/*
1737 * If ratelimit_pages is too high then we can get into dirty-data overload
1738 * if a large number of processes all perform writes at the same time.
1739 * If it is too low then SMP machines will call the (expensive)
1740 * get_writeback_state too often.
1741 *
1742 * Here we set ratelimit_pages to a level which ensures that when all CPUs are
1743 * dirtying in parallel, we cannot go more than 3% (1/32) over the dirty memory
1744 * thresholds.
1745 */
1746
1747void writeback_set_ratelimit(void)
1748{
1749 unsigned long background_thresh;
1750 unsigned long dirty_thresh;
1751 global_dirty_limits(&background_thresh, &dirty_thresh);
1752 global_dirty_limit = dirty_thresh;
1753 ratelimit_pages = dirty_thresh / (num_online_cpus() * 32);
1754 if (ratelimit_pages < 16)
1755 ratelimit_pages = 16;
1756}
1757
1758static int
1759ratelimit_handler(struct notifier_block *self, unsigned long action,
1760 void *hcpu)
1761{
1762
1763 switch (action & ~CPU_TASKS_FROZEN) {
1764 case CPU_ONLINE:
1765 case CPU_DEAD:
1766 writeback_set_ratelimit();
1767 return NOTIFY_OK;
1768 default:
1769 return NOTIFY_DONE;
1770 }
1771}
1772
1773static struct notifier_block ratelimit_nb = {
1774 .notifier_call = ratelimit_handler,
1775 .next = NULL,
1776};
1777
1778/*
1779 * Called early on to tune the page writeback dirty limits.
1780 *
1781 * We used to scale dirty pages according to how total memory
1782 * related to pages that could be allocated for buffers (by
1783 * comparing nr_free_buffer_pages() to vm_total_pages.
1784 *
1785 * However, that was when we used "dirty_ratio" to scale with
1786 * all memory, and we don't do that any more. "dirty_ratio"
1787 * is now applied to total non-HIGHPAGE memory (by subtracting
1788 * totalhigh_pages from vm_total_pages), and as such we can't
1789 * get into the old insane situation any more where we had
1790 * large amounts of dirty pages compared to a small amount of
1791 * non-HIGHMEM memory.
1792 *
1793 * But we might still want to scale the dirty_ratio by how
1794 * much memory the box has..
1795 */
1796void __init page_writeback_init(void)
1797{
1798 writeback_set_ratelimit();
1799 register_cpu_notifier(&ratelimit_nb);
1800
1801 fprop_global_init(&writeout_completions);
1802}
1803
1804/**
1805 * tag_pages_for_writeback - tag pages to be written by write_cache_pages
1806 * @mapping: address space structure to write
1807 * @start: starting page index
1808 * @end: ending page index (inclusive)
1809 *
1810 * This function scans the page range from @start to @end (inclusive) and tags
1811 * all pages that have DIRTY tag set with a special TOWRITE tag. The idea is
1812 * that write_cache_pages (or whoever calls this function) will then use
1813 * TOWRITE tag to identify pages eligible for writeback. This mechanism is
1814 * used to avoid livelocking of writeback by a process steadily creating new
1815 * dirty pages in the file (thus it is important for this function to be quick
1816 * so that it can tag pages faster than a dirtying process can create them).
1817 */
1818/*
1819 * We tag pages in batches of WRITEBACK_TAG_BATCH to reduce tree_lock latency.
1820 */
1821void tag_pages_for_writeback(struct address_space *mapping,
1822 pgoff_t start, pgoff_t end)
1823{
1824#define WRITEBACK_TAG_BATCH 4096
1825 unsigned long tagged;
1826
1827 do {
1828 spin_lock_irq(&mapping->tree_lock);
1829 tagged = radix_tree_range_tag_if_tagged(&mapping->page_tree,
1830 &start, end, WRITEBACK_TAG_BATCH,
1831 PAGECACHE_TAG_DIRTY, PAGECACHE_TAG_TOWRITE);
1832 spin_unlock_irq(&mapping->tree_lock);
1833 WARN_ON_ONCE(tagged > WRITEBACK_TAG_BATCH);
1834 cond_resched();
1835 /* We check 'start' to handle wrapping when end == ~0UL */
1836 } while (tagged >= WRITEBACK_TAG_BATCH && start);
1837}
1838EXPORT_SYMBOL(tag_pages_for_writeback);
1839
1840/**
1841 * write_cache_pages - walk the list of dirty pages of the given address space and write all of them.
