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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/sched/signal.h>
40#include <linux/mm_inline.h>
41#include <trace/events/writeback.h>
42
43#include "internal.h"
44
45/*
46 * Sleep at most 200ms at a time in balance_dirty_pages().
47 */
48#define MAX_PAUSE max(HZ/5, 1)
49
50/*
51 * Try to keep balance_dirty_pages() call intervals higher than this many pages
52 * by raising pause time to max_pause when falls below it.
53 */
54#define DIRTY_POLL_THRESH (128 >> (PAGE_SHIFT - 10))
55
56/*
57 * Estimate write bandwidth at 200ms intervals.
58 */
59#define BANDWIDTH_INTERVAL max(HZ/5, 1)
60
61#define RATELIMIT_CALC_SHIFT 10
62
63/*
64 * After a CPU has dirtied this many pages, balance_dirty_pages_ratelimited
65 * will look to see if it needs to force writeback or throttling.
66 */
67static long ratelimit_pages = 32;
68
69/* The following parameters are exported via /proc/sys/vm */
70
71/*
72 * Start background writeback (via writeback threads) at this percentage
73 */
74int dirty_background_ratio = 10;
75
76/*
77 * dirty_background_bytes starts at 0 (disabled) so that it is a function of
78 * dirty_background_ratio * the amount of dirtyable memory
79 */
80unsigned long dirty_background_bytes;
81
82/*
83 * free highmem will not be subtracted from the total free memory
84 * for calculating free ratios if vm_highmem_is_dirtyable is true
85 */
86int vm_highmem_is_dirtyable;
87
88/*
89 * The generator of dirty data starts writeback at this percentage
90 */
91int vm_dirty_ratio = 20;
92
93/*
94 * vm_dirty_bytes starts at 0 (disabled) so that it is a function of
95 * vm_dirty_ratio * the amount of dirtyable memory
96 */
97unsigned long vm_dirty_bytes;
98
99/*
100 * The interval between `kupdate'-style writebacks
101 */
102unsigned int dirty_writeback_interval = 5 * 100; /* centiseconds */
103
104EXPORT_SYMBOL_GPL(dirty_writeback_interval);
105
106/*
107 * The longest time for which data is allowed to remain dirty
108 */
109unsigned int dirty_expire_interval = 30 * 100; /* centiseconds */
110
111/*
112 * Flag that makes the machine dump writes/reads and block dirtyings.
113 */
114int block_dump;
115
116/*
117 * Flag that puts the machine in "laptop mode". Doubles as a timeout in jiffies:
118 * a full sync is triggered after this time elapses without any disk activity.
119 */
120int laptop_mode;
121
122EXPORT_SYMBOL(laptop_mode);
123
124/* End of sysctl-exported parameters */
125
126struct wb_domain global_wb_domain;
127
128/* consolidated parameters for balance_dirty_pages() and its subroutines */
129struct dirty_throttle_control {
130#ifdef CONFIG_CGROUP_WRITEBACK
131 struct wb_domain *dom;
132 struct dirty_throttle_control *gdtc; /* only set in memcg dtc's */
133#endif
134 struct bdi_writeback *wb;
135 struct fprop_local_percpu *wb_completions;
136
137 unsigned long avail; /* dirtyable */
138 unsigned long dirty; /* file_dirty + write + nfs */
139 unsigned long thresh; /* dirty threshold */
140 unsigned long bg_thresh; /* dirty background threshold */
141
142 unsigned long wb_dirty; /* per-wb counterparts */
143 unsigned long wb_thresh;
144 unsigned long wb_bg_thresh;
145
146 unsigned long pos_ratio;
147};
148
149/*
150 * Length of period for aging writeout fractions of bdis. This is an
151 * arbitrarily chosen number. The longer the period, the slower fractions will
152 * reflect changes in current writeout rate.
153 */
154#define VM_COMPLETIONS_PERIOD_LEN (3*HZ)
155
156#ifdef CONFIG_CGROUP_WRITEBACK
157
158#define GDTC_INIT(__wb) .wb = (__wb), \
159 .dom = &global_wb_domain, \
160 .wb_completions = &(__wb)->completions
161
162#define GDTC_INIT_NO_WB .dom = &global_wb_domain
163
164#define MDTC_INIT(__wb, __gdtc) .wb = (__wb), \
165 .dom = mem_cgroup_wb_domain(__wb), \
166 .wb_completions = &(__wb)->memcg_completions, \
167 .gdtc = __gdtc
168
169static bool mdtc_valid(struct dirty_throttle_control *dtc)
170{
171 return dtc->dom;
172}
173
174static struct wb_domain *dtc_dom(struct dirty_throttle_control *dtc)
175{
176 return dtc->dom;
177}
178
179static struct dirty_throttle_control *mdtc_gdtc(struct dirty_throttle_control *mdtc)
180{
181 return mdtc->gdtc;
182}
183
184static struct fprop_local_percpu *wb_memcg_completions(struct bdi_writeback *wb)
185{
186 return &wb->memcg_completions;
187}
188
189static void wb_min_max_ratio(struct bdi_writeback *wb,
190 unsigned long *minp, unsigned long *maxp)
191{
192 unsigned long this_bw = wb->avg_write_bandwidth;
193 unsigned long tot_bw = atomic_long_read(&wb->bdi->tot_write_bandwidth);
194 unsigned long long min = wb->bdi->min_ratio;
195 unsigned long long max = wb->bdi->max_ratio;
196
197 /*
198 * @wb may already be clean by the time control reaches here and
199 * the total may not include its bw.
200 */
201 if (this_bw < tot_bw) {
202 if (min) {
203 min *= this_bw;
204 do_div(min, tot_bw);
205 }
206 if (max < 100) {
207 max *= this_bw;
208 do_div(max, tot_bw);
209 }
210 }
211
212 *minp = min;
213 *maxp = max;
214}
215
216#else /* CONFIG_CGROUP_WRITEBACK */
217
218#define GDTC_INIT(__wb) .wb = (__wb), \
219 .wb_completions = &(__wb)->completions
220#define GDTC_INIT_NO_WB
221#define MDTC_INIT(__wb, __gdtc)
222
223static bool mdtc_valid(struct dirty_throttle_control *dtc)
224{
225 return false;
226}
227
228static struct wb_domain *dtc_dom(struct dirty_throttle_control *dtc)
229{
230 return &global_wb_domain;
231}
232
233static struct dirty_throttle_control *mdtc_gdtc(struct dirty_throttle_control *mdtc)
234{
235 return NULL;
236}
237
238static struct fprop_local_percpu *wb_memcg_completions(struct bdi_writeback *wb)
239{
240 return NULL;
241}
242
243static void wb_min_max_ratio(struct bdi_writeback *wb,
244 unsigned long *minp, unsigned long *maxp)
245{
246 *minp = wb->bdi->min_ratio;
247 *maxp = wb->bdi->max_ratio;
248}
249
250#endif /* CONFIG_CGROUP_WRITEBACK */
251
252/*
253 * In a memory zone, there is a certain amount of pages we consider
254 * available for the page cache, which is essentially the number of
255 * free and reclaimable pages, minus some zone reserves to protect
256 * lowmem and the ability to uphold the zone's watermarks without
257 * requiring writeback.
258 *
259 * This number of dirtyable pages is the base value of which the
260 * user-configurable dirty ratio is the effictive number of pages that
261 * are allowed to be actually dirtied. Per individual zone, or
262 * globally by using the sum of dirtyable pages over all zones.
263 *
264 * Because the user is allowed to specify the dirty limit globally as
265 * absolute number of bytes, calculating the per-zone dirty limit can
266 * require translating the configured limit into a percentage of
267 * global dirtyable memory first.
268 */
269
270/**
271 * node_dirtyable_memory - number of dirtyable pages in a node
272 * @pgdat: the node
273 *
274 * Returns the node's number of pages potentially available for dirty
275 * page cache. This is the base value for the per-node dirty limits.
276 */
277static unsigned long node_dirtyable_memory(struct pglist_data *pgdat)
278{
279 unsigned long nr_pages = 0;
280 int z;
281
282 for (z = 0; z < MAX_NR_ZONES; z++) {
283 struct zone *zone = pgdat->node_zones + z;
284
285 if (!populated_zone(zone))
286 continue;
287
288 nr_pages += zone_page_state(zone, NR_FREE_PAGES);
289 }
290
291 /*
292 * Pages reserved for the kernel should not be considered
293 * dirtyable, to prevent a situation where reclaim has to
294 * clean pages in order to balance the zones.
295 */
296 nr_pages -= min(nr_pages, pgdat->totalreserve_pages);
297
298 nr_pages += node_page_state(pgdat, NR_INACTIVE_FILE);
299 nr_pages += node_page_state(pgdat, NR_ACTIVE_FILE);
300
301 return nr_pages;
302}
303
304static unsigned long highmem_dirtyable_memory(unsigned long total)
305{
306#ifdef CONFIG_HIGHMEM
307 int node;
308 unsigned long x = 0;
309 int i;
310
311 for_each_node_state(node, N_HIGH_MEMORY) {
312 for (i = ZONE_NORMAL + 1; i < MAX_NR_ZONES; i++) {
313 struct zone *z;
314 unsigned long nr_pages;
315
316 if (!is_highmem_idx(i))
317 continue;
318
319 z = &NODE_DATA(node)->node_zones[i];
320 if (!populated_zone(z))
321 continue;
322
323 nr_pages = zone_page_state(z, NR_FREE_PAGES);
324 /* watch for underflows */
325 nr_pages -= min(nr_pages, high_wmark_pages(z));
326 nr_pages += zone_page_state(z, NR_ZONE_INACTIVE_FILE);
327 nr_pages += zone_page_state(z, NR_ZONE_ACTIVE_FILE);
328 x += nr_pages;
329 }
330 }
331
332 /*
333 * Unreclaimable memory (kernel memory or anonymous memory
334 * without swap) can bring down the dirtyable pages below
335 * the zone's dirty balance reserve and the above calculation
336 * will underflow. However we still want to add in nodes
337 * which are below threshold (negative values) to get a more
338 * accurate calculation but make sure that the total never
339 * underflows.
340 */
341 if ((long)x < 0)
342 x = 0;
343
344 /*
345 * Make sure that the number of highmem pages is never larger
346 * than the number of the total dirtyable memory. This can only
347 * occur in very strange VM situations but we want to make sure
348 * that this does not occur.
349 */
350 return min(x, total);
351#else
352 return 0;
353#endif
354}
355
356/**
357 * global_dirtyable_memory - number of globally dirtyable pages
358 *
359 * Returns the global number of pages potentially available for dirty
360 * page cache. This is the base value for the global dirty limits.
361 */
362static unsigned long global_dirtyable_memory(void)
363{
364 unsigned long x;
365
366 x = global_zone_page_state(NR_FREE_PAGES);
367 /*
368 * Pages reserved for the kernel should not be considered
369 * dirtyable, to prevent a situation where reclaim has to
370 * clean pages in order to balance the zones.
371 */
372 x -= min(x, totalreserve_pages);
373
374 x += global_node_page_state(NR_INACTIVE_FILE);
375 x += global_node_page_state(NR_ACTIVE_FILE);
376
377 if (!vm_highmem_is_dirtyable)
378 x -= highmem_dirtyable_memory(x);
379
380 return x + 1; /* Ensure that we never return 0 */
381}
382
383/**
384 * domain_dirty_limits - calculate thresh and bg_thresh for a wb_domain
385 * @dtc: dirty_throttle_control of interest
386 *
387 * Calculate @dtc->thresh and ->bg_thresh considering
388 * vm_dirty_{bytes|ratio} and dirty_background_{bytes|ratio}. The caller
389 * must ensure that @dtc->avail is set before calling this function. The
390 * dirty limits will be lifted by 1/4 for PF_LESS_THROTTLE (ie. nfsd) and
391 * real-time tasks.
392 */
393static void domain_dirty_limits(struct dirty_throttle_control *dtc)
394{
395 const unsigned long available_memory = dtc->avail;
396 struct dirty_throttle_control *gdtc = mdtc_gdtc(dtc);
397 unsigned long bytes = vm_dirty_bytes;
398 unsigned long bg_bytes = dirty_background_bytes;
399 /* convert ratios to per-PAGE_SIZE for higher precision */
400 unsigned long ratio = (vm_dirty_ratio * PAGE_SIZE) / 100;
401 unsigned long bg_ratio = (dirty_background_ratio * PAGE_SIZE) / 100;
402 unsigned long thresh;
403 unsigned long bg_thresh;
404 struct task_struct *tsk;
405
406 /* gdtc is !NULL iff @dtc is for memcg domain */
407 if (gdtc) {
408 unsigned long global_avail = gdtc->avail;
409
410 /*
411 * The byte settings can't be applied directly to memcg
412 * domains. Convert them to ratios by scaling against
413 * globally available memory. As the ratios are in
414 * per-PAGE_SIZE, they can be obtained by dividing bytes by
415 * number of pages.
416 */
417 if (bytes)
418 ratio = min(DIV_ROUND_UP(bytes, global_avail),
419 PAGE_SIZE);
420 if (bg_bytes)
421 bg_ratio = min(DIV_ROUND_UP(bg_bytes, global_avail),
422 PAGE_SIZE);
423 bytes = bg_bytes = 0;
424 }
425
426 if (bytes)
427 thresh = DIV_ROUND_UP(bytes, PAGE_SIZE);
428 else
429 thresh = (ratio * available_memory) / PAGE_SIZE;
430
431 if (bg_bytes)
432 bg_thresh = DIV_ROUND_UP(bg_bytes, PAGE_SIZE);
433 else
434 bg_thresh = (bg_ratio * available_memory) / PAGE_SIZE;
435
436 if (bg_thresh >= thresh)
437 bg_thresh = thresh / 2;
438 tsk = current;
439 if (tsk->flags & PF_LESS_THROTTLE || rt_task(tsk)) {
440 bg_thresh += bg_thresh / 4 + global_wb_domain.dirty_limit / 32;
441 thresh += thresh / 4 + global_wb_domain.dirty_limit / 32;
442 }
443 dtc->thresh = thresh;
444 dtc->bg_thresh = bg_thresh;
445
446 /* we should eventually report the domain in the TP */
447 if (!gdtc)
448 trace_global_dirty_state(bg_thresh, thresh);
449}
450
451/**
452 * global_dirty_limits - background-writeback and dirty-throttling thresholds
453 * @pbackground: out parameter for bg_thresh
454 * @pdirty: out parameter for thresh
455 *
456 * Calculate bg_thresh and thresh for global_wb_domain. See
457 * domain_dirty_limits() for details.
458 */
459void global_dirty_limits(unsigned long *pbackground, unsigned long *pdirty)
460{
461 struct dirty_throttle_control gdtc = { GDTC_INIT_NO_WB };
462
463 gdtc.avail = global_dirtyable_memory();
464 domain_dirty_limits(&gdtc);
465
466 *pbackground = gdtc.bg_thresh;
467 *pdirty = gdtc.thresh;
468}
469
470/**
471 * node_dirty_limit - maximum number of dirty pages allowed in a node
472 * @pgdat: the node
473 *
474 * Returns the maximum number of dirty pages allowed in a node, based
475 * on the node's dirtyable memory.
476 */
477static unsigned long node_dirty_limit(struct pglist_data *pgdat)
478{
479 unsigned long node_memory = node_dirtyable_memory(pgdat);
480 struct task_struct *tsk = current;
481 unsigned long dirty;
482
483 if (vm_dirty_bytes)
484 dirty = DIV_ROUND_UP(vm_dirty_bytes, PAGE_SIZE) *
485 node_memory / global_dirtyable_memory();
486 else
487 dirty = vm_dirty_ratio * node_memory / 100;
488
489 if (tsk->flags & PF_LESS_THROTTLE || rt_task(tsk))
490 dirty += dirty / 4;
491
492 return dirty;
493}
494
495/**
496 * node_dirty_ok - tells whether a node is within its dirty limits
497 * @pgdat: the node to check
498 *
499 * Returns %true when the dirty pages in @pgdat are within the node's
500 * dirty limit, %false if the limit is exceeded.
501 */
502bool node_dirty_ok(struct pglist_data *pgdat)
503{
504 unsigned long limit = node_dirty_limit(pgdat);
505 unsigned long nr_pages = 0;
506
507 nr_pages += node_page_state(pgdat, NR_FILE_DIRTY);
508 nr_pages += node_page_state(pgdat, NR_UNSTABLE_NFS);
509 nr_pages += node_page_state(pgdat, NR_WRITEBACK);
510
511 return nr_pages <= limit;
512}
513
514int dirty_background_ratio_handler(struct ctl_table *table, int write,
515 void __user *buffer, size_t *lenp,
516 loff_t *ppos)
517{
518 int ret;
519
520 ret = proc_dointvec_minmax(table, write, buffer, lenp, ppos);
521 if (ret == 0 && write)
522 dirty_background_bytes = 0;
523 return ret;
524}
525
526int dirty_background_bytes_handler(struct ctl_table *table, int write,
527 void __user *buffer, size_t *lenp,
528 loff_t *ppos)
529{
530 int ret;
531
532 ret = proc_doulongvec_minmax(table, write, buffer, lenp, ppos);
533 if (ret == 0 && write)
534 dirty_background_ratio = 0;
535 return ret;
536}
537
538int dirty_ratio_handler(struct ctl_table *table, int write,
539 void __user *buffer, size_t *lenp,
540 loff_t *ppos)
541{
542 int old_ratio = vm_dirty_ratio;
543 int ret;
544
545 ret = proc_dointvec_minmax(table, write, buffer, lenp, ppos);
546 if (ret == 0 && write && vm_dirty_ratio != old_ratio) {
547 writeback_set_ratelimit();
548 vm_dirty_bytes = 0;
549 }
550 return ret;
551}
552
553int dirty_bytes_handler(struct ctl_table *table, int write,
554 void __user *buffer, size_t *lenp,
555 loff_t *ppos)
556{
557 unsigned long old_bytes = vm_dirty_bytes;
558 int ret;
559
560 ret = proc_doulongvec_minmax(table, write, buffer, lenp, ppos);
561 if (ret == 0 && write && vm_dirty_bytes != old_bytes) {
562 writeback_set_ratelimit();
563 vm_dirty_ratio = 0;
564 }
565 return ret;
566}
567
568static unsigned long wp_next_time(unsigned long cur_time)
569{
570 cur_time += VM_COMPLETIONS_PERIOD_LEN;
571 /* 0 has a special meaning... */
572 if (!cur_time)
573 return 1;
574 return cur_time;
575}
576
577static void wb_domain_writeout_inc(struct wb_domain *dom,
578 struct fprop_local_percpu *completions,
579 unsigned int max_prop_frac)
580{
581 __fprop_inc_percpu_max(&dom->completions, completions,
582 max_prop_frac);
583 /* First event after period switching was turned off? */
584 if (unlikely(!dom->period_time)) {
585 /*
586 * We can race with other __bdi_writeout_inc calls here but
587 * it does not cause any harm since the resulting time when
588 * timer will fire and what is in writeout_period_time will be
589 * roughly the same.
590 */
591 dom->period_time = wp_next_time(jiffies);
592 mod_timer(&dom->period_timer, dom->period_time);
593 }
594}
595
596/*
597 * Increment @wb's writeout completion count and the global writeout
598 * completion count. Called from test_clear_page_writeback().
599 */
600static inline void __wb_writeout_inc(struct bdi_writeback *wb)
601{
602 struct wb_domain *cgdom;
603
604 inc_wb_stat(wb, WB_WRITTEN);
605 wb_domain_writeout_inc(&global_wb_domain, &wb->completions,
606 wb->bdi->max_prop_frac);
607
608 cgdom = mem_cgroup_wb_domain(wb);
609 if (cgdom)
610 wb_domain_writeout_inc(cgdom, wb_memcg_completions(wb),
611 wb->bdi->max_prop_frac);
612}
613
614void wb_writeout_inc(struct bdi_writeback *wb)
615{
616 unsigned long flags;
617
618 local_irq_save(flags);
619 __wb_writeout_inc(wb);
620 local_irq_restore(flags);
621}
622EXPORT_SYMBOL_GPL(wb_writeout_inc);
623
624/*
625 * On idle system, we can be called long after we scheduled because we use
626 * deferred timers so count with missed periods.
627 */
628static void writeout_period(struct timer_list *t)
629{
630 struct wb_domain *dom = from_timer(dom, t, period_timer);
631 int miss_periods = (jiffies - dom->period_time) /
632 VM_COMPLETIONS_PERIOD_LEN;
633
634 if (fprop_new_period(&dom->completions, miss_periods + 1)) {
635 dom->period_time = wp_next_time(dom->period_time +
636 miss_periods * VM_COMPLETIONS_PERIOD_LEN);
637 mod_timer(&dom->period_timer, dom->period_time);
638 } else {
639 /*
640 * Aging has zeroed all fractions. Stop wasting CPU on period
641 * updates.
642 */
643 dom->period_time = 0;
644 }
645}
646
647int wb_domain_init(struct wb_domain *dom, gfp_t gfp)
648{
649 memset(dom, 0, sizeof(*dom));
650
651 spin_lock_init(&dom->lock);
652
653 timer_setup(&dom->period_timer, writeout_period, TIMER_DEFERRABLE);
654
655 dom->dirty_limit_tstamp = jiffies;
656
657 return fprop_global_init(&dom->completions, gfp);
658}
659
660#ifdef CONFIG_CGROUP_WRITEBACK
661void wb_domain_exit(struct wb_domain *dom)
662{
663 del_timer_sync(&dom->period_timer);
664 fprop_global_destroy(&dom->completions);
665}
666#endif
667
668/*
669 * bdi_min_ratio keeps the sum of the minimum dirty shares of all
670 * registered backing devices, which, for obvious reasons, can not
671 * exceed 100%.
672 */
673static unsigned int bdi_min_ratio;
674
675int bdi_set_min_ratio(struct backing_dev_info *bdi, unsigned int min_ratio)
676{
677 int ret = 0;
678
679 spin_lock_bh(&bdi_lock);
680 if (min_ratio > bdi->max_ratio) {
681 ret = -EINVAL;
682 } else {
683 min_ratio -= bdi->min_ratio;
684 if (bdi_min_ratio + min_ratio < 100) {
685 bdi_min_ratio += min_ratio;
686 bdi->min_ratio += min_ratio;
687 } else {
688 ret = -EINVAL;
689 }
690 }
691 spin_unlock_bh(&bdi_lock);
692
693 return ret;
694}
695
696int bdi_set_max_ratio(struct backing_dev_info *bdi, unsigned max_ratio)
697{
698 int ret = 0;
699
700 if (max_ratio > 100)
701 return -EINVAL;
702
703 spin_lock_bh(&bdi_lock);
704 if (bdi->min_ratio > max_ratio) {
705 ret = -EINVAL;
706 } else {
707 bdi->max_ratio = max_ratio;
708 bdi->max_prop_frac = (FPROP_FRAC_BASE * max_ratio) / 100;
709 }
710 spin_unlock_bh(&bdi_lock);
711
712 return ret;
713}
714EXPORT_SYMBOL(bdi_set_max_ratio);
715
716static unsigned long dirty_freerun_ceiling(unsigned long thresh,
717 unsigned long bg_thresh)
718{
719 return (thresh + bg_thresh) / 2;
720}
721
722static unsigned long hard_dirty_limit(struct wb_domain *dom,
723 unsigned long thresh)
724{
725 return max(thresh, dom->dirty_limit);
726}
727
728/*
729 * Memory which can be further allocated to a memcg domain is capped by
730 * system-wide clean memory excluding the amount being used in the domain.
731 */
732static void mdtc_calc_avail(struct dirty_throttle_control *mdtc,
733 unsigned long filepages, unsigned long headroom)
734{
735 struct dirty_throttle_control *gdtc = mdtc_gdtc(mdtc);
736 unsigned long clean = filepages - min(filepages, mdtc->dirty);
737 unsigned long global_clean = gdtc->avail - min(gdtc->avail, gdtc->dirty);
738 unsigned long other_clean = global_clean - min(global_clean, clean);
739
740 mdtc->avail = filepages + min(headroom, other_clean);
741}
742
743/**
744 * __wb_calc_thresh - @wb's share of dirty throttling threshold
745 * @dtc: dirty_throttle_context of interest
746 *
747 * Returns @wb's dirty limit in pages. The term "dirty" in the context of
748 * dirty balancing includes all PG_dirty, PG_writeback and NFS unstable pages.
749 *
750 * Note that balance_dirty_pages() will only seriously take it as a hard limit
751 * when sleeping max_pause per page is not enough to keep the dirty pages under
752 * control. For example, when the device is completely stalled due to some error
753 * conditions, or when there are 1000 dd tasks writing to a slow 10MB/s USB key.
754 * In the other normal situations, it acts more gently by throttling the tasks
755 * more (rather than completely block them) when the wb dirty pages go high.
756 *
757 * It allocates high/low dirty limits to fast/slow devices, in order to prevent
758 * - starving fast devices
759 * - piling up dirty pages (that will take long time to sync) on slow devices
760 *
761 * The wb's share of dirty limit will be adapting to its throughput and
762 * bounded by the bdi->min_ratio and/or bdi->max_ratio parameters, if set.
763 */
764static unsigned long __wb_calc_thresh(struct dirty_throttle_control *dtc)
765{
766 struct wb_domain *dom = dtc_dom(dtc);
767 unsigned long thresh = dtc->thresh;
768 u64 wb_thresh;
769 long numerator, denominator;
770 unsigned long wb_min_ratio, wb_max_ratio;
771
772 /*
773 * Calculate this BDI's share of the thresh ratio.
774 */
775 fprop_fraction_percpu(&dom->completions, dtc->wb_completions,
776 &numerator, &denominator);
777
778 wb_thresh = (thresh * (100 - bdi_min_ratio)) / 100;
779 wb_thresh *= numerator;
780 do_div(wb_thresh, denominator);
781
782 wb_min_max_ratio(dtc->wb, &wb_min_ratio, &wb_max_ratio);
783
784 wb_thresh += (thresh * wb_min_ratio) / 100;
785 if (wb_thresh > (thresh * wb_max_ratio) / 100)
786 wb_thresh = thresh * wb_max_ratio / 100;
787
788 return wb_thresh;
789}
790
791unsigned long wb_calc_thresh(struct bdi_writeback *wb, unsigned long thresh)
792{
793 struct dirty_throttle_control gdtc = { GDTC_INIT(wb),
794 .thresh = thresh };
795 return __wb_calc_thresh(&gdtc);
796}
797
798/*
799 * setpoint - dirty 3
800 * f(dirty) := 1.0 + (----------------)
801 * limit - setpoint
802 *
803 * it's a 3rd order polynomial that subjects to
804 *
805 * (1) f(freerun) = 2.0 => rampup dirty_ratelimit reasonably fast
806 * (2) f(setpoint) = 1.0 => the balance point
807 * (3) f(limit) = 0 => the hard limit
808 * (4) df/dx <= 0 => negative feedback control
809 * (5) the closer to setpoint, the smaller |df/dx| (and the reverse)
810 * => fast response on large errors; small oscillation near setpoint
811 */
812static long long pos_ratio_polynom(unsigned long setpoint,
813 unsigned long dirty,
814 unsigned long limit)
815{
816 long long pos_ratio;
817 long x;
818
819 x = div64_s64(((s64)setpoint - (s64)dirty) << RATELIMIT_CALC_SHIFT,
820 (limit - setpoint) | 1);
821 pos_ratio = x;
822 pos_ratio = pos_ratio * x >> RATELIMIT_CALC_SHIFT;
823 pos_ratio = pos_ratio * x >> RATELIMIT_CALC_SHIFT;
824 pos_ratio += 1 << RATELIMIT_CALC_SHIFT;
825
826 return clamp(pos_ratio, 0LL, 2LL << RATELIMIT_CALC_SHIFT);
827}
828
829/*
830 * Dirty position control.
831 *
832 * (o) global/bdi setpoints
833 *
834 * We want the dirty pages be balanced around the global/wb setpoints.
835 * When the number of dirty pages is higher/lower than the setpoint, the
836 * dirty position control ratio (and hence task dirty ratelimit) will be
837 * decreased/increased to bring the dirty pages back to the setpoint.
838 *
839 * pos_ratio = 1 << RATELIMIT_CALC_SHIFT
840 *
841 * if (dirty < setpoint) scale up pos_ratio
842 * if (dirty > setpoint) scale down pos_ratio
843 *
844 * if (wb_dirty < wb_setpoint) scale up pos_ratio
845 * if (wb_dirty > wb_setpoint) scale down pos_ratio
846 *
847 * task_ratelimit = dirty_ratelimit * pos_ratio >> RATELIMIT_CALC_SHIFT
848 *
849 * (o) global control line
850 *
851 * ^ pos_ratio
852 * |
853 * | |<===== global dirty control scope ======>|
854 * 2.0 .............*
855 * | .*
856 * | . *
857 * | . *
858 * | . *
859 * | . *
860 * | . *
861 * 1.0 ................................*
862 * | . . *
863 * | . . *
864 * | . . *
865 * | . . *
866 * | . . *
867 * 0 +------------.------------------.----------------------*------------->
868 * freerun^ setpoint^ limit^ dirty pages
869 *
870 * (o) wb control line
871 *
872 * ^ pos_ratio
873 * |
874 * | *
875 * | *
876 * | *
877 * | *
878 * | * |<=========== span ============>|
879 * 1.0 .......................*
880 * | . *
881 * | . *
882 * | . *
883 * | . *
884 * | . *
885 * | . *
886 * | . *
887 * | . *
888 * | . *
889 * | . *
890 * | . *
891 * 1/4 ...............................................* * * * * * * * * * * *
892 * | . .
