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1/*
2 * mm/page-writeback.c
3 *
4 * Copyright (C) 2002, Linus Torvalds.
5 * Copyright (C) 2007 Red Hat, Inc., Peter Zijlstra <pzijlstr@redhat.com>
6 *
7 * Contains functions related to writing back dirty pages at the
8 * address_space level.
9 *
10 * 10Apr2002 Andrew Morton
11 * Initial version
12 */
13
14#include <linux/kernel.h>
15#include <linux/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 <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 * Try to keep balance_dirty_pages() call intervals higher than this many pages
46 * by raising pause time to max_pause when falls below it.
47 */
48#define DIRTY_POLL_THRESH (128 >> (PAGE_SHIFT - 10))
49
50/*
51 * Estimate write bandwidth at 200ms intervals.
52 */
53#define BANDWIDTH_INTERVAL max(HZ/5, 1)
54
55#define RATELIMIT_CALC_SHIFT 10
56
57/*
58 * After a CPU has dirtied this many pages, balance_dirty_pages_ratelimited
59 * will look to see if it needs to force writeback or throttling.
60 */
61static long ratelimit_pages = 32;
62
63/* The following parameters are exported via /proc/sys/vm */
64
65/*
66 * Start background writeback (via writeback threads) at this percentage
67 */
68int dirty_background_ratio = 10;
69
70/*
71 * dirty_background_bytes starts at 0 (disabled) so that it is a function of
72 * dirty_background_ratio * the amount of dirtyable memory
73 */
74unsigned long dirty_background_bytes;
75
76/*
77 * free highmem will not be subtracted from the total free memory
78 * for calculating free ratios if vm_highmem_is_dirtyable is true
79 */
80int vm_highmem_is_dirtyable;
81
82/*
83 * The generator of dirty data starts writeback at this percentage
84 */
85int vm_dirty_ratio = 20;
86
87/*
88 * vm_dirty_bytes starts at 0 (disabled) so that it is a function of
89 * vm_dirty_ratio * the amount of dirtyable memory
90 */
91unsigned long vm_dirty_bytes;
92
93/*
94 * The interval between `kupdate'-style writebacks
95 */
96unsigned int dirty_writeback_interval = 5 * 100; /* centiseconds */
97
98EXPORT_SYMBOL_GPL(dirty_writeback_interval);
99
100/*
101 * The longest time for which data is allowed to remain dirty
102 */
103unsigned int dirty_expire_interval = 30 * 100; /* centiseconds */
104
105/*
106 * Flag that makes the machine dump writes/reads and block dirtyings.
107 */
108int block_dump;
109
110/*
111 * Flag that puts the machine in "laptop mode". Doubles as a timeout in jiffies:
112 * a full sync is triggered after this time elapses without any disk activity.
113 */
114int laptop_mode;
115
116EXPORT_SYMBOL(laptop_mode);
117
118/* End of sysctl-exported parameters */
119
120unsigned long global_dirty_limit;
121
122/*
123 * Scale the writeback cache size proportional to the relative writeout speeds.
124 *
125 * We do this by keeping a floating proportion between BDIs, based on page
126 * writeback completions [end_page_writeback()]. Those devices that write out
127 * pages fastest will get the larger share, while the slower will get a smaller
128 * share.
129 *
130 * We use page writeout completions because we are interested in getting rid of
131 * dirty pages. Having them written out is the primary goal.
132 *
133 * We introduce a concept of time, a period over which we measure these events,
134 * because demand can/will vary over time. The length of this period itself is
135 * measured in page writeback completions.
136 *
137 */
138static struct prop_descriptor vm_completions;
139
140/*
141 * Work out the current dirty-memory clamping and background writeout
142 * thresholds.
143 *
144 * The main aim here is to lower them aggressively if there is a lot of mapped
145 * memory around. To avoid stressing page reclaim with lots of unreclaimable
146 * pages. It is better to clamp down on writers than to start swapping, and
147 * performing lots of scanning.
148 *
149 * We only allow 1/2 of the currently-unmapped memory to be dirtied.
150 *
151 * We don't permit the clamping level to fall below 5% - that is getting rather
152 * excessive.
153 *
154 * We make sure that the background writeout level is below the adjusted
155 * clamping level.
156 */
157
158/*
159 * In a memory zone, there is a certain amount of pages we consider
160 * available for the page cache, which is essentially the number of
161 * free and reclaimable pages, minus some zone reserves to protect
162 * lowmem and the ability to uphold the zone's watermarks without
163 * requiring writeback.
164 *
165 * This number of dirtyable pages is the base value of which the
166 * user-configurable dirty ratio is the effictive number of pages that
167 * are allowed to be actually dirtied. Per individual zone, or
168 * globally by using the sum of dirtyable pages over all zones.
169 *
170 * Because the user is allowed to specify the dirty limit globally as
171 * absolute number of bytes, calculating the per-zone dirty limit can
172 * require translating the configured limit into a percentage of
173 * global dirtyable memory first.
174 */
175
176static unsigned long highmem_dirtyable_memory(unsigned long total)
177{
178#ifdef CONFIG_HIGHMEM
179 int node;
180 unsigned long x = 0;
181
182 for_each_node_state(node, N_HIGH_MEMORY) {
183 struct zone *z =
184 &NODE_DATA(node)->node_zones[ZONE_HIGHMEM];
185
186 x += zone_page_state(z, NR_FREE_PAGES) +
187 zone_reclaimable_pages(z) - z->dirty_balance_reserve;
188 }
189 /*
190 * Make sure that the number of highmem pages is never larger
191 * than the number of the total dirtyable memory. This can only
192 * occur in very strange VM situations but we want to make sure
193 * that this does not occur.
194 */
195 return min(x, total);
196#else
197 return 0;
198#endif
199}
200
201/**
202 * global_dirtyable_memory - number of globally dirtyable pages
203 *
204 * Returns the global number of pages potentially available for dirty
205 * page cache. This is the base value for the global dirty limits.
206 */
207static unsigned long global_dirtyable_memory(void)
208{
209 unsigned long x;
210
211 x = global_page_state(NR_FREE_PAGES) + global_reclaimable_pages() -
212 dirty_balance_reserve;
213
214 if (!vm_highmem_is_dirtyable)
215 x -= highmem_dirtyable_memory(x);
216
217 return x + 1; /* Ensure that we never return 0 */
218}
219
220/*
221 * global_dirty_limits - background-writeback and dirty-throttling thresholds
222 *
223 * Calculate the dirty thresholds based on sysctl parameters
224 * - vm.dirty_background_ratio or vm.dirty_background_bytes
225 * - vm.dirty_ratio or vm.dirty_bytes
226 * The dirty limits will be lifted by 1/4 for PF_LESS_THROTTLE (ie. nfsd) and
227 * real-time tasks.
228 */
229void global_dirty_limits(unsigned long *pbackground, unsigned long *pdirty)
230{
231 unsigned long background;
232 unsigned long dirty;
233 unsigned long uninitialized_var(available_memory);
234 struct task_struct *tsk;
235
236 if (!vm_dirty_bytes || !dirty_background_bytes)
237 available_memory = global_dirtyable_memory();
238
239 if (vm_dirty_bytes)
240 dirty = DIV_ROUND_UP(vm_dirty_bytes, PAGE_SIZE);
241 else
242 dirty = (vm_dirty_ratio * available_memory) / 100;
243
244 if (dirty_background_bytes)
245 background = DIV_ROUND_UP(dirty_background_bytes, PAGE_SIZE);
246 else
247 background = (dirty_background_ratio * available_memory) / 100;
248
249 if (background >= dirty)
250 background = dirty / 2;
251 tsk = current;
252 if (tsk->flags & PF_LESS_THROTTLE || rt_task(tsk)) {
253 background += background / 4;
254 dirty += dirty / 4;
255 }
256 *pbackground = background;
257 *pdirty = dirty;
258 trace_global_dirty_state(background, dirty);
259}
260
261/**
262 * zone_dirtyable_memory - number of dirtyable pages in a zone
263 * @zone: the zone
264 *
265 * Returns the zone's number of pages potentially available for dirty
266 * page cache. This is the base value for the per-zone dirty limits.
267 */
268static unsigned long zone_dirtyable_memory(struct zone *zone)
269{
270 /*
271 * The effective global number of dirtyable pages may exclude
272 * highmem as a big-picture measure to keep the ratio between
273 * dirty memory and lowmem reasonable.
274 *
275 * But this function is purely about the individual zone and a
276 * highmem zone can hold its share of dirty pages, so we don't
277 * care about vm_highmem_is_dirtyable here.
278 */
279 return zone_page_state(zone, NR_FREE_PAGES) +
280 zone_reclaimable_pages(zone) -
281 zone->dirty_balance_reserve;
282}
283
284/**
285 * zone_dirty_limit - maximum number of dirty pages allowed in a zone
286 * @zone: the zone
287 *
288 * Returns the maximum number of dirty pages allowed in a zone, based
289 * on the zone's dirtyable memory.
290 */
291static unsigned long zone_dirty_limit(struct zone *zone)
292{
293 unsigned long zone_memory = zone_dirtyable_memory(zone);
294 struct task_struct *tsk = current;
295 unsigned long dirty;
296
297 if (vm_dirty_bytes)
298 dirty = DIV_ROUND_UP(vm_dirty_bytes, PAGE_SIZE) *
299 zone_memory / global_dirtyable_memory();
300 else
301 dirty = vm_dirty_ratio * zone_memory / 100;
302
303 if (tsk->flags & PF_LESS_THROTTLE || rt_task(tsk))
304 dirty += dirty / 4;
305
306 return dirty;
307}
308
309/**
310 * zone_dirty_ok - tells whether a zone is within its dirty limits
311 * @zone: the zone to check
312 *
313 * Returns %true when the dirty pages in @zone are within the zone's
314 * dirty limit, %false if the limit is exceeded.
315 */
316bool zone_dirty_ok(struct zone *zone)
317{
318 unsigned long limit = zone_dirty_limit(zone);
319
320 return zone_page_state(zone, NR_FILE_DIRTY) +
321 zone_page_state(zone, NR_UNSTABLE_NFS) +
322 zone_page_state(zone, NR_WRITEBACK) <= limit;
323}
324
325/*
326 * couple the period to the dirty_ratio:
327 *
328 * period/2 ~ roundup_pow_of_two(dirty limit)
329 */
330static int calc_period_shift(void)
331{
332 unsigned long dirty_total;
333
334 if (vm_dirty_bytes)
335 dirty_total = vm_dirty_bytes / PAGE_SIZE;
336 else
337 dirty_total = (vm_dirty_ratio * global_dirtyable_memory()) /
338 100;
339 return 2 + ilog2(dirty_total - 1);
340}
341
342/*
343 * update the period when the dirty threshold changes.
