Line data Source code
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 0 : *minp = wb->bdi->min_ratio;
242 0 : *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 0 : unsigned long nr_pages = 0;
275 : int z;
276 :
277 0 : for (z = 0; z < MAX_NR_ZONES; z++) {
278 0 : struct zone *zone = pgdat->node_zones + z;
279 :
280 0 : if (!populated_zone(zone))
281 0 : continue;
282 :
283 0 : 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 0 : nr_pages -= min(nr_pages, pgdat->totalreserve_pages);
292 :
293 0 : nr_pages += node_page_state(pgdat, NR_INACTIVE_FILE);
294 0 : 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 1 : 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 1 : x -= min(x, totalreserve_pages);
356 :
357 1 : x += global_node_page_state(NR_INACTIVE_FILE);
358 1 : x += global_node_page_state(NR_ACTIVE_FILE);
359 :
360 : if (!vm_highmem_is_dirtyable)
361 : x -= highmem_dirtyable_memory(x);
362 :
363 1 : 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 1 : static void domain_dirty_limits(struct dirty_throttle_control *dtc)
376 : {
377 1 : const unsigned long available_memory = dtc->avail;
378 1 : struct dirty_throttle_control *gdtc = mdtc_gdtc(dtc);
379 1 : unsigned long bytes = vm_dirty_bytes;
380 1 : unsigned long bg_bytes = dirty_background_bytes;
381 : /* convert ratios to per-PAGE_SIZE for higher precision */
382 1 : unsigned long ratio = (vm_dirty_ratio * PAGE_SIZE) / 100;
383 1 : 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 1 : if (bytes)
409 0 : thresh = DIV_ROUND_UP(bytes, PAGE_SIZE);
410 : else
411 1 : thresh = (ratio * available_memory) / PAGE_SIZE;
412 :
413 1 : if (bg_bytes)
414 0 : bg_thresh = DIV_ROUND_UP(bg_bytes, PAGE_SIZE);
415 : else
416 1 : bg_thresh = (bg_ratio * available_memory) / PAGE_SIZE;
417 :
418 1 : if (bg_thresh >= thresh)
419 0 : bg_thresh = thresh / 2;
420 1 : tsk = current;
421 2 : if (rt_task(tsk)) {
422 0 : bg_thresh += bg_thresh / 4 + global_wb_domain.dirty_limit / 32;
423 0 : thresh += thresh / 4 + global_wb_domain.dirty_limit / 32;
424 : }
425 1 : dtc->thresh = thresh;
426 1 : 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 1 : }
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 1 : void global_dirty_limits(unsigned long *pbackground, unsigned long *pdirty)
442 : {
443 1 : struct dirty_throttle_control gdtc = { GDTC_INIT_NO_WB };
444 :
445 1 : gdtc.avail = global_dirtyable_memory();
446 1 : domain_dirty_limits(&gdtc);
447 :
448 1 : *pbackground = gdtc.bg_thresh;
449 1 : *pdirty = gdtc.thresh;
450 1 : }
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 0 : static unsigned long node_dirty_limit(struct pglist_data *pgdat)
460 : {
461 0 : unsigned long node_memory = node_dirtyable_memory(pgdat);
462 0 : struct task_struct *tsk = current;
463 : unsigned long dirty;
464 :
465 0 : if (vm_dirty_bytes)
466 0 : dirty = DIV_ROUND_UP(vm_dirty_bytes, PAGE_SIZE) *
467 0 : node_memory / global_dirtyable_memory();
468 : else
469 0 : dirty = vm_dirty_ratio * node_memory / 100;
470 :
471 0 : if (rt_task(tsk))
472 0 : dirty += dirty / 4;
473 :
474 0 : 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 0 : bool node_dirty_ok(struct pglist_data *pgdat)
485 : {
486 0 : unsigned long limit = node_dirty_limit(pgdat);
487 0 : unsigned long nr_pages = 0;
488 :
489 0 : nr_pages += node_page_state(pgdat, NR_FILE_DIRTY);
490 0 : nr_pages += node_page_state(pgdat, NR_WRITEBACK);
491 :
492 0 : return nr_pages <= limit;
493 : }
494 :
495 : #ifdef CONFIG_SYSCTL
496 0 : 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 0 : ret = proc_dointvec_minmax(table, write, buffer, lenp, ppos);
502 0 : if (ret == 0 && write)
503 0 : dirty_background_bytes = 0;
504 0 : return ret;
505 : }
506 :
507 0 : 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 0 : ret = proc_doulongvec_minmax(table, write, buffer, lenp, ppos);
513 0 : if (ret == 0 && write)
514 0 : dirty_background_ratio = 0;
515 0 : return ret;
516 : }
517 :
518 0 : static int dirty_ratio_handler(struct ctl_table *table, int write, void *buffer,
519 : size_t *lenp, loff_t *ppos)
520 : {
521 0 : int old_ratio = vm_dirty_ratio;
522 : int ret;
523 :
524 0 : ret = proc_dointvec_minmax(table, write, buffer, lenp, ppos);
525 0 : if (ret == 0 && write && vm_dirty_ratio != old_ratio) {
526 0 : writeback_set_ratelimit();
527 0 : vm_dirty_bytes = 0;
528 : }
529 0 : return ret;
530 : }
531 :
532 0 : static int dirty_bytes_handler(struct ctl_table *table, int write,
533 : void *buffer, size_t *lenp, loff_t *ppos)
534 : {
535 0 : unsigned long old_bytes = vm_dirty_bytes;
536 : int ret;
537 :
538 0 : ret = proc_doulongvec_minmax(table, write, buffer, lenp, ppos);
539 0 : if (ret == 0 && write && vm_dirty_bytes != old_bytes) {
540 0 : writeback_set_ratelimit();
541 0 : vm_dirty_ratio = 0;
542 : }
543 0 : return ret;
544 : }
545 : #endif
546 :
547 : static unsigned long wp_next_time(unsigned long cur_time)
548 : {
549 0 : cur_time += VM_COMPLETIONS_PERIOD_LEN;
550 : /* 0 has a special meaning... */
551 0 : if (!cur_time)
552 : return 1;
553 : return cur_time;
554 : }
555 :
556 0 : 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 0 : __fprop_add_percpu_max(&dom->completions, completions,
561 : max_prop_frac, nr);
562 : /* First event after period switching was turned off? */
563 0 : 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 0 : dom->period_time = wp_next_time(jiffies);
571 0 : mod_timer(&dom->period_timer, dom->period_time);
572 : }
573 0 : }
574 :
575 : /*
576 : * Increment @wb's writeout completion count and the global writeout
577 : * completion count. Called from __folio_end_writeback().