893 * | . .
894 * | . .
895 * 0 +----------------------.-------------------------------.------------->
896 * wb_setpoint^ x_intercept^
897 *
898 * The wb control line won't drop below pos_ratio=1/4, so that wb_dirty can
899 * be smoothly throttled down to normal if it starts high in situations like
900 * - start writing to a slow SD card and a fast disk at the same time. The SD
901 * card's wb_dirty may rush to many times higher than wb_setpoint.
902 * - the wb dirty thresh drops quickly due to change of JBOD workload
903 */
904static void wb_position_ratio(struct dirty_throttle_control *dtc)
905{
906 struct bdi_writeback *wb = dtc->wb;
907 unsigned long write_bw = wb->avg_write_bandwidth;
908 unsigned long freerun = dirty_freerun_ceiling(dtc->thresh, dtc->bg_thresh);
909 unsigned long limit = hard_dirty_limit(dtc_dom(dtc), dtc->thresh);
910 unsigned long wb_thresh = dtc->wb_thresh;
911 unsigned long x_intercept;
912 unsigned long setpoint; /* dirty pages' target balance point */
913 unsigned long wb_setpoint;
914 unsigned long span;
915 long long pos_ratio; /* for scaling up/down the rate limit */
916 long x;
917
918 dtc->pos_ratio = 0;
919
920 if (unlikely(dtc->dirty >= limit))
921 return;
922
923 /*
924 * global setpoint
925 *
926 * See comment for pos_ratio_polynom().
927 */
928 setpoint = (freerun + limit) / 2;
929 pos_ratio = pos_ratio_polynom(setpoint, dtc->dirty, limit);
930
931 /*
932 * The strictlimit feature is a tool preventing mistrusted filesystems
933 * from growing a large number of dirty pages before throttling. For
934 * such filesystems balance_dirty_pages always checks wb counters
935 * against wb limits. Even if global "nr_dirty" is under "freerun".
936 * This is especially important for fuse which sets bdi->max_ratio to
937 * 1% by default. Without strictlimit feature, fuse writeback may
938 * consume arbitrary amount of RAM because it is accounted in
939 * NR_WRITEBACK_TEMP which is not involved in calculating "nr_dirty".
940 *
941 * Here, in wb_position_ratio(), we calculate pos_ratio based on
942 * two values: wb_dirty and wb_thresh. Let's consider an example:
943 * total amount of RAM is 16GB, bdi->max_ratio is equal to 1%, global
944 * limits are set by default to 10% and 20% (background and throttle).
945 * Then wb_thresh is 1% of 20% of 16GB. This amounts to ~8K pages.
946 * wb_calc_thresh(wb, bg_thresh) is about ~4K pages. wb_setpoint is
947 * about ~6K pages (as the average of background and throttle wb
948 * limits). The 3rd order polynomial will provide positive feedback if
949 * wb_dirty is under wb_setpoint and vice versa.
950 *
951 * Note, that we cannot use global counters in these calculations
952 * because we want to throttle process writing to a strictlimit wb
953 * much earlier than global "freerun" is reached (~23MB vs. ~2.3GB
954 * in the example above).
955 */
956 if (unlikely(wb->bdi->capabilities & BDI_CAP_STRICTLIMIT)) {
957 long long wb_pos_ratio;
958
959 if (dtc->wb_dirty < 8) {
960 dtc->pos_ratio = min_t(long long, pos_ratio * 2,
961 2 << RATELIMIT_CALC_SHIFT);
962 return;
963 }
964
965 if (dtc->wb_dirty >= wb_thresh)
966 return;
967
968 wb_setpoint = dirty_freerun_ceiling(wb_thresh,
969 dtc->wb_bg_thresh);
970
971 if (wb_setpoint == 0 || wb_setpoint == wb_thresh)
972 return;
973
974 wb_pos_ratio = pos_ratio_polynom(wb_setpoint, dtc->wb_dirty,
975 wb_thresh);
976
977 /*
978 * Typically, for strictlimit case, wb_setpoint << setpoint
979 * and pos_ratio >> wb_pos_ratio. In the other words global
980 * state ("dirty") is not limiting factor and we have to
981 * make decision based on wb counters. But there is an
982 * important case when global pos_ratio should get precedence:
983 * global limits are exceeded (e.g. due to activities on other
984 * wb's) while given strictlimit wb is below limit.
985 *
986 * "pos_ratio * wb_pos_ratio" would work for the case above,
987 * but it would look too non-natural for the case of all
988 * activity in the system coming from a single strictlimit wb
989 * with bdi->max_ratio == 100%.
990 *
991 * Note that min() below somewhat changes the dynamics of the
992 * control system. Normally, pos_ratio value can be well over 3
993 * (when globally we are at freerun and wb is well below wb
994 * setpoint). Now the maximum pos_ratio in the same situation
995 * is 2. We might want to tweak this if we observe the control
996 * system is too slow to adapt.
997 */
998 dtc->pos_ratio = min(pos_ratio, wb_pos_ratio);
999 return;
1000 }
1001
1002 /*
1003 * We have computed basic pos_ratio above based on global situation. If
1004 * the wb is over/under its share of dirty pages, we want to scale
1005 * pos_ratio further down/up. That is done by the following mechanism.
1006 */
1007
1008 /*
1009 * wb setpoint
1010 *
1011 * f(wb_dirty) := 1.0 + k * (wb_dirty - wb_setpoint)
1012 *
1013 * x_intercept - wb_dirty
1014 * := --------------------------
1015 * x_intercept - wb_setpoint
1016 *
1017 * The main wb control line is a linear function that subjects to
1018 *
1019 * (1) f(wb_setpoint) = 1.0
1020 * (2) k = - 1 / (8 * write_bw) (in single wb case)
1021 * or equally: x_intercept = wb_setpoint + 8 * write_bw
1022 *
1023 * For single wb case, the dirty pages are observed to fluctuate
1024 * regularly within range
1025 * [wb_setpoint - write_bw/2, wb_setpoint + write_bw/2]
1026 * for various filesystems, where (2) can yield in a reasonable 12.5%
1027 * fluctuation range for pos_ratio.
1028 *
1029 * For JBOD case, wb_thresh (not wb_dirty!) could fluctuate up to its
1030 * own size, so move the slope over accordingly and choose a slope that
1031 * yields 100% pos_ratio fluctuation on suddenly doubled wb_thresh.
1032 */
1033 if (unlikely(wb_thresh > dtc->thresh))
1034 wb_thresh = dtc->thresh;
1035 /*
1036 * It's very possible that wb_thresh is close to 0 not because the
1037 * device is slow, but that it has remained inactive for long time.
1038 * Honour such devices a reasonable good (hopefully IO efficient)
1039 * threshold, so that the occasional writes won't be blocked and active
1040 * writes can rampup the threshold quickly.
1041 */
1042 wb_thresh = max(wb_thresh, (limit - dtc->dirty) / 8);
1043 /*
1044 * scale global setpoint to wb's:
1045 * wb_setpoint = setpoint * wb_thresh / thresh
1046 */
1047 x = div_u64((u64)wb_thresh << 16, dtc->thresh | 1);
1048 wb_setpoint = setpoint * (u64)x >> 16;
1049 /*
1050 * Use span=(8*write_bw) in single wb case as indicated by
1051 * (thresh - wb_thresh ~= 0) and transit to wb_thresh in JBOD case.
1052 *
1053 * wb_thresh thresh - wb_thresh
1054 * span = --------- * (8 * write_bw) + ------------------ * wb_thresh
1055 * thresh thresh
1056 */
1057 span = (dtc->thresh - wb_thresh + 8 * write_bw) * (u64)x >> 16;
1058 x_intercept = wb_setpoint + span;
1059
1060 if (dtc->wb_dirty < x_intercept - span / 4) {
1061 pos_ratio = div64_u64(pos_ratio * (x_intercept - dtc->wb_dirty),
1062 (x_intercept - wb_setpoint) | 1);
1063 } else
1064 pos_ratio /= 4;
1065
1066 /*
1067 * wb reserve area, safeguard against dirty pool underrun and disk idle
1068 * It may push the desired control point of global dirty pages higher
1069 * than setpoint.
1070 */
1071 x_intercept = wb_thresh / 2;
1072 if (dtc->wb_dirty < x_intercept) {
1073 if (dtc->wb_dirty > x_intercept / 8)
1074 pos_ratio = div_u64(pos_ratio * x_intercept,
1075 dtc->wb_dirty);
1076 else
1077 pos_ratio *= 8;
1078 }
1079
1080 dtc->pos_ratio = pos_ratio;
1081}
1082
1083static void wb_update_write_bandwidth(struct bdi_writeback *wb,
1084 unsigned long elapsed,
1085 unsigned long written)
1086{
1087 const unsigned long period = roundup_pow_of_two(3 * HZ);
1088 unsigned long avg = wb->avg_write_bandwidth;
1089 unsigned long old = wb->write_bandwidth;
1090 u64 bw;
1091
1092 /*
1093 * bw = written * HZ / elapsed
1094 *
1095 * bw * elapsed + write_bandwidth * (period - elapsed)
1096 * write_bandwidth = ---------------------------------------------------
1097 * period
1098 *
1099 * @written may have decreased due to account_page_redirty().
1100 * Avoid underflowing @bw calculation.
1101 */
1102 bw = written - min(written, wb->written_stamp);
1103 bw *= HZ;
1104 if (unlikely(elapsed > period)) {
1105 do_div(bw, elapsed);
1106 avg = bw;
1107 goto out;
1108 }
1109 bw += (u64)wb->write_bandwidth * (period - elapsed);
1110 bw >>= ilog2(period);
1111
1112 /*
1113 * one more level of smoothing, for filtering out sudden spikes
1114 */
1115 if (avg > old && old >= (unsigned long)bw)
1116 avg -= (avg - old) >> 3;
1117
1118 if (avg < old && old <= (unsigned long)bw)
1119 avg += (old - avg) >> 3;
1120
1121out:
1122 /* keep avg > 0 to guarantee that tot > 0 if there are dirty wbs */
1123 avg = max(avg, 1LU);
1124 if (wb_has_dirty_io(wb)) {
1125 long delta = avg - wb->avg_write_bandwidth;
1126 WARN_ON_ONCE(atomic_long_add_return(delta,
1127 &wb->bdi->tot_write_bandwidth) <= 0);
1128 }
1129 wb->write_bandwidth = bw;
1130 wb->avg_write_bandwidth = avg;
1131}
1132
1133static void update_dirty_limit(struct dirty_throttle_control *dtc)
1134{
1135 struct wb_domain *dom = dtc_dom(dtc);
1136 unsigned long thresh = dtc->thresh;
1137 unsigned long limit = dom->dirty_limit;
1138
1139 /*
1140 * Follow up in one step.
1141 */
1142 if (limit < thresh) {
1143 limit = thresh;
1144 goto update;
1145 }
1146
1147 /*
1148 * Follow down slowly. Use the higher one as the target, because thresh
1149 * may drop below dirty. This is exactly the reason to introduce
1150 * dom->dirty_limit which is guaranteed to lie above the dirty pages.
1151 */
1152 thresh = max(thresh, dtc->dirty);
1153 if (limit > thresh) {
1154 limit -= (limit - thresh) >> 5;
1155 goto update;
1156 }
1157 return;
1158update:
1159 dom->dirty_limit = limit;
1160}
1161
1162static void domain_update_bandwidth(struct dirty_throttle_control *dtc,
1163 unsigned long now)
1164{
1165 struct wb_domain *dom = dtc_dom(dtc);
1166
1167 /*
1168 * check locklessly first to optimize away locking for the most time
1169 */
1170 if (time_before(now, dom->dirty_limit_tstamp + BANDWIDTH_INTERVAL))
1171 return;
1172
1173 spin_lock(&dom->lock);
1174 if (time_after_eq(now, dom->dirty_limit_tstamp + BANDWIDTH_INTERVAL)) {
1175 update_dirty_limit(dtc);
1176 dom->dirty_limit_tstamp = now;
1177 }
1178 spin_unlock(&dom->lock);
1179}
1180
1181/*
1182 * Maintain wb->dirty_ratelimit, the base dirty throttle rate.
1183 *
1184 * Normal wb tasks will be curbed at or below it in long term.
1185 * Obviously it should be around (write_bw / N) when there are N dd tasks.
1186 */
1187static void wb_update_dirty_ratelimit(struct dirty_throttle_control *dtc,
1188 unsigned long dirtied,
1189 unsigned long elapsed)
1190{
1191 struct bdi_writeback *wb = dtc->wb;
1192 unsigned long dirty = dtc->dirty;
1193 unsigned long freerun = dirty_freerun_ceiling(dtc->thresh, dtc->bg_thresh);
1194 unsigned long limit = hard_dirty_limit(dtc_dom(dtc), dtc->thresh);
1195 unsigned long setpoint = (freerun + limit) / 2;
1196 unsigned long write_bw = wb->avg_write_bandwidth;
1197 unsigned long dirty_ratelimit = wb->dirty_ratelimit;
1198 unsigned long dirty_rate;
1199 unsigned long task_ratelimit;
1200 unsigned long balanced_dirty_ratelimit;
1201 unsigned long step;
1202 unsigned long x;
1203 unsigned long shift;
1204
1205 /*
1206 * The dirty rate will match the writeout rate in long term, except
1207 * when dirty pages are truncated by userspace or re-dirtied by FS.
1208 */
1209 dirty_rate = (dirtied - wb->dirtied_stamp) * HZ / elapsed;
1210
1211 /*
1212 * task_ratelimit reflects each dd's dirty rate for the past 200ms.
1213 */
1214 task_ratelimit = (u64)dirty_ratelimit *
1215 dtc->pos_ratio >> RATELIMIT_CALC_SHIFT;
1216 task_ratelimit++; /* it helps rampup dirty_ratelimit from tiny values */
1217
1218 /*
1219 * A linear estimation of the "balanced" throttle rate. The theory is,
1220 * if there are N dd tasks, each throttled at task_ratelimit, the wb's
1221 * dirty_rate will be measured to be (N * task_ratelimit). So the below
1222 * formula will yield the balanced rate limit (write_bw / N).
1223 *
1224 * Note that the expanded form is not a pure rate feedback:
1225 * rate_(i+1) = rate_(i) * (write_bw / dirty_rate) (1)
1226 * but also takes pos_ratio into account:
1227 * rate_(i+1) = rate_(i) * (write_bw / dirty_rate) * pos_ratio (2)
1228 *
1229 * (1) is not realistic because pos_ratio also takes part in balancing
1230 * the dirty rate. Consider the state
1231 * pos_ratio = 0.5 (3)
1232 * rate = 2 * (write_bw / N) (4)
1233 * If (1) is used, it will stuck in that state! Because each dd will
1234 * be throttled at
1235 * task_ratelimit = pos_ratio * rate = (write_bw / N) (5)
1236 * yielding
1237 * dirty_rate = N * task_ratelimit = write_bw (6)
1238 * put (6) into (1) we get
1239 * rate_(i+1) = rate_(i) (7)
1240 *
1241 * So we end up using (2) to always keep
1242 * rate_(i+1) ~= (write_bw / N) (8)
1243 * regardless of the value of pos_ratio. As long as (8) is satisfied,
1244 * pos_ratio is able to drive itself to 1.0, which is not only where
1245 * the dirty count meet the setpoint, but also where the slope of
1246 * pos_ratio is most flat and hence task_ratelimit is least fluctuated.
1247 */
1248 balanced_dirty_ratelimit = div_u64((u64)task_ratelimit * write_bw,
1249 dirty_rate | 1);
1250 /*
1251 * balanced_dirty_ratelimit ~= (write_bw / N) <= write_bw
1252 */
1253 if (unlikely(balanced_dirty_ratelimit > write_bw))
1254 balanced_dirty_ratelimit = write_bw;
1255
1256 /*
1257 * We could safely do this and return immediately:
1258 *
1259 * wb->dirty_ratelimit = balanced_dirty_ratelimit;
1260 *
1261 * However to get a more stable dirty_ratelimit, the below elaborated
1262 * code makes use of task_ratelimit to filter out singular points and
1263 * limit the step size.
1264 *
1265 * The below code essentially only uses the relative value of
1266 *
1267 * task_ratelimit - dirty_ratelimit
1268 * = (pos_ratio - 1) * dirty_ratelimit
1269 *
1270 * which reflects the direction and size of dirty position error.
1271 */
1272
1273 /*
1274 * dirty_ratelimit will follow balanced_dirty_ratelimit iff
1275 * task_ratelimit is on the same side of dirty_ratelimit, too.
1276 * For example, when
1277 * - dirty_ratelimit > balanced_dirty_ratelimit
1278 * - dirty_ratelimit > task_ratelimit (dirty pages are above setpoint)
1279 * lowering dirty_ratelimit will help meet both the position and rate
1280 * control targets. Otherwise, don't update dirty_ratelimit if it will
1281 * only help meet the rate target. After all, what the users ultimately
1282 * feel and care are stable dirty rate and small position error.
1283 *
1284 * |task_ratelimit - dirty_ratelimit| is used to limit the step size
1285 * and filter out the singular points of balanced_dirty_ratelimit. Which
1286 * keeps jumping around randomly and can even leap far away at times
1287 * due to the small 200ms estimation period of dirty_rate (we want to
1288 * keep that period small to reduce time lags).
1289 */
1290 step = 0;
1291
1292 /*
1293 * For strictlimit case, calculations above were based on wb counters
1294 * and limits (starting from pos_ratio = wb_position_ratio() and up to
1295 * balanced_dirty_ratelimit = task_ratelimit * write_bw / dirty_rate).
1296 * Hence, to calculate "step" properly, we have to use wb_dirty as
1297 * "dirty" and wb_setpoint as "setpoint".
1298 *
1299 * We rampup dirty_ratelimit forcibly if wb_dirty is low because
1300 * it's possible that wb_thresh is close to zero due to inactivity
1301 * of backing device.
1302 */
1303 if (unlikely(wb->bdi->capabilities & BDI_CAP_STRICTLIMIT)) {
1304 dirty = dtc->wb_dirty;
1305 if (dtc->wb_dirty < 8)
1306 setpoint = dtc->wb_dirty + 1;
1307 else
1308 setpoint = (dtc->wb_thresh + dtc->wb_bg_thresh) / 2;
1309 }
1310
1311 if (dirty < setpoint) {
1312 x = min3(wb->balanced_dirty_ratelimit,
1313 balanced_dirty_ratelimit, task_ratelimit);
1314 if (dirty_ratelimit < x)
1315 step = x - dirty_ratelimit;
1316 } else {
1317 x = max3(wb->balanced_dirty_ratelimit,
1318 balanced_dirty_ratelimit, task_ratelimit);
1319 if (dirty_ratelimit > x)
1320 step = dirty_ratelimit - x;
1321 }
1322
1323 /*
1324 * Don't pursue 100% rate matching. It's impossible since the balanced
1325 * rate itself is constantly fluctuating. So decrease the track speed
1326 * when it gets close to the target. Helps eliminate pointless tremors.
1327 */
1328 shift = dirty_ratelimit / (2 * step + 1);
1329 if (shift < BITS_PER_LONG)
1330 step = DIV_ROUND_UP(step >> shift, 8);
1331 else
1332 step = 0;
1333
1334 if (dirty_ratelimit < balanced_dirty_ratelimit)
1335 dirty_ratelimit += step;
1336 else
1337 dirty_ratelimit -= step;
1338
1339 wb->dirty_ratelimit = max(dirty_ratelimit, 1UL);
1340 wb->balanced_dirty_ratelimit = balanced_dirty_ratelimit;
1341
1342 trace_bdi_dirty_ratelimit(wb, dirty_rate, task_ratelimit);
1343}
1344
1345static void __wb_update_bandwidth(struct dirty_throttle_control *gdtc,
1346 struct dirty_throttle_control *mdtc,
1347 unsigned long start_time,
1348 bool update_ratelimit)
1349{
1350 struct bdi_writeback *wb = gdtc->wb;
1351 unsigned long now = jiffies;
1352 unsigned long elapsed = now - wb->bw_time_stamp;
1353 unsigned long dirtied;
1354 unsigned long written;
1355
1356 lockdep_assert_held(&wb->list_lock);
1357
1358 /*
1359 * rate-limit, only update once every 200ms.
1360 */
1361 if (elapsed < BANDWIDTH_INTERVAL)
1362 return;
1363
1364 dirtied = percpu_counter_read(&wb->stat[WB_DIRTIED]);
1365 written = percpu_counter_read(&wb->stat[WB_WRITTEN]);
1366
1367 /*
1368 * Skip quiet periods when disk bandwidth is under-utilized.
1369 * (at least 1s idle time between two flusher runs)
1370 */
1371 if (elapsed > HZ && time_before(wb->bw_time_stamp, start_time))
1372 goto snapshot;
1373
1374 if (update_ratelimit) {
1375 domain_update_bandwidth(gdtc, now);
1376 wb_update_dirty_ratelimit(gdtc, dirtied, elapsed);
1377
1378 /*
1379 * @mdtc is always NULL if !CGROUP_WRITEBACK but the
1380 * compiler has no way to figure that out. Help it.
1381 */
1382 if (IS_ENABLED(CONFIG_CGROUP_WRITEBACK) && mdtc) {
1383 domain_update_bandwidth(mdtc, now);
1384 wb_update_dirty_ratelimit(mdtc, dirtied, elapsed);
1385 }
1386 }
1387 wb_update_write_bandwidth(wb, elapsed, written);
1388
1389snapshot:
1390 wb->dirtied_stamp = dirtied;
1391 wb->written_stamp = written;
1392 wb->bw_time_stamp = now;
1393}
1394
1395void wb_update_bandwidth(struct bdi_writeback *wb, unsigned long start_time)
1396{
1397 struct dirty_throttle_control gdtc = { GDTC_INIT(wb) };
1398
1399 __wb_update_bandwidth(&gdtc, NULL, start_time, false);
1400}
1401
1402/*
1403 * After a task dirtied this many pages, balance_dirty_pages_ratelimited()
1404 * will look to see if it needs to start dirty throttling.
1405 *
1406 * If dirty_poll_interval is too low, big NUMA machines will call the expensive
1407 * global_zone_page_state() too often. So scale it near-sqrt to the safety margin
1408 * (the number of pages we may dirty without exceeding the dirty limits).
1409 */
1410static unsigned long dirty_poll_interval(unsigned long dirty,
1411 unsigned long thresh)
1412{
1413 if (thresh > dirty)
1414 return 1UL << (ilog2(thresh - dirty) >> 1);
1415
1416 return 1;
1417}
1418
1419static unsigned long wb_max_pause(struct bdi_writeback *wb,
1420 unsigned long wb_dirty)
1421{
1422 unsigned long bw = wb->avg_write_bandwidth;
1423 unsigned long t;
1424
1425 /*
1426 * Limit pause time for small memory systems. If sleeping for too long
1427 * time, a small pool of dirty/writeback pages may go empty and disk go
1428 * idle.
1429 *
1430 * 8 serves as the safety ratio.
1431 */
1432 t = wb_dirty / (1 + bw / roundup_pow_of_two(1 + HZ / 8));
1433 t++;
1434
1435 return min_t(unsigned long, t, MAX_PAUSE);
1436}
1437
1438static long wb_min_pause(struct bdi_writeback *wb,
1439 long max_pause,
1440 unsigned long task_ratelimit,
1441 unsigned long dirty_ratelimit,
1442 int *nr_dirtied_pause)
1443{
1444 long hi = ilog2(wb->avg_write_bandwidth);
1445 long lo = ilog2(wb->dirty_ratelimit);
1446 long t; /* target pause */
1447 long pause; /* estimated next pause */
1448 int pages; /* target nr_dirtied_pause */
1449
1450 /* target for 10ms pause on 1-dd case */
1451 t = max(1, HZ / 100);
1452
1453 /*
1454 * Scale up pause time for concurrent dirtiers in order to reduce CPU
1455 * overheads.
1456 *
1457 * (N * 10ms) on 2^N concurrent tasks.
1458 */
1459 if (hi > lo)
1460 t += (hi - lo) * (10 * HZ) / 1024;
1461
1462 /*
1463 * This is a bit convoluted. We try to base the next nr_dirtied_pause
1464 * on the much more stable dirty_ratelimit. However the next pause time
1465 * will be computed based on task_ratelimit and the two rate limits may
1466 * depart considerably at some time. Especially if task_ratelimit goes
1467 * below dirty_ratelimit/2 and the target pause is max_pause, the next
1468 * pause time will be max_pause*2 _trimmed down_ to max_pause. As a
1469 * result task_ratelimit won't be executed faithfully, which could
1470 * eventually bring down dirty_ratelimit.
1471 *
1472 * We apply two rules to fix it up:
1473 * 1) try to estimate the next pause time and if necessary, use a lower
1474 * nr_dirtied_pause so as not to exceed max_pause. When this happens,
1475 * nr_dirtied_pause will be "dancing" with task_ratelimit.
1476 * 2) limit the target pause time to max_pause/2, so that the normal
1477 * small fluctuations of task_ratelimit won't trigger rule (1) and
1478 * nr_dirtied_pause will remain as stable as dirty_ratelimit.
1479 */
1480 t = min(t, 1 + max_pause / 2);
1481 pages = dirty_ratelimit * t / roundup_pow_of_two(HZ);
1482
1483 /*
1484 * Tiny nr_dirtied_pause is found to hurt I/O performance in the test
1485 * case fio-mmap-randwrite-64k, which does 16*{sync read, async write}.
1486 * When the 16 consecutive reads are often interrupted by some dirty
1487 * throttling pause during the async writes, cfq will go into idles
1488 * (deadline is fine). So push nr_dirtied_pause as high as possible
1489 * until reaches DIRTY_POLL_THRESH=32 pages.
1490 */
1491 if (pages < DIRTY_POLL_THRESH) {
1492 t = max_pause;
1493 pages = dirty_ratelimit * t / roundup_pow_of_two(HZ);
1494 if (pages > DIRTY_POLL_THRESH) {
1495 pages = DIRTY_POLL_THRESH;
1496 t = HZ * DIRTY_POLL_THRESH / dirty_ratelimit;
1497 }
1498 }
1499
1500 pause = HZ * pages / (task_ratelimit + 1);
1501 if (pause > max_pause) {
1502 t = max_pause;
1503 pages = task_ratelimit * t / roundup_pow_of_two(HZ);
1504 }
1505
1506 *nr_dirtied_pause = pages;
1507 /*
1508 * The minimal pause time will normally be half the target pause time.
1509 */
1510 return pages >= DIRTY_POLL_THRESH ? 1 + t / 2 : t;
1511}
1512
1513static inline void wb_dirty_limits(struct dirty_throttle_control *dtc)
1514{
1515 struct bdi_writeback *wb = dtc->wb;
1516 unsigned long wb_reclaimable;
1517
1518 /*
1519 * wb_thresh is not treated as some limiting factor as
1520 * dirty_thresh, due to reasons
1521 * - in JBOD setup, wb_thresh can fluctuate a lot
1522 * - in a system with HDD and USB key, the USB key may somehow
1523 * go into state (wb_dirty >> wb_thresh) either because
1524 * wb_dirty starts high, or because wb_thresh drops low.
1525 * In this case we don't want to hard throttle the USB key
1526 * dirtiers for 100 seconds until wb_dirty drops under
1527 * wb_thresh. Instead the auxiliary wb control line in
1528 * wb_position_ratio() will let the dirtier task progress
1529 * at some rate <= (write_bw / 2) for bringing down wb_dirty.
1530 */
1531 dtc->wb_thresh = __wb_calc_thresh(dtc);
1532 dtc->wb_bg_thresh = dtc->thresh ?
1533 div_u64((u64)dtc->wb_thresh * dtc->bg_thresh, dtc->thresh) : 0;
1534
1535 /*
1536 * In order to avoid the stacked BDI deadlock we need
1537 * to ensure we accurately count the 'dirty' pages when
1538 * the threshold is low.
1539 *
1540 * Otherwise it would be possible to get thresh+n pages
1541 * reported dirty, even though there are thresh-m pages
1542 * actually dirty; with m+n sitting in the percpu
1543 * deltas.
1544 */
1545 if (dtc->wb_thresh < 2 * wb_stat_error()) {
1546 wb_reclaimable = wb_stat_sum(wb, WB_RECLAIMABLE);
1547 dtc->wb_dirty = wb_reclaimable + wb_stat_sum(wb, WB_WRITEBACK);
1548 } else {
1549 wb_reclaimable = wb_stat(wb, WB_RECLAIMABLE);
1550 dtc->wb_dirty = wb_reclaimable + wb_stat(wb, WB_WRITEBACK);
1551 }
1552}
1553
1554/*
1555 * balance_dirty_pages() must be called by processes which are generating dirty
1556 * data. It looks at the number of dirty pages in the machine and will force
1557 * the caller to wait once crossing the (background_thresh + dirty_thresh) / 2.