1842 * @mapping: address space structure to write
1843 * @wbc: subtract the number of written pages from *@wbc->nr_to_write
1844 * @writepage: function called for each page
1845 * @data: data passed to writepage function
1846 *
1847 * If a page is already under I/O, write_cache_pages() skips it, even
1848 * if it's dirty. This is desirable behaviour for memory-cleaning writeback,
1849 * but it is INCORRECT for data-integrity system calls such as fsync(). fsync()
1850 * and msync() need to guarantee that all the data which was dirty at the time
1851 * the call was made get new I/O started against them. If wbc->sync_mode is
1852 * WB_SYNC_ALL then we were called for data integrity and we must wait for
1853 * existing IO to complete.
1854 *
1855 * To avoid livelocks (when other process dirties new pages), we first tag
1856 * pages which should be written back with TOWRITE tag and only then start
1857 * writing them. For data-integrity sync we have to be careful so that we do
1858 * not miss some pages (e.g., because some other process has cleared TOWRITE
1859 * tag we set). The rule we follow is that TOWRITE tag can be cleared only
1860 * by the process clearing the DIRTY tag (and submitting the page for IO).
1861 */
1862int write_cache_pages(struct address_space *mapping,
1863 struct writeback_control *wbc, writepage_t writepage,
1864 void *data)
1865{
1866 int ret = 0;
1867 int done = 0;
1868 struct pagevec pvec;
1869 int nr_pages;
1870 pgoff_t uninitialized_var(writeback_index);
1871 pgoff_t index;
1872 pgoff_t end; /* Inclusive */
1873 pgoff_t done_index;
1874 int cycled;
1875 int range_whole = 0;
1876 int tag;
1877
1878 pagevec_init(&pvec, 0);
1879 if (wbc->range_cyclic) {
1880 writeback_index = mapping->writeback_index; /* prev offset */
1881 index = writeback_index;
1882 if (index == 0)
1883 cycled = 1;
1884 else
1885 cycled = 0;
1886 end = -1;
1887 } else {
1888 index = wbc->range_start >> PAGE_CACHE_SHIFT;
1889 end = wbc->range_end >> PAGE_CACHE_SHIFT;
1890 if (wbc->range_start == 0 && wbc->range_end == LLONG_MAX)
1891 range_whole = 1;
1892 cycled = 1; /* ignore range_cyclic tests */
1893 }
1894 if (wbc->sync_mode == WB_SYNC_ALL || wbc->tagged_writepages)
1895 tag = PAGECACHE_TAG_TOWRITE;
1896 else
1897 tag = PAGECACHE_TAG_DIRTY;
1898retry:
1899 if (wbc->sync_mode == WB_SYNC_ALL || wbc->tagged_writepages)
1900 tag_pages_for_writeback(mapping, index, end);
1901 done_index = index;
1902 while (!done && (index <= end)) {
1903 int i;
1904
1905 nr_pages = pagevec_lookup_tag(&pvec, mapping, &index, tag,
1906 min(end - index, (pgoff_t)PAGEVEC_SIZE-1) + 1);
1907 if (nr_pages == 0)
1908 break;
1909
1910 for (i = 0; i < nr_pages; i++) {
1911 struct page *page = pvec.pages[i];
1912
1913 /*
1914 * At this point, the page may be truncated or
1915 * invalidated (changing page->mapping to NULL), or
1916 * even swizzled back from swapper_space to tmpfs file
1917 * mapping. However, page->index will not change
1918 * because we have a reference on the page.
1919 */
1920 if (page->index > end) {
1921 /*
1922 * can't be range_cyclic (1st pass) because
1923 * end == -1 in that case.