344 */
345static void update_completion_period(void)
346{
347 int shift = calc_period_shift();
348 prop_change_shift(&vm_completions, shift);
349
350 writeback_set_ratelimit();
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 update_completion_period();
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 update_completion_period();
402 vm_dirty_ratio = 0;
403 }
404 return ret;
405}
406
407/*
408 * Increment the BDI's writeout completion count and the global writeout
409 * completion count. Called from test_clear_page_writeback().
410 */
411static inline void __bdi_writeout_inc(struct backing_dev_info *bdi)
412{
413 __inc_bdi_stat(bdi, BDI_WRITTEN);
414 __prop_inc_percpu_max(&vm_completions, &bdi->completions,
415 bdi->max_prop_frac);
416}
417
418void bdi_writeout_inc(struct backing_dev_info *bdi)
419{
420 unsigned long flags;
421
422 local_irq_save(flags);
423 __bdi_writeout_inc(bdi);
424 local_irq_restore(flags);
425}
426EXPORT_SYMBOL_GPL(bdi_writeout_inc);
427
428/*
429 * Obtain an accurate fraction of the BDI's portion.
430 */
431static void bdi_writeout_fraction(struct backing_dev_info *bdi,
432 long *numerator, long *denominator)
433{
434 prop_fraction_percpu(&vm_completions, &bdi->completions,
435 numerator, denominator);
436}
437
438/*
439 * bdi_min_ratio keeps the sum of the minimum dirty shares of all
440 * registered backing devices, which, for obvious reasons, can not
441 * exceed 100%.
442 */
443static unsigned int bdi_min_ratio;
444
445int bdi_set_min_ratio(struct backing_dev_info *bdi, unsigned int min_ratio)
446{
447 int ret = 0;
448
449 spin_lock_bh(&bdi_lock);
450 if (min_ratio > bdi->max_ratio) {
451 ret = -EINVAL;
452 } else {
453 min_ratio -= bdi->min_ratio;
454 if (bdi_min_ratio + min_ratio < 100) {
455 bdi_min_ratio += min_ratio;
456 bdi->min_ratio += min_ratio;
457 } else {
458 ret = -EINVAL;
459 }
460 }
461 spin_unlock_bh(&bdi_lock);
462
463 return ret;
464}
465
466int bdi_set_max_ratio(struct backing_dev_info *bdi, unsigned max_ratio)
467{
468 int ret = 0;
469
470 if (max_ratio > 100)
471 return -EINVAL;
472
473 spin_lock_bh(&bdi_lock);
474 if (bdi->min_ratio > max_ratio) {
475 ret = -EINVAL;
476 } else {
477 bdi->max_ratio = max_ratio;
478 bdi->max_prop_frac = (PROP_FRAC_BASE * max_ratio) / 100;
479 }
480 spin_unlock_bh(&bdi_lock);
481
482 return ret;
483}
484EXPORT_SYMBOL(bdi_set_max_ratio);
485
486static unsigned long dirty_freerun_ceiling(unsigned long thresh,
487 unsigned long bg_thresh)
488{
489 return (thresh + bg_thresh) / 2;
490}
491
492static unsigned long hard_dirty_limit(unsigned long thresh)
493{
494 return max(thresh, global_dirty_limit);
495}
496
497/**
498 * bdi_dirty_limit - @bdi's share of dirty throttling threshold
499 * @bdi: the backing_dev_info to query
500 * @dirty: global dirty limit in pages
501 *
502 * Returns @bdi's dirty limit in pages. The term "dirty" in the context of
503 * dirty balancing includes all PG_dirty, PG_writeback and NFS unstable pages.
504 *
505 * Note that balance_dirty_pages() will only seriously take it as a hard limit
506 * when sleeping max_pause per page is not enough to keep the dirty pages under
507 * control. For example, when the device is completely stalled due to some error
508 * conditions, or when there are 1000 dd tasks writing to a slow 10MB/s USB key.
509 * In the other normal situations, it acts more gently by throttling the tasks
510 * more (rather than completely block them) when the bdi dirty pages go high.
511 *
512 * It allocates high/low dirty limits to fast/slow devices, in order to prevent
513 * - starving fast devices
514 * - piling up dirty pages (that will take long time to sync) on slow devices
515 *
516 * The bdi's share of dirty limit will be adapting to its throughput and
517 * bounded by the bdi->min_ratio and/or bdi->max_ratio parameters, if set.
518 */
519unsigned long bdi_dirty_limit(struct backing_dev_info *bdi, unsigned long dirty)
520{
521 u64 bdi_dirty;
522 long numerator, denominator;
523
524 /*
525 * Calculate this BDI's share of the dirty ratio.
526 */
527 bdi_writeout_fraction(bdi, &numerator, &denominator);
528
529 bdi_dirty = (dirty * (100 - bdi_min_ratio)) / 100;
530 bdi_dirty *= numerator;
531 do_div(bdi_dirty, denominator);
532
533 bdi_dirty += (dirty * bdi->min_ratio) / 100;
534 if (bdi_dirty > (dirty * bdi->max_ratio) / 100)
535 bdi_dirty = dirty * bdi->max_ratio / 100;
536
537 return bdi_dirty;
538}
539
540/*
541 * Dirty position control.
542 *
543 * (o) global/bdi setpoints
544 *
545 * We want the dirty pages be balanced around the global/bdi setpoints.
546 * When the number of dirty pages is higher/lower than the setpoint, the
547 * dirty position control ratio (and hence task dirty ratelimit) will be
548 * decreased/increased to bring the dirty pages back to the setpoint.
549 *
550 * pos_ratio = 1 << RATELIMIT_CALC_SHIFT
551 *
552 * if (dirty < setpoint) scale up pos_ratio
553 * if (dirty > setpoint) scale down pos_ratio
554 *
555 * if (bdi_dirty < bdi_setpoint) scale up pos_ratio
556 * if (bdi_dirty > bdi_setpoint) scale down pos_ratio
557 *
558 * task_ratelimit = dirty_ratelimit * pos_ratio >> RATELIMIT_CALC_SHIFT
559 *
560 * (o) global control line
561 *
562 * ^ pos_ratio
563 * |
564 * | |<===== global dirty control scope ======>|
565 * 2.0 .............*
566 * | .*
567 * | . *
568 * | . *
569 * | . *
570 * | . *
571 * | . *
572 * 1.0 ................................*
573 * | . . *
574 * | . . *
575 * | . . *
576 * | . . *
577 * | . . *
578 * 0 +------------.------------------.----------------------*------------->
579 * freerun^ setpoint^ limit^ dirty pages
580 *
581 * (o) bdi control line
582 *
583 * ^ pos_ratio
584 * |
585 * | *
586 * | *
587 * | *
588 * | *
589 * | * |<=========== span ============>|
590 * 1.0 .......................*
591 * | . *
592 * | . *
593 * | . *
594 * | . *
595 * | . *
596 * | . *
597 * | . *
598 * | . *
599 * | . *
600 * | . *
601 * | . *
602 * 1/4 ...............................................* * * * * * * * * * * *
603 * | . .
604 * | . .
605 * | . .
606 * 0 +----------------------.-------------------------------.------------->
607 * bdi_setpoint^ x_intercept^
608 *
609 * The bdi control line won't drop below pos_ratio=1/4, so that bdi_dirty can
610 * be smoothly throttled down to normal if it starts high in situations like
611 * - start writing to a slow SD card and a fast disk at the same time. The SD
612 * card's bdi_dirty may rush to many times higher than bdi_setpoint.
613 * - the bdi dirty thresh drops quickly due to change of JBOD workload
614 */
615static unsigned long bdi_position_ratio(struct backing_dev_info *bdi,
616 unsigned long thresh,
617 unsigned long bg_thresh,
618 unsigned long dirty,
619 unsigned long bdi_thresh,
620 unsigned long bdi_dirty)
621{
622 unsigned long write_bw = bdi->avg_write_bandwidth;
623 unsigned long freerun = dirty_freerun_ceiling(thresh, bg_thresh);
624 unsigned long limit = hard_dirty_limit(thresh);
625 unsigned long x_intercept;
626 unsigned long setpoint; /* dirty pages' target balance point */
627 unsigned long bdi_setpoint;
628 unsigned long span;
629 long long pos_ratio; /* for scaling up/down the rate limit */
630 long x;
631
632 if (unlikely(dirty >= limit))
633 return 0;
634
635 /*
636 * global setpoint
637 *
638 * setpoint - dirty 3
639 * f(dirty) := 1.0 + (----------------)
640 * limit - setpoint
641 *
642 * it's a 3rd order polynomial that subjects to
643 *
644 * (1) f(freerun) = 2.0 => rampup dirty_ratelimit reasonably fast
645 * (2) f(setpoint) = 1.0 => the balance point
646 * (3) f(limit) = 0 => the hard limit
647 * (4) df/dx <= 0 => negative feedback control
648 * (5) the closer to setpoint, the smaller |df/dx| (and the reverse)
649 * => fast response on large errors; small oscillation near setpoint
650 */
651 setpoint = (freerun + limit) / 2;
652 x = div_s64((setpoint - dirty) << RATELIMIT_CALC_SHIFT,
653 limit - setpoint + 1);
654 pos_ratio = x;
655 pos_ratio = pos_ratio * x >> RATELIMIT_CALC_SHIFT;
656 pos_ratio = pos_ratio * x >> RATELIMIT_CALC_SHIFT;
657 pos_ratio += 1 << RATELIMIT_CALC_SHIFT;
658
659 /*
660 * We have computed basic pos_ratio above based on global situation. If
661 * the bdi is over/under its share of dirty pages, we want to scale
662 * pos_ratio further down/up. That is done by the following mechanism.