578 : */
579 0 : static inline void __wb_writeout_add(struct bdi_writeback *wb, long nr)
580 : {
581 : struct wb_domain *cgdom;
582 :
583 0 : wb_stat_mod(wb, WB_WRITTEN, nr);
584 0 : wb_domain_writeout_add(&global_wb_domain, &wb->completions,
585 0 : wb->bdi->max_prop_frac, nr);
586 :
587 0 : 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 0 : }
592 :
593 0 : void wb_writeout_inc(struct bdi_writeback *wb)
594 : {
595 : unsigned long flags;
596 :
597 0 : local_irq_save(flags);
598 0 : __wb_writeout_add(wb, 1);
599 0 : local_irq_restore(flags);
600 0 : }
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 0 : static void writeout_period(struct timer_list *t)
608 : {
609 0 : struct wb_domain *dom = from_timer(dom, t, period_timer);
610 0 : int miss_periods = (jiffies - dom->period_time) /
611 : VM_COMPLETIONS_PERIOD_LEN;
612 :
613 0 : if (fprop_new_period(&dom->completions, miss_periods + 1)) {
614 0 : dom->period_time = wp_next_time(dom->period_time +
615 0 : miss_periods * VM_COMPLETIONS_PERIOD_LEN);
616 0 : 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 0 : dom->period_time = 0;
623 : }
624 0 : }
625 :
626 1 : int wb_domain_init(struct wb_domain *dom, gfp_t gfp)
627 : {
628 2 : memset(dom, 0, sizeof(*dom));
629 :
630 1 : spin_lock_init(&dom->lock);
631 :
632 1 : timer_setup(&dom->period_timer, writeout_period, TIMER_DEFERRABLE);
633 :
634 1 : dom->dirty_limit_tstamp = jiffies;
635 :
636 1 : 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 0 : unsigned long max_dirty_pages = global_dirtyable_memory();
657 :
658 0 : 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 0 : global_dirty_limits(&background_thresh, &dirty_thresh);
671 0 : 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 0 : global_dirty_limits(&background_thresh, &dirty_thresh);
683 0 : bytes = (dirty_thresh * PAGE_SIZE * ratio) / BDI_RATIO_SCALE / 100;
684 :
685 : return bytes;
686 : }
687 :
688 0 : static int __bdi_set_min_ratio(struct backing_dev_info *bdi, unsigned int min_ratio)
689 : {
690 : unsigned int delta;
691 0 : int ret = 0;
692 :
693 0 : if (min_ratio > 100 * BDI_RATIO_SCALE)
694 : return -EINVAL;
695 0 : min_ratio *= BDI_RATIO_SCALE;
696 :
697 0 : spin_lock_bh(&bdi_lock);
698 0 : if (min_ratio > bdi->max_ratio) {
699 : ret = -EINVAL;
700 : } else {
701 0 : if (min_ratio < bdi->min_ratio) {
702 0 : delta = bdi->min_ratio - min_ratio;
703 0 : bdi_min_ratio -= delta;
704 0 : bdi->min_ratio = min_ratio;
705 : } else {
706 0 : delta = min_ratio - bdi->min_ratio;
707 0 : if (bdi_min_ratio + delta < 100 * BDI_RATIO_SCALE) {
708 0 : bdi_min_ratio += delta;
709 0 : bdi->min_ratio = min_ratio;
710 : } else {
711 : ret = -EINVAL;
712 : }
713 : }
714 : }
715 0 : spin_unlock_bh(&bdi_lock);
716 :
717 : return ret;
718 : }
719 :
720 0 : static int __bdi_set_max_ratio(struct backing_dev_info *bdi, unsigned int max_ratio)
721 : {
722 0 : int ret = 0;
723 :
724 0 : if (max_ratio > 100 * BDI_RATIO_SCALE)
725 : return -EINVAL;
726 :
727 0 : spin_lock_bh(&bdi_lock);
728 0 : if (bdi->min_ratio > max_ratio) {
729 : ret = -EINVAL;
730 : } else {
731 0 : bdi->max_ratio = max_ratio;
732 0 : bdi->max_prop_frac = (FPROP_FRAC_BASE * max_ratio) / 100;
733 : }
734 0 : spin_unlock_bh(&bdi_lock);
735 :
736 0 : return ret;
737 : }
738 :
739 0 : int bdi_set_min_ratio_no_scale(struct backing_dev_info *bdi, unsigned int min_ratio)
740 : {
741 0 : return __bdi_set_min_ratio(bdi, min_ratio);
742 : }
743 :
744 0 : int bdi_set_max_ratio_no_scale(struct backing_dev_info *bdi, unsigned int max_ratio)
745 : {
746 0 : return __bdi_set_max_ratio(bdi, max_ratio);
747 : }
748 :
749 0 : int bdi_set_min_ratio(struct backing_dev_info *bdi, unsigned int min_ratio)
750 : {
751 0 : return __bdi_set_min_ratio(bdi, min_ratio * BDI_RATIO_SCALE);
752 : }
753 :
754 0 : int bdi_set_max_ratio(struct backing_dev_info *bdi, unsigned int max_ratio)
755 : {
756 0 : return __bdi_set_max_ratio(bdi, max_ratio * BDI_RATIO_SCALE);
757 : }
758 : EXPORT_SYMBOL(bdi_set_max_ratio);
759 :
760 0 : u64 bdi_get_min_bytes(struct backing_dev_info *bdi)
761 : {
762 0 : return bdi_get_bytes(bdi->min_ratio);
763 : }
764 :
765 0 : int bdi_set_min_bytes(struct backing_dev_info *bdi, u64 min_bytes)
766 : {
767 : int ret;
768 0 : unsigned long pages = min_bytes >> PAGE_SHIFT;
769 : unsigned long min_ratio;
770 :
771 0 : ret = bdi_check_pages_limit(pages);
772 0 : if (ret)
773 : return ret;
774 :
775 0 : min_ratio = bdi_ratio_from_pages(pages);
776 0 : return __bdi_set_min_ratio(bdi, min_ratio);
777 : }
778 :
779 0 : u64 bdi_get_max_bytes(struct backing_dev_info *bdi)
780 : {
781 0 : return bdi_get_bytes(bdi->max_ratio);
782 : }
783 :
784 0 : int bdi_set_max_bytes(struct backing_dev_info *bdi, u64 max_bytes)
785 : {
786 : int ret;
787 0 : unsigned long pages = max_bytes >> PAGE_SHIFT;
788 : unsigned long max_ratio;
789 :
790 0 : ret = bdi_check_pages_limit(pages);
791 0 : if (ret)
792 : return ret;
793 :
794 0 : max_ratio = bdi_ratio_from_pages(pages);
795 0 : return __bdi_set_max_ratio(bdi, max_ratio);
796 : }
797 :
798 0 : int bdi_set_strict_limit(struct backing_dev_info *bdi, unsigned int strict_limit)
799 : {
800 0 : if (strict_limit > 1)
801 : return -EINVAL;
802 :
803 0 : spin_lock_bh(&bdi_lock);
804 0 : if (strict_limit)
805 0 : bdi->capabilities |= BDI_CAP_STRICTLIMIT;
806 : else
807 0 : bdi->capabilities &= ~BDI_CAP_STRICTLIMIT;
808 0 : spin_unlock_bh(&bdi_lock);
809 :
810 0 : return 0;
811 : }
812 :
813 : static unsigned long dirty_freerun_ceiling(unsigned long thresh,
814 : unsigned long bg_thresh)
815 : {
816 0 : return (thresh + bg_thresh) / 2;
817 : }
818 :
819 : static unsigned long hard_dirty_limit(struct wb_domain *dom,
820 : unsigned long thresh)
821 : {
822 0 : 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 0 : static unsigned long __wb_calc_thresh(struct dirty_throttle_control *dtc)
862 : {
863 0 : struct wb_domain *dom = dtc_dom(dtc);
864 0 : 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 0 : fprop_fraction_percpu(&dom->completions, dtc->wb_completions,
873 : &numerator, &denominator);
874 :
875 0 : wb_thresh = (thresh * (100 * BDI_RATIO_SCALE - bdi_min_ratio)) / (100 * BDI_RATIO_SCALE);
876 0 : wb_thresh *= numerator;
877 0 : wb_thresh = div64_ul(wb_thresh, denominator);
878 :
879 0 : wb_min_max_ratio(dtc->wb, &wb_min_ratio, &wb_max_ratio);
880 :
881 0 : wb_thresh += (thresh * wb_min_ratio) / (100 * BDI_RATIO_SCALE);
882 0 : if (wb_thresh > (thresh * wb_max_ratio) / (100 * BDI_RATIO_SCALE))
883 0 : wb_thresh = thresh * wb_max_ratio / (100 * BDI_RATIO_SCALE);
884 :
885 0 : return wb_thresh;
886 : }
887 :
888 0 : unsigned long wb_calc_thresh(struct bdi_writeback *wb, unsigned long thresh)
889 : {
890 0 : struct dirty_throttle_control gdtc = { GDTC_INIT(wb),
891 : .thresh = thresh };
892 0 : 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 0 : x = div64_s64(((s64)setpoint - (s64)dirty) << RATELIMIT_CALC_SHIFT,
917 0 : (limit - setpoint) | 1);
918 0 : pos_ratio = x;
919 0 : pos_ratio = pos_ratio * x >> RATELIMIT_CALC_SHIFT;
920 0 : pos_ratio = pos_ratio * x >> RATELIMIT_CALC_SHIFT;
921 0 : pos_ratio += 1 << RATELIMIT_CALC_SHIFT;
922 :
923 0 : 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 0 : static void wb_position_ratio(struct dirty_throttle_control *dtc)
1002 : {
1003 0 : struct bdi_writeback *wb = dtc->wb;
1004 0 : unsigned long write_bw = READ_ONCE(wb->avg_write_bandwidth);
1005 0 : unsigned long freerun = dirty_freerun_ceiling(dtc->thresh, dtc->bg_thresh);
1006 0 : unsigned long limit = hard_dirty_limit(dtc_dom(dtc), dtc->thresh);
1007 0 : 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 0 : dtc->pos_ratio = 0;
1016 :
1017 0 : if (unlikely(dtc->dirty >= limit))
1018 : return;
1019 :
1020 : /*
1021 : * global setpoint
1022 : *
1023 : * See comment for pos_ratio_polynom().
