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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
6 *
7 * Contains functions related to writing back dirty pages at the
8 * address_space level.
9 *
10 * 10Apr2002 Andrew Morton
11 * Initial version
12 */
13
14 #include <linux/kernel.h>
15 #include <linux/export.h>
16 #include <linux/spinlock.h>
17 #include <linux/fs.h>
18 #include <linux/mm.h>
19 #include <linux/swap.h>
20 #include <linux/slab.h>
21 #include <linux/pagemap.h>
22 #include <linux/writeback.h>
23 #include <linux/init.h>
24 #include <linux/backing-dev.h>
25 #include <linux/task_io_accounting_ops.h>
26 #include <linux/blkdev.h>
27 #include <linux/mpage.h>
28 #include <linux/rmap.h>
29 #include <linux/percpu.h>
30 #include <linux/notifier.h>
31 #include <linux/smp.h>
32 #include <linux/sysctl.h>
33 #include <linux/cpu.h>
34 #include <linux/syscalls.h>
35 #include <linux/buffer_head.h> /* __set_page_dirty_buffers */
36 #include <linux/pagevec.h>
37 #include <linux/timer.h>
38 #include <linux/sched/rt.h>
39 #include <linux/mm_inline.h>
40 #include <trace/events/writeback.h>
41
42 #include "internal.h"
43
44 /*
45 * Sleep at most 200ms at a time in balance_dirty_pages().
46 */
47 #define MAX_PAUSE max(HZ/5, 1)
48
49 /*
50 * Try to keep balance_dirty_pages() call intervals higher than this many pages
51 * by raising pause time to max_pause when falls below it.
52 */
53 #define DIRTY_POLL_THRESH (128 >> (PAGE_SHIFT - 10))
54
55 /*
56 * Estimate write bandwidth at 200ms intervals.
57 */
58 #define BANDWIDTH_INTERVAL max(HZ/5, 1)
59
60 #define RATELIMIT_CALC_SHIFT 10
61
62 /*
63 * After a CPU has dirtied this many pages, balance_dirty_pages_ratelimited
64 * will look to see if it needs to force writeback or throttling.
65 */
66 static long ratelimit_pages = 32;
67
68 /* The following parameters are exported via /proc/sys/vm */
69
70 /*
71 * Start background writeback (via writeback threads) at this percentage
72 */
73 int dirty_background_ratio = 10;
74
75 /*
76 * dirty_background_bytes starts at 0 (disabled) so that it is a function of
77 * dirty_background_ratio * the amount of dirtyable memory
78 */
79 unsigned long dirty_background_bytes;
80
81 /*
82 * free highmem will not be subtracted from the total free memory
83 * for calculating free ratios if vm_highmem_is_dirtyable is true
84 */
85 int vm_highmem_is_dirtyable;
86
87 /*
88 * The generator of dirty data starts writeback at this percentage
89 */
90 int vm_dirty_ratio = 20;
91
92 /*
93 * vm_dirty_bytes starts at 0 (disabled) so that it is a function of
94 * vm_dirty_ratio * the amount of dirtyable memory
95 */
96 unsigned long vm_dirty_bytes;
97
98 /*
99 * The interval between `kupdate'-style writebacks
100 */
101 unsigned int dirty_writeback_interval = 5 * 100; /* centiseconds */
102
103 EXPORT_SYMBOL_GPL(dirty_writeback_interval);
104
105 /*
106 * The longest time for which data is allowed to remain dirty
107 */
108 unsigned int dirty_expire_interval = 30 * 100; /* centiseconds */
109
110 /*
111 * Flag that makes the machine dump writes/reads and block dirtyings.
112 */
113 int block_dump;
114
115 /*
116 * Flag that puts the machine in "laptop mode". Doubles as a timeout in jiffies:
117 * a full sync is triggered after this time elapses without any disk activity.
