Loading...
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/module.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>
36#include <linux/pagevec.h>
37#include <trace/events/writeback.h>
38
39/*
40 * Sleep at most 200ms at a time in balance_dirty_pages().
41 */
42#define MAX_PAUSE max(HZ/5, 1)
43
44/*
45 * Estimate write bandwidth at 200ms intervals.
46 */
47#define BANDWIDTH_INTERVAL max(HZ/5, 1)
48
49/*
50 * After a CPU has dirtied this many pages, balance_dirty_pages_ratelimited
51 * will look to see if it needs to force writeback or throttling.
52 */
53static long ratelimit_pages = 32;
54
55/*
56 * When balance_dirty_pages decides that the caller needs to perform some
57 * non-background writeback, this is how many pages it will attempt to write.
58 * It should be somewhat larger than dirtied pages to ensure that reasonably
59 * large amounts of I/O are submitted.
60 */
61static inline long sync_writeback_pages(unsigned long dirtied)
62{
63 if (dirtied < ratelimit_pages)
64 dirtied = ratelimit_pages;
65
66 return dirtied + dirtied / 2;
67}
68
69/* The following parameters are exported via /proc/sys/vm */
70
71/*
72 * Start background writeback (via writeback threads) at this percentage
73 */
74int dirty_background_ratio = 10;
75
76/*
77 * dirty_background_bytes starts at 0 (disabled) so that it is a function of
78 * dirty_background_ratio * the amount of dirtyable memory
79 */
80unsigned long dirty_background_bytes;
81
82/*
83 * free highmem will not be subtracted from the total free memory
84 * for calculating free ratios if vm_highmem_is_dirtyable is true
85 */
86int vm_highmem_is_dirtyable;
87
88/*
89 * The generator of dirty data starts writeback at this percentage
90 */
91int vm_dirty_ratio = 20;
92
93/*
94 * vm_dirty_bytes starts at 0 (disabled) so that it is a function of
95 * vm_dirty_ratio * the amount of dirtyable memory
96 */
97unsigned long vm_dirty_bytes;
98
99/*
100 * The interval between `kupdate'-style writebacks
101 */
102unsigned int dirty_writeback_interval = 5 * 100; /* centiseconds */
103
104/*
105 * The longest time for which data is allowed to remain dirty
106 */
107unsigned int dirty_expire_interval = 30 * 100; /* centiseconds */
108
109/*
110 * Flag that makes the machine dump writes/reads and block dirtyings.
111 */
112int block_dump;
113
114/*
115 * Flag that puts the machine in "laptop mode". Doubles as a timeout in jiffies:
116 * a full sync is triggered after this time elapses without any disk activity.
117 */
118int laptop_mode;
119
120EXPORT_SYMBOL(laptop_mode);
121
122/* End of sysctl-exported parameters */
123
124unsigned long global_dirty_limit;
125
126/*
127 * Scale the writeback cache size proportional to the relative writeout speeds.
128 *
129 * We do this by keeping a floating proportion between BDIs, based on page
130 * writeback completions [end_page_writeback()]. Those devices that write out
131 * pages fastest will get the larger share, while the slower will get a smaller
132 * share.
133 *
134 * We use page writeout completions because we are interested in getting rid of
135 * dirty pages. Having them written out is the primary goal.
136 *
137 * We introduce a concept of time, a period over which we measure these events,
138 * because demand can/will vary over time. The length of this period itself is
139 * measured in page writeback completions.
140 *
141 */
142static struct prop_descriptor vm_completions;
143static struct prop_descriptor vm_dirties;
144
145/*
146 * couple the period to the dirty_ratio:
147 *
148 * period/2 ~ roundup_pow_of_two(dirty limit)
149 */
150static int calc_period_shift(void)
151{
152 unsigned long dirty_total;
153
154 if (vm_dirty_bytes)
155 dirty_total = vm_dirty_bytes / PAGE_SIZE;
156 else
157 dirty_total = (vm_dirty_ratio * determine_dirtyable_memory()) /
158 100;
159 return 2 + ilog2(dirty_total - 1);
160}
161
162/*
163 * update the period when the dirty threshold changes.
164 */
165static void update_completion_period(void)
166{
167 int shift = calc_period_shift();
168 prop_change_shift(&vm_completions, shift);
169 prop_change_shift(&vm_dirties, shift);
170}
171
172int dirty_background_ratio_handler(struct ctl_table *table, int write,
173 void __user *buffer, size_t *lenp,
174 loff_t *ppos)
175{
176 int ret;
177
178 ret = proc_dointvec_minmax(table, write, buffer, lenp, ppos);
179 if (ret == 0 && write)
180 dirty_background_bytes = 0;
181 return ret;
182}
183
184int dirty_background_bytes_handler(struct ctl_table *table, int write,
185 void __user *buffer, size_t *lenp,
186 loff_t *ppos)
187{
188 int ret;
189
190 ret = proc_doulongvec_minmax(table, write, buffer, lenp, ppos);
191 if (ret == 0 && write)
192 dirty_background_ratio = 0;
193 return ret;
194}
195
196int dirty_ratio_handler(struct ctl_table *table, int write,
197 void __user *buffer, size_t *lenp,
198 loff_t *ppos)
199{
200 int old_ratio = vm_dirty_ratio;
201 int ret;
202
203 ret = proc_dointvec_minmax(table, write, buffer, lenp, ppos);
204 if (ret == 0 && write && vm_dirty_ratio != old_ratio) {
205 update_completion_period();
206 vm_dirty_bytes = 0;
207 }
208 return ret;
209}
210
211
212int dirty_bytes_handler(struct ctl_table *table, int write,
213 void __user *buffer, size_t *lenp,
214 loff_t *ppos)
215{
216 unsigned long old_bytes = vm_dirty_bytes;
217 int ret;
218
219 ret = proc_doulongvec_minmax(table, write, buffer, lenp, ppos);
220 if (ret == 0 && write && vm_dirty_bytes != old_bytes) {
221 update_completion_period();
222 vm_dirty_ratio = 0;
223 }
224 return ret;
225}
226
227/*
228 * Increment the BDI's writeout completion count and the global writeout
229 * completion count. Called from test_clear_page_writeback().
230 */
231static inline void __bdi_writeout_inc(struct backing_dev_info *bdi)
232{
233 __inc_bdi_stat(bdi, BDI_WRITTEN);
234 __prop_inc_percpu_max(&vm_completions, &bdi->completions,
235 bdi->max_prop_frac);
236}
237
238void bdi_writeout_inc(struct backing_dev_info *bdi)
239{
240 unsigned long flags;
241
242 local_irq_save(flags);
243 __bdi_writeout_inc(bdi);
244 local_irq_restore(flags);
245}
246EXPORT_SYMBOL_GPL(bdi_writeout_inc);
247
248void task_dirty_inc(struct task_struct *tsk)
249{
250 prop_inc_single(&vm_dirties, &tsk->dirties);
251}
252
253/*
254 * Obtain an accurate fraction of the BDI's portion.