1024 : */
1025 0 : setpoint = (freerun + limit) / 2;
1026 0 : 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 0 : if (unlikely(wb->bdi->capabilities & BDI_CAP_STRICTLIMIT)) {
1054 : long long wb_pos_ratio;
1055 :
1056 0 : if (dtc->wb_dirty < 8) {
1057 0 : dtc->pos_ratio = min_t(long long, pos_ratio * 2,
1058 : 2 << RATELIMIT_CALC_SHIFT);
1059 0 : return;
1060 : }
1061 :
1062 0 : if (dtc->wb_dirty >= wb_thresh)
1063 : return;
1064 :
1065 0 : wb_setpoint = dirty_freerun_ceiling(wb_thresh,
1066 : dtc->wb_bg_thresh);
1067 :
1068 0 : if (wb_setpoint == 0 || wb_setpoint == wb_thresh)
1069 : return;
1070 :
1071 0 : 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 0 : dtc->pos_ratio = min(pos_ratio, wb_pos_ratio);
1096 0 : 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 0 : if (unlikely(wb_thresh > dtc->thresh))
1131 0 : 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 0 : 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 0 : x = div_u64((u64)wb_thresh << 16, dtc->thresh | 1);
1145 0 : 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 0 : span = (dtc->thresh - wb_thresh + 8 * write_bw) * (u64)x >> 16;
1155 0 : x_intercept = wb_setpoint + span;
1156 :
1157 0 : if (dtc->wb_dirty < x_intercept - span / 4) {
1158 0 : pos_ratio = div64_u64(pos_ratio * (x_intercept - dtc->wb_dirty),
1159 0 : (x_intercept - wb_setpoint) | 1);
1160 : } else
1161 0 : 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 0 : x_intercept = wb_thresh / 2;
1169 0 : if (dtc->wb_dirty < x_intercept) {
1170 0 : if (dtc->wb_dirty > x_intercept / 8)
1171 0 : pos_ratio = div_u64(pos_ratio * x_intercept,
1172 : dtc->wb_dirty);
1173 : else
1174 0 : pos_ratio *= 8;
1175 : }
1176 :
1177 0 : dtc->pos_ratio = pos_ratio;
1178 : }
1179 :
1180 0 : static void wb_update_write_bandwidth(struct bdi_writeback *wb,
1181 : unsigned long elapsed,
1182 : unsigned long written)
1183 : {
1184 0 : const unsigned long period = roundup_pow_of_two(3 * HZ);
1185 0 : unsigned long avg = wb->avg_write_bandwidth;
1186 0 : unsigned long old = wb->write_bandwidth;
1187 : u64 bw;
1188 :
1189 : /*
1190 : * bw = written * HZ / elapsed
1191 : *
1192 : * bw * elapsed + write_bandwidth * (period - elapsed)
1193 : * write_bandwidth = ---------------------------------------------------
1194 : * period
1195 : *
1196 : * @written may have decreased due to folio_account_redirty().
1197 : * Avoid underflowing @bw calculation.
1198 : */
1199 0 : bw = written - min(written, wb->written_stamp);
1200 0 : bw *= HZ;
1201 0 : if (unlikely(elapsed > period)) {
1202 0 : bw = div64_ul(bw, elapsed);
1203 0 : avg = bw;
1204 0 : goto out;
1205 : }
1206 0 : bw += (u64)wb->write_bandwidth * (period - elapsed);
1207 0 : bw >>= ilog2(period);
1208 :
1209 : /*
1210 : * one more level of smoothing, for filtering out sudden spikes
1211 : */
1212 0 : if (avg > old && old >= (unsigned long)bw)
1213 0 : avg -= (avg - old) >> 3;
1214 :
1215 0 : if (avg < old && old <= (unsigned long)bw)
1216 0 : avg += (old - avg) >> 3;
1217 :
1218 : out:
1219 : /* keep avg > 0 to guarantee that tot > 0 if there are dirty wbs */
1220 0 : avg = max(avg, 1LU);
1221 0 : if (wb_has_dirty_io(wb)) {
1222 0 : long delta = avg - wb->avg_write_bandwidth;
1223 0 : WARN_ON_ONCE(atomic_long_add_return(delta,
1224 : &wb->bdi->tot_write_bandwidth) <= 0);
1225 : }
1226 0 : wb->write_bandwidth = bw;
1227 0 : WRITE_ONCE(wb->avg_write_bandwidth, avg);
1228 0 : }
1229 :
1230 : static void update_dirty_limit(struct dirty_throttle_control *dtc)
1231 : {
1232 0 : struct wb_domain *dom = dtc_dom(dtc);
1233 0 : unsigned long thresh = dtc->thresh;
1234 0 : unsigned long limit = dom->dirty_limit;
1235 :
1236 : /*
1237 : * Follow up in one step.
1238 : */
1239 0 : 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 0 : thresh = max(thresh, dtc->dirty);
1250 0 : if (limit > thresh) {
1251 0 : limit -= (limit - thresh) >> 5;
1252 : goto update;
1253 : }
1254 : return;
1255 : update:
1256 0 : dom->dirty_limit = limit;
1257 : }
1258 :
1259 0 : static void domain_update_dirty_limit(struct dirty_throttle_control *dtc,
1260 : unsigned long now)
1261 : {
1262 0 : struct wb_domain *dom = dtc_dom(dtc);
1263 :
1264 : /*
1265 : * check locklessly first to optimize away locking for the most time
1266 : */
1267 0 : if (time_before(now, dom->dirty_limit_tstamp + BANDWIDTH_INTERVAL))
1268 : return;
1269 :
1270 0 : spin_lock(&dom->lock);
1271 0 : if (time_after_eq(now, dom->dirty_limit_tstamp + BANDWIDTH_INTERVAL)) {
1272 0 : update_dirty_limit(dtc);
1273 0 : dom->dirty_limit_tstamp = now;
1274 : }
1275 0 : 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 0 : static void wb_update_dirty_ratelimit(struct dirty_throttle_control *dtc,
1285 : unsigned long dirtied,
1286 : unsigned long elapsed)
1287 : {
1288 0 : struct bdi_writeback *wb = dtc->wb;
1289 0 : unsigned long dirty = dtc->dirty;
1290 0 : unsigned long freerun = dirty_freerun_ceiling(dtc->thresh, dtc->bg_thresh);
1291 0 : unsigned long limit = hard_dirty_limit(dtc_dom(dtc), dtc->thresh);
1292 0 : unsigned long setpoint = (freerun + limit) / 2;
1293 0 : unsigned long write_bw = wb->avg_write_bandwidth;
1294 0 : 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 0 : 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 0 : task_ratelimit = (u64)dirty_ratelimit *
1312 0 : dtc->pos_ratio >> RATELIMIT_CALC_SHIFT;
1313 0 : 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 0 : 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 0 : if (unlikely(balanced_dirty_ratelimit > write_bw))
1351 0 : 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 0 : 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 0 : if (unlikely(wb->bdi->capabilities & BDI_CAP_STRICTLIMIT)) {
1401 0 : dirty = dtc->wb_dirty;
1402 0 : if (dtc->wb_dirty < 8)
1403 0 : setpoint = dtc->wb_dirty + 1;
1404 : else
1405 0 : setpoint = (dtc->wb_thresh + dtc->wb_bg_thresh) / 2;
1406 : }
1407 :
1408 0 : if (dirty < setpoint) {
1409 0 : x = min3(wb->balanced_dirty_ratelimit,
1410 : balanced_dirty_ratelimit, task_ratelimit);
1411 0 : if (dirty_ratelimit < x)
1412 0 : step = x - dirty_ratelimit;
1413 : } else {
1414 0 : x = max3(wb->balanced_dirty_ratelimit,
1415 : balanced_dirty_ratelimit, task_ratelimit);
1416 0 : if (dirty_ratelimit > x)
1417 0 : 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 0 : shift = dirty_ratelimit / (2 * step + 1);
1426 0 : if (shift < BITS_PER_LONG)
1427 0 : step = DIV_ROUND_UP(step >> shift, 8);
1428 : else
1429 : step = 0;
1430 :
1431 0 : if (dirty_ratelimit < balanced_dirty_ratelimit)
1432 0 : dirty_ratelimit += step;
1433 : else
1434 0 : dirty_ratelimit -= step;
1435 :
1436 0 : WRITE_ONCE(wb->dirty_ratelimit, max(dirty_ratelimit, 1UL));
1437 0 : wb->balanced_dirty_ratelimit = balanced_dirty_ratelimit;
1438 :
1439 0 : trace_bdi_dirty_ratelimit(wb, dirty_rate, task_ratelimit);
1440 0 : }
1441 :
1442 0 : static void __wb_update_bandwidth(struct dirty_throttle_control *gdtc,
1443 : struct dirty_throttle_control *mdtc,
1444 : bool update_ratelimit)
1445 : {
1446 0 : struct bdi_writeback *wb = gdtc->wb;
1447 0 : unsigned long now = jiffies;
1448 : unsigned long elapsed;
1449 : unsigned long dirtied;
1450 : unsigned long written;
1451 :
1452 0 : 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 0 : elapsed = max(now - wb->bw_time_stamp, 1UL);
1461 0 : dirtied = percpu_counter_read(&wb->stat[WB_DIRTIED]);
1462 0 : written = percpu_counter_read(&wb->stat[WB_WRITTEN]);
1463 :
1464 0 : if (update_ratelimit) {
1465 0 : domain_update_dirty_limit(gdtc, now);
1466 0 : 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 0 : wb_update_write_bandwidth(wb, elapsed, written);
1478 :
1479 0 : wb->dirtied_stamp = dirtied;
1480 0 : wb->written_stamp = written;
1481 0 : WRITE_ONCE(wb->bw_time_stamp, now);
1482 0 : spin_unlock(&wb->list_lock);
1483 0 : }
1484 :
1485 0 : void wb_update_bandwidth(struct bdi_writeback *wb)
1486 : {
1487 0 : struct dirty_throttle_control gdtc = { GDTC_INIT(wb) };
1488 :
1489 0 : __wb_update_bandwidth(&gdtc, NULL, false);
1490 0 : }
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 0 : unsigned long now = jiffies;
1498 0 : unsigned long elapsed = now - READ_ONCE(wb->bw_time_stamp);
1499 :
1500 0 : if (elapsed > WB_BANDWIDTH_IDLE_JIF &&
1501 0 : !atomic_read(&wb->writeback_inodes)) {
1502 0 : spin_lock(&wb->list_lock);
1503 0 : wb->dirtied_stamp = wb_stat(wb, WB_DIRTIED);
1504 0 : wb->written_stamp = wb_stat(wb, WB_WRITTEN);
1505 0 : WRITE_ONCE(wb->bw_time_stamp, now);
1506 0 : 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 0 : if (thresh > dirty)
1522 0 : 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 0 : 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 0 : t = wb_dirty / (1 + bw / roundup_pow_of_two(1 + HZ / 8));
1541 0 : t++;
1542 :
1543 0 : return min_t(unsigned long, t, MAX_PAUSE);
1544 : }
1545 :
1546 0 : 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 0 : long hi = ilog2(READ_ONCE(wb->avg_write_bandwidth));
1553 0 : 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 0 : 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 0 : if (hi > lo)
1568 0 : 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 0 : t = min(t, 1 + max_pause / 2);
1589 0 : 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 0 : if (pages < DIRTY_POLL_THRESH) {
1600 0 : t = max_pause;
1601 0 : pages = dirty_ratelimit * t / roundup_pow_of_two(HZ);
1602 0 : if (pages > DIRTY_POLL_THRESH) {
1603 0 : pages = DIRTY_POLL_THRESH;
1604 0 : t = HZ * DIRTY_POLL_THRESH / dirty_ratelimit;
1605 : }
1606 : }
1607 :
1608 0 : pause = HZ * pages / (task_ratelimit + 1);
1609 0 : if (pause > max_pause) {
1610 0 : t = max_pause;
1611 0 : pages = task_ratelimit * t / roundup_pow_of_two(HZ);
1612 : }
1613 :
1614 0 : *nr_dirtied_pause = pages;
1615 : /*
1616 : * The minimal pause time will normally be half the target pause time.