118 */
119 int laptop_mode;
120
121 EXPORT_SYMBOL(laptop_mode);
122
123 /* End of sysctl-exported parameters */
124
125 struct wb_domain global_wb_domain;
126
127 /* consolidated parameters for balance_dirty_pages() and its subroutines */
128 struct dirty_throttle_control {
129 #ifdef CONFIG_CGROUP_WRITEBACK
130 struct wb_domain *dom;
131 struct dirty_throttle_control *gdtc; /* only set in memcg dtc's */
132 #endif
133 struct bdi_writeback *wb;
134 struct fprop_local_percpu *wb_completions;
135
136 unsigned long avail; /* dirtyable */
137 unsigned long dirty; /* file_dirty + write + nfs */
138 unsigned long thresh; /* dirty threshold */
139 unsigned long bg_thresh; /* dirty background threshold */
140
141 unsigned long wb_dirty; /* per-wb counterparts */
142 unsigned long wb_thresh;
143 unsigned long wb_bg_thresh;
144
145 unsigned long pos_ratio;
146 };
147
148 /*
149 * Length of period for aging writeout fractions of bdis. This is an
150 * arbitrarily chosen number. The longer the period, the slower fractions will
151 * reflect changes in current writeout rate.
152 */
153 #define VM_COMPLETIONS_PERIOD_LEN (3*HZ)
154
155 #ifdef CONFIG_CGROUP_WRITEBACK
156
157 #define GDTC_INIT(__wb) .wb = (__wb), \
158 .dom = &global_wb_domain, \
159 .wb_completions = &(__wb)->completions
160
161 #define GDTC_INIT_NO_WB .dom = &global_wb_domain
162
163 #define MDTC_INIT(__wb, __gdtc) .wb = (__wb), \
164 .dom = mem_cgroup_wb_domain(__wb), \
165 .wb_completions = &(__wb)->memcg_completions, \
166 .gdtc = __gdtc
167
168 static bool mdtc_valid(struct dirty_throttle_control *dtc)
169 {
170 return dtc->dom;
171 }
172
173 static struct wb_domain *dtc_dom(struct dirty_throttle_control *dtc)
174 {
175 return dtc->dom;
176 }
177
178 static struct dirty_throttle_control *mdtc_gdtc(struct dirty_throttle_control *mdtc)
179 {
180 return mdtc->gdtc;
181 }
182
183 static struct fprop_local_percpu *wb_memcg_completions(struct bdi_writeback *wb)
184 {
185 return &wb->memcg_completions;
186 }
187
188 static void wb_min_max_ratio(struct bdi_writeback *wb,
189 unsigned long *minp, unsigned long *maxp)
190 {
191 unsigned long this_bw = wb->avg_write_bandwidth;
192 unsigned long tot_bw = atomic_long_read(&wb->bdi->tot_write_bandwidth);
193 unsigned long long min = wb->bdi->min_ratio;
194 unsigned long long max = wb->bdi->max_ratio;
195
196 /*
197 * @wb may already be clean by the time control reaches here and
198 * the total may not include its bw.
199 */
200 if (this_bw < tot_bw) {
201 if (min) {
202 min *= this_bw;
203 do_div(min, tot_bw);
204 }
205 if (max < 100) {
206 max *= this_bw;
207 do_div(max, tot_bw);
208 }
209 }
210
211 *minp = min;
212 *maxp = max;
213 }
214
215 #else /* CONFIG_CGROUP_WRITEBACK */
216
217 #define GDTC_INIT(__wb) .wb = (__wb), \
218 .wb_completions = &(__wb)->completions
219 #define GDTC_INIT_NO_WB
220 #define MDTC_INIT(__wb, __gdtc)
221
222 static bool mdtc_valid(struct dirty_throttle_control *dtc)
223 {
224 return false;
225 }
226
227 static struct wb_domain *dtc_dom(struct dirty_throttle_control *dtc)
228 {
229 return &global_wb_domain;
230 }
231
232 static struct dirty_throttle_control *mdtc_gdtc(struct dirty_throttle_control *mdtc)
233 {
234 return NULL;
235 }
236
237 static struct fprop_local_percpu *wb_memcg_completions(struct bdi_writeback *wb)
238 {
239 return NULL;
240 }
241
242 static void wb_min_max_ratio(struct bdi_writeback *wb,
243 unsigned long *minp, unsigned long *maxp)
244 {
245 *minp = wb->bdi->min_ratio;
246 *maxp = wb->bdi->max_ratio;
247 }
248
249 #endif /* CONFIG_CGROUP_WRITEBACK */
250
251 /*
252 * In a memory zone, there is a certain amount of pages we consider
253 * available for the page cache, which is essentially the number of
254 * free and reclaimable pages, minus some zone reserves to protect
255 * lowmem and the ability to uphold the zone's watermarks without
256 * requiring writeback.