255 */
256static void bdi_writeout_fraction(struct backing_dev_info *bdi,
257 long *numerator, long *denominator)
258{
259 prop_fraction_percpu(&vm_completions, &bdi->completions,
260 numerator, denominator);
261}
262
263static inline void task_dirties_fraction(struct task_struct *tsk,
264 long *numerator, long *denominator)
265{
266 prop_fraction_single(&vm_dirties, &tsk->dirties,
267 numerator, denominator);
268}
269
270/*
271 * task_dirty_limit - scale down dirty throttling threshold for one task
272 *
273 * task specific dirty limit:
274 *
275 * dirty -= (dirty/8) * p_{t}
276 *
277 * To protect light/slow dirtying tasks from heavier/fast ones, we start
278 * throttling individual tasks before reaching the bdi dirty limit.
279 * Relatively low thresholds will be allocated to heavy dirtiers. So when
280 * dirty pages grow large, heavy dirtiers will be throttled first, which will
281 * effectively curb the growth of dirty pages. Light dirtiers with high enough
282 * dirty threshold may never get throttled.
283 */
284#define TASK_LIMIT_FRACTION 8
285static unsigned long task_dirty_limit(struct task_struct *tsk,
286 unsigned long bdi_dirty)
287{
288 long numerator, denominator;
289 unsigned long dirty = bdi_dirty;
290 u64 inv = dirty / TASK_LIMIT_FRACTION;
291
292 task_dirties_fraction(tsk, &numerator, &denominator);
293 inv *= numerator;
294 do_div(inv, denominator);
295
296 dirty -= inv;
297
298 return max(dirty, bdi_dirty/2);
299}
300
301/* Minimum limit for any task */
302static unsigned long task_min_dirty_limit(unsigned long bdi_dirty)
303{
304 return bdi_dirty - bdi_dirty / TASK_LIMIT_FRACTION;
305}
306
307/*
308 *
309 */
310static unsigned int bdi_min_ratio;
311
312int bdi_set_min_ratio(struct backing_dev_info *bdi, unsigned int min_ratio)
313{
314 int ret = 0;
315
316 spin_lock_bh(&bdi_lock);
317 if (min_ratio > bdi->max_ratio) {
318 ret = -EINVAL;
319 } else {
320 min_ratio -= bdi->min_ratio;
321 if (bdi_min_ratio + min_ratio < 100) {
322 bdi_min_ratio += min_ratio;
323 bdi->min_ratio += min_ratio;
324 } else {
325 ret = -EINVAL;
326 }
327 }
328 spin_unlock_bh(&bdi_lock);
329
330 return ret;
331}
332
333int bdi_set_max_ratio(struct backing_dev_info *bdi, unsigned max_ratio)
334{
335 int ret = 0;
336
337 if (max_ratio > 100)
338 return -EINVAL;
339
340 spin_lock_bh(&bdi_lock);
341 if (bdi->min_ratio > max_ratio) {
342 ret = -EINVAL;
343 } else {
344 bdi->max_ratio = max_ratio;
345 bdi->max_prop_frac = (PROP_FRAC_BASE * max_ratio) / 100;
346 }
347 spin_unlock_bh(&bdi_lock);
348
349 return ret;
350}
351EXPORT_SYMBOL(bdi_set_max_ratio);
352
353/*
354 * Work out the current dirty-memory clamping and background writeout
355 * thresholds.
356 *
357 * The main aim here is to lower them aggressively if there is a lot of mapped
358 * memory around. To avoid stressing page reclaim with lots of unreclaimable
359 * pages. It is better to clamp down on writers than to start swapping, and
360 * performing lots of scanning.
361 *
362 * We only allow 1/2 of the currently-unmapped memory to be dirtied.
363 *
364 * We don't permit the clamping level to fall below 5% - that is getting rather
365 * excessive.
366 *
367 * We make sure that the background writeout level is below the adjusted
368 * clamping level.
369 */
370
371static unsigned long highmem_dirtyable_memory(unsigned long total)
372{
373#ifdef CONFIG_HIGHMEM
374 int node;
375 unsigned long x = 0;
376
377 for_each_node_state(node, N_HIGH_MEMORY) {
378 struct zone *z =
379 &NODE_DATA(node)->node_zones[ZONE_HIGHMEM];
380
381 x += zone_page_state(z, NR_FREE_PAGES) +
382 zone_reclaimable_pages(z);
383 }
384 /*
385 * Make sure that the number of highmem pages is never larger
386 * than the number of the total dirtyable memory. This can only
387 * occur in very strange VM situations but we want to make sure
388 * that this does not occur.
389 */
390 return min(x, total);
391#else
392 return 0;
393#endif
394}
395
396/**
397 * determine_dirtyable_memory - amount of memory that may be used
398 *
399 * Returns the numebr of pages that can currently be freed and used
400 * by the kernel for direct mappings.
401 */
402unsigned long determine_dirtyable_memory(void)
403{
404 unsigned long x;
405
406 x = global_page_state(NR_FREE_PAGES) + global_reclaimable_pages();
407
408 if (!vm_highmem_is_dirtyable)
409 x -= highmem_dirtyable_memory(x);
410
411 return x + 1; /* Ensure that we never return 0 */
412}
413
414static unsigned long hard_dirty_limit(unsigned long thresh)
415{
416 return max(thresh, global_dirty_limit);
417}
418
419/*
420 * global_dirty_limits - background-writeback and dirty-throttling thresholds
421 *
422 * Calculate the dirty thresholds based on sysctl parameters
423 * - vm.dirty_background_ratio or vm.dirty_background_bytes
424 * - vm.dirty_ratio or vm.dirty_bytes
425 * The dirty limits will be lifted by 1/4 for PF_LESS_THROTTLE (ie. nfsd) and
426 * real-time tasks.
427 */
428void global_dirty_limits(unsigned long *pbackground, unsigned long *pdirty)
429{
430 unsigned long background;
431 unsigned long dirty;
432 unsigned long uninitialized_var(available_memory);
433 struct task_struct *tsk;
434
435 if (!vm_dirty_bytes || !dirty_background_bytes)
436 available_memory = determine_dirtyable_memory();
437
438 if (vm_dirty_bytes)
439 dirty = DIV_ROUND_UP(vm_dirty_bytes, PAGE_SIZE);
440 else
441 dirty = (vm_dirty_ratio * available_memory) / 100;
442
443 if (dirty_background_bytes)
444 background = DIV_ROUND_UP(dirty_background_bytes, PAGE_SIZE);
445 else
446 background = (dirty_background_ratio * available_memory) / 100;
447
448 if (background >= dirty)
449 background = dirty / 2;
450 tsk = current;
451 if (tsk->flags & PF_LESS_THROTTLE || rt_task(tsk)) {
452 background += background / 4;
453 dirty += dirty / 4;
454 }
455 *pbackground = background;
456 *pdirty = dirty;
457 trace_global_dirty_state(background, dirty);
458}
459
460/**
461 * bdi_dirty_limit - @bdi's share of dirty throttling threshold
462 * @bdi: the backing_dev_info to query
463 * @dirty: global dirty limit in pages
464 *
465 * Returns @bdi's dirty limit in pages. The term "dirty" in the context of
466 * dirty balancing includes all PG_dirty, PG_writeback and NFS unstable pages.
