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1/*
2 * mm/page-writeback.c
3 *
4 * Copyright (C) 2002, Linus Torvalds.
5 * Copyright (C) 2007 Red Hat, Inc., Peter Zijlstra <pzijlstr@redhat.com>
6 *
7 * Contains functions related to writing back dirty pages at the
8 * address_space level.
9 *
10 * 10Apr2002 Andrew Morton
11 * Initial version
12 */
13
14#include <linux/kernel.h>
15#include <linux/export.h>
16#include <linux/spinlock.h>
17#include <linux/fs.h>
18#include <linux/mm.h>
19#include <linux/swap.h>
20#include <linux/slab.h>
21#include <linux/pagemap.h>
22#include <linux/writeback.h>
23#include <linux/init.h>
24#include <linux/backing-dev.h>
25#include <linux/task_io_accounting_ops.h>
26#include <linux/blkdev.h>
27#include <linux/mpage.h>
28#include <linux/rmap.h>
29#include <linux/percpu.h>
30#include <linux/notifier.h>
31#include <linux/smp.h>
32#include <linux/sysctl.h>
33#include <linux/cpu.h>
34#include <linux/syscalls.h>
35#include <linux/buffer_head.h> /* __set_page_dirty_buffers */
36#include <linux/pagevec.h>
37#include <linux/timer.h>
38#include <linux/sched/rt.h>
39#include <linux/mm_inline.h>
40#include <trace/events/writeback.h>
41
42#include "internal.h"
43
44/*
45 * Sleep at most 200ms at a time in balance_dirty_pages().
46 */
47#define MAX_PAUSE max(HZ/5, 1)
48
49/*
50 * Try to keep balance_dirty_pages() call intervals higher than this many pages
51 * by raising pause time to max_pause when falls below it.
52 */
53#define DIRTY_POLL_THRESH (128 >> (PAGE_SHIFT - 10))
54
55/*
56 * Estimate write bandwidth at 200ms intervals.
57 */
58#define BANDWIDTH_INTERVAL max(HZ/5, 1)
59
60#define RATELIMIT_CALC_SHIFT 10
61
62/*
63 * After a CPU has dirtied this many pages, balance_dirty_pages_ratelimited
64 * will look to see if it needs to force writeback or throttling.
65 */
66static long ratelimit_pages = 32;
67
68/* The following parameters are exported via /proc/sys/vm */
69
70/*
71 * Start background writeback (via writeback threads) at this percentage
72 */
73int dirty_background_ratio = 10;
74
75/*
76 * dirty_background_bytes starts at 0 (disabled) so that it is a function of
77 * dirty_background_ratio * the amount of dirtyable memory
78 */
79unsigned long dirty_background_bytes;
80
81/*
82 * free highmem will not be subtracted from the total free memory
83 * for calculating free ratios if vm_highmem_is_dirtyable is true
84 */
85int vm_highmem_is_dirtyable;
86
87/*
88 * The generator of dirty data starts writeback at this percentage
89 */
90int vm_dirty_ratio = 20;
91
92/*
93 * vm_dirty_bytes starts at 0 (disabled) so that it is a function of
94 * vm_dirty_ratio * the amount of dirtyable memory
95 */
96unsigned long vm_dirty_bytes;
97
98/*
99 * The interval between `kupdate'-style writebacks
100 */
101unsigned int dirty_writeback_interval = 5 * 100; /* centiseconds */
102
103EXPORT_SYMBOL_GPL(dirty_writeback_interval);
104
105/*
106 * The longest time for which data is allowed to remain dirty
107 */
108unsigned int dirty_expire_interval = 30 * 100; /* centiseconds */
109
110/*
111 * Flag that makes the machine dump writes/reads and block dirtyings.
112 */
113int block_dump;
114
115/*
116 * Flag that puts the machine in "laptop mode". Doubles as a timeout in jiffies:
117 * a full sync is triggered after this time elapses without any disk activity.
118 */
119int laptop_mode;
120
121EXPORT_SYMBOL(laptop_mode);
122
123/* End of sysctl-exported parameters */
124
125unsigned long global_dirty_limit;
126
127/*
128 * Scale the writeback cache size proportional to the relative writeout speeds.
129 *
130 * We do this by keeping a floating proportion between BDIs, based on page
131 * writeback completions [end_page_writeback()]. Those devices that write out
132 * pages fastest will get the larger share, while the slower will get a smaller
133 * share.
134 *
135 * We use page writeout completions because we are interested in getting rid of
136 * dirty pages. Having them written out is the primary goal.
137 *
138 * We introduce a concept of time, a period over which we measure these events,
139 * because demand can/will vary over time. The length of this period itself is
140 * measured in page writeback completions.
141 *
142 */
143static struct fprop_global writeout_completions;
144
145static void writeout_period(unsigned long t);
146/* Timer for aging of writeout_completions */
147static struct timer_list writeout_period_timer =
148 TIMER_DEFERRED_INITIALIZER(writeout_period, 0, 0);
149static unsigned long writeout_period_time = 0;
150
151/*
152 * Length of period for aging writeout fractions of bdis. This is an
153 * arbitrarily chosen number. The longer the period, the slower fractions will
154 * reflect changes in current writeout rate.
155 */
156#define VM_COMPLETIONS_PERIOD_LEN (3*HZ)
157
158/*
159 * Work out the current dirty-memory clamping and background writeout
160 * thresholds.
161 *
162 * The main aim here is to lower them aggressively if there is a lot of mapped
163 * memory around. To avoid stressing page reclaim with lots of unreclaimable
164 * pages. It is better to clamp down on writers than to start swapping, and
165 * performing lots of scanning.
166 *
167 * We only allow 1/2 of the currently-unmapped memory to be dirtied.
168 *
169 * We don't permit the clamping level to fall below 5% - that is getting rather
170 * excessive.
171 *
172 * We make sure that the background writeout level is below the adjusted
173 * clamping level.
174 */
175
176/*
177 * In a memory zone, there is a certain amount of pages we consider
178 * available for the page cache, which is essentially the number of
179 * free and reclaimable pages, minus some zone reserves to protect
180 * lowmem and the ability to uphold the zone's watermarks without
181 * requiring writeback.
182 *
183 * This number of dirtyable pages is the base value of which the
184 * user-configurable dirty ratio is the effictive number of pages that
185 * are allowed to be actually dirtied. Per individual zone, or
186 * globally by using the sum of dirtyable pages over all zones.
187 *
188 * Because the user is allowed to specify the dirty limit globally as
189 * absolute number of bytes, calculating the per-zone dirty limit can
190 * require translating the configured limit into a percentage of
191 * global dirtyable memory first.
192 */
193
194/**
195 * zone_dirtyable_memory - number of dirtyable pages in a zone
196 * @zone: the zone
197 *
198 * Returns the zone's number of pages potentially available for dirty
199 * page cache. This is the base value for the per-zone dirty limits.
200 */
201static unsigned long zone_dirtyable_memory(struct zone *zone)
202{
203 unsigned long nr_pages;
204
205 nr_pages = zone_page_state(zone, NR_FREE_PAGES);
206 nr_pages -= min(nr_pages, zone->dirty_balance_reserve);
207
208 nr_pages += zone_page_state(zone, NR_INACTIVE_FILE);
209 nr_pages += zone_page_state(zone, NR_ACTIVE_FILE);
210
211 return nr_pages;
212}
213
214static unsigned long highmem_dirtyable_memory(unsigned long total)
215{
216#ifdef CONFIG_HIGHMEM
217 int node;
218 unsigned long x = 0;
219
220 for_each_node_state(node, N_HIGH_MEMORY) {
221 struct zone *z = &NODE_DATA(node)->node_zones[ZONE_HIGHMEM];
222
223 x += zone_dirtyable_memory(z);
224 }
225 /*
226 * Unreclaimable memory (kernel memory or anonymous memory
227 * without swap) can bring down the dirtyable pages below
228 * the zone's dirty balance reserve and the above calculation
229 * will underflow. However we still want to add in nodes
230 * which are below threshold (negative values) to get a more
231 * accurate calculation but make sure that the total never
232 * underflows.
233 */
234 if ((long)x < 0)
235 x = 0;
236
237 /*
238 * Make sure that the number of highmem pages is never larger
239 * than the number of the total dirtyable memory. This can only
240 * occur in very strange VM situations but we want to make sure
241 * that this does not occur.
242 */
243 return min(x, total);
244#else
245 return 0;
246#endif
247}
248
249/**
250 * global_dirtyable_memory - number of globally dirtyable pages
251 *
252 * Returns the global number of pages potentially available for dirty
253 * page cache. This is the base value for the global dirty limits.
254 */
255static unsigned long global_dirtyable_memory(void)
256{
257 unsigned long x;
258
259 x = global_page_state(NR_FREE_PAGES);
260 x -= min(x, dirty_balance_reserve);
261
262 x += global_page_state(NR_INACTIVE_FILE);
263 x += global_page_state(NR_ACTIVE_FILE);
264
265 if (!vm_highmem_is_dirtyable)
266 x -= highmem_dirtyable_memory(x);
267
268 return x + 1; /* Ensure that we never return 0 */
269}
270
271/*
272 * global_dirty_limits - background-writeback and dirty-throttling thresholds
273 *
274 * Calculate the dirty thresholds based on sysctl parameters
275 * - vm.dirty_background_ratio or vm.dirty_background_bytes
276 * - vm.dirty_ratio or vm.dirty_bytes
277 * The dirty limits will be lifted by 1/4 for PF_LESS_THROTTLE (ie. nfsd) and
278 * real-time tasks.
279 */
280void global_dirty_limits(unsigned long *pbackground, unsigned long *pdirty)
281{
282 unsigned long background;
283 unsigned long dirty;
284 unsigned long uninitialized_var(available_memory);
285 struct task_struct *tsk;
286
287 if (!vm_dirty_bytes || !dirty_background_bytes)
288 available_memory = global_dirtyable_memory();
289
290 if (vm_dirty_bytes)
291 dirty = DIV_ROUND_UP(vm_dirty_bytes, PAGE_SIZE);
292 else
293 dirty = (vm_dirty_ratio * available_memory) / 100;
294
295 if (dirty_background_bytes)
296 background = DIV_ROUND_UP(dirty_background_bytes, PAGE_SIZE);
297 else
298 background = (dirty_background_ratio * available_memory) / 100;
299
300 if (background >= dirty)
301 background = dirty / 2;
302 tsk = current;
303 if (tsk->flags & PF_LESS_THROTTLE || rt_task(tsk)) {
304 background += background / 4;
305 dirty += dirty / 4;
306 }
307 *pbackground = background;
308 *pdirty = dirty;
309 trace_global_dirty_state(background, dirty);
310}
311
312/**
313 * zone_dirty_limit - maximum number of dirty pages allowed in a zone
314 * @zone: the zone
315 *
316 * Returns the maximum number of dirty pages allowed in a zone, based
317 * on the zone's dirtyable memory.
318 */
319static unsigned long zone_dirty_limit(struct zone *zone)
320{
321 unsigned long zone_memory = zone_dirtyable_memory(zone);
322 struct task_struct *tsk = current;
323 unsigned long dirty;
324
325 if (vm_dirty_bytes)
326 dirty = DIV_ROUND_UP(vm_dirty_bytes, PAGE_SIZE) *
327 zone_memory / global_dirtyable_memory();
328 else
329 dirty = vm_dirty_ratio * zone_memory / 100;
330
331 if (tsk->flags & PF_LESS_THROTTLE || rt_task(tsk))
332 dirty += dirty / 4;
333
334 return dirty;
335}
336
337/**
338 * zone_dirty_ok - tells whether a zone is within its dirty limits
339 * @zone: the zone to check
340 *
341 * Returns %true when the dirty pages in @zone are within the zone's
342 * dirty limit, %false if the limit is exceeded.
343 */
344bool zone_dirty_ok(struct zone *zone)
345{
346 unsigned long limit = zone_dirty_limit(zone);
347
348 return zone_page_state(zone, NR_FILE_DIRTY) +
349 zone_page_state(zone, NR_UNSTABLE_NFS) +
350 zone_page_state(zone, NR_WRITEBACK) <= limit;
351}
352
353int dirty_background_ratio_handler(struct ctl_table *table, int write,
354 void __user *buffer, size_t *lenp,
355 loff_t *ppos)
356{
357 int ret;
358
359 ret = proc_dointvec_minmax(table, write, buffer, lenp, ppos);
360 if (ret == 0 && write)
361 dirty_background_bytes = 0;
362 return ret;
363}
364
365int dirty_background_bytes_handler(struct ctl_table *table, int write,
366 void __user *buffer, size_t *lenp,
367 loff_t *ppos)
368{
369 int ret;
370
371 ret = proc_doulongvec_minmax(table, write, buffer, lenp, ppos);
372 if (ret == 0 && write)
373 dirty_background_ratio = 0;
374 return ret;
375}
376
377int dirty_ratio_handler(struct ctl_table *table, int write,
378 void __user *buffer, size_t *lenp,
379 loff_t *ppos)
380{
381 int old_ratio = vm_dirty_ratio;
382 int ret;
383
384 ret = proc_dointvec_minmax(table, write, buffer, lenp, ppos);
385 if (ret == 0 && write && vm_dirty_ratio != old_ratio) {
386 writeback_set_ratelimit();
387 vm_dirty_bytes = 0;
388 }
389 return ret;
390}
391
392int dirty_bytes_handler(struct ctl_table *table, int write,
393 void __user *buffer, size_t *lenp,
394 loff_t *ppos)
395{
396 unsigned long old_bytes = vm_dirty_bytes;
397 int ret;
398
399 ret = proc_doulongvec_minmax(table, write, buffer, lenp, ppos);
400 if (ret == 0 && write && vm_dirty_bytes != old_bytes) {
401 writeback_set_ratelimit();
402 vm_dirty_ratio = 0;
403 }
404 return ret;
405}
406
407static unsigned long wp_next_time(unsigned long cur_time)
408{
409 cur_time += VM_COMPLETIONS_PERIOD_LEN;
410 /* 0 has a special meaning... */
411 if (!cur_time)
412 return 1;
413 return cur_time;
414}
415
416/*
417 * Increment the BDI's writeout completion count and the global writeout
418 * completion count. Called from test_clear_page_writeback().
419 */
420static inline void __bdi_writeout_inc(struct backing_dev_info *bdi)
421{
422 __inc_bdi_stat(bdi, BDI_WRITTEN);
423 __fprop_inc_percpu_max(&writeout_completions, &bdi->completions,
424 bdi->max_prop_frac);
425 /* First event after period switching was turned off? */
426 if (!unlikely(writeout_period_time)) {
427 /*
428 * We can race with other __bdi_writeout_inc calls here but
429 * it does not cause any harm since the resulting time when
430 * timer will fire and what is in writeout_period_time will be
431 * roughly the same.
432 */
433 writeout_period_time = wp_next_time(jiffies);
434 mod_timer(&writeout_period_timer, writeout_period_time);
435 }
436}
437
438void bdi_writeout_inc(struct backing_dev_info *bdi)
439{
440 unsigned long flags;
441
442 local_irq_save(flags);
443 __bdi_writeout_inc(bdi);
444 local_irq_restore(flags);
445}
446EXPORT_SYMBOL_GPL(bdi_writeout_inc);
447
448/*
449 * Obtain an accurate fraction of the BDI's portion.
450 */
451static void bdi_writeout_fraction(struct backing_dev_info *bdi,
452 long *numerator, long *denominator)
453{
454 fprop_fraction_percpu(&writeout_completions, &bdi->completions,
455 numerator, denominator);
456}
457
458/*
459 * On idle system, we can be called long after we scheduled because we use
460 * deferred timers so count with missed periods.
461 */
462static void writeout_period(unsigned long t)
463{
464 int miss_periods = (jiffies - writeout_period_time) /
465 VM_COMPLETIONS_PERIOD_LEN;
466
467 if (fprop_new_period(&writeout_completions, miss_periods + 1)) {
468 writeout_period_time = wp_next_time(writeout_period_time +
469 miss_periods * VM_COMPLETIONS_PERIOD_LEN);
470 mod_timer(&writeout_period_timer, writeout_period_time);
471 } else {
472 /*
473 * Aging has zeroed all fractions. Stop wasting CPU on period
474 * updates.
475 */
476 writeout_period_time = 0;
477 }
478}
479
480/*
481 * bdi_min_ratio keeps the sum of the minimum dirty shares of all
482 * registered backing devices, which, for obvious reasons, can not
483 * exceed 100%.
484 */
485static unsigned int bdi_min_ratio;
486
487int bdi_set_min_ratio(struct backing_dev_info *bdi, unsigned int min_ratio)
488{
489 int ret = 0;
490
491 spin_lock_bh(&bdi_lock);
492 if (min_ratio > bdi->max_ratio) {
493 ret = -EINVAL;
494 } else {
495 min_ratio -= bdi->min_ratio;
496 if (bdi_min_ratio + min_ratio < 100) {
497 bdi_min_ratio += min_ratio;
498 bdi->min_ratio += min_ratio;
499 } else {
500 ret = -EINVAL;
501 }
502 }
503 spin_unlock_bh(&bdi_lock);
504
505 return ret;
506}
507
508int bdi_set_max_ratio(struct backing_dev_info *bdi, unsigned max_ratio)
509{
510 int ret = 0;
511
512 if (max_ratio > 100)
513 return -EINVAL;
514
515 spin_lock_bh(&bdi_lock);
516 if (bdi->min_ratio > max_ratio) {
517 ret = -EINVAL;
518 } else {
519 bdi->max_ratio = max_ratio;
520 bdi->max_prop_frac = (FPROP_FRAC_BASE * max_ratio) / 100;
521 }
522 spin_unlock_bh(&bdi_lock);
523
524 return ret;
525}
526EXPORT_SYMBOL(bdi_set_max_ratio);
527
528static unsigned long dirty_freerun_ceiling(unsigned long thresh,
529 unsigned long bg_thresh)
530{
531 return (thresh + bg_thresh) / 2;
532}
533
534static unsigned long hard_dirty_limit(unsigned long thresh)
535{
536 return max(thresh, global_dirty_limit);
537}
538
539/**
540 * bdi_dirty_limit - @bdi's share of dirty throttling threshold
541 * @bdi: the backing_dev_info to query
542 * @dirty: global dirty limit in pages
543 *
544 * Returns @bdi's dirty limit in pages. The term "dirty" in the context of
545 * dirty balancing includes all PG_dirty, PG_writeback and NFS unstable pages.
546 *
547 * Note that balance_dirty_pages() will only seriously take it as a hard limit
548 * when sleeping max_pause per page is not enough to keep the dirty pages under
549 * control. For example, when the device is completely stalled due to some error
550 * conditions, or when there are 1000 dd tasks writing to a slow 10MB/s USB key.
551 * In the other normal situations, it acts more gently by throttling the tasks
552 * more (rather than completely block them) when the bdi dirty pages go high.
553 *
554 * It allocates high/low dirty limits to fast/slow devices, in order to prevent
555 * - starving fast devices
556 * - piling up dirty pages (that will take long time to sync) on slow devices
557 *
558 * The bdi's share of dirty limit will be adapting to its throughput and
559 * bounded by the bdi->min_ratio and/or bdi->max_ratio parameters, if set.
560 */
561unsigned long bdi_dirty_limit(struct backing_dev_info *bdi, unsigned long dirty)
562{
563 u64 bdi_dirty;
564 long numerator, denominator;
565
566 /*
567 * Calculate this BDI's share of the dirty ratio.
568 */
569 bdi_writeout_fraction(bdi, &numerator, &denominator);
570
571 bdi_dirty = (dirty * (100 - bdi_min_ratio)) / 100;
572 bdi_dirty *= numerator;
573 do_div(bdi_dirty, denominator);
574
575 bdi_dirty += (dirty * bdi->min_ratio) / 100;
576 if (bdi_dirty > (dirty * bdi->max_ratio) / 100)
577 bdi_dirty = dirty * bdi->max_ratio / 100;
578
579 return bdi_dirty;
580}
581
582/*
583 * setpoint - dirty 3
584 * f(dirty) := 1.0 + (----------------)
585 * limit - setpoint
586 *
587 * it's a 3rd order polynomial that subjects to
588 *
589 * (1) f(freerun) = 2.0 => rampup dirty_ratelimit reasonably fast
590 * (2) f(setpoint) = 1.0 => the balance point
591 * (3) f(limit) = 0 => the hard limit
592 * (4) df/dx <= 0 => negative feedback control
593 * (5) the closer to setpoint, the smaller |df/dx| (and the reverse)
594 * => fast response on large errors; small oscillation near setpoint
595 */
596static long long pos_ratio_polynom(unsigned long setpoint,
597 unsigned long dirty,
598 unsigned long limit)
599{
600 long long pos_ratio;
601 long x;
602
603 x = div64_s64(((s64)setpoint - (s64)dirty) << RATELIMIT_CALC_SHIFT,
604 limit - setpoint + 1);
605 pos_ratio = x;
606 pos_ratio = pos_ratio * x >> RATELIMIT_CALC_SHIFT;
607 pos_ratio = pos_ratio * x >> RATELIMIT_CALC_SHIFT;
608 pos_ratio += 1 << RATELIMIT_CALC_SHIFT;
609
610 return clamp(pos_ratio, 0LL, 2LL << RATELIMIT_CALC_SHIFT);
611}
612
613/*
614 * Dirty position control.
615 *
616 * (o) global/bdi setpoints
617 *
618 * We want the dirty pages be balanced around the global/bdi setpoints.
619 * When the number of dirty pages is higher/lower than the setpoint, the
620 * dirty position control ratio (and hence task dirty ratelimit) will be
621 * decreased/increased to bring the dirty pages back to the setpoint.
622 *
623 * pos_ratio = 1 << RATELIMIT_CALC_SHIFT
624 *
625 * if (dirty < setpoint) scale up pos_ratio
626 * if (dirty > setpoint) scale down pos_ratio
627 *
628 * if (bdi_dirty < bdi_setpoint) scale up pos_ratio
629 * if (bdi_dirty > bdi_setpoint) scale down pos_ratio
630 *
631 * task_ratelimit = dirty_ratelimit * pos_ratio >> RATELIMIT_CALC_SHIFT
632 *
633 * (o) global control line
634 *
635 * ^ pos_ratio
636 * |
637 * | |<===== global dirty control scope ======>|
638 * 2.0 .............*
639 * | .*
640 * | . *
641 * | . *
642 * | . *
643 * | . *
644 * | . *
645 * 1.0 ................................*
646 * | . . *
647 * | . . *
648 * | . . *
649 * | . . *
650 * | . . *
651 * 0 +------------.------------------.----------------------*------------->
652 * freerun^ setpoint^ limit^ dirty pages
653 *
654 * (o) bdi control line
655 *
656 * ^ pos_ratio
657 * |
658 * | *
659 * | *
660 * | *
661 * | *
662 * | * |<=========== span ============>|
663 * 1.0 .......................*
664 * | . *
665 * | . *
666 * | . *
667 * | . *
668 * | . *
669 * | . *
670 * | . *
671 * | . *
672 * | . *
673 * | . *
674 * | . *
675 * 1/4 ...............................................* * * * * * * * * * * *
676 * | . .
677 * | . .
678 * | . .
679 * 0 +----------------------.-------------------------------.------------->
680 * bdi_setpoint^ x_intercept^
681 *
682 * The bdi control line won't drop below pos_ratio=1/4, so that bdi_dirty can
683 * be smoothly throttled down to normal if it starts high in situations like
684 * - start writing to a slow SD card and a fast disk at the same time. The SD
685 * card's bdi_dirty may rush to many times higher than bdi_setpoint.
686 * - the bdi dirty thresh drops quickly due to change of JBOD workload
687 */
688static unsigned long bdi_position_ratio(struct backing_dev_info *bdi,
689 unsigned long thresh,
690 unsigned long bg_thresh,
691 unsigned long dirty,
692 unsigned long bdi_thresh,
693 unsigned long bdi_dirty)
694{
695 unsigned long write_bw = bdi->avg_write_bandwidth;
696 unsigned long freerun = dirty_freerun_ceiling(thresh, bg_thresh);
697 unsigned long limit = hard_dirty_limit(thresh);
698 unsigned long x_intercept;
699 unsigned long setpoint; /* dirty pages' target balance point */
700 unsigned long bdi_setpoint;
701 unsigned long span;
702 long long pos_ratio; /* for scaling up/down the rate limit */
703 long x;
704
705 if (unlikely(dirty >= limit))
706 return 0;
707
708 /*
709 * global setpoint
710 *
711 * See comment for pos_ratio_polynom().
712 */
713 setpoint = (freerun + limit) / 2;
714 pos_ratio = pos_ratio_polynom(setpoint, dirty, limit);
715
716 /*
717 * The strictlimit feature is a tool preventing mistrusted filesystems
718 * from growing a large number of dirty pages before throttling. For
719 * such filesystems balance_dirty_pages always checks bdi counters
720 * against bdi limits. Even if global "nr_dirty" is under "freerun".
721 * This is especially important for fuse which sets bdi->max_ratio to
722 * 1% by default. Without strictlimit feature, fuse writeback may
723 * consume arbitrary amount of RAM because it is accounted in
724 * NR_WRITEBACK_TEMP which is not involved in calculating "nr_dirty".
725 *
726 * Here, in bdi_position_ratio(), we calculate pos_ratio based on
727 * two values: bdi_dirty and bdi_thresh. Let's consider an example:
728 * total amount of RAM is 16GB, bdi->max_ratio is equal to 1%, global
729 * limits are set by default to 10% and 20% (background and throttle).