1924 */
1925 done = 1;
1926 break;
1927 }
1928
1929 done_index = page->index;
1930
1931 lock_page(page);
1932
1933 /*
1934 * Page truncated or invalidated. We can freely skip it
1935 * then, even for data integrity operations: the page
1936 * has disappeared concurrently, so there could be no
1937 * real expectation of this data interity operation
1938 * even if there is now a new, dirty page at the same
1939 * pagecache address.
1940 */
1941 if (unlikely(page->mapping != mapping)) {
1942continue_unlock:
1943 unlock_page(page);
1944 continue;
1945 }
1946
1947 if (!PageDirty(page)) {
1948 /* someone wrote it for us */
1949 goto continue_unlock;
1950 }
1951
1952 if (PageWriteback(page)) {
1953 if (wbc->sync_mode != WB_SYNC_NONE)
1954 wait_on_page_writeback(page);
1955 else
1956 goto continue_unlock;
1957 }
1958
1959 BUG_ON(PageWriteback(page));
1960 if (!clear_page_dirty_for_io(page))
1961 goto continue_unlock;
1962
1963 trace_wbc_writepage(wbc, mapping->backing_dev_info);
1964 ret = (*writepage)(page, wbc, data);
1965 if (unlikely(ret)) {
1966 if (ret == AOP_WRITEPAGE_ACTIVATE) {
1967 unlock_page(page);
1968 ret = 0;
1969 } else {
1970 /*
1971 * done_index is set past this page,
1972 * so media errors will not choke
1973 * background writeout for the entire
1974 * file. This has consequences for
1975 * range_cyclic semantics (ie. it may
1976 * not be suitable for data integrity
1977 * writeout).
1978 */
1979 done_index = page->index + 1;
1980 done = 1;
1981 break;
1982 }
1983 }
1984
1985 /*
1986 * We stop writing back only if we are not doing
1987 * integrity sync. In case of integrity sync we have to
1988 * keep going until we have written all the pages
1989 * we tagged for writeback prior to entering this loop.
1990 */
1991 if (--wbc->nr_to_write <= 0 &&
1992 wbc->sync_mode == WB_SYNC_NONE) {
1993 done = 1;
1994 break;
1995 }
1996 }
1997 pagevec_release(&pvec);
1998 cond_resched();
1999 }
2000 if (!cycled && !done) {
2001 /*
2002 * range_cyclic:
2003 * We hit the last page and there is more work to be done: wrap
2004 * back to the start of the file
2005 */
2006 cycled = 1;
2007 index = 0;
2008 end = writeback_index - 1;
2009 goto retry;
2010 }
2011 if (wbc->range_cyclic || (range_whole && wbc->nr_to_write > 0))
2012 mapping->writeback_index = done_index;
2013
2014 return ret;
2015}
2016EXPORT_SYMBOL(write_cache_pages);
2017
2018/*
2019 * Function used by generic_writepages to call the real writepage
2020 * function and set the mapping flags on error
2021 */
2022static int __writepage(struct page *page, struct writeback_control *wbc,
2023 void *data)
2024{
2025 struct address_space *mapping = data;
2026 int ret = mapping->a_ops->writepage(page, wbc);
2027 mapping_set_error(mapping, ret);
2028 return ret;
2029}
2030
2031/**
2032 * generic_writepages - walk the list of dirty pages of the given address space and writepage() all of them.
2033 * @mapping: address space structure to write
2034 * @wbc: subtract the number of written pages from *@wbc->nr_to_write
2035 *
2036 * This is a library function, which implements the writepages()
2037 * address_space_operation.