1558 * If we're over `background_thresh' then the writeback threads are woken to
1559 * perform some writeout.
1560 */
1561static void balance_dirty_pages(struct bdi_writeback *wb,
1562 unsigned long pages_dirtied)
1563{
1564 struct dirty_throttle_control gdtc_stor = { GDTC_INIT(wb) };
1565 struct dirty_throttle_control mdtc_stor = { MDTC_INIT(wb, &gdtc_stor) };
1566 struct dirty_throttle_control * const gdtc = &gdtc_stor;
1567 struct dirty_throttle_control * const mdtc = mdtc_valid(&mdtc_stor) ?
1568 &mdtc_stor : NULL;
1569 struct dirty_throttle_control *sdtc;
1570 unsigned long nr_reclaimable; /* = file_dirty + unstable_nfs */
1571 long period;
1572 long pause;
1573 long max_pause;
1574 long min_pause;
1575 int nr_dirtied_pause;
1576 bool dirty_exceeded = false;
1577 unsigned long task_ratelimit;
1578 unsigned long dirty_ratelimit;
1579 struct backing_dev_info *bdi = wb->bdi;
1580 bool strictlimit = bdi->capabilities & BDI_CAP_STRICTLIMIT;
1581 unsigned long start_time = jiffies;
1582
1583 for (;;) {
1584 unsigned long now = jiffies;
1585 unsigned long dirty, thresh, bg_thresh;
1586 unsigned long m_dirty = 0; /* stop bogus uninit warnings */
1587 unsigned long m_thresh = 0;
1588 unsigned long m_bg_thresh = 0;
1589
1590 /*
1591 * Unstable writes are a feature of certain networked
1592 * filesystems (i.e. NFS) in which data may have been
1593 * written to the server's write cache, but has not yet
1594 * been flushed to permanent storage.
1595 */
1596 nr_reclaimable = global_node_page_state(NR_FILE_DIRTY) +
1597 global_node_page_state(NR_UNSTABLE_NFS);
1598 gdtc->avail = global_dirtyable_memory();
1599 gdtc->dirty = nr_reclaimable + global_node_page_state(NR_WRITEBACK);
1600
1601 domain_dirty_limits(gdtc);
1602
1603 if (unlikely(strictlimit)) {
1604 wb_dirty_limits(gdtc);
1605
1606 dirty = gdtc->wb_dirty;
1607 thresh = gdtc->wb_thresh;
1608 bg_thresh = gdtc->wb_bg_thresh;
1609 } else {
1610 dirty = gdtc->dirty;
1611 thresh = gdtc->thresh;
1612 bg_thresh = gdtc->bg_thresh;
1613 }
1614
1615 if (mdtc) {
1616 unsigned long filepages, headroom, writeback;
1617
1618 /*
1619 * If @wb belongs to !root memcg, repeat the same
1620 * basic calculations for the memcg domain.
1621 */
1622 mem_cgroup_wb_stats(wb, &filepages, &headroom,
1623 &mdtc->dirty, &writeback);
1624 mdtc->dirty += writeback;
1625 mdtc_calc_avail(mdtc, filepages, headroom);
1626
1627 domain_dirty_limits(mdtc);
1628
1629 if (unlikely(strictlimit)) {
1630 wb_dirty_limits(mdtc);
1631 m_dirty = mdtc->wb_dirty;
1632 m_thresh = mdtc->wb_thresh;
1633 m_bg_thresh = mdtc->wb_bg_thresh;
1634 } else {
1635 m_dirty = mdtc->dirty;
1636 m_thresh = mdtc->thresh;
1637 m_bg_thresh = mdtc->bg_thresh;
1638 }
1639 }
1640
1641 /*
1642 * Throttle it only when the background writeback cannot
1643 * catch-up. This avoids (excessively) small writeouts
1644 * when the wb limits are ramping up in case of !strictlimit.
1645 *
1646 * In strictlimit case make decision based on the wb counters
1647 * and limits. Small writeouts when the wb limits are ramping
1648 * up are the price we consciously pay for strictlimit-ing.
1649 *
1650 * If memcg domain is in effect, @dirty should be under
1651 * both global and memcg freerun ceilings.
1652 */
1653 if (dirty <= dirty_freerun_ceiling(thresh, bg_thresh) &&
1654 (!mdtc ||
1655 m_dirty <= dirty_freerun_ceiling(m_thresh, m_bg_thresh))) {
1656 unsigned long intv = dirty_poll_interval(dirty, thresh);
1657 unsigned long m_intv = ULONG_MAX;
1658
1659 current->dirty_paused_when = now;
1660 current->nr_dirtied = 0;
1661 if (mdtc)
1662 m_intv = dirty_poll_interval(m_dirty, m_thresh);
1663 current->nr_dirtied_pause = min(intv, m_intv);
1664 break;
1665 }
1666
1667 if (unlikely(!writeback_in_progress(wb)))
1668 wb_start_background_writeback(wb);
1669
1670 /*
1671 * Calculate global domain's pos_ratio and select the
1672 * global dtc by default.
1673 */
1674 if (!strictlimit)
1675 wb_dirty_limits(gdtc);
1676
1677 dirty_exceeded = (gdtc->wb_dirty > gdtc->wb_thresh) &&
1678 ((gdtc->dirty > gdtc->thresh) || strictlimit);
1679
1680 wb_position_ratio(gdtc);
1681 sdtc = gdtc;
1682
1683 if (mdtc) {
1684 /*
1685 * If memcg domain is in effect, calculate its
1686 * pos_ratio. @wb should satisfy constraints from
1687 * both global and memcg domains. Choose the one
1688 * w/ lower pos_ratio.
1689 */
1690 if (!strictlimit)
1691 wb_dirty_limits(mdtc);
1692
1693 dirty_exceeded |= (mdtc->wb_dirty > mdtc->wb_thresh) &&
1694 ((mdtc->dirty > mdtc->thresh) || strictlimit);
1695
1696 wb_position_ratio(mdtc);
1697 if (mdtc->pos_ratio < gdtc->pos_ratio)
1698 sdtc = mdtc;
1699 }
1700
1701 if (dirty_exceeded && !wb->dirty_exceeded)
1702 wb->dirty_exceeded = 1;
1703
1704 if (time_is_before_jiffies(wb->bw_time_stamp +
1705 BANDWIDTH_INTERVAL)) {
1706 spin_lock(&wb->list_lock);
1707 __wb_update_bandwidth(gdtc, mdtc, start_time, true);
1708 spin_unlock(&wb->list_lock);
1709 }
1710
1711 /* throttle according to the chosen dtc */
1712 dirty_ratelimit = wb->dirty_ratelimit;
1713 task_ratelimit = ((u64)dirty_ratelimit * sdtc->pos_ratio) >>
1714 RATELIMIT_CALC_SHIFT;
1715 max_pause = wb_max_pause(wb, sdtc->wb_dirty);
1716 min_pause = wb_min_pause(wb, max_pause,
1717 task_ratelimit, dirty_ratelimit,
1718 &nr_dirtied_pause);
1719
1720 if (unlikely(task_ratelimit == 0)) {
1721 period = max_pause;
1722 pause = max_pause;
1723 goto pause;
1724 }
1725 period = HZ * pages_dirtied / task_ratelimit;
1726 pause = period;
1727 if (current->dirty_paused_when)
1728 pause -= now - current->dirty_paused_when;
1729 /*
1730 * For less than 1s think time (ext3/4 may block the dirtier
1731 * for up to 800ms from time to time on 1-HDD; so does xfs,
1732 * however at much less frequency), try to compensate it in
1733 * future periods by updating the virtual time; otherwise just
1734 * do a reset, as it may be a light dirtier.
1735 */
1736 if (pause < min_pause) {
1737 trace_balance_dirty_pages(wb,
1738 sdtc->thresh,
1739 sdtc->bg_thresh,
1740 sdtc->dirty,
1741 sdtc->wb_thresh,
1742 sdtc->wb_dirty,
1743 dirty_ratelimit,
1744 task_ratelimit,
1745 pages_dirtied,
1746 period,
1747 min(pause, 0L),
1748 start_time);
1749 if (pause < -HZ) {
1750 current->dirty_paused_when = now;
1751 current->nr_dirtied = 0;
1752 } else if (period) {
1753 current->dirty_paused_when += period;
1754 current->nr_dirtied = 0;
1755 } else if (current->nr_dirtied_pause <= pages_dirtied)
1756 current->nr_dirtied_pause += pages_dirtied;
1757 break;
1758 }
1759 if (unlikely(pause > max_pause)) {
1760 /* for occasional dropped task_ratelimit */
1761 now += min(pause - max_pause, max_pause);
1762 pause = max_pause;
1763 }
1764
1765pause:
1766 trace_balance_dirty_pages(wb,
1767 sdtc->thresh,
1768 sdtc->bg_thresh,
1769 sdtc->dirty,
1770 sdtc->wb_thresh,
1771 sdtc->wb_dirty,
1772 dirty_ratelimit,
1773 task_ratelimit,
1774 pages_dirtied,
1775 period,
1776 pause,
1777 start_time);
1778 __set_current_state(TASK_KILLABLE);
1779 wb->dirty_sleep = now;
1780 io_schedule_timeout(pause);
1781
1782 current->dirty_paused_when = now + pause;
1783 current->nr_dirtied = 0;
1784 current->nr_dirtied_pause = nr_dirtied_pause;
1785
1786 /*
1787 * This is typically equal to (dirty < thresh) and can also
1788 * keep "1000+ dd on a slow USB stick" under control.
1789 */
1790 if (task_ratelimit)
1791 break;
1792
1793 /*
1794 * In the case of an unresponding NFS server and the NFS dirty
1795 * pages exceeds dirty_thresh, give the other good wb's a pipe
1796 * to go through, so that tasks on them still remain responsive.
1797 *
1798 * In theory 1 page is enough to keep the consumer-producer
1799 * pipe going: the flusher cleans 1 page => the task dirties 1
1800 * more page. However wb_dirty has accounting errors. So use
1801 * the larger and more IO friendly wb_stat_error.
1802 */
1803 if (sdtc->wb_dirty <= wb_stat_error())
1804 break;
1805
1806 if (fatal_signal_pending(current))
1807 break;
1808 }
1809
1810 if (!dirty_exceeded && wb->dirty_exceeded)
1811 wb->dirty_exceeded = 0;
1812
1813 if (writeback_in_progress(wb))
1814 return;
1815
1816 /*
1817 * In laptop mode, we wait until hitting the higher threshold before
1818 * starting background writeout, and then write out all the way down
1819 * to the lower threshold. So slow writers cause minimal disk activity.
1820 *
1821 * In normal mode, we start background writeout at the lower
1822 * background_thresh, to keep the amount of dirty memory low.
1823 */
1824 if (laptop_mode)
1825 return;
1826
1827 if (nr_reclaimable > gdtc->bg_thresh)
1828 wb_start_background_writeback(wb);
1829}
1830
1831static DEFINE_PER_CPU(int, bdp_ratelimits);
1832
1833/*
1834 * Normal tasks are throttled by
1835 * loop {
1836 * dirty tsk->nr_dirtied_pause pages;
1837 * take a snap in balance_dirty_pages();
1838 * }
1839 * However there is a worst case. If every task exit immediately when dirtied
1840 * (tsk->nr_dirtied_pause - 1) pages, balance_dirty_pages() will never be
1841 * called to throttle the page dirties. The solution is to save the not yet
1842 * throttled page dirties in dirty_throttle_leaks on task exit and charge them
1843 * randomly into the running tasks. This works well for the above worst case,
1844 * as the new task will pick up and accumulate the old task's leaked dirty
1845 * count and eventually get throttled.
1846 */
1847DEFINE_PER_CPU(int, dirty_throttle_leaks) = 0;
1848
1849/**
1850 * balance_dirty_pages_ratelimited - balance dirty memory state
1851 * @mapping: address_space which was dirtied
1852 *
1853 * Processes which are dirtying memory should call in here once for each page
1854 * which was newly dirtied. The function will periodically check the system's
1855 * dirty state and will initiate writeback if needed.
1856 *
1857 * On really big machines, get_writeback_state is expensive, so try to avoid
1858 * calling it too often (ratelimiting). But once we're over the dirty memory
1859 * limit we decrease the ratelimiting by a lot, to prevent individual processes
1860 * from overshooting the limit by (ratelimit_pages) each.
1861 */
1862void balance_dirty_pages_ratelimited(struct address_space *mapping)
1863{
1864 struct inode *inode = mapping->host;
1865 struct backing_dev_info *bdi = inode_to_bdi(inode);
1866 struct bdi_writeback *wb = NULL;
1867 int ratelimit;
1868 int *p;
1869
1870 if (!bdi_cap_account_dirty(bdi))
1871 return;
1872
1873 if (inode_cgwb_enabled(inode))
1874 wb = wb_get_create_current(bdi, GFP_KERNEL);
1875 if (!wb)
1876 wb = &bdi->wb;
1877
1878 ratelimit = current->nr_dirtied_pause;
1879 if (wb->dirty_exceeded)
1880 ratelimit = min(ratelimit, 32 >> (PAGE_SHIFT - 10));
1881
1882 preempt_disable();
1883 /*
1884 * This prevents one CPU to accumulate too many dirtied pages without
1885 * calling into balance_dirty_pages(), which can happen when there are
1886 * 1000+ tasks, all of them start dirtying pages at exactly the same
1887 * time, hence all honoured too large initial task->nr_dirtied_pause.
1888 */
1889 p = this_cpu_ptr(&bdp_ratelimits);
1890 if (unlikely(current->nr_dirtied >= ratelimit))
1891 *p = 0;
1892 else if (unlikely(*p >= ratelimit_pages)) {
1893 *p = 0;
1894 ratelimit = 0;
1895 }
1896 /*
1897 * Pick up the dirtied pages by the exited tasks. This avoids lots of
1898 * short-lived tasks (eg. gcc invocations in a kernel build) escaping
1899 * the dirty throttling and livelock other long-run dirtiers.
1900 */
1901 p = this_cpu_ptr(&dirty_throttle_leaks);
1902 if (*p > 0 && current->nr_dirtied < ratelimit) {
1903 unsigned long nr_pages_dirtied;
1904 nr_pages_dirtied = min(*p, ratelimit - current->nr_dirtied);
1905 *p -= nr_pages_dirtied;
1906 current->nr_dirtied += nr_pages_dirtied;
1907 }
1908 preempt_enable();
1909
1910 if (unlikely(current->nr_dirtied >= ratelimit))
1911 balance_dirty_pages(wb, current->nr_dirtied);
1912
1913 wb_put(wb);
1914}
1915EXPORT_SYMBOL(balance_dirty_pages_ratelimited);
1916
1917/**
1918 * wb_over_bg_thresh - does @wb need to be written back?
1919 * @wb: bdi_writeback of interest
1920 *
1921 * Determines whether background writeback should keep writing @wb or it's
1922 * clean enough. Returns %true if writeback should continue.
1923 */
1924bool wb_over_bg_thresh(struct bdi_writeback *wb)
1925{
1926 struct dirty_throttle_control gdtc_stor = { GDTC_INIT(wb) };
1927 struct dirty_throttle_control mdtc_stor = { MDTC_INIT(wb, &gdtc_stor) };
1928 struct dirty_throttle_control * const gdtc = &gdtc_stor;
1929 struct dirty_throttle_control * const mdtc = mdtc_valid(&mdtc_stor) ?
1930 &mdtc_stor : NULL;
1931
1932 /*
1933 * Similar to balance_dirty_pages() but ignores pages being written
1934 * as we're trying to decide whether to put more under writeback.
1935 */
1936 gdtc->avail = global_dirtyable_memory();
1937 gdtc->dirty = global_node_page_state(NR_FILE_DIRTY) +
1938 global_node_page_state(NR_UNSTABLE_NFS);
1939 domain_dirty_limits(gdtc);
1940
1941 if (gdtc->dirty > gdtc->bg_thresh)
1942 return true;
1943
1944 if (wb_stat(wb, WB_RECLAIMABLE) >
1945 wb_calc_thresh(gdtc->wb, gdtc->bg_thresh))
1946 return true;
1947
1948 if (mdtc) {
1949 unsigned long filepages, headroom, writeback;
1950
1951 mem_cgroup_wb_stats(wb, &filepages, &headroom, &mdtc->dirty,
1952 &writeback);
1953 mdtc_calc_avail(mdtc, filepages, headroom);
1954 domain_dirty_limits(mdtc); /* ditto, ignore writeback */
1955
1956 if (mdtc->dirty > mdtc->bg_thresh)
1957 return true;
1958
1959 if (wb_stat(wb, WB_RECLAIMABLE) >
1960 wb_calc_thresh(mdtc->wb, mdtc->bg_thresh))
1961 return true;
1962 }
1963
1964 return false;
1965}
1966
1967/*
1968 * sysctl handler for /proc/sys/vm/dirty_writeback_centisecs
1969 */
1970int dirty_writeback_centisecs_handler(struct ctl_table *table, int write,
1971 void __user *buffer, size_t *length, loff_t *ppos)
1972{
1973 unsigned int old_interval = dirty_writeback_interval;
1974 int ret;
1975
1976 ret = proc_dointvec(table, write, buffer, length, ppos);
1977
1978 /*
1979 * Writing 0 to dirty_writeback_interval will disable periodic writeback
1980 * and a different non-zero value will wakeup the writeback threads.
1981 * wb_wakeup_delayed() would be more appropriate, but it's a pain to
1982 * iterate over all bdis and wbs.
1983 * The reason we do this is to make the change take effect immediately.
1984 */
1985 if (!ret && write && dirty_writeback_interval &&
1986 dirty_writeback_interval != old_interval)
1987 wakeup_flusher_threads(WB_REASON_PERIODIC);
1988
1989 return ret;
1990}
1991
1992#ifdef CONFIG_BLOCK
1993void laptop_mode_timer_fn(struct timer_list *t)
1994{
1995 struct backing_dev_info *backing_dev_info =
1996 from_timer(backing_dev_info, t, laptop_mode_wb_timer);
1997
1998 wakeup_flusher_threads_bdi(backing_dev_info, WB_REASON_LAPTOP_TIMER);
1999}
2000
2001/*
2002 * We've spun up the disk and we're in laptop mode: schedule writeback
2003 * of all dirty data a few seconds from now. If the flush is already scheduled
2004 * then push it back - the user is still using the disk.
2005 */
2006void laptop_io_completion(struct backing_dev_info *info)
2007{
2008 mod_timer(&info->laptop_mode_wb_timer, jiffies + laptop_mode);
2009}
2010
2011/*
2012 * We're in laptop mode and we've just synced. The sync's writes will have
2013 * caused another writeback to be scheduled by laptop_io_completion.
2014 * Nothing needs to be written back anymore, so we unschedule the writeback.
2015 */
2016void laptop_sync_completion(void)
2017{
2018 struct backing_dev_info *bdi;
2019
2020 rcu_read_lock();
2021
2022 list_for_each_entry_rcu(bdi, &bdi_list, bdi_list)
2023 del_timer(&bdi->laptop_mode_wb_timer);
2024
2025 rcu_read_unlock();
2026}
2027#endif
2028
2029/*
2030 * If ratelimit_pages is too high then we can get into dirty-data overload
2031 * if a large number of processes all perform writes at the same time.
2032 * If it is too low then SMP machines will call the (expensive)
2033 * get_writeback_state too often.
2034 *
2035 * Here we set ratelimit_pages to a level which ensures that when all CPUs are
2036 * dirtying in parallel, we cannot go more than 3% (1/32) over the dirty memory
2037 * thresholds.
2038 */
2039
2040void writeback_set_ratelimit(void)
2041{
2042 struct wb_domain *dom = &global_wb_domain;
2043 unsigned long background_thresh;
2044 unsigned long dirty_thresh;
2045
2046 global_dirty_limits(&background_thresh, &dirty_thresh);
2047 dom->dirty_limit = dirty_thresh;
2048 ratelimit_pages = dirty_thresh / (num_online_cpus() * 32);
2049 if (ratelimit_pages < 16)
2050 ratelimit_pages = 16;
2051}
2052
2053static int page_writeback_cpu_online(unsigned int cpu)
2054{
2055 writeback_set_ratelimit();
2056 return 0;
2057}
2058
2059/*
2060 * Called early on to tune the page writeback dirty limits.
2061 *
2062 * We used to scale dirty pages according to how total memory
2063 * related to pages that could be allocated for buffers (by
2064 * comparing nr_free_buffer_pages() to vm_total_pages.
2065 *
2066 * However, that was when we used "dirty_ratio" to scale with
2067 * all memory, and we don't do that any more. "dirty_ratio"
2068 * is now applied to total non-HIGHPAGE memory (by subtracting
2069 * totalhigh_pages from vm_total_pages), and as such we can't
2070 * get into the old insane situation any more where we had
2071 * large amounts of dirty pages compared to a small amount of
2072 * non-HIGHMEM memory.
2073 *
2074 * But we might still want to scale the dirty_ratio by how
2075 * much memory the box has..
2076 */
2077void __init page_writeback_init(void)
2078{
2079 BUG_ON(wb_domain_init(&global_wb_domain, GFP_KERNEL));
2080
2081 cpuhp_setup_state(CPUHP_AP_ONLINE_DYN, "mm/writeback:online",
2082 page_writeback_cpu_online, NULL);
2083 cpuhp_setup_state(CPUHP_MM_WRITEBACK_DEAD, "mm/writeback:dead", NULL,
2084 page_writeback_cpu_online);
2085}
2086
2087/**
2088 * tag_pages_for_writeback - tag pages to be written by write_cache_pages
2089 * @mapping: address space structure to write
2090 * @start: starting page index
2091 * @end: ending page index (inclusive)
2092 *
2093 * This function scans the page range from @start to @end (inclusive) and tags
2094 * all pages that have DIRTY tag set with a special TOWRITE tag. The idea is
2095 * that write_cache_pages (or whoever calls this function) will then use
2096 * TOWRITE tag to identify pages eligible for writeback. This mechanism is
2097 * used to avoid livelocking of writeback by a process steadily creating new
2098 * dirty pages in the file (thus it is important for this function to be quick
2099 * so that it can tag pages faster than a dirtying process can create them).
2100 */
2101/*
2102 * We tag pages in batches of WRITEBACK_TAG_BATCH to reduce the i_pages lock
2103 * latency.
2104 */
2105void tag_pages_for_writeback(struct address_space *mapping,
2106 pgoff_t start, pgoff_t end)
2107{
2108#define WRITEBACK_TAG_BATCH 4096
2109 unsigned long tagged = 0;
2110 struct radix_tree_iter iter;
2111 void **slot;
2112
2113 xa_lock_irq(&mapping->i_pages);
2114 radix_tree_for_each_tagged(slot, &mapping->i_pages, &iter, start,
2115 PAGECACHE_TAG_DIRTY) {
2116 if (iter.index > end)
2117 break;
2118 radix_tree_iter_tag_set(&mapping->i_pages, &iter,
2119 PAGECACHE_TAG_TOWRITE);
2120 tagged++;
2121 if ((tagged % WRITEBACK_TAG_BATCH) != 0)
2122 continue;
2123 slot = radix_tree_iter_resume(slot, &iter);
2124 xa_unlock_irq(&mapping->i_pages);
2125 cond_resched();
2126 xa_lock_irq(&mapping->i_pages);
2127 }
2128 xa_unlock_irq(&mapping->i_pages);
2129}
2130EXPORT_SYMBOL(tag_pages_for_writeback);
2131
2132/**
2133 * write_cache_pages - walk the list of dirty pages of the given address space and write all of them.
2134 * @mapping: address space structure to write
2135 * @wbc: subtract the number of written pages from *@wbc->nr_to_write
2136 * @writepage: function called for each page
2137 * @data: data passed to writepage function
2138 *
2139 * If a page is already under I/O, write_cache_pages() skips it, even
2140 * if it's dirty. This is desirable behaviour for memory-cleaning writeback,
2141 * but it is INCORRECT for data-integrity system calls such as fsync(). fsync()
2142 * and msync() need to guarantee that all the data which was dirty at the time
2143 * the call was made get new I/O started against them. If wbc->sync_mode is
2144 * WB_SYNC_ALL then we were called for data integrity and we must wait for
2145 * existing IO to complete.
2146 *
2147 * To avoid livelocks (when other process dirties new pages), we first tag
2148 * pages which should be written back with TOWRITE tag and only then start
2149 * writing them. For data-integrity sync we have to be careful so that we do
2150 * not miss some pages (e.g., because some other process has cleared TOWRITE
2151 * tag we set). The rule we follow is that TOWRITE tag can be cleared only
2152 * by the process clearing the DIRTY tag (and submitting the page for IO).
2153 */
2154int write_cache_pages(struct address_space *mapping,
2155 struct writeback_control *wbc, writepage_t writepage,
2156 void *data)
2157{
2158 int ret = 0;
2159 int done = 0;
2160 struct pagevec pvec;
2161 int nr_pages;
2162 pgoff_t uninitialized_var(writeback_index);
2163 pgoff_t index;
2164 pgoff_t end; /* Inclusive */
2165 pgoff_t done_index;
2166 int cycled;
2167 int range_whole = 0;
2168 int tag;
2169
2170 pagevec_init(&pvec);
2171 if (wbc->range_cyclic) {
2172 writeback_index = mapping->writeback_index; /* prev offset */
2173 index = writeback_index;
2174 if (index == 0)
2175 cycled = 1;
2176 else
2177 cycled = 0;
2178 end = -1;
2179 } else {
2180 index = wbc->range_start >> PAGE_SHIFT;
2181 end = wbc->range_end >> PAGE_SHIFT;
2182 if (wbc->range_start == 0 && wbc->range_end == LLONG_MAX)
2183 range_whole = 1;
2184 cycled = 1; /* ignore range_cyclic tests */
2185 }
2186 if (wbc->sync_mode == WB_SYNC_ALL || wbc->tagged_writepages)
2187 tag = PAGECACHE_TAG_TOWRITE;
2188 else
2189 tag = PAGECACHE_TAG_DIRTY;
2190retry:
2191 if (wbc->sync_mode == WB_SYNC_ALL || wbc->tagged_writepages)
2192 tag_pages_for_writeback(mapping, index, end);
2193 done_index = index;
2194 while (!done && (index <= end)) {
2195 int i;
2196
2197 nr_pages = pagevec_lookup_range_tag(&pvec, mapping, &index, end,
2198 tag);
2199 if (nr_pages == 0)
2200 break;
2201
2202 for (i = 0; i < nr_pages; i++) {
2203 struct page *page = pvec.pages[i];
2204
2205 done_index = page->index;
2206
2207 lock_page(page);
2208
2209 /*
2210 * Page truncated or invalidated. We can freely skip it
2211 * then, even for data integrity operations: the page
2212 * has disappeared concurrently, so there could be no
2213 * real expectation of this data interity operation
2214 * even if there is now a new, dirty page at the same
2215 * pagecache address.
2216 */
2217 if (unlikely(page->mapping != mapping)) {
2218continue_unlock:
2219 unlock_page(page);
2220 continue;
2221 }
2222
2223 if (!PageDirty(page)) {
2224 /* someone wrote it for us */
2225 goto continue_unlock;
2226 }
2227
2228 if (PageWriteback(page)) {
2229 if (wbc->sync_mode != WB_SYNC_NONE)
2230 wait_on_page_writeback(page);
2231 else
2232 goto continue_unlock;
2233 }
2234
2235 BUG_ON(PageWriteback(page));
2236 if (!clear_page_dirty_for_io(page))
2237 goto continue_unlock;
2238
2239 trace_wbc_writepage(wbc, inode_to_bdi(mapping->host));
2240 ret = (*writepage)(page, wbc, data);
2241 if (unlikely(ret)) {
2242 if (ret == AOP_WRITEPAGE_ACTIVATE) {
2243 unlock_page(page);
2244 ret = 0;
2245 } else {
2246 /*
2247 * done_index is set past this page,
2248 * so media errors will not choke
2249 * background writeout for the entire
2250 * file. This has consequences for
2251 * range_cyclic semantics (ie. it may
2252 * not be suitable for data integrity
2253 * writeout).
2254 */
2255 done_index = page->index + 1;
2256 done = 1;
2257 break;
2258 }
2259 }
2260
2261 /*
2262 * We stop writing back only if we are not doing
2263 * integrity sync. In case of integrity sync we have to
2264 * keep going until we have written all the pages
2265 * we tagged for writeback prior to entering this loop.
2266 */
2267 if (--wbc->nr_to_write <= 0 &&
2268 wbc->sync_mode == WB_SYNC_NONE) {
2269 done = 1;
2270 break;
2271 }
2272 }
2273 pagevec_release(&pvec);
2274 cond_resched();
2275 }
2276 if (!cycled && !done) {
2277 /*
2278 * range_cyclic:
2279 * We hit the last page and there is more work to be done: wrap
2280 * back to the start of the file
2281 */
2282 cycled = 1;
2283 index = 0;
2284 end = writeback_index - 1;
2285 goto retry;
2286 }
2287 if (wbc->range_cyclic || (range_whole && wbc->nr_to_write > 0))
2288 mapping->writeback_index = done_index;
2289
2290 return ret;
2291}
2292EXPORT_SYMBOL(write_cache_pages);
2293
2294/*
2295 * Function used by generic_writepages to call the real writepage
2296 * function and set the mapping flags on error
2297 */
2298static int __writepage(struct page *page, struct writeback_control *wbc,
2299 void *data)
2300{
2301 struct address_space *mapping = data;
2302 int ret = mapping->a_ops->writepage(page, wbc);
2303 mapping_set_error(mapping, ret);
2304 return ret;
2305}
2306
2307/**
2308 * generic_writepages - walk the list of dirty pages of the given address space and writepage() all of them.