1617 : */
1618 0 : return pages >= DIRTY_POLL_THRESH ? 1 + t / 2 : t;
1619 : }
1620 :
1621 0 : static inline void wb_dirty_limits(struct dirty_throttle_control *dtc)
1622 : {
1623 0 : 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 0 : dtc->wb_thresh = __wb_calc_thresh(dtc);
1640 0 : dtc->wb_bg_thresh = dtc->thresh ?
1641 0 : 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 0 : if (dtc->wb_thresh < 2 * wb_stat_error()) {
1654 0 : wb_reclaimable = wb_stat_sum(wb, WB_RECLAIMABLE);
1655 0 : dtc->wb_dirty = wb_reclaimable + wb_stat_sum(wb, WB_WRITEBACK);
1656 : } else {
1657 0 : wb_reclaimable = wb_stat(wb, WB_RECLAIMABLE);
1658 0 : dtc->wb_dirty = wb_reclaimable + wb_stat(wb, WB_WRITEBACK);
1659 : }
1660 0 : }
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 0 : static int balance_dirty_pages(struct bdi_writeback *wb,
1670 : unsigned long pages_dirtied, unsigned int flags)
1671 : {
1672 0 : struct dirty_throttle_control gdtc_stor = { GDTC_INIT(wb) };
1673 : struct dirty_throttle_control mdtc_stor = { MDTC_INIT(wb, &gdtc_stor) };
1674 0 : struct dirty_throttle_control * const gdtc = &gdtc_stor;
1675 0 : 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 0 : bool dirty_exceeded = false;
1685 : unsigned long task_ratelimit;
1686 : unsigned long dirty_ratelimit;
1687 0 : struct backing_dev_info *bdi = wb->bdi;
1688 0 : bool strictlimit = bdi->capabilities & BDI_CAP_STRICTLIMIT;
1689 0 : unsigned long start_time = jiffies;
1690 0 : int ret = 0;
1691 :
1692 : for (;;) {
1693 0 : unsigned long now = jiffies;
1694 : unsigned long dirty, thresh, bg_thresh;
1695 0 : unsigned long m_dirty = 0; /* stop bogus uninit warnings */
1696 0 : unsigned long m_thresh = 0;
1697 0 : unsigned long m_bg_thresh = 0;
1698 :
1699 0 : nr_reclaimable = global_node_page_state(NR_FILE_DIRTY);
1700 0 : gdtc->avail = global_dirtyable_memory();
1701 0 : gdtc->dirty = nr_reclaimable + global_node_page_state(NR_WRITEBACK);
1702 :
1703 0 : domain_dirty_limits(gdtc);
1704 :
1705 0 : if (unlikely(strictlimit)) {
1706 0 : wb_dirty_limits(gdtc);
1707 :
1708 0 : dirty = gdtc->wb_dirty;
1709 0 : thresh = gdtc->wb_thresh;
1710 0 : bg_thresh = gdtc->wb_bg_thresh;
1711 : } else {
1712 0 : dirty = gdtc->dirty;
1713 0 : thresh = gdtc->thresh;
1714 0 : 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 0 : if (!laptop_mode && nr_reclaimable > gdtc->bg_thresh &&
1753 0 : !writeback_in_progress(wb))
1754 0 : 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 0 : 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 0 : intv = dirty_poll_interval(dirty, thresh);
1776 0 : m_intv = ULONG_MAX;
1777 :
1778 0 : current->dirty_paused_when = now;
1779 0 : current->nr_dirtied = 0;
1780 : if (mdtc)
1781 : m_intv = dirty_poll_interval(m_dirty, m_thresh);
1782 0 : current->nr_dirtied_pause = min(intv, m_intv);
1783 0 : break;
1784 : }
1785 :
1786 : /* Start writeback even when in laptop mode */
1787 0 : if (unlikely(!writeback_in_progress(wb)))
1788 0 : wb_start_background_writeback(wb);
1789 :
1790 0 : mem_cgroup_flush_foreign(wb);
1791 :
1792 : /*
1793 : * Calculate global domain's pos_ratio and select the
1794 : * global dtc by default.
1795 : */
1796 0 : if (!strictlimit) {
1797 0 : wb_dirty_limits(gdtc);
1798 :
1799 0 : if ((current->flags & PF_LOCAL_THROTTLE) &&
1800 0 : gdtc->wb_dirty <
1801 0 : 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 0 : dirty_exceeded = (gdtc->wb_dirty > gdtc->wb_thresh) &&
1811 0 : ((gdtc->dirty > gdtc->thresh) || strictlimit);
1812 :
1813 0 : wb_position_ratio(gdtc);
1814 0 : 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 0 : if (dirty_exceeded != wb->dirty_exceeded)
1846 0 : wb->dirty_exceeded = dirty_exceeded;
1847 :
1848 0 : if (time_is_before_jiffies(READ_ONCE(wb->bw_time_stamp) +
1849 : BANDWIDTH_INTERVAL))
1850 0 : __wb_update_bandwidth(gdtc, mdtc, true);
1851 :
1852 : /* throttle according to the chosen dtc */
1853 0 : dirty_ratelimit = READ_ONCE(wb->dirty_ratelimit);
1854 0 : task_ratelimit = ((u64)dirty_ratelimit * sdtc->pos_ratio) >>
1855 : RATELIMIT_CALC_SHIFT;
1856 0 : max_pause = wb_max_pause(wb, sdtc->wb_dirty);
1857 0 : min_pause = wb_min_pause(wb, max_pause,
1858 : task_ratelimit, dirty_ratelimit,
1859 : &nr_dirtied_pause);
1860 :
1861 0 : if (unlikely(task_ratelimit == 0)) {
1862 : period = max_pause;
1863 : pause = max_pause;
1864 : goto pause;
1865 : }
1866 0 : period = HZ * pages_dirtied / task_ratelimit;
1867 0 : pause = period;
1868 0 : if (current->dirty_paused_when)
1869 0 : 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 0 : if (pause < min_pause) {
1878 0 : 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 0 : min(pause, 0L),
1889 : start_time);
1890 0 : if (pause < -HZ) {
1891 0 : current->dirty_paused_when = now;
1892 0 : current->nr_dirtied = 0;
1893 0 : } else if (period) {
1894 0 : current->dirty_paused_when += period;
1895 0 : current->nr_dirtied = 0;
1896 0 : } else if (current->nr_dirtied_pause <= pages_dirtied)
1897 0 : current->nr_dirtied_pause += pages_dirtied;
1898 : break;
1899 : }
1900 0 : if (unlikely(pause > max_pause)) {
1901 : /* for occasional dropped task_ratelimit */
1902 0 : now += min(pause - max_pause, max_pause);
1903 0 : pause = max_pause;
1904 : }
1905 :
1906 : pause:
1907 0 : 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 0 : if (flags & BDP_ASYNC) {
1920 : ret = -EAGAIN;
1921 : break;
1922 : }
1923 0 : __set_current_state(TASK_KILLABLE);
1924 0 : wb->dirty_sleep = now;
1925 0 : io_schedule_timeout(pause);
1926 :
1927 0 : current->dirty_paused_when = now + pause;
1928 0 : current->nr_dirtied = 0;
1929 0 : 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 0 : 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 0 : if (sdtc->wb_dirty <= wb_stat_error())
1949 : break;
1950 :
1951 0 : if (fatal_signal_pending(current))
1952 : break;
1953 : }
1954 0 : 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 0 : int balance_dirty_pages_ratelimited_flags(struct address_space *mapping,
1993 : unsigned int flags)
1994 : {
1995 0 : struct inode *inode = mapping->host;
1996 0 : struct backing_dev_info *bdi = inode_to_bdi(inode);
1997 0 : struct bdi_writeback *wb = NULL;
1998 : int ratelimit;
1999 0 : int ret = 0;
2000 : int *p;
2001 :
2002 0 : if (!(bdi->capabilities & BDI_CAP_WRITEBACK))
2003 : return ret;
2004 :
2005 0 : if (inode_cgwb_enabled(inode))
2006 : wb = wb_get_create_current(bdi, GFP_KERNEL);
2007 : if (!wb)
2008 0 : wb = &bdi->wb;
2009 :
2010 0 : ratelimit = current->nr_dirtied_pause;
2011 0 : if (wb->dirty_exceeded)
2012 0 : ratelimit = min(ratelimit, 32 >> (PAGE_SHIFT - 10));
2013 :
2014 0 : 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 0 : p = this_cpu_ptr(&bdp_ratelimits);
2022 0 : if (unlikely(current->nr_dirtied >= ratelimit))
2023 0 : *p = 0;