2038 */
2039int generic_writepages(struct address_space *mapping,
2040 struct writeback_control *wbc)
2041{
2042 struct blk_plug plug;
2043 int ret;
2044
2045 /* deal with chardevs and other special file */
2046 if (!mapping->a_ops->writepage)
2047 return 0;
2048
2049 blk_start_plug(&plug);
2050 ret = write_cache_pages(mapping, wbc, __writepage, mapping);
2051 blk_finish_plug(&plug);
2052 return ret;
2053}
2054
2055EXPORT_SYMBOL(generic_writepages);
2056
2057int do_writepages(struct address_space *mapping, struct writeback_control *wbc)
2058{
2059 int ret;
2060
2061 if (wbc->nr_to_write <= 0)
2062 return 0;
2063 if (mapping->a_ops->writepages)
2064 ret = mapping->a_ops->writepages(mapping, wbc);
2065 else
2066 ret = generic_writepages(mapping, wbc);
2067 return ret;
2068}
2069
2070/**
2071 * write_one_page - write out a single page and optionally wait on I/O
2072 * @page: the page to write
2073 * @wait: if true, wait on writeout
2074 *
2075 * The page must be locked by the caller and will be unlocked upon return.
2076 *
2077 * write_one_page() returns a negative error code if I/O failed.
2078 */
2079int write_one_page(struct page *page, int wait)
2080{
2081 struct address_space *mapping = page->mapping;
2082 int ret = 0;
2083 struct writeback_control wbc = {
2084 .sync_mode = WB_SYNC_ALL,
2085 .nr_to_write = 1,
2086 };
2087
2088 BUG_ON(!PageLocked(page));
2089
2090 if (wait)
2091 wait_on_page_writeback(page);
2092
2093 if (clear_page_dirty_for_io(page)) {
2094 page_cache_get(page);
2095 ret = mapping->a_ops->writepage(page, &wbc);
2096 if (ret == 0 && wait) {
2097 wait_on_page_writeback(page);
2098 if (PageError(page))
2099 ret = -EIO;
2100 }
2101 page_cache_release(page);
2102 } else {
2103 unlock_page(page);
2104 }
2105 return ret;
2106}
2107EXPORT_SYMBOL(write_one_page);
2108
2109/*
2110 * For address_spaces which do not use buffers nor write back.
2111 */
2112int __set_page_dirty_no_writeback(struct page *page)
2113{
2114 if (!PageDirty(page))
2115 return !TestSetPageDirty(page);
2116 return 0;
2117}
2118
2119/*
2120 * Helper function for set_page_dirty family.
2121 * NOTE: This relies on being atomic wrt interrupts.
2122 */
2123void account_page_dirtied(struct page *page, struct address_space *mapping)
2124{
2125 trace_writeback_dirty_page(page, mapping);
2126
2127 if (mapping_cap_account_dirty(mapping)) {
2128 __inc_zone_page_state(page, NR_FILE_DIRTY);
2129 __inc_zone_page_state(page, NR_DIRTIED);
2130 __inc_bdi_stat(mapping->backing_dev_info, BDI_RECLAIMABLE);
2131 __inc_bdi_stat(mapping->backing_dev_info, BDI_DIRTIED);
2132 task_io_account_write(PAGE_CACHE_SIZE);
2133 current->nr_dirtied++;
2134 this_cpu_inc(bdp_ratelimits);
2135 }
2136}
2137EXPORT_SYMBOL(account_page_dirtied);
2138
2139/*
2140 * Helper function for set_page_writeback family.
2141 *
2142 * The caller must hold mem_cgroup_begin/end_update_page_stat() lock
2143 * while calling this function.
2144 * See test_set_page_writeback for example.
2145 *
2146 * NOTE: Unlike account_page_dirtied this does not rely on being atomic
2147 * wrt interrupts.
2148 */
2149void account_page_writeback(struct page *page)
2150{
2151 mem_cgroup_inc_page_stat(page, MEM_CGROUP_STAT_WRITEBACK);
2152 inc_zone_page_state(page, NR_WRITEBACK);
2153}
2154EXPORT_SYMBOL(account_page_writeback);
2155
2156/*
2157 * For address_spaces which do not use buffers. Just tag the page as dirty in
2158 * its radix tree.
2159 *
2160 * This is also used when a single buffer is being dirtied: we want to set the
2161 * page dirty in that case, but not all the buffers. This is a "bottom-up"
2162 * dirtying, whereas __set_page_dirty_buffers() is a "top-down" dirtying.
2163 *
2164 * Most callers have locked the page, which pins the address_space in memory.
