interconnect: qcom: icc-rpm: Fix peak rate calculation
[linux-2.6-microblaze.git] / mm / page-writeback.c
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  */
67 static 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  */
74 static 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  */
80 static 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  */
86 static int vm_highmem_is_dirtyable;
87
88 /*
89  * The generator of dirty data starts writeback at this percentage
90  */
91 static 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  */
97 static unsigned long vm_dirty_bytes;
98
99 /*
100  * The interval between `kupdate'-style writebacks
101  */
102 unsigned int dirty_writeback_interval = 5 * 100; /* centiseconds */
103
104 EXPORT_SYMBOL_GPL(dirty_writeback_interval);
105
106 /*
107  * The longest time for which data is allowed to remain dirty
108  */
109 unsigned 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  */
115 int laptop_mode;
116
117 EXPORT_SYMBOL(laptop_mode);
118
119 /* End of sysctl-exported parameters */
120
121 struct wb_domain global_wb_domain;
122
123 /* consolidated parameters for balance_dirty_pages() and its subroutines */
124 struct 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
164 static bool mdtc_valid(struct dirty_throttle_control *dtc)
165 {
166         return dtc->dom;
167 }
168
169 static struct wb_domain *dtc_dom(struct dirty_throttle_control *dtc)
170 {
171         return dtc->dom;
172 }
173
174 static struct dirty_throttle_control *mdtc_gdtc(struct dirty_throttle_control *mdtc)
175 {
176         return mdtc->gdtc;
177 }
178
179 static struct fprop_local_percpu *wb_memcg_completions(struct bdi_writeback *wb)
180 {
181         return &wb->memcg_completions;
182 }
183
184 static 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
218 static bool mdtc_valid(struct dirty_throttle_control *dtc)
219 {
220         return false;
221 }
222
223 static struct wb_domain *dtc_dom(struct dirty_throttle_control *dtc)
224 {
225         return &global_wb_domain;
226 }
227
228 static struct dirty_throttle_control *mdtc_gdtc(struct dirty_throttle_control *mdtc)
229 {
230         return NULL;
231 }
232
233 static struct fprop_local_percpu *wb_memcg_completions(struct bdi_writeback *wb)
234 {
235         return NULL;
236 }
237
238 static 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  */
272 static 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
299 static 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  */
345 static 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  */
375 static 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  */
441 void 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  */
459 static 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  */
484 bool 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
496 static 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
507 static 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
518 static 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
532 static 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
547 static 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
556 static 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  */
579 static 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
593 void 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 }
601 EXPORT_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  */
607 static 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
626 int 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
640 void 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  */
652 static unsigned int bdi_min_ratio;
653
654 static 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
664 static 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
676 static 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
688 static 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
720 static 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
739 int 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
744 int 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
749 int 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
754 int 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 }
758 EXPORT_SYMBOL(bdi_set_max_ratio);
759
760 u64 bdi_get_min_bytes(struct backing_dev_info *bdi)
761 {
762         return bdi_get_bytes(bdi->min_ratio);
763 }
764
765 int 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
779 u64 bdi_get_max_bytes(struct backing_dev_info *bdi)
780 {
781         return bdi_get_bytes(bdi->max_ratio);
782 }
783
784 int 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
798 int 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
813 static unsigned long dirty_freerun_ceiling(unsigned long thresh,
814                                            unsigned long bg_thresh)
815 {
816         return (thresh + bg_thresh) / 2;
817 }
818
819 static 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  */
829 static 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  */
861 static 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
888 unsigned 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  */
909 static 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  */
1001 static 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
1180 static void wb_update_write_bandwidth(struct bdi_writeback *wb,
1181                                       unsigned long elapsed,
1182                                       unsigned long written)
1183 {
1184         const unsigned long period = roundup_pow_of_two(3 * HZ);
1185         unsigned long avg = wb->avg_write_bandwidth;
1186         unsigned long old = wb->write_bandwidth;
1187         u64 bw;
1188
1189         /*
1190          * bw = written * HZ / elapsed
1191          *
1192          *                   bw * elapsed + write_bandwidth * (period - elapsed)
1193          * write_bandwidth = ---------------------------------------------------
1194          *                                          period
1195          *
1196          * @written may have decreased due to folio_redirty_for_writepage().
1197          * Avoid underflowing @bw calculation.