2024 0 : else if (unlikely(*p >= ratelimit_pages)) {
2025 0 : *p = 0;
2026 0 : 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 0 : p = this_cpu_ptr(&dirty_throttle_leaks);
2034 0 : if (*p > 0 && current->nr_dirtied < ratelimit) {
2035 : unsigned long nr_pages_dirtied;
2036 0 : nr_pages_dirtied = min(*p, ratelimit - current->nr_dirtied);
2037 0 : *p -= nr_pages_dirtied;
2038 0 : current->nr_dirtied += nr_pages_dirtied;
2039 : }
2040 0 : preempt_enable();
2041 :
2042 0 : if (unlikely(current->nr_dirtied >= ratelimit))
2043 0 : 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 0 : void balance_dirty_pages_ratelimited(struct address_space *mapping)
2063 : {
2064 0 : balance_dirty_pages_ratelimited_flags(mapping, 0);
2065 0 : }
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 0 : bool wb_over_bg_thresh(struct bdi_writeback *wb)
2078 : {
2079 0 : struct dirty_throttle_control gdtc_stor = { GDTC_INIT(wb) };
2080 : struct dirty_throttle_control mdtc_stor = { MDTC_INIT(wb, &gdtc_stor) };
2081 0 : struct dirty_throttle_control * const gdtc = &gdtc_stor;
2082 0 : 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 0 : gdtc->avail = global_dirtyable_memory();
2092 0 : gdtc->dirty = global_node_page_state(NR_FILE_DIRTY);
2093 0 : domain_dirty_limits(gdtc);
2094 :
2095 0 : if (gdtc->dirty > gdtc->bg_thresh)
2096 : return true;
2097 :
2098 0 : thresh = wb_calc_thresh(gdtc->wb, gdtc->bg_thresh);
2099 0 : if (thresh < 2 * wb_stat_error())
2100 0 : reclaimable = wb_stat_sum(wb, WB_RECLAIMABLE);
2101 : else
2102 0 : reclaimable = wb_stat(wb, WB_RECLAIMABLE);
2103 :
2104 0 : 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 0 : static int dirty_writeback_centisecs_handler(struct ctl_table *table, int write,
2136 : void *buffer, size_t *length, loff_t *ppos)
2137 : {
2138 0 : unsigned int old_interval = dirty_writeback_interval;
2139 : int ret;
2140 :
2141 0 : 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 0 : if (!ret && write && dirty_writeback_interval &&
2151 : dirty_writeback_interval != old_interval)
2152 0 : wakeup_flusher_threads(WB_REASON_PERIODIC);
2153 :
2154 0 : return ret;
2155 : }
2156 : #endif
2157 :
2158 0 : void laptop_mode_timer_fn(struct timer_list *t)
2159 : {
2160 0 : struct backing_dev_info *backing_dev_info =
2161 0 : from_timer(backing_dev_info, t, laptop_mode_wb_timer);
2162 :
2163 0 : wakeup_flusher_threads_bdi(backing_dev_info, WB_REASON_LAPTOP_TIMER);
2164 0 : }
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 0 : void laptop_io_completion(struct backing_dev_info *info)
2172 : {
2173 0 : mod_timer(&info->laptop_mode_wb_timer, jiffies + laptop_mode);
2174 0 : }
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 0 : void laptop_sync_completion(void)
2182 : {
2183 : struct backing_dev_info *bdi;
2184 :
2185 : rcu_read_lock();
2186 :
2187 0 : list_for_each_entry_rcu(bdi, &bdi_list, bdi_list)
2188 0 : del_timer(&bdi->laptop_mode_wb_timer);
2189 :
2190 : rcu_read_unlock();
2191 0 : }
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 1 : void writeback_set_ratelimit(void)
2203 : {
2204 1 : struct wb_domain *dom = &global_wb_domain;
2205 : unsigned long background_thresh;
2206 : unsigned long dirty_thresh;
2207 :
2208 1 : global_dirty_limits(&background_thresh, &dirty_thresh);
2209 1 : dom->dirty_limit = dirty_thresh;
2210 1 : ratelimit_pages = dirty_thresh / (num_online_cpus() * 32);
2211 1 : if (ratelimit_pages < 16)
2212 0 : ratelimit_pages = 16;
2213 1 : }
2214 :
2215 1 : static int page_writeback_cpu_online(unsigned int cpu)
2216 : {
2217 1 : writeback_set_ratelimit();
2218 1 : 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 1 : void __init page_writeback_init(void)
2315 : {
2316 1 : BUG_ON(wb_domain_init(&global_wb_domain, GFP_KERNEL));
2317 :
2318 1 : cpuhp_setup_state(CPUHP_AP_ONLINE_DYN, "mm/writeback:online",
2319 : page_writeback_cpu_online, NULL);
2320 1 : cpuhp_setup_state(CPUHP_MM_WRITEBACK_DEAD, "mm/writeback:dead", NULL,
2321 : page_writeback_cpu_online);
2322 : #ifdef CONFIG_SYSCTL
2323 1 : register_sysctl_init("vm", vm_page_writeback_sysctls);
2324 : #endif
2325 1 : }
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 0 : void tag_pages_for_writeback(struct address_space *mapping,
2342 : pgoff_t start, pgoff_t end)
2343 : {
2344 0 : XA_STATE(xas, &mapping->i_pages, start);
2345 0 : unsigned int tagged = 0;
2346 : void *page;
2347 :
2348 0 : xas_lock_irq(&xas);
2349 0 : xas_for_each_marked(&xas, page, end, PAGECACHE_TAG_DIRTY) {
2350 0 : xas_set_mark(&xas, PAGECACHE_TAG_TOWRITE);
2351 0 : if (++tagged % XA_CHECK_SCHED)
2352 0 : continue;
2353 :
2354 0 : xas_pause(&xas);
2355 0 : xas_unlock_irq(&xas);
2356 0 : cond_resched();
2357 0 : xas_lock_irq(&xas);
2358 : }
2359 0 : xas_unlock_irq(&xas);
2360 0 : }
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 0 : int write_cache_pages(struct address_space *mapping,
2395 : struct writeback_control *wbc, writepage_t writepage,
2396 : void *data)
2397 : {
2398 0 : int ret = 0;
2399 0 : 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 0 : int range_whole = 0;
2407 : xa_mark_t tag;
2408 :
2409 0 : folio_batch_init(&fbatch);
2410 0 : if (wbc->range_cyclic) {
2411 0 : index = mapping->writeback_index; /* prev offset */
2412 0 : end = -1;
2413 : } else {
2414 0 : index = wbc->range_start >> PAGE_SHIFT;
2415 0 : end = wbc->range_end >> PAGE_SHIFT;
2416 0 : if (wbc->range_start == 0 && wbc->range_end == LLONG_MAX)
2417 0 : range_whole = 1;
2418 : }
2419 0 : if (wbc->sync_mode == WB_SYNC_ALL || wbc->tagged_writepages) {
2420 0 : tag_pages_for_writeback(mapping, index, end);
2421 0 : tag = PAGECACHE_TAG_TOWRITE;
2422 : } else {
2423 : tag = PAGECACHE_TAG_DIRTY;
2424 : }
2425 0 : done_index = index;
2426 0 : while (!done && (index <= end)) {
2427 : int i;
2428 :
2429 0 : nr_folios = filemap_get_folios_tag(mapping, &index, end,
2430 : tag, &fbatch);
2431 :
2432 0 : if (nr_folios == 0)
2433 : break;
2434 :
2435 0 : for (i = 0; i < nr_folios; i++) {
2436 0 : struct folio *folio = fbatch.folios[i];
2437 : unsigned long nr;
2438 :
2439 0 : done_index = folio->index;
2440 :
2441 0 : 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 0 : if (unlikely(folio->mapping != mapping)) {
2452 : continue_unlock:
2453 0 : folio_unlock(folio);
2454 0 : continue;
2455 : }
2456 :
2457 0 : if (!folio_test_dirty(folio)) {
2458 : /* someone wrote it for us */
2459 : goto continue_unlock;
2460 : }
2461 :
2462 0 : if (folio_test_writeback(folio)) {
2463 0 : if (wbc->sync_mode != WB_SYNC_NONE)
2464 0 : folio_wait_writeback(folio);
2465 : else
2466 : goto continue_unlock;
2467 : }
2468 :
2469 0 : BUG_ON(folio_test_writeback(folio));
2470 0 : if (!folio_clear_dirty_for_io(folio))
2471 : goto continue_unlock;
2472 :
2473 0 : trace_wbc_writepage(wbc, inode_to_bdi(mapping->host));