730 * Then bdi_thresh is 1% of 20% of 16GB. This amounts to ~8K pages.
731 * bdi_dirty_limit(bdi, bg_thresh) is about ~4K pages. bdi_setpoint is
732 * about ~6K pages (as the average of background and throttle bdi
733 * limits). The 3rd order polynomial will provide positive feedback if
734 * bdi_dirty is under bdi_setpoint and vice versa.
735 *
736 * Note, that we cannot use global counters in these calculations
737 * because we want to throttle process writing to a strictlimit BDI
738 * much earlier than global "freerun" is reached (~23MB vs. ~2.3GB
739 * in the example above).
740 */
741 if (unlikely(bdi->capabilities & BDI_CAP_STRICTLIMIT)) {
742 long long bdi_pos_ratio;
743 unsigned long bdi_bg_thresh;
744
745 if (bdi_dirty < 8)
746 return min_t(long long, pos_ratio * 2,
747 2 << RATELIMIT_CALC_SHIFT);
748
749 if (bdi_dirty >= bdi_thresh)
750 return 0;
751
752 bdi_bg_thresh = div_u64((u64)bdi_thresh * bg_thresh, thresh);
753 bdi_setpoint = dirty_freerun_ceiling(bdi_thresh,
754 bdi_bg_thresh);
755
756 if (bdi_setpoint == 0 || bdi_setpoint == bdi_thresh)
757 return 0;
758
759 bdi_pos_ratio = pos_ratio_polynom(bdi_setpoint, bdi_dirty,
760 bdi_thresh);
761
762 /*
763 * Typically, for strictlimit case, bdi_setpoint << setpoint
764 * and pos_ratio >> bdi_pos_ratio. In the other words global
765 * state ("dirty") is not limiting factor and we have to
766 * make decision based on bdi counters. But there is an
767 * important case when global pos_ratio should get precedence:
768 * global limits are exceeded (e.g. due to activities on other
769 * BDIs) while given strictlimit BDI is below limit.
770 *
771 * "pos_ratio * bdi_pos_ratio" would work for the case above,
772 * but it would look too non-natural for the case of all
773 * activity in the system coming from a single strictlimit BDI
774 * with bdi->max_ratio == 100%.
775 *
776 * Note that min() below somewhat changes the dynamics of the
777 * control system. Normally, pos_ratio value can be well over 3
778 * (when globally we are at freerun and bdi is well below bdi
779 * setpoint). Now the maximum pos_ratio in the same situation
780 * is 2. We might want to tweak this if we observe the control
781 * system is too slow to adapt.
782 */
783 return min(pos_ratio, bdi_pos_ratio);
784 }
785
786 /*
787 * We have computed basic pos_ratio above based on global situation. If
788 * the bdi is over/under its share of dirty pages, we want to scale
789 * pos_ratio further down/up. That is done by the following mechanism.
790 */
791
792 /*
793 * bdi setpoint
794 *
795 * f(bdi_dirty) := 1.0 + k * (bdi_dirty - bdi_setpoint)
796 *
797 * x_intercept - bdi_dirty
798 * := --------------------------
799 * x_intercept - bdi_setpoint
800 *
801 * The main bdi control line is a linear function that subjects to
802 *
803 * (1) f(bdi_setpoint) = 1.0
804 * (2) k = - 1 / (8 * write_bw) (in single bdi case)
805 * or equally: x_intercept = bdi_setpoint + 8 * write_bw
806 *
807 * For single bdi case, the dirty pages are observed to fluctuate
808 * regularly within range
809 * [bdi_setpoint - write_bw/2, bdi_setpoint + write_bw/2]
810 * for various filesystems, where (2) can yield in a reasonable 12.5%
811 * fluctuation range for pos_ratio.
812 *
813 * For JBOD case, bdi_thresh (not bdi_dirty!) could fluctuate up to its
814 * own size, so move the slope over accordingly and choose a slope that
815 * yields 100% pos_ratio fluctuation on suddenly doubled bdi_thresh.
816 */
817 if (unlikely(bdi_thresh > thresh))
818 bdi_thresh = thresh;
819 /*
820 * It's very possible that bdi_thresh is close to 0 not because the
821 * device is slow, but that it has remained inactive for long time.
822 * Honour such devices a reasonable good (hopefully IO efficient)
823 * threshold, so that the occasional writes won't be blocked and active
824 * writes can rampup the threshold quickly.
825 */
826 bdi_thresh = max(bdi_thresh, (limit - dirty) / 8);
827 /*
828 * scale global setpoint to bdi's:
829 * bdi_setpoint = setpoint * bdi_thresh / thresh
830 */
831 x = div_u64((u64)bdi_thresh << 16, thresh + 1);
832 bdi_setpoint = setpoint * (u64)x >> 16;
833 /*
834 * Use span=(8*write_bw) in single bdi case as indicated by
835 * (thresh - bdi_thresh ~= 0) and transit to bdi_thresh in JBOD case.
836 *
837 * bdi_thresh thresh - bdi_thresh
838 * span = ---------- * (8 * write_bw) + ------------------- * bdi_thresh
839 * thresh thresh
840 */
841 span = (thresh - bdi_thresh + 8 * write_bw) * (u64)x >> 16;
842 x_intercept = bdi_setpoint + span;
843
844 if (bdi_dirty < x_intercept - span / 4) {
845 pos_ratio = div64_u64(pos_ratio * (x_intercept - bdi_dirty),
846 x_intercept - bdi_setpoint + 1);
847 } else
848 pos_ratio /= 4;
849
850 /*
851 * bdi reserve area, safeguard against dirty pool underrun and disk idle
852 * It may push the desired control point of global dirty pages higher
853 * than setpoint.
854 */
855 x_intercept = bdi_thresh / 2;
856 if (bdi_dirty < x_intercept) {
857 if (bdi_dirty > x_intercept / 8)
858 pos_ratio = div_u64(pos_ratio * x_intercept, bdi_dirty);
859 else
860 pos_ratio *= 8;
861 }
862
863 return pos_ratio;
864}
865
866static void bdi_update_write_bandwidth(struct backing_dev_info *bdi,
867 unsigned long elapsed,
868 unsigned long written)
869{
870 const unsigned long period = roundup_pow_of_two(3 * HZ);
871 unsigned long avg = bdi->avg_write_bandwidth;
872 unsigned long old = bdi->write_bandwidth;
873 u64 bw;
874
875 /*
876 * bw = written * HZ / elapsed
877 *
878 * bw * elapsed + write_bandwidth * (period - elapsed)
879 * write_bandwidth = ---------------------------------------------------
880 * period
881 */
882 bw = written - bdi->written_stamp;
883 bw *= HZ;
884 if (unlikely(elapsed > period)) {
885 do_div(bw, elapsed);
886 avg = bw;
887 goto out;
888 }
889 bw += (u64)bdi->write_bandwidth * (period - elapsed);
890 bw >>= ilog2(period);
891
892 /*
893 * one more level of smoothing, for filtering out sudden spikes
894 */
895 if (avg > old && old >= (unsigned long)bw)
896 avg -= (avg - old) >> 3;
897
898 if (avg < old && old <= (unsigned long)bw)
899 avg += (old - avg) >> 3;
900
901out:
902 bdi->write_bandwidth = bw;
903 bdi->avg_write_bandwidth = avg;
904}
905
906/*
907 * The global dirtyable memory and dirty threshold could be suddenly knocked
908 * down by a large amount (eg. on the startup of KVM in a swapless system).
909 * This may throw the system into deep dirty exceeded state and throttle
910 * heavy/light dirtiers alike. To retain good responsiveness, maintain
911 * global_dirty_limit for tracking slowly down to the knocked down dirty
912 * threshold.
913 */
914static void update_dirty_limit(unsigned long thresh, unsigned long dirty)
915{
916 unsigned long limit = global_dirty_limit;
917
918 /*
919 * Follow up in one step.
920 */
921 if (limit < thresh) {
922 limit = thresh;
923 goto update;
924 }
925
926 /*
927 * Follow down slowly. Use the higher one as the target, because thresh
928 * may drop below dirty. This is exactly the reason to introduce
929 * global_dirty_limit which is guaranteed to lie above the dirty pages.
930 */
931 thresh = max(thresh, dirty);
932 if (limit > thresh) {
933 limit -= (limit - thresh) >> 5;
934 goto update;
935 }
936 return;
937update:
938 global_dirty_limit = limit;
939}
940
941static void global_update_bandwidth(unsigned long thresh,
942 unsigned long dirty,
943 unsigned long now)
944{
945 static DEFINE_SPINLOCK(dirty_lock);
946 static unsigned long update_time;
947
948 /*
949 * check locklessly first to optimize away locking for the most time
950 */
951 if (time_before(now, update_time + BANDWIDTH_INTERVAL))
952 return;
953
954 spin_lock(&dirty_lock);
955 if (time_after_eq(now, update_time + BANDWIDTH_INTERVAL)) {
956 update_dirty_limit(thresh, dirty);
957 update_time = now;
958 }
959 spin_unlock(&dirty_lock);
960}
961
962/*
963 * Maintain bdi->dirty_ratelimit, the base dirty throttle rate.
964 *
965 * Normal bdi tasks will be curbed at or below it in long term.
966 * Obviously it should be around (write_bw / N) when there are N dd tasks.
967 */
968static void bdi_update_dirty_ratelimit(struct backing_dev_info *bdi,
969 unsigned long thresh,
970 unsigned long bg_thresh,
971 unsigned long dirty,
972 unsigned long bdi_thresh,
973 unsigned long bdi_dirty,
974 unsigned long dirtied,
975 unsigned long elapsed)
976{
977 unsigned long freerun = dirty_freerun_ceiling(thresh, bg_thresh);
978 unsigned long limit = hard_dirty_limit(thresh);
979 unsigned long setpoint = (freerun + limit) / 2;
980 unsigned long write_bw = bdi->avg_write_bandwidth;
981 unsigned long dirty_ratelimit = bdi->dirty_ratelimit;
982 unsigned long dirty_rate;
983 unsigned long task_ratelimit;
984 unsigned long balanced_dirty_ratelimit;
985 unsigned long pos_ratio;
986 unsigned long step;
987 unsigned long x;
988
989 /*
990 * The dirty rate will match the writeout rate in long term, except
991 * when dirty pages are truncated by userspace or re-dirtied by FS.
992 */
993 dirty_rate = (dirtied - bdi->dirtied_stamp) * HZ / elapsed;
994
995 pos_ratio = bdi_position_ratio(bdi, thresh, bg_thresh, dirty,
996 bdi_thresh, bdi_dirty);
997 /*
998 * task_ratelimit reflects each dd's dirty rate for the past 200ms.
999 */
1000 task_ratelimit = (u64)dirty_ratelimit *
1001 pos_ratio >> RATELIMIT_CALC_SHIFT;
1002 task_ratelimit++; /* it helps rampup dirty_ratelimit from tiny values */
1003
1004 /*
1005 * A linear estimation of the "balanced" throttle rate. The theory is,
1006 * if there are N dd tasks, each throttled at task_ratelimit, the bdi's
1007 * dirty_rate will be measured to be (N * task_ratelimit). So the below
1008 * formula will yield the balanced rate limit (write_bw / N).
1009 *
1010 * Note that the expanded form is not a pure rate feedback:
1011 * rate_(i+1) = rate_(i) * (write_bw / dirty_rate) (1)
1012 * but also takes pos_ratio into account:
1013 * rate_(i+1) = rate_(i) * (write_bw / dirty_rate) * pos_ratio (2)
1014 *
1015 * (1) is not realistic because pos_ratio also takes part in balancing
1016 * the dirty rate. Consider the state
1017 * pos_ratio = 0.5 (3)
1018 * rate = 2 * (write_bw / N) (4)
1019 * If (1) is used, it will stuck in that state! Because each dd will
1020 * be throttled at
1021 * task_ratelimit = pos_ratio * rate = (write_bw / N) (5)
1022 * yielding
1023 * dirty_rate = N * task_ratelimit = write_bw (6)
1024 * put (6) into (1) we get
1025 * rate_(i+1) = rate_(i) (7)
1026 *
1027 * So we end up using (2) to always keep
1028 * rate_(i+1) ~= (write_bw / N) (8)
1029 * regardless of the value of pos_ratio. As long as (8) is satisfied,
1030 * pos_ratio is able to drive itself to 1.0, which is not only where
1031 * the dirty count meet the setpoint, but also where the slope of
1032 * pos_ratio is most flat and hence task_ratelimit is least fluctuated.
1033 */
1034 balanced_dirty_ratelimit = div_u64((u64)task_ratelimit * write_bw,
1035 dirty_rate | 1);
1036 /*
1037 * balanced_dirty_ratelimit ~= (write_bw / N) <= write_bw
1038 */
1039 if (unlikely(balanced_dirty_ratelimit > write_bw))
1040 balanced_dirty_ratelimit = write_bw;
1041
1042 /*
1043 * We could safely do this and return immediately:
1044 *
1045 * bdi->dirty_ratelimit = balanced_dirty_ratelimit;
1046 *
1047 * However to get a more stable dirty_ratelimit, the below elaborated
1048 * code makes use of task_ratelimit to filter out singular points and
1049 * limit the step size.
1050 *
1051 * The below code essentially only uses the relative value of
1052 *
1053 * task_ratelimit - dirty_ratelimit
1054 * = (pos_ratio - 1) * dirty_ratelimit
1055 *
1056 * which reflects the direction and size of dirty position error.
1057 */
1058
1059 /*
1060 * dirty_ratelimit will follow balanced_dirty_ratelimit iff
1061 * task_ratelimit is on the same side of dirty_ratelimit, too.
1062 * For example, when
1063 * - dirty_ratelimit > balanced_dirty_ratelimit
1064 * - dirty_ratelimit > task_ratelimit (dirty pages are above setpoint)
1065 * lowering dirty_ratelimit will help meet both the position and rate
1066 * control targets. Otherwise, don't update dirty_ratelimit if it will
1067 * only help meet the rate target. After all, what the users ultimately
1068 * feel and care are stable dirty rate and small position error.
1069 *
1070 * |task_ratelimit - dirty_ratelimit| is used to limit the step size
1071 * and filter out the singular points of balanced_dirty_ratelimit. Which
1072 * keeps jumping around randomly and can even leap far away at times
1073 * due to the small 200ms estimation period of dirty_rate (we want to
1074 * keep that period small to reduce time lags).
1075 */
1076 step = 0;
1077
1078 /*
1079 * For strictlimit case, calculations above were based on bdi counters
1080 * and limits (starting from pos_ratio = bdi_position_ratio() and up to
1081 * balanced_dirty_ratelimit = task_ratelimit * write_bw / dirty_rate).
1082 * Hence, to calculate "step" properly, we have to use bdi_dirty as
1083 * "dirty" and bdi_setpoint as "setpoint".
1084 *
1085 * We rampup dirty_ratelimit forcibly if bdi_dirty is low because
1086 * it's possible that bdi_thresh is close to zero due to inactivity
1087 * of backing device (see the implementation of bdi_dirty_limit()).
1088 */
1089 if (unlikely(bdi->capabilities & BDI_CAP_STRICTLIMIT)) {
1090 dirty = bdi_dirty;
1091 if (bdi_dirty < 8)
1092 setpoint = bdi_dirty + 1;
1093 else
1094 setpoint = (bdi_thresh +
1095 bdi_dirty_limit(bdi, bg_thresh)) / 2;
1096 }
1097
1098 if (dirty < setpoint) {
1099 x = min(bdi->balanced_dirty_ratelimit,
1100 min(balanced_dirty_ratelimit, task_ratelimit));
1101 if (dirty_ratelimit < x)
1102 step = x - dirty_ratelimit;
1103 } else {
1104 x = max(bdi->balanced_dirty_ratelimit,
1105 max(balanced_dirty_ratelimit, task_ratelimit));
1106 if (dirty_ratelimit > x)
1107 step = dirty_ratelimit - x;
1108 }
1109
1110 /*
1111 * Don't pursue 100% rate matching. It's impossible since the balanced
1112 * rate itself is constantly fluctuating. So decrease the track speed
1113 * when it gets close to the target. Helps eliminate pointless tremors.
1114 */
1115 step >>= dirty_ratelimit / (2 * step + 1);
1116 /*
1117 * Limit the tracking speed to avoid overshooting.
1118 */
1119 step = (step + 7) / 8;
1120
1121 if (dirty_ratelimit < balanced_dirty_ratelimit)
1122 dirty_ratelimit += step;
1123 else
1124 dirty_ratelimit -= step;
1125
1126 bdi->dirty_ratelimit = max(dirty_ratelimit, 1UL);
1127 bdi->balanced_dirty_ratelimit = balanced_dirty_ratelimit;
1128
1129 trace_bdi_dirty_ratelimit(bdi, dirty_rate, task_ratelimit);
1130}
1131
1132void __bdi_update_bandwidth(struct backing_dev_info *bdi,
1133 unsigned long thresh,
1134 unsigned long bg_thresh,
1135 unsigned long dirty,
1136 unsigned long bdi_thresh,
1137 unsigned long bdi_dirty,
1138 unsigned long start_time)
1139{
1140 unsigned long now = jiffies;
1141 unsigned long elapsed = now - bdi->bw_time_stamp;
1142 unsigned long dirtied;
1143 unsigned long written;
1144
1145 /*
1146 * rate-limit, only update once every 200ms.
1147 */
1148 if (elapsed < BANDWIDTH_INTERVAL)
1149 return;
1150
1151 dirtied = percpu_counter_read(&bdi->bdi_stat[BDI_DIRTIED]);
1152 written = percpu_counter_read(&bdi->bdi_stat[BDI_WRITTEN]);
1153
1154 /*
1155 * Skip quiet periods when disk bandwidth is under-utilized.
1156 * (at least 1s idle time between two flusher runs)
1157 */
1158 if (elapsed > HZ && time_before(bdi->bw_time_stamp, start_time))
1159 goto snapshot;
1160
1161 if (thresh) {
1162 global_update_bandwidth(thresh, dirty, now);
1163 bdi_update_dirty_ratelimit(bdi, thresh, bg_thresh, dirty,
1164 bdi_thresh, bdi_dirty,
1165 dirtied, elapsed);
1166 }
1167 bdi_update_write_bandwidth(bdi, elapsed, written);
1168
1169snapshot:
1170 bdi->dirtied_stamp = dirtied;
1171 bdi->written_stamp = written;
1172 bdi->bw_time_stamp = now;
1173}
1174
1175static void bdi_update_bandwidth(struct backing_dev_info *bdi,
1176 unsigned long thresh,
1177 unsigned long bg_thresh,
1178 unsigned long dirty,
1179 unsigned long bdi_thresh,
1180 unsigned long bdi_dirty,
1181 unsigned long start_time)
1182{
1183 if (time_is_after_eq_jiffies(bdi->bw_time_stamp + BANDWIDTH_INTERVAL))
1184 return;
1185 spin_lock(&bdi->wb.list_lock);
1186 __bdi_update_bandwidth(bdi, thresh, bg_thresh, dirty,
1187 bdi_thresh, bdi_dirty, start_time);
1188 spin_unlock(&bdi->wb.list_lock);
1189}
1190
1191/*
1192 * After a task dirtied this many pages, balance_dirty_pages_ratelimited()
1193 * will look to see if it needs to start dirty throttling.
1194 *
1195 * If dirty_poll_interval is too low, big NUMA machines will call the expensive
1196 * global_page_state() too often. So scale it near-sqrt to the safety margin
1197 * (the number of pages we may dirty without exceeding the dirty limits).
1198 */
1199static unsigned long dirty_poll_interval(unsigned long dirty,
1200 unsigned long thresh)
1201{
1202 if (thresh > dirty)
1203 return 1UL << (ilog2(thresh - dirty) >> 1);
1204
1205 return 1;
1206}
1207
1208static unsigned long bdi_max_pause(struct backing_dev_info *bdi,
1209 unsigned long bdi_dirty)
1210{
1211 unsigned long bw = bdi->avg_write_bandwidth;
1212 unsigned long t;
1213
1214 /*
1215 * Limit pause time for small memory systems. If sleeping for too long
1216 * time, a small pool of dirty/writeback pages may go empty and disk go
1217 * idle.
1218 *
1219 * 8 serves as the safety ratio.
1220 */
1221 t = bdi_dirty / (1 + bw / roundup_pow_of_two(1 + HZ / 8));
1222 t++;
1223
1224 return min_t(unsigned long, t, MAX_PAUSE);
1225}
1226
1227static long bdi_min_pause(struct backing_dev_info *bdi,
1228 long max_pause,
1229 unsigned long task_ratelimit,
1230 unsigned long dirty_ratelimit,
1231 int *nr_dirtied_pause)
1232{
1233 long hi = ilog2(bdi->avg_write_bandwidth);
1234 long lo = ilog2(bdi->dirty_ratelimit);
1235 long t; /* target pause */
1236 long pause; /* estimated next pause */
1237 int pages; /* target nr_dirtied_pause */
1238
1239 /* target for 10ms pause on 1-dd case */
1240 t = max(1, HZ / 100);
1241
1242 /*
1243 * Scale up pause time for concurrent dirtiers in order to reduce CPU
1244 * overheads.
1245 *
1246 * (N * 10ms) on 2^N concurrent tasks.
1247 */
1248 if (hi > lo)
1249 t += (hi - lo) * (10 * HZ) / 1024;
1250
1251 /*
1252 * This is a bit convoluted. We try to base the next nr_dirtied_pause
1253 * on the much more stable dirty_ratelimit. However the next pause time
1254 * will be computed based on task_ratelimit and the two rate limits may
1255 * depart considerably at some time. Especially if task_ratelimit goes
1256 * below dirty_ratelimit/2 and the target pause is max_pause, the next
1257 * pause time will be max_pause*2 _trimmed down_ to max_pause. As a
1258 * result task_ratelimit won't be executed faithfully, which could
1259 * eventually bring down dirty_ratelimit.
1260 *
1261 * We apply two rules to fix it up:
1262 * 1) try to estimate the next pause time and if necessary, use a lower
1263 * nr_dirtied_pause so as not to exceed max_pause. When this happens,
1264 * nr_dirtied_pause will be "dancing" with task_ratelimit.
1265 * 2) limit the target pause time to max_pause/2, so that the normal
1266 * small fluctuations of task_ratelimit won't trigger rule (1) and
1267 * nr_dirtied_pause will remain as stable as dirty_ratelimit.
1268 */
1269 t = min(t, 1 + max_pause / 2);
1270 pages = dirty_ratelimit * t / roundup_pow_of_two(HZ);
1271
1272 /*
1273 * Tiny nr_dirtied_pause is found to hurt I/O performance in the test
1274 * case fio-mmap-randwrite-64k, which does 16*{sync read, async write}.
1275 * When the 16 consecutive reads are often interrupted by some dirty
1276 * throttling pause during the async writes, cfq will go into idles
1277 * (deadline is fine). So push nr_dirtied_pause as high as possible
1278 * until reaches DIRTY_POLL_THRESH=32 pages.
1279 */
1280 if (pages < DIRTY_POLL_THRESH) {
1281 t = max_pause;
1282 pages = dirty_ratelimit * t / roundup_pow_of_two(HZ);
1283 if (pages > DIRTY_POLL_THRESH) {
1284 pages = DIRTY_POLL_THRESH;
1285 t = HZ * DIRTY_POLL_THRESH / dirty_ratelimit;
1286 }
1287 }
1288
1289 pause = HZ * pages / (task_ratelimit + 1);
1290 if (pause > max_pause) {
1291 t = max_pause;
1292 pages = task_ratelimit * t / roundup_pow_of_two(HZ);
1293 }
1294
1295 *nr_dirtied_pause = pages;
1296 /*
1297 * The minimal pause time will normally be half the target pause time.
1298 */
1299 return pages >= DIRTY_POLL_THRESH ? 1 + t / 2 : t;
1300}
1301
1302static inline void bdi_dirty_limits(struct backing_dev_info *bdi,
1303 unsigned long dirty_thresh,
1304 unsigned long background_thresh,
1305 unsigned long *bdi_dirty,
1306 unsigned long *bdi_thresh,
1307 unsigned long *bdi_bg_thresh)
1308{
1309 unsigned long bdi_reclaimable;
1310
1311 /*
1312 * bdi_thresh is not treated as some limiting factor as
1313 * dirty_thresh, due to reasons
1314 * - in JBOD setup, bdi_thresh can fluctuate a lot
1315 * - in a system with HDD and USB key, the USB key may somehow
1316 * go into state (bdi_dirty >> bdi_thresh) either because
1317 * bdi_dirty starts high, or because bdi_thresh drops low.
1318 * In this case we don't want to hard throttle the USB key
1319 * dirtiers for 100 seconds until bdi_dirty drops under
1320 * bdi_thresh. Instead the auxiliary bdi control line in
1321 * bdi_position_ratio() will let the dirtier task progress
1322 * at some rate <= (write_bw / 2) for bringing down bdi_dirty.
1323 */
1324 *bdi_thresh = bdi_dirty_limit(bdi, dirty_thresh);
1325
1326 if (bdi_bg_thresh)
1327 *bdi_bg_thresh = div_u64((u64)*bdi_thresh *
1328 background_thresh,
1329 dirty_thresh);
1330
1331 /*
1332 * In order to avoid the stacked BDI deadlock we need
1333 * to ensure we accurately count the 'dirty' pages when
1334 * the threshold is low.
1335 *
1336 * Otherwise it would be possible to get thresh+n pages
1337 * reported dirty, even though there are thresh-m pages
1338 * actually dirty; with m+n sitting in the percpu
1339 * deltas.