467 * And the "limit" in the name is not seriously taken as hard limit in
468 * balance_dirty_pages().
469 *
470 * It allocates high/low dirty limits to fast/slow devices, in order to prevent
471 * - starving fast devices
472 * - piling up dirty pages (that will take long time to sync) on slow devices
473 *
474 * The bdi's share of dirty limit will be adapting to its throughput and
475 * bounded by the bdi->min_ratio and/or bdi->max_ratio parameters, if set.
476 */
477unsigned long bdi_dirty_limit(struct backing_dev_info *bdi, unsigned long dirty)
478{
479 u64 bdi_dirty;
480 long numerator, denominator;
481
482 /*
483 * Calculate this BDI's share of the dirty ratio.
484 */
485 bdi_writeout_fraction(bdi, &numerator, &denominator);
486
487 bdi_dirty = (dirty * (100 - bdi_min_ratio)) / 100;
488 bdi_dirty *= numerator;
489 do_div(bdi_dirty, denominator);
490
491 bdi_dirty += (dirty * bdi->min_ratio) / 100;
492 if (bdi_dirty > (dirty * bdi->max_ratio) / 100)
493 bdi_dirty = dirty * bdi->max_ratio / 100;
494
495 return bdi_dirty;
496}
497
498static void bdi_update_write_bandwidth(struct backing_dev_info *bdi,
499 unsigned long elapsed,
500 unsigned long written)
501{
502 const unsigned long period = roundup_pow_of_two(3 * HZ);
503 unsigned long avg = bdi->avg_write_bandwidth;
504 unsigned long old = bdi->write_bandwidth;
505 u64 bw;
506
507 /*
508 * bw = written * HZ / elapsed
509 *
510 * bw * elapsed + write_bandwidth * (period - elapsed)
511 * write_bandwidth = ---------------------------------------------------
512 * period
513 */
514 bw = written - bdi->written_stamp;
515 bw *= HZ;
516 if (unlikely(elapsed > period)) {
517 do_div(bw, elapsed);
518 avg = bw;
519 goto out;
520 }
521 bw += (u64)bdi->write_bandwidth * (period - elapsed);
522 bw >>= ilog2(period);
523
524 /*
525 * one more level of smoothing, for filtering out sudden spikes
526 */
527 if (avg > old && old >= (unsigned long)bw)
528 avg -= (avg - old) >> 3;
529
530 if (avg < old && old <= (unsigned long)bw)
531 avg += (old - avg) >> 3;
532
533out:
534 bdi->write_bandwidth = bw;
535 bdi->avg_write_bandwidth = avg;
536}
537
538/*
539 * The global dirtyable memory and dirty threshold could be suddenly knocked
540 * down by a large amount (eg. on the startup of KVM in a swapless system).
541 * This may throw the system into deep dirty exceeded state and throttle
542 * heavy/light dirtiers alike. To retain good responsiveness, maintain
543 * global_dirty_limit for tracking slowly down to the knocked down dirty
544 * threshold.
545 */
546static void update_dirty_limit(unsigned long thresh, unsigned long dirty)
547{
548 unsigned long limit = global_dirty_limit;
549
550 /*
551 * Follow up in one step.
552 */
553 if (limit < thresh) {
554 limit = thresh;
555 goto update;
556 }
557
558 /*
559 * Follow down slowly. Use the higher one as the target, because thresh
560 * may drop below dirty. This is exactly the reason to introduce
561 * global_dirty_limit which is guaranteed to lie above the dirty pages.
562 */
563 thresh = max(thresh, dirty);
564 if (limit > thresh) {
565 limit -= (limit - thresh) >> 5;
566 goto update;
567 }
568 return;
569update:
570 global_dirty_limit = limit;
571}
572
573static void global_update_bandwidth(unsigned long thresh,
574 unsigned long dirty,
575 unsigned long now)
576{
577 static DEFINE_SPINLOCK(dirty_lock);
578 static unsigned long update_time;
579
580 /*
581 * check locklessly first to optimize away locking for the most time
582 */
583 if (time_before(now, update_time + BANDWIDTH_INTERVAL))
584 return;
585
586 spin_lock(&dirty_lock);
587 if (time_after_eq(now, update_time + BANDWIDTH_INTERVAL)) {
588 update_dirty_limit(thresh, dirty);
589 update_time = now;
590 }
591 spin_unlock(&dirty_lock);
592}
593
594void __bdi_update_bandwidth(struct backing_dev_info *bdi,
595 unsigned long thresh,
596 unsigned long dirty,
597 unsigned long bdi_thresh,
598 unsigned long bdi_dirty,
599 unsigned long start_time)
600{
601 unsigned long now = jiffies;
602 unsigned long elapsed = now - bdi->bw_time_stamp;
603 unsigned long written;
604
605 /*
606 * rate-limit, only update once every 200ms.
607 */
608 if (elapsed < BANDWIDTH_INTERVAL)
609 return;
610
611 written = percpu_counter_read(&bdi->bdi_stat[BDI_WRITTEN]);
612
613 /*
614 * Skip quiet periods when disk bandwidth is under-utilized.
615 * (at least 1s idle time between two flusher runs)
616 */
617 if (elapsed > HZ && time_before(bdi->bw_time_stamp, start_time))
618 goto snapshot;
619
620 if (thresh)
621 global_update_bandwidth(thresh, dirty, now);
622
623 bdi_update_write_bandwidth(bdi, elapsed, written);
624
625snapshot:
626 bdi->written_stamp = written;
627 bdi->bw_time_stamp = now;
628}
629
630static void bdi_update_bandwidth(struct backing_dev_info *bdi,
631 unsigned long thresh,
632 unsigned long dirty,
633 unsigned long bdi_thresh,
634 unsigned long bdi_dirty,
635 unsigned long start_time)
636{
637 if (time_is_after_eq_jiffies(bdi->bw_time_stamp + BANDWIDTH_INTERVAL))
638 return;
639 spin_lock(&bdi->wb.list_lock);
640 __bdi_update_bandwidth(bdi, thresh, dirty, bdi_thresh, bdi_dirty,
641 start_time);
642 spin_unlock(&bdi->wb.list_lock);
643}
644
645/*
646 * balance_dirty_pages() must be called by processes which are generating dirty
647 * data. It looks at the number of dirty pages in the machine and will force
648 * the caller to perform writeback if the system is over `vm_dirty_ratio'.
649 * If we're over `background_thresh' then the writeback threads are woken to
650 * perform some writeout.
651 */
652static void balance_dirty_pages(struct address_space *mapping,
653 unsigned long write_chunk)
654{
655 unsigned long nr_reclaimable, bdi_nr_reclaimable;
656 unsigned long nr_dirty; /* = file_dirty + writeback + unstable_nfs */
657 unsigned long bdi_dirty;
658 unsigned long background_thresh;
659 unsigned long dirty_thresh;
660 unsigned long bdi_thresh;
661 unsigned long task_bdi_thresh;
662 unsigned long min_task_bdi_thresh;
663 unsigned long pages_written = 0;
664 unsigned long pause = 1;
665 bool dirty_exceeded = false;
666 bool clear_dirty_exceeded = true;
667 struct backing_dev_info *bdi = mapping->backing_dev_info;
668 unsigned long start_time = jiffies;
669
670 for (;;) {
671 nr_reclaimable = global_page_state(NR_FILE_DIRTY) +
672 global_page_state(NR_UNSTABLE_NFS);
673 nr_dirty = nr_reclaimable + global_page_state(NR_WRITEBACK);
674
675 global_dirty_limits(&background_thresh, &dirty_thresh);
676
677 /*
678 * Throttle it only when the background writeback cannot
679 * catch-up. This avoids (excessively) small writeouts
680 * when the bdi limits are ramping up.