2474 0 : error = writepage(folio, wbc, data);
2475 0 : nr = folio_nr_pages(folio);
2476 0 : 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 0 : if (error == AOP_WRITEPAGE_ACTIVATE) {
2490 0 : folio_unlock(folio);
2491 0 : error = 0;
2492 0 : } else if (wbc->sync_mode != WB_SYNC_ALL) {
2493 0 : ret = error;
2494 0 : done_index = folio->index + nr;
2495 0 : done = 1;
2496 0 : break;
2497 : }
2498 0 : if (!ret)
2499 0 : 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 0 : wbc->nr_to_write -= nr;
2509 0 : if (wbc->nr_to_write <= 0 &&
2510 0 : wbc->sync_mode == WB_SYNC_NONE) {
2511 : done = 1;
2512 : break;
2513 : }
2514 : }
2515 0 : folio_batch_release(&fbatch);
2516 0 : 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 0 : if (wbc->range_cyclic && !done)
2525 0 : done_index = 0;
2526 0 : if (wbc->range_cyclic || (range_whole && wbc->nr_to_write > 0))
2527 0 : mapping->writeback_index = done_index;
2528 :
2529 0 : return ret;
2530 : }
2531 : EXPORT_SYMBOL(write_cache_pages);
2532 :
2533 0 : static int writepage_cb(struct folio *folio, struct writeback_control *wbc,
2534 : void *data)
2535 : {
2536 0 : struct address_space *mapping = data;
2537 0 : int ret = mapping->a_ops->writepage(&folio->page, wbc);
2538 0 : mapping_set_error(mapping, ret);
2539 0 : return ret;
2540 : }
2541 :
2542 0 : int do_writepages(struct address_space *mapping, struct writeback_control *wbc)
2543 : {
2544 : int ret;
2545 : struct bdi_writeback *wb;
2546 :
2547 0 : if (wbc->nr_to_write <= 0)
2548 : return 0;
2549 0 : wb = inode_to_wb_wbc(mapping->host, wbc);
2550 : wb_bandwidth_estimate_start(wb);
2551 : while (1) {
2552 0 : if (mapping->a_ops->writepages) {
2553 0 : ret = mapping->a_ops->writepages(mapping, wbc);
2554 0 : } else if (mapping->a_ops->writepage) {
2555 : struct blk_plug plug;
2556 :
2557 0 : blk_start_plug(&plug);
2558 0 : ret = write_cache_pages(mapping, wbc, writepage_cb,
2559 : mapping);
2560 0 : blk_finish_plug(&plug);
2561 : } else {
2562 : /* deal with chardevs and other special files */
2563 : ret = 0;
2564 : }
2565 0 : 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 0 : 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 0 : if (time_is_before_jiffies(READ_ONCE(wb->bw_time_stamp) +
2583 : BANDWIDTH_INTERVAL))
2584 0 : wb_update_bandwidth(wb);
2585 : return ret;
2586 : }
2587 :
2588 : /*
2589 : * For address_spaces which do not use buffers nor write back.
2590 : */
2591 0 : bool noop_dirty_folio(struct address_space *mapping, struct folio *folio)
2592 : {
2593 0 : if (!folio_test_dirty(folio))
2594 0 : 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 0 : static void folio_account_dirtied(struct folio *folio,
2607 : struct address_space *mapping)
2608 : {
2609 0 : struct inode *inode = mapping->host;
2610 :
2611 0 : trace_writeback_dirty_folio(folio, mapping);
2612 :
2613 0 : if (mapping_can_writeback(mapping)) {
2614 : struct bdi_writeback *wb;
2615 0 : long nr = folio_nr_pages(folio);
2616 :
2617 0 : inode_attach_wb(inode, folio);
2618 0 : wb = inode_to_wb(inode);
2619 :
2620 0 : __lruvec_stat_mod_folio(folio, NR_FILE_DIRTY, nr);
2621 0 : __zone_stat_mod_folio(folio, NR_ZONE_WRITE_PENDING, nr);
2622 0 : __node_stat_mod_folio(folio, NR_DIRTIED, nr);
2623 0 : wb_stat_mod(wb, WB_RECLAIMABLE, nr);
2624 0 : wb_stat_mod(wb, WB_DIRTIED, nr);
2625 0 : task_io_account_write(nr * PAGE_SIZE);
2626 0 : current->nr_dirtied += nr;
2627 0 : __this_cpu_add(bdp_ratelimits, nr);
2628 :
2629 0 : mem_cgroup_track_foreign_dirty(folio, wb);
2630 : }
2631 0 : }
2632 :
2633 : /*
2634 : * Helper function for deaccounting dirty page without writeback.
2635 : *
2636 : * Caller must hold folio_memcg_lock().
2637 : */
2638 0 : void folio_account_cleaned(struct folio *folio, struct bdi_writeback *wb)
2639 : {
2640 0 : long nr = folio_nr_pages(folio);
2641 :
2642 0 : lruvec_stat_mod_folio(folio, NR_FILE_DIRTY, -nr);
2643 0 : zone_stat_mod_folio(folio, NR_ZONE_WRITE_PENDING, -nr);
2644 0 : wb_stat_mod(wb, WB_RECLAIMABLE, -nr);
2645 0 : task_io_account_cancelled_write(nr * PAGE_SIZE);
2646 0 : }
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 0 : void __folio_mark_dirty(struct folio *folio, struct address_space *mapping,
2662 : int warn)
2663 : {
2664 : unsigned long flags;
2665 :
2666 0 : xa_lock_irqsave(&mapping->i_pages, flags);
2667 0 : if (folio->mapping) { /* Race with truncate? */
2668 0 : WARN_ON_ONCE(warn && !folio_test_uptodate(folio));
2669 0 : folio_account_dirtied(folio, mapping);
2670 0 : __xa_set_mark(&mapping->i_pages, folio_index(folio),
2671 : PAGECACHE_TAG_DIRTY);
2672 : }
2673 0 : xa_unlock_irqrestore(&mapping->i_pages, flags);
2674 0 : }
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 set_page_dirty 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 0 : bool filemap_dirty_folio(struct address_space *mapping, struct folio *folio)
2696 : {
2697 0 : folio_memcg_lock(folio);
2698 0 : if (folio_test_set_dirty(folio)) {
2699 : folio_memcg_unlock(folio);
2700 : return false;
2701 : }
2702 :
2703 0 : __folio_mark_dirty(folio, mapping, !folio_test_private(folio));
2704 0 : folio_memcg_unlock(folio);
2705 :
2706 0 : if (mapping->host) {
2707 : /* !PageAnon && !swapper_space */
2708 0 : __mark_inode_dirty(mapping->host, I_DIRTY_PAGES);
2709 : }
2710 : return true;
2711 : }
2712 : EXPORT_SYMBOL(filemap_dirty_folio);
2713 :
2714 : /**
2715 : * folio_account_redirty - Manually account for redirtying a page.
2716 : * @folio: The folio which is being redirtied.
2717 : *
2718 : * Most filesystems should call folio_redirty_for_writepage() instead
2719 : * of this fuction. If your filesystem is doing writeback outside the
2720 : * context of a writeback_control(), it can call this when redirtying
2721 : * a folio, to de-account the dirty counters (NR_DIRTIED, WB_DIRTIED,
2722 : * tsk->nr_dirtied), so that they match the written counters (NR_WRITTEN,
2723 : * WB_WRITTEN) in long term. The mismatches will lead to systematic errors
2724 : * in balanced_dirty_ratelimit and the dirty pages position control.
2725 : */
2726 0 : void folio_account_redirty(struct folio *folio)
2727 : {
2728 0 : struct address_space *mapping = folio->mapping;
2729 :
2730 0 : if (mapping && mapping_can_writeback(mapping)) {
2731 0 : struct inode *inode = mapping->host;
2732 : struct bdi_writeback *wb;
2733 0 : struct wb_lock_cookie cookie = {};
2734 0 : long nr = folio_nr_pages(folio);
2735 :
2736 0 : wb = unlocked_inode_to_wb_begin(inode, &cookie);
2737 0 : current->nr_dirtied -= nr;
2738 0 : node_stat_mod_folio(folio, NR_DIRTIED, -nr);
2739 0 : wb_stat_mod(wb, WB_DIRTIED, -nr);
2740 0 : unlocked_inode_to_wb_end(inode, &cookie);
2741 : }
2742 0 : }
2743 : EXPORT_SYMBOL(folio_account_redirty);
2744 :
2745 : /**
2746 : * folio_redirty_for_writepage - Decline to write a dirty folio.