1340 */
1341 if (*bdi_thresh < 2 * bdi_stat_error(bdi)) {
1342 bdi_reclaimable = bdi_stat_sum(bdi, BDI_RECLAIMABLE);
1343 *bdi_dirty = bdi_reclaimable +
1344 bdi_stat_sum(bdi, BDI_WRITEBACK);
1345 } else {
1346 bdi_reclaimable = bdi_stat(bdi, BDI_RECLAIMABLE);
1347 *bdi_dirty = bdi_reclaimable +
1348 bdi_stat(bdi, BDI_WRITEBACK);
1349 }
1350}
1351
1352/*
1353 * balance_dirty_pages() must be called by processes which are generating dirty
1354 * data. It looks at the number of dirty pages in the machine and will force
1355 * the caller to wait once crossing the (background_thresh + dirty_thresh) / 2.
1356 * If we're over `background_thresh' then the writeback threads are woken to
1357 * perform some writeout.
1358 */
1359static void balance_dirty_pages(struct address_space *mapping,
1360 unsigned long pages_dirtied)
1361{
1362 unsigned long nr_reclaimable; /* = file_dirty + unstable_nfs */
1363 unsigned long nr_dirty; /* = file_dirty + writeback + unstable_nfs */
1364 unsigned long background_thresh;
1365 unsigned long dirty_thresh;
1366 long period;
1367 long pause;
1368 long max_pause;
1369 long min_pause;
1370 int nr_dirtied_pause;
1371 bool dirty_exceeded = false;
1372 unsigned long task_ratelimit;
1373 unsigned long dirty_ratelimit;
1374 unsigned long pos_ratio;
1375 struct backing_dev_info *bdi = mapping->backing_dev_info;
1376 bool strictlimit = bdi->capabilities & BDI_CAP_STRICTLIMIT;
1377 unsigned long start_time = jiffies;
1378
1379 for (;;) {
1380 unsigned long now = jiffies;
1381 unsigned long uninitialized_var(bdi_thresh);
1382 unsigned long thresh;
1383 unsigned long uninitialized_var(bdi_dirty);
1384 unsigned long dirty;
1385 unsigned long bg_thresh;
1386
1387 /*
1388 * Unstable writes are a feature of certain networked
1389 * filesystems (i.e. NFS) in which data may have been
1390 * written to the server's write cache, but has not yet
1391 * been flushed to permanent storage.
1392 */
1393 nr_reclaimable = global_page_state(NR_FILE_DIRTY) +
1394 global_page_state(NR_UNSTABLE_NFS);
1395 nr_dirty = nr_reclaimable + global_page_state(NR_WRITEBACK);
1396
1397 global_dirty_limits(&background_thresh, &dirty_thresh);
1398
1399 if (unlikely(strictlimit)) {
1400 bdi_dirty_limits(bdi, dirty_thresh, background_thresh,
1401 &bdi_dirty, &bdi_thresh, &bg_thresh);
1402
1403 dirty = bdi_dirty;
1404 thresh = bdi_thresh;
1405 } else {
1406 dirty = nr_dirty;
1407 thresh = dirty_thresh;
1408 bg_thresh = background_thresh;
1409 }
1410
1411 /*
1412 * Throttle it only when the background writeback cannot
1413 * catch-up. This avoids (excessively) small writeouts
1414 * when the bdi limits are ramping up in case of !strictlimit.
1415 *
1416 * In strictlimit case make decision based on the bdi counters
1417 * and limits. Small writeouts when the bdi limits are ramping
1418 * up are the price we consciously pay for strictlimit-ing.
1419 */
1420 if (dirty <= dirty_freerun_ceiling(thresh, bg_thresh)) {
1421 current->dirty_paused_when = now;
1422 current->nr_dirtied = 0;
1423 current->nr_dirtied_pause =
1424 dirty_poll_interval(dirty, thresh);
1425 break;
1426 }
1427
1428 if (unlikely(!writeback_in_progress(bdi)))
1429 bdi_start_background_writeback(bdi);
1430
1431 if (!strictlimit)
1432 bdi_dirty_limits(bdi, dirty_thresh, background_thresh,
1433 &bdi_dirty, &bdi_thresh, NULL);
1434
1435 dirty_exceeded = (bdi_dirty > bdi_thresh) &&
1436 ((nr_dirty > dirty_thresh) || strictlimit);
1437 if (dirty_exceeded && !bdi->dirty_exceeded)
1438 bdi->dirty_exceeded = 1;
1439
1440 bdi_update_bandwidth(bdi, dirty_thresh, background_thresh,
1441 nr_dirty, bdi_thresh, bdi_dirty,
1442 start_time);
1443
1444 dirty_ratelimit = bdi->dirty_ratelimit;
1445 pos_ratio = bdi_position_ratio(bdi, dirty_thresh,
1446 background_thresh, nr_dirty,
1447 bdi_thresh, bdi_dirty);
1448 task_ratelimit = ((u64)dirty_ratelimit * pos_ratio) >>
1449 RATELIMIT_CALC_SHIFT;
1450 max_pause = bdi_max_pause(bdi, bdi_dirty);
1451 min_pause = bdi_min_pause(bdi, max_pause,
1452 task_ratelimit, dirty_ratelimit,
1453 &nr_dirtied_pause);
1454
1455 if (unlikely(task_ratelimit == 0)) {
1456 period = max_pause;
1457 pause = max_pause;
1458 goto pause;
1459 }
1460 period = HZ * pages_dirtied / task_ratelimit;
1461 pause = period;
1462 if (current->dirty_paused_when)
1463 pause -= now - current->dirty_paused_when;
1464 /*
1465 * For less than 1s think time (ext3/4 may block the dirtier
1466 * for up to 800ms from time to time on 1-HDD; so does xfs,
1467 * however at much less frequency), try to compensate it in
1468 * future periods by updating the virtual time; otherwise just
1469 * do a reset, as it may be a light dirtier.
1470 */
1471 if (pause < min_pause) {
1472 trace_balance_dirty_pages(bdi,
1473 dirty_thresh,
1474 background_thresh,
1475 nr_dirty,
1476 bdi_thresh,
1477 bdi_dirty,
1478 dirty_ratelimit,
1479 task_ratelimit,
1480 pages_dirtied,
1481 period,
1482 min(pause, 0L),
1483 start_time);
1484 if (pause < -HZ) {
1485 current->dirty_paused_when = now;
1486 current->nr_dirtied = 0;
1487 } else if (period) {
1488 current->dirty_paused_when += period;
1489 current->nr_dirtied = 0;
1490 } else if (current->nr_dirtied_pause <= pages_dirtied)
1491 current->nr_dirtied_pause += pages_dirtied;
1492 break;
1493 }
1494 if (unlikely(pause > max_pause)) {
1495 /* for occasional dropped task_ratelimit */
1496 now += min(pause - max_pause, max_pause);
1497 pause = max_pause;
1498 }
1499
1500pause:
1501 trace_balance_dirty_pages(bdi,
1502 dirty_thresh,
1503 background_thresh,
1504 nr_dirty,
1505 bdi_thresh,
1506 bdi_dirty,
1507 dirty_ratelimit,
1508 task_ratelimit,
1509 pages_dirtied,
1510 period,
1511 pause,
1512 start_time);
1513 __set_current_state(TASK_KILLABLE);
1514 io_schedule_timeout(pause);
1515
1516 current->dirty_paused_when = now + pause;
1517 current->nr_dirtied = 0;
1518 current->nr_dirtied_pause = nr_dirtied_pause;
1519
1520 /*
1521 * This is typically equal to (nr_dirty < dirty_thresh) and can
1522 * also keep "1000+ dd on a slow USB stick" under control.
1523 */
1524 if (task_ratelimit)
1525 break;
1526
1527 /*
1528 * In the case of an unresponding NFS server and the NFS dirty
1529 * pages exceeds dirty_thresh, give the other good bdi's a pipe
1530 * to go through, so that tasks on them still remain responsive.
1531 *
1532 * In theory 1 page is enough to keep the comsumer-producer
1533 * pipe going: the flusher cleans 1 page => the task dirties 1
1534 * more page. However bdi_dirty has accounting errors. So use
1535 * the larger and more IO friendly bdi_stat_error.
1536 */
1537 if (bdi_dirty <= bdi_stat_error(bdi))
1538 break;
1539
1540 if (fatal_signal_pending(current))
1541 break;
1542 }
1543
1544 if (!dirty_exceeded && bdi->dirty_exceeded)
1545 bdi->dirty_exceeded = 0;
1546
1547 if (writeback_in_progress(bdi))
1548 return;
1549
1550 /*
1551 * In laptop mode, we wait until hitting the higher threshold before
1552 * starting background writeout, and then write out all the way down
1553 * to the lower threshold. So slow writers cause minimal disk activity.
1554 *
1555 * In normal mode, we start background writeout at the lower
1556 * background_thresh, to keep the amount of dirty memory low.
1557 */
1558 if (laptop_mode)
1559 return;
1560
1561 if (nr_reclaimable > background_thresh)
1562 bdi_start_background_writeback(bdi);
1563}
1564
1565void set_page_dirty_balance(struct page *page)
1566{
1567 if (set_page_dirty(page)) {
1568 struct address_space *mapping = page_mapping(page);
1569
1570 if (mapping)
1571 balance_dirty_pages_ratelimited(mapping);
1572 }
1573}
1574
1575static DEFINE_PER_CPU(int, bdp_ratelimits);
1576
1577/*
1578 * Normal tasks are throttled by
1579 * loop {
1580 * dirty tsk->nr_dirtied_pause pages;
1581 * take a snap in balance_dirty_pages();
1582 * }
1583 * However there is a worst case. If every task exit immediately when dirtied
1584 * (tsk->nr_dirtied_pause - 1) pages, balance_dirty_pages() will never be
1585 * called to throttle the page dirties. The solution is to save the not yet
1586 * throttled page dirties in dirty_throttle_leaks on task exit and charge them
1587 * randomly into the running tasks. This works well for the above worst case,
1588 * as the new task will pick up and accumulate the old task's leaked dirty
1589 * count and eventually get throttled.
1590 */
1591DEFINE_PER_CPU(int, dirty_throttle_leaks) = 0;
1592
1593/**
1594 * balance_dirty_pages_ratelimited - balance dirty memory state
1595 * @mapping: address_space which was dirtied
1596 *
1597 * Processes which are dirtying memory should call in here once for each page
1598 * which was newly dirtied. The function will periodically check the system's
1599 * dirty state and will initiate writeback if needed.
1600 *
1601 * On really big machines, get_writeback_state is expensive, so try to avoid
1602 * calling it too often (ratelimiting). But once we're over the dirty memory
1603 * limit we decrease the ratelimiting by a lot, to prevent individual processes
1604 * from overshooting the limit by (ratelimit_pages) each.
1605 */
1606void balance_dirty_pages_ratelimited(struct address_space *mapping)
1607{
1608 struct backing_dev_info *bdi = mapping->backing_dev_info;
1609 int ratelimit;
1610 int *p;
1611
1612 if (!bdi_cap_account_dirty(bdi))
1613 return;
1614
1615 ratelimit = current->nr_dirtied_pause;
1616 if (bdi->dirty_exceeded)
1617 ratelimit = min(ratelimit, 32 >> (PAGE_SHIFT - 10));
1618
1619 preempt_disable();
1620 /*
1621 * This prevents one CPU to accumulate too many dirtied pages without
1622 * calling into balance_dirty_pages(), which can happen when there are
1623 * 1000+ tasks, all of them start dirtying pages at exactly the same
1624 * time, hence all honoured too large initial task->nr_dirtied_pause.
1625 */
1626 p = &__get_cpu_var(bdp_ratelimits);
1627 if (unlikely(current->nr_dirtied >= ratelimit))
1628 *p = 0;
1629 else if (unlikely(*p >= ratelimit_pages)) {
1630 *p = 0;
1631 ratelimit = 0;
1632 }
1633 /*
1634 * Pick up the dirtied pages by the exited tasks. This avoids lots of
1635 * short-lived tasks (eg. gcc invocations in a kernel build) escaping
1636 * the dirty throttling and livelock other long-run dirtiers.
1637 */
1638 p = &__get_cpu_var(dirty_throttle_leaks);
1639 if (*p > 0 && current->nr_dirtied < ratelimit) {
1640 unsigned long nr_pages_dirtied;
1641 nr_pages_dirtied = min(*p, ratelimit - current->nr_dirtied);
1642 *p -= nr_pages_dirtied;
1643 current->nr_dirtied += nr_pages_dirtied;
1644 }
1645 preempt_enable();
1646
1647 if (unlikely(current->nr_dirtied >= ratelimit))
1648 balance_dirty_pages(mapping, current->nr_dirtied);
1649}
1650EXPORT_SYMBOL(balance_dirty_pages_ratelimited);
1651
1652void throttle_vm_writeout(gfp_t gfp_mask)
1653{
1654 unsigned long background_thresh;
1655 unsigned long dirty_thresh;
1656
1657 for ( ; ; ) {
1658 global_dirty_limits(&background_thresh, &dirty_thresh);
1659 dirty_thresh = hard_dirty_limit(dirty_thresh);
1660
1661 /*
1662 * Boost the allowable dirty threshold a bit for page
1663 * allocators so they don't get DoS'ed by heavy writers
1664 */
1665 dirty_thresh += dirty_thresh / 10; /* wheeee... */
1666
1667 if (global_page_state(NR_UNSTABLE_NFS) +
1668 global_page_state(NR_WRITEBACK) <= dirty_thresh)
1669 break;
1670 congestion_wait(BLK_RW_ASYNC, HZ/10);
1671
1672 /*
1673 * The caller might hold locks which can prevent IO completion
1674 * or progress in the filesystem. So we cannot just sit here
1675 * waiting for IO to complete.
1676 */
1677 if ((gfp_mask & (__GFP_FS|__GFP_IO)) != (__GFP_FS|__GFP_IO))
1678 break;
1679 }
1680}
1681
1682/*
1683 * sysctl handler for /proc/sys/vm/dirty_writeback_centisecs
1684 */
1685int dirty_writeback_centisecs_handler(ctl_table *table, int write,
1686 void __user *buffer, size_t *length, loff_t *ppos)
1687{
1688 proc_dointvec(table, write, buffer, length, ppos);
1689 return 0;
1690}
1691
1692#ifdef CONFIG_BLOCK
1693void laptop_mode_timer_fn(unsigned long data)
1694{
1695 struct request_queue *q = (struct request_queue *)data;
1696 int nr_pages = global_page_state(NR_FILE_DIRTY) +
1697 global_page_state(NR_UNSTABLE_NFS);
1698
1699 /*
1700 * We want to write everything out, not just down to the dirty
1701 * threshold
1702 */
1703 if (bdi_has_dirty_io(&q->backing_dev_info))
1704 bdi_start_writeback(&q->backing_dev_info, nr_pages,
1705 WB_REASON_LAPTOP_TIMER);
1706}
1707
1708/*
1709 * We've spun up the disk and we're in laptop mode: schedule writeback
1710 * of all dirty data a few seconds from now. If the flush is already scheduled
1711 * then push it back - the user is still using the disk.
1712 */
1713void laptop_io_completion(struct backing_dev_info *info)
1714{
1715 mod_timer(&info->laptop_mode_wb_timer, jiffies + laptop_mode);
1716}
1717
1718/*
1719 * We're in laptop mode and we've just synced. The sync's writes will have
1720 * caused another writeback to be scheduled by laptop_io_completion.
1721 * Nothing needs to be written back anymore, so we unschedule the writeback.
1722 */
1723void laptop_sync_completion(void)
1724{
1725 struct backing_dev_info *bdi;
1726
1727 rcu_read_lock();
1728
1729 list_for_each_entry_rcu(bdi, &bdi_list, bdi_list)
1730 del_timer(&bdi->laptop_mode_wb_timer);
1731
1732 rcu_read_unlock();
1733}
1734#endif
1735
1736/*
1737 * If ratelimit_pages is too high then we can get into dirty-data overload
1738 * if a large number of processes all perform writes at the same time.
1739 * If it is too low then SMP machines will call the (expensive)
1740 * get_writeback_state too often.
1741 *
1742 * Here we set ratelimit_pages to a level which ensures that when all CPUs are
1743 * dirtying in parallel, we cannot go more than 3% (1/32) over the dirty memory
1744 * thresholds.
1745 */
1746
1747void writeback_set_ratelimit(void)
1748{
1749 unsigned long background_thresh;
1750 unsigned long dirty_thresh;
1751 global_dirty_limits(&background_thresh, &dirty_thresh);
1752 global_dirty_limit = dirty_thresh;
1753 ratelimit_pages = dirty_thresh / (num_online_cpus() * 32);
1754 if (ratelimit_pages < 16)
1755 ratelimit_pages = 16;
1756}
1757
1758static int
1759ratelimit_handler(struct notifier_block *self, unsigned long action,
1760 void *hcpu)
1761{
1762
1763 switch (action & ~CPU_TASKS_FROZEN) {
1764 case CPU_ONLINE:
1765 case CPU_DEAD:
1766 writeback_set_ratelimit();
1767 return NOTIFY_OK;
1768 default:
1769 return NOTIFY_DONE;
1770 }
1771}
1772
1773static struct notifier_block ratelimit_nb = {
1774 .notifier_call = ratelimit_handler,
1775 .next = NULL,
1776};
1777
1778/*
1779 * Called early on to tune the page writeback dirty limits.
1780 *
1781 * We used to scale dirty pages according to how total memory
1782 * related to pages that could be allocated for buffers (by
1783 * comparing nr_free_buffer_pages() to vm_total_pages.
1784 *
1785 * However, that was when we used "dirty_ratio" to scale with
1786 * all memory, and we don't do that any more. "dirty_ratio"
1787 * is now applied to total non-HIGHPAGE memory (by subtracting
1788 * totalhigh_pages from vm_total_pages), and as such we can't
1789 * get into the old insane situation any more where we had
1790 * large amounts of dirty pages compared to a small amount of
1791 * non-HIGHMEM memory.
1792 *
1793 * But we might still want to scale the dirty_ratio by how
1794 * much memory the box has..
1795 */
1796void __init page_writeback_init(void)
1797{
1798 writeback_set_ratelimit();
1799 register_cpu_notifier(&ratelimit_nb);
1800
1801 fprop_global_init(&writeout_completions);
1802}
1803
1804/**
1805 * tag_pages_for_writeback - tag pages to be written by write_cache_pages
1806 * @mapping: address space structure to write
1807 * @start: starting page index
1808 * @end: ending page index (inclusive)
1809 *
1810 * This function scans the page range from @start to @end (inclusive) and tags
1811 * all pages that have DIRTY tag set with a special TOWRITE tag. The idea is
1812 * that write_cache_pages (or whoever calls this function) will then use
1813 * TOWRITE tag to identify pages eligible for writeback. This mechanism is
1814 * used to avoid livelocking of writeback by a process steadily creating new
1815 * dirty pages in the file (thus it is important for this function to be quick
1816 * so that it can tag pages faster than a dirtying process can create them).
1817 */
1818/*
1819 * We tag pages in batches of WRITEBACK_TAG_BATCH to reduce tree_lock latency.
1820 */
1821void tag_pages_for_writeback(struct address_space *mapping,
1822 pgoff_t start, pgoff_t end)
1823{
1824#define WRITEBACK_TAG_BATCH 4096
1825 unsigned long tagged;
1826
1827 do {
1828 spin_lock_irq(&mapping->tree_lock);
1829 tagged = radix_tree_range_tag_if_tagged(&mapping->page_tree,
1830 &start, end, WRITEBACK_TAG_BATCH,
1831 PAGECACHE_TAG_DIRTY, PAGECACHE_TAG_TOWRITE);
1832 spin_unlock_irq(&mapping->tree_lock);
1833 WARN_ON_ONCE(tagged > WRITEBACK_TAG_BATCH);
1834 cond_resched();
1835 /* We check 'start' to handle wrapping when end == ~0UL */
1836 } while (tagged >= WRITEBACK_TAG_BATCH && start);
1837}
1838EXPORT_SYMBOL(tag_pages_for_writeback);
1839
1840/**
1841 * write_cache_pages - walk the list of dirty pages of the given address space and write all of them.
1842 * @mapping: address space structure to write
1843 * @wbc: subtract the number of written pages from *@wbc->nr_to_write
1844 * @writepage: function called for each page
1845 * @data: data passed to writepage function
1846 *
1847 * If a page is already under I/O, write_cache_pages() skips it, even
1848 * if it's dirty. This is desirable behaviour for memory-cleaning writeback,
1849 * but it is INCORRECT for data-integrity system calls such as fsync(). fsync()
1850 * and msync() need to guarantee that all the data which was dirty at the time
1851 * the call was made get new I/O started against them. If wbc->sync_mode is
1852 * WB_SYNC_ALL then we were called for data integrity and we must wait for
1853 * existing IO to complete.
1854 *
1855 * To avoid livelocks (when other process dirties new pages), we first tag
1856 * pages which should be written back with TOWRITE tag and only then start
1857 * writing them. For data-integrity sync we have to be careful so that we do
1858 * not miss some pages (e.g., because some other process has cleared TOWRITE
1859 * tag we set). The rule we follow is that TOWRITE tag can be cleared only
1860 * by the process clearing the DIRTY tag (and submitting the page for IO).
1861 */
1862int write_cache_pages(struct address_space *mapping,
1863 struct writeback_control *wbc, writepage_t writepage,
1864 void *data)
1865{
1866 int ret = 0;
1867 int done = 0;
1868 struct pagevec pvec;
1869 int nr_pages;
1870 pgoff_t uninitialized_var(writeback_index);
1871 pgoff_t index;
1872 pgoff_t end; /* Inclusive */
1873 pgoff_t done_index;
1874 int cycled;
1875 int range_whole = 0;
1876 int tag;
1877
1878 pagevec_init(&pvec, 0);
1879 if (wbc->range_cyclic) {
1880 writeback_index = mapping->writeback_index; /* prev offset */
1881 index = writeback_index;
1882 if (index == 0)
1883 cycled = 1;
1884 else
1885 cycled = 0;
1886 end = -1;
1887 } else {
1888 index = wbc->range_start >> PAGE_CACHE_SHIFT;
1889 end = wbc->range_end >> PAGE_CACHE_SHIFT;
1890 if (wbc->range_start == 0 && wbc->range_end == LLONG_MAX)
1891 range_whole = 1;
1892 cycled = 1; /* ignore range_cyclic tests */
1893 }
1894 if (wbc->sync_mode == WB_SYNC_ALL || wbc->tagged_writepages)
1895 tag = PAGECACHE_TAG_TOWRITE;
1896 else
1897 tag = PAGECACHE_TAG_DIRTY;
1898retry:
1899 if (wbc->sync_mode == WB_SYNC_ALL || wbc->tagged_writepages)
1900 tag_pages_for_writeback(mapping, index, end);
1901 done_index = index;
1902 while (!done && (index <= end)) {
1903 int i;
1904
1905 nr_pages = pagevec_lookup_tag(&pvec, mapping, &index, tag,
1906 min(end - index, (pgoff_t)PAGEVEC_SIZE-1) + 1);
1907 if (nr_pages == 0)
1908 break;
1909
1910 for (i = 0; i < nr_pages; i++) {
1911 struct page *page = pvec.pages[i];
1912
1913 /*
1914 * At this point, the page may be truncated or
1915 * invalidated (changing page->mapping to NULL), or
1916 * even swizzled back from swapper_space to tmpfs file
1917 * mapping. However, page->index will not change
1918 * because we have a reference on the page.
1919 */
1920 if (page->index > end) {
1921 /*
1922 * can't be range_cyclic (1st pass) because
1923 * end == -1 in that case.
1924 */
1925 done = 1;
1926 break;
1927 }
1928
1929 done_index = page->index;
1930
1931 lock_page(page);
1932
1933 /*
1934 * Page truncated or invalidated. We can freely skip it
1935 * then, even for data integrity operations: the page
1936 * has disappeared concurrently, so there could be no
1937 * real expectation of this data interity operation
1938 * even if there is now a new, dirty page at the same
1939 * pagecache address.
1940 */
1941 if (unlikely(page->mapping != mapping)) {
1942continue_unlock:
1943 unlock_page(page);
1944 continue;
1945 }
1946
1947 if (!PageDirty(page)) {
1948 /* someone wrote it for us */
1949 goto continue_unlock;
1950 }
1951
1952 if (PageWriteback(page)) {
1953 if (wbc->sync_mode != WB_SYNC_NONE)
1954 wait_on_page_writeback(page);
1955 else
1956 goto continue_unlock;
1957 }
1958
1959 BUG_ON(PageWriteback(page));
1960 if (!clear_page_dirty_for_io(page))
1961 goto continue_unlock;
1962
1963 trace_wbc_writepage(wbc, mapping->backing_dev_info);
1964 ret = (*writepage)(page, wbc, data);
1965 if (unlikely(ret)) {
1966 if (ret == AOP_WRITEPAGE_ACTIVATE) {
1967 unlock_page(page);
1968 ret = 0;
1969 } else {
1970 /*
1971 * done_index is set past this page,
1972 * so media errors will not choke
1973 * background writeout for the entire
1974 * file. This has consequences for
1975 * range_cyclic semantics (ie. it may
1976 * not be suitable for data integrity
1977 * writeout).
1978 */
1979 done_index = page->index + 1;
1980 done = 1;
1981 break;
1982 }
1983 }
1984
1985 /*
1986 * We stop writing back only if we are not doing
1987 * integrity sync. In case of integrity sync we have to
1988 * keep going until we have written all the pages
1989 * we tagged for writeback prior to entering this loop.