681 */
682 if (nr_dirty <= (background_thresh + dirty_thresh) / 2)
683 break;
684
685 bdi_thresh = bdi_dirty_limit(bdi, dirty_thresh);
686 min_task_bdi_thresh = task_min_dirty_limit(bdi_thresh);
687 task_bdi_thresh = task_dirty_limit(current, bdi_thresh);
688
689 /*
690 * In order to avoid the stacked BDI deadlock we need
691 * to ensure we accurately count the 'dirty' pages when
692 * the threshold is low.
693 *
694 * Otherwise it would be possible to get thresh+n pages
695 * reported dirty, even though there are thresh-m pages
696 * actually dirty; with m+n sitting in the percpu
697 * deltas.
698 */
699 if (task_bdi_thresh < 2 * bdi_stat_error(bdi)) {
700 bdi_nr_reclaimable = bdi_stat_sum(bdi, BDI_RECLAIMABLE);
701 bdi_dirty = bdi_nr_reclaimable +
702 bdi_stat_sum(bdi, BDI_WRITEBACK);
703 } else {
704 bdi_nr_reclaimable = bdi_stat(bdi, BDI_RECLAIMABLE);
705 bdi_dirty = bdi_nr_reclaimable +
706 bdi_stat(bdi, BDI_WRITEBACK);
707 }
708
709 /*
710 * The bdi thresh is somehow "soft" limit derived from the
711 * global "hard" limit. The former helps to prevent heavy IO
712 * bdi or process from holding back light ones; The latter is
713 * the last resort safeguard.
714 */
715 dirty_exceeded = (bdi_dirty > task_bdi_thresh) ||
716 (nr_dirty > dirty_thresh);
717 clear_dirty_exceeded = (bdi_dirty <= min_task_bdi_thresh) &&
718 (nr_dirty <= dirty_thresh);
719
720 if (!dirty_exceeded)
721 break;
722
723 if (!bdi->dirty_exceeded)
724 bdi->dirty_exceeded = 1;
725
726 bdi_update_bandwidth(bdi, dirty_thresh, nr_dirty,
727 bdi_thresh, bdi_dirty, start_time);
728
729 /* Note: nr_reclaimable denotes nr_dirty + nr_unstable.
730 * Unstable writes are a feature of certain networked
731 * filesystems (i.e. NFS) in which data may have been
732 * written to the server's write cache, but has not yet
733 * been flushed to permanent storage.
734 * Only move pages to writeback if this bdi is over its
735 * threshold otherwise wait until the disk writes catch
736 * up.
737 */
738 trace_balance_dirty_start(bdi);
739 if (bdi_nr_reclaimable > task_bdi_thresh) {
740 pages_written += writeback_inodes_wb(&bdi->wb,
741 write_chunk);
742 trace_balance_dirty_written(bdi, pages_written);
743 if (pages_written >= write_chunk)
744 break; /* We've done our duty */
745 }
746 __set_current_state(TASK_UNINTERRUPTIBLE);
747 io_schedule_timeout(pause);
748 trace_balance_dirty_wait(bdi);
749
750 dirty_thresh = hard_dirty_limit(dirty_thresh);
751 /*
752 * max-pause area. If dirty exceeded but still within this
753 * area, no need to sleep for more than 200ms: (a) 8 pages per
754 * 200ms is typically more than enough to curb heavy dirtiers;
755 * (b) the pause time limit makes the dirtiers more responsive.
756 */
757 if (nr_dirty < dirty_thresh &&
758 bdi_dirty < (task_bdi_thresh + bdi_thresh) / 2 &&
759 time_after(jiffies, start_time + MAX_PAUSE))
760 break;
761
762 /*
763 * Increase the delay for each loop, up to our previous
764 * default of taking a 100ms nap.
765 */
766 pause <<= 1;
767 if (pause > HZ / 10)
768 pause = HZ / 10;
769 }
770
771 /* Clear dirty_exceeded flag only when no task can exceed the limit */
772 if (clear_dirty_exceeded && bdi->dirty_exceeded)
773 bdi->dirty_exceeded = 0;
774
775 if (writeback_in_progress(bdi))
776 return;
777
778 /*
779 * In laptop mode, we wait until hitting the higher threshold before
780 * starting background writeout, and then write out all the way down
781 * to the lower threshold. So slow writers cause minimal disk activity.
782 *
783 * In normal mode, we start background writeout at the lower
784 * background_thresh, to keep the amount of dirty memory low.
785 */
786 if ((laptop_mode && pages_written) ||
787 (!laptop_mode && (nr_reclaimable > background_thresh)))
788 bdi_start_background_writeback(bdi);
789}
790
791void set_page_dirty_balance(struct page *page, int page_mkwrite)
792{
793 if (set_page_dirty(page) || page_mkwrite) {
794 struct address_space *mapping = page_mapping(page);
795
796 if (mapping)
797 balance_dirty_pages_ratelimited(mapping);
798 }
799}
800
801static DEFINE_PER_CPU(unsigned long, bdp_ratelimits) = 0;
802
803/**
804 * balance_dirty_pages_ratelimited_nr - balance dirty memory state
805 * @mapping: address_space which was dirtied
806 * @nr_pages_dirtied: number of pages which the caller has just dirtied
807 *
808 * Processes which are dirtying memory should call in here once for each page
809 * which was newly dirtied. The function will periodically check the system's
810 * dirty state and will initiate writeback if needed.
811 *
812 * On really big machines, get_writeback_state is expensive, so try to avoid
813 * calling it too often (ratelimiting). But once we're over the dirty memory
814 * limit we decrease the ratelimiting by a lot, to prevent individual processes
815 * from overshooting the limit by (ratelimit_pages) each.
816 */
817void balance_dirty_pages_ratelimited_nr(struct address_space *mapping,
818 unsigned long nr_pages_dirtied)
819{
820 struct backing_dev_info *bdi = mapping->backing_dev_info;
821 unsigned long ratelimit;
822 unsigned long *p;
823
824 if (!bdi_cap_account_dirty(bdi))
825 return;
826
827 ratelimit = ratelimit_pages;
828 if (mapping->backing_dev_info->dirty_exceeded)
829 ratelimit = 8;
830
831 /*
832 * Check the rate limiting. Also, we do not want to throttle real-time
833 * tasks in balance_dirty_pages(). Period.