1198          */
1199         bw = written - min(written, wb->written_stamp);
1200         bw *= HZ;
1201         if (unlikely(elapsed > period)) {
1202                 bw = div64_ul(bw, elapsed);
1203                 avg = bw;
1204                 goto out;
1205         }
1206         bw += (u64)wb->write_bandwidth * (period - elapsed);
1207         bw >>= ilog2(period);
1208
1209         /*
1210          * one more level of smoothing, for filtering out sudden spikes
1211          */
1212         if (avg > old && old >= (unsigned long)bw)
1213                 avg -= (avg - old) >> 3;
1214
1215         if (avg < old && old <= (unsigned long)bw)
1216                 avg += (old - avg) >> 3;
1217
1218 out:
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
1230 static 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;
1255 update:
1256         dom->dirty_limit = limit;
1257 }
1258
1259 static 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  */
1284 static 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
1442 static 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
1485 void 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
1495 static 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  */
1518 static 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
1527 static 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
1546 static 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
1621 static 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  */
1669 static 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
1774 free_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
1906 pause:
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
1957 static 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  */
1973 DEFINE_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  */
1992 int 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 }
2048 EXPORT_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  */
2062 void balance_dirty_pages_ratelimited(struct address_space *mapping)
2063 {
2064         balance_dirty_pages_ratelimited_flags(mapping, 0);
2065 }
2066 EXPORT_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  */
2077 bool 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  */
2135 static 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
2158 void 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  */
2171 void 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  */
2181 void 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
2202 void 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
2215 static 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 */
2224 static const unsigned long dirty_bytes_min = 2 * PAGE_SIZE;
2225
2226 static 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  */
2314 void __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  */
2341 void 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 }
2361 EXPORT_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  */
2394 int write_cache_pages(struct address_space *mapping,
2395                       struct writeback_control *wbc, writepage_t writepage,
2396                       void *data)
2397 {
2398         int ret = 0;
2399         int done = 0;
2400         int error;
2401         struct folio_batch fbatch;
2402         int nr_folios;
2403         pgoff_t index;
2404         pgoff_t end;            /* Inclusive */
2405         pgoff_t done_index;
2406         int range_whole = 0;
2407         xa_mark_t tag;
2408
2409         folio_batch_init(&fbatch);
2410         if (wbc->range_cyclic) {
2411                 index = mapping->writeback_index; /* prev offset */
2412                 end = -1;
2413         } else {
2414                 index = wbc->range_start >> PAGE_SHIFT;
2415                 end = wbc->range_end >> PAGE_SHIFT;
2416                 if (wbc->range_start == 0 && wbc->range_end == LLONG_MAX)
2417                         range_whole = 1;
2418         }
2419         if (wbc->sync_mode == WB_SYNC_ALL || wbc->tagged_writepages) {
2420                 tag_pages_for_writeback(mapping, index, end);
2421                 tag = PAGECACHE_TAG_TOWRITE;
2422         } else {
2423                 tag = PAGECACHE_TAG_DIRTY;
2424         }
2425         done_index = index;
2426         while (!done && (index <= end)) {
2427                 int i;
2428
2429                 nr_folios = filemap_get_folios_tag(mapping, &index, end,
2430                                 tag, &fbatch);
2431
2432                 if (nr_folios == 0)
2433                         break;
2434
2435                 for (i = 0; i < nr_folios; i++) {
2436                         struct folio *folio = fbatch.folios[i];
2437                         unsigned long nr;
2438
2439                         done_index = folio->index;
2440
2441                         folio_lock(folio);
2442
2443                         /*
2444                          * Page truncated or invalidated. We can freely skip it
2445                          * then, even for data integrity operations: the page
2446                          * has disappeared concurrently, so there could be no
2447                          * real expectation of this data integrity operation
2448                          * even if there is now a new, dirty page at the same
2449                          * pagecache address.
2450                          */
2451                         if (unlikely(folio->mapping != mapping)) {
2452 continue_unlock:
2453                                 folio_unlock(folio);
2454                                 continue;
2455                         }
2456
2457                         if (!folio_test_dirty(folio)) {
2458                                 /* someone wrote it for us */
2459                                 goto continue_unlock;
2460                         }
2461
2462                         if (folio_test_writeback(folio)) {
2463                                 if (wbc->sync_mode != WB_SYNC_NONE)
2464                                         folio_wait_writeback(folio);
2465                                 else
2466                                         goto continue_unlock;
2467                         }
2468
2469                         BUG_ON(folio_test_writeback(folio));
2470                         if (!folio_clear_dirty_for_io(folio))
2471                                 goto continue_unlock;
2472
2473                         trace_wbc_writepage(wbc, inode_to_bdi(mapping->host));
2474                         error = writepage(folio, wbc, data);
2475                         nr = folio_nr_pages(folio);
2476                         if (unlikely(error)) {
2477                                 /*
2478                                  * Handle errors according to the type of
2479                                  * writeback. There's no need to continue for
2480                                  * background writeback. Just push done_index
2481                                  * past this page so media errors won't choke
2482                                  * writeout for the entire file. For integrity
2483                                  * writeback, we must process the entire dirty
2484                                  * set regardless of errors because the fs may
2485                                  * still have state to clear for each page. In
2486                                  * that case we continue processing and return
2487                                  * the first error.