663 */
664
665 /*
666 * bdi setpoint
667 *
668 * f(bdi_dirty) := 1.0 + k * (bdi_dirty - bdi_setpoint)
669 *
670 * x_intercept - bdi_dirty
671 * := --------------------------
672 * x_intercept - bdi_setpoint
673 *
674 * The main bdi control line is a linear function that subjects to
675 *
676 * (1) f(bdi_setpoint) = 1.0
677 * (2) k = - 1 / (8 * write_bw) (in single bdi case)
678 * or equally: x_intercept = bdi_setpoint + 8 * write_bw
679 *
680 * For single bdi case, the dirty pages are observed to fluctuate
681 * regularly within range
682 * [bdi_setpoint - write_bw/2, bdi_setpoint + write_bw/2]
683 * for various filesystems, where (2) can yield in a reasonable 12.5%
684 * fluctuation range for pos_ratio.
685 *
686 * For JBOD case, bdi_thresh (not bdi_dirty!) could fluctuate up to its
687 * own size, so move the slope over accordingly and choose a slope that
688 * yields 100% pos_ratio fluctuation on suddenly doubled bdi_thresh.
689 */
690 if (unlikely(bdi_thresh > thresh))
691 bdi_thresh = thresh;
692 /*
693 * It's very possible that bdi_thresh is close to 0 not because the
694 * device is slow, but that it has remained inactive for long time.
695 * Honour such devices a reasonable good (hopefully IO efficient)
696 * threshold, so that the occasional writes won't be blocked and active
697 * writes can rampup the threshold quickly.
698 */
699 bdi_thresh = max(bdi_thresh, (limit - dirty) / 8);
700 /*
701 * scale global setpoint to bdi's:
702 * bdi_setpoint = setpoint * bdi_thresh / thresh
703 */
704 x = div_u64((u64)bdi_thresh << 16, thresh + 1);
705 bdi_setpoint = setpoint * (u64)x >> 16;
706 /*
707 * Use span=(8*write_bw) in single bdi case as indicated by
708 * (thresh - bdi_thresh ~= 0) and transit to bdi_thresh in JBOD case.
709 *
710 * bdi_thresh thresh - bdi_thresh
711 * span = ---------- * (8 * write_bw) + ------------------- * bdi_thresh
712 * thresh thresh
713 */
714 span = (thresh - bdi_thresh + 8 * write_bw) * (u64)x >> 16;
715 x_intercept = bdi_setpoint + span;
716
717 if (bdi_dirty < x_intercept - span / 4) {
718 pos_ratio = div_u64(pos_ratio * (x_intercept - bdi_dirty),
719 x_intercept - bdi_setpoint + 1);
720 } else
721 pos_ratio /= 4;
722
723 /*
724 * bdi reserve area, safeguard against dirty pool underrun and disk idle
725 * It may push the desired control point of global dirty pages higher
726 * than setpoint.
727 */
728 x_intercept = bdi_thresh / 2;
729 if (bdi_dirty < x_intercept) {
730 if (bdi_dirty > x_intercept / 8)
731 pos_ratio = div_u64(pos_ratio * x_intercept, bdi_dirty);
732 else
733 pos_ratio *= 8;
734 }
735
736 return pos_ratio;
737}
738
739static void bdi_update_write_bandwidth(struct backing_dev_info *bdi,
740 unsigned long elapsed,
741 unsigned long written)
742{
743 const unsigned long period = roundup_pow_of_two(3 * HZ);
744 unsigned long avg = bdi->avg_write_bandwidth;
745 unsigned long old = bdi->write_bandwidth;
746 u64 bw;
747
748 /*
749 * bw = written * HZ / elapsed
750 *
751 * bw * elapsed + write_bandwidth * (period - elapsed)
752 * write_bandwidth = ---------------------------------------------------
753 * period
754 */
755 bw = written - bdi->written_stamp;
756 bw *= HZ;
757 if (unlikely(elapsed > period)) {
758 do_div(bw, elapsed);
759 avg = bw;
760 goto out;
761 }
762 bw += (u64)bdi->write_bandwidth * (period - elapsed);
763 bw >>= ilog2(period);
764
765 /*
766 * one more level of smoothing, for filtering out sudden spikes
767 */
768 if (avg > old && old >= (unsigned long)bw)
769 avg -= (avg - old) >> 3;
770
771 if (avg < old && old <= (unsigned long)bw)
772 avg += (old - avg) >> 3;
773
774out:
775 bdi->write_bandwidth = bw;
776 bdi->avg_write_bandwidth = avg;
777}
778
779/*
780 * The global dirtyable memory and dirty threshold could be suddenly knocked
781 * down by a large amount (eg. on the startup of KVM in a swapless system).
782 * This may throw the system into deep dirty exceeded state and throttle
783 * heavy/light dirtiers alike. To retain good responsiveness, maintain
784 * global_dirty_limit for tracking slowly down to the knocked down dirty
785 * threshold.
786 */
787static void update_dirty_limit(unsigned long thresh, unsigned long dirty)
788{
789 unsigned long limit = global_dirty_limit;
790
791 /*
792 * Follow up in one step.
793 */
794 if (limit < thresh) {
795 limit = thresh;
796 goto update;
797 }
798
799 /*
800 * Follow down slowly. Use the higher one as the target, because thresh
801 * may drop below dirty. This is exactly the reason to introduce
802 * global_dirty_limit which is guaranteed to lie above the dirty pages.
803 */
804 thresh = max(thresh, dirty);
805 if (limit > thresh) {
806 limit -= (limit - thresh) >> 5;
807 goto update;
808 }
809 return;
810update:
811 global_dirty_limit = limit;
812}
813
814static void global_update_bandwidth(unsigned long thresh,
815 unsigned long dirty,
816 unsigned long now)
817{
818 static DEFINE_SPINLOCK(dirty_lock);
819 static unsigned long update_time;
820
821 /*
822 * check locklessly first to optimize away locking for the most time
823 */
824 if (time_before(now, update_time + BANDWIDTH_INTERVAL))
825 return;
826
827 spin_lock(&dirty_lock);
828 if (time_after_eq(now, update_time + BANDWIDTH_INTERVAL)) {
829 update_dirty_limit(thresh, dirty);
830 update_time = now;
831 }
832 spin_unlock(&dirty_lock);
833}
834
835/*
836 * Maintain bdi->dirty_ratelimit, the base dirty throttle rate.
837 *
838 * Normal bdi tasks will be curbed at or below it in long term.
839 * Obviously it should be around (write_bw / N) when there are N dd tasks.
840 */
841static void bdi_update_dirty_ratelimit(struct backing_dev_info *bdi,
842 unsigned long thresh,
843 unsigned long bg_thresh,
844 unsigned long dirty,
845 unsigned long bdi_thresh,
846 unsigned long bdi_dirty,
847 unsigned long dirtied,
848 unsigned long elapsed)
849{
850 unsigned long freerun = dirty_freerun_ceiling(thresh, bg_thresh);
851 unsigned long limit = hard_dirty_limit(thresh);
852 unsigned long setpoint = (freerun + limit) / 2;
853 unsigned long write_bw = bdi->avg_write_bandwidth;
854 unsigned long dirty_ratelimit = bdi->dirty_ratelimit;
855 unsigned long dirty_rate;
856 unsigned long task_ratelimit;
857 unsigned long balanced_dirty_ratelimit;
858 unsigned long pos_ratio;
859 unsigned long step;
860 unsigned long x;
861
862 /*
863 * The dirty rate will match the writeout rate in long term, except
864 * when dirty pages are truncated by userspace or re-dirtied by FS.
865 */
866 dirty_rate = (dirtied - bdi->dirtied_stamp) * HZ / elapsed;
867
868 pos_ratio = bdi_position_ratio(bdi, thresh, bg_thresh, dirty,
869 bdi_thresh, bdi_dirty);
870 /*
871 * task_ratelimit reflects each dd's dirty rate for the past 200ms.
872 */
873 task_ratelimit = (u64)dirty_ratelimit *
874 pos_ratio >> RATELIMIT_CALC_SHIFT;
875 task_ratelimit++; /* it helps rampup dirty_ratelimit from tiny values */
876
877 /*
878 * A linear estimation of the "balanced" throttle rate. The theory is,
879 * if there are N dd tasks, each throttled at task_ratelimit, the bdi's
880 * dirty_rate will be measured to be (N * task_ratelimit). So the below
881 * formula will yield the balanced rate limit (write_bw / N).
882 *
883 * Note that the expanded form is not a pure rate feedback:
884 * rate_(i+1) = rate_(i) * (write_bw / dirty_rate) (1)
885 * but also takes pos_ratio into account:
886 * rate_(i+1) = rate_(i) * (write_bw / dirty_rate) * pos_ratio (2)
887 *
888 * (1) is not realistic because pos_ratio also takes part in balancing
889 * the dirty rate. Consider the state
890 * pos_ratio = 0.5 (3)
891 * rate = 2 * (write_bw / N) (4)
892 * If (1) is used, it will stuck in that state! Because each dd will
893 * be throttled at
894 * task_ratelimit = pos_ratio * rate = (write_bw / N) (5)
895 * yielding
896 * dirty_rate = N * task_ratelimit = write_bw (6)
897 * put (6) into (1) we get
898 * rate_(i+1) = rate_(i) (7)
899 *
900 * So we end up using (2) to always keep
901 * rate_(i+1) ~= (write_bw / N) (8)
902 * regardless of the value of pos_ratio. As long as (8) is satisfied,
903 * pos_ratio is able to drive itself to 1.0, which is not only where
904 * the dirty count meet the setpoint, but also where the slope of
905 * pos_ratio is most flat and hence task_ratelimit is least fluctuated.
906 */
907 balanced_dirty_ratelimit = div_u64((u64)task_ratelimit * write_bw,
908 dirty_rate | 1);
909 /*
910 * balanced_dirty_ratelimit ~= (write_bw / N) <= write_bw
911 */
912 if (unlikely(balanced_dirty_ratelimit > write_bw))
913 balanced_dirty_ratelimit = write_bw;
914
915 /*
916 * We could safely do this and return immediately:
917 *
918 * bdi->dirty_ratelimit = balanced_dirty_ratelimit;
919 *
920 * However to get a more stable dirty_ratelimit, the below elaborated
921 * code makes use of task_ratelimit to filter out sigular points and
922 * limit the step size.
923 *
924 * The below code essentially only uses the relative value of
925 *
926 * task_ratelimit - dirty_ratelimit
927 * = (pos_ratio - 1) * dirty_ratelimit
928 *
929 * which reflects the direction and size of dirty position error.
930 */
931
932 /*
933 * dirty_ratelimit will follow balanced_dirty_ratelimit iff
934 * task_ratelimit is on the same side of dirty_ratelimit, too.