257 *
258 * This number of dirtyable pages is the base value of which the
259 * user-configurable dirty ratio is the effictive number of pages that
260 * are allowed to be actually dirtied. Per individual zone, or
261 * globally by using the sum of dirtyable pages over all zones.
262 *
263 * Because the user is allowed to specify the dirty limit globally as
264 * absolute number of bytes, calculating the per-zone dirty limit can
265 * require translating the configured limit into a percentage of
266 * global dirtyable memory first.
267 */
268
269 /**
270 * node_dirtyable_memory - number of dirtyable pages in a node
271 * @pgdat: the node
272 *
273 * Returns the node's number of pages potentially available for dirty
274 * page cache. This is the base value for the per-node dirty limits.
275 */
276 static unsigned long node_dirtyable_memory(struct pglist_data *pgdat)
277 {
278 unsigned long nr_pages = 0;
279 int z;
280
281 for (z = 0; z < MAX_NR_ZONES; z++) {
282 struct zone *zone = pgdat->node_zones + z;
283
284 if (!populated_zone(zone))
285 continue;
286
287 nr_pages += zone_page_state(zone, NR_FREE_PAGES);
288 }
289
290 /*
291 * Pages reserved for the kernel should not be considered
292 * dirtyable, to prevent a situation where reclaim has to
293 * clean pages in order to balance the zones.
294 */
295 nr_pages -= min(nr_pages, pgdat->totalreserve_pages);
296
297 nr_pages += node_page_state(pgdat, NR_INACTIVE_FILE);
298 nr_pages += node_page_state(pgdat, NR_ACTIVE_FILE);
299
300 return nr_pages;
301 }
302
303 static unsigned long highmem_dirtyable_memory(unsigned long total)
304 {
305 #ifdef CONFIG_HIGHMEM
306 int node;
307 unsigned long x = 0;
308 int i;
309
310 for_each_node_state(node, N_HIGH_MEMORY) {
311 for (i = ZONE_NORMAL + 1; i < MAX_NR_ZONES; i++) {
312 struct zone *z;
313 unsigned long nr_pages;
314
315 if (!is_highmem_idx(i))
316 continue;
317
318 z = &NODE_DATA(node)->node_zones[i];
319 if (!populated_zone(z))
320 continue;
321
322 nr_pages = zone_page_state(z, NR_FREE_PAGES);
323 /* watch for underflows */
324 nr_pages -= min(nr_pages, high_wmark_pages(z));
325 nr_pages += zone_page_state(z, NR_ZONE_INACTIVE_FILE);
326 nr_pages += zone_page_state(z, NR_ZONE_ACTIVE_FILE);
327 x += nr_pages;
328 }
329 }
330
331 /*
332 * Unreclaimable memory (kernel memory or anonymous memory
333 * without swap) can bring down the dirtyable pages below
334 * the zone's dirty balance reserve and the above calculation
335 * will underflow. However we still want to add in nodes
336 * which are below threshold (negative values) to get a more
337 * accurate calculation but make sure that the total never
338 * underflows.
339 */
340 if ((long)x < 0)
341 x = 0;
342
343 /*
344 * Make sure that the number of highmem pages is never larger
345 * than the number of the total dirtyable memory. This can only
346 * occur in very strange VM situations but we want to make sure
347 * that this does not occur.
348 */
349 return min(x, total);
350 #else
351 return 0;
352 #endif
353 }
354
355 /**
356 * global_dirtyable_memory - number of globally dirtyable pages
357 *
358 * Returns the global number of pages potentially available for dirty
359 * page cache. This is the base value for the global dirty limits.
360 */
361 static unsigned long global_dirtyable_memory(void)
362 {
363 unsigned long x;
364
365 x = global_page_state(NR_FREE_PAGES);
366 /*
367 * Pages reserved for the kernel should not be considered
368 * dirtyable, to prevent a situation where reclaim has to
369 * clean pages in order to balance the zones.