2488                                  */
2489                                 if (error == AOP_WRITEPAGE_ACTIVATE) {
2490                                         folio_unlock(folio);
2491                                         error = 0;
2492                                 } else if (wbc->sync_mode != WB_SYNC_ALL) {
2493                                         ret = error;
2494                                         done_index = folio->index + nr;
2495                                         done = 1;
2496                                         break;
2497                                 }
2498                                 if (!ret)
2499                                         ret = error;
2500                         }
2501
2502                         /*
2503                          * We stop writing back only if we are not doing
2504                          * integrity sync. In case of integrity sync we have to
2505                          * keep going until we have written all the pages
2506                          * we tagged for writeback prior to entering this loop.
2507                          */
2508                         wbc->nr_to_write -= nr;
2509                         if (wbc->nr_to_write <= 0 &&
2510                             wbc->sync_mode == WB_SYNC_NONE) {
2511                                 done = 1;
2512                                 break;
2513                         }
2514                 }
2515                 folio_batch_release(&fbatch);
2516                 cond_resched();
2517         }
2518
2519         /*
2520          * If we hit the last page and there is more work to be done: wrap
2521          * back the index back to the start of the file for the next
2522          * time we are called.
2523          */
2524         if (wbc->range_cyclic && !done)
2525                 done_index = 0;
2526         if (wbc->range_cyclic || (range_whole && wbc->nr_to_write > 0))
2527                 mapping->writeback_index = done_index;
2528
2529         return ret;
2530 }
2531 EXPORT_SYMBOL(write_cache_pages);
2532
2533 static int writepage_cb(struct folio *folio, struct writeback_control *wbc,
2534                 void *data)
2535 {
2536         struct address_space *mapping = data;
2537         int ret = mapping->a_ops->writepage(&folio->page, wbc);
2538         mapping_set_error(mapping, ret);
2539         return ret;
2540 }
2541
2542 int do_writepages(struct address_space *mapping, struct writeback_control *wbc)
2543 {
2544         int ret;
2545         struct bdi_writeback *wb;
2546
2547         if (wbc->nr_to_write <= 0)
2548                 return 0;
2549         wb = inode_to_wb_wbc(mapping->host, wbc);
2550         wb_bandwidth_estimate_start(wb);
2551         while (1) {
2552                 if (mapping->a_ops->writepages) {
2553                         ret = mapping->a_ops->writepages(mapping, wbc);
2554                 } else if (mapping->a_ops->writepage) {
2555                         struct blk_plug plug;
2556
2557                         blk_start_plug(&plug);
2558                         ret = write_cache_pages(mapping, wbc, writepage_cb,
2559                                                 mapping);
2560                         blk_finish_plug(&plug);
2561                 } else {
2562                         /* deal with chardevs and other special files */
2563                         ret = 0;
2564                 }
2565                 if (ret != -ENOMEM || wbc->sync_mode != WB_SYNC_ALL)
2566                         break;
2567
2568                 /*
2569                  * Lacking an allocation context or the locality or writeback
2570                  * state of any of the inode's pages, throttle based on
2571                  * writeback activity on the local node. It's as good a
2572                  * guess as any.
2573                  */
2574                 reclaim_throttle(NODE_DATA(numa_node_id()),
2575                         VMSCAN_THROTTLE_WRITEBACK);
2576         }
2577         /*
2578          * Usually few pages are written by now from those we've just submitted
2579          * but if there's constant writeback being submitted, this makes sure
2580          * writeback bandwidth is updated once in a while.
2581          */
2582         if (time_is_before_jiffies(READ_ONCE(wb->bw_time_stamp) +
2583                                    BANDWIDTH_INTERVAL))
2584                 wb_update_bandwidth(wb);
2585         return ret;
2586 }
2587
2588 /*
2589  * For address_spaces which do not use buffers nor write back.
2590  */
2591 bool noop_dirty_folio(struct address_space *mapping, struct folio *folio)
2592 {
2593         if (!folio_test_dirty(folio))
2594                 return !folio_test_set_dirty(folio);
2595         return false;
2596 }
2597 EXPORT_SYMBOL(noop_dirty_folio);
2598
2599 /*
2600  * Helper function for set_page_dirty family.