834 */
835 preempt_disable();
836 p = &__get_cpu_var(bdp_ratelimits);
837 *p += nr_pages_dirtied;
838 if (unlikely(*p >= ratelimit)) {
839 ratelimit = sync_writeback_pages(*p);
840 *p = 0;
841 preempt_enable();
842 balance_dirty_pages(mapping, ratelimit);
843 return;
844 }
845 preempt_enable();
846}
847EXPORT_SYMBOL(balance_dirty_pages_ratelimited_nr);
848
849void throttle_vm_writeout(gfp_t gfp_mask)
850{
851 unsigned long background_thresh;
852 unsigned long dirty_thresh;
853
854 for ( ; ; ) {
855 global_dirty_limits(&background_thresh, &dirty_thresh);
856
857 /*
858 * Boost the allowable dirty threshold a bit for page
859 * allocators so they don't get DoS'ed by heavy writers
860 */
861 dirty_thresh += dirty_thresh / 10; /* wheeee... */
862
863 if (global_page_state(NR_UNSTABLE_NFS) +
864 global_page_state(NR_WRITEBACK) <= dirty_thresh)
865 break;
866 congestion_wait(BLK_RW_ASYNC, HZ/10);
867
868 /*
869 * The caller might hold locks which can prevent IO completion
870 * or progress in the filesystem. So we cannot just sit here
871 * waiting for IO to complete.
872 */
873 if ((gfp_mask & (__GFP_FS|__GFP_IO)) != (__GFP_FS|__GFP_IO))
874 break;
875 }
876}
877
878/*
879 * sysctl handler for /proc/sys/vm/dirty_writeback_centisecs
880 */
881int dirty_writeback_centisecs_handler(ctl_table *table, int write,
882 void __user *buffer, size_t *length, loff_t *ppos)
883{
884 proc_dointvec(table, write, buffer, length, ppos);
885 bdi_arm_supers_timer();
886 return 0;
887}
888
889#ifdef CONFIG_BLOCK
890void laptop_mode_timer_fn(unsigned long data)
891{
892 struct request_queue *q = (struct request_queue *)data;
893 int nr_pages = global_page_state(NR_FILE_DIRTY) +
894 global_page_state(NR_UNSTABLE_NFS);
895
896 /*
897 * We want to write everything out, not just down to the dirty
898 * threshold
899 */
900 if (bdi_has_dirty_io(&q->backing_dev_info))
901 bdi_start_writeback(&q->backing_dev_info, nr_pages);
902}
903
904/*
905 * We've spun up the disk and we're in laptop mode: schedule writeback
906 * of all dirty data a few seconds from now. If the flush is already scheduled
907 * then push it back - the user is still using the disk.
908 */
909void laptop_io_completion(struct backing_dev_info *info)
910{
911 mod_timer(&info->laptop_mode_wb_timer, jiffies + laptop_mode);
912}
913
914/*
915 * We're in laptop mode and we've just synced. The sync's writes will have
916 * caused another writeback to be scheduled by laptop_io_completion.
917 * Nothing needs to be written back anymore, so we unschedule the writeback.
918 */
919void laptop_sync_completion(void)
920{
921 struct backing_dev_info *bdi;
922
923 rcu_read_lock();
924
925 list_for_each_entry_rcu(bdi, &bdi_list, bdi_list)
926 del_timer(&bdi->laptop_mode_wb_timer);
927
928 rcu_read_unlock();
929}
930#endif
931
932/*
933 * If ratelimit_pages is too high then we can get into dirty-data overload
934 * if a large number of processes all perform writes at the same time.
935 * If it is too low then SMP machines will call the (expensive)
936 * get_writeback_state too often.
937 *
938 * Here we set ratelimit_pages to a level which ensures that when all CPUs are
939 * dirtying in parallel, we cannot go more than 3% (1/32) over the dirty memory
940 * thresholds before writeback cuts in.
941 *
942 * But the limit should not be set too high. Because it also controls the
943 * amount of memory which the balance_dirty_pages() caller has to write back.
944 * If this is too large then the caller will block on the IO queue all the
945 * time. So limit it to four megabytes - the balance_dirty_pages() caller
946 * will write six megabyte chunks, max.
947 */
948
949void writeback_set_ratelimit(void)
950{
951 ratelimit_pages = vm_total_pages / (num_online_cpus() * 32);
952 if (ratelimit_pages < 16)
953 ratelimit_pages = 16;
954 if (ratelimit_pages * PAGE_CACHE_SIZE > 4096 * 1024)
955 ratelimit_pages = (4096 * 1024) / PAGE_CACHE_SIZE;
956}
957
958static int __cpuinit
959ratelimit_handler(struct notifier_block *self, unsigned long u, void *v)
960{
961 writeback_set_ratelimit();
962 return NOTIFY_DONE;
963}
964
965static struct notifier_block __cpuinitdata ratelimit_nb = {
966 .notifier_call = ratelimit_handler,
967 .next = NULL,
968};
969
970/*
971 * Called early on to tune the page writeback dirty limits.
972 *
973 * We used to scale dirty pages according to how total memory
974 * related to pages that could be allocated for buffers (by
975 * comparing nr_free_buffer_pages() to vm_total_pages.
976 *
977 * However, that was when we used "dirty_ratio" to scale with
978 * all memory, and we don't do that any more. "dirty_ratio"
979 * is now applied to total non-HIGHPAGE memory (by subtracting
980 * totalhigh_pages from vm_total_pages), and as such we can't
981 * get into the old insane situation any more where we had
982 * large amounts of dirty pages compared to a small amount of
983 * non-HIGHMEM memory.
984 *
985 * But we might still want to scale the dirty_ratio by how
986 * much memory the box has..
987 */
988void __init page_writeback_init(void)
989{
990 int shift;
991
992 writeback_set_ratelimit();
993 register_cpu_notifier(&ratelimit_nb);
994
995 shift = calc_period_shift();
996 prop_descriptor_init(&vm_completions, shift);
997 prop_descriptor_init(&vm_dirties, shift);
998}
999
1000/**
1001 * tag_pages_for_writeback - tag pages to be written by write_cache_pages
1002 * @mapping: address space structure to write
1003 * @start: starting page index
1004 * @end: ending page index (inclusive)
1005 *
1006 * This function scans the page range from @start to @end (inclusive) and tags
1007 * all pages that have DIRTY tag set with a special TOWRITE tag. The idea is
1008 * that write_cache_pages (or whoever calls this function) will then use
1009 * TOWRITE tag to identify pages eligible for writeback. This mechanism is
1010 * used to avoid livelocking of writeback by a process steadily creating new
1011 * dirty pages in the file (thus it is important for this function to be quick
1012 * so that it can tag pages faster than a dirtying process can create them).
1013 */
1014/*
1015 * We tag pages in batches of WRITEBACK_TAG_BATCH to reduce tree_lock latency.
1016 */
1017void tag_pages_for_writeback(struct address_space *mapping,
1018 pgoff_t start, pgoff_t end)
1019{
1020#define WRITEBACK_TAG_BATCH 4096
1021 unsigned long tagged;
1022
1023 do {
1024 spin_lock_irq(&mapping->tree_lock);
1025 tagged = radix_tree_range_tag_if_tagged(&mapping->page_tree,
1026 &start, end, WRITEBACK_TAG_BATCH,
1027 PAGECACHE_TAG_DIRTY, PAGECACHE_TAG_TOWRITE);
1028 spin_unlock_irq(&mapping->tree_lock);
1029 WARN_ON_ONCE(tagged > WRITEBACK_TAG_BATCH);
1030 cond_resched();
1031 /* We check 'start' to handle wrapping when end == ~0UL */
1032 } while (tagged >= WRITEBACK_TAG_BATCH && start);
1033}
1034EXPORT_SYMBOL(tag_pages_for_writeback);
1035
1036/**
1037 * write_cache_pages - walk the list of dirty pages of the given address space and write all of them.