370 */
371 x -= min(x, totalreserve_pages);
372
373 x += global_node_page_state(NR_INACTIVE_FILE);
374 x += global_node_page_state(NR_ACTIVE_FILE);
375
376 if (!vm_highmem_is_dirtyable)
377 x -= highmem_dirtyable_memory(x);
378
379 return x + 1; /* Ensure that we never return 0 */
380 }
381
382 /**
383 * domain_dirty_limits - calculate thresh and bg_thresh for a wb_domain
384 * @dtc: dirty_throttle_control of interest
385 *
386 * Calculate @dtc->thresh and ->bg_thresh considering
387 * vm_dirty_{bytes|ratio} and dirty_background_{bytes|ratio}. The caller
388 * must ensure that @dtc->avail is set before calling this function. The
389 * dirty limits will be lifted by 1/4 for PF_LESS_THROTTLE (ie. nfsd) and
390 * real-time tasks.
391 */
392 static void domain_dirty_limits(struct dirty_throttle_control *dtc)
393 {
394 const unsigned long available_memory = dtc->avail;
395 struct dirty_throttle_control *gdtc = mdtc_gdtc(dtc);
396 unsigned long bytes = vm_dirty_bytes;
397 unsigned long bg_bytes = dirty_background_bytes;
398 /* convert ratios to per-PAGE_SIZE for higher precision */
399 unsigned long ratio = (vm_dirty_ratio * PAGE_SIZE) / 100;
400 unsigned long bg_ratio = (dirty_background_ratio * PAGE_SIZE) / 100;
401 unsigned long thresh;
402 unsigned long bg_thresh;
403 struct task_struct *tsk;
404
405 /* gdtc is !NULL iff @dtc is for memcg domain */
406 if (gdtc) {
407 unsigned long global_avail = gdtc->avail;
408
409 /*
410 * The byte settings can't be applied directly to memcg
411 * domains. Convert them to ratios by scaling against
412 * globally available memory. As the ratios are in
413 * per-PAGE_SIZE, they can be obtained by dividing bytes by
414 * number of pages.
415 */
416 if (bytes)
417 ratio = min(DIV_ROUND_UP(bytes, global_avail),
418 PAGE_SIZE);
419 if (bg_bytes)
420 bg_ratio = min(DIV_ROUND_UP(bg_bytes, global_avail),
421 PAGE_SIZE);
422 bytes = bg_bytes = 0;
423 }
424
425 if (bytes)
426 thresh = DIV_ROUND_UP(bytes, PAGE_SIZE);
427 else
428 thresh = (ratio * available_memory) / PAGE_SIZE;
429
430 if (bg_bytes)
431 bg_thresh = DIV_ROUND_UP(bg_bytes, PAGE_SIZE);
432 else
433 bg_thresh = (bg_ratio * available_memory) / PAGE_SIZE;
434
435 if (bg_thresh >= thresh)
436 bg_thresh = thresh / 2;
437 tsk = current;
438 if (tsk->flags & PF_LESS_THROTTLE || rt_task(tsk)) {
439 bg_thresh += bg_thresh / 4 + global_wb_domain.dirty_limit / 32;
440 thresh += thresh / 4 + global_wb_domain.dirty_limit / 32;
441 }
442 dtc->thresh = thresh;
443 dtc->bg_thresh = bg_thresh;
444
445 /* we should eventually report the domain in the TP */
446 if (!gdtc)
447 trace_global_dirty_state(bg_thresh, thresh);
448 }
449
450 /**
451 * global_dirty_limits - background-writeback and dirty-throttling thresholds
452 * @pbackground: out parameter for bg_thresh
453 * @pdirty: out parameter for thresh
454 *
455 * Calculate bg_thresh and thresh for global_wb_domain. See
456 * domain_dirty_limits() for details.
457 */
458 void global_dirty_limits(unsigned long *pbackground, unsigned long *pdirty)
459 {
460 struct dirty_throttle_control gdtc = { GDTC_INIT_NO_WB };
461
462 gdtc.avail = global_dirtyable_memory();
463 domain_dirty_limits(&gdtc);
464
465 *pbackground = gdtc.bg_thresh;
466 *pdirty = gdtc.thresh;
467 }
468
469 /**
470 * node_dirty_limit - maximum number of dirty pages allowed in a node
471 * @pgdat: the node
472 *
473 * Returns the maximum number of dirty pages allowed in a node, based
474 * on the node's dirtyable memory.