2165 * But zap_pte_range() does not lock the page, however in that case the
2166 * mapping is pinned by the vma's ->vm_file reference.
2167 *
2168 * We take care to handle the case where the page was truncated from the
2169 * mapping by re-checking page_mapping() inside tree_lock.
2170 */
2171int __set_page_dirty_nobuffers(struct page *page)
2172{
2173 if (!TestSetPageDirty(page)) {
2174 struct address_space *mapping = page_mapping(page);
2175 struct address_space *mapping2;
2176 unsigned long flags;
2177
2178 if (!mapping)
2179 return 1;
2180
2181 spin_lock_irqsave(&mapping->tree_lock, flags);
2182 mapping2 = page_mapping(page);
2183 if (mapping2) { /* Race with truncate? */
2184 BUG_ON(mapping2 != mapping);
2185 WARN_ON_ONCE(!PagePrivate(page) && !PageUptodate(page));
2186 account_page_dirtied(page, mapping);
2187 radix_tree_tag_set(&mapping->page_tree,
2188 page_index(page), PAGECACHE_TAG_DIRTY);
2189 }
2190 spin_unlock_irqrestore(&mapping->tree_lock, flags);
2191 if (mapping->host) {
2192 /* !PageAnon && !swapper_space */
2193 __mark_inode_dirty(mapping->host, I_DIRTY_PAGES);
2194 }
2195 return 1;
2196 }
2197 return 0;
2198}
2199EXPORT_SYMBOL(__set_page_dirty_nobuffers);
2200
2201/*
2202 * Call this whenever redirtying a page, to de-account the dirty counters
2203 * (NR_DIRTIED, BDI_DIRTIED, tsk->nr_dirtied), so that they match the written
2204 * counters (NR_WRITTEN, BDI_WRITTEN) in long term. The mismatches will lead to
2205 * systematic errors in balanced_dirty_ratelimit and the dirty pages position
2206 * control.
2207 */
2208void account_page_redirty(struct page *page)
2209{
2210 struct address_space *mapping = page->mapping;
2211 if (mapping && mapping_cap_account_dirty(mapping)) {
2212 current->nr_dirtied--;
2213 dec_zone_page_state(page, NR_DIRTIED);
2214 dec_bdi_stat(mapping->backing_dev_info, BDI_DIRTIED);
2215 }
2216}
2217EXPORT_SYMBOL(account_page_redirty);
2218
2219/*
2220 * When a writepage implementation decides that it doesn't want to write this
2221 * page for some reason, it should redirty the locked page via
2222 * redirty_page_for_writepage() and it should then unlock the page and return 0
2223 */
2224int redirty_page_for_writepage(struct writeback_control *wbc, struct page *page)
2225{
2226 wbc->pages_skipped++;
2227 account_page_redirty(page);
2228 return __set_page_dirty_nobuffers(page);
2229}
2230EXPORT_SYMBOL(redirty_page_for_writepage);
2231
2232/*
2233 * Dirty a page.
2234 *
2235 * For pages with a mapping this should be done under the page lock
2236 * for the benefit of asynchronous memory errors who prefer a consistent
2237 * dirty state. This rule can be broken in some special cases,
2238 * but should be better not to.
2239 *
2240 * If the mapping doesn't provide a set_page_dirty a_op, then
2241 * just fall through and assume that it wants buffer_heads.
2242 */
2243int set_page_dirty(struct page *page)
2244{
2245 struct address_space *mapping = page_mapping(page);
2246
2247 if (likely(mapping)) {
2248 int (*spd)(struct page *) = mapping->a_ops->set_page_dirty;
2249 /*
2250 * readahead/lru_deactivate_page could remain
2251 * PG_readahead/PG_reclaim due to race with end_page_writeback
2252 * About readahead, if the page is written, the flags would be
2253 * reset. So no problem.
2254 * About lru_deactivate_page, if the page is redirty, the flag
2255 * will be reset. So no problem. but if the page is used by readahead
2256 * it will confuse readahead and make it restart the size rampup
2257 * process. But it's a trivial problem.