2309 * @mapping: address space structure to write
2310 * @wbc: subtract the number of written pages from *@wbc->nr_to_write
2311 *
2312 * This is a library function, which implements the writepages()
2313 * address_space_operation.
2314 */
2315int generic_writepages(struct address_space *mapping,
2316 struct writeback_control *wbc)
2317{
2318 struct blk_plug plug;
2319 int ret;
2320
2321 /* deal with chardevs and other special file */
2322 if (!mapping->a_ops->writepage)
2323 return 0;
2324
2325 blk_start_plug(&plug);
2326 ret = write_cache_pages(mapping, wbc, __writepage, mapping);
2327 blk_finish_plug(&plug);
2328 return ret;
2329}
2330
2331EXPORT_SYMBOL(generic_writepages);
2332
2333int do_writepages(struct address_space *mapping, struct writeback_control *wbc)
2334{
2335 int ret;
2336
2337 if (wbc->nr_to_write <= 0)
2338 return 0;
2339 while (1) {
2340 if (mapping->a_ops->writepages)
2341 ret = mapping->a_ops->writepages(mapping, wbc);
2342 else
2343 ret = generic_writepages(mapping, wbc);
2344 if ((ret != -ENOMEM) || (wbc->sync_mode != WB_SYNC_ALL))
2345 break;
2346 cond_resched();
2347 congestion_wait(BLK_RW_ASYNC, HZ/50);
2348 }
2349 return ret;
2350}
2351
2352/**
2353 * write_one_page - write out a single page and wait on I/O
2354 * @page: the page to write
2355 *
2356 * The page must be locked by the caller and will be unlocked upon return.
2357 *
2358 * Note that the mapping's AS_EIO/AS_ENOSPC flags will be cleared when this
2359 * function returns.
2360 */
2361int write_one_page(struct page *page)
2362{
2363 struct address_space *mapping = page->mapping;
2364 int ret = 0;
2365 struct writeback_control wbc = {
2366 .sync_mode = WB_SYNC_ALL,
2367 .nr_to_write = 1,
2368 };
2369
2370 BUG_ON(!PageLocked(page));
2371
2372 wait_on_page_writeback(page);
2373
2374 if (clear_page_dirty_for_io(page)) {
2375 get_page(page);
2376 ret = mapping->a_ops->writepage(page, &wbc);
2377 if (ret == 0)
2378 wait_on_page_writeback(page);
2379 put_page(page);
2380 } else {
2381 unlock_page(page);
2382 }
2383
2384 if (!ret)
2385 ret = filemap_check_errors(mapping);
2386 return ret;
2387}
2388EXPORT_SYMBOL(write_one_page);
2389
2390/*
2391 * For address_spaces which do not use buffers nor write back.
2392 */
2393int __set_page_dirty_no_writeback(struct page *page)
2394{
2395 if (!PageDirty(page))
2396 return !TestSetPageDirty(page);
2397 return 0;
2398}
2399
2400/*
2401 * Helper function for set_page_dirty family.
2402 *
2403 * Caller must hold lock_page_memcg().
2404 *
2405 * NOTE: This relies on being atomic wrt interrupts.
2406 */
2407void account_page_dirtied(struct page *page, struct address_space *mapping)
2408{
2409 struct inode *inode = mapping->host;
2410
2411 trace_writeback_dirty_page(page, mapping);
2412
2413 if (mapping_cap_account_dirty(mapping)) {
2414 struct bdi_writeback *wb;
2415
2416 inode_attach_wb(inode, page);
2417 wb = inode_to_wb(inode);
2418
2419 __inc_lruvec_page_state(page, NR_FILE_DIRTY);
2420 __inc_zone_page_state(page, NR_ZONE_WRITE_PENDING);
2421 __inc_node_page_state(page, NR_DIRTIED);
2422 inc_wb_stat(wb, WB_RECLAIMABLE);
2423 inc_wb_stat(wb, WB_DIRTIED);
2424 task_io_account_write(PAGE_SIZE);
2425 current->nr_dirtied++;
2426 this_cpu_inc(bdp_ratelimits);
2427 }
2428}
2429EXPORT_SYMBOL(account_page_dirtied);
2430
2431/*
2432 * Helper function for deaccounting dirty page without writeback.
2433 *
2434 * Caller must hold lock_page_memcg().
2435 */
2436void account_page_cleaned(struct page *page, struct address_space *mapping,
2437 struct bdi_writeback *wb)
2438{
2439 if (mapping_cap_account_dirty(mapping)) {
2440 dec_lruvec_page_state(page, NR_FILE_DIRTY);
2441 dec_zone_page_state(page, NR_ZONE_WRITE_PENDING);
2442 dec_wb_stat(wb, WB_RECLAIMABLE);
2443 task_io_account_cancelled_write(PAGE_SIZE);
2444 }
2445}
2446
2447/*
2448 * For address_spaces which do not use buffers. Just tag the page as dirty in
2449 * its radix tree.
2450 *
2451 * This is also used when a single buffer is being dirtied: we want to set the
2452 * page dirty in that case, but not all the buffers. This is a "bottom-up"
2453 * dirtying, whereas __set_page_dirty_buffers() is a "top-down" dirtying.
2454 *
2455 * The caller must ensure this doesn't race with truncation. Most will simply
2456 * hold the page lock, but e.g. zap_pte_range() calls with the page mapped and
2457 * the pte lock held, which also locks out truncation.
2458 */
2459int __set_page_dirty_nobuffers(struct page *page)
2460{
2461 lock_page_memcg(page);
2462 if (!TestSetPageDirty(page)) {
2463 struct address_space *mapping = page_mapping(page);
2464 unsigned long flags;
2465
2466 if (!mapping) {
2467 unlock_page_memcg(page);
2468 return 1;
2469 }
2470
2471 xa_lock_irqsave(&mapping->i_pages, flags);
2472 BUG_ON(page_mapping(page) != mapping);
2473 WARN_ON_ONCE(!PagePrivate(page) && !PageUptodate(page));
2474 account_page_dirtied(page, mapping);
2475 radix_tree_tag_set(&mapping->i_pages, page_index(page),
2476 PAGECACHE_TAG_DIRTY);
2477 xa_unlock_irqrestore(&mapping->i_pages, flags);
2478 unlock_page_memcg(page);
2479
2480 if (mapping->host) {
2481 /* !PageAnon && !swapper_space */
2482 __mark_inode_dirty(mapping->host, I_DIRTY_PAGES);
2483 }
2484 return 1;
2485 }
2486 unlock_page_memcg(page);
2487 return 0;
2488}
2489EXPORT_SYMBOL(__set_page_dirty_nobuffers);
2490
2491/*
2492 * Call this whenever redirtying a page, to de-account the dirty counters
2493 * (NR_DIRTIED, BDI_DIRTIED, tsk->nr_dirtied), so that they match the written
2494 * counters (NR_WRITTEN, BDI_WRITTEN) in long term. The mismatches will lead to
2495 * systematic errors in balanced_dirty_ratelimit and the dirty pages position
2496 * control.
2497 */
2498void account_page_redirty(struct page *page)
2499{
2500 struct address_space *mapping = page->mapping;
2501
2502 if (mapping && mapping_cap_account_dirty(mapping)) {
2503 struct inode *inode = mapping->host;
2504 struct bdi_writeback *wb;
2505 struct wb_lock_cookie cookie = {};
2506
2507 wb = unlocked_inode_to_wb_begin(inode, &cookie);
2508 current->nr_dirtied--;
2509 dec_node_page_state(page, NR_DIRTIED);
2510 dec_wb_stat(wb, WB_DIRTIED);
2511 unlocked_inode_to_wb_end(inode, &cookie);
2512 }
2513}
2514EXPORT_SYMBOL(account_page_redirty);
2515
2516/*
2517 * When a writepage implementation decides that it doesn't want to write this
2518 * page for some reason, it should redirty the locked page via
2519 * redirty_page_for_writepage() and it should then unlock the page and return 0
2520 */
2521int redirty_page_for_writepage(struct writeback_control *wbc, struct page *page)
2522{
2523 int ret;
2524
2525 wbc->pages_skipped++;
2526 ret = __set_page_dirty_nobuffers(page);
2527 account_page_redirty(page);
2528 return ret;
2529}
2530EXPORT_SYMBOL(redirty_page_for_writepage);
2531
2532/*
2533 * Dirty a page.
2534 *
2535 * For pages with a mapping this should be done under the page lock
2536 * for the benefit of asynchronous memory errors who prefer a consistent
2537 * dirty state. This rule can be broken in some special cases,
2538 * but should be better not to.
2539 *
2540 * If the mapping doesn't provide a set_page_dirty a_op, then
2541 * just fall through and assume that it wants buffer_heads.
2542 */
2543int set_page_dirty(struct page *page)
2544{
2545 struct address_space *mapping = page_mapping(page);
2546
2547 page = compound_head(page);
2548 if (likely(mapping)) {
2549 int (*spd)(struct page *) = mapping->a_ops->set_page_dirty;
2550 /*
2551 * readahead/lru_deactivate_page could remain
2552 * PG_readahead/PG_reclaim due to race with end_page_writeback
2553 * About readahead, if the page is written, the flags would be
2554 * reset. So no problem.
2555 * About lru_deactivate_page, if the page is redirty, the flag
2556 * will be reset. So no problem. but if the page is used by readahead
2557 * it will confuse readahead and make it restart the size rampup
2558 * process. But it's a trivial problem.
2559 */
2560 if (PageReclaim(page))
2561 ClearPageReclaim(page);
2562#ifdef CONFIG_BLOCK
2563 if (!spd)
2564 spd = __set_page_dirty_buffers;
2565#endif
2566 return (*spd)(page);
2567 }
2568 if (!PageDirty(page)) {
2569 if (!TestSetPageDirty(page))
2570 return 1;
2571 }
2572 return 0;
2573}
2574EXPORT_SYMBOL(set_page_dirty);
2575
2576/*
2577 * set_page_dirty() is racy if the caller has no reference against
2578 * page->mapping->host, and if the page is unlocked. This is because another
2579 * CPU could truncate the page off the mapping and then free the mapping.
2580 *
2581 * Usually, the page _is_ locked, or the caller is a user-space process which
2582 * holds a reference on the inode by having an open file.
2583 *
2584 * In other cases, the page should be locked before running set_page_dirty().
2585 */
2586int set_page_dirty_lock(struct page *page)
2587{
2588 int ret;
2589
2590 lock_page(page);
2591 ret = set_page_dirty(page);
2592 unlock_page(page);
2593 return ret;
2594}
2595EXPORT_SYMBOL(set_page_dirty_lock);
2596
2597/*
2598 * This cancels just the dirty bit on the kernel page itself, it does NOT
2599 * actually remove dirty bits on any mmap's that may be around. It also
2600 * leaves the page tagged dirty, so any sync activity will still find it on
2601 * the dirty lists, and in particular, clear_page_dirty_for_io() will still
2602 * look at the dirty bits in the VM.
2603 *
2604 * Doing this should *normally* only ever be done when a page is truncated,
2605 * and is not actually mapped anywhere at all. However, fs/buffer.c does
2606 * this when it notices that somebody has cleaned out all the buffers on a
2607 * page without actually doing it through the VM. Can you say "ext3 is
2608 * horribly ugly"? Thought you could.
2609 */
2610void __cancel_dirty_page(struct page *page)
2611{
2612 struct address_space *mapping = page_mapping(page);
2613
2614 if (mapping_cap_account_dirty(mapping)) {
2615 struct inode *inode = mapping->host;
2616 struct bdi_writeback *wb;
2617 struct wb_lock_cookie cookie = {};
2618
2619 lock_page_memcg(page);
2620 wb = unlocked_inode_to_wb_begin(inode, &cookie);
2621
2622 if (TestClearPageDirty(page))
2623 account_page_cleaned(page, mapping, wb);
2624
2625 unlocked_inode_to_wb_end(inode, &cookie);
2626 unlock_page_memcg(page);
2627 } else {
2628 ClearPageDirty(page);
2629 }
2630}
2631EXPORT_SYMBOL(__cancel_dirty_page);
2632
2633/*
2634 * Clear a page's dirty flag, while caring for dirty memory accounting.
2635 * Returns true if the page was previously dirty.
2636 *
2637 * This is for preparing to put the page under writeout. We leave the page
2638 * tagged as dirty in the radix tree so that a concurrent write-for-sync
2639 * can discover it via a PAGECACHE_TAG_DIRTY walk. The ->writepage
2640 * implementation will run either set_page_writeback() or set_page_dirty(),
2641 * at which stage we bring the page's dirty flag and radix-tree dirty tag
2642 * back into sync.
2643 *
2644 * This incoherency between the page's dirty flag and radix-tree tag is
2645 * unfortunate, but it only exists while the page is locked.
2646 */
2647int clear_page_dirty_for_io(struct page *page)
2648{
2649 struct address_space *mapping = page_mapping(page);
2650 int ret = 0;
2651
2652 BUG_ON(!PageLocked(page));
2653
2654 if (mapping && mapping_cap_account_dirty(mapping)) {
2655 struct inode *inode = mapping->host;
2656 struct bdi_writeback *wb;
2657 struct wb_lock_cookie cookie = {};
2658
2659 /*
2660 * Yes, Virginia, this is indeed insane.
2661 *
2662 * We use this sequence to make sure that
2663 * (a) we account for dirty stats properly
2664 * (b) we tell the low-level filesystem to
2665 * mark the whole page dirty if it was
2666 * dirty in a pagetable. Only to then
2667 * (c) clean the page again and return 1 to
2668 * cause the writeback.
2669 *
2670 * This way we avoid all nasty races with the
2671 * dirty bit in multiple places and clearing
2672 * them concurrently from different threads.
2673 *
2674 * Note! Normally the "set_page_dirty(page)"
2675 * has no effect on the actual dirty bit - since
2676 * that will already usually be set. But we
2677 * need the side effects, and it can help us
2678 * avoid races.
2679 *
2680 * We basically use the page "master dirty bit"
2681 * as a serialization point for all the different
2682 * threads doing their things.
2683 */
2684 if (page_mkclean(page))
2685 set_page_dirty(page);
2686 /*
2687 * We carefully synchronise fault handlers against
2688 * installing a dirty pte and marking the page dirty
2689 * at this point. We do this by having them hold the
2690 * page lock while dirtying the page, and pages are
2691 * always locked coming in here, so we get the desired
2692 * exclusion.
2693 */
2694 wb = unlocked_inode_to_wb_begin(inode, &cookie);
2695 if (TestClearPageDirty(page)) {
2696 dec_lruvec_page_state(page, NR_FILE_DIRTY);
2697 dec_zone_page_state(page, NR_ZONE_WRITE_PENDING);
2698 dec_wb_stat(wb, WB_RECLAIMABLE);
2699 ret = 1;
2700 }
2701 unlocked_inode_to_wb_end(inode, &cookie);
2702 return ret;
2703 }
2704 return TestClearPageDirty(page);
2705}
2706EXPORT_SYMBOL(clear_page_dirty_for_io);
2707
2708int test_clear_page_writeback(struct page *page)
2709{
2710 struct address_space *mapping = page_mapping(page);
2711 struct mem_cgroup *memcg;
2712 struct lruvec *lruvec;
2713 int ret;
2714
2715 memcg = lock_page_memcg(page);
2716 lruvec = mem_cgroup_page_lruvec(page, page_pgdat(page));
2717 if (mapping && mapping_use_writeback_tags(mapping)) {
2718 struct inode *inode = mapping->host;
2719 struct backing_dev_info *bdi = inode_to_bdi(inode);
2720 unsigned long flags;
2721
2722 xa_lock_irqsave(&mapping->i_pages, flags);
2723 ret = TestClearPageWriteback(page);
2724 if (ret) {
2725 radix_tree_tag_clear(&mapping->i_pages, page_index(page),
2726 PAGECACHE_TAG_WRITEBACK);
2727 if (bdi_cap_account_writeback(bdi)) {
2728 struct bdi_writeback *wb = inode_to_wb(inode);
2729
2730 dec_wb_stat(wb, WB_WRITEBACK);
2731 __wb_writeout_inc(wb);
2732 }
2733 }
2734
2735 if (mapping->host && !mapping_tagged(mapping,
2736 PAGECACHE_TAG_WRITEBACK))
2737 sb_clear_inode_writeback(mapping->host);
2738
2739 xa_unlock_irqrestore(&mapping->i_pages, flags);
2740 } else {
2741 ret = TestClearPageWriteback(page);
2742 }
2743 /*
2744 * NOTE: Page might be free now! Writeback doesn't hold a page
2745 * reference on its own, it relies on truncation to wait for
2746 * the clearing of PG_writeback. The below can only access
2747 * page state that is static across allocation cycles.
2748 */
2749 if (ret) {
2750 dec_lruvec_state(lruvec, NR_WRITEBACK);
2751 dec_zone_page_state(page, NR_ZONE_WRITE_PENDING);
2752 inc_node_page_state(page, NR_WRITTEN);
2753 }
2754 __unlock_page_memcg(memcg);
2755 return ret;
2756}
2757
2758int __test_set_page_writeback(struct page *page, bool keep_write)
2759{
2760 struct address_space *mapping = page_mapping(page);
2761 int ret;
2762
2763 lock_page_memcg(page);
2764 if (mapping && mapping_use_writeback_tags(mapping)) {
2765 struct inode *inode = mapping->host;
2766 struct backing_dev_info *bdi = inode_to_bdi(inode);
2767 unsigned long flags;
2768
2769 xa_lock_irqsave(&mapping->i_pages, flags);
2770 ret = TestSetPageWriteback(page);
2771 if (!ret) {
2772 bool on_wblist;
2773
2774 on_wblist = mapping_tagged(mapping,
2775 PAGECACHE_TAG_WRITEBACK);
2776
2777 radix_tree_tag_set(&mapping->i_pages, page_index(page),
2778 PAGECACHE_TAG_WRITEBACK);
2779 if (bdi_cap_account_writeback(bdi))
2780 inc_wb_stat(inode_to_wb(inode), WB_WRITEBACK);
2781
2782 /*
2783 * We can come through here when swapping anonymous
2784 * pages, so we don't necessarily have an inode to track
2785 * for sync.
2786 */
2787 if (mapping->host && !on_wblist)
2788 sb_mark_inode_writeback(mapping->host);
2789 }
2790 if (!PageDirty(page))
2791 radix_tree_tag_clear(&mapping->i_pages, page_index(page),
2792 PAGECACHE_TAG_DIRTY);
2793 if (!keep_write)
2794 radix_tree_tag_clear(&mapping->i_pages, page_index(page),
2795 PAGECACHE_TAG_TOWRITE);
2796 xa_unlock_irqrestore(&mapping->i_pages, flags);
2797 } else {
2798 ret = TestSetPageWriteback(page);
2799 }
2800 if (!ret) {
2801 inc_lruvec_page_state(page, NR_WRITEBACK);
2802 inc_zone_page_state(page, NR_ZONE_WRITE_PENDING);
2803 }
2804 unlock_page_memcg(page);
2805 return ret;
2806
2807}
2808EXPORT_SYMBOL(__test_set_page_writeback);
2809
2810/*
2811 * Return true if any of the pages in the mapping are marked with the
2812 * passed tag.
2813 */
2814int mapping_tagged(struct address_space *mapping, int tag)
2815{
2816 return radix_tree_tagged(&mapping->i_pages, tag);
2817}
2818EXPORT_SYMBOL(mapping_tagged);
2819
2820/**
2821 * wait_for_stable_page() - wait for writeback to finish, if necessary.
2822 * @page: The page to wait on.
2823 *
2824 * This function determines if the given page is related to a backing device
2825 * that requires page contents to be held stable during writeback. If so, then
2826 * it will wait for any pending writeback to complete.
2827 */
2828void wait_for_stable_page(struct page *page)
2829{
2830 if (bdi_cap_stable_pages_required(inode_to_bdi(page->mapping->host)))
2831 wait_on_page_writeback(page);
2832}
2833EXPORT_SYMBOL_GPL(wait_for_stable_page);
1// SPDX-License-Identifier: GPL-2.0-only
2/*
3 * mm/page-writeback.c
4 *
5 * Copyright (C) 2002, Linus Torvalds.
6 * Copyright (C) 2007 Red Hat, Inc., Peter Zijlstra
7 *
8 * Contains functions related to writing back dirty pages at the
9 * address_space level.
10 *
11 * 10Apr2002 Andrew Morton
12 * Initial version
13 */
14
15#include <linux/kernel.h>
16#include <linux/math64.h>
17#include <linux/export.h>
18#include <linux/spinlock.h>
19#include <linux/fs.h>
20#include <linux/mm.h>
21#include <linux/swap.h>
22#include <linux/slab.h>
23#include <linux/pagemap.h>
24#include <linux/writeback.h>
25#include <linux/init.h>
26#include <linux/backing-dev.h>
27#include <linux/task_io_accounting_ops.h>
28#include <linux/blkdev.h>
29#include <linux/mpage.h>
30#include <linux/rmap.h>
31#include <linux/percpu.h>
32#include <linux/smp.h>
33#include <linux/sysctl.h>
34#include <linux/cpu.h>
35#include <linux/syscalls.h>
36#include <linux/pagevec.h>
37#include <linux/timer.h>
38#include <linux/sched/rt.h>
39#include <linux/sched/signal.h>
40#include <linux/mm_inline.h>
41#include <trace/events/writeback.h>
42
43#include "internal.h"
44
45/*
46 * Sleep at most 200ms at a time in balance_dirty_pages().
47 */
48#define MAX_PAUSE max(HZ/5, 1)
49
50/*
51 * Try to keep balance_dirty_pages() call intervals higher than this many pages
52 * by raising pause time to max_pause when falls below it.
53 */
54#define DIRTY_POLL_THRESH (128 >> (PAGE_SHIFT - 10))
55
56/*
57 * Estimate write bandwidth at 200ms intervals.
58 */
59#define BANDWIDTH_INTERVAL max(HZ/5, 1)
60
61#define RATELIMIT_CALC_SHIFT 10
62
63/*
64 * After a CPU has dirtied this many pages, balance_dirty_pages_ratelimited
65 * will look to see if it needs to force writeback or throttling.
66 */
67static long ratelimit_pages = 32;
68
69/* The following parameters are exported via /proc/sys/vm */
70
71/*
72 * Start background writeback (via writeback threads) at this percentage
73 */
74static int dirty_background_ratio = 10;
75
76/*
77 * dirty_background_bytes starts at 0 (disabled) so that it is a function of
78 * dirty_background_ratio * the amount of dirtyable memory
79 */
80static unsigned long dirty_background_bytes;
81
82/*
83 * free highmem will not be subtracted from the total free memory
84 * for calculating free ratios if vm_highmem_is_dirtyable is true
85 */
86static int vm_highmem_is_dirtyable;
87
88/*
89 * The generator of dirty data starts writeback at this percentage
90 */
91static int vm_dirty_ratio = 20;
92
93/*
94 * vm_dirty_bytes starts at 0 (disabled) so that it is a function of
95 * vm_dirty_ratio * the amount of dirtyable memory
96 */
97static unsigned long vm_dirty_bytes;
98
99/*
100 * The interval between `kupdate'-style writebacks
101 */
102unsigned int dirty_writeback_interval = 5 * 100; /* centiseconds */
103
104EXPORT_SYMBOL_GPL(dirty_writeback_interval);
105
106/*
107 * The longest time for which data is allowed to remain dirty
108 */
109unsigned int dirty_expire_interval = 30 * 100; /* centiseconds */
110
111/*
112 * Flag that puts the machine in "laptop mode". Doubles as a timeout in jiffies:
113 * a full sync is triggered after this time elapses without any disk activity.
114 */
115int laptop_mode;
116
117EXPORT_SYMBOL(laptop_mode);
118
119/* End of sysctl-exported parameters */
120
121struct wb_domain global_wb_domain;
122
123/* consolidated parameters for balance_dirty_pages() and its subroutines */
124struct dirty_throttle_control {
125#ifdef CONFIG_CGROUP_WRITEBACK
126 struct wb_domain *dom;
127 struct dirty_throttle_control *gdtc; /* only set in memcg dtc's */
128#endif
129 struct bdi_writeback *wb;
130 struct fprop_local_percpu *wb_completions;
131
132 unsigned long avail; /* dirtyable */
133 unsigned long dirty; /* file_dirty + write + nfs */
134 unsigned long thresh; /* dirty threshold */
135 unsigned long bg_thresh; /* dirty background threshold */
136
137 unsigned long wb_dirty; /* per-wb counterparts */
138 unsigned long wb_thresh;
139 unsigned long wb_bg_thresh;
140
141 unsigned long pos_ratio;
142};
143
144/*
145 * Length of period for aging writeout fractions of bdis. This is an
146 * arbitrarily chosen number. The longer the period, the slower fractions will
147 * reflect changes in current writeout rate.
148 */
149#define VM_COMPLETIONS_PERIOD_LEN (3*HZ)
150
151#ifdef CONFIG_CGROUP_WRITEBACK
152
153#define GDTC_INIT(__wb) .wb = (__wb), \
154 .dom = &global_wb_domain, \
155 .wb_completions = &(__wb)->completions
156
157#define GDTC_INIT_NO_WB .dom = &global_wb_domain
158
159#define MDTC_INIT(__wb, __gdtc) .wb = (__wb), \
160 .dom = mem_cgroup_wb_domain(__wb), \
161 .wb_completions = &(__wb)->memcg_completions, \
162 .gdtc = __gdtc
163
164static bool mdtc_valid(struct dirty_throttle_control *dtc)
165{
166 return dtc->dom;
167}
168
169static struct wb_domain *dtc_dom(struct dirty_throttle_control *dtc)
170{
171 return dtc->dom;
172}
173
174static struct dirty_throttle_control *mdtc_gdtc(struct dirty_throttle_control *mdtc)
175{
176 return mdtc->gdtc;
177}
178
179static struct fprop_local_percpu *wb_memcg_completions(struct bdi_writeback *wb)
180{
181 return &wb->memcg_completions;
182}
183
184static void wb_min_max_ratio(struct bdi_writeback *wb,
185 unsigned long *minp, unsigned long *maxp)
186{
187 unsigned long this_bw = READ_ONCE(wb->avg_write_bandwidth);
188 unsigned long tot_bw = atomic_long_read(&wb->bdi->tot_write_bandwidth);
189 unsigned long long min = wb->bdi->min_ratio;
190 unsigned long long max = wb->bdi->max_ratio;
191
192 /*
193 * @wb may already be clean by the time control reaches here and
194 * the total may not include its bw.
195 */
196 if (this_bw < tot_bw) {
197 if (min) {
198 min *= this_bw;
199 min = div64_ul(min, tot_bw);
200 }
201 if (max < 100 * BDI_RATIO_SCALE) {
202 max *= this_bw;
203 max = div64_ul(max, tot_bw);
204 }
205 }
206
207 *minp = min;
208 *maxp = max;
209}
210
211#else /* CONFIG_CGROUP_WRITEBACK */
212
213#define GDTC_INIT(__wb) .wb = (__wb), \
214 .wb_completions = &(__wb)->completions
215#define GDTC_INIT_NO_WB
216#define MDTC_INIT(__wb, __gdtc)
217
218static bool mdtc_valid(struct dirty_throttle_control *dtc)
219{
220 return false;
221}
222
223static struct wb_domain *dtc_dom(struct dirty_throttle_control *dtc)
224{
225 return &global_wb_domain;
226}
227
228static struct dirty_throttle_control *mdtc_gdtc(struct dirty_throttle_control *mdtc)
229{
230 return NULL;
231}
232
233static struct fprop_local_percpu *wb_memcg_completions(struct bdi_writeback *wb)
234{
235 return NULL;
236}
237
238static void wb_min_max_ratio(struct bdi_writeback *wb,
239 unsigned long *minp, unsigned long *maxp)
240{
241 *minp = wb->bdi->min_ratio;
242 *maxp = wb->bdi->max_ratio;
243}
244
245#endif /* CONFIG_CGROUP_WRITEBACK */
246
247/*
248 * In a memory zone, there is a certain amount of pages we consider
249 * available for the page cache, which is essentially the number of
250 * free and reclaimable pages, minus some zone reserves to protect
251 * lowmem and the ability to uphold the zone's watermarks without
252 * requiring writeback.
253 *
254 * This number of dirtyable pages is the base value of which the
255 * user-configurable dirty ratio is the effective number of pages that
256 * are allowed to be actually dirtied. Per individual zone, or
257 * globally by using the sum of dirtyable pages over all zones.