1038 * @mapping: address space structure to write
1039 * @wbc: subtract the number of written pages from *@wbc->nr_to_write
1040 * @writepage: function called for each page
1041 * @data: data passed to writepage function
1042 *
1043 * If a page is already under I/O, write_cache_pages() skips it, even
1044 * if it's dirty. This is desirable behaviour for memory-cleaning writeback,
1045 * but it is INCORRECT for data-integrity system calls such as fsync(). fsync()
1046 * and msync() need to guarantee that all the data which was dirty at the time
1047 * the call was made get new I/O started against them. If wbc->sync_mode is
1048 * WB_SYNC_ALL then we were called for data integrity and we must wait for
1049 * existing IO to complete.
1050 *
1051 * To avoid livelocks (when other process dirties new pages), we first tag
1052 * pages which should be written back with TOWRITE tag and only then start
1053 * writing them. For data-integrity sync we have to be careful so that we do
1054 * not miss some pages (e.g., because some other process has cleared TOWRITE
1055 * tag we set). The rule we follow is that TOWRITE tag can be cleared only
1056 * by the process clearing the DIRTY tag (and submitting the page for IO).
1057 */
1058int write_cache_pages(struct address_space *mapping,
1059 struct writeback_control *wbc, writepage_t writepage,
1060 void *data)
1061{
1062 int ret = 0;
1063 int done = 0;
1064 struct pagevec pvec;
1065 int nr_pages;
1066 pgoff_t uninitialized_var(writeback_index);
1067 pgoff_t index;
1068 pgoff_t end; /* Inclusive */
1069 pgoff_t done_index;
1070 int cycled;
1071 int range_whole = 0;
1072 int tag;
1073
1074 pagevec_init(&pvec, 0);
1075 if (wbc->range_cyclic) {
1076 writeback_index = mapping->writeback_index; /* prev offset */
1077 index = writeback_index;
1078 if (index == 0)
1079 cycled = 1;
1080 else
1081 cycled = 0;
1082 end = -1;
1083 } else {
1084 index = wbc->range_start >> PAGE_CACHE_SHIFT;
1085 end = wbc->range_end >> PAGE_CACHE_SHIFT;
1086 if (wbc->range_start == 0 && wbc->range_end == LLONG_MAX)
1087 range_whole = 1;
1088 cycled = 1; /* ignore range_cyclic tests */
1089 }
1090 if (wbc->sync_mode == WB_SYNC_ALL || wbc->tagged_writepages)
1091 tag = PAGECACHE_TAG_TOWRITE;
1092 else
1093 tag = PAGECACHE_TAG_DIRTY;
1094retry:
1095 if (wbc->sync_mode == WB_SYNC_ALL || wbc->tagged_writepages)
1096 tag_pages_for_writeback(mapping, index, end);
1097 done_index = index;
1098 while (!done && (index <= end)) {
1099 int i;
1100
1101 nr_pages = pagevec_lookup_tag(&pvec, mapping, &index, tag,
1102 min(end - index, (pgoff_t)PAGEVEC_SIZE-1) + 1);
1103 if (nr_pages == 0)
1104 break;
1105
1106 for (i = 0; i < nr_pages; i++) {
1107 struct page *page = pvec.pages[i];
1108
1109 /*
1110 * At this point, the page may be truncated or
1111 * invalidated (changing page->mapping to NULL), or
1112 * even swizzled back from swapper_space to tmpfs file
1113 * mapping. However, page->index will not change
1114 * because we have a reference on the page.
1115 */
1116 if (page->index > end) {
1117 /*
1118 * can't be range_cyclic (1st pass) because
1119 * end == -1 in that case.
1120 */
1121 done = 1;
1122 break;
1123 }
1124
1125 done_index = page->index;
1126
1127 lock_page(page);
1128
1129 /*
1130 * Page truncated or invalidated. We can freely skip it
1131 * then, even for data integrity operations: the page
1132 * has disappeared concurrently, so there could be no
1133 * real expectation of this data interity operation
1134 * even if there is now a new, dirty page at the same
1135 * pagecache address.
1136 */
1137 if (unlikely(page->mapping != mapping)) {
1138continue_unlock:
1139 unlock_page(page);
1140 continue;
1141 }
1142
1143 if (!PageDirty(page)) {
1144 /* someone wrote it for us */
1145 goto continue_unlock;
1146 }
1147
1148 if (PageWriteback(page)) {
1149 if (wbc->sync_mode != WB_SYNC_NONE)
1150 wait_on_page_writeback(page);
1151 else
1152 goto continue_unlock;
1153 }
1154
1155 BUG_ON(PageWriteback(page));
1156 if (!clear_page_dirty_for_io(page))
1157 goto continue_unlock;
1158
1159 trace_wbc_writepage(wbc, mapping->backing_dev_info);
1160 ret = (*writepage)(page, wbc, data);
1161 if (unlikely(ret)) {
1162 if (ret == AOP_WRITEPAGE_ACTIVATE) {
1163 unlock_page(page);
1164 ret = 0;
1165 } else {
1166 /*
1167 * done_index is set past this page,
1168 * so media errors will not choke
1169 * background writeout for the entire
1170 * file. This has consequences for
1171 * range_cyclic semantics (ie. it may
1172 * not be suitable for data integrity
1173 * writeout).
1174 */
1175 done_index = page->index + 1;
1176 done = 1;
1177 break;
1178 }
1179 }
1180
1181 /*
1182 * We stop writing back only if we are not doing
1183 * integrity sync. In case of integrity sync we have to
1184 * keep going until we have written all the pages
1185 * we tagged for writeback prior to entering this loop.
1186 */
1187 if (--wbc->nr_to_write <= 0 &&
1188 wbc->sync_mode == WB_SYNC_NONE) {
1189 done = 1;
1190 break;
1191 }
1192 }
1193 pagevec_release(&pvec);
1194 cond_resched();
1195 }
1196 if (!cycled && !done) {
1197 /*
1198 * range_cyclic:
1199 * We hit the last page and there is more work to be done: wrap
1200 * back to the start of the file
1201 */
1202 cycled = 1;
1203 index = 0;
1204 end = writeback_index - 1;
1205 goto retry;
1206 }
1207 if (wbc->range_cyclic || (range_whole && wbc->nr_to_write > 0))
1208 mapping->writeback_index = done_index;
1209
1210 return ret;
1211}
1212EXPORT_SYMBOL(write_cache_pages);
1213
1214/*
1215 * Function used by generic_writepages to call the real writepage
1216 * function and set the mapping flags on error
1217 */
1218static int __writepage(struct page *page, struct writeback_control *wbc,
1219 void *data)
1220{
1221 struct address_space *mapping = data;
1222 int ret = mapping->a_ops->writepage(page, wbc);
1223 mapping_set_error(mapping, ret);
1224 return ret;
1225}
1226
1227/**
1228 * generic_writepages - walk the list of dirty pages of the given address space and writepage() all of them.