475 */
476 static unsigned long node_dirty_limit(struct pglist_data *pgdat)
477 {
478 unsigned long node_memory = node_dirtyable_memory(pgdat);
479 struct task_struct *tsk = current;
480 unsigned long dirty;
481
482 if (vm_dirty_bytes)
483 dirty = DIV_ROUND_UP(vm_dirty_bytes, PAGE_SIZE) *
484 node_memory / global_dirtyable_memory();
485 else
486 dirty = vm_dirty_ratio * node_memory / 100;
487
488 if (tsk->flags & PF_LESS_THROTTLE || rt_task(tsk))
489 dirty += dirty / 4;
490
491 return dirty;
492 }
493
494 /**
495 * node_dirty_ok - tells whether a node is within its dirty limits
496 * @pgdat: the node to check
497 *
498 * Returns %true when the dirty pages in @pgdat are within the node's
499 * dirty limit, %false if the limit is exceeded.
500 */
501 bool node_dirty_ok(struct pglist_data *pgdat)
502 {
503 unsigned long limit = node_dirty_limit(pgdat);
504 unsigned long nr_pages = 0;
505
506 nr_pages += node_page_state(pgdat, NR_FILE_DIRTY);
507 nr_pages += node_page_state(pgdat, NR_UNSTABLE_NFS);
508 nr_pages += node_page_state(pgdat, NR_WRITEBACK);
509
510 return nr_pages <= limit;
511 }
512
513 int dirty_background_ratio_handler(struct ctl_table *table, int write,
514 void __user *buffer, size_t *lenp,
515 loff_t *ppos)
516 {
517 int ret;
518
519 ret = proc_dointvec_minmax(table, write, buffer, lenp, ppos);
520 if (ret == 0 && write)
521 dirty_background_bytes = 0;
522 return ret;
523 }
524
525 int dirty_background_bytes_handler(struct ctl_table *table, int write,
526 void __user *buffer, size_t *lenp,
527 loff_t *ppos)
528 {
529 int ret;
530
531 ret = proc_doulongvec_minmax(table, write, buffer, lenp, ppos);
532 if (ret == 0 && write)
533 dirty_background_ratio = 0;
534 return ret;
535 }
536
537 int dirty_ratio_handler(struct ctl_table *table, int write,
538 void __user *buffer, size_t *lenp,
539 loff_t *ppos)
540 {
541 int old_ratio = vm_dirty_ratio;
542 int ret;
543
544 ret = proc_dointvec_minmax(table, write, buffer, lenp, ppos);
545 if (ret == 0 && write && vm_dirty_ratio != old_ratio) {
546 writeback_set_ratelimit();
547 vm_dirty_bytes = 0;
548 }
549 return ret;
550 }
551
552 int dirty_bytes_handler(struct ctl_table *table, int write,
553 void __user *buffer, size_t *lenp,
554 loff_t *ppos)
555 {
556 unsigned long old_bytes = vm_dirty_bytes;
557 int ret;
558
559 ret = proc_doulongvec_minmax(table, write, buffer, lenp, ppos);
560 if (ret == 0 && write && vm_dirty_bytes != old_bytes) {
561 writeback_set_ratelimit();
562 vm_dirty_ratio = 0;
563 }
564 return ret;
565 }
566
567 static unsigned long wp_next_time(unsigned long cur_time)
568 {
569 cur_time += VM_COMPLETIONS_PERIOD_LEN;
570 /* 0 has a special meaning... */
571 if (!cur_time)
572 return 1;
573 return cur_time;
574 }
575
576 static void wb_domain_writeout_inc(struct wb_domain *dom,
577 struct fprop_local_percpu *completions,
578 unsigned int max_prop_frac)
579 {
580 __fprop_inc_percpu_max(&dom->completions, completions,
581 max_prop_frac);
582 /* First event after period switching was turned off? */
583 if (!unlikely(dom->period_time)) {
584 /*
585 * We can race with other __bdi_writeout_inc calls here but
586 * it does not cause any harm since the resulting time when
587 * timer will fire and what is in writeout_period_time will be
588 * roughly the same.