935 * For example, when
936 * - dirty_ratelimit > balanced_dirty_ratelimit
937 * - dirty_ratelimit > task_ratelimit (dirty pages are above setpoint)
938 * lowering dirty_ratelimit will help meet both the position and rate
939 * control targets. Otherwise, don't update dirty_ratelimit if it will
940 * only help meet the rate target. After all, what the users ultimately
941 * feel and care are stable dirty rate and small position error.
942 *
943 * |task_ratelimit - dirty_ratelimit| is used to limit the step size
944 * and filter out the sigular points of balanced_dirty_ratelimit. Which
945 * keeps jumping around randomly and can even leap far away at times
946 * due to the small 200ms estimation period of dirty_rate (we want to
947 * keep that period small to reduce time lags).
948 */
949 step = 0;
950 if (dirty < setpoint) {
951 x = min(bdi->balanced_dirty_ratelimit,
952 min(balanced_dirty_ratelimit, task_ratelimit));
953 if (dirty_ratelimit < x)
954 step = x - dirty_ratelimit;
955 } else {
956 x = max(bdi->balanced_dirty_ratelimit,
957 max(balanced_dirty_ratelimit, task_ratelimit));
958 if (dirty_ratelimit > x)
959 step = dirty_ratelimit - x;
960 }
961
962 /*
963 * Don't pursue 100% rate matching. It's impossible since the balanced
964 * rate itself is constantly fluctuating. So decrease the track speed
965 * when it gets close to the target. Helps eliminate pointless tremors.
966 */
967 step >>= dirty_ratelimit / (2 * step + 1);
968 /*
969 * Limit the tracking speed to avoid overshooting.
970 */
971 step = (step + 7) / 8;
972
973 if (dirty_ratelimit < balanced_dirty_ratelimit)
974 dirty_ratelimit += step;
975 else
976 dirty_ratelimit -= step;
977
978 bdi->dirty_ratelimit = max(dirty_ratelimit, 1UL);
979 bdi->balanced_dirty_ratelimit = balanced_dirty_ratelimit;
980
981 trace_bdi_dirty_ratelimit(bdi, dirty_rate, task_ratelimit);
982}
983
984void __bdi_update_bandwidth(struct backing_dev_info *bdi,
985 unsigned long thresh,
986 unsigned long bg_thresh,
987 unsigned long dirty,
988 unsigned long bdi_thresh,
989 unsigned long bdi_dirty,
990 unsigned long start_time)
991{
992 unsigned long now = jiffies;
993 unsigned long elapsed = now - bdi->bw_time_stamp;
994 unsigned long dirtied;
995 unsigned long written;
996
997 /*
998 * rate-limit, only update once every 200ms.
999 */
1000 if (elapsed < BANDWIDTH_INTERVAL)
1001 return;
1002
1003 dirtied = percpu_counter_read(&bdi->bdi_stat[BDI_DIRTIED]);
1004 written = percpu_counter_read(&bdi->bdi_stat[BDI_WRITTEN]);
1005
1006 /*
1007 * Skip quiet periods when disk bandwidth is under-utilized.
1008 * (at least 1s idle time between two flusher runs)
1009 */
1010 if (elapsed > HZ && time_before(bdi->bw_time_stamp, start_time))
1011 goto snapshot;
1012
1013 if (thresh) {
1014 global_update_bandwidth(thresh, dirty, now);
1015 bdi_update_dirty_ratelimit(bdi, thresh, bg_thresh, dirty,
1016 bdi_thresh, bdi_dirty,
1017 dirtied, elapsed);
1018 }
1019 bdi_update_write_bandwidth(bdi, elapsed, written);
1020
1021snapshot:
1022 bdi->dirtied_stamp = dirtied;
1023 bdi->written_stamp = written;
1024 bdi->bw_time_stamp = now;
1025}
1026
1027static void bdi_update_bandwidth(struct backing_dev_info *bdi,
1028 unsigned long thresh,
1029 unsigned long bg_thresh,
1030 unsigned long dirty,
1031 unsigned long bdi_thresh,
1032 unsigned long bdi_dirty,
1033 unsigned long start_time)
1034{
1035 if (time_is_after_eq_jiffies(bdi->bw_time_stamp + BANDWIDTH_INTERVAL))
1036 return;
1037 spin_lock(&bdi->wb.list_lock);
1038 __bdi_update_bandwidth(bdi, thresh, bg_thresh, dirty,
1039 bdi_thresh, bdi_dirty, start_time);
1040 spin_unlock(&bdi->wb.list_lock);
1041}
1042
1043/*
1044 * After a task dirtied this many pages, balance_dirty_pages_ratelimited_nr()
1045 * will look to see if it needs to start dirty throttling.
1046 *
1047 * If dirty_poll_interval is too low, big NUMA machines will call the expensive
1048 * global_page_state() too often. So scale it near-sqrt to the safety margin
1049 * (the number of pages we may dirty without exceeding the dirty limits).
1050 */
1051static unsigned long dirty_poll_interval(unsigned long dirty,
1052 unsigned long thresh)
1053{
1054 if (thresh > dirty)
1055 return 1UL << (ilog2(thresh - dirty) >> 1);
1056
1057 return 1;
1058}
1059
1060static long bdi_max_pause(struct backing_dev_info *bdi,
1061 unsigned long bdi_dirty)
1062{
1063 long bw = bdi->avg_write_bandwidth;
1064 long t;
1065
1066 /*
1067 * Limit pause time for small memory systems. If sleeping for too long
1068 * time, a small pool of dirty/writeback pages may go empty and disk go
1069 * idle.
1070 *
1071 * 8 serves as the safety ratio.
1072 */
1073 t = bdi_dirty / (1 + bw / roundup_pow_of_two(1 + HZ / 8));
1074 t++;
1075
1076 return min_t(long, t, MAX_PAUSE);
1077}
1078
1079static long bdi_min_pause(struct backing_dev_info *bdi,
1080 long max_pause,
1081 unsigned long task_ratelimit,
1082 unsigned long dirty_ratelimit,
1083 int *nr_dirtied_pause)
1084{
1085 long hi = ilog2(bdi->avg_write_bandwidth);
1086 long lo = ilog2(bdi->dirty_ratelimit);
1087 long t; /* target pause */
1088 long pause; /* estimated next pause */
1089 int pages; /* target nr_dirtied_pause */
1090
1091 /* target for 10ms pause on 1-dd case */
1092 t = max(1, HZ / 100);
1093
1094 /*
1095 * Scale up pause time for concurrent dirtiers in order to reduce CPU
1096 * overheads.
1097 *
1098 * (N * 10ms) on 2^N concurrent tasks.
1099 */
1100 if (hi > lo)
1101 t += (hi - lo) * (10 * HZ) / 1024;
1102
1103 /*
1104 * This is a bit convoluted. We try to base the next nr_dirtied_pause
1105 * on the much more stable dirty_ratelimit. However the next pause time
1106 * will be computed based on task_ratelimit and the two rate limits may
1107 * depart considerably at some time. Especially if task_ratelimit goes
1108 * below dirty_ratelimit/2 and the target pause is max_pause, the next
1109 * pause time will be max_pause*2 _trimmed down_ to max_pause. As a
1110 * result task_ratelimit won't be executed faithfully, which could
1111 * eventually bring down dirty_ratelimit.
1112 *
1113 * We apply two rules to fix it up:
1114 * 1) try to estimate the next pause time and if necessary, use a lower
1115 * nr_dirtied_pause so as not to exceed max_pause. When this happens,
1116 * nr_dirtied_pause will be "dancing" with task_ratelimit.
1117 * 2) limit the target pause time to max_pause/2, so that the normal
1118 * small fluctuations of task_ratelimit won't trigger rule (1) and
1119 * nr_dirtied_pause will remain as stable as dirty_ratelimit.
1120 */
1121 t = min(t, 1 + max_pause / 2);
1122 pages = dirty_ratelimit * t / roundup_pow_of_two(HZ);
1123
1124 /*
1125 * Tiny nr_dirtied_pause is found to hurt I/O performance in the test
1126 * case fio-mmap-randwrite-64k, which does 16*{sync read, async write}.
1127 * When the 16 consecutive reads are often interrupted by some dirty
1128 * throttling pause during the async writes, cfq will go into idles
1129 * (deadline is fine). So push nr_dirtied_pause as high as possible
1130 * until reaches DIRTY_POLL_THRESH=32 pages.
1131 */
1132 if (pages < DIRTY_POLL_THRESH) {
1133 t = max_pause;
1134 pages = dirty_ratelimit * t / roundup_pow_of_two(HZ);
1135 if (pages > DIRTY_POLL_THRESH) {
1136 pages = DIRTY_POLL_THRESH;
1137 t = HZ * DIRTY_POLL_THRESH / dirty_ratelimit;
1138 }
1139 }
1140
1141 pause = HZ * pages / (task_ratelimit + 1);
1142 if (pause > max_pause) {
1143 t = max_pause;
1144 pages = task_ratelimit * t / roundup_pow_of_two(HZ);
1145 }
1146
1147 *nr_dirtied_pause = pages;
1148 /*
1149 * The minimal pause time will normally be half the target pause time.
1150 */
1151 return pages >= DIRTY_POLL_THRESH ? 1 + t / 2 : t;
1152}
1153
1154/*
1155 * balance_dirty_pages() must be called by processes which are generating dirty
1156 * data. It looks at the number of dirty pages in the machine and will force
1157 * the caller to wait once crossing the (background_thresh + dirty_thresh) / 2.
1158 * If we're over `background_thresh' then the writeback threads are woken to
1159 * perform some writeout.
1160 */
1161static void balance_dirty_pages(struct address_space *mapping,
1162 unsigned long pages_dirtied)
1163{
1164 unsigned long nr_reclaimable; /* = file_dirty + unstable_nfs */
1165 unsigned long bdi_reclaimable;
1166 unsigned long nr_dirty; /* = file_dirty + writeback + unstable_nfs */
1167 unsigned long bdi_dirty;
1168 unsigned long freerun;
1169 unsigned long background_thresh;
1170 unsigned long dirty_thresh;
1171 unsigned long bdi_thresh;
1172 long period;
1173 long pause;
1174 long max_pause;
1175 long min_pause;
1176 int nr_dirtied_pause;
1177 bool dirty_exceeded = false;
1178 unsigned long task_ratelimit;
1179 unsigned long dirty_ratelimit;
1180 unsigned long pos_ratio;
1181 struct backing_dev_info *bdi = mapping->backing_dev_info;
1182 unsigned long start_time = jiffies;
1183
1184 for (;;) {
1185 unsigned long now = jiffies;
1186
1187 /*
1188 * Unstable writes are a feature of certain networked
1189 * filesystems (i.e. NFS) in which data may have been
1190 * written to the server's write cache, but has not yet
1191 * been flushed to permanent storage.