1229 * @mapping: address space structure to write
1230 * @wbc: subtract the number of written pages from *@wbc->nr_to_write
1231 *
1232 * This is a library function, which implements the writepages()
1233 * address_space_operation.
1234 */
1235int generic_writepages(struct address_space *mapping,
1236 struct writeback_control *wbc)
1237{
1238 struct blk_plug plug;
1239 int ret;
1240
1241 /* deal with chardevs and other special file */
1242 if (!mapping->a_ops->writepage)
1243 return 0;
1244
1245 blk_start_plug(&plug);
1246 ret = write_cache_pages(mapping, wbc, __writepage, mapping);
1247 blk_finish_plug(&plug);
1248 return ret;
1249}
1250
1251EXPORT_SYMBOL(generic_writepages);
1252
1253int do_writepages(struct address_space *mapping, struct writeback_control *wbc)
1254{
1255 int ret;
1256
1257 if (wbc->nr_to_write <= 0)
1258 return 0;
1259 if (mapping->a_ops->writepages)
1260 ret = mapping->a_ops->writepages(mapping, wbc);
1261 else
1262 ret = generic_writepages(mapping, wbc);
1263 return ret;
1264}
1265
1266/**
1267 * write_one_page - write out a single page and optionally wait on I/O
1268 * @page: the page to write
1269 * @wait: if true, wait on writeout
1270 *
1271 * The page must be locked by the caller and will be unlocked upon return.
1272 *
1273 * write_one_page() returns a negative error code if I/O failed.
1274 */
1275int write_one_page(struct page *page, int wait)
1276{
1277 struct address_space *mapping = page->mapping;
1278 int ret = 0;
1279 struct writeback_control wbc = {
1280 .sync_mode = WB_SYNC_ALL,
1281 .nr_to_write = 1,
1282 };
1283
1284 BUG_ON(!PageLocked(page));
1285
1286 if (wait)
1287 wait_on_page_writeback(page);
1288
1289 if (clear_page_dirty_for_io(page)) {
1290 page_cache_get(page);
1291 ret = mapping->a_ops->writepage(page, &wbc);
1292 if (ret == 0 && wait) {
1293 wait_on_page_writeback(page);
1294 if (PageError(page))
1295 ret = -EIO;
1296 }
1297 page_cache_release(page);
1298 } else {
1299 unlock_page(page);
1300 }
1301 return ret;
1302}
1303EXPORT_SYMBOL(write_one_page);
1304
1305/*
1306 * For address_spaces which do not use buffers nor write back.
1307 */
1308int __set_page_dirty_no_writeback(struct page *page)
1309{
1310 if (!PageDirty(page))
1311 return !TestSetPageDirty(page);
1312 return 0;
1313}
1314
1315/*
1316 * Helper function for set_page_dirty family.
1317 * NOTE: This relies on being atomic wrt interrupts.
1318 */
1319void account_page_dirtied(struct page *page, struct address_space *mapping)
1320{
1321 if (mapping_cap_account_dirty(mapping)) {
1322 __inc_zone_page_state(page, NR_FILE_DIRTY);
1323 __inc_zone_page_state(page, NR_DIRTIED);
1324 __inc_bdi_stat(mapping->backing_dev_info, BDI_RECLAIMABLE);
1325 task_dirty_inc(current);
1326 task_io_account_write(PAGE_CACHE_SIZE);
1327 }
1328}
1329EXPORT_SYMBOL(account_page_dirtied);
1330
1331/*
1332 * Helper function for set_page_writeback family.
1333 * NOTE: Unlike account_page_dirtied this does not rely on being atomic
1334 * wrt interrupts.
1335 */
1336void account_page_writeback(struct page *page)
1337{
1338 inc_zone_page_state(page, NR_WRITEBACK);
1339}
1340EXPORT_SYMBOL(account_page_writeback);
1341
1342/*
1343 * For address_spaces which do not use buffers. Just tag the page as dirty in
1344 * its radix tree.
1345 *
1346 * This is also used when a single buffer is being dirtied: we want to set the
1347 * page dirty in that case, but not all the buffers. This is a "bottom-up"
1348 * dirtying, whereas __set_page_dirty_buffers() is a "top-down" dirtying.
1349 *
1350 * Most callers have locked the page, which pins the address_space in memory.
1351 * But zap_pte_range() does not lock the page, however in that case the
1352 * mapping is pinned by the vma's ->vm_file reference.
1353 *
1354 * We take care to handle the case where the page was truncated from the
1355 * mapping by re-checking page_mapping() inside tree_lock.
1356 */
1357int __set_page_dirty_nobuffers(struct page *page)
1358{
1359 if (!TestSetPageDirty(page)) {
1360 struct address_space *mapping = page_mapping(page);
1361 struct address_space *mapping2;
1362
1363 if (!mapping)
1364 return 1;
1365
1366 spin_lock_irq(&mapping->tree_lock);
1367 mapping2 = page_mapping(page);
1368 if (mapping2) { /* Race with truncate? */
1369 BUG_ON(mapping2 != mapping);
1370 WARN_ON_ONCE(!PagePrivate(page) && !PageUptodate(page));
1371 account_page_dirtied(page, mapping);
1372 radix_tree_tag_set(&mapping->page_tree,
1373 page_index(page), PAGECACHE_TAG_DIRTY);
1374 }
1375 spin_unlock_irq(&mapping->tree_lock);
1376 if (mapping->host) {
1377 /* !PageAnon && !swapper_space */
1378 __mark_inode_dirty(mapping->host, I_DIRTY_PAGES);
1379 }
1380 return 1;
1381 }
1382 return 0;
1383}
1384EXPORT_SYMBOL(__set_page_dirty_nobuffers);
1385
1386/*
1387 * When a writepage implementation decides that it doesn't want to write this
1388 * page for some reason, it should redirty the locked page via
1389 * redirty_page_for_writepage() and it should then unlock the page and return 0
1390 */
1391int redirty_page_for_writepage(struct writeback_control *wbc, struct page *page)
1392{
1393 wbc->pages_skipped++;
1394 return __set_page_dirty_nobuffers(page);
1395}
1396EXPORT_SYMBOL(redirty_page_for_writepage);
1397
1398/*
1399 * Dirty a page.
1400 *
1401 * For pages with a mapping this should be done under the page lock
1402 * for the benefit of asynchronous memory errors who prefer a consistent
1403 * dirty state. This rule can be broken in some special cases,
1404 * but should be better not to.
1405 *
1406 * If the mapping doesn't provide a set_page_dirty a_op, then
1407 * just fall through and assume that it wants buffer_heads.
1408 */
1409int set_page_dirty(struct page *page)
1410{
1411 struct address_space *mapping = page_mapping(page);
1412
1413 if (likely(mapping)) {
1414 int (*spd)(struct page *) = mapping->a_ops->set_page_dirty;
1415 /*
1416 * readahead/lru_deactivate_page could remain
1417 * PG_readahead/PG_reclaim due to race with end_page_writeback
1418 * About readahead, if the page is written, the flags would be
1419 * reset. So no problem.