258 *
259 * Because the user is allowed to specify the dirty limit globally as
260 * absolute number of bytes, calculating the per-zone dirty limit can
261 * require translating the configured limit into a percentage of
262 * global dirtyable memory first.
263 */
264
265/**
266 * node_dirtyable_memory - number of dirtyable pages in a node
267 * @pgdat: the node
268 *
269 * Return: the node's number of pages potentially available for dirty
270 * page cache. This is the base value for the per-node dirty limits.
271 */
272static unsigned long node_dirtyable_memory(struct pglist_data *pgdat)
273{
274 unsigned long nr_pages = 0;
275 int z;
276
277 for (z = 0; z < MAX_NR_ZONES; z++) {
278 struct zone *zone = pgdat->node_zones + z;
279
280 if (!populated_zone(zone))
281 continue;
282
283 nr_pages += zone_page_state(zone, NR_FREE_PAGES);
284 }
285
286 /*
287 * Pages reserved for the kernel should not be considered
288 * dirtyable, to prevent a situation where reclaim has to
289 * clean pages in order to balance the zones.
290 */
291 nr_pages -= min(nr_pages, pgdat->totalreserve_pages);
292
293 nr_pages += node_page_state(pgdat, NR_INACTIVE_FILE);
294 nr_pages += node_page_state(pgdat, NR_ACTIVE_FILE);
295
296 return nr_pages;
297}
298
299static unsigned long highmem_dirtyable_memory(unsigned long total)
300{
301#ifdef CONFIG_HIGHMEM
302 int node;
303 unsigned long x = 0;
304 int i;
305
306 for_each_node_state(node, N_HIGH_MEMORY) {
307 for (i = ZONE_NORMAL + 1; i < MAX_NR_ZONES; i++) {
308 struct zone *z;
309 unsigned long nr_pages;
310
311 if (!is_highmem_idx(i))
312 continue;
313
314 z = &NODE_DATA(node)->node_zones[i];
315 if (!populated_zone(z))
316 continue;
317
318 nr_pages = zone_page_state(z, NR_FREE_PAGES);
319 /* watch for underflows */
320 nr_pages -= min(nr_pages, high_wmark_pages(z));
321 nr_pages += zone_page_state(z, NR_ZONE_INACTIVE_FILE);
322 nr_pages += zone_page_state(z, NR_ZONE_ACTIVE_FILE);
323 x += nr_pages;
324 }
325 }
326
327 /*
328 * Make sure that the number of highmem pages is never larger
329 * than the number of the total dirtyable memory. This can only
330 * occur in very strange VM situations but we want to make sure
331 * that this does not occur.
332 */
333 return min(x, total);
334#else
335 return 0;
336#endif
337}
338
339/**
340 * global_dirtyable_memory - number of globally dirtyable pages
341 *
342 * Return: the global number of pages potentially available for dirty
343 * page cache. This is the base value for the global dirty limits.
344 */
345static unsigned long global_dirtyable_memory(void)
346{
347 unsigned long x;
348
349 x = global_zone_page_state(NR_FREE_PAGES);
350 /*
351 * Pages reserved for the kernel should not be considered
352 * dirtyable, to prevent a situation where reclaim has to
353 * clean pages in order to balance the zones.
354 */
355 x -= min(x, totalreserve_pages);
356
357 x += global_node_page_state(NR_INACTIVE_FILE);
358 x += global_node_page_state(NR_ACTIVE_FILE);
359
360 if (!vm_highmem_is_dirtyable)
361 x -= highmem_dirtyable_memory(x);
362
363 return x + 1; /* Ensure that we never return 0 */
364}
365
366/**
367 * domain_dirty_limits - calculate thresh and bg_thresh for a wb_domain
368 * @dtc: dirty_throttle_control of interest
369 *
370 * Calculate @dtc->thresh and ->bg_thresh considering
371 * vm_dirty_{bytes|ratio} and dirty_background_{bytes|ratio}. The caller
372 * must ensure that @dtc->avail is set before calling this function. The
373 * dirty limits will be lifted by 1/4 for real-time tasks.
374 */
375static void domain_dirty_limits(struct dirty_throttle_control *dtc)
376{
377 const unsigned long available_memory = dtc->avail;
378 struct dirty_throttle_control *gdtc = mdtc_gdtc(dtc);
379 unsigned long bytes = vm_dirty_bytes;
380 unsigned long bg_bytes = dirty_background_bytes;
381 /* convert ratios to per-PAGE_SIZE for higher precision */
382 unsigned long ratio = (vm_dirty_ratio * PAGE_SIZE) / 100;
383 unsigned long bg_ratio = (dirty_background_ratio * PAGE_SIZE) / 100;
384 unsigned long thresh;
385 unsigned long bg_thresh;
386 struct task_struct *tsk;
387
388 /* gdtc is !NULL iff @dtc is for memcg domain */
389 if (gdtc) {
390 unsigned long global_avail = gdtc->avail;
391
392 /*
393 * The byte settings can't be applied directly to memcg
394 * domains. Convert them to ratios by scaling against
395 * globally available memory. As the ratios are in
396 * per-PAGE_SIZE, they can be obtained by dividing bytes by
397 * number of pages.
398 */
399 if (bytes)
400 ratio = min(DIV_ROUND_UP(bytes, global_avail),
401 PAGE_SIZE);
402 if (bg_bytes)
403 bg_ratio = min(DIV_ROUND_UP(bg_bytes, global_avail),
404 PAGE_SIZE);
405 bytes = bg_bytes = 0;
406 }
407
408 if (bytes)
409 thresh = DIV_ROUND_UP(bytes, PAGE_SIZE);
410 else
411 thresh = (ratio * available_memory) / PAGE_SIZE;
412
413 if (bg_bytes)
414 bg_thresh = DIV_ROUND_UP(bg_bytes, PAGE_SIZE);
415 else
416 bg_thresh = (bg_ratio * available_memory) / PAGE_SIZE;
417
418 if (bg_thresh >= thresh)
419 bg_thresh = thresh / 2;
420 tsk = current;
421 if (rt_task(tsk)) {
422 bg_thresh += bg_thresh / 4 + global_wb_domain.dirty_limit / 32;
423 thresh += thresh / 4 + global_wb_domain.dirty_limit / 32;
424 }
425 dtc->thresh = thresh;
426 dtc->bg_thresh = bg_thresh;
427
428 /* we should eventually report the domain in the TP */
429 if (!gdtc)
430 trace_global_dirty_state(bg_thresh, thresh);
431}
432
433/**
434 * global_dirty_limits - background-writeback and dirty-throttling thresholds
435 * @pbackground: out parameter for bg_thresh
436 * @pdirty: out parameter for thresh
437 *
438 * Calculate bg_thresh and thresh for global_wb_domain. See
439 * domain_dirty_limits() for details.
440 */
441void global_dirty_limits(unsigned long *pbackground, unsigned long *pdirty)
442{
443 struct dirty_throttle_control gdtc = { GDTC_INIT_NO_WB };
444
445 gdtc.avail = global_dirtyable_memory();
446 domain_dirty_limits(&gdtc);
447
448 *pbackground = gdtc.bg_thresh;
449 *pdirty = gdtc.thresh;
450}
451
452/**
453 * node_dirty_limit - maximum number of dirty pages allowed in a node
454 * @pgdat: the node
455 *
456 * Return: the maximum number of dirty pages allowed in a node, based
457 * on the node's dirtyable memory.
458 */
459static unsigned long node_dirty_limit(struct pglist_data *pgdat)
460{
461 unsigned long node_memory = node_dirtyable_memory(pgdat);
462 struct task_struct *tsk = current;
463 unsigned long dirty;
464
465 if (vm_dirty_bytes)
466 dirty = DIV_ROUND_UP(vm_dirty_bytes, PAGE_SIZE) *
467 node_memory / global_dirtyable_memory();
468 else
469 dirty = vm_dirty_ratio * node_memory / 100;
470
471 if (rt_task(tsk))
472 dirty += dirty / 4;
473
474 return dirty;
475}
476
477/**
478 * node_dirty_ok - tells whether a node is within its dirty limits
479 * @pgdat: the node to check
480 *
481 * Return: %true when the dirty pages in @pgdat are within the node's
482 * dirty limit, %false if the limit is exceeded.
483 */
484bool node_dirty_ok(struct pglist_data *pgdat)
485{
486 unsigned long limit = node_dirty_limit(pgdat);
487 unsigned long nr_pages = 0;
488
489 nr_pages += node_page_state(pgdat, NR_FILE_DIRTY);
490 nr_pages += node_page_state(pgdat, NR_WRITEBACK);
491
492 return nr_pages <= limit;
493}
494
495#ifdef CONFIG_SYSCTL
496static int dirty_background_ratio_handler(struct ctl_table *table, int write,
497 void *buffer, size_t *lenp, loff_t *ppos)
498{
499 int ret;
500
501 ret = proc_dointvec_minmax(table, write, buffer, lenp, ppos);
502 if (ret == 0 && write)
503 dirty_background_bytes = 0;
504 return ret;
505}
506
507static int dirty_background_bytes_handler(struct ctl_table *table, int write,
508 void *buffer, size_t *lenp, loff_t *ppos)
509{
510 int ret;
511
512 ret = proc_doulongvec_minmax(table, write, buffer, lenp, ppos);
513 if (ret == 0 && write)
514 dirty_background_ratio = 0;
515 return ret;
516}
517
518static int dirty_ratio_handler(struct ctl_table *table, int write, void *buffer,
519 size_t *lenp, loff_t *ppos)
520{
521 int old_ratio = vm_dirty_ratio;
522 int ret;
523
524 ret = proc_dointvec_minmax(table, write, buffer, lenp, ppos);
525 if (ret == 0 && write && vm_dirty_ratio != old_ratio) {
526 writeback_set_ratelimit();
527 vm_dirty_bytes = 0;
528 }
529 return ret;
530}
531
532static int dirty_bytes_handler(struct ctl_table *table, int write,
533 void *buffer, size_t *lenp, loff_t *ppos)
534{
535 unsigned long old_bytes = vm_dirty_bytes;
536 int ret;
537
538 ret = proc_doulongvec_minmax(table, write, buffer, lenp, ppos);
539 if (ret == 0 && write && vm_dirty_bytes != old_bytes) {
540 writeback_set_ratelimit();
541 vm_dirty_ratio = 0;
542 }
543 return ret;
544}
545#endif
546
547static unsigned long wp_next_time(unsigned long cur_time)
548{
549 cur_time += VM_COMPLETIONS_PERIOD_LEN;
550 /* 0 has a special meaning... */
551 if (!cur_time)
552 return 1;
553 return cur_time;
554}
555
556static void wb_domain_writeout_add(struct wb_domain *dom,
557 struct fprop_local_percpu *completions,
558 unsigned int max_prop_frac, long nr)
559{
560 __fprop_add_percpu_max(&dom->completions, completions,
561 max_prop_frac, nr);
562 /* First event after period switching was turned off? */
563 if (unlikely(!dom->period_time)) {
564 /*
565 * We can race with other __bdi_writeout_inc calls here but
566 * it does not cause any harm since the resulting time when
567 * timer will fire and what is in writeout_period_time will be
568 * roughly the same.
569 */
570 dom->period_time = wp_next_time(jiffies);
571 mod_timer(&dom->period_timer, dom->period_time);
572 }
573}
574
575/*
576 * Increment @wb's writeout completion count and the global writeout
577 * completion count. Called from __folio_end_writeback().
578 */
579static inline void __wb_writeout_add(struct bdi_writeback *wb, long nr)
580{
581 struct wb_domain *cgdom;
582
583 wb_stat_mod(wb, WB_WRITTEN, nr);
584 wb_domain_writeout_add(&global_wb_domain, &wb->completions,
585 wb->bdi->max_prop_frac, nr);
586
587 cgdom = mem_cgroup_wb_domain(wb);
588 if (cgdom)
589 wb_domain_writeout_add(cgdom, wb_memcg_completions(wb),
590 wb->bdi->max_prop_frac, nr);
591}
592
593void wb_writeout_inc(struct bdi_writeback *wb)
594{
595 unsigned long flags;
596
597 local_irq_save(flags);
598 __wb_writeout_add(wb, 1);
599 local_irq_restore(flags);
600}
601EXPORT_SYMBOL_GPL(wb_writeout_inc);
602
603/*
604 * On idle system, we can be called long after we scheduled because we use
605 * deferred timers so count with missed periods.
606 */
607static void writeout_period(struct timer_list *t)
608{
609 struct wb_domain *dom = from_timer(dom, t, period_timer);
610 int miss_periods = (jiffies - dom->period_time) /
611 VM_COMPLETIONS_PERIOD_LEN;
612
613 if (fprop_new_period(&dom->completions, miss_periods + 1)) {
614 dom->period_time = wp_next_time(dom->period_time +
615 miss_periods * VM_COMPLETIONS_PERIOD_LEN);
616 mod_timer(&dom->period_timer, dom->period_time);
617 } else {
618 /*
619 * Aging has zeroed all fractions. Stop wasting CPU on period
620 * updates.
621 */
622 dom->period_time = 0;
623 }
624}
625
626int wb_domain_init(struct wb_domain *dom, gfp_t gfp)
627{
628 memset(dom, 0, sizeof(*dom));
629
630 spin_lock_init(&dom->lock);
631
632 timer_setup(&dom->period_timer, writeout_period, TIMER_DEFERRABLE);
633
634 dom->dirty_limit_tstamp = jiffies;
635
636 return fprop_global_init(&dom->completions, gfp);
637}
638
639#ifdef CONFIG_CGROUP_WRITEBACK
640void wb_domain_exit(struct wb_domain *dom)
641{
642 del_timer_sync(&dom->period_timer);
643 fprop_global_destroy(&dom->completions);
644}
645#endif
646
647/*
648 * bdi_min_ratio keeps the sum of the minimum dirty shares of all
649 * registered backing devices, which, for obvious reasons, can not
650 * exceed 100%.
651 */
652static unsigned int bdi_min_ratio;
653
654static int bdi_check_pages_limit(unsigned long pages)
655{
656 unsigned long max_dirty_pages = global_dirtyable_memory();
657
658 if (pages > max_dirty_pages)
659 return -EINVAL;
660
661 return 0;
662}
663
664static unsigned long bdi_ratio_from_pages(unsigned long pages)
665{
666 unsigned long background_thresh;
667 unsigned long dirty_thresh;
668 unsigned long ratio;
669
670 global_dirty_limits(&background_thresh, &dirty_thresh);
671 ratio = div64_u64(pages * 100ULL * BDI_RATIO_SCALE, dirty_thresh);
672
673 return ratio;
674}
675
676static u64 bdi_get_bytes(unsigned int ratio)
677{
678 unsigned long background_thresh;
679 unsigned long dirty_thresh;
680 u64 bytes;
681
682 global_dirty_limits(&background_thresh, &dirty_thresh);
683 bytes = (dirty_thresh * PAGE_SIZE * ratio) / BDI_RATIO_SCALE / 100;
684
685 return bytes;
686}
687
688static int __bdi_set_min_ratio(struct backing_dev_info *bdi, unsigned int min_ratio)
689{
690 unsigned int delta;
691 int ret = 0;
692
693 if (min_ratio > 100 * BDI_RATIO_SCALE)
694 return -EINVAL;
695 min_ratio *= BDI_RATIO_SCALE;
696
697 spin_lock_bh(&bdi_lock);
698 if (min_ratio > bdi->max_ratio) {
699 ret = -EINVAL;
700 } else {
701 if (min_ratio < bdi->min_ratio) {
702 delta = bdi->min_ratio - min_ratio;
703 bdi_min_ratio -= delta;
704 bdi->min_ratio = min_ratio;
705 } else {
706 delta = min_ratio - bdi->min_ratio;
707 if (bdi_min_ratio + delta < 100 * BDI_RATIO_SCALE) {
708 bdi_min_ratio += delta;
709 bdi->min_ratio = min_ratio;
710 } else {
711 ret = -EINVAL;
712 }
713 }
714 }
715 spin_unlock_bh(&bdi_lock);
716
717 return ret;
718}
719
720static int __bdi_set_max_ratio(struct backing_dev_info *bdi, unsigned int max_ratio)
721{
722 int ret = 0;
723
724 if (max_ratio > 100 * BDI_RATIO_SCALE)
725 return -EINVAL;
726
727 spin_lock_bh(&bdi_lock);
728 if (bdi->min_ratio > max_ratio) {
729 ret = -EINVAL;
730 } else {
731 bdi->max_ratio = max_ratio;
732 bdi->max_prop_frac = (FPROP_FRAC_BASE * max_ratio) / 100;
733 }
734 spin_unlock_bh(&bdi_lock);
735
736 return ret;
737}
738
739int bdi_set_min_ratio_no_scale(struct backing_dev_info *bdi, unsigned int min_ratio)
740{
741 return __bdi_set_min_ratio(bdi, min_ratio);
742}
743
744int bdi_set_max_ratio_no_scale(struct backing_dev_info *bdi, unsigned int max_ratio)
745{
746 return __bdi_set_max_ratio(bdi, max_ratio);
747}
748
749int bdi_set_min_ratio(struct backing_dev_info *bdi, unsigned int min_ratio)
750{
751 return __bdi_set_min_ratio(bdi, min_ratio * BDI_RATIO_SCALE);
752}
753
754int bdi_set_max_ratio(struct backing_dev_info *bdi, unsigned int max_ratio)
755{
756 return __bdi_set_max_ratio(bdi, max_ratio * BDI_RATIO_SCALE);
757}
758EXPORT_SYMBOL(bdi_set_max_ratio);
759
760u64 bdi_get_min_bytes(struct backing_dev_info *bdi)
761{
762 return bdi_get_bytes(bdi->min_ratio);
763}
764
765int bdi_set_min_bytes(struct backing_dev_info *bdi, u64 min_bytes)
766{
767 int ret;
768 unsigned long pages = min_bytes >> PAGE_SHIFT;
769 unsigned long min_ratio;
770
771 ret = bdi_check_pages_limit(pages);
772 if (ret)
773 return ret;
774
775 min_ratio = bdi_ratio_from_pages(pages);
776 return __bdi_set_min_ratio(bdi, min_ratio);
777}
778
779u64 bdi_get_max_bytes(struct backing_dev_info *bdi)
780{
781 return bdi_get_bytes(bdi->max_ratio);
782}
783
784int bdi_set_max_bytes(struct backing_dev_info *bdi, u64 max_bytes)
785{
786 int ret;
787 unsigned long pages = max_bytes >> PAGE_SHIFT;
788 unsigned long max_ratio;
789
790 ret = bdi_check_pages_limit(pages);
791 if (ret)
792 return ret;
793
794 max_ratio = bdi_ratio_from_pages(pages);
795 return __bdi_set_max_ratio(bdi, max_ratio);
796}
797
798int bdi_set_strict_limit(struct backing_dev_info *bdi, unsigned int strict_limit)
799{
800 if (strict_limit > 1)
801 return -EINVAL;
802
803 spin_lock_bh(&bdi_lock);
804 if (strict_limit)
805 bdi->capabilities |= BDI_CAP_STRICTLIMIT;
806 else
807 bdi->capabilities &= ~BDI_CAP_STRICTLIMIT;
808 spin_unlock_bh(&bdi_lock);
809
810 return 0;
811}
812
813static unsigned long dirty_freerun_ceiling(unsigned long thresh,
814 unsigned long bg_thresh)
815{
816 return (thresh + bg_thresh) / 2;
817}
818
819static unsigned long hard_dirty_limit(struct wb_domain *dom,
820 unsigned long thresh)
821{
822 return max(thresh, dom->dirty_limit);
823}
824
825/*
826 * Memory which can be further allocated to a memcg domain is capped by
827 * system-wide clean memory excluding the amount being used in the domain.
828 */
829static void mdtc_calc_avail(struct dirty_throttle_control *mdtc,
830 unsigned long filepages, unsigned long headroom)
831{
832 struct dirty_throttle_control *gdtc = mdtc_gdtc(mdtc);
833 unsigned long clean = filepages - min(filepages, mdtc->dirty);
834 unsigned long global_clean = gdtc->avail - min(gdtc->avail, gdtc->dirty);
835 unsigned long other_clean = global_clean - min(global_clean, clean);
836
837 mdtc->avail = filepages + min(headroom, other_clean);
838}
839
840/**
841 * __wb_calc_thresh - @wb's share of dirty throttling threshold
842 * @dtc: dirty_throttle_context of interest
843 *
844 * Note that balance_dirty_pages() will only seriously take it as a hard limit
845 * when sleeping max_pause per page is not enough to keep the dirty pages under
846 * control. For example, when the device is completely stalled due to some error
847 * conditions, or when there are 1000 dd tasks writing to a slow 10MB/s USB key.
848 * In the other normal situations, it acts more gently by throttling the tasks
849 * more (rather than completely block them) when the wb dirty pages go high.
850 *
851 * It allocates high/low dirty limits to fast/slow devices, in order to prevent
852 * - starving fast devices
853 * - piling up dirty pages (that will take long time to sync) on slow devices
854 *
855 * The wb's share of dirty limit will be adapting to its throughput and
856 * bounded by the bdi->min_ratio and/or bdi->max_ratio parameters, if set.
857 *
858 * Return: @wb's dirty limit in pages. The term "dirty" in the context of
859 * dirty balancing includes all PG_dirty and PG_writeback pages.
860 */
861static unsigned long __wb_calc_thresh(struct dirty_throttle_control *dtc)
862{
863 struct wb_domain *dom = dtc_dom(dtc);
864 unsigned long thresh = dtc->thresh;
865 u64 wb_thresh;
866 unsigned long numerator, denominator;
867 unsigned long wb_min_ratio, wb_max_ratio;
868
869 /*
870 * Calculate this BDI's share of the thresh ratio.
871 */
872 fprop_fraction_percpu(&dom->completions, dtc->wb_completions,
873 &numerator, &denominator);
874
875 wb_thresh = (thresh * (100 * BDI_RATIO_SCALE - bdi_min_ratio)) / (100 * BDI_RATIO_SCALE);
876 wb_thresh *= numerator;
877 wb_thresh = div64_ul(wb_thresh, denominator);
878
879 wb_min_max_ratio(dtc->wb, &wb_min_ratio, &wb_max_ratio);
880
881 wb_thresh += (thresh * wb_min_ratio) / (100 * BDI_RATIO_SCALE);
882 if (wb_thresh > (thresh * wb_max_ratio) / (100 * BDI_RATIO_SCALE))
883 wb_thresh = thresh * wb_max_ratio / (100 * BDI_RATIO_SCALE);
884
885 return wb_thresh;
886}
887
888unsigned long wb_calc_thresh(struct bdi_writeback *wb, unsigned long thresh)
889{
890 struct dirty_throttle_control gdtc = { GDTC_INIT(wb),
891 .thresh = thresh };
892 return __wb_calc_thresh(&gdtc);
893}
894
895/*
896 * setpoint - dirty 3
897 * f(dirty) := 1.0 + (----------------)
898 * limit - setpoint
899 *
900 * it's a 3rd order polynomial that subjects to
901 *
902 * (1) f(freerun) = 2.0 => rampup dirty_ratelimit reasonably fast
903 * (2) f(setpoint) = 1.0 => the balance point
904 * (3) f(limit) = 0 => the hard limit
905 * (4) df/dx <= 0 => negative feedback control
906 * (5) the closer to setpoint, the smaller |df/dx| (and the reverse)
907 * => fast response on large errors; small oscillation near setpoint
908 */
909static long long pos_ratio_polynom(unsigned long setpoint,
910 unsigned long dirty,
911 unsigned long limit)
912{
913 long long pos_ratio;
914 long x;
915
916 x = div64_s64(((s64)setpoint - (s64)dirty) << RATELIMIT_CALC_SHIFT,
917 (limit - setpoint) | 1);
918 pos_ratio = x;
919 pos_ratio = pos_ratio * x >> RATELIMIT_CALC_SHIFT;
920 pos_ratio = pos_ratio * x >> RATELIMIT_CALC_SHIFT;
921 pos_ratio += 1 << RATELIMIT_CALC_SHIFT;
922
923 return clamp(pos_ratio, 0LL, 2LL << RATELIMIT_CALC_SHIFT);
924}
925
926/*
927 * Dirty position control.
928 *
929 * (o) global/bdi setpoints
930 *
931 * We want the dirty pages be balanced around the global/wb setpoints.
932 * When the number of dirty pages is higher/lower than the setpoint, the
933 * dirty position control ratio (and hence task dirty ratelimit) will be
934 * decreased/increased to bring the dirty pages back to the setpoint.
935 *
936 * pos_ratio = 1 << RATELIMIT_CALC_SHIFT
937 *
938 * if (dirty < setpoint) scale up pos_ratio
939 * if (dirty > setpoint) scale down pos_ratio
940 *
941 * if (wb_dirty < wb_setpoint) scale up pos_ratio
942 * if (wb_dirty > wb_setpoint) scale down pos_ratio
943 *
944 * task_ratelimit = dirty_ratelimit * pos_ratio >> RATELIMIT_CALC_SHIFT
945 *
946 * (o) global control line
947 *
948 * ^ pos_ratio
949 * |
950 * | |<===== global dirty control scope ======>|
951 * 2.0 * * * * * * *
952 * | .*
953 * | . *
954 * | . *
955 * | . *
956 * | . *
957 * | . *
958 * 1.0 ................................*
959 * | . . *
960 * | . . *
961 * | . . *
962 * | . . *
963 * | . . *
964 * 0 +------------.------------------.----------------------*------------->
965 * freerun^ setpoint^ limit^ dirty pages
966 *
967 * (o) wb control line
968 *
969 * ^ pos_ratio
970 * |
971 * | *
972 * | *
973 * | *
974 * | *
975 * | * |<=========== span ============>|
976 * 1.0 .......................*
977 * | . *
978 * | . *
979 * | . *
980 * | . *
981 * | . *
982 * | . *
983 * | . *
984 * | . *
985 * | . *
986 * | . *
987 * | . *
988 * 1/4 ...............................................* * * * * * * * * * * *
989 * | . .
990 * | . .
991 * | . .
992 * 0 +----------------------.-------------------------------.------------->
993 * wb_setpoint^ x_intercept^
994 *
995 * The wb control line won't drop below pos_ratio=1/4, so that wb_dirty can
996 * be smoothly throttled down to normal if it starts high in situations like
997 * - start writing to a slow SD card and a fast disk at the same time. The SD
998 * card's wb_dirty may rush to many times higher than wb_setpoint.
999 * - the wb dirty thresh drops quickly due to change of JBOD workload
1000 */
1001static void wb_position_ratio(struct dirty_throttle_control *dtc)
1002{
1003 struct bdi_writeback *wb = dtc->wb;
1004 unsigned long write_bw = READ_ONCE(wb->avg_write_bandwidth);
1005 unsigned long freerun = dirty_freerun_ceiling(dtc->thresh, dtc->bg_thresh);
1006 unsigned long limit = hard_dirty_limit(dtc_dom(dtc), dtc->thresh);
1007 unsigned long wb_thresh = dtc->wb_thresh;
1008 unsigned long x_intercept;
1009 unsigned long setpoint; /* dirty pages' target balance point */
1010 unsigned long wb_setpoint;
1011 unsigned long span;
1012 long long pos_ratio; /* for scaling up/down the rate limit */
1013 long x;
1014
1015 dtc->pos_ratio = 0;
1016
1017 if (unlikely(dtc->dirty >= limit))
1018 return;
1019
1020 /*
1021 * global setpoint
1022 *
1023 * See comment for pos_ratio_polynom().
1024 */
1025 setpoint = (freerun + limit) / 2;
1026 pos_ratio = pos_ratio_polynom(setpoint, dtc->dirty, limit);
1027
1028 /*
1029 * The strictlimit feature is a tool preventing mistrusted filesystems
1030 * from growing a large number of dirty pages before throttling. For
1031 * such filesystems balance_dirty_pages always checks wb counters
1032 * against wb limits. Even if global "nr_dirty" is under "freerun".
1033 * This is especially important for fuse which sets bdi->max_ratio to
1034 * 1% by default. Without strictlimit feature, fuse writeback may
1035 * consume arbitrary amount of RAM because it is accounted in
1036 * NR_WRITEBACK_TEMP which is not involved in calculating "nr_dirty".
1037 *
1038 * Here, in wb_position_ratio(), we calculate pos_ratio based on
1039 * two values: wb_dirty and wb_thresh. Let's consider an example:
1040 * total amount of RAM is 16GB, bdi->max_ratio is equal to 1%, global
1041 * limits are set by default to 10% and 20% (background and throttle).
1042 * Then wb_thresh is 1% of 20% of 16GB. This amounts to ~8K pages.
1043 * wb_calc_thresh(wb, bg_thresh) is about ~4K pages. wb_setpoint is
1044 * about ~6K pages (as the average of background and throttle wb
1045 * limits). The 3rd order polynomial will provide positive feedback if
1046 * wb_dirty is under wb_setpoint and vice versa.
1047 *
1048 * Note, that we cannot use global counters in these calculations
1049 * because we want to throttle process writing to a strictlimit wb
1050 * much earlier than global "freerun" is reached (~23MB vs. ~2.3GB
1051 * in the example above).