1990 */
1991 if (--wbc->nr_to_write <= 0 &&
1992 wbc->sync_mode == WB_SYNC_NONE) {
1993 done = 1;
1994 break;
1995 }
1996 }
1997 pagevec_release(&pvec);
1998 cond_resched();
1999 }
2000 if (!cycled && !done) {
2001 /*
2002 * range_cyclic:
2003 * We hit the last page and there is more work to be done: wrap
2004 * back to the start of the file
2005 */
2006 cycled = 1;
2007 index = 0;
2008 end = writeback_index - 1;
2009 goto retry;
2010 }
2011 if (wbc->range_cyclic || (range_whole && wbc->nr_to_write > 0))
2012 mapping->writeback_index = done_index;
2013
2014 return ret;
2015}
2016EXPORT_SYMBOL(write_cache_pages);
2017
2018/*
2019 * Function used by generic_writepages to call the real writepage
2020 * function and set the mapping flags on error
2021 */
2022static int __writepage(struct page *page, struct writeback_control *wbc,
2023 void *data)
2024{
2025 struct address_space *mapping = data;
2026 int ret = mapping->a_ops->writepage(page, wbc);
2027 mapping_set_error(mapping, ret);
2028 return ret;
2029}
2030
2031/**
2032 * generic_writepages - walk the list of dirty pages of the given address space and writepage() all of them.
2033 * @mapping: address space structure to write
2034 * @wbc: subtract the number of written pages from *@wbc->nr_to_write
2035 *
2036 * This is a library function, which implements the writepages()
2037 * address_space_operation.
2038 */
2039int generic_writepages(struct address_space *mapping,
2040 struct writeback_control *wbc)
2041{
2042 struct blk_plug plug;
2043 int ret;
2044
2045 /* deal with chardevs and other special file */
2046 if (!mapping->a_ops->writepage)
2047 return 0;
2048
2049 blk_start_plug(&plug);
2050 ret = write_cache_pages(mapping, wbc, __writepage, mapping);
2051 blk_finish_plug(&plug);
2052 return ret;
2053}
2054
2055EXPORT_SYMBOL(generic_writepages);
2056
2057int do_writepages(struct address_space *mapping, struct writeback_control *wbc)
2058{
2059 int ret;
2060
2061 if (wbc->nr_to_write <= 0)
2062 return 0;
2063 if (mapping->a_ops->writepages)
2064 ret = mapping->a_ops->writepages(mapping, wbc);
2065 else
2066 ret = generic_writepages(mapping, wbc);
2067 return ret;
2068}
2069
2070/**
2071 * write_one_page - write out a single page and optionally wait on I/O
2072 * @page: the page to write
2073 * @wait: if true, wait on writeout
2074 *
2075 * The page must be locked by the caller and will be unlocked upon return.
2076 *
2077 * write_one_page() returns a negative error code if I/O failed.
2078 */
2079int write_one_page(struct page *page, int wait)
2080{
2081 struct address_space *mapping = page->mapping;
2082 int ret = 0;
2083 struct writeback_control wbc = {
2084 .sync_mode = WB_SYNC_ALL,
2085 .nr_to_write = 1,
2086 };
2087
2088 BUG_ON(!PageLocked(page));
2089
2090 if (wait)
2091 wait_on_page_writeback(page);
2092
2093 if (clear_page_dirty_for_io(page)) {
2094 page_cache_get(page);
2095 ret = mapping->a_ops->writepage(page, &wbc);
2096 if (ret == 0 && wait) {
2097 wait_on_page_writeback(page);
2098 if (PageError(page))
2099 ret = -EIO;
2100 }
2101 page_cache_release(page);
2102 } else {
2103 unlock_page(page);
2104 }
2105 return ret;
2106}
2107EXPORT_SYMBOL(write_one_page);
2108
2109/*
2110 * For address_spaces which do not use buffers nor write back.
2111 */
2112int __set_page_dirty_no_writeback(struct page *page)
2113{
2114 if (!PageDirty(page))
2115 return !TestSetPageDirty(page);
2116 return 0;
2117}
2118
2119/*
2120 * Helper function for set_page_dirty family.
2121 * NOTE: This relies on being atomic wrt interrupts.
2122 */
2123void account_page_dirtied(struct page *page, struct address_space *mapping)
2124{
2125 trace_writeback_dirty_page(page, mapping);
2126
2127 if (mapping_cap_account_dirty(mapping)) {
2128 __inc_zone_page_state(page, NR_FILE_DIRTY);
2129 __inc_zone_page_state(page, NR_DIRTIED);
2130 __inc_bdi_stat(mapping->backing_dev_info, BDI_RECLAIMABLE);
2131 __inc_bdi_stat(mapping->backing_dev_info, BDI_DIRTIED);
2132 task_io_account_write(PAGE_CACHE_SIZE);
2133 current->nr_dirtied++;
2134 this_cpu_inc(bdp_ratelimits);
2135 }
2136}
2137EXPORT_SYMBOL(account_page_dirtied);
2138
2139/*
2140 * Helper function for set_page_writeback family.
2141 *
2142 * The caller must hold mem_cgroup_begin/end_update_page_stat() lock
2143 * while calling this function.
2144 * See test_set_page_writeback for example.
2145 *
2146 * NOTE: Unlike account_page_dirtied this does not rely on being atomic
2147 * wrt interrupts.
2148 */
2149void account_page_writeback(struct page *page)
2150{
2151 mem_cgroup_inc_page_stat(page, MEM_CGROUP_STAT_WRITEBACK);
2152 inc_zone_page_state(page, NR_WRITEBACK);
2153}
2154EXPORT_SYMBOL(account_page_writeback);
2155
2156/*
2157 * For address_spaces which do not use buffers. Just tag the page as dirty in
2158 * its radix tree.
2159 *
2160 * This is also used when a single buffer is being dirtied: we want to set the
2161 * page dirty in that case, but not all the buffers. This is a "bottom-up"
2162 * dirtying, whereas __set_page_dirty_buffers() is a "top-down" dirtying.
2163 *
2164 * Most callers have locked the page, which pins the address_space in memory.
2165 * But zap_pte_range() does not lock the page, however in that case the
2166 * mapping is pinned by the vma's ->vm_file reference.
2167 *
2168 * We take care to handle the case where the page was truncated from the
2169 * mapping by re-checking page_mapping() inside tree_lock.
2170 */
2171int __set_page_dirty_nobuffers(struct page *page)
2172{
2173 if (!TestSetPageDirty(page)) {
2174 struct address_space *mapping = page_mapping(page);
2175 struct address_space *mapping2;
2176 unsigned long flags;
2177
2178 if (!mapping)
2179 return 1;
2180
2181 spin_lock_irqsave(&mapping->tree_lock, flags);
2182 mapping2 = page_mapping(page);
2183 if (mapping2) { /* Race with truncate? */
2184 BUG_ON(mapping2 != mapping);
2185 WARN_ON_ONCE(!PagePrivate(page) && !PageUptodate(page));
2186 account_page_dirtied(page, mapping);
2187 radix_tree_tag_set(&mapping->page_tree,
2188 page_index(page), PAGECACHE_TAG_DIRTY);
2189 }
2190 spin_unlock_irqrestore(&mapping->tree_lock, flags);
2191 if (mapping->host) {
2192 /* !PageAnon && !swapper_space */
2193 __mark_inode_dirty(mapping->host, I_DIRTY_PAGES);
2194 }
2195 return 1;
2196 }
2197 return 0;
2198}
2199EXPORT_SYMBOL(__set_page_dirty_nobuffers);
2200
2201/*
2202 * Call this whenever redirtying a page, to de-account the dirty counters
2203 * (NR_DIRTIED, BDI_DIRTIED, tsk->nr_dirtied), so that they match the written
2204 * counters (NR_WRITTEN, BDI_WRITTEN) in long term. The mismatches will lead to
2205 * systematic errors in balanced_dirty_ratelimit and the dirty pages position
2206 * control.
2207 */
2208void account_page_redirty(struct page *page)
2209{
2210 struct address_space *mapping = page->mapping;
2211 if (mapping && mapping_cap_account_dirty(mapping)) {
2212 current->nr_dirtied--;
2213 dec_zone_page_state(page, NR_DIRTIED);
2214 dec_bdi_stat(mapping->backing_dev_info, BDI_DIRTIED);
2215 }
2216}
2217EXPORT_SYMBOL(account_page_redirty);
2218
2219/*
2220 * When a writepage implementation decides that it doesn't want to write this
2221 * page for some reason, it should redirty the locked page via
2222 * redirty_page_for_writepage() and it should then unlock the page and return 0
2223 */
2224int redirty_page_for_writepage(struct writeback_control *wbc, struct page *page)
2225{
2226 wbc->pages_skipped++;
2227 account_page_redirty(page);
2228 return __set_page_dirty_nobuffers(page);
2229}
2230EXPORT_SYMBOL(redirty_page_for_writepage);
2231
2232/*
2233 * Dirty a page.
2234 *
2235 * For pages with a mapping this should be done under the page lock
2236 * for the benefit of asynchronous memory errors who prefer a consistent
2237 * dirty state. This rule can be broken in some special cases,
2238 * but should be better not to.
2239 *
2240 * If the mapping doesn't provide a set_page_dirty a_op, then
2241 * just fall through and assume that it wants buffer_heads.
2242 */
2243int set_page_dirty(struct page *page)
2244{
2245 struct address_space *mapping = page_mapping(page);
2246
2247 if (likely(mapping)) {
2248 int (*spd)(struct page *) = mapping->a_ops->set_page_dirty;
2249 /*
2250 * readahead/lru_deactivate_page could remain
2251 * PG_readahead/PG_reclaim due to race with end_page_writeback
2252 * About readahead, if the page is written, the flags would be
2253 * reset. So no problem.
2254 * About lru_deactivate_page, if the page is redirty, the flag
2255 * will be reset. So no problem. but if the page is used by readahead
2256 * it will confuse readahead and make it restart the size rampup
2257 * process. But it's a trivial problem.
2258 */
2259 ClearPageReclaim(page);
2260#ifdef CONFIG_BLOCK
2261 if (!spd)
2262 spd = __set_page_dirty_buffers;
2263#endif
2264 return (*spd)(page);
2265 }
2266 if (!PageDirty(page)) {
2267 if (!TestSetPageDirty(page))
2268 return 1;
2269 }
2270 return 0;
2271}
2272EXPORT_SYMBOL(set_page_dirty);
2273
2274/*
2275 * set_page_dirty() is racy if the caller has no reference against
2276 * page->mapping->host, and if the page is unlocked. This is because another
2277 * CPU could truncate the page off the mapping and then free the mapping.
2278 *
2279 * Usually, the page _is_ locked, or the caller is a user-space process which
2280 * holds a reference on the inode by having an open file.
2281 *
2282 * In other cases, the page should be locked before running set_page_dirty().
2283 */
2284int set_page_dirty_lock(struct page *page)
2285{
2286 int ret;
2287
2288 lock_page(page);
2289 ret = set_page_dirty(page);
2290 unlock_page(page);
2291 return ret;
2292}
2293EXPORT_SYMBOL(set_page_dirty_lock);
2294
2295/*
2296 * Clear a page's dirty flag, while caring for dirty memory accounting.
2297 * Returns true if the page was previously dirty.
2298 *
2299 * This is for preparing to put the page under writeout. We leave the page
2300 * tagged as dirty in the radix tree so that a concurrent write-for-sync
2301 * can discover it via a PAGECACHE_TAG_DIRTY walk. The ->writepage
2302 * implementation will run either set_page_writeback() or set_page_dirty(),
2303 * at which stage we bring the page's dirty flag and radix-tree dirty tag
2304 * back into sync.
2305 *
2306 * This incoherency between the page's dirty flag and radix-tree tag is
2307 * unfortunate, but it only exists while the page is locked.
2308 */
2309int clear_page_dirty_for_io(struct page *page)
2310{
2311 struct address_space *mapping = page_mapping(page);
2312
2313 BUG_ON(!PageLocked(page));
2314
2315 if (mapping && mapping_cap_account_dirty(mapping)) {
2316 /*
2317 * Yes, Virginia, this is indeed insane.
2318 *
2319 * We use this sequence to make sure that
2320 * (a) we account for dirty stats properly
2321 * (b) we tell the low-level filesystem to
2322 * mark the whole page dirty if it was
2323 * dirty in a pagetable. Only to then
2324 * (c) clean the page again and return 1 to
2325 * cause the writeback.
2326 *
2327 * This way we avoid all nasty races with the
2328 * dirty bit in multiple places and clearing
2329 * them concurrently from different threads.
2330 *
2331 * Note! Normally the "set_page_dirty(page)"
2332 * has no effect on the actual dirty bit - since
2333 * that will already usually be set. But we
2334 * need the side effects, and it can help us
2335 * avoid races.
2336 *
2337 * We basically use the page "master dirty bit"
2338 * as a serialization point for all the different
2339 * threads doing their things.
2340 */
2341 if (page_mkclean(page))
2342 set_page_dirty(page);
2343 /*
2344 * We carefully synchronise fault handlers against
2345 * installing a dirty pte and marking the page dirty
2346 * at this point. We do this by having them hold the
2347 * page lock at some point after installing their
2348 * pte, but before marking the page dirty.
2349 * Pages are always locked coming in here, so we get
2350 * the desired exclusion. See mm/memory.c:do_wp_page()
2351 * for more comments.
2352 */
2353 if (TestClearPageDirty(page)) {
2354 dec_zone_page_state(page, NR_FILE_DIRTY);
2355 dec_bdi_stat(mapping->backing_dev_info,
2356 BDI_RECLAIMABLE);
2357 return 1;
2358 }
2359 return 0;
2360 }
2361 return TestClearPageDirty(page);
2362}
2363EXPORT_SYMBOL(clear_page_dirty_for_io);
2364
2365int test_clear_page_writeback(struct page *page)
2366{
2367 struct address_space *mapping = page_mapping(page);
2368 int ret;
2369 bool locked;
2370 unsigned long memcg_flags;
2371
2372 mem_cgroup_begin_update_page_stat(page, &locked, &memcg_flags);
2373 if (mapping) {
2374 struct backing_dev_info *bdi = mapping->backing_dev_info;
2375 unsigned long flags;
2376
2377 spin_lock_irqsave(&mapping->tree_lock, flags);
2378 ret = TestClearPageWriteback(page);
2379 if (ret) {
2380 radix_tree_tag_clear(&mapping->page_tree,
2381 page_index(page),
2382 PAGECACHE_TAG_WRITEBACK);
2383 if (bdi_cap_account_writeback(bdi)) {
2384 __dec_bdi_stat(bdi, BDI_WRITEBACK);
2385 __bdi_writeout_inc(bdi);
2386 }
2387 }
2388 spin_unlock_irqrestore(&mapping->tree_lock, flags);
2389 } else {
2390 ret = TestClearPageWriteback(page);
2391 }
2392 if (ret) {
2393 mem_cgroup_dec_page_stat(page, MEM_CGROUP_STAT_WRITEBACK);
2394 dec_zone_page_state(page, NR_WRITEBACK);
2395 inc_zone_page_state(page, NR_WRITTEN);
2396 }
2397 mem_cgroup_end_update_page_stat(page, &locked, &memcg_flags);
2398 return ret;
2399}
2400
2401int test_set_page_writeback(struct page *page)
2402{
2403 struct address_space *mapping = page_mapping(page);
2404 int ret;
2405 bool locked;
2406 unsigned long memcg_flags;
2407
2408 mem_cgroup_begin_update_page_stat(page, &locked, &memcg_flags);
2409 if (mapping) {
2410 struct backing_dev_info *bdi = mapping->backing_dev_info;
2411 unsigned long flags;
2412
2413 spin_lock_irqsave(&mapping->tree_lock, flags);
2414 ret = TestSetPageWriteback(page);
2415 if (!ret) {
2416 radix_tree_tag_set(&mapping->page_tree,
2417 page_index(page),
2418 PAGECACHE_TAG_WRITEBACK);
2419 if (bdi_cap_account_writeback(bdi))
2420 __inc_bdi_stat(bdi, BDI_WRITEBACK);
2421 }
2422 if (!PageDirty(page))
2423 radix_tree_tag_clear(&mapping->page_tree,
2424 page_index(page),
2425 PAGECACHE_TAG_DIRTY);
2426 radix_tree_tag_clear(&mapping->page_tree,
2427 page_index(page),
2428 PAGECACHE_TAG_TOWRITE);
2429 spin_unlock_irqrestore(&mapping->tree_lock, flags);
2430 } else {
2431 ret = TestSetPageWriteback(page);
2432 }
2433 if (!ret)
2434 account_page_writeback(page);
2435 mem_cgroup_end_update_page_stat(page, &locked, &memcg_flags);
2436 return ret;
2437
2438}
2439EXPORT_SYMBOL(test_set_page_writeback);
2440
2441/*
2442 * Return true if any of the pages in the mapping are marked with the
2443 * passed tag.
2444 */
2445int mapping_tagged(struct address_space *mapping, int tag)
2446{
2447 return radix_tree_tagged(&mapping->page_tree, tag);
2448}
2449EXPORT_SYMBOL(mapping_tagged);
2450
2451/**
2452 * wait_for_stable_page() - wait for writeback to finish, if necessary.
2453 * @page: The page to wait on.
2454 *
2455 * This function determines if the given page is related to a backing device
2456 * that requires page contents to be held stable during writeback. If so, then
2457 * it will wait for any pending writeback to complete.
2458 */
2459void wait_for_stable_page(struct page *page)
2460{
2461 struct address_space *mapping = page_mapping(page);
2462 struct backing_dev_info *bdi = mapping->backing_dev_info;
2463
2464 if (!bdi_cap_stable_pages_required(bdi))
2465 return;
2466
2467 wait_on_page_writeback(page);
2468}
2469EXPORT_SYMBOL_GPL(wait_for_stable_page);
1/*
2 * mm/page-writeback.c
3 *
4 * Copyright (C) 2002, Linus Torvalds.
5 * Copyright (C) 2007 Red Hat, Inc., Peter Zijlstra
6 *
7 * Contains functions related to writing back dirty pages at the
8 * address_space level.
9 *
10 * 10Apr2002 Andrew Morton
11 * Initial version
12 */
13
14#include <linux/kernel.h>
15#include <linux/export.h>
16#include <linux/spinlock.h>
17#include <linux/fs.h>
18#include <linux/mm.h>
19#include <linux/swap.h>
20#include <linux/slab.h>
21#include <linux/pagemap.h>
22#include <linux/writeback.h>
23#include <linux/init.h>
24#include <linux/backing-dev.h>
25#include <linux/task_io_accounting_ops.h>
26#include <linux/blkdev.h>
27#include <linux/mpage.h>
28#include <linux/rmap.h>
29#include <linux/percpu.h>
30#include <linux/notifier.h>
31#include <linux/smp.h>
32#include <linux/sysctl.h>
33#include <linux/cpu.h>
34#include <linux/syscalls.h>
35#include <linux/buffer_head.h> /* __set_page_dirty_buffers */
36#include <linux/pagevec.h>
37#include <linux/timer.h>
38#include <linux/sched/rt.h>
39#include <linux/mm_inline.h>
40#include <trace/events/writeback.h>
41
42#include "internal.h"
43
44/*
45 * Sleep at most 200ms at a time in balance_dirty_pages().
46 */
47#define MAX_PAUSE max(HZ/5, 1)
48
49/*
50 * Try to keep balance_dirty_pages() call intervals higher than this many pages
51 * by raising pause time to max_pause when falls below it.
52 */
53#define DIRTY_POLL_THRESH (128 >> (PAGE_SHIFT - 10))
54
55/*
56 * Estimate write bandwidth at 200ms intervals.
57 */
58#define BANDWIDTH_INTERVAL max(HZ/5, 1)
59
60#define RATELIMIT_CALC_SHIFT 10
61
62/*
63 * After a CPU has dirtied this many pages, balance_dirty_pages_ratelimited
64 * will look to see if it needs to force writeback or throttling.
65 */
66static long ratelimit_pages = 32;
67
68/* The following parameters are exported via /proc/sys/vm */
69
70/*
71 * Start background writeback (via writeback threads) at this percentage
72 */
73int dirty_background_ratio = 10;
74
75/*
76 * dirty_background_bytes starts at 0 (disabled) so that it is a function of
77 * dirty_background_ratio * the amount of dirtyable memory
78 */
79unsigned long dirty_background_bytes;
80
81/*
82 * free highmem will not be subtracted from the total free memory
83 * for calculating free ratios if vm_highmem_is_dirtyable is true
84 */
85int vm_highmem_is_dirtyable;
86
87/*
88 * The generator of dirty data starts writeback at this percentage
89 */
90int vm_dirty_ratio = 20;
91
92/*
93 * vm_dirty_bytes starts at 0 (disabled) so that it is a function of
94 * vm_dirty_ratio * the amount of dirtyable memory
95 */
96unsigned long vm_dirty_bytes;
97
98/*
99 * The interval between `kupdate'-style writebacks
100 */
101unsigned int dirty_writeback_interval = 5 * 100; /* centiseconds */
102
103EXPORT_SYMBOL_GPL(dirty_writeback_interval);
104
105/*
106 * The longest time for which data is allowed to remain dirty
107 */
108unsigned int dirty_expire_interval = 30 * 100; /* centiseconds */
109
110/*
111 * Flag that makes the machine dump writes/reads and block dirtyings.
112 */
113int block_dump;
114
115/*
116 * Flag that puts the machine in "laptop mode". Doubles as a timeout in jiffies:
117 * a full sync is triggered after this time elapses without any disk activity.
118 */
119int laptop_mode;
120
121EXPORT_SYMBOL(laptop_mode);
122
123/* End of sysctl-exported parameters */
124
125struct wb_domain global_wb_domain;
126
127/* consolidated parameters for balance_dirty_pages() and its subroutines */
128struct dirty_throttle_control {
129#ifdef CONFIG_CGROUP_WRITEBACK
130 struct wb_domain *dom;
131 struct dirty_throttle_control *gdtc; /* only set in memcg dtc's */
132#endif
133 struct bdi_writeback *wb;
134 struct fprop_local_percpu *wb_completions;
135
136 unsigned long avail; /* dirtyable */
137 unsigned long dirty; /* file_dirty + write + nfs */
138 unsigned long thresh; /* dirty threshold */
139 unsigned long bg_thresh; /* dirty background threshold */
140
141 unsigned long wb_dirty; /* per-wb counterparts */
142 unsigned long wb_thresh;
143 unsigned long wb_bg_thresh;
144
145 unsigned long pos_ratio;
146};
147
148/*
149 * Length of period for aging writeout fractions of bdis. This is an
150 * arbitrarily chosen number. The longer the period, the slower fractions will
151 * reflect changes in current writeout rate.
152 */
153#define VM_COMPLETIONS_PERIOD_LEN (3*HZ)
154
155#ifdef CONFIG_CGROUP_WRITEBACK
156
157#define GDTC_INIT(__wb) .wb = (__wb), \
158 .dom = &global_wb_domain, \
159 .wb_completions = &(__wb)->completions
160
161#define GDTC_INIT_NO_WB .dom = &global_wb_domain
162
163#define MDTC_INIT(__wb, __gdtc) .wb = (__wb), \
164 .dom = mem_cgroup_wb_domain(__wb), \
165 .wb_completions = &(__wb)->memcg_completions, \
166 .gdtc = __gdtc
167
168static bool mdtc_valid(struct dirty_throttle_control *dtc)
169{
170 return dtc->dom;
171}
172
173static struct wb_domain *dtc_dom(struct dirty_throttle_control *dtc)
174{
175 return dtc->dom;
176}
177
178static struct dirty_throttle_control *mdtc_gdtc(struct dirty_throttle_control *mdtc)
179{
180 return mdtc->gdtc;
181}
182
183static struct fprop_local_percpu *wb_memcg_completions(struct bdi_writeback *wb)
184{
185 return &wb->memcg_completions;
186}
187
188static void wb_min_max_ratio(struct bdi_writeback *wb,
189 unsigned long *minp, unsigned long *maxp)
190{
191 unsigned long this_bw = wb->avg_write_bandwidth;
192 unsigned long tot_bw = atomic_long_read(&wb->bdi->tot_write_bandwidth);
193 unsigned long long min = wb->bdi->min_ratio;
194 unsigned long long max = wb->bdi->max_ratio;
195
196 /*
197 * @wb may already be clean by the time control reaches here and
198 * the total may not include its bw.
199 */
200 if (this_bw < tot_bw) {
201 if (min) {
202 min *= this_bw;
203 do_div(min, tot_bw);
204 }
205 if (max < 100) {
206 max *= this_bw;
207 do_div(max, tot_bw);
208 }
209 }
210
211 *minp = min;
212 *maxp = max;
213}
214
215#else /* CONFIG_CGROUP_WRITEBACK */
216
217#define GDTC_INIT(__wb) .wb = (__wb), \
218 .wb_completions = &(__wb)->completions
219#define GDTC_INIT_NO_WB
220#define MDTC_INIT(__wb, __gdtc)
221
222static bool mdtc_valid(struct dirty_throttle_control *dtc)
223{
224 return false;
225}
226
227static struct wb_domain *dtc_dom(struct dirty_throttle_control *dtc)
228{
229 return &global_wb_domain;
230}
231
232static struct dirty_throttle_control *mdtc_gdtc(struct dirty_throttle_control *mdtc)
233{
234 return NULL;
235}
236
237static struct fprop_local_percpu *wb_memcg_completions(struct bdi_writeback *wb)
238{
239 return NULL;
240}
241
242static void wb_min_max_ratio(struct bdi_writeback *wb,
243 unsigned long *minp, unsigned long *maxp)
244{
245 *minp = wb->bdi->min_ratio;
246 *maxp = wb->bdi->max_ratio;
247}
248
249#endif /* CONFIG_CGROUP_WRITEBACK */
250
251/*
252 * In a memory zone, there is a certain amount of pages we consider
253 * available for the page cache, which is essentially the number of
254 * free and reclaimable pages, minus some zone reserves to protect
255 * lowmem and the ability to uphold the zone's watermarks without
256 * requiring writeback.