1192 */
1193 nr_reclaimable = global_page_state(NR_FILE_DIRTY) +
1194 global_page_state(NR_UNSTABLE_NFS);
1195 nr_dirty = nr_reclaimable + global_page_state(NR_WRITEBACK);
1196
1197 global_dirty_limits(&background_thresh, &dirty_thresh);
1198
1199 /*
1200 * Throttle it only when the background writeback cannot
1201 * catch-up. This avoids (excessively) small writeouts
1202 * when the bdi limits are ramping up.
1203 */
1204 freerun = dirty_freerun_ceiling(dirty_thresh,
1205 background_thresh);
1206 if (nr_dirty <= freerun) {
1207 current->dirty_paused_when = now;
1208 current->nr_dirtied = 0;
1209 current->nr_dirtied_pause =
1210 dirty_poll_interval(nr_dirty, dirty_thresh);
1211 break;
1212 }
1213
1214 if (unlikely(!writeback_in_progress(bdi)))
1215 bdi_start_background_writeback(bdi);
1216
1217 /*
1218 * bdi_thresh is not treated as some limiting factor as
1219 * dirty_thresh, due to reasons
1220 * - in JBOD setup, bdi_thresh can fluctuate a lot
1221 * - in a system with HDD and USB key, the USB key may somehow
1222 * go into state (bdi_dirty >> bdi_thresh) either because
1223 * bdi_dirty starts high, or because bdi_thresh drops low.
1224 * In this case we don't want to hard throttle the USB key
1225 * dirtiers for 100 seconds until bdi_dirty drops under
1226 * bdi_thresh. Instead the auxiliary bdi control line in
1227 * bdi_position_ratio() will let the dirtier task progress
1228 * at some rate <= (write_bw / 2) for bringing down bdi_dirty.
1229 */
1230 bdi_thresh = bdi_dirty_limit(bdi, dirty_thresh);
1231
1232 /*
1233 * In order to avoid the stacked BDI deadlock we need
1234 * to ensure we accurately count the 'dirty' pages when
1235 * the threshold is low.
1236 *
1237 * Otherwise it would be possible to get thresh+n pages
1238 * reported dirty, even though there are thresh-m pages
1239 * actually dirty; with m+n sitting in the percpu
1240 * deltas.
1241 */
1242 if (bdi_thresh < 2 * bdi_stat_error(bdi)) {
1243 bdi_reclaimable = bdi_stat_sum(bdi, BDI_RECLAIMABLE);
1244 bdi_dirty = bdi_reclaimable +
1245 bdi_stat_sum(bdi, BDI_WRITEBACK);
1246 } else {
1247 bdi_reclaimable = bdi_stat(bdi, BDI_RECLAIMABLE);
1248 bdi_dirty = bdi_reclaimable +
1249 bdi_stat(bdi, BDI_WRITEBACK);
1250 }
1251
1252 dirty_exceeded = (bdi_dirty > bdi_thresh) &&
1253 (nr_dirty > dirty_thresh);
1254 if (dirty_exceeded && !bdi->dirty_exceeded)
1255 bdi->dirty_exceeded = 1;
1256
1257 bdi_update_bandwidth(bdi, dirty_thresh, background_thresh,
1258 nr_dirty, bdi_thresh, bdi_dirty,
1259 start_time);
1260
1261 dirty_ratelimit = bdi->dirty_ratelimit;
1262 pos_ratio = bdi_position_ratio(bdi, dirty_thresh,
1263 background_thresh, nr_dirty,
1264 bdi_thresh, bdi_dirty);
1265 task_ratelimit = ((u64)dirty_ratelimit * pos_ratio) >>
1266 RATELIMIT_CALC_SHIFT;
1267 max_pause = bdi_max_pause(bdi, bdi_dirty);
1268 min_pause = bdi_min_pause(bdi, max_pause,
1269 task_ratelimit, dirty_ratelimit,
1270 &nr_dirtied_pause);
1271
1272 if (unlikely(task_ratelimit == 0)) {
1273 period = max_pause;
1274 pause = max_pause;
1275 goto pause;
1276 }
1277 period = HZ * pages_dirtied / task_ratelimit;
1278 pause = period;
1279 if (current->dirty_paused_when)
1280 pause -= now - current->dirty_paused_when;
1281 /*
1282 * For less than 1s think time (ext3/4 may block the dirtier
1283 * for up to 800ms from time to time on 1-HDD; so does xfs,
1284 * however at much less frequency), try to compensate it in
1285 * future periods by updating the virtual time; otherwise just
1286 * do a reset, as it may be a light dirtier.
1287 */
1288 if (pause < min_pause) {
1289 trace_balance_dirty_pages(bdi,
1290 dirty_thresh,
1291 background_thresh,
1292 nr_dirty,
1293 bdi_thresh,
1294 bdi_dirty,
1295 dirty_ratelimit,
1296 task_ratelimit,
1297 pages_dirtied,
1298 period,
1299 min(pause, 0L),
1300 start_time);
1301 if (pause < -HZ) {
1302 current->dirty_paused_when = now;
1303 current->nr_dirtied = 0;
1304 } else if (period) {
1305 current->dirty_paused_when += period;
1306 current->nr_dirtied = 0;
1307 } else if (current->nr_dirtied_pause <= pages_dirtied)
1308 current->nr_dirtied_pause += pages_dirtied;
1309 break;
1310 }
1311 if (unlikely(pause > max_pause)) {
1312 /* for occasional dropped task_ratelimit */
1313 now += min(pause - max_pause, max_pause);
1314 pause = max_pause;
1315 }
1316
1317pause:
1318 trace_balance_dirty_pages(bdi,
1319 dirty_thresh,
1320 background_thresh,
1321 nr_dirty,
1322 bdi_thresh,
1323 bdi_dirty,
1324 dirty_ratelimit,
1325 task_ratelimit,
1326 pages_dirtied,
1327 period,
1328 pause,
1329 start_time);
1330 __set_current_state(TASK_KILLABLE);
1331 io_schedule_timeout(pause);
1332
1333 current->dirty_paused_when = now + pause;
1334 current->nr_dirtied = 0;
1335 current->nr_dirtied_pause = nr_dirtied_pause;
1336
1337 /*
1338 * This is typically equal to (nr_dirty < dirty_thresh) and can
1339 * also keep "1000+ dd on a slow USB stick" under control.
1340 */
1341 if (task_ratelimit)
1342 break;
1343
1344 /*
1345 * In the case of an unresponding NFS server and the NFS dirty
1346 * pages exceeds dirty_thresh, give the other good bdi's a pipe
1347 * to go through, so that tasks on them still remain responsive.
1348 *
1349 * In theory 1 page is enough to keep the comsumer-producer
1350 * pipe going: the flusher cleans 1 page => the task dirties 1
1351 * more page. However bdi_dirty has accounting errors. So use
1352 * the larger and more IO friendly bdi_stat_error.
1353 */
1354 if (bdi_dirty <= bdi_stat_error(bdi))
1355 break;
1356
1357 if (fatal_signal_pending(current))
1358 break;
1359 }
1360
1361 if (!dirty_exceeded && bdi->dirty_exceeded)
1362 bdi->dirty_exceeded = 0;
1363
1364 if (writeback_in_progress(bdi))
1365 return;
1366
1367 /*
1368 * In laptop mode, we wait until hitting the higher threshold before
1369 * starting background writeout, and then write out all the way down
1370 * to the lower threshold. So slow writers cause minimal disk activity.
1371 *
1372 * In normal mode, we start background writeout at the lower
1373 * background_thresh, to keep the amount of dirty memory low.
1374 */
1375 if (laptop_mode)
1376 return;
1377
1378 if (nr_reclaimable > background_thresh)
1379 bdi_start_background_writeback(bdi);
1380}
1381
1382void set_page_dirty_balance(struct page *page, int page_mkwrite)
1383{
1384 if (set_page_dirty(page) || page_mkwrite) {
1385 struct address_space *mapping = page_mapping(page);
1386
1387 if (mapping)
1388 balance_dirty_pages_ratelimited(mapping);
1389 }
1390}
1391
1392static DEFINE_PER_CPU(int, bdp_ratelimits);
1393
1394/*
1395 * Normal tasks are throttled by
1396 * loop {
1397 * dirty tsk->nr_dirtied_pause pages;
1398 * take a snap in balance_dirty_pages();
1399 * }
1400 * However there is a worst case. If every task exit immediately when dirtied
1401 * (tsk->nr_dirtied_pause - 1) pages, balance_dirty_pages() will never be
1402 * called to throttle the page dirties. The solution is to save the not yet
1403 * throttled page dirties in dirty_throttle_leaks on task exit and charge them
1404 * randomly into the running tasks. This works well for the above worst case,
1405 * as the new task will pick up and accumulate the old task's leaked dirty
1406 * count and eventually get throttled.
1407 */
1408DEFINE_PER_CPU(int, dirty_throttle_leaks) = 0;
1409
1410/**
1411 * balance_dirty_pages_ratelimited_nr - balance dirty memory state
1412 * @mapping: address_space which was dirtied
1413 * @nr_pages_dirtied: number of pages which the caller has just dirtied
1414 *
1415 * Processes which are dirtying memory should call in here once for each page
1416 * which was newly dirtied. The function will periodically check the system's
1417 * dirty state and will initiate writeback if needed.
1418 *
1419 * On really big machines, get_writeback_state is expensive, so try to avoid
1420 * calling it too often (ratelimiting). But once we're over the dirty memory
1421 * limit we decrease the ratelimiting by a lot, to prevent individual processes
1422 * from overshooting the limit by (ratelimit_pages) each.