589 */
590 dom->period_time = wp_next_time(jiffies);
591 mod_timer(&dom->period_timer, dom->period_time);
592 }
593 }
594
595 /*
596 * Increment @wb's writeout completion count and the global writeout
597 * completion count. Called from test_clear_page_writeback().
598 */
599 static inline void __wb_writeout_inc(struct bdi_writeback *wb)
600 {
601 struct wb_domain *cgdom;
602
603 __inc_wb_stat(wb, WB_WRITTEN);
604 wb_domain_writeout_inc(&global_wb_domain, &wb->completions,
605 wb->bdi->max_prop_frac);
606
607 cgdom = mem_cgroup_wb_domain(wb);
608 if (cgdom)
609 wb_domain_writeout_inc(cgdom, wb_memcg_completions(wb),
610 wb->bdi->max_prop_frac);
611 }
612
613 void wb_writeout_inc(struct bdi_writeback *wb)
614 {
615 unsigned long flags;
616
617 local_irq_save(flags);
618 __wb_writeout_inc(wb);
619 local_irq_restore(flags);
620 }
621 EXPORT_SYMBOL_GPL(wb_writeout_inc);
622
623 /*
624 * On idle system, we can be called long after we scheduled because we use
625 * deferred timers so count with missed periods.
626 */
627 static void writeout_period(unsigned long t)
628 {
629 struct wb_domain *dom = (void *)t;
630 int miss_periods = (jiffies - dom->period_time) /
631 VM_COMPLETIONS_PERIOD_LEN;
632
633 if (fprop_new_period(&dom->completions, miss_periods + 1)) {
634 dom->period_time = wp_next_time(dom->period_time +
635 miss_periods * VM_COMPLETIONS_PERIOD_LEN);
636 mod_timer(&dom->period_timer, dom->period_time);
637 } else {
638 /*
639 * Aging has zeroed all fractions. Stop wasting CPU on period
640 * updates.
641 */
642 dom->period_time = 0;
643 }
644 }
645
646 int wb_domain_init(struct wb_domain *dom, gfp_t gfp)
647 {
648 memset(dom, 0, sizeof(*dom));
649
650 spin_lock_init(&dom->lock);
651
652 init_timer_deferrable(&dom->period_timer);
653 dom->period_timer.function = writeout_period;
654 dom->period_timer.data = (unsigned long)dom;
655
656 dom->dirty_limit_tstamp = jiffies;
657
658 return fprop_global_init(&dom->completions, gfp);
659 }
660
661 #ifdef CONFIG_CGROUP_WRITEBACK
662 void wb_domain_exit(struct wb_domain *dom)
663 {
664 del_timer_sync(&dom->period_timer);
665 fprop_global_destroy(&dom->completions);
666 }
667 #endif
668
669 /*
670 * bdi_min_ratio keeps the sum of the minimum dirty shares of all
671 * registered backing devices, which, for obvious reasons, can not
672 * exceed 100%.
673 */
674 static unsigned int bdi_min_ratio;
675
676 int bdi_set_min_ratio(struct backing_dev_info *bdi, unsigned int min_ratio)
677 {
678 int ret = 0;
679
680 spin_lock_bh(&bdi_lock);
681 if (min_ratio > bdi->max_ratio) {
682 ret = -EINVAL;
683 } else {
684 min_ratio -= bdi->min_ratio;
685 if (bdi_min_ratio + min_ratio < 100) {
686 bdi_min_ratio += min_ratio;
687 bdi->min_ratio += min_ratio;
688 } else {
689 ret = -EINVAL;
690 }
691 }
692 spin_unlock_bh(&bdi_lock);
693
694 return ret;
695 }
696
697 int bdi_set_max_ratio(struct backing_dev_info *bdi, unsigned max_ratio)
698 {
699 int ret = 0;
700
701 if (max_ratio > 100)
702 return -EINVAL;
703
704 spin_lock_bh(&bdi_lock);
705 if (bdi->min_ratio > max_ratio) {
706 ret = -EINVAL;
707 } else {
708 bdi->max_ratio = max_ratio;
709 bdi->max_prop_frac = (FPROP_FRAC_BASE * max_ratio) / 100;
710 }
711 spin_unlock_bh(&bdi_lock);
712
713 return ret;
714 }
715 EXPORT_SYMBOL(bdi_set_max_ratio);
716
717 static unsigned long dirty_freerun_ceiling(unsigned long thresh,
718 unsigned long bg_thresh)
719 {
720 return (thresh + bg_thresh) / 2;
721 }
722
723 static unsigned long hard_dirty_limit(struct wb_domain *dom,
724 unsigned long thresh)
725 {
726 return max(thresh, dom->dirty_limit);
727 }
728
729 /*
730 * Memory which can be further allocated to a memcg domain is capped by
731 * system-wide clean memory excluding the amount being used in the domain.