1420 * About lru_deactivate_page, if the page is redirty, the flag
1421 * will be reset. So no problem. but if the page is used by readahead
1422 * it will confuse readahead and make it restart the size rampup
1423 * process. But it's a trivial problem.
1424 */
1425 ClearPageReclaim(page);
1426#ifdef CONFIG_BLOCK
1427 if (!spd)
1428 spd = __set_page_dirty_buffers;
1429#endif
1430 return (*spd)(page);
1431 }
1432 if (!PageDirty(page)) {
1433 if (!TestSetPageDirty(page))
1434 return 1;
1435 }
1436 return 0;
1437}
1438EXPORT_SYMBOL(set_page_dirty);
1439
1440/*
1441 * set_page_dirty() is racy if the caller has no reference against
1442 * page->mapping->host, and if the page is unlocked. This is because another
1443 * CPU could truncate the page off the mapping and then free the mapping.
1444 *
1445 * Usually, the page _is_ locked, or the caller is a user-space process which
1446 * holds a reference on the inode by having an open file.
1447 *
1448 * In other cases, the page should be locked before running set_page_dirty().
1449 */
1450int set_page_dirty_lock(struct page *page)
1451{
1452 int ret;
1453
1454 lock_page(page);
1455 ret = set_page_dirty(page);
1456 unlock_page(page);
1457 return ret;
1458}
1459EXPORT_SYMBOL(set_page_dirty_lock);
1460
1461/*
1462 * Clear a page's dirty flag, while caring for dirty memory accounting.
1463 * Returns true if the page was previously dirty.
1464 *
1465 * This is for preparing to put the page under writeout. We leave the page
1466 * tagged as dirty in the radix tree so that a concurrent write-for-sync
1467 * can discover it via a PAGECACHE_TAG_DIRTY walk. The ->writepage
1468 * implementation will run either set_page_writeback() or set_page_dirty(),
1469 * at which stage we bring the page's dirty flag and radix-tree dirty tag
1470 * back into sync.
1471 *
1472 * This incoherency between the page's dirty flag and radix-tree tag is
1473 * unfortunate, but it only exists while the page is locked.
1474 */
1475int clear_page_dirty_for_io(struct page *page)
1476{
1477 struct address_space *mapping = page_mapping(page);
1478
1479 BUG_ON(!PageLocked(page));
1480
1481 if (mapping && mapping_cap_account_dirty(mapping)) {
1482 /*
1483 * Yes, Virginia, this is indeed insane.
1484 *
1485 * We use this sequence to make sure that
1486 * (a) we account for dirty stats properly
1487 * (b) we tell the low-level filesystem to
1488 * mark the whole page dirty if it was
1489 * dirty in a pagetable. Only to then
1490 * (c) clean the page again and return 1 to
1491 * cause the writeback.
1492 *
1493 * This way we avoid all nasty races with the
1494 * dirty bit in multiple places and clearing
1495 * them concurrently from different threads.
1496 *
1497 * Note! Normally the "set_page_dirty(page)"
1498 * has no effect on the actual dirty bit - since
1499 * that will already usually be set. But we
1500 * need the side effects, and it can help us
1501 * avoid races.
1502 *
1503 * We basically use the page "master dirty bit"
1504 * as a serialization point for all the different
1505 * threads doing their things.
1506 */
1507 if (page_mkclean(page))
1508 set_page_dirty(page);
1509 /*
1510 * We carefully synchronise fault handlers against
1511 * installing a dirty pte and marking the page dirty
1512 * at this point. We do this by having them hold the
1513 * page lock at some point after installing their
1514 * pte, but before marking the page dirty.
1515 * Pages are always locked coming in here, so we get
1516 * the desired exclusion. See mm/memory.c:do_wp_page()
1517 * for more comments.
1518 */
1519 if (TestClearPageDirty(page)) {
1520 dec_zone_page_state(page, NR_FILE_DIRTY);
1521 dec_bdi_stat(mapping->backing_dev_info,
1522 BDI_RECLAIMABLE);
1523 return 1;
1524 }
1525 return 0;
1526 }
1527 return TestClearPageDirty(page);
1528}
1529EXPORT_SYMBOL(clear_page_dirty_for_io);
1530
1531int test_clear_page_writeback(struct page *page)
1532{
1533 struct address_space *mapping = page_mapping(page);
1534 int ret;
1535
1536 if (mapping) {
1537 struct backing_dev_info *bdi = mapping->backing_dev_info;
1538 unsigned long flags;
1539
1540 spin_lock_irqsave(&mapping->tree_lock, flags);
1541 ret = TestClearPageWriteback(page);
1542 if (ret) {
1543 radix_tree_tag_clear(&mapping->page_tree,
1544 page_index(page),
1545 PAGECACHE_TAG_WRITEBACK);
1546 if (bdi_cap_account_writeback(bdi)) {
1547 __dec_bdi_stat(bdi, BDI_WRITEBACK);
1548 __bdi_writeout_inc(bdi);
1549 }
1550 }
1551 spin_unlock_irqrestore(&mapping->tree_lock, flags);
1552 } else {
1553 ret = TestClearPageWriteback(page);
1554 }
1555 if (ret) {
1556 dec_zone_page_state(page, NR_WRITEBACK);
1557 inc_zone_page_state(page, NR_WRITTEN);
1558 }
1559 return ret;
1560}
1561
1562int test_set_page_writeback(struct page *page)
1563{
1564 struct address_space *mapping = page_mapping(page);
1565 int ret;
1566
1567 if (mapping) {
1568 struct backing_dev_info *bdi = mapping->backing_dev_info;
1569 unsigned long flags;
1570
1571 spin_lock_irqsave(&mapping->tree_lock, flags);
1572 ret = TestSetPageWriteback(page);
1573 if (!ret) {
1574 radix_tree_tag_set(&mapping->page_tree,
1575 page_index(page),
1576 PAGECACHE_TAG_WRITEBACK);
1577 if (bdi_cap_account_writeback(bdi))
1578 __inc_bdi_stat(bdi, BDI_WRITEBACK);
1579 }
1580 if (!PageDirty(page))
1581 radix_tree_tag_clear(&mapping->page_tree,
1582 page_index(page),
1583 PAGECACHE_TAG_DIRTY);
1584 radix_tree_tag_clear(&mapping->page_tree,
1585 page_index(page),
1586 PAGECACHE_TAG_TOWRITE);
1587 spin_unlock_irqrestore(&mapping->tree_lock, flags);
1588 } else {
1589 ret = TestSetPageWriteback(page);
1590 }
1591 if (!ret)
1592 account_page_writeback(page);
1593 return ret;
1594
1595}
1596EXPORT_SYMBOL(test_set_page_writeback);
1597
1598/*
1599 * Return true if any of the pages in the mapping are marked with the
1600 * passed tag.
1601 */
1602int mapping_tagged(struct address_space *mapping, int tag)
1603{
1604 return radix_tree_tagged(&mapping->page_tree, tag);
1605}
1606EXPORT_SYMBOL(mapping_tagged);
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);