1423 */
1424void balance_dirty_pages_ratelimited_nr(struct address_space *mapping,
1425 unsigned long nr_pages_dirtied)
1426{
1427 struct backing_dev_info *bdi = mapping->backing_dev_info;
1428 int ratelimit;
1429 int *p;
1430
1431 if (!bdi_cap_account_dirty(bdi))
1432 return;
1433
1434 ratelimit = current->nr_dirtied_pause;
1435 if (bdi->dirty_exceeded)
1436 ratelimit = min(ratelimit, 32 >> (PAGE_SHIFT - 10));
1437
1438 preempt_disable();
1439 /*
1440 * This prevents one CPU to accumulate too many dirtied pages without
1441 * calling into balance_dirty_pages(), which can happen when there are
1442 * 1000+ tasks, all of them start dirtying pages at exactly the same
1443 * time, hence all honoured too large initial task->nr_dirtied_pause.
1444 */
1445 p = &__get_cpu_var(bdp_ratelimits);
1446 if (unlikely(current->nr_dirtied >= ratelimit))
1447 *p = 0;
1448 else if (unlikely(*p >= ratelimit_pages)) {
1449 *p = 0;
1450 ratelimit = 0;
1451 }
1452 /*
1453 * Pick up the dirtied pages by the exited tasks. This avoids lots of
1454 * short-lived tasks (eg. gcc invocations in a kernel build) escaping
1455 * the dirty throttling and livelock other long-run dirtiers.
1456 */
1457 p = &__get_cpu_var(dirty_throttle_leaks);
1458 if (*p > 0 && current->nr_dirtied < ratelimit) {
1459 nr_pages_dirtied = min(*p, ratelimit - current->nr_dirtied);
1460 *p -= nr_pages_dirtied;
1461 current->nr_dirtied += nr_pages_dirtied;
1462 }
1463 preempt_enable();
1464
1465 if (unlikely(current->nr_dirtied >= ratelimit))
1466 balance_dirty_pages(mapping, current->nr_dirtied);
1467}
1468EXPORT_SYMBOL(balance_dirty_pages_ratelimited_nr);
1469
1470void throttle_vm_writeout(gfp_t gfp_mask)
1471{
1472 unsigned long background_thresh;
1473 unsigned long dirty_thresh;
1474
1475 for ( ; ; ) {
1476 global_dirty_limits(&background_thresh, &dirty_thresh);
1477 dirty_thresh = hard_dirty_limit(dirty_thresh);
1478
1479 /*
1480 * Boost the allowable dirty threshold a bit for page
1481 * allocators so they don't get DoS'ed by heavy writers
1482 */
1483 dirty_thresh += dirty_thresh / 10; /* wheeee... */
1484
1485 if (global_page_state(NR_UNSTABLE_NFS) +
1486 global_page_state(NR_WRITEBACK) <= dirty_thresh)
1487 break;
1488 congestion_wait(BLK_RW_ASYNC, HZ/10);
1489
1490 /*
1491 * The caller might hold locks which can prevent IO completion
1492 * or progress in the filesystem. So we cannot just sit here
1493 * waiting for IO to complete.
1494 */
1495 if ((gfp_mask & (__GFP_FS|__GFP_IO)) != (__GFP_FS|__GFP_IO))
1496 break;
1497 }
1498}
1499
1500/*
1501 * sysctl handler for /proc/sys/vm/dirty_writeback_centisecs
1502 */
1503int dirty_writeback_centisecs_handler(ctl_table *table, int write,
1504 void __user *buffer, size_t *length, loff_t *ppos)
1505{
1506 proc_dointvec(table, write, buffer, length, ppos);
1507 bdi_arm_supers_timer();
1508 return 0;
1509}
1510
1511#ifdef CONFIG_BLOCK
1512void laptop_mode_timer_fn(unsigned long data)
1513{
1514 struct request_queue *q = (struct request_queue *)data;
1515 int nr_pages = global_page_state(NR_FILE_DIRTY) +
1516 global_page_state(NR_UNSTABLE_NFS);
1517
1518 /*
1519 * We want to write everything out, not just down to the dirty
1520 * threshold
1521 */
1522 if (bdi_has_dirty_io(&q->backing_dev_info))
1523 bdi_start_writeback(&q->backing_dev_info, nr_pages,
1524 WB_REASON_LAPTOP_TIMER);
1525}
1526
1527/*
1528 * We've spun up the disk and we're in laptop mode: schedule writeback
1529 * of all dirty data a few seconds from now. If the flush is already scheduled
1530 * then push it back - the user is still using the disk.
1531 */
1532void laptop_io_completion(struct backing_dev_info *info)
1533{
1534 mod_timer(&info->laptop_mode_wb_timer, jiffies + laptop_mode);
1535}
1536
1537/*
1538 * We're in laptop mode and we've just synced. The sync's writes will have
1539 * caused another writeback to be scheduled by laptop_io_completion.
1540 * Nothing needs to be written back anymore, so we unschedule the writeback.
1541 */
1542void laptop_sync_completion(void)
1543{
1544 struct backing_dev_info *bdi;
1545
1546 rcu_read_lock();
1547
1548 list_for_each_entry_rcu(bdi, &bdi_list, bdi_list)
1549 del_timer(&bdi->laptop_mode_wb_timer);
1550
1551 rcu_read_unlock();
1552}
1553#endif
1554
1555/*
1556 * If ratelimit_pages is too high then we can get into dirty-data overload
1557 * if a large number of processes all perform writes at the same time.
1558 * If it is too low then SMP machines will call the (expensive)
1559 * get_writeback_state too often.
1560 *
1561 * Here we set ratelimit_pages to a level which ensures that when all CPUs are
1562 * dirtying in parallel, we cannot go more than 3% (1/32) over the dirty memory
1563 * thresholds.
1564 */
1565
1566void writeback_set_ratelimit(void)
1567{
1568 unsigned long background_thresh;
1569 unsigned long dirty_thresh;
1570 global_dirty_limits(&background_thresh, &dirty_thresh);
1571 global_dirty_limit = dirty_thresh;
1572 ratelimit_pages = dirty_thresh / (num_online_cpus() * 32);
1573 if (ratelimit_pages < 16)
1574 ratelimit_pages = 16;
1575}
1576
1577static int __cpuinit
1578ratelimit_handler(struct notifier_block *self, unsigned long u, void *v)
1579{
1580 writeback_set_ratelimit();
1581 return NOTIFY_DONE;
1582}
1583
1584static struct notifier_block __cpuinitdata ratelimit_nb = {
1585 .notifier_call = ratelimit_handler,
1586 .next = NULL,
1587};
1588
1589/*
1590 * Called early on to tune the page writeback dirty limits.
1591 *
1592 * We used to scale dirty pages according to how total memory
1593 * related to pages that could be allocated for buffers (by
1594 * comparing nr_free_buffer_pages() to vm_total_pages.
1595 *
1596 * However, that was when we used "dirty_ratio" to scale with
1597 * all memory, and we don't do that any more. "dirty_ratio"
1598 * is now applied to total non-HIGHPAGE memory (by subtracting
1599 * totalhigh_pages from vm_total_pages), and as such we can't
1600 * get into the old insane situation any more where we had
1601 * large amounts of dirty pages compared to a small amount of
1602 * non-HIGHMEM memory.
1603 *
1604 * But we might still want to scale the dirty_ratio by how
1605 * much memory the box has..
1606 */
1607void __init page_writeback_init(void)
1608{
1609 int shift;
1610
1611 writeback_set_ratelimit();
1612 register_cpu_notifier(&ratelimit_nb);
1613
1614 shift = calc_period_shift();
1615 prop_descriptor_init(&vm_completions, shift);
1616}
1617
1618/**
1619 * tag_pages_for_writeback - tag pages to be written by write_cache_pages
1620 * @mapping: address space structure to write
1621 * @start: starting page index
1622 * @end: ending page index (inclusive)
1623 *
1624 * This function scans the page range from @start to @end (inclusive) and tags
1625 * all pages that have DIRTY tag set with a special TOWRITE tag. The idea is
1626 * that write_cache_pages (or whoever calls this function) will then use
1627 * TOWRITE tag to identify pages eligible for writeback. This mechanism is
1628 * used to avoid livelocking of writeback by a process steadily creating new
1629 * dirty pages in the file (thus it is important for this function to be quick
1630 * so that it can tag pages faster than a dirtying process can create them).
1631 */
1632/*
1633 * We tag pages in batches of WRITEBACK_TAG_BATCH to reduce tree_lock latency.
1634 */
1635void tag_pages_for_writeback(struct address_space *mapping,
1636 pgoff_t start, pgoff_t end)
1637{
1638#define WRITEBACK_TAG_BATCH 4096
1639 unsigned long tagged;
1640
1641 do {
1642 spin_lock_irq(&mapping->tree_lock);
1643 tagged = radix_tree_range_tag_if_tagged(&mapping->page_tree,
1644 &start, end, WRITEBACK_TAG_BATCH,
1645 PAGECACHE_TAG_DIRTY, PAGECACHE_TAG_TOWRITE);
1646 spin_unlock_irq(&mapping->tree_lock);
1647 WARN_ON_ONCE(tagged > WRITEBACK_TAG_BATCH);
1648 cond_resched();
1649 /* We check 'start' to handle wrapping when end == ~0UL */
1650 } while (tagged >= WRITEBACK_TAG_BATCH && start);
1651}
1652EXPORT_SYMBOL(tag_pages_for_writeback);
1653
1654/**
1655 * write_cache_pages - walk the list of dirty pages of the given address space and write all of them.
1656 * @mapping: address space structure to write
1657 * @wbc: subtract the number of written pages from *@wbc->nr_to_write
1658 * @writepage: function called for each page
1659 * @data: data passed to writepage function
1660 *
1661 * If a page is already under I/O, write_cache_pages() skips it, even
1662 * if it's dirty. This is desirable behaviour for memory-cleaning writeback,
1663 * but it is INCORRECT for data-integrity system calls such as fsync(). fsync()
1664 * and msync() need to guarantee that all the data which was dirty at the time
1665 * the call was made get new I/O started against them. If wbc->sync_mode is
1666 * WB_SYNC_ALL then we were called for data integrity and we must wait for
1667 * existing IO to complete.
1668 *
1669 * To avoid livelocks (when other process dirties new pages), we first tag
1670 * pages which should be written back with TOWRITE tag and only then start
1671 * writing them. For data-integrity sync we have to be careful so that we do
1672 * not miss some pages (e.g., because some other process has cleared TOWRITE
1673 * tag we set). The rule we follow is that TOWRITE tag can be cleared only
1674 * by the process clearing the DIRTY tag (and submitting the page for IO).