732 */
733 static void mdtc_calc_avail(struct dirty_throttle_control *mdtc,
734 unsigned long filepages, unsigned long headroom)
735 {
736 struct dirty_throttle_control *gdtc = mdtc_gdtc(mdtc);
737 unsigned long clean = filepages - min(filepages, mdtc->dirty);
738 unsigned long global_clean = gdtc->avail - min(gdtc->avail, gdtc->dirty);
739 unsigned long other_clean = global_clean - min(global_clean, clean);
740
741 mdtc->avail = filepages + min(headroom, other_clean);
742 }
743
744 /**
745 * __wb_calc_thresh - @wb's share of dirty throttling threshold
746 * @dtc: dirty_throttle_context of interest
747 *
748 * Returns @wb's dirty limit in pages. The term "dirty" in the context of
749 * dirty balancing includes all PG_dirty, PG_writeback and NFS unstable pages.
750 *
751 * Note that balance_dirty_pages() will only seriously take it as a hard limit
752 * when sleeping max_pause per page is not enough to keep the dirty pages under
753 * control. For example, when the device is completely stalled due to some error
754 * conditions, or when there are 1000 dd tasks writing to a slow 10MB/s USB key.
755 * In the other normal situations, it acts more gently by throttling the tasks
756 * more (rather than completely block them) when the wb dirty pages go high.
757 *
758 * It allocates high/low dirty limits to fast/slow devices, in order to prevent
759 * - starving fast devices
760 * - piling up dirty pages (that will take long time to sync) on slow devices
761 *
762 * The wb's share of dirty limit will be adapting to its throughput and
763 * bounded by the bdi->min_ratio and/or bdi->max_ratio parameters, if set.
764 */
765 static unsigned long __wb_calc_thresh(struct dirty_throttle_control *dtc)
766 {
767 struct wb_domain *dom = dtc_dom(dtc);
768 unsigned long thresh = dtc->thresh;
769 u64 wb_thresh;
770 long numerator, denominator;
771 unsigned long wb_min_ratio, wb_max_ratio;
772
773 /*
774 * Calculate this BDI's share of the thresh ratio.
775 */
776 fprop_fraction_percpu(&dom->completions, dtc->wb_completions,
777 &numerator, &denominator);
778
779 wb_thresh = (thresh * (100 - bdi_min_ratio)) / 100;
780 wb_thresh *= numerator;
781 do_div(wb_thresh, denominator);
782
783 wb_min_max_ratio(dtc->wb, &wb_min_ratio, &wb_max_ratio);
784
785 wb_thresh += (thresh * wb_min_ratio) / 100;
786 if (wb_thresh > (thresh * wb_max_ratio) / 100)
787 wb_thresh = thresh * wb_max_ratio / 100;
788
789 return wb_thresh;
790 }
791
792 unsigned long wb_calc_thresh(struct bdi_writeback *wb, unsigned long thresh)
793 {
794 struct dirty_throttle_control gdtc = { GDTC_INIT(wb),
795 .thresh = thresh };
796 return __wb_calc_thresh(&gdtc);
797 }
798
799 /*
800 * setpoint - dirty 3
801 * f(dirty) := 1.0 + (----------------)
802 * limit - setpoint
803 *
804 * it's a 3rd order polynomial that subjects to
805 *
806 * (1) f(freerun) = 2.0 => rampup dirty_ratelimit reasonably fast
807 * (2) f(setpoint) = 1.0 => the balance point
808 * (3) f(limit) = 0 => the hard limit
809 * (4) df/dx <= 0 => negative feedback control
810 * (5) the closer to setpoint, the smaller |df/dx| (and the reverse)
811 * => fast response on large errors; small oscillation near setpoint
812 */
813 static long long pos_ratio_polynom(unsigned long setpoint,
814 unsigned long dirty,
815 unsigned long limit)
816 {
817 long long pos_ratio;
818 long x;
819
820 x = div64_s64(((s64)setpoint - (s64)dirty) << RATELIMIT_CALC_SHIFT,
821 (limit - setpoint) | 1);
822 pos_ratio = x;
823 pos_ratio = pos_ratio * x >> RATELIMIT_CALC_SHIFT;
824 pos_ratio = pos_ratio * x >> RATELIMIT_CALC_SHIFT;
825 pos_ratio += 1 << RATELIMIT_CALC_SHIFT;
826
827 return clamp(pos_ratio, 0LL, 2LL << RATELIMIT_CALC_SHIFT);
828 }
829
830 /*
831 * Dirty position control.