2258 */
2259 ClearPageReclaim(page);
2260#ifdef CONFIG_BLOCK
2261 if (!spd)
2262 spd = __set_page_dirty_buffers;
2263#endif
2264 return (*spd)(page);
2265 }
2266 if (!PageDirty(page)) {
2267 if (!TestSetPageDirty(page))
2268 return 1;
2269 }
2270 return 0;
2271}
2272EXPORT_SYMBOL(set_page_dirty);
2273
2274/*
2275 * set_page_dirty() is racy if the caller has no reference against
2276 * page->mapping->host, and if the page is unlocked. This is because another
2277 * CPU could truncate the page off the mapping and then free the mapping.
2278 *
2279 * Usually, the page _is_ locked, or the caller is a user-space process which
2280 * holds a reference on the inode by having an open file.
2281 *
2282 * In other cases, the page should be locked before running set_page_dirty().
2283 */
2284int set_page_dirty_lock(struct page *page)
2285{
2286 int ret;
2287
2288 lock_page(page);
2289 ret = set_page_dirty(page);
2290 unlock_page(page);
2291 return ret;
2292}
2293EXPORT_SYMBOL(set_page_dirty_lock);
2294
2295/*
2296 * Clear a page's dirty flag, while caring for dirty memory accounting.
2297 * Returns true if the page was previously dirty.
2298 *
2299 * This is for preparing to put the page under writeout. We leave the page
2300 * tagged as dirty in the radix tree so that a concurrent write-for-sync
2301 * can discover it via a PAGECACHE_TAG_DIRTY walk. The ->writepage
2302 * implementation will run either set_page_writeback() or set_page_dirty(),
2303 * at which stage we bring the page's dirty flag and radix-tree dirty tag
2304 * back into sync.
2305 *
2306 * This incoherency between the page's dirty flag and radix-tree tag is
2307 * unfortunate, but it only exists while the page is locked.
2308 */
2309int clear_page_dirty_for_io(struct page *page)
2310{
2311 struct address_space *mapping = page_mapping(page);
2312
2313 BUG_ON(!PageLocked(page));
2314
2315 if (mapping && mapping_cap_account_dirty(mapping)) {
2316 /*
2317 * Yes, Virginia, this is indeed insane.
2318 *
2319 * We use this sequence to make sure that
2320 * (a) we account for dirty stats properly
2321 * (b) we tell the low-level filesystem to
2322 * mark the whole page dirty if it was
2323 * dirty in a pagetable. Only to then
2324 * (c) clean the page again and return 1 to
2325 * cause the writeback.
2326 *
2327 * This way we avoid all nasty races with the
2328 * dirty bit in multiple places and clearing
2329 * them concurrently from different threads.
2330 *
2331 * Note! Normally the "set_page_dirty(page)"
2332 * has no effect on the actual dirty bit - since
2333 * that will already usually be set. But we
2334 * need the side effects, and it can help us
2335 * avoid races.
2336 *
2337 * We basically use the page "master dirty bit"
2338 * as a serialization point for all the different
2339 * threads doing their things.
2340 */
2341 if (page_mkclean(page))
2342 set_page_dirty(page);
2343 /*
2344 * We carefully synchronise fault handlers against
2345 * installing a dirty pte and marking the page dirty
2346 * at this point. We do this by having them hold the
2347 * page lock at some point after installing their
2348 * pte, but before marking the page dirty.
2349 * Pages are always locked coming in here, so we get
2350 * the desired exclusion. See mm/memory.c:do_wp_page()
2351 * for more comments.