1052 */
1053 if (unlikely(wb->bdi->capabilities & BDI_CAP_STRICTLIMIT)) {
1054 long long wb_pos_ratio;
1055
1056 if (dtc->wb_dirty < 8) {
1057 dtc->pos_ratio = min_t(long long, pos_ratio * 2,
1058 2 << RATELIMIT_CALC_SHIFT);
1059 return;
1060 }
1061
1062 if (dtc->wb_dirty >= wb_thresh)
1063 return;
1064
1065 wb_setpoint = dirty_freerun_ceiling(wb_thresh,
1066 dtc->wb_bg_thresh);
1067
1068 if (wb_setpoint == 0 || wb_setpoint == wb_thresh)
1069 return;
1070
1071 wb_pos_ratio = pos_ratio_polynom(wb_setpoint, dtc->wb_dirty,
1072 wb_thresh);
1073
1074 /*
1075 * Typically, for strictlimit case, wb_setpoint << setpoint
1076 * and pos_ratio >> wb_pos_ratio. In the other words global
1077 * state ("dirty") is not limiting factor and we have to
1078 * make decision based on wb counters. But there is an
1079 * important case when global pos_ratio should get precedence:
1080 * global limits are exceeded (e.g. due to activities on other
1081 * wb's) while given strictlimit wb is below limit.
1082 *
1083 * "pos_ratio * wb_pos_ratio" would work for the case above,
1084 * but it would look too non-natural for the case of all
1085 * activity in the system coming from a single strictlimit wb
1086 * with bdi->max_ratio == 100%.
1087 *
1088 * Note that min() below somewhat changes the dynamics of the
1089 * control system. Normally, pos_ratio value can be well over 3
1090 * (when globally we are at freerun and wb is well below wb
1091 * setpoint). Now the maximum pos_ratio in the same situation
1092 * is 2. We might want to tweak this if we observe the control
1093 * system is too slow to adapt.
1094 */
1095 dtc->pos_ratio = min(pos_ratio, wb_pos_ratio);
1096 return;
1097 }
1098
1099 /*
1100 * We have computed basic pos_ratio above based on global situation. If
1101 * the wb is over/under its share of dirty pages, we want to scale
1102 * pos_ratio further down/up. That is done by the following mechanism.
1103 */
1104
1105 /*
1106 * wb setpoint
1107 *
1108 * f(wb_dirty) := 1.0 + k * (wb_dirty - wb_setpoint)
1109 *
1110 * x_intercept - wb_dirty
1111 * := --------------------------
1112 * x_intercept - wb_setpoint
1113 *
1114 * The main wb control line is a linear function that subjects to
1115 *
1116 * (1) f(wb_setpoint) = 1.0
1117 * (2) k = - 1 / (8 * write_bw) (in single wb case)
1118 * or equally: x_intercept = wb_setpoint + 8 * write_bw
1119 *
1120 * For single wb case, the dirty pages are observed to fluctuate
1121 * regularly within range
1122 * [wb_setpoint - write_bw/2, wb_setpoint + write_bw/2]
1123 * for various filesystems, where (2) can yield in a reasonable 12.5%
1124 * fluctuation range for pos_ratio.
1125 *
1126 * For JBOD case, wb_thresh (not wb_dirty!) could fluctuate up to its
1127 * own size, so move the slope over accordingly and choose a slope that
1128 * yields 100% pos_ratio fluctuation on suddenly doubled wb_thresh.
1129 */
1130 if (unlikely(wb_thresh > dtc->thresh))
1131 wb_thresh = dtc->thresh;
1132 /*
1133 * It's very possible that wb_thresh is close to 0 not because the
1134 * device is slow, but that it has remained inactive for long time.
1135 * Honour such devices a reasonable good (hopefully IO efficient)
1136 * threshold, so that the occasional writes won't be blocked and active
1137 * writes can rampup the threshold quickly.
1138 */
1139 wb_thresh = max(wb_thresh, (limit - dtc->dirty) / 8);
1140 /*
1141 * scale global setpoint to wb's:
1142 * wb_setpoint = setpoint * wb_thresh / thresh
1143 */
1144 x = div_u64((u64)wb_thresh << 16, dtc->thresh | 1);
1145 wb_setpoint = setpoint * (u64)x >> 16;
1146 /*
1147 * Use span=(8*write_bw) in single wb case as indicated by
1148 * (thresh - wb_thresh ~= 0) and transit to wb_thresh in JBOD case.
1149 *
1150 * wb_thresh thresh - wb_thresh
1151 * span = --------- * (8 * write_bw) + ------------------ * wb_thresh
1152 * thresh thresh
1153 */
1154 span = (dtc->thresh - wb_thresh + 8 * write_bw) * (u64)x >> 16;
1155 x_intercept = wb_setpoint + span;
1156
1157 if (dtc->wb_dirty < x_intercept - span / 4) {
1158 pos_ratio = div64_u64(pos_ratio * (x_intercept - dtc->wb_dirty),
1159 (x_intercept - wb_setpoint) | 1);
1160 } else
1161 pos_ratio /= 4;
1162
1163 /*
1164 * wb reserve area, safeguard against dirty pool underrun and disk idle
1165 * It may push the desired control point of global dirty pages higher
1166 * than setpoint.
1167 */
1168 x_intercept = wb_thresh / 2;
1169 if (dtc->wb_dirty < x_intercept) {
1170 if (dtc->wb_dirty > x_intercept / 8)
1171 pos_ratio = div_u64(pos_ratio * x_intercept,
1172 dtc->wb_dirty);
1173 else
1174 pos_ratio *= 8;
1175 }
1176
1177 dtc->pos_ratio = pos_ratio;
1178}
1179
1180static void wb_update_write_bandwidth(struct bdi_writeback *wb,
1181 unsigned long elapsed,
1182 unsigned long written)
1183{
1184 const unsigned long period = roundup_pow_of_two(3 * HZ);
1185 unsigned long avg = wb->avg_write_bandwidth;
1186 unsigned long old = wb->write_bandwidth;
1187 u64 bw;
1188
1189 /*
1190 * bw = written * HZ / elapsed
1191 *
1192 * bw * elapsed + write_bandwidth * (period - elapsed)
1193 * write_bandwidth = ---------------------------------------------------
1194 * period
1195 *
1196 * @written may have decreased due to folio_account_redirty().
1197 * Avoid underflowing @bw calculation.
1198 */
1199 bw = written - min(written, wb->written_stamp);
1200 bw *= HZ;
1201 if (unlikely(elapsed > period)) {
1202 bw = div64_ul(bw, elapsed);
1203 avg = bw;
1204 goto out;
1205 }
1206 bw += (u64)wb->write_bandwidth * (period - elapsed);
1207 bw >>= ilog2(period);
1208
1209 /*
1210 * one more level of smoothing, for filtering out sudden spikes
1211 */
1212 if (avg > old && old >= (unsigned long)bw)
1213 avg -= (avg - old) >> 3;
1214
1215 if (avg < old && old <= (unsigned long)bw)
1216 avg += (old - avg) >> 3;
1217
1218out:
1219 /* keep avg > 0 to guarantee that tot > 0 if there are dirty wbs */
1220 avg = max(avg, 1LU);
1221 if (wb_has_dirty_io(wb)) {
1222 long delta = avg - wb->avg_write_bandwidth;
1223 WARN_ON_ONCE(atomic_long_add_return(delta,
1224 &wb->bdi->tot_write_bandwidth) <= 0);
1225 }
1226 wb->write_bandwidth = bw;
1227 WRITE_ONCE(wb->avg_write_bandwidth, avg);
1228}
1229
1230static void update_dirty_limit(struct dirty_throttle_control *dtc)
1231{
1232 struct wb_domain *dom = dtc_dom(dtc);
1233 unsigned long thresh = dtc->thresh;
1234 unsigned long limit = dom->dirty_limit;
1235
1236 /*
1237 * Follow up in one step.
1238 */
1239 if (limit < thresh) {
1240 limit = thresh;
1241 goto update;
1242 }
1243
1244 /*
1245 * Follow down slowly. Use the higher one as the target, because thresh
1246 * may drop below dirty. This is exactly the reason to introduce
1247 * dom->dirty_limit which is guaranteed to lie above the dirty pages.
1248 */
1249 thresh = max(thresh, dtc->dirty);
1250 if (limit > thresh) {
1251 limit -= (limit - thresh) >> 5;
1252 goto update;
1253 }
1254 return;
1255update:
1256 dom->dirty_limit = limit;
1257}
1258
1259static void domain_update_dirty_limit(struct dirty_throttle_control *dtc,
1260 unsigned long now)
1261{
1262 struct wb_domain *dom = dtc_dom(dtc);
1263
1264 /*
1265 * check locklessly first to optimize away locking for the most time
1266 */
1267 if (time_before(now, dom->dirty_limit_tstamp + BANDWIDTH_INTERVAL))
1268 return;
1269
1270 spin_lock(&dom->lock);
1271 if (time_after_eq(now, dom->dirty_limit_tstamp + BANDWIDTH_INTERVAL)) {
1272 update_dirty_limit(dtc);
1273 dom->dirty_limit_tstamp = now;
1274 }
1275 spin_unlock(&dom->lock);
1276}
1277
1278/*
1279 * Maintain wb->dirty_ratelimit, the base dirty throttle rate.
1280 *
1281 * Normal wb tasks will be curbed at or below it in long term.
1282 * Obviously it should be around (write_bw / N) when there are N dd tasks.
1283 */
1284static void wb_update_dirty_ratelimit(struct dirty_throttle_control *dtc,
1285 unsigned long dirtied,
1286 unsigned long elapsed)
1287{
1288 struct bdi_writeback *wb = dtc->wb;
1289 unsigned long dirty = dtc->dirty;
1290 unsigned long freerun = dirty_freerun_ceiling(dtc->thresh, dtc->bg_thresh);
1291 unsigned long limit = hard_dirty_limit(dtc_dom(dtc), dtc->thresh);
1292 unsigned long setpoint = (freerun + limit) / 2;
1293 unsigned long write_bw = wb->avg_write_bandwidth;
1294 unsigned long dirty_ratelimit = wb->dirty_ratelimit;
1295 unsigned long dirty_rate;
1296 unsigned long task_ratelimit;
1297 unsigned long balanced_dirty_ratelimit;
1298 unsigned long step;
1299 unsigned long x;
1300 unsigned long shift;
1301
1302 /*
1303 * The dirty rate will match the writeout rate in long term, except
1304 * when dirty pages are truncated by userspace or re-dirtied by FS.
1305 */
1306 dirty_rate = (dirtied - wb->dirtied_stamp) * HZ / elapsed;
1307
1308 /*
1309 * task_ratelimit reflects each dd's dirty rate for the past 200ms.
1310 */
1311 task_ratelimit = (u64)dirty_ratelimit *
1312 dtc->pos_ratio >> RATELIMIT_CALC_SHIFT;
1313 task_ratelimit++; /* it helps rampup dirty_ratelimit from tiny values */
1314
1315 /*
1316 * A linear estimation of the "balanced" throttle rate. The theory is,
1317 * if there are N dd tasks, each throttled at task_ratelimit, the wb's
1318 * dirty_rate will be measured to be (N * task_ratelimit). So the below
1319 * formula will yield the balanced rate limit (write_bw / N).
1320 *
1321 * Note that the expanded form is not a pure rate feedback:
1322 * rate_(i+1) = rate_(i) * (write_bw / dirty_rate) (1)
1323 * but also takes pos_ratio into account:
1324 * rate_(i+1) = rate_(i) * (write_bw / dirty_rate) * pos_ratio (2)
1325 *
1326 * (1) is not realistic because pos_ratio also takes part in balancing
1327 * the dirty rate. Consider the state
1328 * pos_ratio = 0.5 (3)
1329 * rate = 2 * (write_bw / N) (4)
1330 * If (1) is used, it will stuck in that state! Because each dd will
1331 * be throttled at
1332 * task_ratelimit = pos_ratio * rate = (write_bw / N) (5)
1333 * yielding
1334 * dirty_rate = N * task_ratelimit = write_bw (6)
1335 * put (6) into (1) we get
1336 * rate_(i+1) = rate_(i) (7)
1337 *
1338 * So we end up using (2) to always keep
1339 * rate_(i+1) ~= (write_bw / N) (8)
1340 * regardless of the value of pos_ratio. As long as (8) is satisfied,
1341 * pos_ratio is able to drive itself to 1.0, which is not only where
1342 * the dirty count meet the setpoint, but also where the slope of
1343 * pos_ratio is most flat and hence task_ratelimit is least fluctuated.
1344 */
1345 balanced_dirty_ratelimit = div_u64((u64)task_ratelimit * write_bw,
1346 dirty_rate | 1);
1347 /*
1348 * balanced_dirty_ratelimit ~= (write_bw / N) <= write_bw
1349 */
1350 if (unlikely(balanced_dirty_ratelimit > write_bw))
1351 balanced_dirty_ratelimit = write_bw;
1352
1353 /*
1354 * We could safely do this and return immediately:
1355 *
1356 * wb->dirty_ratelimit = balanced_dirty_ratelimit;
1357 *
1358 * However to get a more stable dirty_ratelimit, the below elaborated
1359 * code makes use of task_ratelimit to filter out singular points and
1360 * limit the step size.
1361 *
1362 * The below code essentially only uses the relative value of
1363 *
1364 * task_ratelimit - dirty_ratelimit
1365 * = (pos_ratio - 1) * dirty_ratelimit
1366 *
1367 * which reflects the direction and size of dirty position error.
1368 */
1369
1370 /*
1371 * dirty_ratelimit will follow balanced_dirty_ratelimit iff
1372 * task_ratelimit is on the same side of dirty_ratelimit, too.
1373 * For example, when
1374 * - dirty_ratelimit > balanced_dirty_ratelimit
1375 * - dirty_ratelimit > task_ratelimit (dirty pages are above setpoint)
1376 * lowering dirty_ratelimit will help meet both the position and rate
1377 * control targets. Otherwise, don't update dirty_ratelimit if it will
1378 * only help meet the rate target. After all, what the users ultimately
1379 * feel and care are stable dirty rate and small position error.
1380 *
1381 * |task_ratelimit - dirty_ratelimit| is used to limit the step size
1382 * and filter out the singular points of balanced_dirty_ratelimit. Which
1383 * keeps jumping around randomly and can even leap far away at times
1384 * due to the small 200ms estimation period of dirty_rate (we want to
1385 * keep that period small to reduce time lags).
1386 */
1387 step = 0;
1388
1389 /*
1390 * For strictlimit case, calculations above were based on wb counters
1391 * and limits (starting from pos_ratio = wb_position_ratio() and up to
1392 * balanced_dirty_ratelimit = task_ratelimit * write_bw / dirty_rate).
1393 * Hence, to calculate "step" properly, we have to use wb_dirty as
1394 * "dirty" and wb_setpoint as "setpoint".
1395 *
1396 * We rampup dirty_ratelimit forcibly if wb_dirty is low because
1397 * it's possible that wb_thresh is close to zero due to inactivity
1398 * of backing device.
1399 */
1400 if (unlikely(wb->bdi->capabilities & BDI_CAP_STRICTLIMIT)) {
1401 dirty = dtc->wb_dirty;
1402 if (dtc->wb_dirty < 8)
1403 setpoint = dtc->wb_dirty + 1;
1404 else
1405 setpoint = (dtc->wb_thresh + dtc->wb_bg_thresh) / 2;
1406 }
1407
1408 if (dirty < setpoint) {
1409 x = min3(wb->balanced_dirty_ratelimit,
1410 balanced_dirty_ratelimit, task_ratelimit);
1411 if (dirty_ratelimit < x)
1412 step = x - dirty_ratelimit;
1413 } else {
1414 x = max3(wb->balanced_dirty_ratelimit,
1415 balanced_dirty_ratelimit, task_ratelimit);
1416 if (dirty_ratelimit > x)
1417 step = dirty_ratelimit - x;
1418 }
1419
1420 /*
1421 * Don't pursue 100% rate matching. It's impossible since the balanced
1422 * rate itself is constantly fluctuating. So decrease the track speed
1423 * when it gets close to the target. Helps eliminate pointless tremors.
1424 */
1425 shift = dirty_ratelimit / (2 * step + 1);
1426 if (shift < BITS_PER_LONG)
1427 step = DIV_ROUND_UP(step >> shift, 8);
1428 else
1429 step = 0;
1430
1431 if (dirty_ratelimit < balanced_dirty_ratelimit)
1432 dirty_ratelimit += step;
1433 else
1434 dirty_ratelimit -= step;
1435
1436 WRITE_ONCE(wb->dirty_ratelimit, max(dirty_ratelimit, 1UL));
1437 wb->balanced_dirty_ratelimit = balanced_dirty_ratelimit;
1438
1439 trace_bdi_dirty_ratelimit(wb, dirty_rate, task_ratelimit);
1440}
1441
1442static void __wb_update_bandwidth(struct dirty_throttle_control *gdtc,
1443 struct dirty_throttle_control *mdtc,
1444 bool update_ratelimit)
1445{
1446 struct bdi_writeback *wb = gdtc->wb;
1447 unsigned long now = jiffies;
1448 unsigned long elapsed;
1449 unsigned long dirtied;
1450 unsigned long written;
1451
1452 spin_lock(&wb->list_lock);
1453
1454 /*
1455 * Lockless checks for elapsed time are racy and delayed update after
1456 * IO completion doesn't do it at all (to make sure written pages are
1457 * accounted reasonably quickly). Make sure elapsed >= 1 to avoid
1458 * division errors.
1459 */
1460 elapsed = max(now - wb->bw_time_stamp, 1UL);
1461 dirtied = percpu_counter_read(&wb->stat[WB_DIRTIED]);
1462 written = percpu_counter_read(&wb->stat[WB_WRITTEN]);
1463
1464 if (update_ratelimit) {
1465 domain_update_dirty_limit(gdtc, now);
1466 wb_update_dirty_ratelimit(gdtc, dirtied, elapsed);
1467
1468 /*
1469 * @mdtc is always NULL if !CGROUP_WRITEBACK but the
1470 * compiler has no way to figure that out. Help it.
1471 */
1472 if (IS_ENABLED(CONFIG_CGROUP_WRITEBACK) && mdtc) {
1473 domain_update_dirty_limit(mdtc, now);
1474 wb_update_dirty_ratelimit(mdtc, dirtied, elapsed);
1475 }
1476 }
1477 wb_update_write_bandwidth(wb, elapsed, written);
1478
1479 wb->dirtied_stamp = dirtied;
1480 wb->written_stamp = written;
1481 WRITE_ONCE(wb->bw_time_stamp, now);
1482 spin_unlock(&wb->list_lock);
1483}
1484
1485void wb_update_bandwidth(struct bdi_writeback *wb)
1486{
1487 struct dirty_throttle_control gdtc = { GDTC_INIT(wb) };
1488
1489 __wb_update_bandwidth(&gdtc, NULL, false);
1490}
1491
1492/* Interval after which we consider wb idle and don't estimate bandwidth */
1493#define WB_BANDWIDTH_IDLE_JIF (HZ)
1494
1495static void wb_bandwidth_estimate_start(struct bdi_writeback *wb)
1496{
1497 unsigned long now = jiffies;
1498 unsigned long elapsed = now - READ_ONCE(wb->bw_time_stamp);
1499
1500 if (elapsed > WB_BANDWIDTH_IDLE_JIF &&
1501 !atomic_read(&wb->writeback_inodes)) {
1502 spin_lock(&wb->list_lock);
1503 wb->dirtied_stamp = wb_stat(wb, WB_DIRTIED);
1504 wb->written_stamp = wb_stat(wb, WB_WRITTEN);
1505 WRITE_ONCE(wb->bw_time_stamp, now);
1506 spin_unlock(&wb->list_lock);
1507 }
1508}
1509
1510/*
1511 * After a task dirtied this many pages, balance_dirty_pages_ratelimited()
1512 * will look to see if it needs to start dirty throttling.
1513 *
1514 * If dirty_poll_interval is too low, big NUMA machines will call the expensive
1515 * global_zone_page_state() too often. So scale it near-sqrt to the safety margin
1516 * (the number of pages we may dirty without exceeding the dirty limits).
1517 */
1518static unsigned long dirty_poll_interval(unsigned long dirty,
1519 unsigned long thresh)
1520{
1521 if (thresh > dirty)
1522 return 1UL << (ilog2(thresh - dirty) >> 1);
1523
1524 return 1;
1525}
1526
1527static unsigned long wb_max_pause(struct bdi_writeback *wb,
1528 unsigned long wb_dirty)
1529{
1530 unsigned long bw = READ_ONCE(wb->avg_write_bandwidth);
1531 unsigned long t;
1532
1533 /*
1534 * Limit pause time for small memory systems. If sleeping for too long
1535 * time, a small pool of dirty/writeback pages may go empty and disk go
1536 * idle.
1537 *
1538 * 8 serves as the safety ratio.
1539 */
1540 t = wb_dirty / (1 + bw / roundup_pow_of_two(1 + HZ / 8));
1541 t++;
1542
1543 return min_t(unsigned long, t, MAX_PAUSE);
1544}
1545
1546static long wb_min_pause(struct bdi_writeback *wb,
1547 long max_pause,
1548 unsigned long task_ratelimit,
1549 unsigned long dirty_ratelimit,
1550 int *nr_dirtied_pause)
1551{
1552 long hi = ilog2(READ_ONCE(wb->avg_write_bandwidth));
1553 long lo = ilog2(READ_ONCE(wb->dirty_ratelimit));
1554 long t; /* target pause */
1555 long pause; /* estimated next pause */
1556 int pages; /* target nr_dirtied_pause */
1557
1558 /* target for 10ms pause on 1-dd case */
1559 t = max(1, HZ / 100);
1560
1561 /*
1562 * Scale up pause time for concurrent dirtiers in order to reduce CPU
1563 * overheads.
1564 *
1565 * (N * 10ms) on 2^N concurrent tasks.
1566 */
1567 if (hi > lo)
1568 t += (hi - lo) * (10 * HZ) / 1024;
1569
1570 /*
1571 * This is a bit convoluted. We try to base the next nr_dirtied_pause
1572 * on the much more stable dirty_ratelimit. However the next pause time
1573 * will be computed based on task_ratelimit and the two rate limits may
1574 * depart considerably at some time. Especially if task_ratelimit goes
1575 * below dirty_ratelimit/2 and the target pause is max_pause, the next
1576 * pause time will be max_pause*2 _trimmed down_ to max_pause. As a
1577 * result task_ratelimit won't be executed faithfully, which could
1578 * eventually bring down dirty_ratelimit.
1579 *
1580 * We apply two rules to fix it up:
1581 * 1) try to estimate the next pause time and if necessary, use a lower
1582 * nr_dirtied_pause so as not to exceed max_pause. When this happens,
1583 * nr_dirtied_pause will be "dancing" with task_ratelimit.
1584 * 2) limit the target pause time to max_pause/2, so that the normal
1585 * small fluctuations of task_ratelimit won't trigger rule (1) and
1586 * nr_dirtied_pause will remain as stable as dirty_ratelimit.
1587 */
1588 t = min(t, 1 + max_pause / 2);
1589 pages = dirty_ratelimit * t / roundup_pow_of_two(HZ);
1590
1591 /*
1592 * Tiny nr_dirtied_pause is found to hurt I/O performance in the test
1593 * case fio-mmap-randwrite-64k, which does 16*{sync read, async write}.
1594 * When the 16 consecutive reads are often interrupted by some dirty
1595 * throttling pause during the async writes, cfq will go into idles
1596 * (deadline is fine). So push nr_dirtied_pause as high as possible
1597 * until reaches DIRTY_POLL_THRESH=32 pages.
1598 */
1599 if (pages < DIRTY_POLL_THRESH) {
1600 t = max_pause;
1601 pages = dirty_ratelimit * t / roundup_pow_of_two(HZ);
1602 if (pages > DIRTY_POLL_THRESH) {
1603 pages = DIRTY_POLL_THRESH;
1604 t = HZ * DIRTY_POLL_THRESH / dirty_ratelimit;
1605 }
1606 }
1607
1608 pause = HZ * pages / (task_ratelimit + 1);
1609 if (pause > max_pause) {
1610 t = max_pause;
1611 pages = task_ratelimit * t / roundup_pow_of_two(HZ);
1612 }
1613
1614 *nr_dirtied_pause = pages;
1615 /*
1616 * The minimal pause time will normally be half the target pause time.
1617 */
1618 return pages >= DIRTY_POLL_THRESH ? 1 + t / 2 : t;
1619}
1620
1621static inline void wb_dirty_limits(struct dirty_throttle_control *dtc)
1622{
1623 struct bdi_writeback *wb = dtc->wb;
1624 unsigned long wb_reclaimable;
1625
1626 /*
1627 * wb_thresh is not treated as some limiting factor as
1628 * dirty_thresh, due to reasons
1629 * - in JBOD setup, wb_thresh can fluctuate a lot
1630 * - in a system with HDD and USB key, the USB key may somehow
1631 * go into state (wb_dirty >> wb_thresh) either because
1632 * wb_dirty starts high, or because wb_thresh drops low.
1633 * In this case we don't want to hard throttle the USB key
1634 * dirtiers for 100 seconds until wb_dirty drops under
1635 * wb_thresh. Instead the auxiliary wb control line in
1636 * wb_position_ratio() will let the dirtier task progress
1637 * at some rate <= (write_bw / 2) for bringing down wb_dirty.
1638 */
1639 dtc->wb_thresh = __wb_calc_thresh(dtc);
1640 dtc->wb_bg_thresh = dtc->thresh ?
1641 div_u64((u64)dtc->wb_thresh * dtc->bg_thresh, dtc->thresh) : 0;
1642
1643 /*
1644 * In order to avoid the stacked BDI deadlock we need
1645 * to ensure we accurately count the 'dirty' pages when
1646 * the threshold is low.
1647 *
1648 * Otherwise it would be possible to get thresh+n pages
1649 * reported dirty, even though there are thresh-m pages
1650 * actually dirty; with m+n sitting in the percpu
1651 * deltas.
1652 */
1653 if (dtc->wb_thresh < 2 * wb_stat_error()) {
1654 wb_reclaimable = wb_stat_sum(wb, WB_RECLAIMABLE);
1655 dtc->wb_dirty = wb_reclaimable + wb_stat_sum(wb, WB_WRITEBACK);
1656 } else {
1657 wb_reclaimable = wb_stat(wb, WB_RECLAIMABLE);
1658 dtc->wb_dirty = wb_reclaimable + wb_stat(wb, WB_WRITEBACK);
1659 }
1660}
1661
1662/*
1663 * balance_dirty_pages() must be called by processes which are generating dirty
1664 * data. It looks at the number of dirty pages in the machine and will force
1665 * the caller to wait once crossing the (background_thresh + dirty_thresh) / 2.
1666 * If we're over `background_thresh' then the writeback threads are woken to
1667 * perform some writeout.
1668 */
1669static int balance_dirty_pages(struct bdi_writeback *wb,
1670 unsigned long pages_dirtied, unsigned int flags)
1671{
1672 struct dirty_throttle_control gdtc_stor = { GDTC_INIT(wb) };
1673 struct dirty_throttle_control mdtc_stor = { MDTC_INIT(wb, &gdtc_stor) };
1674 struct dirty_throttle_control * const gdtc = &gdtc_stor;
1675 struct dirty_throttle_control * const mdtc = mdtc_valid(&mdtc_stor) ?
1676 &mdtc_stor : NULL;
1677 struct dirty_throttle_control *sdtc;
1678 unsigned long nr_reclaimable; /* = file_dirty */
1679 long period;
1680 long pause;
1681 long max_pause;
1682 long min_pause;
1683 int nr_dirtied_pause;
1684 bool dirty_exceeded = false;
1685 unsigned long task_ratelimit;
1686 unsigned long dirty_ratelimit;
1687 struct backing_dev_info *bdi = wb->bdi;
1688 bool strictlimit = bdi->capabilities & BDI_CAP_STRICTLIMIT;
1689 unsigned long start_time = jiffies;
1690 int ret = 0;
1691
1692 for (;;) {
1693 unsigned long now = jiffies;
1694 unsigned long dirty, thresh, bg_thresh;
1695 unsigned long m_dirty = 0; /* stop bogus uninit warnings */
1696 unsigned long m_thresh = 0;
1697 unsigned long m_bg_thresh = 0;
1698
1699 nr_reclaimable = global_node_page_state(NR_FILE_DIRTY);
1700 gdtc->avail = global_dirtyable_memory();
1701 gdtc->dirty = nr_reclaimable + global_node_page_state(NR_WRITEBACK);
1702
1703 domain_dirty_limits(gdtc);
1704
1705 if (unlikely(strictlimit)) {
1706 wb_dirty_limits(gdtc);
1707
1708 dirty = gdtc->wb_dirty;
1709 thresh = gdtc->wb_thresh;
1710 bg_thresh = gdtc->wb_bg_thresh;
1711 } else {
1712 dirty = gdtc->dirty;
1713 thresh = gdtc->thresh;
1714 bg_thresh = gdtc->bg_thresh;
1715 }
1716
1717 if (mdtc) {
1718 unsigned long filepages, headroom, writeback;
1719
1720 /*
1721 * If @wb belongs to !root memcg, repeat the same
1722 * basic calculations for the memcg domain.