2601  *
2602  * Caller must hold folio_memcg_lock().
2603  *
2604  * NOTE: This relies on being atomic wrt interrupts.
2605  */
2606 static void folio_account_dirtied(struct folio *folio,
2607                 struct address_space *mapping)
2608 {
2609         struct inode *inode = mapping->host;
2610
2611         trace_writeback_dirty_folio(folio, mapping);
2612
2613         if (mapping_can_writeback(mapping)) {
2614                 struct bdi_writeback *wb;
2615                 long nr = folio_nr_pages(folio);
2616
2617                 inode_attach_wb(inode, folio);
2618                 wb = inode_to_wb(inode);
2619
2620                 __lruvec_stat_mod_folio(folio, NR_FILE_DIRTY, nr);
2621                 __zone_stat_mod_folio(folio, NR_ZONE_WRITE_PENDING, nr);
2622                 __node_stat_mod_folio(folio, NR_DIRTIED, nr);
2623                 wb_stat_mod(wb, WB_RECLAIMABLE, nr);
2624                 wb_stat_mod(wb, WB_DIRTIED, nr);
2625                 task_io_account_write(nr * PAGE_SIZE);
2626                 current->nr_dirtied += nr;
2627                 __this_cpu_add(bdp_ratelimits, nr);
2628
2629                 mem_cgroup_track_foreign_dirty(folio, wb);
2630         }
2631 }
2632
2633 /*
2634  * Helper function for deaccounting dirty page without writeback.
2635  *
2636  * Caller must hold folio_memcg_lock().
2637  */
2638 void folio_account_cleaned(struct folio *folio, struct bdi_writeback *wb)
2639 {
2640         long nr = folio_nr_pages(folio);
2641
2642         lruvec_stat_mod_folio(folio, NR_FILE_DIRTY, -nr);
2643         zone_stat_mod_folio(folio, NR_ZONE_WRITE_PENDING, -nr);
2644         wb_stat_mod(wb, WB_RECLAIMABLE, -nr);
2645         task_io_account_cancelled_write(nr * PAGE_SIZE);
2646 }
2647
2648 /*
2649  * Mark the folio dirty, and set it dirty in the page cache, and mark
2650  * the inode dirty.
2651  *
2652  * If warn is true, then emit a warning if the folio is not uptodate and has
2653  * not been truncated.
2654  *
2655  * The caller must hold folio_memcg_lock().  Most callers have the folio
2656  * locked.  A few have the folio blocked from truncation through other
2657  * means (eg zap_vma_pages() has it mapped and is holding the page table
2658  * lock).  This can also be called from mark_buffer_dirty(), which I
2659  * cannot prove is always protected against truncate.
2660  */
2661 void __folio_mark_dirty(struct folio *folio, struct address_space *mapping,
2662                              int warn)
2663 {
2664         unsigned long flags;
2665
2666         xa_lock_irqsave(&mapping->i_pages, flags);
2667         if (folio->mapping) {   /* Race with truncate? */
2668                 WARN_ON_ONCE(warn && !folio_test_uptodate(folio));
2669                 folio_account_dirtied(folio, mapping);
2670                 __xa_set_mark(&mapping->i_pages, folio_index(folio),
2671                                 PAGECACHE_TAG_DIRTY);
2672         }
2673         xa_unlock_irqrestore(&mapping->i_pages, flags);
2674 }
2675
2676 /**
2677  * filemap_dirty_folio - Mark a folio dirty for filesystems which do not use buffer_heads.
2678  * @mapping: Address space this folio belongs to.
2679  * @folio: Folio to be marked as dirty.
2680  *
2681  * Filesystems which do not use buffer heads should call this function
2682  * from their dirty_folio address space operation.  It ignores the
2683  * contents of folio_get_private(), so if the filesystem marks individual
2684  * blocks as dirty, the filesystem should handle that itself.
2685  *
2686  * This is also sometimes used by filesystems which use buffer_heads when
2687  * a single buffer is being dirtied: we want to set the folio dirty in
2688  * that case, but not all the buffers.  This is a "bottom-up" dirtying,
2689  * whereas block_dirty_folio() is a "top-down" dirtying.
2690  *
2691  * The caller must ensure this doesn't race with truncation.  Most will
2692  * simply hold the folio lock, but e.g. zap_pte_range() calls with the
2693  * folio mapped and the pte lock held, which also locks out truncation.