257 *
258 * This number of dirtyable pages is the base value of which the
259 * user-configurable dirty ratio is the effictive number of pages that
260 * are allowed to be actually dirtied. Per individual zone, or
261 * globally by using the sum of dirtyable pages over all zones.
262 *
263 * Because the user is allowed to specify the dirty limit globally as
264 * absolute number of bytes, calculating the per-zone dirty limit can
265 * require translating the configured limit into a percentage of
266 * global dirtyable memory first.
267 */
268
269/**
270 * node_dirtyable_memory - number of dirtyable pages in a node
271 * @pgdat: the node
272 *
273 * Returns the node's number of pages potentially available for dirty
274 * page cache. This is the base value for the per-node dirty limits.
275 */
276static unsigned long node_dirtyable_memory(struct pglist_data *pgdat)
277{
278 unsigned long nr_pages = 0;
279 int z;
280
281 for (z = 0; z < MAX_NR_ZONES; z++) {
282 struct zone *zone = pgdat->node_zones + z;
283
284 if (!populated_zone(zone))
285 continue;
286
287 nr_pages += zone_page_state(zone, NR_FREE_PAGES);
288 }
289
290 /*
291 * Pages reserved for the kernel should not be considered
292 * dirtyable, to prevent a situation where reclaim has to
293 * clean pages in order to balance the zones.
294 */
295 nr_pages -= min(nr_pages, pgdat->totalreserve_pages);
296
297 nr_pages += node_page_state(pgdat, NR_INACTIVE_FILE);
298 nr_pages += node_page_state(pgdat, NR_ACTIVE_FILE);
299
300 return nr_pages;
301}
302
303static unsigned long highmem_dirtyable_memory(unsigned long total)
304{
305#ifdef CONFIG_HIGHMEM
306 int node;
307 unsigned long x = 0;
308 int i;
309
310 for_each_node_state(node, N_HIGH_MEMORY) {
311 for (i = ZONE_NORMAL + 1; i < MAX_NR_ZONES; i++) {
312 struct zone *z;
313 unsigned long nr_pages;
314
315 if (!is_highmem_idx(i))
316 continue;
317
318 z = &NODE_DATA(node)->node_zones[i];
319 if (!populated_zone(z))
320 continue;
321
322 nr_pages = zone_page_state(z, NR_FREE_PAGES);
323 /* watch for underflows */
324 nr_pages -= min(nr_pages, high_wmark_pages(z));
325 nr_pages += zone_page_state(z, NR_ZONE_INACTIVE_FILE);
326 nr_pages += zone_page_state(z, NR_ZONE_ACTIVE_FILE);
327 x += nr_pages;
328 }
329 }
330
331 /*
332 * Unreclaimable memory (kernel memory or anonymous memory
333 * without swap) can bring down the dirtyable pages below
334 * the zone's dirty balance reserve and the above calculation
335 * will underflow. However we still want to add in nodes
336 * which are below threshold (negative values) to get a more
337 * accurate calculation but make sure that the total never
338 * underflows.
339 */
340 if ((long)x < 0)
341 x = 0;
342
343 /*
344 * Make sure that the number of highmem pages is never larger
345 * than the number of the total dirtyable memory. This can only
346 * occur in very strange VM situations but we want to make sure
347 * that this does not occur.
348 */
349 return min(x, total);
350#else
351 return 0;
352#endif
353}
354
355/**
356 * global_dirtyable_memory - number of globally dirtyable pages
357 *
358 * Returns the global number of pages potentially available for dirty
359 * page cache. This is the base value for the global dirty limits.
360 */
361static unsigned long global_dirtyable_memory(void)
362{
363 unsigned long x;
364
365 x = global_page_state(NR_FREE_PAGES);
366 /*
367 * Pages reserved for the kernel should not be considered
368 * dirtyable, to prevent a situation where reclaim has to
369 * clean pages in order to balance the zones.
370 */
371 x -= min(x, totalreserve_pages);
372
373 x += global_node_page_state(NR_INACTIVE_FILE);
374 x += global_node_page_state(NR_ACTIVE_FILE);
375
376 if (!vm_highmem_is_dirtyable)
377 x -= highmem_dirtyable_memory(x);
378
379 return x + 1; /* Ensure that we never return 0 */
380}
381
382/**
383 * domain_dirty_limits - calculate thresh and bg_thresh for a wb_domain
384 * @dtc: dirty_throttle_control of interest
385 *
386 * Calculate @dtc->thresh and ->bg_thresh considering
387 * vm_dirty_{bytes|ratio} and dirty_background_{bytes|ratio}. The caller
388 * must ensure that @dtc->avail is set before calling this function. The
389 * dirty limits will be lifted by 1/4 for PF_LESS_THROTTLE (ie. nfsd) and
390 * real-time tasks.
391 */
392static void domain_dirty_limits(struct dirty_throttle_control *dtc)
393{
394 const unsigned long available_memory = dtc->avail;
395 struct dirty_throttle_control *gdtc = mdtc_gdtc(dtc);
396 unsigned long bytes = vm_dirty_bytes;
397 unsigned long bg_bytes = dirty_background_bytes;
398 /* convert ratios to per-PAGE_SIZE for higher precision */
399 unsigned long ratio = (vm_dirty_ratio * PAGE_SIZE) / 100;
400 unsigned long bg_ratio = (dirty_background_ratio * PAGE_SIZE) / 100;
401 unsigned long thresh;
402 unsigned long bg_thresh;
403 struct task_struct *tsk;
404
405 /* gdtc is !NULL iff @dtc is for memcg domain */
406 if (gdtc) {
407 unsigned long global_avail = gdtc->avail;
408
409 /*
410 * The byte settings can't be applied directly to memcg
411 * domains. Convert them to ratios by scaling against
412 * globally available memory. As the ratios are in
413 * per-PAGE_SIZE, they can be obtained by dividing bytes by
414 * number of pages.
415 */
416 if (bytes)
417 ratio = min(DIV_ROUND_UP(bytes, global_avail),
418 PAGE_SIZE);
419 if (bg_bytes)
420 bg_ratio = min(DIV_ROUND_UP(bg_bytes, global_avail),
421 PAGE_SIZE);
422 bytes = bg_bytes = 0;
423 }
424
425 if (bytes)
426 thresh = DIV_ROUND_UP(bytes, PAGE_SIZE);
427 else
428 thresh = (ratio * available_memory) / PAGE_SIZE;
429
430 if (bg_bytes)
431 bg_thresh = DIV_ROUND_UP(bg_bytes, PAGE_SIZE);
432 else
433 bg_thresh = (bg_ratio * available_memory) / PAGE_SIZE;
434
435 if (bg_thresh >= thresh)
436 bg_thresh = thresh / 2;
437 tsk = current;
438 if (tsk->flags & PF_LESS_THROTTLE || rt_task(tsk)) {
439 bg_thresh += bg_thresh / 4 + global_wb_domain.dirty_limit / 32;
440 thresh += thresh / 4 + global_wb_domain.dirty_limit / 32;
441 }
442 dtc->thresh = thresh;
443 dtc->bg_thresh = bg_thresh;
444
445 /* we should eventually report the domain in the TP */
446 if (!gdtc)
447 trace_global_dirty_state(bg_thresh, thresh);
448}
449
450/**
451 * global_dirty_limits - background-writeback and dirty-throttling thresholds
452 * @pbackground: out parameter for bg_thresh
453 * @pdirty: out parameter for thresh
454 *
455 * Calculate bg_thresh and thresh for global_wb_domain. See
456 * domain_dirty_limits() for details.
457 */
458void global_dirty_limits(unsigned long *pbackground, unsigned long *pdirty)
459{
460 struct dirty_throttle_control gdtc = { GDTC_INIT_NO_WB };
461
462 gdtc.avail = global_dirtyable_memory();
463 domain_dirty_limits(&gdtc);
464
465 *pbackground = gdtc.bg_thresh;
466 *pdirty = gdtc.thresh;
467}
468
469/**
470 * node_dirty_limit - maximum number of dirty pages allowed in a node
471 * @pgdat: the node
472 *
473 * Returns the maximum number of dirty pages allowed in a node, based
474 * on the node's dirtyable memory.
475 */
476static unsigned long node_dirty_limit(struct pglist_data *pgdat)
477{
478 unsigned long node_memory = node_dirtyable_memory(pgdat);
479 struct task_struct *tsk = current;
480 unsigned long dirty;
481
482 if (vm_dirty_bytes)
483 dirty = DIV_ROUND_UP(vm_dirty_bytes, PAGE_SIZE) *
484 node_memory / global_dirtyable_memory();
485 else
486 dirty = vm_dirty_ratio * node_memory / 100;
487
488 if (tsk->flags & PF_LESS_THROTTLE || rt_task(tsk))
489 dirty += dirty / 4;
490
491 return dirty;
492}
493
494/**
495 * node_dirty_ok - tells whether a node is within its dirty limits
496 * @pgdat: the node to check
497 *
498 * Returns %true when the dirty pages in @pgdat are within the node's
499 * dirty limit, %false if the limit is exceeded.
500 */
501bool node_dirty_ok(struct pglist_data *pgdat)
502{
503 unsigned long limit = node_dirty_limit(pgdat);
504 unsigned long nr_pages = 0;
505
506 nr_pages += node_page_state(pgdat, NR_FILE_DIRTY);
507 nr_pages += node_page_state(pgdat, NR_UNSTABLE_NFS);
508 nr_pages += node_page_state(pgdat, NR_WRITEBACK);
509
510 return nr_pages <= limit;
511}
512
513int dirty_background_ratio_handler(struct ctl_table *table, int write,
514 void __user *buffer, size_t *lenp,
515 loff_t *ppos)
516{
517 int ret;
518
519 ret = proc_dointvec_minmax(table, write, buffer, lenp, ppos);
520 if (ret == 0 && write)
521 dirty_background_bytes = 0;
522 return ret;
523}
524
525int dirty_background_bytes_handler(struct ctl_table *table, int write,
526 void __user *buffer, size_t *lenp,
527 loff_t *ppos)
528{
529 int ret;
530
531 ret = proc_doulongvec_minmax(table, write, buffer, lenp, ppos);
532 if (ret == 0 && write)
533 dirty_background_ratio = 0;
534 return ret;
535}
536
537int dirty_ratio_handler(struct ctl_table *table, int write,
538 void __user *buffer, size_t *lenp,
539 loff_t *ppos)
540{
541 int old_ratio = vm_dirty_ratio;
542 int ret;
543
544 ret = proc_dointvec_minmax(table, write, buffer, lenp, ppos);
545 if (ret == 0 && write && vm_dirty_ratio != old_ratio) {
546 writeback_set_ratelimit();
547 vm_dirty_bytes = 0;
548 }
549 return ret;
550}
551
552int dirty_bytes_handler(struct ctl_table *table, int write,
553 void __user *buffer, size_t *lenp,
554 loff_t *ppos)
555{
556 unsigned long old_bytes = vm_dirty_bytes;
557 int ret;
558
559 ret = proc_doulongvec_minmax(table, write, buffer, lenp, ppos);
560 if (ret == 0 && write && vm_dirty_bytes != old_bytes) {
561 writeback_set_ratelimit();
562 vm_dirty_ratio = 0;
563 }
564 return ret;
565}
566
567static unsigned long wp_next_time(unsigned long cur_time)
568{
569 cur_time += VM_COMPLETIONS_PERIOD_LEN;
570 /* 0 has a special meaning... */
571 if (!cur_time)
572 return 1;
573 return cur_time;
574}
575
576static void wb_domain_writeout_inc(struct wb_domain *dom,
577 struct fprop_local_percpu *completions,
578 unsigned int max_prop_frac)
579{
580 __fprop_inc_percpu_max(&dom->completions, completions,
581 max_prop_frac);
582 /* First event after period switching was turned off? */
583 if (!unlikely(dom->period_time)) {
584 /*
585 * We can race with other __bdi_writeout_inc calls here but
586 * it does not cause any harm since the resulting time when
587 * timer will fire and what is in writeout_period_time will be
588 * roughly the same.
589 */
590 dom->period_time = wp_next_time(jiffies);
591 mod_timer(&dom->period_timer, dom->period_time);
592 }
593}
594
595/*
596 * Increment @wb's writeout completion count and the global writeout
597 * completion count. Called from test_clear_page_writeback().
598 */
599static inline void __wb_writeout_inc(struct bdi_writeback *wb)
600{
601 struct wb_domain *cgdom;
602
603 __inc_wb_stat(wb, WB_WRITTEN);
604 wb_domain_writeout_inc(&global_wb_domain, &wb->completions,
605 wb->bdi->max_prop_frac);
606
607 cgdom = mem_cgroup_wb_domain(wb);
608 if (cgdom)
609 wb_domain_writeout_inc(cgdom, wb_memcg_completions(wb),
610 wb->bdi->max_prop_frac);
611}
612
613void wb_writeout_inc(struct bdi_writeback *wb)
614{
615 unsigned long flags;
616
617 local_irq_save(flags);
618 __wb_writeout_inc(wb);
619 local_irq_restore(flags);
620}
621EXPORT_SYMBOL_GPL(wb_writeout_inc);
622
623/*
624 * On idle system, we can be called long after we scheduled because we use
625 * deferred timers so count with missed periods.
626 */
627static void writeout_period(unsigned long t)
628{
629 struct wb_domain *dom = (void *)t;
630 int miss_periods = (jiffies - dom->period_time) /
631 VM_COMPLETIONS_PERIOD_LEN;
632
633 if (fprop_new_period(&dom->completions, miss_periods + 1)) {
634 dom->period_time = wp_next_time(dom->period_time +
635 miss_periods * VM_COMPLETIONS_PERIOD_LEN);
636 mod_timer(&dom->period_timer, dom->period_time);
637 } else {
638 /*
639 * Aging has zeroed all fractions. Stop wasting CPU on period
640 * updates.
641 */
642 dom->period_time = 0;
643 }
644}
645
646int wb_domain_init(struct wb_domain *dom, gfp_t gfp)
647{
648 memset(dom, 0, sizeof(*dom));
649
650 spin_lock_init(&dom->lock);
651
652 init_timer_deferrable(&dom->period_timer);
653 dom->period_timer.function = writeout_period;
654 dom->period_timer.data = (unsigned long)dom;
655
656 dom->dirty_limit_tstamp = jiffies;
657
658 return fprop_global_init(&dom->completions, gfp);
659}
660
661#ifdef CONFIG_CGROUP_WRITEBACK
662void wb_domain_exit(struct wb_domain *dom)
663{
664 del_timer_sync(&dom->period_timer);
665 fprop_global_destroy(&dom->completions);
666}
667#endif
668
669/*
670 * bdi_min_ratio keeps the sum of the minimum dirty shares of all
671 * registered backing devices, which, for obvious reasons, can not
672 * exceed 100%.
673 */
674static unsigned int bdi_min_ratio;
675
676int bdi_set_min_ratio(struct backing_dev_info *bdi, unsigned int min_ratio)
677{
678 int ret = 0;
679
680 spin_lock_bh(&bdi_lock);
681 if (min_ratio > bdi->max_ratio) {
682 ret = -EINVAL;
683 } else {
684 min_ratio -= bdi->min_ratio;
685 if (bdi_min_ratio + min_ratio < 100) {
686 bdi_min_ratio += min_ratio;
687 bdi->min_ratio += min_ratio;
688 } else {
689 ret = -EINVAL;
690 }
691 }
692 spin_unlock_bh(&bdi_lock);
693
694 return ret;
695}
696
697int bdi_set_max_ratio(struct backing_dev_info *bdi, unsigned max_ratio)
698{
699 int ret = 0;
700
701 if (max_ratio > 100)
702 return -EINVAL;
703
704 spin_lock_bh(&bdi_lock);
705 if (bdi->min_ratio > max_ratio) {
706 ret = -EINVAL;
707 } else {
708 bdi->max_ratio = max_ratio;
709 bdi->max_prop_frac = (FPROP_FRAC_BASE * max_ratio) / 100;
710 }
711 spin_unlock_bh(&bdi_lock);
712
713 return ret;
714}
715EXPORT_SYMBOL(bdi_set_max_ratio);
716
717static unsigned long dirty_freerun_ceiling(unsigned long thresh,
718 unsigned long bg_thresh)
719{
720 return (thresh + bg_thresh) / 2;
721}
722
723static unsigned long hard_dirty_limit(struct wb_domain *dom,
724 unsigned long thresh)
725{
726 return max(thresh, dom->dirty_limit);
727}
728
729/*
730 * Memory which can be further allocated to a memcg domain is capped by
731 * system-wide clean memory excluding the amount being used in the domain.
732 */
733static void mdtc_calc_avail(struct dirty_throttle_control *mdtc,
734 unsigned long filepages, unsigned long headroom)
735{
736 struct dirty_throttle_control *gdtc = mdtc_gdtc(mdtc);
737 unsigned long clean = filepages - min(filepages, mdtc->dirty);
738 unsigned long global_clean = gdtc->avail - min(gdtc->avail, gdtc->dirty);
739 unsigned long other_clean = global_clean - min(global_clean, clean);
740
741 mdtc->avail = filepages + min(headroom, other_clean);
742}
743
744/**
745 * __wb_calc_thresh - @wb's share of dirty throttling threshold
746 * @dtc: dirty_throttle_context of interest
747 *
748 * Returns @wb's dirty limit in pages. The term "dirty" in the context of
749 * dirty balancing includes all PG_dirty, PG_writeback and NFS unstable pages.
750 *
751 * Note that balance_dirty_pages() will only seriously take it as a hard limit
752 * when sleeping max_pause per page is not enough to keep the dirty pages under
753 * control. For example, when the device is completely stalled due to some error
754 * conditions, or when there are 1000 dd tasks writing to a slow 10MB/s USB key.
755 * In the other normal situations, it acts more gently by throttling the tasks
756 * more (rather than completely block them) when the wb dirty pages go high.
757 *
758 * It allocates high/low dirty limits to fast/slow devices, in order to prevent
759 * - starving fast devices
760 * - piling up dirty pages (that will take long time to sync) on slow devices
761 *
762 * The wb's share of dirty limit will be adapting to its throughput and
763 * bounded by the bdi->min_ratio and/or bdi->max_ratio parameters, if set.
764 */
765static unsigned long __wb_calc_thresh(struct dirty_throttle_control *dtc)
766{
767 struct wb_domain *dom = dtc_dom(dtc);
768 unsigned long thresh = dtc->thresh;
769 u64 wb_thresh;
770 long numerator, denominator;
771 unsigned long wb_min_ratio, wb_max_ratio;
772
773 /*
774 * Calculate this BDI's share of the thresh ratio.
775 */
776 fprop_fraction_percpu(&dom->completions, dtc->wb_completions,
777 &numerator, &denominator);
778
779 wb_thresh = (thresh * (100 - bdi_min_ratio)) / 100;
780 wb_thresh *= numerator;
781 do_div(wb_thresh, denominator);
782
783 wb_min_max_ratio(dtc->wb, &wb_min_ratio, &wb_max_ratio);
784
785 wb_thresh += (thresh * wb_min_ratio) / 100;
786 if (wb_thresh > (thresh * wb_max_ratio) / 100)
787 wb_thresh = thresh * wb_max_ratio / 100;
788
789 return wb_thresh;
790}
791
792unsigned long wb_calc_thresh(struct bdi_writeback *wb, unsigned long thresh)
793{
794 struct dirty_throttle_control gdtc = { GDTC_INIT(wb),
795 .thresh = thresh };
796 return __wb_calc_thresh(&gdtc);
797}
798
799/*
800 * setpoint - dirty 3
801 * f(dirty) := 1.0 + (----------------)
802 * limit - setpoint
803 *
804 * it's a 3rd order polynomial that subjects to
805 *
806 * (1) f(freerun) = 2.0 => rampup dirty_ratelimit reasonably fast
807 * (2) f(setpoint) = 1.0 => the balance point
808 * (3) f(limit) = 0 => the hard limit
809 * (4) df/dx <= 0 => negative feedback control
810 * (5) the closer to setpoint, the smaller |df/dx| (and the reverse)
811 * => fast response on large errors; small oscillation near setpoint
812 */
813static long long pos_ratio_polynom(unsigned long setpoint,
814 unsigned long dirty,
815 unsigned long limit)
816{
817 long long pos_ratio;
818 long x;
819
820 x = div64_s64(((s64)setpoint - (s64)dirty) << RATELIMIT_CALC_SHIFT,
821 (limit - setpoint) | 1);
822 pos_ratio = x;
823 pos_ratio = pos_ratio * x >> RATELIMIT_CALC_SHIFT;
824 pos_ratio = pos_ratio * x >> RATELIMIT_CALC_SHIFT;
825 pos_ratio += 1 << RATELIMIT_CALC_SHIFT;
826
827 return clamp(pos_ratio, 0LL, 2LL << RATELIMIT_CALC_SHIFT);
828}
829
830/*
831 * Dirty position control.
832 *
833 * (o) global/bdi setpoints
834 *
835 * We want the dirty pages be balanced around the global/wb setpoints.
836 * When the number of dirty pages is higher/lower than the setpoint, the
837 * dirty position control ratio (and hence task dirty ratelimit) will be
838 * decreased/increased to bring the dirty pages back to the setpoint.
839 *
840 * pos_ratio = 1 << RATELIMIT_CALC_SHIFT
841 *
842 * if (dirty < setpoint) scale up pos_ratio
843 * if (dirty > setpoint) scale down pos_ratio
844 *
845 * if (wb_dirty < wb_setpoint) scale up pos_ratio
846 * if (wb_dirty > wb_setpoint) scale down pos_ratio
847 *
848 * task_ratelimit = dirty_ratelimit * pos_ratio >> RATELIMIT_CALC_SHIFT
849 *
850 * (o) global control line
851 *
852 * ^ pos_ratio
853 * |
854 * | |<===== global dirty control scope ======>|
855 * 2.0 .............*
856 * | .*
857 * | . *
858 * | . *
859 * | . *
860 * | . *
861 * | . *
862 * 1.0 ................................*
863 * | . . *
864 * | . . *
865 * | . . *
866 * | . . *
867 * | . . *
868 * 0 +------------.------------------.----------------------*------------->
869 * freerun^ setpoint^ limit^ dirty pages
870 *
871 * (o) wb control line
872 *
873 * ^ pos_ratio
874 * |
875 * | *
876 * | *
877 * | *
878 * | *
879 * | * |<=========== span ============>|
880 * 1.0 .......................*
881 * | . *
882 * | . *
883 * | . *
884 * | . *
885 * | . *
886 * | . *
887 * | . *
888 * | . *
889 * | . *
890 * | . *
891 * | . *
892 * 1/4 ...............................................* * * * * * * * * * * *
893 * | . .
894 * | . .
895 * | . .
896 * 0 +----------------------.-------------------------------.------------->
897 * wb_setpoint^ x_intercept^
898 *
899 * The wb control line won't drop below pos_ratio=1/4, so that wb_dirty can
900 * be smoothly throttled down to normal if it starts high in situations like
901 * - start writing to a slow SD card and a fast disk at the same time. The SD
902 * card's wb_dirty may rush to many times higher than wb_setpoint.
903 * - the wb dirty thresh drops quickly due to change of JBOD workload
904 */
905static void wb_position_ratio(struct dirty_throttle_control *dtc)
906{
907 struct bdi_writeback *wb = dtc->wb;
908 unsigned long write_bw = wb->avg_write_bandwidth;
909 unsigned long freerun = dirty_freerun_ceiling(dtc->thresh, dtc->bg_thresh);
910 unsigned long limit = hard_dirty_limit(dtc_dom(dtc), dtc->thresh);
911 unsigned long wb_thresh = dtc->wb_thresh;
912 unsigned long x_intercept;
913 unsigned long setpoint; /* dirty pages' target balance point */
914 unsigned long wb_setpoint;
915 unsigned long span;
916 long long pos_ratio; /* for scaling up/down the rate limit */
917 long x;
918
919 dtc->pos_ratio = 0;
920
921 if (unlikely(dtc->dirty >= limit))
922 return;
923
924 /*
925 * global setpoint
926 *
927 * See comment for pos_ratio_polynom().
928 */
929 setpoint = (freerun + limit) / 2;
930 pos_ratio = pos_ratio_polynom(setpoint, dtc->dirty, limit);
931
932 /*
933 * The strictlimit feature is a tool preventing mistrusted filesystems
934 * from growing a large number of dirty pages before throttling. For
935 * such filesystems balance_dirty_pages always checks wb counters
936 * against wb limits. Even if global "nr_dirty" is under "freerun".
937 * This is especially important for fuse which sets bdi->max_ratio to
938 * 1% by default. Without strictlimit feature, fuse writeback may
939 * consume arbitrary amount of RAM because it is accounted in
940 * NR_WRITEBACK_TEMP which is not involved in calculating "nr_dirty".