1723 */
1724 mem_cgroup_wb_stats(wb, &filepages, &headroom,
1725 &mdtc->dirty, &writeback);
1726 mdtc->dirty += writeback;
1727 mdtc_calc_avail(mdtc, filepages, headroom);
1728
1729 domain_dirty_limits(mdtc);
1730
1731 if (unlikely(strictlimit)) {
1732 wb_dirty_limits(mdtc);
1733 m_dirty = mdtc->wb_dirty;
1734 m_thresh = mdtc->wb_thresh;
1735 m_bg_thresh = mdtc->wb_bg_thresh;
1736 } else {
1737 m_dirty = mdtc->dirty;
1738 m_thresh = mdtc->thresh;
1739 m_bg_thresh = mdtc->bg_thresh;
1740 }
1741 }
1742
1743 /*
1744 * In laptop mode, we wait until hitting the higher threshold
1745 * before starting background writeout, and then write out all
1746 * the way down to the lower threshold. So slow writers cause
1747 * minimal disk activity.
1748 *
1749 * In normal mode, we start background writeout at the lower
1750 * background_thresh, to keep the amount of dirty memory low.
1751 */
1752 if (!laptop_mode && nr_reclaimable > gdtc->bg_thresh &&
1753 !writeback_in_progress(wb))
1754 wb_start_background_writeback(wb);
1755
1756 /*
1757 * Throttle it only when the background writeback cannot
1758 * catch-up. This avoids (excessively) small writeouts
1759 * when the wb limits are ramping up in case of !strictlimit.
1760 *
1761 * In strictlimit case make decision based on the wb counters
1762 * and limits. Small writeouts when the wb limits are ramping
1763 * up are the price we consciously pay for strictlimit-ing.
1764 *
1765 * If memcg domain is in effect, @dirty should be under
1766 * both global and memcg freerun ceilings.
1767 */
1768 if (dirty <= dirty_freerun_ceiling(thresh, bg_thresh) &&
1769 (!mdtc ||
1770 m_dirty <= dirty_freerun_ceiling(m_thresh, m_bg_thresh))) {
1771 unsigned long intv;
1772 unsigned long m_intv;
1773
1774free_running:
1775 intv = dirty_poll_interval(dirty, thresh);
1776 m_intv = ULONG_MAX;
1777
1778 current->dirty_paused_when = now;
1779 current->nr_dirtied = 0;
1780 if (mdtc)
1781 m_intv = dirty_poll_interval(m_dirty, m_thresh);
1782 current->nr_dirtied_pause = min(intv, m_intv);
1783 break;
1784 }
1785
1786 /* Start writeback even when in laptop mode */
1787 if (unlikely(!writeback_in_progress(wb)))
1788 wb_start_background_writeback(wb);
1789
1790 mem_cgroup_flush_foreign(wb);
1791
1792 /*
1793 * Calculate global domain's pos_ratio and select the
1794 * global dtc by default.
1795 */
1796 if (!strictlimit) {
1797 wb_dirty_limits(gdtc);
1798
1799 if ((current->flags & PF_LOCAL_THROTTLE) &&
1800 gdtc->wb_dirty <
1801 dirty_freerun_ceiling(gdtc->wb_thresh,
1802 gdtc->wb_bg_thresh))
1803 /*
1804 * LOCAL_THROTTLE tasks must not be throttled
1805 * when below the per-wb freerun ceiling.
1806 */
1807 goto free_running;
1808 }
1809
1810 dirty_exceeded = (gdtc->wb_dirty > gdtc->wb_thresh) &&
1811 ((gdtc->dirty > gdtc->thresh) || strictlimit);
1812
1813 wb_position_ratio(gdtc);
1814 sdtc = gdtc;
1815
1816 if (mdtc) {
1817 /*
1818 * If memcg domain is in effect, calculate its
1819 * pos_ratio. @wb should satisfy constraints from
1820 * both global and memcg domains. Choose the one
1821 * w/ lower pos_ratio.
1822 */
1823 if (!strictlimit) {
1824 wb_dirty_limits(mdtc);
1825
1826 if ((current->flags & PF_LOCAL_THROTTLE) &&
1827 mdtc->wb_dirty <
1828 dirty_freerun_ceiling(mdtc->wb_thresh,
1829 mdtc->wb_bg_thresh))
1830 /*
1831 * LOCAL_THROTTLE tasks must not be
1832 * throttled when below the per-wb
1833 * freerun ceiling.
1834 */
1835 goto free_running;
1836 }
1837 dirty_exceeded |= (mdtc->wb_dirty > mdtc->wb_thresh) &&
1838 ((mdtc->dirty > mdtc->thresh) || strictlimit);
1839
1840 wb_position_ratio(mdtc);
1841 if (mdtc->pos_ratio < gdtc->pos_ratio)
1842 sdtc = mdtc;
1843 }
1844
1845 if (dirty_exceeded != wb->dirty_exceeded)
1846 wb->dirty_exceeded = dirty_exceeded;
1847
1848 if (time_is_before_jiffies(READ_ONCE(wb->bw_time_stamp) +
1849 BANDWIDTH_INTERVAL))
1850 __wb_update_bandwidth(gdtc, mdtc, true);
1851
1852 /* throttle according to the chosen dtc */
1853 dirty_ratelimit = READ_ONCE(wb->dirty_ratelimit);
1854 task_ratelimit = ((u64)dirty_ratelimit * sdtc->pos_ratio) >>
1855 RATELIMIT_CALC_SHIFT;
1856 max_pause = wb_max_pause(wb, sdtc->wb_dirty);
1857 min_pause = wb_min_pause(wb, max_pause,
1858 task_ratelimit, dirty_ratelimit,
1859 &nr_dirtied_pause);
1860
1861 if (unlikely(task_ratelimit == 0)) {
1862 period = max_pause;
1863 pause = max_pause;
1864 goto pause;
1865 }
1866 period = HZ * pages_dirtied / task_ratelimit;
1867 pause = period;
1868 if (current->dirty_paused_when)
1869 pause -= now - current->dirty_paused_when;
1870 /*
1871 * For less than 1s think time (ext3/4 may block the dirtier
1872 * for up to 800ms from time to time on 1-HDD; so does xfs,
1873 * however at much less frequency), try to compensate it in
1874 * future periods by updating the virtual time; otherwise just
1875 * do a reset, as it may be a light dirtier.
1876 */
1877 if (pause < min_pause) {
1878 trace_balance_dirty_pages(wb,
1879 sdtc->thresh,
1880 sdtc->bg_thresh,
1881 sdtc->dirty,
1882 sdtc->wb_thresh,
1883 sdtc->wb_dirty,
1884 dirty_ratelimit,
1885 task_ratelimit,
1886 pages_dirtied,
1887 period,
1888 min(pause, 0L),
1889 start_time);
1890 if (pause < -HZ) {
1891 current->dirty_paused_when = now;
1892 current->nr_dirtied = 0;
1893 } else if (period) {
1894 current->dirty_paused_when += period;
1895 current->nr_dirtied = 0;
1896 } else if (current->nr_dirtied_pause <= pages_dirtied)
1897 current->nr_dirtied_pause += pages_dirtied;
1898 break;
1899 }
1900 if (unlikely(pause > max_pause)) {
1901 /* for occasional dropped task_ratelimit */
1902 now += min(pause - max_pause, max_pause);
1903 pause = max_pause;
1904 }
1905
1906pause:
1907 trace_balance_dirty_pages(wb,
1908 sdtc->thresh,
1909 sdtc->bg_thresh,
1910 sdtc->dirty,
1911 sdtc->wb_thresh,
1912 sdtc->wb_dirty,
1913 dirty_ratelimit,
1914 task_ratelimit,
1915 pages_dirtied,
1916 period,
1917 pause,
1918 start_time);
1919 if (flags & BDP_ASYNC) {
1920 ret = -EAGAIN;
1921 break;
1922 }
1923 __set_current_state(TASK_KILLABLE);
1924 wb->dirty_sleep = now;
1925 io_schedule_timeout(pause);
1926
1927 current->dirty_paused_when = now + pause;
1928 current->nr_dirtied = 0;
1929 current->nr_dirtied_pause = nr_dirtied_pause;
1930
1931 /*
1932 * This is typically equal to (dirty < thresh) and can also
1933 * keep "1000+ dd on a slow USB stick" under control.
1934 */
1935 if (task_ratelimit)
1936 break;
1937
1938 /*
1939 * In the case of an unresponsive NFS server and the NFS dirty
1940 * pages exceeds dirty_thresh, give the other good wb's a pipe
1941 * to go through, so that tasks on them still remain responsive.
1942 *
1943 * In theory 1 page is enough to keep the consumer-producer
1944 * pipe going: the flusher cleans 1 page => the task dirties 1
1945 * more page. However wb_dirty has accounting errors. So use
1946 * the larger and more IO friendly wb_stat_error.
1947 */
1948 if (sdtc->wb_dirty <= wb_stat_error())
1949 break;
1950
1951 if (fatal_signal_pending(current))
1952 break;
1953 }
1954 return ret;
1955}
1956
1957static DEFINE_PER_CPU(int, bdp_ratelimits);
1958
1959/*
1960 * Normal tasks are throttled by
1961 * loop {
1962 * dirty tsk->nr_dirtied_pause pages;
1963 * take a snap in balance_dirty_pages();
1964 * }
1965 * However there is a worst case. If every task exit immediately when dirtied
1966 * (tsk->nr_dirtied_pause - 1) pages, balance_dirty_pages() will never be
1967 * called to throttle the page dirties. The solution is to save the not yet
1968 * throttled page dirties in dirty_throttle_leaks on task exit and charge them
1969 * randomly into the running tasks. This works well for the above worst case,
1970 * as the new task will pick up and accumulate the old task's leaked dirty
1971 * count and eventually get throttled.
1972 */
1973DEFINE_PER_CPU(int, dirty_throttle_leaks) = 0;
1974
1975/**
1976 * balance_dirty_pages_ratelimited_flags - Balance dirty memory state.
1977 * @mapping: address_space which was dirtied.
1978 * @flags: BDP flags.
1979 *
1980 * Processes which are dirtying memory should call in here once for each page
1981 * which was newly dirtied. The function will periodically check the system's
1982 * dirty state and will initiate writeback if needed.
1983 *
1984 * See balance_dirty_pages_ratelimited() for details.
1985 *
1986 * Return: If @flags contains BDP_ASYNC, it may return -EAGAIN to
1987 * indicate that memory is out of balance and the caller must wait
1988 * for I/O to complete. Otherwise, it will return 0 to indicate
1989 * that either memory was already in balance, or it was able to sleep
1990 * until the amount of dirty memory returned to balance.
1991 */
1992int balance_dirty_pages_ratelimited_flags(struct address_space *mapping,
1993 unsigned int flags)
1994{
1995 struct inode *inode = mapping->host;
1996 struct backing_dev_info *bdi = inode_to_bdi(inode);
1997 struct bdi_writeback *wb = NULL;
1998 int ratelimit;
1999 int ret = 0;
2000 int *p;
2001
2002 if (!(bdi->capabilities & BDI_CAP_WRITEBACK))
2003 return ret;
2004
2005 if (inode_cgwb_enabled(inode))
2006 wb = wb_get_create_current(bdi, GFP_KERNEL);
2007 if (!wb)
2008 wb = &bdi->wb;
2009
2010 ratelimit = current->nr_dirtied_pause;
2011 if (wb->dirty_exceeded)
2012 ratelimit = min(ratelimit, 32 >> (PAGE_SHIFT - 10));
2013
2014 preempt_disable();
2015 /*
2016 * This prevents one CPU to accumulate too many dirtied pages without
2017 * calling into balance_dirty_pages(), which can happen when there are
2018 * 1000+ tasks, all of them start dirtying pages at exactly the same
2019 * time, hence all honoured too large initial task->nr_dirtied_pause.
2020 */
2021 p = this_cpu_ptr(&bdp_ratelimits);
2022 if (unlikely(current->nr_dirtied >= ratelimit))
2023 *p = 0;
2024 else if (unlikely(*p >= ratelimit_pages)) {
2025 *p = 0;
2026 ratelimit = 0;
2027 }
2028 /*
2029 * Pick up the dirtied pages by the exited tasks. This avoids lots of
2030 * short-lived tasks (eg. gcc invocations in a kernel build) escaping
2031 * the dirty throttling and livelock other long-run dirtiers.
2032 */
2033 p = this_cpu_ptr(&dirty_throttle_leaks);
2034 if (*p > 0 && current->nr_dirtied < ratelimit) {
2035 unsigned long nr_pages_dirtied;
2036 nr_pages_dirtied = min(*p, ratelimit - current->nr_dirtied);
2037 *p -= nr_pages_dirtied;
2038 current->nr_dirtied += nr_pages_dirtied;
2039 }
2040 preempt_enable();
2041
2042 if (unlikely(current->nr_dirtied >= ratelimit))
2043 ret = balance_dirty_pages(wb, current->nr_dirtied, flags);
2044
2045 wb_put(wb);
2046 return ret;
2047}
2048EXPORT_SYMBOL_GPL(balance_dirty_pages_ratelimited_flags);
2049
2050/**
2051 * balance_dirty_pages_ratelimited - balance dirty memory state.
2052 * @mapping: address_space which was dirtied.
2053 *
2054 * Processes which are dirtying memory should call in here once for each page
2055 * which was newly dirtied. The function will periodically check the system's
2056 * dirty state and will initiate writeback if needed.
2057 *
2058 * Once we're over the dirty memory limit we decrease the ratelimiting
2059 * by a lot, to prevent individual processes from overshooting the limit
2060 * by (ratelimit_pages) each.
2061 */
2062void balance_dirty_pages_ratelimited(struct address_space *mapping)
2063{
2064 balance_dirty_pages_ratelimited_flags(mapping, 0);
2065}
2066EXPORT_SYMBOL(balance_dirty_pages_ratelimited);
2067
2068/**
2069 * wb_over_bg_thresh - does @wb need to be written back?
2070 * @wb: bdi_writeback of interest
2071 *
2072 * Determines whether background writeback should keep writing @wb or it's
2073 * clean enough.
2074 *
2075 * Return: %true if writeback should continue.
2076 */
2077bool wb_over_bg_thresh(struct bdi_writeback *wb)
2078{
2079 struct dirty_throttle_control gdtc_stor = { GDTC_INIT(wb) };
2080 struct dirty_throttle_control mdtc_stor = { MDTC_INIT(wb, &gdtc_stor) };
2081 struct dirty_throttle_control * const gdtc = &gdtc_stor;
2082 struct dirty_throttle_control * const mdtc = mdtc_valid(&mdtc_stor) ?
2083 &mdtc_stor : NULL;
2084 unsigned long reclaimable;
2085 unsigned long thresh;
2086
2087 /*
2088 * Similar to balance_dirty_pages() but ignores pages being written
2089 * as we're trying to decide whether to put more under writeback.
2090 */
2091 gdtc->avail = global_dirtyable_memory();
2092 gdtc->dirty = global_node_page_state(NR_FILE_DIRTY);
2093 domain_dirty_limits(gdtc);
2094
2095 if (gdtc->dirty > gdtc->bg_thresh)
2096 return true;
2097
2098 thresh = wb_calc_thresh(gdtc->wb, gdtc->bg_thresh);
2099 if (thresh < 2 * wb_stat_error())
2100 reclaimable = wb_stat_sum(wb, WB_RECLAIMABLE);
2101 else
2102 reclaimable = wb_stat(wb, WB_RECLAIMABLE);
2103
2104 if (reclaimable > thresh)
2105 return true;
2106
2107 if (mdtc) {
2108 unsigned long filepages, headroom, writeback;
2109
2110 mem_cgroup_wb_stats(wb, &filepages, &headroom, &mdtc->dirty,
2111 &writeback);
2112 mdtc_calc_avail(mdtc, filepages, headroom);
2113 domain_dirty_limits(mdtc); /* ditto, ignore writeback */
2114
2115 if (mdtc->dirty > mdtc->bg_thresh)
2116 return true;
2117
2118 thresh = wb_calc_thresh(mdtc->wb, mdtc->bg_thresh);
2119 if (thresh < 2 * wb_stat_error())
2120 reclaimable = wb_stat_sum(wb, WB_RECLAIMABLE);
2121 else
2122 reclaimable = wb_stat(wb, WB_RECLAIMABLE);
2123
2124 if (reclaimable > thresh)
2125 return true;
2126 }
2127
2128 return false;
2129}
2130
2131#ifdef CONFIG_SYSCTL
2132/*
2133 * sysctl handler for /proc/sys/vm/dirty_writeback_centisecs
2134 */
2135static int dirty_writeback_centisecs_handler(struct ctl_table *table, int write,
2136 void *buffer, size_t *length, loff_t *ppos)
2137{
2138 unsigned int old_interval = dirty_writeback_interval;
2139 int ret;
2140
2141 ret = proc_dointvec(table, write, buffer, length, ppos);
2142
2143 /*
2144 * Writing 0 to dirty_writeback_interval will disable periodic writeback
2145 * and a different non-zero value will wakeup the writeback threads.
2146 * wb_wakeup_delayed() would be more appropriate, but it's a pain to
2147 * iterate over all bdis and wbs.
2148 * The reason we do this is to make the change take effect immediately.
2149 */
2150 if (!ret && write && dirty_writeback_interval &&
2151 dirty_writeback_interval != old_interval)
2152 wakeup_flusher_threads(WB_REASON_PERIODIC);
2153
2154 return ret;
2155}
2156#endif
2157
2158void laptop_mode_timer_fn(struct timer_list *t)
2159{
2160 struct backing_dev_info *backing_dev_info =
2161 from_timer(backing_dev_info, t, laptop_mode_wb_timer);
2162
2163 wakeup_flusher_threads_bdi(backing_dev_info, WB_REASON_LAPTOP_TIMER);
2164}
2165
2166/*
2167 * We've spun up the disk and we're in laptop mode: schedule writeback
2168 * of all dirty data a few seconds from now. If the flush is already scheduled
2169 * then push it back - the user is still using the disk.
2170 */
2171void laptop_io_completion(struct backing_dev_info *info)
2172{
2173 mod_timer(&info->laptop_mode_wb_timer, jiffies + laptop_mode);
2174}
2175
2176/*
2177 * We're in laptop mode and we've just synced. The sync's writes will have
2178 * caused another writeback to be scheduled by laptop_io_completion.
2179 * Nothing needs to be written back anymore, so we unschedule the writeback.
2180 */
2181void laptop_sync_completion(void)
2182{
2183 struct backing_dev_info *bdi;
2184
2185 rcu_read_lock();
2186
2187 list_for_each_entry_rcu(bdi, &bdi_list, bdi_list)
2188 del_timer(&bdi->laptop_mode_wb_timer);
2189
2190 rcu_read_unlock();
2191}
2192
2193/*
2194 * If ratelimit_pages is too high then we can get into dirty-data overload
2195 * if a large number of processes all perform writes at the same time.
2196 *
2197 * Here we set ratelimit_pages to a level which ensures that when all CPUs are
2198 * dirtying in parallel, we cannot go more than 3% (1/32) over the dirty memory
2199 * thresholds.
2200 */
2201
2202void writeback_set_ratelimit(void)
2203{
2204 struct wb_domain *dom = &global_wb_domain;
2205 unsigned long background_thresh;
2206 unsigned long dirty_thresh;
2207
2208 global_dirty_limits(&background_thresh, &dirty_thresh);
2209 dom->dirty_limit = dirty_thresh;
2210 ratelimit_pages = dirty_thresh / (num_online_cpus() * 32);
2211 if (ratelimit_pages < 16)
2212 ratelimit_pages = 16;
2213}
2214
2215static int page_writeback_cpu_online(unsigned int cpu)
2216{
2217 writeback_set_ratelimit();
2218 return 0;
2219}
2220
2221#ifdef CONFIG_SYSCTL
2222
2223/* this is needed for the proc_doulongvec_minmax of vm_dirty_bytes */
2224static const unsigned long dirty_bytes_min = 2 * PAGE_SIZE;
2225
2226static struct ctl_table vm_page_writeback_sysctls[] = {
2227 {
2228 .procname = "dirty_background_ratio",
2229 .data = &dirty_background_ratio,
2230 .maxlen = sizeof(dirty_background_ratio),
2231 .mode = 0644,
2232 .proc_handler = dirty_background_ratio_handler,
2233 .extra1 = SYSCTL_ZERO,
2234 .extra2 = SYSCTL_ONE_HUNDRED,
2235 },
2236 {
2237 .procname = "dirty_background_bytes",
2238 .data = &dirty_background_bytes,
2239 .maxlen = sizeof(dirty_background_bytes),
2240 .mode = 0644,
2241 .proc_handler = dirty_background_bytes_handler,
2242 .extra1 = SYSCTL_LONG_ONE,
2243 },
2244 {
2245 .procname = "dirty_ratio",
2246 .data = &vm_dirty_ratio,
2247 .maxlen = sizeof(vm_dirty_ratio),
2248 .mode = 0644,
2249 .proc_handler = dirty_ratio_handler,
2250 .extra1 = SYSCTL_ZERO,
2251 .extra2 = SYSCTL_ONE_HUNDRED,
2252 },
2253 {
2254 .procname = "dirty_bytes",
2255 .data = &vm_dirty_bytes,
2256 .maxlen = sizeof(vm_dirty_bytes),
2257 .mode = 0644,
2258 .proc_handler = dirty_bytes_handler,
2259 .extra1 = (void *)&dirty_bytes_min,
2260 },
2261 {
2262 .procname = "dirty_writeback_centisecs",
2263 .data = &dirty_writeback_interval,
2264 .maxlen = sizeof(dirty_writeback_interval),
2265 .mode = 0644,
2266 .proc_handler = dirty_writeback_centisecs_handler,
2267 },
2268 {
2269 .procname = "dirty_expire_centisecs",
2270 .data = &dirty_expire_interval,
2271 .maxlen = sizeof(dirty_expire_interval),
2272 .mode = 0644,
2273 .proc_handler = proc_dointvec_minmax,
2274 .extra1 = SYSCTL_ZERO,
2275 },
2276#ifdef CONFIG_HIGHMEM
2277 {
2278 .procname = "highmem_is_dirtyable",
2279 .data = &vm_highmem_is_dirtyable,
2280 .maxlen = sizeof(vm_highmem_is_dirtyable),
2281 .mode = 0644,
2282 .proc_handler = proc_dointvec_minmax,
2283 .extra1 = SYSCTL_ZERO,
2284 .extra2 = SYSCTL_ONE,
2285 },
2286#endif
2287 {
2288 .procname = "laptop_mode",
2289 .data = &laptop_mode,
2290 .maxlen = sizeof(laptop_mode),
2291 .mode = 0644,
2292 .proc_handler = proc_dointvec_jiffies,
2293 },
2294 {}
2295};
2296#endif
2297
2298/*
2299 * Called early on to tune the page writeback dirty limits.
2300 *
2301 * We used to scale dirty pages according to how total memory
2302 * related to pages that could be allocated for buffers.
2303 *
2304 * However, that was when we used "dirty_ratio" to scale with
2305 * all memory, and we don't do that any more. "dirty_ratio"
2306 * is now applied to total non-HIGHPAGE memory, and as such we can't
2307 * get into the old insane situation any more where we had
2308 * large amounts of dirty pages compared to a small amount of
2309 * non-HIGHMEM memory.
2310 *
2311 * But we might still want to scale the dirty_ratio by how
2312 * much memory the box has..
2313 */
2314void __init page_writeback_init(void)
2315{
2316 BUG_ON(wb_domain_init(&global_wb_domain, GFP_KERNEL));
2317
2318 cpuhp_setup_state(CPUHP_AP_ONLINE_DYN, "mm/writeback:online",
2319 page_writeback_cpu_online, NULL);
2320 cpuhp_setup_state(CPUHP_MM_WRITEBACK_DEAD, "mm/writeback:dead", NULL,
2321 page_writeback_cpu_online);
2322#ifdef CONFIG_SYSCTL
2323 register_sysctl_init("vm", vm_page_writeback_sysctls);
2324#endif
2325}
2326
2327/**
2328 * tag_pages_for_writeback - tag pages to be written by write_cache_pages
2329 * @mapping: address space structure to write
2330 * @start: starting page index
2331 * @end: ending page index (inclusive)
2332 *
2333 * This function scans the page range from @start to @end (inclusive) and tags
2334 * all pages that have DIRTY tag set with a special TOWRITE tag. The idea is
2335 * that write_cache_pages (or whoever calls this function) will then use
2336 * TOWRITE tag to identify pages eligible for writeback. This mechanism is
2337 * used to avoid livelocking of writeback by a process steadily creating new
2338 * dirty pages in the file (thus it is important for this function to be quick
2339 * so that it can tag pages faster than a dirtying process can create them).
2340 */
2341void tag_pages_for_writeback(struct address_space *mapping,
2342 pgoff_t start, pgoff_t end)
2343{
2344 XA_STATE(xas, &mapping->i_pages, start);
2345 unsigned int tagged = 0;
2346 void *page;
2347
2348 xas_lock_irq(&xas);
2349 xas_for_each_marked(&xas, page, end, PAGECACHE_TAG_DIRTY) {
2350 xas_set_mark(&xas, PAGECACHE_TAG_TOWRITE);
2351 if (++tagged % XA_CHECK_SCHED)
2352 continue;
2353
2354 xas_pause(&xas);
2355 xas_unlock_irq(&xas);
2356 cond_resched();
2357 xas_lock_irq(&xas);
2358 }
2359 xas_unlock_irq(&xas);
2360}
2361EXPORT_SYMBOL(tag_pages_for_writeback);
2362
2363/**
2364 * write_cache_pages - walk the list of dirty pages of the given address space and write all of them.
2365 * @mapping: address space structure to write
2366 * @wbc: subtract the number of written pages from *@wbc->nr_to_write
2367 * @writepage: function called for each page
2368 * @data: data passed to writepage function
2369 *
2370 * If a page is already under I/O, write_cache_pages() skips it, even
2371 * if it's dirty. This is desirable behaviour for memory-cleaning writeback,
2372 * but it is INCORRECT for data-integrity system calls such as fsync(). fsync()
2373 * and msync() need to guarantee that all the data which was dirty at the time
2374 * the call was made get new I/O started against them. If wbc->sync_mode is
2375 * WB_SYNC_ALL then we were called for data integrity and we must wait for
2376 * existing IO to complete.
2377 *
2378 * To avoid livelocks (when other process dirties new pages), we first tag
2379 * pages which should be written back with TOWRITE tag and only then start
2380 * writing them. For data-integrity sync we have to be careful so that we do
2381 * not miss some pages (e.g., because some other process has cleared TOWRITE
2382 * tag we set). The rule we follow is that TOWRITE tag can be cleared only
2383 * by the process clearing the DIRTY tag (and submitting the page for IO).
2384 *
2385 * To avoid deadlocks between range_cyclic writeback and callers that hold
2386 * pages in PageWriteback to aggregate IO until write_cache_pages() returns,
2387 * we do not loop back to the start of the file. Doing so causes a page
2388 * lock/page writeback access order inversion - we should only ever lock
2389 * multiple pages in ascending page->index order, and looping back to the start
2390 * of the file violates that rule and causes deadlocks.
2391 *
2392 * Return: %0 on success, negative error code otherwise
2393 */
2394int write_cache_pages(struct address_space *mapping,
2395 struct writeback_control *wbc, writepage_t writepage,
2396 void *data)
2397{
2398 int ret = 0;
2399 int done = 0;
2400 int error;
2401 struct pagevec pvec;
2402 int nr_pages;
2403 pgoff_t index;
2404 pgoff_t end; /* Inclusive */
2405 pgoff_t done_index;
2406 int range_whole = 0;
2407 xa_mark_t tag;
2408
2409 pagevec_init(&pvec);
2410 if (wbc->range_cyclic) {
2411 index = mapping->writeback_index; /* prev offset */
2412 end = -1;
2413 } else {
2414 index = wbc->range_start >> PAGE_SHIFT;
2415 end = wbc->range_end >> PAGE_SHIFT;
2416 if (wbc->range_start == 0 && wbc->range_end == LLONG_MAX)
2417 range_whole = 1;
2418 }
2419 if (wbc->sync_mode == WB_SYNC_ALL || wbc->tagged_writepages) {
2420 tag_pages_for_writeback(mapping, index, end);
2421 tag = PAGECACHE_TAG_TOWRITE;
2422 } else {
2423 tag = PAGECACHE_TAG_DIRTY;
2424 }
2425 done_index = index;
2426 while (!done && (index <= end)) {
2427 int i;
2428
2429 nr_pages = pagevec_lookup_range_tag(&pvec, mapping, &index, end,
2430 tag);
2431 if (nr_pages == 0)
2432 break;
2433
2434 for (i = 0; i < nr_pages; i++) {
2435 struct page *page = pvec.pages[i];
2436
2437 done_index = page->index;
2438
2439 lock_page(page);
2440
2441 /*
2442 * Page truncated or invalidated. We can freely skip it
2443 * then, even for data integrity operations: the page
2444 * has disappeared concurrently, so there could be no
2445 * real expectation of this data integrity operation
2446 * even if there is now a new, dirty page at the same
2447 * pagecache address.