2694  */
2695 bool filemap_dirty_folio(struct address_space *mapping, struct folio *folio)
2696 {
2697         folio_memcg_lock(folio);
2698         if (folio_test_set_dirty(folio)) {
2699                 folio_memcg_unlock(folio);
2700                 return false;
2701         }
2702
2703         __folio_mark_dirty(folio, mapping, !folio_test_private(folio));
2704         folio_memcg_unlock(folio);
2705
2706         if (mapping->host) {
2707                 /* !PageAnon && !swapper_space */
2708                 __mark_inode_dirty(mapping->host, I_DIRTY_PAGES);
2709         }
2710         return true;
2711 }
2712 EXPORT_SYMBOL(filemap_dirty_folio);
2713
2714 /**
2715  * folio_redirty_for_writepage - Decline to write a dirty folio.
2716  * @wbc: The writeback control.
2717  * @folio: The folio.
2718  *
2719  * When a writepage implementation decides that it doesn't want to write
2720  * @folio for some reason, it should call this function, unlock @folio and
2721  * return 0.
2722  *
2723  * Return: True if we redirtied the folio.  False if someone else dirtied
2724  * it first.
2725  */
2726 bool folio_redirty_for_writepage(struct writeback_control *wbc,
2727                 struct folio *folio)
2728 {
2729         struct address_space *mapping = folio->mapping;
2730         long nr = folio_nr_pages(folio);
2731         bool ret;
2732
2733         wbc->pages_skipped += nr;
2734         ret = filemap_dirty_folio(mapping, folio);
2735         if (mapping && mapping_can_writeback(mapping)) {
2736                 struct inode *inode = mapping->host;
2737                 struct bdi_writeback *wb;
2738                 struct wb_lock_cookie cookie = {};
2739
2740                 wb = unlocked_inode_to_wb_begin(inode, &cookie);
2741                 current->nr_dirtied -= nr;
2742                 node_stat_mod_folio(folio, NR_DIRTIED, -nr);
2743                 wb_stat_mod(wb, WB_DIRTIED, -nr);
2744                 unlocked_inode_to_wb_end(inode, &cookie);
2745         }
2746         return ret;
2747 }
2748 EXPORT_SYMBOL(folio_redirty_for_writepage);
2749
2750 /**
2751  * folio_mark_dirty - Mark a folio as being modified.
2752  * @folio: The folio.
2753  *
2754  * The folio may not be truncated while this function is running.
2755  * Holding the folio lock is sufficient to prevent truncation, but some
2756  * callers cannot acquire a sleeping lock.  These callers instead hold
2757  * the page table lock for a page table which contains at least one page
2758  * in this folio.  Truncation will block on the page table lock as it
2759  * unmaps pages before removing the folio from its mapping.
2760  *
2761  * Return: True if the folio was newly dirtied, false if it was already dirty.
2762  */
2763 bool folio_mark_dirty(struct folio *folio)
2764 {
2765         struct address_space *mapping = folio_mapping(folio);
2766
2767         if (likely(mapping)) {
2768                 /*
2769                  * readahead/folio_deactivate could remain
2770                  * PG_readahead/PG_reclaim due to race with folio_end_writeback
2771                  * About readahead, if the folio is written, the flags would be
2772                  * reset. So no problem.
2773                  * About folio_deactivate, if the folio is redirtied,
2774                  * the flag will be reset. So no problem. but if the
2775                  * folio is used by readahead it will confuse readahead
2776                  * and make it restart the size rampup process. But it's
2777                  * a trivial problem.
2778                  */
2779                 if (folio_test_reclaim(folio))
2780                         folio_clear_reclaim(folio);
2781                 return mapping->a_ops->dirty_folio(mapping, folio);
2782         }
2783
2784         return noop_dirty_folio(mapping, folio);
2785 }
2786 EXPORT_SYMBOL(folio_mark_dirty);
2787
2788 /*
2789  * set_page_dirty() is racy if the caller has no reference against
2790  * page->mapping->host, and if the page is unlocked.  This is because another
2791  * CPU could truncate the page off the mapping and then free the mapping.
2792  *
2793  * Usually, the page _is_ locked, or the caller is a user-space process which
2794  * holds a reference on the inode by having an open file.
2795  *
2796  * In other cases, the page should be locked before running set_page_dirty().