2352 */
2353 if (TestClearPageDirty(page)) {
2354 dec_zone_page_state(page, NR_FILE_DIRTY);
2355 dec_bdi_stat(mapping->backing_dev_info,
2356 BDI_RECLAIMABLE);
2357 return 1;
2358 }
2359 return 0;
2360 }
2361 return TestClearPageDirty(page);
2362}
2363EXPORT_SYMBOL(clear_page_dirty_for_io);
2364
2365int test_clear_page_writeback(struct page *page)
2366{
2367 struct address_space *mapping = page_mapping(page);
2368 int ret;
2369 bool locked;
2370 unsigned long memcg_flags;
2371
2372 mem_cgroup_begin_update_page_stat(page, &locked, &memcg_flags);
2373 if (mapping) {
2374 struct backing_dev_info *bdi = mapping->backing_dev_info;
2375 unsigned long flags;
2376
2377 spin_lock_irqsave(&mapping->tree_lock, flags);
2378 ret = TestClearPageWriteback(page);
2379 if (ret) {
2380 radix_tree_tag_clear(&mapping->page_tree,
2381 page_index(page),
2382 PAGECACHE_TAG_WRITEBACK);
2383 if (bdi_cap_account_writeback(bdi)) {
2384 __dec_bdi_stat(bdi, BDI_WRITEBACK);
2385 __bdi_writeout_inc(bdi);
2386 }
2387 }
2388 spin_unlock_irqrestore(&mapping->tree_lock, flags);
2389 } else {
2390 ret = TestClearPageWriteback(page);
2391 }
2392 if (ret) {
2393 mem_cgroup_dec_page_stat(page, MEM_CGROUP_STAT_WRITEBACK);
2394 dec_zone_page_state(page, NR_WRITEBACK);
2395 inc_zone_page_state(page, NR_WRITTEN);
2396 }
2397 mem_cgroup_end_update_page_stat(page, &locked, &memcg_flags);
2398 return ret;
2399}
2400
2401int test_set_page_writeback(struct page *page)
2402{
2403 struct address_space *mapping = page_mapping(page);
2404 int ret;
2405 bool locked;
2406 unsigned long memcg_flags;
2407
2408 mem_cgroup_begin_update_page_stat(page, &locked, &memcg_flags);
2409 if (mapping) {
2410 struct backing_dev_info *bdi = mapping->backing_dev_info;
2411 unsigned long flags;
2412
2413 spin_lock_irqsave(&mapping->tree_lock, flags);
2414 ret = TestSetPageWriteback(page);
2415 if (!ret) {
2416 radix_tree_tag_set(&mapping->page_tree,
2417 page_index(page),
2418 PAGECACHE_TAG_WRITEBACK);
2419 if (bdi_cap_account_writeback(bdi))
2420 __inc_bdi_stat(bdi, BDI_WRITEBACK);
2421 }
2422 if (!PageDirty(page))
2423 radix_tree_tag_clear(&mapping->page_tree,
2424 page_index(page),
2425 PAGECACHE_TAG_DIRTY);
2426 radix_tree_tag_clear(&mapping->page_tree,
2427 page_index(page),
2428 PAGECACHE_TAG_TOWRITE);
2429 spin_unlock_irqrestore(&mapping->tree_lock, flags);
2430 } else {
2431 ret = TestSetPageWriteback(page);
2432 }
2433 if (!ret)
2434 account_page_writeback(page);
2435 mem_cgroup_end_update_page_stat(page, &locked, &memcg_flags);
2436 return ret;
2437
2438}
2439EXPORT_SYMBOL(test_set_page_writeback);
2440
2441/*
2442 * Return true if any of the pages in the mapping are marked with the
2443 * passed tag.
2444 */
2445int mapping_tagged(struct address_space *mapping, int tag)
2446{
2447 return radix_tree_tagged(&mapping->page_tree, tag);
2448}
2449EXPORT_SYMBOL(mapping_tagged);
2450
2451/**
2452 * wait_for_stable_page() - wait for writeback to finish, if necessary.
2453 * @page: The page to wait on.
2454 *
2455 * This function determines if the given page is related to a backing device
2456 * that requires page contents to be held stable during writeback. If so, then
2457 * it will wait for any pending writeback to complete.
2458 */
2459void wait_for_stable_page(struct page *page)
2460{
2461 struct address_space *mapping = page_mapping(page);
2462 struct backing_dev_info *bdi = mapping->backing_dev_info;
2463
2464 if (!bdi_cap_stable_pages_required(bdi))
2465 return;
2466
2467 wait_on_page_writeback(page);
2468}
2469EXPORT_SYMBOL_GPL(wait_for_stable_page);