1675 */
1676int write_cache_pages(struct address_space *mapping,
1677 struct writeback_control *wbc, writepage_t writepage,
1678 void *data)
1679{
1680 int ret = 0;
1681 int done = 0;
1682 struct pagevec pvec;
1683 int nr_pages;
1684 pgoff_t uninitialized_var(writeback_index);
1685 pgoff_t index;
1686 pgoff_t end; /* Inclusive */
1687 pgoff_t done_index;
1688 int cycled;
1689 int range_whole = 0;
1690 int tag;
1691
1692 pagevec_init(&pvec, 0);
1693 if (wbc->range_cyclic) {
1694 writeback_index = mapping->writeback_index; /* prev offset */
1695 index = writeback_index;
1696 if (index == 0)
1697 cycled = 1;
1698 else
1699 cycled = 0;
1700 end = -1;
1701 } else {
1702 index = wbc->range_start >> PAGE_CACHE_SHIFT;
1703 end = wbc->range_end >> PAGE_CACHE_SHIFT;
1704 if (wbc->range_start == 0 && wbc->range_end == LLONG_MAX)
1705 range_whole = 1;
1706 cycled = 1; /* ignore range_cyclic tests */
1707 }
1708 if (wbc->sync_mode == WB_SYNC_ALL || wbc->tagged_writepages)
1709 tag = PAGECACHE_TAG_TOWRITE;
1710 else
1711 tag = PAGECACHE_TAG_DIRTY;
1712retry:
1713 if (wbc->sync_mode == WB_SYNC_ALL || wbc->tagged_writepages)
1714 tag_pages_for_writeback(mapping, index, end);
1715 done_index = index;
1716 while (!done && (index <= end)) {
1717 int i;
1718
1719 nr_pages = pagevec_lookup_tag(&pvec, mapping, &index, tag,
1720 min(end - index, (pgoff_t)PAGEVEC_SIZE-1) + 1);
1721 if (nr_pages == 0)
1722 break;
1723
1724 for (i = 0; i < nr_pages; i++) {
1725 struct page *page = pvec.pages[i];
1726
1727 /*
1728 * At this point, the page may be truncated or
1729 * invalidated (changing page->mapping to NULL), or
1730 * even swizzled back from swapper_space to tmpfs file
1731 * mapping. However, page->index will not change
1732 * because we have a reference on the page.
1733 */
1734 if (page->index > end) {
1735 /*
1736 * can't be range_cyclic (1st pass) because
1737 * end == -1 in that case.
1738 */
1739 done = 1;
1740 break;
1741 }
1742
1743 done_index = page->index;
1744
1745 lock_page(page);
1746
1747 /*
1748 * Page truncated or invalidated. We can freely skip it
1749 * then, even for data integrity operations: the page
1750 * has disappeared concurrently, so there could be no
1751 * real expectation of this data interity operation
1752 * even if there is now a new, dirty page at the same
1753 * pagecache address.
1754 */
1755 if (unlikely(page->mapping != mapping)) {
1756continue_unlock:
1757 unlock_page(page);
1758 continue;
1759 }
1760
1761 if (!PageDirty(page)) {
1762 /* someone wrote it for us */
1763 goto continue_unlock;
1764 }
1765
1766 if (PageWriteback(page)) {
1767 if (wbc->sync_mode != WB_SYNC_NONE)
1768 wait_on_page_writeback(page);
1769 else
1770 goto continue_unlock;
1771 }
1772
1773 BUG_ON(PageWriteback(page));
1774 if (!clear_page_dirty_for_io(page))
1775 goto continue_unlock;
1776
1777 trace_wbc_writepage(wbc, mapping->backing_dev_info);
1778 ret = (*writepage)(page, wbc, data);
1779 if (unlikely(ret)) {
1780 if (ret == AOP_WRITEPAGE_ACTIVATE) {
1781 unlock_page(page);
1782 ret = 0;
1783 } else {
1784 /*
1785 * done_index is set past this page,
1786 * so media errors will not choke
1787 * background writeout for the entire
1788 * file. This has consequences for
1789 * range_cyclic semantics (ie. it may
1790 * not be suitable for data integrity
1791 * writeout).
1792 */
1793 done_index = page->index + 1;
1794 done = 1;
1795 break;
1796 }
1797 }
1798
1799 /*
1800 * We stop writing back only if we are not doing
1801 * integrity sync. In case of integrity sync we have to
1802 * keep going until we have written all the pages
1803 * we tagged for writeback prior to entering this loop.
1804 */
1805 if (--wbc->nr_to_write <= 0 &&
1806 wbc->sync_mode == WB_SYNC_NONE) {
1807 done = 1;
1808 break;
1809 }
1810 }
1811 pagevec_release(&pvec);
1812 cond_resched();
1813 }
1814 if (!cycled && !done) {
1815 /*
1816 * range_cyclic:
1817 * We hit the last page and there is more work to be done: wrap
1818 * back to the start of the file
1819 */
1820 cycled = 1;
1821 index = 0;
1822 end = writeback_index - 1;
1823 goto retry;
1824 }
1825 if (wbc->range_cyclic || (range_whole && wbc->nr_to_write > 0))
1826 mapping->writeback_index = done_index;
1827
1828 return ret;
1829}
1830EXPORT_SYMBOL(write_cache_pages);
1831
1832/*
1833 * Function used by generic_writepages to call the real writepage
1834 * function and set the mapping flags on error
1835 */
1836static int __writepage(struct page *page, struct writeback_control *wbc,
1837 void *data)
1838{
1839 struct address_space *mapping = data;
1840 int ret = mapping->a_ops->writepage(page, wbc);
1841 mapping_set_error(mapping, ret);
1842 return ret;
1843}
1844
1845/**
1846 * generic_writepages - walk the list of dirty pages of the given address space and writepage() all of them.
1847 * @mapping: address space structure to write
1848 * @wbc: subtract the number of written pages from *@wbc->nr_to_write
1849 *
1850 * This is a library function, which implements the writepages()
1851 * address_space_operation.
1852 */
1853int generic_writepages(struct address_space *mapping,
1854 struct writeback_control *wbc)
1855{
1856 struct blk_plug plug;
1857 int ret;
1858
1859 /* deal with chardevs and other special file */
1860 if (!mapping->a_ops->writepage)
1861 return 0;
1862
1863 blk_start_plug(&plug);
1864 ret = write_cache_pages(mapping, wbc, __writepage, mapping);
1865 blk_finish_plug(&plug);
1866 return ret;
1867}
1868
1869EXPORT_SYMBOL(generic_writepages);
1870
1871int do_writepages(struct address_space *mapping, struct writeback_control *wbc)
1872{
1873 int ret;
1874
1875 if (wbc->nr_to_write <= 0)
1876 return 0;
1877 if (mapping->a_ops->writepages)
1878 ret = mapping->a_ops->writepages(mapping, wbc);
1879 else
1880 ret = generic_writepages(mapping, wbc);
1881 return ret;
1882}
1883
1884/**
1885 * write_one_page - write out a single page and optionally wait on I/O
1886 * @page: the page to write
1887 * @wait: if true, wait on writeout
1888 *
1889 * The page must be locked by the caller and will be unlocked upon return.
1890 *
1891 * write_one_page() returns a negative error code if I/O failed.
1892 */
1893int write_one_page(struct page *page, int wait)
1894{
1895 struct address_space *mapping = page->mapping;
1896 int ret = 0;
1897 struct writeback_control wbc = {
1898 .sync_mode = WB_SYNC_ALL,
1899 .nr_to_write = 1,
1900 };
1901
1902 BUG_ON(!PageLocked(page));
1903
1904 if (wait)
1905 wait_on_page_writeback(page);
1906
1907 if (clear_page_dirty_for_io(page)) {
1908 page_cache_get(page);
1909 ret = mapping->a_ops->writepage(page, &wbc);
1910 if (ret == 0 && wait) {
1911 wait_on_page_writeback(page);
1912 if (PageError(page))
1913 ret = -EIO;
1914 }
1915 page_cache_release(page);
1916 } else {
1917 unlock_page(page);
1918 }
1919 return ret;
1920}
1921EXPORT_SYMBOL(write_one_page);
1922
1923/*
1924 * For address_spaces which do not use buffers nor write back.
1925 */
1926int __set_page_dirty_no_writeback(struct page *page)
1927{
1928 if (!PageDirty(page))
1929 return !TestSetPageDirty(page);
1930 return 0;
1931}
1932
1933/*
1934 * Helper function for set_page_dirty family.
1935 * NOTE: This relies on being atomic wrt interrupts.
1936 */
1937void account_page_dirtied(struct page *page, struct address_space *mapping)
1938{
1939 if (mapping_cap_account_dirty(mapping)) {
1940 __inc_zone_page_state(page, NR_FILE_DIRTY);
1941 __inc_zone_page_state(page, NR_DIRTIED);
1942 __inc_bdi_stat(mapping->backing_dev_info, BDI_RECLAIMABLE);
1943 __inc_bdi_stat(mapping->backing_dev_info, BDI_DIRTIED);
1944 task_io_account_write(PAGE_CACHE_SIZE);
1945 current->nr_dirtied++;
1946 this_cpu_inc(bdp_ratelimits);
1947 }
1948}
1949EXPORT_SYMBOL(account_page_dirtied);
1950
1951/*
1952 * Helper function for set_page_writeback family.
1953 * NOTE: Unlike account_page_dirtied this does not rely on being atomic
1954 * wrt interrupts.
1955 */
1956void account_page_writeback(struct page *page)
1957{
1958 inc_zone_page_state(page, NR_WRITEBACK);
1959}
1960EXPORT_SYMBOL(account_page_writeback);
1961
1962/*
1963 * For address_spaces which do not use buffers. Just tag the page as dirty in
1964 * its radix tree.
1965 *
1966 * This is also used when a single buffer is being dirtied: we want to set the
1967 * page dirty in that case, but not all the buffers. This is a "bottom-up"
1968 * dirtying, whereas __set_page_dirty_buffers() is a "top-down" dirtying.
1969 *
1970 * Most callers have locked the page, which pins the address_space in memory.
1971 * But zap_pte_range() does not lock the page, however in that case the
1972 * mapping is pinned by the vma's ->vm_file reference.
1973 *
1974 * We take care to handle the case where the page was truncated from the
1975 * mapping by re-checking page_mapping() inside tree_lock.