941 *
942 * Here, in wb_position_ratio(), we calculate pos_ratio based on
943 * two values: wb_dirty and wb_thresh. Let's consider an example:
944 * total amount of RAM is 16GB, bdi->max_ratio is equal to 1%, global
945 * limits are set by default to 10% and 20% (background and throttle).
946 * Then wb_thresh is 1% of 20% of 16GB. This amounts to ~8K pages.
947 * wb_calc_thresh(wb, bg_thresh) is about ~4K pages. wb_setpoint is
948 * about ~6K pages (as the average of background and throttle wb
949 * limits). The 3rd order polynomial will provide positive feedback if
950 * wb_dirty is under wb_setpoint and vice versa.
951 *
952 * Note, that we cannot use global counters in these calculations
953 * because we want to throttle process writing to a strictlimit wb
954 * much earlier than global "freerun" is reached (~23MB vs. ~2.3GB
955 * in the example above).
956 */
957 if (unlikely(wb->bdi->capabilities & BDI_CAP_STRICTLIMIT)) {
958 long long wb_pos_ratio;
959
960 if (dtc->wb_dirty < 8) {
961 dtc->pos_ratio = min_t(long long, pos_ratio * 2,
962 2 << RATELIMIT_CALC_SHIFT);
963 return;
964 }
965
966 if (dtc->wb_dirty >= wb_thresh)
967 return;
968
969 wb_setpoint = dirty_freerun_ceiling(wb_thresh,
970 dtc->wb_bg_thresh);
971
972 if (wb_setpoint == 0 || wb_setpoint == wb_thresh)
973 return;
974
975 wb_pos_ratio = pos_ratio_polynom(wb_setpoint, dtc->wb_dirty,
976 wb_thresh);
977
978 /*
979 * Typically, for strictlimit case, wb_setpoint << setpoint
980 * and pos_ratio >> wb_pos_ratio. In the other words global
981 * state ("dirty") is not limiting factor and we have to
982 * make decision based on wb counters. But there is an
983 * important case when global pos_ratio should get precedence:
984 * global limits are exceeded (e.g. due to activities on other
985 * wb's) while given strictlimit wb is below limit.
986 *
987 * "pos_ratio * wb_pos_ratio" would work for the case above,
988 * but it would look too non-natural for the case of all
989 * activity in the system coming from a single strictlimit wb
990 * with bdi->max_ratio == 100%.
991 *
992 * Note that min() below somewhat changes the dynamics of the
993 * control system. Normally, pos_ratio value can be well over 3
994 * (when globally we are at freerun and wb is well below wb
995 * setpoint). Now the maximum pos_ratio in the same situation
996 * is 2. We might want to tweak this if we observe the control
997 * system is too slow to adapt.
998 */
999 dtc->pos_ratio = min(pos_ratio, wb_pos_ratio);
1000 return;
1001 }
1002
1003 /*
1004 * We have computed basic pos_ratio above based on global situation. If
1005 * the wb is over/under its share of dirty pages, we want to scale
1006 * pos_ratio further down/up. That is done by the following mechanism.
1007 */
1008
1009 /*
1010 * wb setpoint
1011 *
1012 * f(wb_dirty) := 1.0 + k * (wb_dirty - wb_setpoint)
1013 *
1014 * x_intercept - wb_dirty
1015 * := --------------------------
1016 * x_intercept - wb_setpoint
1017 *
1018 * The main wb control line is a linear function that subjects to
1019 *
1020 * (1) f(wb_setpoint) = 1.0
1021 * (2) k = - 1 / (8 * write_bw) (in single wb case)
1022 * or equally: x_intercept = wb_setpoint + 8 * write_bw
1023 *
1024 * For single wb case, the dirty pages are observed to fluctuate
1025 * regularly within range
1026 * [wb_setpoint - write_bw/2, wb_setpoint + write_bw/2]
1027 * for various filesystems, where (2) can yield in a reasonable 12.5%
1028 * fluctuation range for pos_ratio.
1029 *
1030 * For JBOD case, wb_thresh (not wb_dirty!) could fluctuate up to its
1031 * own size, so move the slope over accordingly and choose a slope that
1032 * yields 100% pos_ratio fluctuation on suddenly doubled wb_thresh.
1033 */
1034 if (unlikely(wb_thresh > dtc->thresh))
1035 wb_thresh = dtc->thresh;
1036 /*
1037 * It's very possible that wb_thresh is close to 0 not because the
1038 * device is slow, but that it has remained inactive for long time.
1039 * Honour such devices a reasonable good (hopefully IO efficient)
1040 * threshold, so that the occasional writes won't be blocked and active
1041 * writes can rampup the threshold quickly.
1042 */
1043 wb_thresh = max(wb_thresh, (limit - dtc->dirty) / 8);
1044 /*
1045 * scale global setpoint to wb's:
1046 * wb_setpoint = setpoint * wb_thresh / thresh
1047 */
1048 x = div_u64((u64)wb_thresh << 16, dtc->thresh | 1);
1049 wb_setpoint = setpoint * (u64)x >> 16;
1050 /*
1051 * Use span=(8*write_bw) in single wb case as indicated by
1052 * (thresh - wb_thresh ~= 0) and transit to wb_thresh in JBOD case.
1053 *
1054 * wb_thresh thresh - wb_thresh
1055 * span = --------- * (8 * write_bw) + ------------------ * wb_thresh
1056 * thresh thresh
1057 */
1058 span = (dtc->thresh - wb_thresh + 8 * write_bw) * (u64)x >> 16;
1059 x_intercept = wb_setpoint + span;
1060
1061 if (dtc->wb_dirty < x_intercept - span / 4) {
1062 pos_ratio = div64_u64(pos_ratio * (x_intercept - dtc->wb_dirty),
1063 (x_intercept - wb_setpoint) | 1);
1064 } else
1065 pos_ratio /= 4;
1066
1067 /*
1068 * wb reserve area, safeguard against dirty pool underrun and disk idle
1069 * It may push the desired control point of global dirty pages higher
1070 * than setpoint.
1071 */
1072 x_intercept = wb_thresh / 2;
1073 if (dtc->wb_dirty < x_intercept) {
1074 if (dtc->wb_dirty > x_intercept / 8)
1075 pos_ratio = div_u64(pos_ratio * x_intercept,
1076 dtc->wb_dirty);
1077 else
1078 pos_ratio *= 8;
1079 }
1080
1081 dtc->pos_ratio = pos_ratio;
1082}
1083
1084static void wb_update_write_bandwidth(struct bdi_writeback *wb,
1085 unsigned long elapsed,
1086 unsigned long written)
1087{
1088 const unsigned long period = roundup_pow_of_two(3 * HZ);
1089 unsigned long avg = wb->avg_write_bandwidth;
1090 unsigned long old = wb->write_bandwidth;
1091 u64 bw;
1092
1093 /*
1094 * bw = written * HZ / elapsed
1095 *
1096 * bw * elapsed + write_bandwidth * (period - elapsed)
1097 * write_bandwidth = ---------------------------------------------------
1098 * period
1099 *
1100 * @written may have decreased due to account_page_redirty().
1101 * Avoid underflowing @bw calculation.
1102 */
1103 bw = written - min(written, wb->written_stamp);
1104 bw *= HZ;
1105 if (unlikely(elapsed > period)) {
1106 do_div(bw, elapsed);
1107 avg = bw;
1108 goto out;
1109 }
1110 bw += (u64)wb->write_bandwidth * (period - elapsed);
1111 bw >>= ilog2(period);
1112
1113 /*
1114 * one more level of smoothing, for filtering out sudden spikes
1115 */
1116 if (avg > old && old >= (unsigned long)bw)
1117 avg -= (avg - old) >> 3;
1118
1119 if (avg < old && old <= (unsigned long)bw)
1120 avg += (old - avg) >> 3;
1121
1122out:
1123 /* keep avg > 0 to guarantee that tot > 0 if there are dirty wbs */
1124 avg = max(avg, 1LU);
1125 if (wb_has_dirty_io(wb)) {
1126 long delta = avg - wb->avg_write_bandwidth;
1127 WARN_ON_ONCE(atomic_long_add_return(delta,
1128 &wb->bdi->tot_write_bandwidth) <= 0);
1129 }
1130 wb->write_bandwidth = bw;
1131 wb->avg_write_bandwidth = avg;
1132}
1133
1134static void update_dirty_limit(struct dirty_throttle_control *dtc)
1135{
1136 struct wb_domain *dom = dtc_dom(dtc);
1137 unsigned long thresh = dtc->thresh;
1138 unsigned long limit = dom->dirty_limit;
1139
1140 /*
1141 * Follow up in one step.
1142 */
1143 if (limit < thresh) {
1144 limit = thresh;
1145 goto update;
1146 }
1147
1148 /*
1149 * Follow down slowly. Use the higher one as the target, because thresh
1150 * may drop below dirty. This is exactly the reason to introduce
1151 * dom->dirty_limit which is guaranteed to lie above the dirty pages.
1152 */
1153 thresh = max(thresh, dtc->dirty);
1154 if (limit > thresh) {
1155 limit -= (limit - thresh) >> 5;
1156 goto update;
1157 }
1158 return;
1159update:
1160 dom->dirty_limit = limit;
1161}
1162
1163static void domain_update_bandwidth(struct dirty_throttle_control *dtc,
1164 unsigned long now)
1165{
1166 struct wb_domain *dom = dtc_dom(dtc);
1167
1168 /*
1169 * check locklessly first to optimize away locking for the most time
1170 */
1171 if (time_before(now, dom->dirty_limit_tstamp + BANDWIDTH_INTERVAL))
1172 return;
1173
1174 spin_lock(&dom->lock);
1175 if (time_after_eq(now, dom->dirty_limit_tstamp + BANDWIDTH_INTERVAL)) {
1176 update_dirty_limit(dtc);
1177 dom->dirty_limit_tstamp = now;
1178 }
1179 spin_unlock(&dom->lock);
1180}
1181
1182/*
1183 * Maintain wb->dirty_ratelimit, the base dirty throttle rate.
1184 *
1185 * Normal wb tasks will be curbed at or below it in long term.
1186 * Obviously it should be around (write_bw / N) when there are N dd tasks.
1187 */
1188static void wb_update_dirty_ratelimit(struct dirty_throttle_control *dtc,
1189 unsigned long dirtied,
1190 unsigned long elapsed)
1191{
1192 struct bdi_writeback *wb = dtc->wb;
1193 unsigned long dirty = dtc->dirty;
1194 unsigned long freerun = dirty_freerun_ceiling(dtc->thresh, dtc->bg_thresh);
1195 unsigned long limit = hard_dirty_limit(dtc_dom(dtc), dtc->thresh);
1196 unsigned long setpoint = (freerun + limit) / 2;
1197 unsigned long write_bw = wb->avg_write_bandwidth;
1198 unsigned long dirty_ratelimit = wb->dirty_ratelimit;
1199 unsigned long dirty_rate;
1200 unsigned long task_ratelimit;
1201 unsigned long balanced_dirty_ratelimit;
1202 unsigned long step;
1203 unsigned long x;
1204 unsigned long shift;
1205
1206 /*
1207 * The dirty rate will match the writeout rate in long term, except
1208 * when dirty pages are truncated by userspace or re-dirtied by FS.
1209 */
1210 dirty_rate = (dirtied - wb->dirtied_stamp) * HZ / elapsed;
1211
1212 /*
1213 * task_ratelimit reflects each dd's dirty rate for the past 200ms.
1214 */
1215 task_ratelimit = (u64)dirty_ratelimit *
1216 dtc->pos_ratio >> RATELIMIT_CALC_SHIFT;
1217 task_ratelimit++; /* it helps rampup dirty_ratelimit from tiny values */
1218
1219 /*
1220 * A linear estimation of the "balanced" throttle rate. The theory is,
1221 * if there are N dd tasks, each throttled at task_ratelimit, the wb's
1222 * dirty_rate will be measured to be (N * task_ratelimit). So the below
1223 * formula will yield the balanced rate limit (write_bw / N).
1224 *
1225 * Note that the expanded form is not a pure rate feedback:
1226 * rate_(i+1) = rate_(i) * (write_bw / dirty_rate) (1)
1227 * but also takes pos_ratio into account:
1228 * rate_(i+1) = rate_(i) * (write_bw / dirty_rate) * pos_ratio (2)
1229 *
1230 * (1) is not realistic because pos_ratio also takes part in balancing
1231 * the dirty rate. Consider the state
1232 * pos_ratio = 0.5 (3)
1233 * rate = 2 * (write_bw / N) (4)
1234 * If (1) is used, it will stuck in that state! Because each dd will
1235 * be throttled at
1236 * task_ratelimit = pos_ratio * rate = (write_bw / N) (5)
1237 * yielding
1238 * dirty_rate = N * task_ratelimit = write_bw (6)
1239 * put (6) into (1) we get
1240 * rate_(i+1) = rate_(i) (7)
1241 *
1242 * So we end up using (2) to always keep
1243 * rate_(i+1) ~= (write_bw / N) (8)
1244 * regardless of the value of pos_ratio. As long as (8) is satisfied,
1245 * pos_ratio is able to drive itself to 1.0, which is not only where
1246 * the dirty count meet the setpoint, but also where the slope of
1247 * pos_ratio is most flat and hence task_ratelimit is least fluctuated.
1248 */
1249 balanced_dirty_ratelimit = div_u64((u64)task_ratelimit * write_bw,
1250 dirty_rate | 1);
1251 /*
1252 * balanced_dirty_ratelimit ~= (write_bw / N) <= write_bw
1253 */
1254 if (unlikely(balanced_dirty_ratelimit > write_bw))
1255 balanced_dirty_ratelimit = write_bw;
1256
1257 /*
1258 * We could safely do this and return immediately:
1259 *
1260 * wb->dirty_ratelimit = balanced_dirty_ratelimit;
1261 *
1262 * However to get a more stable dirty_ratelimit, the below elaborated
1263 * code makes use of task_ratelimit to filter out singular points and
1264 * limit the step size.
1265 *
1266 * The below code essentially only uses the relative value of
1267 *
1268 * task_ratelimit - dirty_ratelimit
1269 * = (pos_ratio - 1) * dirty_ratelimit
1270 *
1271 * which reflects the direction and size of dirty position error.
1272 */
1273
1274 /*
1275 * dirty_ratelimit will follow balanced_dirty_ratelimit iff
1276 * task_ratelimit is on the same side of dirty_ratelimit, too.
1277 * For example, when
1278 * - dirty_ratelimit > balanced_dirty_ratelimit
1279 * - dirty_ratelimit > task_ratelimit (dirty pages are above setpoint)
1280 * lowering dirty_ratelimit will help meet both the position and rate
1281 * control targets. Otherwise, don't update dirty_ratelimit if it will
1282 * only help meet the rate target. After all, what the users ultimately
1283 * feel and care are stable dirty rate and small position error.
1284 *
1285 * |task_ratelimit - dirty_ratelimit| is used to limit the step size
1286 * and filter out the singular points of balanced_dirty_ratelimit. Which
1287 * keeps jumping around randomly and can even leap far away at times
1288 * due to the small 200ms estimation period of dirty_rate (we want to
1289 * keep that period small to reduce time lags).
1290 */
1291 step = 0;
1292
1293 /*
1294 * For strictlimit case, calculations above were based on wb counters
1295 * and limits (starting from pos_ratio = wb_position_ratio() and up to
1296 * balanced_dirty_ratelimit = task_ratelimit * write_bw / dirty_rate).
1297 * Hence, to calculate "step" properly, we have to use wb_dirty as
1298 * "dirty" and wb_setpoint as "setpoint".
1299 *
1300 * We rampup dirty_ratelimit forcibly if wb_dirty is low because
1301 * it's possible that wb_thresh is close to zero due to inactivity
1302 * of backing device.
1303 */
1304 if (unlikely(wb->bdi->capabilities & BDI_CAP_STRICTLIMIT)) {
1305 dirty = dtc->wb_dirty;
1306 if (dtc->wb_dirty < 8)
1307 setpoint = dtc->wb_dirty + 1;
1308 else
1309 setpoint = (dtc->wb_thresh + dtc->wb_bg_thresh) / 2;
1310 }
1311
1312 if (dirty < setpoint) {
1313 x = min3(wb->balanced_dirty_ratelimit,
1314 balanced_dirty_ratelimit, task_ratelimit);
1315 if (dirty_ratelimit < x)
1316 step = x - dirty_ratelimit;
1317 } else {
1318 x = max3(wb->balanced_dirty_ratelimit,
1319 balanced_dirty_ratelimit, task_ratelimit);
1320 if (dirty_ratelimit > x)
1321 step = dirty_ratelimit - x;
1322 }
1323
1324 /*
1325 * Don't pursue 100% rate matching. It's impossible since the balanced
1326 * rate itself is constantly fluctuating. So decrease the track speed
1327 * when it gets close to the target. Helps eliminate pointless tremors.
1328 */
1329 shift = dirty_ratelimit / (2 * step + 1);
1330 if (shift < BITS_PER_LONG)
1331 step = DIV_ROUND_UP(step >> shift, 8);
1332 else
1333 step = 0;
1334
1335 if (dirty_ratelimit < balanced_dirty_ratelimit)
1336 dirty_ratelimit += step;
1337 else
1338 dirty_ratelimit -= step;
1339
1340 wb->dirty_ratelimit = max(dirty_ratelimit, 1UL);
1341 wb->balanced_dirty_ratelimit = balanced_dirty_ratelimit;
1342
1343 trace_bdi_dirty_ratelimit(wb, dirty_rate, task_ratelimit);
1344}
1345
1346static void __wb_update_bandwidth(struct dirty_throttle_control *gdtc,
1347 struct dirty_throttle_control *mdtc,
1348 unsigned long start_time,
1349 bool update_ratelimit)
1350{
1351 struct bdi_writeback *wb = gdtc->wb;
1352 unsigned long now = jiffies;
1353 unsigned long elapsed = now - wb->bw_time_stamp;
1354 unsigned long dirtied;
1355 unsigned long written;
1356
1357 lockdep_assert_held(&wb->list_lock);
1358
1359 /*
1360 * rate-limit, only update once every 200ms.
1361 */
1362 if (elapsed < BANDWIDTH_INTERVAL)
1363 return;
1364
1365 dirtied = percpu_counter_read(&wb->stat[WB_DIRTIED]);
1366 written = percpu_counter_read(&wb->stat[WB_WRITTEN]);
1367
1368 /*
1369 * Skip quiet periods when disk bandwidth is under-utilized.
1370 * (at least 1s idle time between two flusher runs)
1371 */
1372 if (elapsed > HZ && time_before(wb->bw_time_stamp, start_time))
1373 goto snapshot;
1374
1375 if (update_ratelimit) {
1376 domain_update_bandwidth(gdtc, now);
1377 wb_update_dirty_ratelimit(gdtc, dirtied, elapsed);
1378
1379 /*
1380 * @mdtc is always NULL if !CGROUP_WRITEBACK but the
1381 * compiler has no way to figure that out. Help it.
1382 */
1383 if (IS_ENABLED(CONFIG_CGROUP_WRITEBACK) && mdtc) {
1384 domain_update_bandwidth(mdtc, now);
1385 wb_update_dirty_ratelimit(mdtc, dirtied, elapsed);
1386 }
1387 }
1388 wb_update_write_bandwidth(wb, elapsed, written);
1389
1390snapshot:
1391 wb->dirtied_stamp = dirtied;
1392 wb->written_stamp = written;
1393 wb->bw_time_stamp = now;
1394}
1395
1396void wb_update_bandwidth(struct bdi_writeback *wb, unsigned long start_time)
1397{
1398 struct dirty_throttle_control gdtc = { GDTC_INIT(wb) };
1399
1400 __wb_update_bandwidth(&gdtc, NULL, start_time, false);
1401}
1402
1403/*
1404 * After a task dirtied this many pages, balance_dirty_pages_ratelimited()
1405 * will look to see if it needs to start dirty throttling.
1406 *
1407 * If dirty_poll_interval is too low, big NUMA machines will call the expensive
1408 * global_page_state() too often. So scale it near-sqrt to the safety margin
1409 * (the number of pages we may dirty without exceeding the dirty limits).
1410 */
1411static unsigned long dirty_poll_interval(unsigned long dirty,
1412 unsigned long thresh)
1413{
1414 if (thresh > dirty)
1415 return 1UL << (ilog2(thresh - dirty) >> 1);
1416
1417 return 1;
1418}
1419
1420static unsigned long wb_max_pause(struct bdi_writeback *wb,
1421 unsigned long wb_dirty)
1422{
1423 unsigned long bw = wb->avg_write_bandwidth;
1424 unsigned long t;
1425
1426 /*
1427 * Limit pause time for small memory systems. If sleeping for too long
1428 * time, a small pool of dirty/writeback pages may go empty and disk go
1429 * idle.
1430 *
1431 * 8 serves as the safety ratio.
1432 */
1433 t = wb_dirty / (1 + bw / roundup_pow_of_two(1 + HZ / 8));
1434 t++;
1435
1436 return min_t(unsigned long, t, MAX_PAUSE);
1437}
1438
1439static long wb_min_pause(struct bdi_writeback *wb,
1440 long max_pause,
1441 unsigned long task_ratelimit,
1442 unsigned long dirty_ratelimit,
1443 int *nr_dirtied_pause)
1444{
1445 long hi = ilog2(wb->avg_write_bandwidth);
1446 long lo = ilog2(wb->dirty_ratelimit);
1447 long t; /* target pause */
1448 long pause; /* estimated next pause */
1449 int pages; /* target nr_dirtied_pause */
1450
1451 /* target for 10ms pause on 1-dd case */
1452 t = max(1, HZ / 100);
1453
1454 /*
1455 * Scale up pause time for concurrent dirtiers in order to reduce CPU
1456 * overheads.
1457 *
1458 * (N * 10ms) on 2^N concurrent tasks.
1459 */
1460 if (hi > lo)
1461 t += (hi - lo) * (10 * HZ) / 1024;
1462
1463 /*
1464 * This is a bit convoluted. We try to base the next nr_dirtied_pause
1465 * on the much more stable dirty_ratelimit. However the next pause time
1466 * will be computed based on task_ratelimit and the two rate limits may
1467 * depart considerably at some time. Especially if task_ratelimit goes
1468 * below dirty_ratelimit/2 and the target pause is max_pause, the next
1469 * pause time will be max_pause*2 _trimmed down_ to max_pause. As a
1470 * result task_ratelimit won't be executed faithfully, which could
1471 * eventually bring down dirty_ratelimit.
1472 *
1473 * We apply two rules to fix it up:
1474 * 1) try to estimate the next pause time and if necessary, use a lower
1475 * nr_dirtied_pause so as not to exceed max_pause. When this happens,
1476 * nr_dirtied_pause will be "dancing" with task_ratelimit.
1477 * 2) limit the target pause time to max_pause/2, so that the normal
1478 * small fluctuations of task_ratelimit won't trigger rule (1) and
1479 * nr_dirtied_pause will remain as stable as dirty_ratelimit.
1480 */
1481 t = min(t, 1 + max_pause / 2);
1482 pages = dirty_ratelimit * t / roundup_pow_of_two(HZ);
1483
1484 /*
1485 * Tiny nr_dirtied_pause is found to hurt I/O performance in the test
1486 * case fio-mmap-randwrite-64k, which does 16*{sync read, async write}.
1487 * When the 16 consecutive reads are often interrupted by some dirty
1488 * throttling pause during the async writes, cfq will go into idles
1489 * (deadline is fine). So push nr_dirtied_pause as high as possible
1490 * until reaches DIRTY_POLL_THRESH=32 pages.
1491 */
1492 if (pages < DIRTY_POLL_THRESH) {
1493 t = max_pause;
1494 pages = dirty_ratelimit * t / roundup_pow_of_two(HZ);
1495 if (pages > DIRTY_POLL_THRESH) {
1496 pages = DIRTY_POLL_THRESH;
1497 t = HZ * DIRTY_POLL_THRESH / dirty_ratelimit;
1498 }
1499 }
1500
1501 pause = HZ * pages / (task_ratelimit + 1);
1502 if (pause > max_pause) {
1503 t = max_pause;
1504 pages = task_ratelimit * t / roundup_pow_of_two(HZ);
1505 }
1506
1507 *nr_dirtied_pause = pages;
1508 /*
1509 * The minimal pause time will normally be half the target pause time.
1510 */
1511 return pages >= DIRTY_POLL_THRESH ? 1 + t / 2 : t;
1512}
1513
1514static inline void wb_dirty_limits(struct dirty_throttle_control *dtc)
1515{
1516 struct bdi_writeback *wb = dtc->wb;
1517 unsigned long wb_reclaimable;
1518
1519 /*
1520 * wb_thresh is not treated as some limiting factor as
1521 * dirty_thresh, due to reasons
1522 * - in JBOD setup, wb_thresh can fluctuate a lot
1523 * - in a system with HDD and USB key, the USB key may somehow
1524 * go into state (wb_dirty >> wb_thresh) either because
1525 * wb_dirty starts high, or because wb_thresh drops low.
1526 * In this case we don't want to hard throttle the USB key
1527 * dirtiers for 100 seconds until wb_dirty drops under
1528 * wb_thresh. Instead the auxiliary wb control line in
1529 * wb_position_ratio() will let the dirtier task progress
1530 * at some rate <= (write_bw / 2) for bringing down wb_dirty.
1531 */
1532 dtc->wb_thresh = __wb_calc_thresh(dtc);
1533 dtc->wb_bg_thresh = dtc->thresh ?