2797  */
2798 int set_page_dirty_lock(struct page *page)
2799 {
2800         int ret;
2801
2802         lock_page(page);
2803         ret = set_page_dirty(page);
2804         unlock_page(page);
2805         return ret;
2806 }
2807 EXPORT_SYMBOL(set_page_dirty_lock);
2808
2809 /*
2810  * This cancels just the dirty bit on the kernel page itself, it does NOT
2811  * actually remove dirty bits on any mmap's that may be around. It also
2812  * leaves the page tagged dirty, so any sync activity will still find it on
2813  * the dirty lists, and in particular, clear_page_dirty_for_io() will still
2814  * look at the dirty bits in the VM.
2815  *
2816  * Doing this should *normally* only ever be done when a page is truncated,
2817  * and is not actually mapped anywhere at all. However, fs/buffer.c does
2818  * this when it notices that somebody has cleaned out all the buffers on a
2819  * page without actually doing it through the VM. Can you say "ext3 is
2820  * horribly ugly"? Thought you could.
2821  */
2822 void __folio_cancel_dirty(struct folio *folio)
2823 {
2824         struct address_space *mapping = folio_mapping(folio);
2825
2826         if (mapping_can_writeback(mapping)) {
2827                 struct inode *inode = mapping->host;
2828                 struct bdi_writeback *wb;
2829                 struct wb_lock_cookie cookie = {};
2830
2831                 folio_memcg_lock(folio);
2832                 wb = unlocked_inode_to_wb_begin(inode, &cookie);
2833
2834                 if (folio_test_clear_dirty(folio))
2835                         folio_account_cleaned(folio, wb);
2836
2837                 unlocked_inode_to_wb_end(inode, &cookie);
2838                 folio_memcg_unlock(folio);
2839         } else {
2840                 folio_clear_dirty(folio);
2841         }
2842 }
2843 EXPORT_SYMBOL(__folio_cancel_dirty);
2844
2845 /*
2846  * Clear a folio's dirty flag, while caring for dirty memory accounting.
2847  * Returns true if the folio was previously dirty.
2848  *
2849  * This is for preparing to put the folio under writeout.  We leave
2850  * the folio tagged as dirty in the xarray so that a concurrent
2851  * write-for-sync can discover it via a PAGECACHE_TAG_DIRTY walk.
2852  * The ->writepage implementation will run either folio_start_writeback()
2853  * or folio_mark_dirty(), at which stage we bring the folio's dirty flag
2854  * and xarray dirty tag back into sync.
2855  *
2856  * This incoherency between the folio's dirty flag and xarray tag is
2857  * unfortunate, but it only exists while the folio is locked.
2858  */
2859 bool folio_clear_dirty_for_io(struct folio *folio)
2860 {
2861         struct address_space *mapping = folio_mapping(folio);
2862         bool ret = false;
2863
2864         VM_BUG_ON_FOLIO(!folio_test_locked(folio), folio);
2865
2866         if (mapping && mapping_can_writeback(mapping)) {
2867                 struct inode *inode = mapping->host;
2868                 struct bdi_writeback *wb;
2869                 struct wb_lock_cookie cookie = {};
2870
2871                 /*
2872                  * Yes, Virginia, this is indeed insane.
2873                  *
2874                  * We use this sequence to make sure that
2875                  *  (a) we account for dirty stats properly
2876                  *  (b) we tell the low-level filesystem to
2877                  *      mark the whole folio dirty if it was
2878                  *      dirty in a pagetable. Only to then
2879                  *  (c) clean the folio again and return 1 to
2880                  *      cause the writeback.
2881                  *
2882                  * This way we avoid all nasty races with the
2883                  * dirty bit in multiple places and clearing
2884                  * them concurrently from different threads.
2885                  *
2886                  * Note! Normally the "folio_mark_dirty(folio)"
2887                  * has no effect on the actual dirty bit - since
2888                  * that will already usually be set. But we
2889                  * need the side effects, and it can help us
2890                  * avoid races.
2891                  *
2892                  * We basically use the folio "master dirty bit"
2893                  * as a serialization point for all the different
2894                  * threads doing their things.
2895                  */
2896                 if (folio_mkclean(folio))
2897                         folio_mark_dirty(folio);
2898                 /*
2899                  * We carefully synchronise fault handlers against
2900                  * installing a dirty pte and marking the folio dirty
2901                  * at this point.  We do this by having them hold the
2902                  * page lock while dirtying the folio, and folios are
2903                  * always locked coming in here, so we get the desired
2904                  * exclusion.