2448 */
2449 if (unlikely(page->mapping != mapping)) {
2450continue_unlock:
2451 unlock_page(page);
2452 continue;
2453 }
2454
2455 if (!PageDirty(page)) {
2456 /* someone wrote it for us */
2457 goto continue_unlock;
2458 }
2459
2460 if (PageWriteback(page)) {
2461 if (wbc->sync_mode != WB_SYNC_NONE)
2462 wait_on_page_writeback(page);
2463 else
2464 goto continue_unlock;
2465 }
2466
2467 BUG_ON(PageWriteback(page));
2468 if (!clear_page_dirty_for_io(page))
2469 goto continue_unlock;
2470
2471 trace_wbc_writepage(wbc, inode_to_bdi(mapping->host));
2472 error = (*writepage)(page, wbc, data);
2473 if (unlikely(error)) {
2474 /*
2475 * Handle errors according to the type of
2476 * writeback. There's no need to continue for
2477 * background writeback. Just push done_index
2478 * past this page so media errors won't choke
2479 * writeout for the entire file. For integrity
2480 * writeback, we must process the entire dirty
2481 * set regardless of errors because the fs may
2482 * still have state to clear for each page. In
2483 * that case we continue processing and return
2484 * the first error.
2485 */
2486 if (error == AOP_WRITEPAGE_ACTIVATE) {
2487 unlock_page(page);
2488 error = 0;
2489 } else if (wbc->sync_mode != WB_SYNC_ALL) {
2490 ret = error;
2491 done_index = page->index + 1;
2492 done = 1;
2493 break;
2494 }
2495 if (!ret)
2496 ret = error;
2497 }
2498
2499 /*
2500 * We stop writing back only if we are not doing
2501 * integrity sync. In case of integrity sync we have to
2502 * keep going until we have written all the pages
2503 * we tagged for writeback prior to entering this loop.
2504 */
2505 if (--wbc->nr_to_write <= 0 &&
2506 wbc->sync_mode == WB_SYNC_NONE) {
2507 done = 1;
2508 break;
2509 }
2510 }
2511 pagevec_release(&pvec);
2512 cond_resched();
2513 }
2514
2515 /*
2516 * If we hit the last page and there is more work to be done: wrap
2517 * back the index back to the start of the file for the next
2518 * time we are called.
2519 */
2520 if (wbc->range_cyclic && !done)
2521 done_index = 0;
2522 if (wbc->range_cyclic || (range_whole && wbc->nr_to_write > 0))
2523 mapping->writeback_index = done_index;
2524
2525 return ret;
2526}
2527EXPORT_SYMBOL(write_cache_pages);
2528
2529/*
2530 * Function used by generic_writepages to call the real writepage
2531 * function and set the mapping flags on error
2532 */
2533static int __writepage(struct page *page, struct writeback_control *wbc,
2534 void *data)
2535{
2536 struct address_space *mapping = data;
2537 int ret = mapping->a_ops->writepage(page, wbc);
2538 mapping_set_error(mapping, ret);
2539 return ret;
2540}
2541
2542/**
2543 * generic_writepages - walk the list of dirty pages of the given address space and writepage() all of them.
2544 * @mapping: address space structure to write
2545 * @wbc: subtract the number of written pages from *@wbc->nr_to_write
2546 *
2547 * This is a library function, which implements the writepages()
2548 * address_space_operation.
2549 *
2550 * Return: %0 on success, negative error code otherwise
2551 */
2552int generic_writepages(struct address_space *mapping,
2553 struct writeback_control *wbc)
2554{
2555 struct blk_plug plug;
2556 int ret;
2557
2558 /* deal with chardevs and other special file */
2559 if (!mapping->a_ops->writepage)
2560 return 0;
2561
2562 blk_start_plug(&plug);
2563 ret = write_cache_pages(mapping, wbc, __writepage, mapping);
2564 blk_finish_plug(&plug);
2565 return ret;
2566}
2567
2568EXPORT_SYMBOL(generic_writepages);
2569
2570int do_writepages(struct address_space *mapping, struct writeback_control *wbc)
2571{
2572 int ret;
2573 struct bdi_writeback *wb;
2574
2575 if (wbc->nr_to_write <= 0)
2576 return 0;
2577 wb = inode_to_wb_wbc(mapping->host, wbc);
2578 wb_bandwidth_estimate_start(wb);
2579 while (1) {
2580 if (mapping->a_ops->writepages)
2581 ret = mapping->a_ops->writepages(mapping, wbc);
2582 else
2583 ret = generic_writepages(mapping, wbc);
2584 if ((ret != -ENOMEM) || (wbc->sync_mode != WB_SYNC_ALL))
2585 break;
2586
2587 /*
2588 * Lacking an allocation context or the locality or writeback
2589 * state of any of the inode's pages, throttle based on
2590 * writeback activity on the local node. It's as good a
2591 * guess as any.
2592 */
2593 reclaim_throttle(NODE_DATA(numa_node_id()),
2594 VMSCAN_THROTTLE_WRITEBACK);
2595 }
2596 /*
2597 * Usually few pages are written by now from those we've just submitted
2598 * but if there's constant writeback being submitted, this makes sure
2599 * writeback bandwidth is updated once in a while.
2600 */
2601 if (time_is_before_jiffies(READ_ONCE(wb->bw_time_stamp) +
2602 BANDWIDTH_INTERVAL))
2603 wb_update_bandwidth(wb);
2604 return ret;
2605}
2606
2607/**
2608 * folio_write_one - write out a single folio and wait on I/O.
2609 * @folio: The folio to write.
2610 *
2611 * The folio must be locked by the caller and will be unlocked upon return.
2612 *
2613 * Note that the mapping's AS_EIO/AS_ENOSPC flags will be cleared when this
2614 * function returns.
2615 *
2616 * Return: %0 on success, negative error code otherwise
2617 */
2618int folio_write_one(struct folio *folio)
2619{
2620 struct address_space *mapping = folio->mapping;
2621 int ret = 0;
2622 struct writeback_control wbc = {
2623 .sync_mode = WB_SYNC_ALL,
2624 .nr_to_write = folio_nr_pages(folio),
2625 };
2626
2627 BUG_ON(!folio_test_locked(folio));
2628
2629 folio_wait_writeback(folio);
2630
2631 if (folio_clear_dirty_for_io(folio)) {
2632 folio_get(folio);
2633 ret = mapping->a_ops->writepage(&folio->page, &wbc);
2634 if (ret == 0)
2635 folio_wait_writeback(folio);
2636 folio_put(folio);
2637 } else {
2638 folio_unlock(folio);
2639 }
2640
2641 if (!ret)
2642 ret = filemap_check_errors(mapping);
2643 return ret;
2644}
2645EXPORT_SYMBOL(folio_write_one);
2646
2647/*
2648 * For address_spaces which do not use buffers nor write back.
2649 */
2650bool noop_dirty_folio(struct address_space *mapping, struct folio *folio)
2651{
2652 if (!folio_test_dirty(folio))
2653 return !folio_test_set_dirty(folio);
2654 return false;
2655}
2656EXPORT_SYMBOL(noop_dirty_folio);
2657
2658/*
2659 * Helper function for set_page_dirty family.
2660 *
2661 * Caller must hold lock_page_memcg().
2662 *
2663 * NOTE: This relies on being atomic wrt interrupts.
2664 */
2665static void folio_account_dirtied(struct folio *folio,
2666 struct address_space *mapping)
2667{
2668 struct inode *inode = mapping->host;
2669
2670 trace_writeback_dirty_folio(folio, mapping);
2671
2672 if (mapping_can_writeback(mapping)) {
2673 struct bdi_writeback *wb;
2674 long nr = folio_nr_pages(folio);
2675
2676 inode_attach_wb(inode, &folio->page);
2677 wb = inode_to_wb(inode);
2678
2679 __lruvec_stat_mod_folio(folio, NR_FILE_DIRTY, nr);
2680 __zone_stat_mod_folio(folio, NR_ZONE_WRITE_PENDING, nr);
2681 __node_stat_mod_folio(folio, NR_DIRTIED, nr);
2682 wb_stat_mod(wb, WB_RECLAIMABLE, nr);
2683 wb_stat_mod(wb, WB_DIRTIED, nr);
2684 task_io_account_write(nr * PAGE_SIZE);
2685 current->nr_dirtied += nr;
2686 __this_cpu_add(bdp_ratelimits, nr);
2687
2688 mem_cgroup_track_foreign_dirty(folio, wb);
2689 }
2690}
2691
2692/*
2693 * Helper function for deaccounting dirty page without writeback.
2694 *
2695 * Caller must hold lock_page_memcg().
2696 */
2697void folio_account_cleaned(struct folio *folio, struct bdi_writeback *wb)
2698{
2699 long nr = folio_nr_pages(folio);
2700
2701 lruvec_stat_mod_folio(folio, NR_FILE_DIRTY, -nr);
2702 zone_stat_mod_folio(folio, NR_ZONE_WRITE_PENDING, -nr);
2703 wb_stat_mod(wb, WB_RECLAIMABLE, -nr);
2704 task_io_account_cancelled_write(nr * PAGE_SIZE);
2705}
2706
2707/*
2708 * Mark the folio dirty, and set it dirty in the page cache, and mark
2709 * the inode dirty.
2710 *
2711 * If warn is true, then emit a warning if the folio is not uptodate and has
2712 * not been truncated.
2713 *
2714 * The caller must hold lock_page_memcg(). Most callers have the folio
2715 * locked. A few have the folio blocked from truncation through other
2716 * means (eg zap_page_range() has it mapped and is holding the page table
2717 * lock). This can also be called from mark_buffer_dirty(), which I
2718 * cannot prove is always protected against truncate.
2719 */
2720void __folio_mark_dirty(struct folio *folio, struct address_space *mapping,
2721 int warn)
2722{
2723 unsigned long flags;
2724
2725 xa_lock_irqsave(&mapping->i_pages, flags);
2726 if (folio->mapping) { /* Race with truncate? */
2727 WARN_ON_ONCE(warn && !folio_test_uptodate(folio));
2728 folio_account_dirtied(folio, mapping);
2729 __xa_set_mark(&mapping->i_pages, folio_index(folio),
2730 PAGECACHE_TAG_DIRTY);
2731 }
2732 xa_unlock_irqrestore(&mapping->i_pages, flags);
2733}
2734
2735/**
2736 * filemap_dirty_folio - Mark a folio dirty for filesystems which do not use buffer_heads.
2737 * @mapping: Address space this folio belongs to.
2738 * @folio: Folio to be marked as dirty.
2739 *
2740 * Filesystems which do not use buffer heads should call this function
2741 * from their set_page_dirty address space operation. It ignores the
2742 * contents of folio_get_private(), so if the filesystem marks individual
2743 * blocks as dirty, the filesystem should handle that itself.
2744 *
2745 * This is also sometimes used by filesystems which use buffer_heads when
2746 * a single buffer is being dirtied: we want to set the folio dirty in
2747 * that case, but not all the buffers. This is a "bottom-up" dirtying,
2748 * whereas block_dirty_folio() is a "top-down" dirtying.
2749 *
2750 * The caller must ensure this doesn't race with truncation. Most will
2751 * simply hold the folio lock, but e.g. zap_pte_range() calls with the
2752 * folio mapped and the pte lock held, which also locks out truncation.
2753 */
2754bool filemap_dirty_folio(struct address_space *mapping, struct folio *folio)
2755{
2756 folio_memcg_lock(folio);
2757 if (folio_test_set_dirty(folio)) {
2758 folio_memcg_unlock(folio);
2759 return false;
2760 }
2761
2762 __folio_mark_dirty(folio, mapping, !folio_test_private(folio));
2763 folio_memcg_unlock(folio);
2764
2765 if (mapping->host) {
2766 /* !PageAnon && !swapper_space */
2767 __mark_inode_dirty(mapping->host, I_DIRTY_PAGES);
2768 }
2769 return true;
2770}
2771EXPORT_SYMBOL(filemap_dirty_folio);
2772
2773/**
2774 * folio_account_redirty - Manually account for redirtying a page.
2775 * @folio: The folio which is being redirtied.
2776 *
2777 * Most filesystems should call folio_redirty_for_writepage() instead
2778 * of this fuction. If your filesystem is doing writeback outside the
2779 * context of a writeback_control(), it can call this when redirtying
2780 * a folio, to de-account the dirty counters (NR_DIRTIED, WB_DIRTIED,
2781 * tsk->nr_dirtied), so that they match the written counters (NR_WRITTEN,
2782 * WB_WRITTEN) in long term. The mismatches will lead to systematic errors
2783 * in balanced_dirty_ratelimit and the dirty pages position control.
2784 */
2785void folio_account_redirty(struct folio *folio)
2786{
2787 struct address_space *mapping = folio->mapping;
2788
2789 if (mapping && mapping_can_writeback(mapping)) {
2790 struct inode *inode = mapping->host;
2791 struct bdi_writeback *wb;
2792 struct wb_lock_cookie cookie = {};
2793 long nr = folio_nr_pages(folio);
2794
2795 wb = unlocked_inode_to_wb_begin(inode, &cookie);
2796 current->nr_dirtied -= nr;
2797 node_stat_mod_folio(folio, NR_DIRTIED, -nr);
2798 wb_stat_mod(wb, WB_DIRTIED, -nr);
2799 unlocked_inode_to_wb_end(inode, &cookie);
2800 }
2801}
2802EXPORT_SYMBOL(folio_account_redirty);
2803
2804/**
2805 * folio_redirty_for_writepage - Decline to write a dirty folio.
2806 * @wbc: The writeback control.
2807 * @folio: The folio.
2808 *
2809 * When a writepage implementation decides that it doesn't want to write
2810 * @folio for some reason, it should call this function, unlock @folio and
2811 * return 0.
2812 *
2813 * Return: True if we redirtied the folio. False if someone else dirtied
2814 * it first.
2815 */
2816bool folio_redirty_for_writepage(struct writeback_control *wbc,
2817 struct folio *folio)
2818{
2819 bool ret;
2820 long nr = folio_nr_pages(folio);
2821
2822 wbc->pages_skipped += nr;
2823 ret = filemap_dirty_folio(folio->mapping, folio);
2824 folio_account_redirty(folio);
2825
2826 return ret;
2827}
2828EXPORT_SYMBOL(folio_redirty_for_writepage);
2829
2830/**
2831 * folio_mark_dirty - Mark a folio as being modified.
2832 * @folio: The folio.
2833 *
2834 * The folio may not be truncated while this function is running.
2835 * Holding the folio lock is sufficient to prevent truncation, but some
2836 * callers cannot acquire a sleeping lock. These callers instead hold
2837 * the page table lock for a page table which contains at least one page
2838 * in this folio. Truncation will block on the page table lock as it
2839 * unmaps pages before removing the folio from its mapping.
2840 *
2841 * Return: True if the folio was newly dirtied, false if it was already dirty.
2842 */
2843bool folio_mark_dirty(struct folio *folio)
2844{
2845 struct address_space *mapping = folio_mapping(folio);
2846
2847 if (likely(mapping)) {
2848 /*
2849 * readahead/lru_deactivate_page could remain
2850 * PG_readahead/PG_reclaim due to race with folio_end_writeback
2851 * About readahead, if the folio is written, the flags would be
2852 * reset. So no problem.
2853 * About lru_deactivate_page, if the folio is redirtied,
2854 * the flag will be reset. So no problem. but if the
2855 * folio is used by readahead it will confuse readahead
2856 * and make it restart the size rampup process. But it's
2857 * a trivial problem.
2858 */
2859 if (folio_test_reclaim(folio))
2860 folio_clear_reclaim(folio);
2861 return mapping->a_ops->dirty_folio(mapping, folio);
2862 }
2863
2864 return noop_dirty_folio(mapping, folio);
2865}
2866EXPORT_SYMBOL(folio_mark_dirty);
2867
2868/*
2869 * set_page_dirty() is racy if the caller has no reference against
2870 * page->mapping->host, and if the page is unlocked. This is because another
2871 * CPU could truncate the page off the mapping and then free the mapping.
2872 *
2873 * Usually, the page _is_ locked, or the caller is a user-space process which
2874 * holds a reference on the inode by having an open file.
2875 *
2876 * In other cases, the page should be locked before running set_page_dirty().
2877 */
2878int set_page_dirty_lock(struct page *page)
2879{
2880 int ret;
2881
2882 lock_page(page);
2883 ret = set_page_dirty(page);
2884 unlock_page(page);
2885 return ret;
2886}
2887EXPORT_SYMBOL(set_page_dirty_lock);
2888
2889/*
2890 * This cancels just the dirty bit on the kernel page itself, it does NOT
2891 * actually remove dirty bits on any mmap's that may be around. It also
2892 * leaves the page tagged dirty, so any sync activity will still find it on
2893 * the dirty lists, and in particular, clear_page_dirty_for_io() will still
2894 * look at the dirty bits in the VM.
2895 *
2896 * Doing this should *normally* only ever be done when a page is truncated,
2897 * and is not actually mapped anywhere at all. However, fs/buffer.c does
2898 * this when it notices that somebody has cleaned out all the buffers on a
2899 * page without actually doing it through the VM. Can you say "ext3 is
2900 * horribly ugly"? Thought you could.
2901 */
2902void __folio_cancel_dirty(struct folio *folio)
2903{
2904 struct address_space *mapping = folio_mapping(folio);
2905
2906 if (mapping_can_writeback(mapping)) {
2907 struct inode *inode = mapping->host;
2908 struct bdi_writeback *wb;
2909 struct wb_lock_cookie cookie = {};
2910
2911 folio_memcg_lock(folio);
2912 wb = unlocked_inode_to_wb_begin(inode, &cookie);
2913
2914 if (folio_test_clear_dirty(folio))
2915 folio_account_cleaned(folio, wb);
2916
2917 unlocked_inode_to_wb_end(inode, &cookie);
2918 folio_memcg_unlock(folio);
2919 } else {
2920 folio_clear_dirty(folio);
2921 }
2922}
2923EXPORT_SYMBOL(__folio_cancel_dirty);
2924
2925/*
2926 * Clear a folio's dirty flag, while caring for dirty memory accounting.
2927 * Returns true if the folio was previously dirty.
2928 *
2929 * This is for preparing to put the folio under writeout. We leave
2930 * the folio tagged as dirty in the xarray so that a concurrent
2931 * write-for-sync can discover it via a PAGECACHE_TAG_DIRTY walk.
2932 * The ->writepage implementation will run either folio_start_writeback()
2933 * or folio_mark_dirty(), at which stage we bring the folio's dirty flag
2934 * and xarray dirty tag back into sync.
2935 *
2936 * This incoherency between the folio's dirty flag and xarray tag is
2937 * unfortunate, but it only exists while the folio is locked.
2938 */
2939bool folio_clear_dirty_for_io(struct folio *folio)
2940{
2941 struct address_space *mapping = folio_mapping(folio);
2942 bool ret = false;
2943
2944 VM_BUG_ON_FOLIO(!folio_test_locked(folio), folio);
2945
2946 if (mapping && mapping_can_writeback(mapping)) {
2947 struct inode *inode = mapping->host;
2948 struct bdi_writeback *wb;
2949 struct wb_lock_cookie cookie = {};
2950
2951 /*
2952 * Yes, Virginia, this is indeed insane.
2953 *
2954 * We use this sequence to make sure that
2955 * (a) we account for dirty stats properly
2956 * (b) we tell the low-level filesystem to
2957 * mark the whole folio dirty if it was
2958 * dirty in a pagetable. Only to then
2959 * (c) clean the folio again and return 1 to
2960 * cause the writeback.
2961 *
2962 * This way we avoid all nasty races with the
2963 * dirty bit in multiple places and clearing
2964 * them concurrently from different threads.
2965 *
2966 * Note! Normally the "folio_mark_dirty(folio)"
2967 * has no effect on the actual dirty bit - since
2968 * that will already usually be set. But we
2969 * need the side effects, and it can help us
2970 * avoid races.
2971 *
2972 * We basically use the folio "master dirty bit"
2973 * as a serialization point for all the different
2974 * threads doing their things.
2975 */
2976 if (folio_mkclean(folio))
2977 folio_mark_dirty(folio);
2978 /*
2979 * We carefully synchronise fault handlers against
2980 * installing a dirty pte and marking the folio dirty
2981 * at this point. We do this by having them hold the
2982 * page lock while dirtying the folio, and folios are
2983 * always locked coming in here, so we get the desired
2984 * exclusion.
2985 */
2986 wb = unlocked_inode_to_wb_begin(inode, &cookie);
2987 if (folio_test_clear_dirty(folio)) {
2988 long nr = folio_nr_pages(folio);
2989 lruvec_stat_mod_folio(folio, NR_FILE_DIRTY, -nr);
2990 zone_stat_mod_folio(folio, NR_ZONE_WRITE_PENDING, -nr);
2991 wb_stat_mod(wb, WB_RECLAIMABLE, -nr);
2992 ret = true;
2993 }
2994 unlocked_inode_to_wb_end(inode, &cookie);
2995 return ret;
2996 }
2997 return folio_test_clear_dirty(folio);
2998}
2999EXPORT_SYMBOL(folio_clear_dirty_for_io);
3000
3001static void wb_inode_writeback_start(struct bdi_writeback *wb)
3002{
3003 atomic_inc(&wb->writeback_inodes);
3004}
3005
3006static void wb_inode_writeback_end(struct bdi_writeback *wb)
3007{
3008 unsigned long flags;
3009 atomic_dec(&wb->writeback_inodes);
3010 /*
3011 * Make sure estimate of writeback throughput gets updated after
3012 * writeback completed. We delay the update by BANDWIDTH_INTERVAL
3013 * (which is the interval other bandwidth updates use for batching) so
3014 * that if multiple inodes end writeback at a similar time, they get
3015 * batched into one bandwidth update.
3016 */
3017 spin_lock_irqsave(&wb->work_lock, flags);
3018 if (test_bit(WB_registered, &wb->state))
3019 queue_delayed_work(bdi_wq, &wb->bw_dwork, BANDWIDTH_INTERVAL);
3020 spin_unlock_irqrestore(&wb->work_lock, flags);
3021}
3022
3023bool __folio_end_writeback(struct folio *folio)
3024{
3025 long nr = folio_nr_pages(folio);
3026 struct address_space *mapping = folio_mapping(folio);
3027 bool ret;
3028
3029 folio_memcg_lock(folio);
3030 if (mapping && mapping_use_writeback_tags(mapping)) {
3031 struct inode *inode = mapping->host;
3032 struct backing_dev_info *bdi = inode_to_bdi(inode);
3033 unsigned long flags;
3034
3035 xa_lock_irqsave(&mapping->i_pages, flags);
3036 ret = folio_test_clear_writeback(folio);
3037 if (ret) {
3038 __xa_clear_mark(&mapping->i_pages, folio_index(folio),
3039 PAGECACHE_TAG_WRITEBACK);
3040 if (bdi->capabilities & BDI_CAP_WRITEBACK_ACCT) {
3041 struct bdi_writeback *wb = inode_to_wb(inode);
3042
3043 wb_stat_mod(wb, WB_WRITEBACK, -nr);
3044 __wb_writeout_add(wb, nr);
3045 if (!mapping_tagged(mapping,
3046 PAGECACHE_TAG_WRITEBACK))
3047 wb_inode_writeback_end(wb);
3048 }
3049 }
3050
3051 if (mapping->host && !mapping_tagged(mapping,
3052 PAGECACHE_TAG_WRITEBACK))
3053 sb_clear_inode_writeback(mapping->host);
3054
3055 xa_unlock_irqrestore(&mapping->i_pages, flags);
3056 } else {
3057 ret = folio_test_clear_writeback(folio);
3058 }
3059 if (ret) {
3060 lruvec_stat_mod_folio(folio, NR_WRITEBACK, -nr);
3061 zone_stat_mod_folio(folio, NR_ZONE_WRITE_PENDING, -nr);
3062 node_stat_mod_folio(folio, NR_WRITTEN, nr);
3063 }
3064 folio_memcg_unlock(folio);
3065 return ret;
3066}
3067
3068bool __folio_start_writeback(struct folio *folio, bool keep_write)
3069{
3070 long nr = folio_nr_pages(folio);
3071 struct address_space *mapping = folio_mapping(folio);
3072 bool ret;
3073 int access_ret;
3074
3075 folio_memcg_lock(folio);
3076 if (mapping && mapping_use_writeback_tags(mapping)) {
3077 XA_STATE(xas, &mapping->i_pages, folio_index(folio));
3078 struct inode *inode = mapping->host;
3079 struct backing_dev_info *bdi = inode_to_bdi(inode);
3080 unsigned long flags;
3081
3082 xas_lock_irqsave(&xas, flags);
3083 xas_load(&xas);
3084 ret = folio_test_set_writeback(folio);
3085 if (!ret) {
3086 bool on_wblist;
3087
3088 on_wblist = mapping_tagged(mapping,
3089 PAGECACHE_TAG_WRITEBACK);
3090
3091 xas_set_mark(&xas, PAGECACHE_TAG_WRITEBACK);
3092 if (bdi->capabilities & BDI_CAP_WRITEBACK_ACCT) {
3093 struct bdi_writeback *wb = inode_to_wb(inode);
3094
3095 wb_stat_mod(wb, WB_WRITEBACK, nr);
3096 if (!on_wblist)
3097 wb_inode_writeback_start(wb);
3098 }
3099
3100 /*
3101 * We can come through here when swapping
3102 * anonymous folios, so we don't necessarily
3103 * have an inode to track for sync.
3104 */
3105 if (mapping->host && !on_wblist)
3106 sb_mark_inode_writeback(mapping->host);
3107 }
3108 if (!folio_test_dirty(folio))
3109 xas_clear_mark(&xas, PAGECACHE_TAG_DIRTY);
3110 if (!keep_write)
3111 xas_clear_mark(&xas, PAGECACHE_TAG_TOWRITE);
3112 xas_unlock_irqrestore(&xas, flags);
3113 } else {
3114 ret = folio_test_set_writeback(folio);
3115 }
3116 if (!ret) {
3117 lruvec_stat_mod_folio(folio, NR_WRITEBACK, nr);
3118 zone_stat_mod_folio(folio, NR_ZONE_WRITE_PENDING, nr);
3119 }
3120 folio_memcg_unlock(folio);
3121 access_ret = arch_make_folio_accessible(folio);
3122 /*
3123 * If writeback has been triggered on a page that cannot be made
3124 * accessible, it is too late to recover here.
3125 */
3126 VM_BUG_ON_FOLIO(access_ret != 0, folio);
3127
3128 return ret;
3129}
3130EXPORT_SYMBOL(__folio_start_writeback);
3131
3132/**
3133 * folio_wait_writeback - Wait for a folio to finish writeback.
3134 * @folio: The folio to wait for.
3135 *
3136 * If the folio is currently being written back to storage, wait for the
3137 * I/O to complete.
3138 *
3139 * Context: Sleeps. Must be called in process context and with
3140 * no spinlocks held. Caller should hold a reference on the folio.
3141 * If the folio is not locked, writeback may start again after writeback
3142 * has finished.
3143 */
3144void folio_wait_writeback(struct folio *folio)
3145{
3146 while (folio_test_writeback(folio)) {
3147 trace_folio_wait_writeback(folio, folio_mapping(folio));
3148 folio_wait_bit(folio, PG_writeback);
3149 }
3150}
3151EXPORT_SYMBOL_GPL(folio_wait_writeback);
3152
3153/**
3154 * folio_wait_writeback_killable - Wait for a folio to finish writeback.
3155 * @folio: The folio to wait for.
3156 *
3157 * If the folio is currently being written back to storage, wait for the
3158 * I/O to complete or a fatal signal to arrive.
3159 *
3160 * Context: Sleeps. Must be called in process context and with
3161 * no spinlocks held. Caller should hold a reference on the folio.
3162 * If the folio is not locked, writeback may start again after writeback
3163 * has finished.
3164 * Return: 0 on success, -EINTR if we get a fatal signal while waiting.
3165 */
3166int folio_wait_writeback_killable(struct folio *folio)
3167{
3168 while (folio_test_writeback(folio)) {
3169 trace_folio_wait_writeback(folio, folio_mapping(folio));
3170 if (folio_wait_bit_killable(folio, PG_writeback))
3171 return -EINTR;
3172 }
3173
3174 return 0;
3175}
3176EXPORT_SYMBOL_GPL(folio_wait_writeback_killable);
3177
3178/**
3179 * folio_wait_stable() - wait for writeback to finish, if necessary.
3180 * @folio: The folio to wait on.
3181 *
3182 * This function determines if the given folio is related to a backing
3183 * device that requires folio contents to be held stable during writeback.
3184 * If so, then it will wait for any pending writeback to complete.
3185 *
3186 * Context: Sleeps. Must be called in process context and with
3187 * no spinlocks held. Caller should hold a reference on the folio.
3188 * If the folio is not locked, writeback may start again after writeback
3189 * has finished.
3190 */
3191void folio_wait_stable(struct folio *folio)
3192{
3193 if (folio_inode(folio)->i_sb->s_iflags & SB_I_STABLE_WRITES)
3194 folio_wait_writeback(folio);
3195}
3196EXPORT_SYMBOL_GPL(folio_wait_stable);