1534 div_u64((u64)dtc->wb_thresh * dtc->bg_thresh, dtc->thresh) : 0;
1535
1536 /*
1537 * In order to avoid the stacked BDI deadlock we need
1538 * to ensure we accurately count the 'dirty' pages when
1539 * the threshold is low.
1540 *
1541 * Otherwise it would be possible to get thresh+n pages
1542 * reported dirty, even though there are thresh-m pages
1543 * actually dirty; with m+n sitting in the percpu
1544 * deltas.
1545 */
1546 if (dtc->wb_thresh < 2 * wb_stat_error(wb)) {
1547 wb_reclaimable = wb_stat_sum(wb, WB_RECLAIMABLE);
1548 dtc->wb_dirty = wb_reclaimable + wb_stat_sum(wb, WB_WRITEBACK);
1549 } else {
1550 wb_reclaimable = wb_stat(wb, WB_RECLAIMABLE);
1551 dtc->wb_dirty = wb_reclaimable + wb_stat(wb, WB_WRITEBACK);
1552 }
1553}
1554
1555/*
1556 * balance_dirty_pages() must be called by processes which are generating dirty
1557 * data. It looks at the number of dirty pages in the machine and will force
1558 * the caller to wait once crossing the (background_thresh + dirty_thresh) / 2.
1559 * If we're over `background_thresh' then the writeback threads are woken to
1560 * perform some writeout.
1561 */
1562static void balance_dirty_pages(struct address_space *mapping,
1563 struct bdi_writeback *wb,
1564 unsigned long pages_dirtied)
1565{
1566 struct dirty_throttle_control gdtc_stor = { GDTC_INIT(wb) };
1567 struct dirty_throttle_control mdtc_stor = { MDTC_INIT(wb, &gdtc_stor) };
1568 struct dirty_throttle_control * const gdtc = &gdtc_stor;
1569 struct dirty_throttle_control * const mdtc = mdtc_valid(&mdtc_stor) ?
1570 &mdtc_stor : NULL;
1571 struct dirty_throttle_control *sdtc;
1572 unsigned long nr_reclaimable; /* = file_dirty + unstable_nfs */
1573 long period;
1574 long pause;
1575 long max_pause;
1576 long min_pause;
1577 int nr_dirtied_pause;
1578 bool dirty_exceeded = false;
1579 unsigned long task_ratelimit;
1580 unsigned long dirty_ratelimit;
1581 struct backing_dev_info *bdi = wb->bdi;
1582 bool strictlimit = bdi->capabilities & BDI_CAP_STRICTLIMIT;
1583 unsigned long start_time = jiffies;
1584
1585 for (;;) {
1586 unsigned long now = jiffies;
1587 unsigned long dirty, thresh, bg_thresh;
1588 unsigned long m_dirty = 0; /* stop bogus uninit warnings */
1589 unsigned long m_thresh = 0;
1590 unsigned long m_bg_thresh = 0;
1591
1592 /*
1593 * Unstable writes are a feature of certain networked
1594 * filesystems (i.e. NFS) in which data may have been
1595 * written to the server's write cache, but has not yet
1596 * been flushed to permanent storage.
1597 */
1598 nr_reclaimable = global_node_page_state(NR_FILE_DIRTY) +
1599 global_node_page_state(NR_UNSTABLE_NFS);
1600 gdtc->avail = global_dirtyable_memory();
1601 gdtc->dirty = nr_reclaimable + global_node_page_state(NR_WRITEBACK);
1602
1603 domain_dirty_limits(gdtc);
1604
1605 if (unlikely(strictlimit)) {
1606 wb_dirty_limits(gdtc);
1607
1608 dirty = gdtc->wb_dirty;
1609 thresh = gdtc->wb_thresh;
1610 bg_thresh = gdtc->wb_bg_thresh;
1611 } else {
1612 dirty = gdtc->dirty;
1613 thresh = gdtc->thresh;
1614 bg_thresh = gdtc->bg_thresh;
1615 }
1616
1617 if (mdtc) {
1618 unsigned long filepages, headroom, writeback;
1619
1620 /*
1621 * If @wb belongs to !root memcg, repeat the same
1622 * basic calculations for the memcg domain.
1623 */
1624 mem_cgroup_wb_stats(wb, &filepages, &headroom,
1625 &mdtc->dirty, &writeback);
1626 mdtc->dirty += writeback;
1627 mdtc_calc_avail(mdtc, filepages, headroom);
1628
1629 domain_dirty_limits(mdtc);
1630
1631 if (unlikely(strictlimit)) {
1632 wb_dirty_limits(mdtc);
1633 m_dirty = mdtc->wb_dirty;
1634 m_thresh = mdtc->wb_thresh;
1635 m_bg_thresh = mdtc->wb_bg_thresh;
1636 } else {
1637 m_dirty = mdtc->dirty;
1638 m_thresh = mdtc->thresh;
1639 m_bg_thresh = mdtc->bg_thresh;
1640 }
1641 }
1642
1643 /*
1644 * Throttle it only when the background writeback cannot
1645 * catch-up. This avoids (excessively) small writeouts
1646 * when the wb limits are ramping up in case of !strictlimit.
1647 *
1648 * In strictlimit case make decision based on the wb counters
1649 * and limits. Small writeouts when the wb limits are ramping
1650 * up are the price we consciously pay for strictlimit-ing.
1651 *
1652 * If memcg domain is in effect, @dirty should be under
1653 * both global and memcg freerun ceilings.
1654 */
1655 if (dirty <= dirty_freerun_ceiling(thresh, bg_thresh) &&
1656 (!mdtc ||
1657 m_dirty <= dirty_freerun_ceiling(m_thresh, m_bg_thresh))) {
1658 unsigned long intv = dirty_poll_interval(dirty, thresh);
1659 unsigned long m_intv = ULONG_MAX;
1660
1661 current->dirty_paused_when = now;
1662 current->nr_dirtied = 0;
1663 if (mdtc)
1664 m_intv = dirty_poll_interval(m_dirty, m_thresh);
1665 current->nr_dirtied_pause = min(intv, m_intv);
1666 break;
1667 }
1668
1669 if (unlikely(!writeback_in_progress(wb)))
1670 wb_start_background_writeback(wb);
1671
1672 /*
1673 * Calculate global domain's pos_ratio and select the
1674 * global dtc by default.
1675 */
1676 if (!strictlimit)
1677 wb_dirty_limits(gdtc);
1678
1679 dirty_exceeded = (gdtc->wb_dirty > gdtc->wb_thresh) &&
1680 ((gdtc->dirty > gdtc->thresh) || strictlimit);
1681
1682 wb_position_ratio(gdtc);
1683 sdtc = gdtc;
1684
1685 if (mdtc) {
1686 /*
1687 * If memcg domain is in effect, calculate its
1688 * pos_ratio. @wb should satisfy constraints from
1689 * both global and memcg domains. Choose the one
1690 * w/ lower pos_ratio.
1691 */
1692 if (!strictlimit)
1693 wb_dirty_limits(mdtc);
1694
1695 dirty_exceeded |= (mdtc->wb_dirty > mdtc->wb_thresh) &&
1696 ((mdtc->dirty > mdtc->thresh) || strictlimit);
1697
1698 wb_position_ratio(mdtc);
1699 if (mdtc->pos_ratio < gdtc->pos_ratio)
1700 sdtc = mdtc;
1701 }
1702
1703 if (dirty_exceeded && !wb->dirty_exceeded)
1704 wb->dirty_exceeded = 1;
1705
1706 if (time_is_before_jiffies(wb->bw_time_stamp +
1707 BANDWIDTH_INTERVAL)) {
1708 spin_lock(&wb->list_lock);
1709 __wb_update_bandwidth(gdtc, mdtc, start_time, true);
1710 spin_unlock(&wb->list_lock);
1711 }
1712
1713 /* throttle according to the chosen dtc */
1714 dirty_ratelimit = wb->dirty_ratelimit;
1715 task_ratelimit = ((u64)dirty_ratelimit * sdtc->pos_ratio) >>
1716 RATELIMIT_CALC_SHIFT;
1717 max_pause = wb_max_pause(wb, sdtc->wb_dirty);
1718 min_pause = wb_min_pause(wb, max_pause,
1719 task_ratelimit, dirty_ratelimit,
1720 &nr_dirtied_pause);
1721
1722 if (unlikely(task_ratelimit == 0)) {
1723 period = max_pause;
1724 pause = max_pause;
1725 goto pause;
1726 }
1727 period = HZ * pages_dirtied / task_ratelimit;
1728 pause = period;
1729 if (current->dirty_paused_when)
1730 pause -= now - current->dirty_paused_when;
1731 /*
1732 * For less than 1s think time (ext3/4 may block the dirtier
1733 * for up to 800ms from time to time on 1-HDD; so does xfs,
1734 * however at much less frequency), try to compensate it in
1735 * future periods by updating the virtual time; otherwise just
1736 * do a reset, as it may be a light dirtier.
1737 */
1738 if (pause < min_pause) {
1739 trace_balance_dirty_pages(wb,
1740 sdtc->thresh,
1741 sdtc->bg_thresh,
1742 sdtc->dirty,
1743 sdtc->wb_thresh,
1744 sdtc->wb_dirty,
1745 dirty_ratelimit,
1746 task_ratelimit,
1747 pages_dirtied,
1748 period,
1749 min(pause, 0L),
1750 start_time);
1751 if (pause < -HZ) {
1752 current->dirty_paused_when = now;
1753 current->nr_dirtied = 0;
1754 } else if (period) {
1755 current->dirty_paused_when += period;
1756 current->nr_dirtied = 0;
1757 } else if (current->nr_dirtied_pause <= pages_dirtied)
1758 current->nr_dirtied_pause += pages_dirtied;
1759 break;
1760 }
1761 if (unlikely(pause > max_pause)) {
1762 /* for occasional dropped task_ratelimit */
1763 now += min(pause - max_pause, max_pause);
1764 pause = max_pause;
1765 }
1766
1767pause:
1768 trace_balance_dirty_pages(wb,
1769 sdtc->thresh,
1770 sdtc->bg_thresh,
1771 sdtc->dirty,
1772 sdtc->wb_thresh,
1773 sdtc->wb_dirty,
1774 dirty_ratelimit,
1775 task_ratelimit,
1776 pages_dirtied,
1777 period,
1778 pause,
1779 start_time);
1780 __set_current_state(TASK_KILLABLE);
1781 wb->dirty_sleep = now;
1782 io_schedule_timeout(pause);
1783
1784 current->dirty_paused_when = now + pause;
1785 current->nr_dirtied = 0;
1786 current->nr_dirtied_pause = nr_dirtied_pause;
1787
1788 /*
1789 * This is typically equal to (dirty < thresh) and can also
1790 * keep "1000+ dd on a slow USB stick" under control.
1791 */
1792 if (task_ratelimit)
1793 break;
1794
1795 /*
1796 * In the case of an unresponding NFS server and the NFS dirty
1797 * pages exceeds dirty_thresh, give the other good wb's a pipe
1798 * to go through, so that tasks on them still remain responsive.
1799 *
1800 * In theory 1 page is enough to keep the comsumer-producer
1801 * pipe going: the flusher cleans 1 page => the task dirties 1
1802 * more page. However wb_dirty has accounting errors. So use
1803 * the larger and more IO friendly wb_stat_error.
1804 */
1805 if (sdtc->wb_dirty <= wb_stat_error(wb))
1806 break;
1807
1808 if (fatal_signal_pending(current))
1809 break;
1810 }
1811
1812 if (!dirty_exceeded && wb->dirty_exceeded)
1813 wb->dirty_exceeded = 0;
1814
1815 if (writeback_in_progress(wb))
1816 return;
1817
1818 /*
1819 * In laptop mode, we wait until hitting the higher threshold before
1820 * starting background writeout, and then write out all the way down
1821 * to the lower threshold. So slow writers cause minimal disk activity.
1822 *
1823 * In normal mode, we start background writeout at the lower
1824 * background_thresh, to keep the amount of dirty memory low.
1825 */
1826 if (laptop_mode)
1827 return;
1828
1829 if (nr_reclaimable > gdtc->bg_thresh)
1830 wb_start_background_writeback(wb);
1831}
1832
1833static DEFINE_PER_CPU(int, bdp_ratelimits);
1834
1835/*
1836 * Normal tasks are throttled by
1837 * loop {
1838 * dirty tsk->nr_dirtied_pause pages;
1839 * take a snap in balance_dirty_pages();
1840 * }
1841 * However there is a worst case. If every task exit immediately when dirtied
1842 * (tsk->nr_dirtied_pause - 1) pages, balance_dirty_pages() will never be
1843 * called to throttle the page dirties. The solution is to save the not yet
1844 * throttled page dirties in dirty_throttle_leaks on task exit and charge them
1845 * randomly into the running tasks. This works well for the above worst case,
1846 * as the new task will pick up and accumulate the old task's leaked dirty
1847 * count and eventually get throttled.
1848 */
1849DEFINE_PER_CPU(int, dirty_throttle_leaks) = 0;
1850
1851/**
1852 * balance_dirty_pages_ratelimited - balance dirty memory state
1853 * @mapping: address_space which was dirtied
1854 *
1855 * Processes which are dirtying memory should call in here once for each page
1856 * which was newly dirtied. The function will periodically check the system's
1857 * dirty state and will initiate writeback if needed.
1858 *
1859 * On really big machines, get_writeback_state is expensive, so try to avoid
1860 * calling it too often (ratelimiting). But once we're over the dirty memory
1861 * limit we decrease the ratelimiting by a lot, to prevent individual processes
1862 * from overshooting the limit by (ratelimit_pages) each.
1863 */
1864void balance_dirty_pages_ratelimited(struct address_space *mapping)
1865{
1866 struct inode *inode = mapping->host;
1867 struct backing_dev_info *bdi = inode_to_bdi(inode);
1868 struct bdi_writeback *wb = NULL;
1869 int ratelimit;
1870 int *p;
1871
1872 if (!bdi_cap_account_dirty(bdi))
1873 return;
1874
1875 if (inode_cgwb_enabled(inode))
1876 wb = wb_get_create_current(bdi, GFP_KERNEL);
1877 if (!wb)
1878 wb = &bdi->wb;
1879
1880 ratelimit = current->nr_dirtied_pause;
1881 if (wb->dirty_exceeded)
1882 ratelimit = min(ratelimit, 32 >> (PAGE_SHIFT - 10));
1883
1884 preempt_disable();
1885 /*
1886 * This prevents one CPU to accumulate too many dirtied pages without
1887 * calling into balance_dirty_pages(), which can happen when there are
1888 * 1000+ tasks, all of them start dirtying pages at exactly the same
1889 * time, hence all honoured too large initial task->nr_dirtied_pause.
1890 */
1891 p = this_cpu_ptr(&bdp_ratelimits);
1892 if (unlikely(current->nr_dirtied >= ratelimit))
1893 *p = 0;
1894 else if (unlikely(*p >= ratelimit_pages)) {
1895 *p = 0;
1896 ratelimit = 0;
1897 }
1898 /*
1899 * Pick up the dirtied pages by the exited tasks. This avoids lots of
1900 * short-lived tasks (eg. gcc invocations in a kernel build) escaping
1901 * the dirty throttling and livelock other long-run dirtiers.
1902 */
1903 p = this_cpu_ptr(&dirty_throttle_leaks);
1904 if (*p > 0 && current->nr_dirtied < ratelimit) {
1905 unsigned long nr_pages_dirtied;
1906 nr_pages_dirtied = min(*p, ratelimit - current->nr_dirtied);
1907 *p -= nr_pages_dirtied;
1908 current->nr_dirtied += nr_pages_dirtied;
1909 }
1910 preempt_enable();
1911
1912 if (unlikely(current->nr_dirtied >= ratelimit))
1913 balance_dirty_pages(mapping, wb, current->nr_dirtied);
1914
1915 wb_put(wb);
1916}
1917EXPORT_SYMBOL(balance_dirty_pages_ratelimited);
1918
1919/**
1920 * wb_over_bg_thresh - does @wb need to be written back?
1921 * @wb: bdi_writeback of interest
1922 *
1923 * Determines whether background writeback should keep writing @wb or it's
1924 * clean enough. Returns %true if writeback should continue.
1925 */
1926bool wb_over_bg_thresh(struct bdi_writeback *wb)
1927{
1928 struct dirty_throttle_control gdtc_stor = { GDTC_INIT(wb) };
1929 struct dirty_throttle_control mdtc_stor = { MDTC_INIT(wb, &gdtc_stor) };
1930 struct dirty_throttle_control * const gdtc = &gdtc_stor;
1931 struct dirty_throttle_control * const mdtc = mdtc_valid(&mdtc_stor) ?
1932 &mdtc_stor : NULL;
1933
1934 /*
1935 * Similar to balance_dirty_pages() but ignores pages being written
1936 * as we're trying to decide whether to put more under writeback.
1937 */
1938 gdtc->avail = global_dirtyable_memory();
1939 gdtc->dirty = global_node_page_state(NR_FILE_DIRTY) +
1940 global_node_page_state(NR_UNSTABLE_NFS);
1941 domain_dirty_limits(gdtc);
1942
1943 if (gdtc->dirty > gdtc->bg_thresh)
1944 return true;
1945
1946 if (wb_stat(wb, WB_RECLAIMABLE) >
1947 wb_calc_thresh(gdtc->wb, gdtc->bg_thresh))
1948 return true;
1949
1950 if (mdtc) {
1951 unsigned long filepages, headroom, writeback;
1952
1953 mem_cgroup_wb_stats(wb, &filepages, &headroom, &mdtc->dirty,
1954 &writeback);
1955 mdtc_calc_avail(mdtc, filepages, headroom);
1956 domain_dirty_limits(mdtc); /* ditto, ignore writeback */
1957
1958 if (mdtc->dirty > mdtc->bg_thresh)
1959 return true;
1960
1961 if (wb_stat(wb, WB_RECLAIMABLE) >
1962 wb_calc_thresh(mdtc->wb, mdtc->bg_thresh))
1963 return true;
1964 }
1965
1966 return false;
1967}
1968
1969/*
1970 * sysctl handler for /proc/sys/vm/dirty_writeback_centisecs
1971 */
1972int dirty_writeback_centisecs_handler(struct ctl_table *table, int write,
1973 void __user *buffer, size_t *length, loff_t *ppos)
1974{
1975 proc_dointvec(table, write, buffer, length, ppos);
1976 return 0;
1977}
1978
1979#ifdef CONFIG_BLOCK
1980void laptop_mode_timer_fn(unsigned long data)
1981{
1982 struct request_queue *q = (struct request_queue *)data;
1983 int nr_pages = global_node_page_state(NR_FILE_DIRTY) +
1984 global_node_page_state(NR_UNSTABLE_NFS);
1985 struct bdi_writeback *wb;
1986
1987 /*
1988 * We want to write everything out, not just down to the dirty
1989 * threshold
1990 */
1991 if (!bdi_has_dirty_io(&q->backing_dev_info))
1992 return;
1993
1994 rcu_read_lock();
1995 list_for_each_entry_rcu(wb, &q->backing_dev_info.wb_list, bdi_node)
1996 if (wb_has_dirty_io(wb))
1997 wb_start_writeback(wb, nr_pages, true,
1998 WB_REASON_LAPTOP_TIMER);
1999 rcu_read_unlock();
2000}
2001
2002/*
2003 * We've spun up the disk and we're in laptop mode: schedule writeback
2004 * of all dirty data a few seconds from now. If the flush is already scheduled
2005 * then push it back - the user is still using the disk.
2006 */
2007void laptop_io_completion(struct backing_dev_info *info)
2008{
2009 mod_timer(&info->laptop_mode_wb_timer, jiffies + laptop_mode);
2010}
2011
2012/*
2013 * We're in laptop mode and we've just synced. The sync's writes will have
2014 * caused another writeback to be scheduled by laptop_io_completion.
2015 * Nothing needs to be written back anymore, so we unschedule the writeback.
2016 */
2017void laptop_sync_completion(void)
2018{
2019 struct backing_dev_info *bdi;
2020
2021 rcu_read_lock();
2022
2023 list_for_each_entry_rcu(bdi, &bdi_list, bdi_list)
2024 del_timer(&bdi->laptop_mode_wb_timer);
2025
2026 rcu_read_unlock();
2027}
2028#endif
2029
2030/*
2031 * If ratelimit_pages is too high then we can get into dirty-data overload
2032 * if a large number of processes all perform writes at the same time.
2033 * If it is too low then SMP machines will call the (expensive)
2034 * get_writeback_state too often.
2035 *
2036 * Here we set ratelimit_pages to a level which ensures that when all CPUs are
2037 * dirtying in parallel, we cannot go more than 3% (1/32) over the dirty memory
2038 * thresholds.
2039 */
2040
2041void writeback_set_ratelimit(void)
2042{
2043 struct wb_domain *dom = &global_wb_domain;
2044 unsigned long background_thresh;
2045 unsigned long dirty_thresh;
2046
2047 global_dirty_limits(&background_thresh, &dirty_thresh);
2048 dom->dirty_limit = dirty_thresh;
2049 ratelimit_pages = dirty_thresh / (num_online_cpus() * 32);
2050 if (ratelimit_pages < 16)
2051 ratelimit_pages = 16;
2052}
2053
2054static int page_writeback_cpu_online(unsigned int cpu)
2055{
2056 writeback_set_ratelimit();
2057 return 0;
2058}
2059
2060/*
2061 * Called early on to tune the page writeback dirty limits.
2062 *
2063 * We used to scale dirty pages according to how total memory
2064 * related to pages that could be allocated for buffers (by
2065 * comparing nr_free_buffer_pages() to vm_total_pages.
2066 *
2067 * However, that was when we used "dirty_ratio" to scale with
2068 * all memory, and we don't do that any more. "dirty_ratio"
2069 * is now applied to total non-HIGHPAGE memory (by subtracting
2070 * totalhigh_pages from vm_total_pages), and as such we can't
2071 * get into the old insane situation any more where we had
2072 * large amounts of dirty pages compared to a small amount of
2073 * non-HIGHMEM memory.
2074 *
2075 * But we might still want to scale the dirty_ratio by how
2076 * much memory the box has..
2077 */
2078void __init page_writeback_init(void)
2079{
2080 BUG_ON(wb_domain_init(&global_wb_domain, GFP_KERNEL));
2081
2082 cpuhp_setup_state(CPUHP_AP_ONLINE_DYN, "mm/writeback:online",
2083 page_writeback_cpu_online, NULL);
2084 cpuhp_setup_state(CPUHP_MM_WRITEBACK_DEAD, "mm/writeback:dead", NULL,
2085 page_writeback_cpu_online);
2086}
2087
2088/**
2089 * tag_pages_for_writeback - tag pages to be written by write_cache_pages
2090 * @mapping: address space structure to write
2091 * @start: starting page index
2092 * @end: ending page index (inclusive)
2093 *
2094 * This function scans the page range from @start to @end (inclusive) and tags
2095 * all pages that have DIRTY tag set with a special TOWRITE tag. The idea is
2096 * that write_cache_pages (or whoever calls this function) will then use
2097 * TOWRITE tag to identify pages eligible for writeback. This mechanism is
2098 * used to avoid livelocking of writeback by a process steadily creating new
2099 * dirty pages in the file (thus it is important for this function to be quick
2100 * so that it can tag pages faster than a dirtying process can create them).
2101 */
2102/*
2103 * We tag pages in batches of WRITEBACK_TAG_BATCH to reduce tree_lock latency.
2104 */
2105void tag_pages_for_writeback(struct address_space *mapping,
2106 pgoff_t start, pgoff_t end)
2107{
2108#define WRITEBACK_TAG_BATCH 4096
2109 unsigned long tagged = 0;
2110 struct radix_tree_iter iter;
2111 void **slot;
2112
2113 spin_lock_irq(&mapping->tree_lock);
2114 radix_tree_for_each_tagged(slot, &mapping->page_tree, &iter, start,
2115 PAGECACHE_TAG_DIRTY) {
2116 if (iter.index > end)
2117 break;
2118 radix_tree_iter_tag_set(&mapping->page_tree, &iter,
2119 PAGECACHE_TAG_TOWRITE);
2120 tagged++;
2121 if ((tagged % WRITEBACK_TAG_BATCH) != 0)
2122 continue;
2123 slot = radix_tree_iter_resume(slot, &iter);
2124 spin_unlock_irq(&mapping->tree_lock);
2125 cond_resched();
2126 spin_lock_irq(&mapping->tree_lock);
2127 }
2128 spin_unlock_irq(&mapping->tree_lock);
2129}
2130EXPORT_SYMBOL(tag_pages_for_writeback);
2131
2132/**
2133 * write_cache_pages - walk the list of dirty pages of the given address space and write all of them.
2134 * @mapping: address space structure to write
2135 * @wbc: subtract the number of written pages from *@wbc->nr_to_write
2136 * @writepage: function called for each page
2137 * @data: data passed to writepage function
2138 *
2139 * If a page is already under I/O, write_cache_pages() skips it, even
2140 * if it's dirty. This is desirable behaviour for memory-cleaning writeback,
2141 * but it is INCORRECT for data-integrity system calls such as fsync(). fsync()
2142 * and msync() need to guarantee that all the data which was dirty at the time
2143 * the call was made get new I/O started against them. If wbc->sync_mode is
2144 * WB_SYNC_ALL then we were called for data integrity and we must wait for
2145 * existing IO to complete.
2146 *
2147 * To avoid livelocks (when other process dirties new pages), we first tag
2148 * pages which should be written back with TOWRITE tag and only then start
2149 * writing them. For data-integrity sync we have to be careful so that we do
2150 * not miss some pages (e.g., because some other process has cleared TOWRITE
2151 * tag we set). The rule we follow is that TOWRITE tag can be cleared only
2152 * by the process clearing the DIRTY tag (and submitting the page for IO).