1976 */
1977int __set_page_dirty_nobuffers(struct page *page)
1978{
1979 if (!TestSetPageDirty(page)) {
1980 struct address_space *mapping = page_mapping(page);
1981 struct address_space *mapping2;
1982
1983 if (!mapping)
1984 return 1;
1985
1986 spin_lock_irq(&mapping->tree_lock);
1987 mapping2 = page_mapping(page);
1988 if (mapping2) { /* Race with truncate? */
1989 BUG_ON(mapping2 != mapping);
1990 WARN_ON_ONCE(!PagePrivate(page) && !PageUptodate(page));
1991 account_page_dirtied(page, mapping);
1992 radix_tree_tag_set(&mapping->page_tree,
1993 page_index(page), PAGECACHE_TAG_DIRTY);
1994 }
1995 spin_unlock_irq(&mapping->tree_lock);
1996 if (mapping->host) {
1997 /* !PageAnon && !swapper_space */
1998 __mark_inode_dirty(mapping->host, I_DIRTY_PAGES);
1999 }
2000 return 1;
2001 }
2002 return 0;
2003}
2004EXPORT_SYMBOL(__set_page_dirty_nobuffers);
2005
2006/*
2007 * Call this whenever redirtying a page, to de-account the dirty counters
2008 * (NR_DIRTIED, BDI_DIRTIED, tsk->nr_dirtied), so that they match the written
2009 * counters (NR_WRITTEN, BDI_WRITTEN) in long term. The mismatches will lead to
2010 * systematic errors in balanced_dirty_ratelimit and the dirty pages position
2011 * control.
2012 */
2013void account_page_redirty(struct page *page)
2014{
2015 struct address_space *mapping = page->mapping;
2016 if (mapping && mapping_cap_account_dirty(mapping)) {
2017 current->nr_dirtied--;
2018 dec_zone_page_state(page, NR_DIRTIED);
2019 dec_bdi_stat(mapping->backing_dev_info, BDI_DIRTIED);
2020 }
2021}
2022EXPORT_SYMBOL(account_page_redirty);
2023
2024/*
2025 * When a writepage implementation decides that it doesn't want to write this
2026 * page for some reason, it should redirty the locked page via
2027 * redirty_page_for_writepage() and it should then unlock the page and return 0
2028 */
2029int redirty_page_for_writepage(struct writeback_control *wbc, struct page *page)
2030{
2031 wbc->pages_skipped++;
2032 account_page_redirty(page);
2033 return __set_page_dirty_nobuffers(page);
2034}
2035EXPORT_SYMBOL(redirty_page_for_writepage);
2036
2037/*
2038 * Dirty a page.
2039 *
2040 * For pages with a mapping this should be done under the page lock
2041 * for the benefit of asynchronous memory errors who prefer a consistent
2042 * dirty state. This rule can be broken in some special cases,
2043 * but should be better not to.
2044 *
2045 * If the mapping doesn't provide a set_page_dirty a_op, then
2046 * just fall through and assume that it wants buffer_heads.
2047 */
2048int set_page_dirty(struct page *page)
2049{
2050 struct address_space *mapping = page_mapping(page);
2051
2052 if (likely(mapping)) {
2053 int (*spd)(struct page *) = mapping->a_ops->set_page_dirty;
2054 /*
2055 * readahead/lru_deactivate_page could remain
2056 * PG_readahead/PG_reclaim due to race with end_page_writeback
2057 * About readahead, if the page is written, the flags would be
2058 * reset. So no problem.
2059 * About lru_deactivate_page, if the page is redirty, the flag
2060 * will be reset. So no problem. but if the page is used by readahead
2061 * it will confuse readahead and make it restart the size rampup
2062 * process. But it's a trivial problem.
2063 */
2064 ClearPageReclaim(page);
2065#ifdef CONFIG_BLOCK
2066 if (!spd)
2067 spd = __set_page_dirty_buffers;
2068#endif
2069 return (*spd)(page);
2070 }
2071 if (!PageDirty(page)) {
2072 if (!TestSetPageDirty(page))
2073 return 1;
2074 }
2075 return 0;
2076}
2077EXPORT_SYMBOL(set_page_dirty);
2078
2079/*
2080 * set_page_dirty() is racy if the caller has no reference against
2081 * page->mapping->host, and if the page is unlocked. This is because another
2082 * CPU could truncate the page off the mapping and then free the mapping.
2083 *
2084 * Usually, the page _is_ locked, or the caller is a user-space process which
2085 * holds a reference on the inode by having an open file.
2086 *
2087 * In other cases, the page should be locked before running set_page_dirty().
2088 */
2089int set_page_dirty_lock(struct page *page)
2090{
2091 int ret;
2092
2093 lock_page(page);
2094 ret = set_page_dirty(page);
2095 unlock_page(page);
2096 return ret;
2097}
2098EXPORT_SYMBOL(set_page_dirty_lock);
2099
2100/*
2101 * Clear a page's dirty flag, while caring for dirty memory accounting.
2102 * Returns true if the page was previously dirty.
2103 *
2104 * This is for preparing to put the page under writeout. We leave the page
2105 * tagged as dirty in the radix tree so that a concurrent write-for-sync
2106 * can discover it via a PAGECACHE_TAG_DIRTY walk. The ->writepage
2107 * implementation will run either set_page_writeback() or set_page_dirty(),
2108 * at which stage we bring the page's dirty flag and radix-tree dirty tag
2109 * back into sync.
2110 *
2111 * This incoherency between the page's dirty flag and radix-tree tag is
2112 * unfortunate, but it only exists while the page is locked.
2113 */
2114int clear_page_dirty_for_io(struct page *page)
2115{
2116 struct address_space *mapping = page_mapping(page);
2117
2118 BUG_ON(!PageLocked(page));
2119
2120 if (mapping && mapping_cap_account_dirty(mapping)) {
2121 /*
2122 * Yes, Virginia, this is indeed insane.
2123 *
2124 * We use this sequence to make sure that
2125 * (a) we account for dirty stats properly
2126 * (b) we tell the low-level filesystem to
2127 * mark the whole page dirty if it was
2128 * dirty in a pagetable. Only to then
2129 * (c) clean the page again and return 1 to
2130 * cause the writeback.
2131 *
2132 * This way we avoid all nasty races with the
2133 * dirty bit in multiple places and clearing
2134 * them concurrently from different threads.
2135 *
2136 * Note! Normally the "set_page_dirty(page)"
2137 * has no effect on the actual dirty bit - since
2138 * that will already usually be set. But we
2139 * need the side effects, and it can help us
2140 * avoid races.
2141 *
2142 * We basically use the page "master dirty bit"
2143 * as a serialization point for all the different
2144 * threads doing their things.
2145 */
2146 if (page_mkclean(page))
2147 set_page_dirty(page);
2148 /*
2149 * We carefully synchronise fault handlers against
2150 * installing a dirty pte and marking the page dirty
2151 * at this point. We do this by having them hold the
2152 * page lock at some point after installing their
2153 * pte, but before marking the page dirty.
2154 * Pages are always locked coming in here, so we get
2155 * the desired exclusion. See mm/memory.c:do_wp_page()
2156 * for more comments.
2157 */
2158 if (TestClearPageDirty(page)) {
2159 dec_zone_page_state(page, NR_FILE_DIRTY);
2160 dec_bdi_stat(mapping->backing_dev_info,
2161 BDI_RECLAIMABLE);
2162 return 1;
2163 }
2164 return 0;
2165 }
2166 return TestClearPageDirty(page);
2167}
2168EXPORT_SYMBOL(clear_page_dirty_for_io);
2169
2170int test_clear_page_writeback(struct page *page)
2171{
2172 struct address_space *mapping = page_mapping(page);
2173 int ret;
2174
2175 if (mapping) {
2176 struct backing_dev_info *bdi = mapping->backing_dev_info;
2177 unsigned long flags;
2178
2179 spin_lock_irqsave(&mapping->tree_lock, flags);
2180 ret = TestClearPageWriteback(page);
2181 if (ret) {
2182 radix_tree_tag_clear(&mapping->page_tree,
2183 page_index(page),
2184 PAGECACHE_TAG_WRITEBACK);
2185 if (bdi_cap_account_writeback(bdi)) {
2186 __dec_bdi_stat(bdi, BDI_WRITEBACK);
2187 __bdi_writeout_inc(bdi);
2188 }
2189 }
2190 spin_unlock_irqrestore(&mapping->tree_lock, flags);
2191 } else {
2192 ret = TestClearPageWriteback(page);
2193 }
2194 if (ret) {
2195 dec_zone_page_state(page, NR_WRITEBACK);
2196 inc_zone_page_state(page, NR_WRITTEN);
2197 }
2198 return ret;
2199}
2200
2201int test_set_page_writeback(struct page *page)
2202{
2203 struct address_space *mapping = page_mapping(page);
2204 int ret;
2205
2206 if (mapping) {
2207 struct backing_dev_info *bdi = mapping->backing_dev_info;
2208 unsigned long flags;
2209
2210 spin_lock_irqsave(&mapping->tree_lock, flags);
2211 ret = TestSetPageWriteback(page);
2212 if (!ret) {
2213 radix_tree_tag_set(&mapping->page_tree,
2214 page_index(page),
2215 PAGECACHE_TAG_WRITEBACK);
2216 if (bdi_cap_account_writeback(bdi))
2217 __inc_bdi_stat(bdi, BDI_WRITEBACK);
2218 }
2219 if (!PageDirty(page))
2220 radix_tree_tag_clear(&mapping->page_tree,
2221 page_index(page),
2222 PAGECACHE_TAG_DIRTY);
2223 radix_tree_tag_clear(&mapping->page_tree,
2224 page_index(page),
2225 PAGECACHE_TAG_TOWRITE);
2226 spin_unlock_irqrestore(&mapping->tree_lock, flags);
2227 } else {
2228 ret = TestSetPageWriteback(page);
2229 }
2230 if (!ret)
2231 account_page_writeback(page);
2232 return ret;
2233
2234}
2235EXPORT_SYMBOL(test_set_page_writeback);
2236
2237/*
2238 * Return true if any of the pages in the mapping are marked with the
2239 * passed tag.
2240 */
2241int mapping_tagged(struct address_space *mapping, int tag)
2242{
2243 return radix_tree_tagged(&mapping->page_tree, tag);
2244}
2245EXPORT_SYMBOL(mapping_tagged);