2747 : * @wbc: The writeback control.
2748 : * @folio: The folio.
2749 : *
2750 : * When a writepage implementation decides that it doesn't want to write
2751 : * @folio for some reason, it should call this function, unlock @folio and
2752 : * return 0.
2753 : *
2754 : * Return: True if we redirtied the folio. False if someone else dirtied
2755 : * it first.
2756 : */
2757 0 : bool folio_redirty_for_writepage(struct writeback_control *wbc,
2758 : struct folio *folio)
2759 : {
2760 : bool ret;
2761 0 : long nr = folio_nr_pages(folio);
2762 :
2763 0 : wbc->pages_skipped += nr;
2764 0 : ret = filemap_dirty_folio(folio->mapping, folio);
2765 0 : folio_account_redirty(folio);
2766 :
2767 0 : return ret;
2768 : }
2769 : EXPORT_SYMBOL(folio_redirty_for_writepage);
2770 :
2771 : /**
2772 : * folio_mark_dirty - Mark a folio as being modified.
2773 : * @folio: The folio.
2774 : *
2775 : * The folio may not be truncated while this function is running.
2776 : * Holding the folio lock is sufficient to prevent truncation, but some
2777 : * callers cannot acquire a sleeping lock. These callers instead hold
2778 : * the page table lock for a page table which contains at least one page
2779 : * in this folio. Truncation will block on the page table lock as it
2780 : * unmaps pages before removing the folio from its mapping.
2781 : *
2782 : * Return: True if the folio was newly dirtied, false if it was already dirty.
2783 : */
2784 0 : bool folio_mark_dirty(struct folio *folio)
2785 : {
2786 0 : struct address_space *mapping = folio_mapping(folio);
2787 :
2788 0 : if (likely(mapping)) {
2789 : /*
2790 : * readahead/folio_deactivate could remain
2791 : * PG_readahead/PG_reclaim due to race with folio_end_writeback
2792 : * About readahead, if the folio is written, the flags would be
2793 : * reset. So no problem.
2794 : * About folio_deactivate, if the folio is redirtied,
2795 : * the flag will be reset. So no problem. but if the
2796 : * folio is used by readahead it will confuse readahead
2797 : * and make it restart the size rampup process. But it's
2798 : * a trivial problem.
2799 : */
2800 0 : if (folio_test_reclaim(folio))
2801 : folio_clear_reclaim(folio);
2802 0 : return mapping->a_ops->dirty_folio(mapping, folio);
2803 : }
2804 :
2805 : return noop_dirty_folio(mapping, folio);
2806 : }
2807 : EXPORT_SYMBOL(folio_mark_dirty);
2808 :
2809 : /*
2810 : * set_page_dirty() is racy if the caller has no reference against
2811 : * page->mapping->host, and if the page is unlocked. This is because another
2812 : * CPU could truncate the page off the mapping and then free the mapping.
2813 : *
2814 : * Usually, the page _is_ locked, or the caller is a user-space process which
2815 : * holds a reference on the inode by having an open file.
2816 : *
2817 : * In other cases, the page should be locked before running set_page_dirty().
2818 : */
2819 0 : int set_page_dirty_lock(struct page *page)
2820 : {
2821 : int ret;
2822 :
2823 0 : lock_page(page);
2824 0 : ret = set_page_dirty(page);
2825 0 : unlock_page(page);
2826 0 : return ret;
2827 : }
2828 : EXPORT_SYMBOL(set_page_dirty_lock);
2829 :
2830 : /*
2831 : * This cancels just the dirty bit on the kernel page itself, it does NOT
2832 : * actually remove dirty bits on any mmap's that may be around. It also
2833 : * leaves the page tagged dirty, so any sync activity will still find it on
2834 : * the dirty lists, and in particular, clear_page_dirty_for_io() will still
2835 : * look at the dirty bits in the VM.
2836 : *
2837 : * Doing this should *normally* only ever be done when a page is truncated,
2838 : * and is not actually mapped anywhere at all. However, fs/buffer.c does
2839 : * this when it notices that somebody has cleaned out all the buffers on a
2840 : * page without actually doing it through the VM. Can you say "ext3 is
2841 : * horribly ugly"? Thought you could.
2842 : */
2843 0 : void __folio_cancel_dirty(struct folio *folio)
2844 : {
2845 0 : struct address_space *mapping = folio_mapping(folio);
2846 :
2847 0 : if (mapping_can_writeback(mapping)) {
2848 0 : struct inode *inode = mapping->host;
2849 : struct bdi_writeback *wb;
2850 : struct wb_lock_cookie cookie = {};
2851 :
2852 0 : folio_memcg_lock(folio);
2853 0 : wb = unlocked_inode_to_wb_begin(inode, &cookie);
2854 :
2855 0 : if (folio_test_clear_dirty(folio))
2856 0 : folio_account_cleaned(folio, wb);
2857 :
2858 0 : unlocked_inode_to_wb_end(inode, &cookie);
2859 0 : folio_memcg_unlock(folio);
2860 : } else {
2861 : folio_clear_dirty(folio);
2862 : }
2863 0 : }
2864 : EXPORT_SYMBOL(__folio_cancel_dirty);
2865 :
2866 : /*
2867 : * Clear a folio's dirty flag, while caring for dirty memory accounting.
2868 : * Returns true if the folio was previously dirty.
2869 : *
2870 : * This is for preparing to put the folio under writeout. We leave
2871 : * the folio tagged as dirty in the xarray so that a concurrent
2872 : * write-for-sync can discover it via a PAGECACHE_TAG_DIRTY walk.
2873 : * The ->writepage implementation will run either folio_start_writeback()
2874 : * or folio_mark_dirty(), at which stage we bring the folio's dirty flag
2875 : * and xarray dirty tag back into sync.
2876 : *
2877 : * This incoherency between the folio's dirty flag and xarray tag is
2878 : * unfortunate, but it only exists while the folio is locked.
2879 : */
2880 0 : bool folio_clear_dirty_for_io(struct folio *folio)
2881 : {
2882 0 : struct address_space *mapping = folio_mapping(folio);
2883 0 : bool ret = false;
2884 :
2885 : VM_BUG_ON_FOLIO(!folio_test_locked(folio), folio);
2886 :
2887 0 : if (mapping && mapping_can_writeback(mapping)) {
2888 0 : struct inode *inode = mapping->host;
2889 : struct bdi_writeback *wb;
2890 : struct wb_lock_cookie cookie = {};
2891 :
2892 : /*
2893 : * Yes, Virginia, this is indeed insane.
2894 : *
2895 : * We use this sequence to make sure that
2896 : * (a) we account for dirty stats properly
2897 : * (b) we tell the low-level filesystem to
2898 : * mark the whole folio dirty if it was
2899 : * dirty in a pagetable. Only to then
2900 : * (c) clean the folio again and return 1 to
2901 : * cause the writeback.
2902 : *
2903 : * This way we avoid all nasty races with the
2904 : * dirty bit in multiple places and clearing
2905 : * them concurrently from different threads.
2906 : *
2907 : * Note! Normally the "folio_mark_dirty(folio)"
2908 : * has no effect on the actual dirty bit - since
2909 : * that will already usually be set. But we
2910 : * need the side effects, and it can help us
2911 : * avoid races.
2912 : *
2913 : * We basically use the folio "master dirty bit"
2914 : * as a serialization point for all the different
2915 : * threads doing their things.
2916 : */
2917 0 : if (folio_mkclean(folio))
2918 0 : folio_mark_dirty(folio);
2919 : /*
2920 : * We carefully synchronise fault handlers against
2921 : * installing a dirty pte and marking the folio dirty
2922 : * at this point. We do this by having them hold the
2923 : * page lock while dirtying the folio, and folios are
2924 : * always locked coming in here, so we get the desired
2925 : * exclusion.
2926 : */
2927 0 : wb = unlocked_inode_to_wb_begin(inode, &cookie);
2928 0 : if (folio_test_clear_dirty(folio)) {
2929 0 : long nr = folio_nr_pages(folio);
2930 0 : lruvec_stat_mod_folio(folio, NR_FILE_DIRTY, -nr);
2931 0 : zone_stat_mod_folio(folio, NR_ZONE_WRITE_PENDING, -nr);
2932 0 : wb_stat_mod(wb, WB_RECLAIMABLE, -nr);
2933 0 : ret = true;
2934 : }
2935 0 : unlocked_inode_to_wb_end(inode, &cookie);
2936 : return ret;
2937 : }
2938 0 : return folio_test_clear_dirty(folio);
2939 : }
2940 : EXPORT_SYMBOL(folio_clear_dirty_for_io);
2941 :
2942 : static void wb_inode_writeback_start(struct bdi_writeback *wb)
2943 : {
2944 0 : atomic_inc(&wb->writeback_inodes);
2945 : }
2946 :
2947 0 : static void wb_inode_writeback_end(struct bdi_writeback *wb)
2948 : {
2949 : unsigned long flags;
2950 0 : atomic_dec(&wb->writeback_inodes);
2951 : /*
2952 : * Make sure estimate of writeback throughput gets updated after
2953 : * writeback completed. We delay the update by BANDWIDTH_INTERVAL
2954 : * (which is the interval other bandwidth updates use for batching) so
2955 : * that if multiple inodes end writeback at a similar time, they get
2956 : * batched into one bandwidth update.