2153 */
2154int write_cache_pages(struct address_space *mapping,
2155 struct writeback_control *wbc, writepage_t writepage,
2156 void *data)
2157{
2158 int ret = 0;
2159 int done = 0;
2160 struct pagevec pvec;
2161 int nr_pages;
2162 pgoff_t uninitialized_var(writeback_index);
2163 pgoff_t index;
2164 pgoff_t end; /* Inclusive */
2165 pgoff_t done_index;
2166 int cycled;
2167 int range_whole = 0;
2168 int tag;
2169
2170 pagevec_init(&pvec, 0);
2171 if (wbc->range_cyclic) {
2172 writeback_index = mapping->writeback_index; /* prev offset */
2173 index = writeback_index;
2174 if (index == 0)
2175 cycled = 1;
2176 else
2177 cycled = 0;
2178 end = -1;
2179 } else {
2180 index = wbc->range_start >> PAGE_SHIFT;
2181 end = wbc->range_end >> PAGE_SHIFT;
2182 if (wbc->range_start == 0 && wbc->range_end == LLONG_MAX)
2183 range_whole = 1;
2184 cycled = 1; /* ignore range_cyclic tests */
2185 }
2186 if (wbc->sync_mode == WB_SYNC_ALL || wbc->tagged_writepages)
2187 tag = PAGECACHE_TAG_TOWRITE;
2188 else
2189 tag = PAGECACHE_TAG_DIRTY;
2190retry:
2191 if (wbc->sync_mode == WB_SYNC_ALL || wbc->tagged_writepages)
2192 tag_pages_for_writeback(mapping, index, end);
2193 done_index = index;
2194 while (!done && (index <= end)) {
2195 int i;
2196
2197 nr_pages = pagevec_lookup_tag(&pvec, mapping, &index, tag,
2198 min(end - index, (pgoff_t)PAGEVEC_SIZE-1) + 1);
2199 if (nr_pages == 0)
2200 break;
2201
2202 for (i = 0; i < nr_pages; i++) {
2203 struct page *page = pvec.pages[i];
2204
2205 /*
2206 * At this point, the page may be truncated or
2207 * invalidated (changing page->mapping to NULL), or
2208 * even swizzled back from swapper_space to tmpfs file
2209 * mapping. However, page->index will not change
2210 * because we have a reference on the page.
2211 */
2212 if (page->index > end) {
2213 /*
2214 * can't be range_cyclic (1st pass) because
2215 * end == -1 in that case.
2216 */
2217 done = 1;
2218 break;
2219 }
2220
2221 done_index = page->index;
2222
2223 lock_page(page);
2224
2225 /*
2226 * Page truncated or invalidated. We can freely skip it
2227 * then, even for data integrity operations: the page
2228 * has disappeared concurrently, so there could be no
2229 * real expectation of this data interity operation
2230 * even if there is now a new, dirty page at the same
2231 * pagecache address.
2232 */
2233 if (unlikely(page->mapping != mapping)) {
2234continue_unlock:
2235 unlock_page(page);
2236 continue;
2237 }
2238
2239 if (!PageDirty(page)) {
2240 /* someone wrote it for us */
2241 goto continue_unlock;
2242 }
2243
2244 if (PageWriteback(page)) {
2245 if (wbc->sync_mode != WB_SYNC_NONE)
2246 wait_on_page_writeback(page);
2247 else
2248 goto continue_unlock;
2249 }
2250
2251 BUG_ON(PageWriteback(page));
2252 if (!clear_page_dirty_for_io(page))
2253 goto continue_unlock;
2254
2255 trace_wbc_writepage(wbc, inode_to_bdi(mapping->host));
2256 ret = (*writepage)(page, wbc, data);
2257 if (unlikely(ret)) {
2258 if (ret == AOP_WRITEPAGE_ACTIVATE) {
2259 unlock_page(page);
2260 ret = 0;
2261 } else {
2262 /*
2263 * done_index is set past this page,
2264 * so media errors will not choke
2265 * background writeout for the entire
2266 * file. This has consequences for
2267 * range_cyclic semantics (ie. it may
2268 * not be suitable for data integrity
2269 * writeout).
2270 */
2271 done_index = page->index + 1;
2272 done = 1;
2273 break;
2274 }
2275 }
2276
2277 /*
2278 * We stop writing back only if we are not doing
2279 * integrity sync. In case of integrity sync we have to
2280 * keep going until we have written all the pages
2281 * we tagged for writeback prior to entering this loop.
2282 */
2283 if (--wbc->nr_to_write <= 0 &&
2284 wbc->sync_mode == WB_SYNC_NONE) {
2285 done = 1;
2286 break;
2287 }
2288 }
2289 pagevec_release(&pvec);
2290 cond_resched();
2291 }
2292 if (!cycled && !done) {
2293 /*
2294 * range_cyclic:
2295 * We hit the last page and there is more work to be done: wrap
2296 * back to the start of the file
2297 */
2298 cycled = 1;
2299 index = 0;
2300 end = writeback_index - 1;
2301 goto retry;
2302 }
2303 if (wbc->range_cyclic || (range_whole && wbc->nr_to_write > 0))
2304 mapping->writeback_index = done_index;
2305
2306 return ret;
2307}
2308EXPORT_SYMBOL(write_cache_pages);
2309
2310/*
2311 * Function used by generic_writepages to call the real writepage
2312 * function and set the mapping flags on error
2313 */
2314static int __writepage(struct page *page, struct writeback_control *wbc,
2315 void *data)
2316{
2317 struct address_space *mapping = data;
2318 int ret = mapping->a_ops->writepage(page, wbc);
2319 mapping_set_error(mapping, ret);
2320 return ret;
2321}
2322
2323/**
2324 * generic_writepages - walk the list of dirty pages of the given address space and writepage() all of them.
2325 * @mapping: address space structure to write
2326 * @wbc: subtract the number of written pages from *@wbc->nr_to_write
2327 *
2328 * This is a library function, which implements the writepages()
2329 * address_space_operation.
2330 */
2331int generic_writepages(struct address_space *mapping,
2332 struct writeback_control *wbc)
2333{
2334 struct blk_plug plug;
2335 int ret;
2336
2337 /* deal with chardevs and other special file */
2338 if (!mapping->a_ops->writepage)
2339 return 0;
2340
2341 blk_start_plug(&plug);
2342 ret = write_cache_pages(mapping, wbc, __writepage, mapping);
2343 blk_finish_plug(&plug);
2344 return ret;
2345}
2346
2347EXPORT_SYMBOL(generic_writepages);
2348
2349int do_writepages(struct address_space *mapping, struct writeback_control *wbc)
2350{
2351 int ret;
2352
2353 if (wbc->nr_to_write <= 0)
2354 return 0;
2355 if (mapping->a_ops->writepages)
2356 ret = mapping->a_ops->writepages(mapping, wbc);
2357 else
2358 ret = generic_writepages(mapping, wbc);
2359 return ret;
2360}
2361
2362/**
2363 * write_one_page - write out a single page and optionally wait on I/O
2364 * @page: the page to write
2365 * @wait: if true, wait on writeout
2366 *
2367 * The page must be locked by the caller and will be unlocked upon return.
2368 *
2369 * write_one_page() returns a negative error code if I/O failed.
2370 */
2371int write_one_page(struct page *page, int wait)
2372{
2373 struct address_space *mapping = page->mapping;
2374 int ret = 0;
2375 struct writeback_control wbc = {
2376 .sync_mode = WB_SYNC_ALL,
2377 .nr_to_write = 1,
2378 };
2379
2380 BUG_ON(!PageLocked(page));
2381
2382 if (wait)
2383 wait_on_page_writeback(page);
2384
2385 if (clear_page_dirty_for_io(page)) {
2386 get_page(page);
2387 ret = mapping->a_ops->writepage(page, &wbc);
2388 if (ret == 0 && wait) {
2389 wait_on_page_writeback(page);
2390 if (PageError(page))
2391 ret = -EIO;
2392 }
2393 put_page(page);
2394 } else {
2395 unlock_page(page);
2396 }
2397 return ret;
2398}
2399EXPORT_SYMBOL(write_one_page);
2400
2401/*
2402 * For address_spaces which do not use buffers nor write back.
2403 */
2404int __set_page_dirty_no_writeback(struct page *page)
2405{
2406 if (!PageDirty(page))
2407 return !TestSetPageDirty(page);
2408 return 0;
2409}
2410
2411/*
2412 * Helper function for set_page_dirty family.
2413 *
2414 * Caller must hold lock_page_memcg().
2415 *
2416 * NOTE: This relies on being atomic wrt interrupts.
2417 */
2418void account_page_dirtied(struct page *page, struct address_space *mapping)
2419{
2420 struct inode *inode = mapping->host;
2421
2422 trace_writeback_dirty_page(page, mapping);
2423
2424 if (mapping_cap_account_dirty(mapping)) {
2425 struct bdi_writeback *wb;
2426
2427 inode_attach_wb(inode, page);
2428 wb = inode_to_wb(inode);
2429
2430 mem_cgroup_inc_page_stat(page, MEM_CGROUP_STAT_DIRTY);
2431 __inc_node_page_state(page, NR_FILE_DIRTY);
2432 __inc_zone_page_state(page, NR_ZONE_WRITE_PENDING);
2433 __inc_node_page_state(page, NR_DIRTIED);
2434 __inc_wb_stat(wb, WB_RECLAIMABLE);
2435 __inc_wb_stat(wb, WB_DIRTIED);
2436 task_io_account_write(PAGE_SIZE);
2437 current->nr_dirtied++;
2438 this_cpu_inc(bdp_ratelimits);
2439 }
2440}
2441EXPORT_SYMBOL(account_page_dirtied);
2442
2443/*
2444 * Helper function for deaccounting dirty page without writeback.
2445 *
2446 * Caller must hold lock_page_memcg().
2447 */
2448void account_page_cleaned(struct page *page, struct address_space *mapping,
2449 struct bdi_writeback *wb)
2450{
2451 if (mapping_cap_account_dirty(mapping)) {
2452 mem_cgroup_dec_page_stat(page, MEM_CGROUP_STAT_DIRTY);
2453 dec_node_page_state(page, NR_FILE_DIRTY);
2454 dec_zone_page_state(page, NR_ZONE_WRITE_PENDING);
2455 dec_wb_stat(wb, WB_RECLAIMABLE);
2456 task_io_account_cancelled_write(PAGE_SIZE);
2457 }
2458}
2459
2460/*
2461 * For address_spaces which do not use buffers. Just tag the page as dirty in
2462 * its radix tree.
2463 *
2464 * This is also used when a single buffer is being dirtied: we want to set the
2465 * page dirty in that case, but not all the buffers. This is a "bottom-up"
2466 * dirtying, whereas __set_page_dirty_buffers() is a "top-down" dirtying.
2467 *
2468 * The caller must ensure this doesn't race with truncation. Most will simply
2469 * hold the page lock, but e.g. zap_pte_range() calls with the page mapped and
2470 * the pte lock held, which also locks out truncation.
2471 */
2472int __set_page_dirty_nobuffers(struct page *page)
2473{
2474 lock_page_memcg(page);
2475 if (!TestSetPageDirty(page)) {
2476 struct address_space *mapping = page_mapping(page);
2477 unsigned long flags;
2478
2479 if (!mapping) {
2480 unlock_page_memcg(page);
2481 return 1;
2482 }
2483
2484 spin_lock_irqsave(&mapping->tree_lock, flags);
2485 BUG_ON(page_mapping(page) != mapping);
2486 WARN_ON_ONCE(!PagePrivate(page) && !PageUptodate(page));
2487 account_page_dirtied(page, mapping);
2488 radix_tree_tag_set(&mapping->page_tree, page_index(page),
2489 PAGECACHE_TAG_DIRTY);
2490 spin_unlock_irqrestore(&mapping->tree_lock, flags);
2491 unlock_page_memcg(page);
2492
2493 if (mapping->host) {
2494 /* !PageAnon && !swapper_space */
2495 __mark_inode_dirty(mapping->host, I_DIRTY_PAGES);
2496 }
2497 return 1;
2498 }
2499 unlock_page_memcg(page);
2500 return 0;
2501}
2502EXPORT_SYMBOL(__set_page_dirty_nobuffers);
2503
2504/*
2505 * Call this whenever redirtying a page, to de-account the dirty counters
2506 * (NR_DIRTIED, BDI_DIRTIED, tsk->nr_dirtied), so that they match the written
2507 * counters (NR_WRITTEN, BDI_WRITTEN) in long term. The mismatches will lead to
2508 * systematic errors in balanced_dirty_ratelimit and the dirty pages position
2509 * control.
2510 */
2511void account_page_redirty(struct page *page)
2512{
2513 struct address_space *mapping = page->mapping;
2514
2515 if (mapping && mapping_cap_account_dirty(mapping)) {
2516 struct inode *inode = mapping->host;
2517 struct bdi_writeback *wb;
2518 bool locked;
2519
2520 wb = unlocked_inode_to_wb_begin(inode, &locked);
2521 current->nr_dirtied--;
2522 dec_node_page_state(page, NR_DIRTIED);
2523 dec_wb_stat(wb, WB_DIRTIED);
2524 unlocked_inode_to_wb_end(inode, locked);
2525 }
2526}
2527EXPORT_SYMBOL(account_page_redirty);
2528
2529/*
2530 * When a writepage implementation decides that it doesn't want to write this
2531 * page for some reason, it should redirty the locked page via
2532 * redirty_page_for_writepage() and it should then unlock the page and return 0
2533 */
2534int redirty_page_for_writepage(struct writeback_control *wbc, struct page *page)
2535{
2536 int ret;
2537
2538 wbc->pages_skipped++;
2539 ret = __set_page_dirty_nobuffers(page);
2540 account_page_redirty(page);
2541 return ret;
2542}
2543EXPORT_SYMBOL(redirty_page_for_writepage);
2544
2545/*
2546 * Dirty a page.
2547 *
2548 * For pages with a mapping this should be done under the page lock
2549 * for the benefit of asynchronous memory errors who prefer a consistent
2550 * dirty state. This rule can be broken in some special cases,
2551 * but should be better not to.
2552 *
2553 * If the mapping doesn't provide a set_page_dirty a_op, then
2554 * just fall through and assume that it wants buffer_heads.
2555 */
2556int set_page_dirty(struct page *page)
2557{
2558 struct address_space *mapping = page_mapping(page);
2559
2560 page = compound_head(page);
2561 if (likely(mapping)) {
2562 int (*spd)(struct page *) = mapping->a_ops->set_page_dirty;
2563 /*
2564 * readahead/lru_deactivate_page could remain
2565 * PG_readahead/PG_reclaim due to race with end_page_writeback
2566 * About readahead, if the page is written, the flags would be
2567 * reset. So no problem.
2568 * About lru_deactivate_page, if the page is redirty, the flag
2569 * will be reset. So no problem. but if the page is used by readahead
2570 * it will confuse readahead and make it restart the size rampup
2571 * process. But it's a trivial problem.
2572 */
2573 if (PageReclaim(page))
2574 ClearPageReclaim(page);
2575#ifdef CONFIG_BLOCK
2576 if (!spd)
2577 spd = __set_page_dirty_buffers;
2578#endif
2579 return (*spd)(page);
2580 }
2581 if (!PageDirty(page)) {
2582 if (!TestSetPageDirty(page))
2583 return 1;
2584 }
2585 return 0;
2586}
2587EXPORT_SYMBOL(set_page_dirty);
2588
2589/*
2590 * set_page_dirty() is racy if the caller has no reference against
2591 * page->mapping->host, and if the page is unlocked. This is because another
2592 * CPU could truncate the page off the mapping and then free the mapping.
2593 *
2594 * Usually, the page _is_ locked, or the caller is a user-space process which
2595 * holds a reference on the inode by having an open file.
2596 *
2597 * In other cases, the page should be locked before running set_page_dirty().
2598 */
2599int set_page_dirty_lock(struct page *page)
2600{
2601 int ret;
2602
2603 lock_page(page);
2604 ret = set_page_dirty(page);
2605 unlock_page(page);
2606 return ret;
2607}
2608EXPORT_SYMBOL(set_page_dirty_lock);
2609
2610/*
2611 * This cancels just the dirty bit on the kernel page itself, it does NOT
2612 * actually remove dirty bits on any mmap's that may be around. It also
2613 * leaves the page tagged dirty, so any sync activity will still find it on
2614 * the dirty lists, and in particular, clear_page_dirty_for_io() will still
2615 * look at the dirty bits in the VM.
2616 *
2617 * Doing this should *normally* only ever be done when a page is truncated,
2618 * and is not actually mapped anywhere at all. However, fs/buffer.c does
2619 * this when it notices that somebody has cleaned out all the buffers on a
2620 * page without actually doing it through the VM. Can you say "ext3 is
2621 * horribly ugly"? Thought you could.
2622 */
2623void cancel_dirty_page(struct page *page)
2624{
2625 struct address_space *mapping = page_mapping(page);
2626
2627 if (mapping_cap_account_dirty(mapping)) {
2628 struct inode *inode = mapping->host;
2629 struct bdi_writeback *wb;
2630 bool locked;
2631
2632 lock_page_memcg(page);
2633 wb = unlocked_inode_to_wb_begin(inode, &locked);
2634
2635 if (TestClearPageDirty(page))
2636 account_page_cleaned(page, mapping, wb);
2637
2638 unlocked_inode_to_wb_end(inode, locked);
2639 unlock_page_memcg(page);
2640 } else {
2641 ClearPageDirty(page);
2642 }
2643}
2644EXPORT_SYMBOL(cancel_dirty_page);
2645
2646/*
2647 * Clear a page's dirty flag, while caring for dirty memory accounting.
2648 * Returns true if the page was previously dirty.
2649 *
2650 * This is for preparing to put the page under writeout. We leave the page
2651 * tagged as dirty in the radix tree so that a concurrent write-for-sync
2652 * can discover it via a PAGECACHE_TAG_DIRTY walk. The ->writepage
2653 * implementation will run either set_page_writeback() or set_page_dirty(),
2654 * at which stage we bring the page's dirty flag and radix-tree dirty tag
2655 * back into sync.
2656 *
2657 * This incoherency between the page's dirty flag and radix-tree tag is
2658 * unfortunate, but it only exists while the page is locked.
2659 */
2660int clear_page_dirty_for_io(struct page *page)
2661{
2662 struct address_space *mapping = page_mapping(page);
2663 int ret = 0;
2664
2665 BUG_ON(!PageLocked(page));
2666
2667 if (mapping && mapping_cap_account_dirty(mapping)) {
2668 struct inode *inode = mapping->host;
2669 struct bdi_writeback *wb;
2670 bool locked;
2671
2672 /*
2673 * Yes, Virginia, this is indeed insane.
2674 *
2675 * We use this sequence to make sure that
2676 * (a) we account for dirty stats properly
2677 * (b) we tell the low-level filesystem to
2678 * mark the whole page dirty if it was
2679 * dirty in a pagetable. Only to then
2680 * (c) clean the page again and return 1 to
2681 * cause the writeback.
2682 *
2683 * This way we avoid all nasty races with the
2684 * dirty bit in multiple places and clearing
2685 * them concurrently from different threads.
2686 *
2687 * Note! Normally the "set_page_dirty(page)"
2688 * has no effect on the actual dirty bit - since
2689 * that will already usually be set. But we
2690 * need the side effects, and it can help us
2691 * avoid races.
2692 *
2693 * We basically use the page "master dirty bit"
2694 * as a serialization point for all the different
2695 * threads doing their things.
2696 */
2697 if (page_mkclean(page))
2698 set_page_dirty(page);
2699 /*
2700 * We carefully synchronise fault handlers against
2701 * installing a dirty pte and marking the page dirty
2702 * at this point. We do this by having them hold the
2703 * page lock while dirtying the page, and pages are
2704 * always locked coming in here, so we get the desired
2705 * exclusion.
2706 */
2707 wb = unlocked_inode_to_wb_begin(inode, &locked);
2708 if (TestClearPageDirty(page)) {
2709 mem_cgroup_dec_page_stat(page, MEM_CGROUP_STAT_DIRTY);
2710 dec_node_page_state(page, NR_FILE_DIRTY);
2711 dec_zone_page_state(page, NR_ZONE_WRITE_PENDING);
2712 dec_wb_stat(wb, WB_RECLAIMABLE);
2713 ret = 1;
2714 }
2715 unlocked_inode_to_wb_end(inode, locked);
2716 return ret;
2717 }
2718 return TestClearPageDirty(page);
2719}
2720EXPORT_SYMBOL(clear_page_dirty_for_io);
2721
2722int test_clear_page_writeback(struct page *page)
2723{
2724 struct address_space *mapping = page_mapping(page);
2725 int ret;
2726
2727 lock_page_memcg(page);
2728 if (mapping && mapping_use_writeback_tags(mapping)) {
2729 struct inode *inode = mapping->host;
2730 struct backing_dev_info *bdi = inode_to_bdi(inode);
2731 unsigned long flags;
2732
2733 spin_lock_irqsave(&mapping->tree_lock, flags);
2734 ret = TestClearPageWriteback(page);
2735 if (ret) {
2736 radix_tree_tag_clear(&mapping->page_tree,
2737 page_index(page),
2738 PAGECACHE_TAG_WRITEBACK);
2739 if (bdi_cap_account_writeback(bdi)) {
2740 struct bdi_writeback *wb = inode_to_wb(inode);
2741
2742 __dec_wb_stat(wb, WB_WRITEBACK);
2743 __wb_writeout_inc(wb);
2744 }
2745 }
2746
2747 if (mapping->host && !mapping_tagged(mapping,
2748 PAGECACHE_TAG_WRITEBACK))
2749 sb_clear_inode_writeback(mapping->host);
2750
2751 spin_unlock_irqrestore(&mapping->tree_lock, flags);
2752 } else {
2753 ret = TestClearPageWriteback(page);
2754 }
2755 if (ret) {
2756 mem_cgroup_dec_page_stat(page, MEM_CGROUP_STAT_WRITEBACK);
2757 dec_node_page_state(page, NR_WRITEBACK);
2758 dec_zone_page_state(page, NR_ZONE_WRITE_PENDING);
2759 inc_node_page_state(page, NR_WRITTEN);
2760 }
2761 unlock_page_memcg(page);
2762 return ret;
2763}
2764
2765int __test_set_page_writeback(struct page *page, bool keep_write)
2766{
2767 struct address_space *mapping = page_mapping(page);
2768 int ret;
2769
2770 lock_page_memcg(page);
2771 if (mapping && mapping_use_writeback_tags(mapping)) {
2772 struct inode *inode = mapping->host;
2773 struct backing_dev_info *bdi = inode_to_bdi(inode);
2774 unsigned long flags;
2775
2776 spin_lock_irqsave(&mapping->tree_lock, flags);
2777 ret = TestSetPageWriteback(page);
2778 if (!ret) {
2779 bool on_wblist;
2780
2781 on_wblist = mapping_tagged(mapping,
2782 PAGECACHE_TAG_WRITEBACK);
2783
2784 radix_tree_tag_set(&mapping->page_tree,
2785 page_index(page),
2786 PAGECACHE_TAG_WRITEBACK);
2787 if (bdi_cap_account_writeback(bdi))
2788 __inc_wb_stat(inode_to_wb(inode), WB_WRITEBACK);
2789
2790 /*
2791 * We can come through here when swapping anonymous
2792 * pages, so we don't necessarily have an inode to track
2793 * for sync.
2794 */
2795 if (mapping->host && !on_wblist)
2796 sb_mark_inode_writeback(mapping->host);
2797 }
2798 if (!PageDirty(page))
2799 radix_tree_tag_clear(&mapping->page_tree,
2800 page_index(page),
2801 PAGECACHE_TAG_DIRTY);
2802 if (!keep_write)
2803 radix_tree_tag_clear(&mapping->page_tree,
2804 page_index(page),
2805 PAGECACHE_TAG_TOWRITE);
2806 spin_unlock_irqrestore(&mapping->tree_lock, flags);
2807 } else {
2808 ret = TestSetPageWriteback(page);
2809 }
2810 if (!ret) {
2811 mem_cgroup_inc_page_stat(page, MEM_CGROUP_STAT_WRITEBACK);
2812 inc_node_page_state(page, NR_WRITEBACK);
2813 inc_zone_page_state(page, NR_ZONE_WRITE_PENDING);
2814 }
2815 unlock_page_memcg(page);
2816 return ret;
2817
2818}
2819EXPORT_SYMBOL(__test_set_page_writeback);
2820
2821/*
2822 * Return true if any of the pages in the mapping are marked with the
2823 * passed tag.
2824 */
2825int mapping_tagged(struct address_space *mapping, int tag)
2826{
2827 return radix_tree_tagged(&mapping->page_tree, tag);
2828}
2829EXPORT_SYMBOL(mapping_tagged);
2830
2831/**
2832 * wait_for_stable_page() - wait for writeback to finish, if necessary.
2833 * @page: The page to wait on.
2834 *
2835 * This function determines if the given page is related to a backing device
2836 * that requires page contents to be held stable during writeback. If so, then
2837 * it will wait for any pending writeback to complete.
2838 */
2839void wait_for_stable_page(struct page *page)
2840{
2841 if (bdi_cap_stable_pages_required(inode_to_bdi(page->mapping->host)))
2842 wait_on_page_writeback(page);
2843}
2844EXPORT_SYMBOL_GPL(wait_for_stable_page);