2905                  */
2906                 wb = unlocked_inode_to_wb_begin(inode, &cookie);
2907                 if (folio_test_clear_dirty(folio)) {
2908                         long nr = folio_nr_pages(folio);
2909                         lruvec_stat_mod_folio(folio, NR_FILE_DIRTY, -nr);
2910                         zone_stat_mod_folio(folio, NR_ZONE_WRITE_PENDING, -nr);
2911                         wb_stat_mod(wb, WB_RECLAIMABLE, -nr);
2912                         ret = true;
2913                 }
2914                 unlocked_inode_to_wb_end(inode, &cookie);
2915                 return ret;
2916         }
2917         return folio_test_clear_dirty(folio);
2918 }
2919 EXPORT_SYMBOL(folio_clear_dirty_for_io);
2920
2921 static void wb_inode_writeback_start(struct bdi_writeback *wb)
2922 {
2923         atomic_inc(&wb->writeback_inodes);
2924 }
2925
2926 static void wb_inode_writeback_end(struct bdi_writeback *wb)
2927 {
2928         unsigned long flags;
2929         atomic_dec(&wb->writeback_inodes);
2930         /*
2931          * Make sure estimate of writeback throughput gets updated after
2932          * writeback completed. We delay the update by BANDWIDTH_INTERVAL
2933          * (which is the interval other bandwidth updates use for batching) so
2934          * that if multiple inodes end writeback at a similar time, they get
2935          * batched into one bandwidth update.
2936          */
2937         spin_lock_irqsave(&wb->work_lock, flags);
2938         if (test_bit(WB_registered, &wb->state))
2939                 queue_delayed_work(bdi_wq, &wb->bw_dwork, BANDWIDTH_INTERVAL);
2940         spin_unlock_irqrestore(&wb->work_lock, flags);
2941 }
2942
2943 bool __folio_end_writeback(struct folio *folio)
2944 {
2945         long nr = folio_nr_pages(folio);
2946         struct address_space *mapping = folio_mapping(folio);
2947         bool ret;
2948
2949         folio_memcg_lock(folio);
2950         if (mapping && mapping_use_writeback_tags(mapping)) {
2951                 struct inode *inode = mapping->host;
2952                 struct backing_dev_info *bdi = inode_to_bdi(inode);
2953                 unsigned long flags;
2954
2955                 xa_lock_irqsave(&mapping->i_pages, flags);
2956                 ret = folio_xor_flags_has_waiters(folio, 1 << PG_writeback);
2957                 __xa_clear_mark(&mapping->i_pages, folio_index(folio),
2958                                         PAGECACHE_TAG_WRITEBACK);
2959                 if (bdi->capabilities & BDI_CAP_WRITEBACK_ACCT) {
2960                         struct bdi_writeback *wb = inode_to_wb(inode);
2961
2962                         wb_stat_mod(wb, WB_WRITEBACK, -nr);
2963                         __wb_writeout_add(wb, nr);
2964                         if (!mapping_tagged(mapping, PAGECACHE_TAG_WRITEBACK))
2965                                 wb_inode_writeback_end(wb);
2966                 }
2967
2968                 if (mapping->host && !mapping_tagged(mapping,
2969                                                      PAGECACHE_TAG_WRITEBACK))
2970                         sb_clear_inode_writeback(mapping->host);
2971
2972                 xa_unlock_irqrestore(&mapping->i_pages, flags);
2973         } else {
2974                 ret = folio_xor_flags_has_waiters(folio, 1 << PG_writeback);
2975         }
2976
2977         lruvec_stat_mod_folio(folio, NR_WRITEBACK, -nr);
2978         zone_stat_mod_folio(folio, NR_ZONE_WRITE_PENDING, -nr);
2979         node_stat_mod_folio(folio, NR_WRITTEN, nr);
2980         folio_memcg_unlock(folio);
2981
2982         return ret;
2983 }
2984
2985 bool __folio_start_writeback(struct folio *folio, bool keep_write)
2986 {
2987         long nr = folio_nr_pages(folio);
2988         struct address_space *mapping = folio_mapping(folio);
2989         bool ret;
2990         int access_ret;
2991
2992         folio_memcg_lock(folio);
2993         if (mapping && mapping_use_writeback_tags(mapping)) {
2994                 XA_STATE(xas, &mapping->i_pages, folio_index(folio));
2995                 struct inode *inode = mapping->host;
2996                 struct backing_dev_info *bdi = inode_to_bdi(inode);
2997                 unsigned long flags;
2998
2999                 xas_lock_irqsave(&xas, flags);
3000                 xas_load(&xas);
3001                 ret = folio_test_set_writeback(folio);
3002                 if (!ret) {
3003                         bool on_wblist;
3004
3005                         on_wblist = mapping_tagged(mapping,
3006                                                    PAGECACHE_TAG_WRITEBACK);
3007
3008                         xas_set_mark(&xas, PAGECACHE_TAG_WRITEBACK);
3009                         if (bdi->capabilities & BDI_CAP_WRITEBACK_ACCT) {
3010                                 struct bdi_writeback *wb = inode_to_wb(inode);
3011
3012                                 wb_stat_mod(wb, WB_WRITEBACK, nr);
3013                                 if (!on_wblist)
3014                                         wb_inode_writeback_start(wb);
3015                         }
3016
3017                         /*
3018                          * We can come through here when swapping
3019                          * anonymous folios, so we don't necessarily
3020                          * have an inode to track for sync.