2957 : */
2958 0 : spin_lock_irqsave(&wb->work_lock, flags);
2959 0 : if (test_bit(WB_registered, &wb->state))
2960 0 : queue_delayed_work(bdi_wq, &wb->bw_dwork, BANDWIDTH_INTERVAL);
2961 0 : spin_unlock_irqrestore(&wb->work_lock, flags);
2962 0 : }
2963 :
2964 0 : bool __folio_end_writeback(struct folio *folio)
2965 : {
2966 0 : long nr = folio_nr_pages(folio);
2967 0 : struct address_space *mapping = folio_mapping(folio);
2968 : bool ret;
2969 :
2970 0 : folio_memcg_lock(folio);
2971 0 : if (mapping && mapping_use_writeback_tags(mapping)) {
2972 0 : struct inode *inode = mapping->host;
2973 0 : struct backing_dev_info *bdi = inode_to_bdi(inode);
2974 : unsigned long flags;
2975 :
2976 0 : xa_lock_irqsave(&mapping->i_pages, flags);
2977 0 : ret = folio_test_clear_writeback(folio);
2978 0 : if (ret) {
2979 0 : __xa_clear_mark(&mapping->i_pages, folio_index(folio),
2980 : PAGECACHE_TAG_WRITEBACK);
2981 0 : if (bdi->capabilities & BDI_CAP_WRITEBACK_ACCT) {
2982 0 : struct bdi_writeback *wb = inode_to_wb(inode);
2983 :
2984 0 : wb_stat_mod(wb, WB_WRITEBACK, -nr);
2985 0 : __wb_writeout_add(wb, nr);
2986 0 : if (!mapping_tagged(mapping,
2987 : PAGECACHE_TAG_WRITEBACK))
2988 0 : wb_inode_writeback_end(wb);
2989 : }
2990 : }
2991 :
2992 0 : if (mapping->host && !mapping_tagged(mapping,
2993 : PAGECACHE_TAG_WRITEBACK))
2994 0 : sb_clear_inode_writeback(mapping->host);
2995 :
2996 0 : xa_unlock_irqrestore(&mapping->i_pages, flags);
2997 : } else {
2998 0 : ret = folio_test_clear_writeback(folio);
2999 : }
3000 0 : if (ret) {
3001 0 : lruvec_stat_mod_folio(folio, NR_WRITEBACK, -nr);
3002 0 : zone_stat_mod_folio(folio, NR_ZONE_WRITE_PENDING, -nr);
3003 0 : node_stat_mod_folio(folio, NR_WRITTEN, nr);
3004 : }
3005 0 : folio_memcg_unlock(folio);
3006 0 : return ret;
3007 : }
3008 :
3009 0 : bool __folio_start_writeback(struct folio *folio, bool keep_write)
3010 : {
3011 0 : long nr = folio_nr_pages(folio);
3012 0 : struct address_space *mapping = folio_mapping(folio);
3013 : bool ret;
3014 : int access_ret;
3015 :
3016 0 : folio_memcg_lock(folio);
3017 0 : if (mapping && mapping_use_writeback_tags(mapping)) {
3018 0 : XA_STATE(xas, &mapping->i_pages, folio_index(folio));
3019 0 : struct inode *inode = mapping->host;
3020 0 : struct backing_dev_info *bdi = inode_to_bdi(inode);
3021 : unsigned long flags;
3022 :
3023 0 : xas_lock_irqsave(&xas, flags);
3024 0 : xas_load(&xas);
3025 0 : ret = folio_test_set_writeback(folio);
3026 0 : if (!ret) {
3027 : bool on_wblist;
3028 :
3029 0 : on_wblist = mapping_tagged(mapping,
3030 : PAGECACHE_TAG_WRITEBACK);
3031 :
3032 0 : xas_set_mark(&xas, PAGECACHE_TAG_WRITEBACK);
3033 0 : if (bdi->capabilities & BDI_CAP_WRITEBACK_ACCT) {
3034 0 : struct bdi_writeback *wb = inode_to_wb(inode);
3035 :
3036 0 : wb_stat_mod(wb, WB_WRITEBACK, nr);
3037 0 : if (!on_wblist)
3038 : wb_inode_writeback_start(wb);
3039 : }
3040 :
3041 : /*
3042 : * We can come through here when swapping
3043 : * anonymous folios, so we don't necessarily
3044 : * have an inode to track for sync.
3045 : */
3046 0 : if (mapping->host && !on_wblist)
3047 0 : sb_mark_inode_writeback(mapping->host);
3048 : }
3049 0 : if (!folio_test_dirty(folio))
3050 0 : xas_clear_mark(&xas, PAGECACHE_TAG_DIRTY);
3051 0 : if (!keep_write)
3052 0 : xas_clear_mark(&xas, PAGECACHE_TAG_TOWRITE);
3053 0 : xas_unlock_irqrestore(&xas, flags);
3054 : } else {
3055 0 : ret = folio_test_set_writeback(folio);
3056 : }
3057 0 : if (!ret) {
3058 0 : lruvec_stat_mod_folio(folio, NR_WRITEBACK, nr);
3059 : zone_stat_mod_folio(folio, NR_ZONE_WRITE_PENDING, nr);
3060 : }
3061 0 : folio_memcg_unlock(folio);
3062 0 : access_ret = arch_make_folio_accessible(folio);
3063 : /*
3064 : * If writeback has been triggered on a page that cannot be made
3065 : * accessible, it is too late to recover here.
3066 : */
3067 : VM_BUG_ON_FOLIO(access_ret != 0, folio);
3068 :
3069 0 : return ret;
3070 : }
3071 : EXPORT_SYMBOL(__folio_start_writeback);
3072 :
3073 : /**
3074 : * folio_wait_writeback - Wait for a folio to finish writeback.
3075 : * @folio: The folio to wait for.
3076 : *
3077 : * If the folio is currently being written back to storage, wait for the
3078 : * I/O to complete.
3079 : *
3080 : * Context: Sleeps. Must be called in process context and with
3081 : * no spinlocks held. Caller should hold a reference on the folio.
3082 : * If the folio is not locked, writeback may start again after writeback
3083 : * has finished.
3084 : */
3085 0 : void folio_wait_writeback(struct folio *folio)
3086 : {
3087 0 : while (folio_test_writeback(folio)) {
3088 0 : trace_folio_wait_writeback(folio, folio_mapping(folio));
3089 0 : folio_wait_bit(folio, PG_writeback);
3090 : }
3091 0 : }
3092 : EXPORT_SYMBOL_GPL(folio_wait_writeback);
3093 :
3094 : /**
3095 : * folio_wait_writeback_killable - Wait for a folio to finish writeback.
3096 : * @folio: The folio to wait for.
3097 : *
3098 : * If the folio is currently being written back to storage, wait for the
3099 : * I/O to complete or a fatal signal to arrive.
3100 : *
3101 : * Context: Sleeps. Must be called in process context and with
3102 : * no spinlocks held. Caller should hold a reference on the folio.
3103 : * If the folio is not locked, writeback may start again after writeback
3104 : * has finished.
3105 : * Return: 0 on success, -EINTR if we get a fatal signal while waiting.
3106 : */
3107 0 : int folio_wait_writeback_killable(struct folio *folio)
3108 : {
3109 0 : while (folio_test_writeback(folio)) {
3110 0 : trace_folio_wait_writeback(folio, folio_mapping(folio));
3111 0 : if (folio_wait_bit_killable(folio, PG_writeback))
3112 : return -EINTR;
3113 : }
3114 :
3115 : return 0;
3116 : }
3117 : EXPORT_SYMBOL_GPL(folio_wait_writeback_killable);
3118 :
3119 : /**
3120 : * folio_wait_stable() - wait for writeback to finish, if necessary.
3121 : * @folio: The folio to wait on.
3122 : *
3123 : * This function determines if the given folio is related to a backing
3124 : * device that requires folio contents to be held stable during writeback.
3125 : * If so, then it will wait for any pending writeback to complete.
3126 : *
3127 : * Context: Sleeps. Must be called in process context and with
3128 : * no spinlocks held. Caller should hold a reference on the folio.
3129 : * If the folio is not locked, writeback may start again after writeback
3130 : * has finished.
3131 : */
3132 0 : void folio_wait_stable(struct folio *folio)
3133 : {
3134 0 : if (folio_inode(folio)->i_sb->s_iflags & SB_I_STABLE_WRITES)
3135 0 : folio_wait_writeback(folio);
3136 0 : }
3137 : EXPORT_SYMBOL_GPL(folio_wait_stable);
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