3021                          */
3022                         if (mapping->host && !on_wblist)
3023                                 sb_mark_inode_writeback(mapping->host);
3024                 }
3025                 if (!folio_test_dirty(folio))
3026                         xas_clear_mark(&xas, PAGECACHE_TAG_DIRTY);
3027                 if (!keep_write)
3028                         xas_clear_mark(&xas, PAGECACHE_TAG_TOWRITE);
3029                 xas_unlock_irqrestore(&xas, flags);
3030         } else {
3031                 ret = folio_test_set_writeback(folio);
3032         }
3033         if (!ret) {
3034                 lruvec_stat_mod_folio(folio, NR_WRITEBACK, nr);
3035                 zone_stat_mod_folio(folio, NR_ZONE_WRITE_PENDING, nr);
3036         }
3037         folio_memcg_unlock(folio);
3038         access_ret = arch_make_folio_accessible(folio);
3039         /*
3040          * If writeback has been triggered on a page that cannot be made
3041          * accessible, it is too late to recover here.
3042          */
3043         VM_BUG_ON_FOLIO(access_ret != 0, folio);
3044
3045         return ret;
3046 }
3047 EXPORT_SYMBOL(__folio_start_writeback);
3048
3049 /**
3050  * folio_wait_writeback - Wait for a folio to finish writeback.
3051  * @folio: The folio to wait for.
3052  *
3053  * If the folio is currently being written back to storage, wait for the
3054  * I/O to complete.
3055  *
3056  * Context: Sleeps.  Must be called in process context and with
3057  * no spinlocks held.  Caller should hold a reference on the folio.
3058  * If the folio is not locked, writeback may start again after writeback
3059  * has finished.
3060  */
3061 void folio_wait_writeback(struct folio *folio)
3062 {
3063         while (folio_test_writeback(folio)) {
3064                 trace_folio_wait_writeback(folio, folio_mapping(folio));
3065                 folio_wait_bit(folio, PG_writeback);
3066         }
3067 }
3068 EXPORT_SYMBOL_GPL(folio_wait_writeback);
3069
3070 /**
3071  * folio_wait_writeback_killable - Wait for a folio to finish writeback.
3072  * @folio: The folio to wait for.
3073  *
3074  * If the folio is currently being written back to storage, wait for the
3075  * I/O to complete or a fatal signal to arrive.
3076  *
3077  * Context: Sleeps.  Must be called in process context and with
3078  * no spinlocks held.  Caller should hold a reference on the folio.
3079  * If the folio is not locked, writeback may start again after writeback
3080  * has finished.
3081  * Return: 0 on success, -EINTR if we get a fatal signal while waiting.
3082  */
3083 int folio_wait_writeback_killable(struct folio *folio)
3084 {
3085         while (folio_test_writeback(folio)) {
3086                 trace_folio_wait_writeback(folio, folio_mapping(folio));
3087                 if (folio_wait_bit_killable(folio, PG_writeback))
3088                         return -EINTR;
3089         }
3090
3091         return 0;
3092 }
3093 EXPORT_SYMBOL_GPL(folio_wait_writeback_killable);
3094
3095 /**
3096  * folio_wait_stable() - wait for writeback to finish, if necessary.
3097  * @folio: The folio to wait on.
3098  *
3099  * This function determines if the given folio is related to a backing
3100  * device that requires folio contents to be held stable during writeback.
3101  * If so, then it will wait for any pending writeback to complete.
3102  *
3103  * Context: Sleeps.  Must be called in process context and with
3104  * no spinlocks held.  Caller should hold a reference on the folio.
3105  * If the folio is not locked, writeback may start again after writeback
3106  * has finished.
3107  */
3108 void folio_wait_stable(struct folio *folio)
3109 {
3110         if (folio_inode(folio)->i_sb->s_iflags & SB_I_STABLE_WRITES)
3111                 folio_wait_writeback(folio);
3112 }
3113 EXPORT_SYMBOL_GPL(folio_wait_stable);