832 *
833 * (o) global/bdi setpoints
834 *
835 * We want the dirty pages be balanced around the global/wb setpoints.
836 * When the number of dirty pages is higher/lower than the setpoint, the
837 * dirty position control ratio (and hence task dirty ratelimit) will be
838 * decreased/increased to bring the dirty pages back to the setpoint.
839 *
840 * pos_ratio = 1 << RATELIMIT_CALC_SHIFT
841 *
842 * if (dirty < setpoint) scale up pos_ratio
843 * if (dirty > setpoint) scale down pos_ratio
844 *
845 * if (wb_dirty < wb_setpoint) scale up pos_ratio
846 * if (wb_dirty > wb_setpoint) scale down pos_ratio
847 *
848 * task_ratelimit = dirty_ratelimit * pos_ratio >> RATELIMIT_CALC_SHIFT
849 *
850 * (o) global control line
851 *
852 * ^ pos_ratio
853 * |
854 * | |<===== global dirty control scope ======>|
855 * 2.0 .............*
856 * | .*
857 * | . *
858 * | . *
859 * | . *
860 * | . *
861 * | . *
862 * 1.0 ................................*
863 * | . . *
864 * | . . *
865 * | . . *
866 * | . . *
867 * | . . *
868 * 0 +------------.------------------.----------------------*------------->
869 * freerun^ setpoint^ limit^ dirty pages
870 *
871 * (o) wb control line
872 *
873 * ^ pos_ratio
874 * |
875 * | *
876 * | *
877 * | *
878 * | *
879 * | * |<=========== span ============>|
880 * 1.0 .......................*
881 * | . *
882 * | . *
883 * | . *
884 * | . *
885 * | . *
886 * | . *
887 * | . *
888 * | . *
889 * | . *
890 * | . *
891 * | . *
892 * 1/4 ...............................................* * * * * * * * * * * *
893 * | . .
894 * | . .
895 * | . .
896 * 0 +----------------------.-------------------------------.------------->
897 * wb_setpoint^ x_intercept^
898 *
899 * The wb control line won't drop below pos_ratio=1/4, so that wb_dirty can
900 * be smoothly throttled down to normal if it starts high in situations like
901 * - start writing to a slow SD card and a fast disk at the same time. The SD
902 * card's wb_dirty may rush to many times higher than wb_setpoint.
903 * - the wb dirty thresh drops quickly due to change of JBOD workload
904 */
905 static void wb_position_ratio(struct dirty_throttle_control *dtc)
906 {
907 struct bdi_writeback *wb = dtc->wb;
908 unsigned long write_bw = wb->avg_write_bandwidth;
909 unsigned long freerun = dirty_freerun_ceiling(dtc->thresh, dtc->bg_thresh);
910 unsigned long limit = hard_dirty_limit(dtc_dom(dtc), dtc->thresh);
911 unsigned long wb_thresh = dtc->wb_thresh;
912 unsigned long x_intercept;
913 unsigned long setpoint; /* dirty pages' target balance point */
914 unsigned long wb_setpoint;
915 unsigned long span;
916 long long pos_ratio; /* for scaling up/down the rate limit */
917 long x;
918
919 dtc->pos_ratio = 0;
920
921 if (unlikely(dtc->dirty >= limit))
922 return;
923
924 /*
925 * global setpoint
926 *
927 * See comment for pos_ratio_polynom().
928 */
929 setpoint = (freerun + limit) / 2;
930 pos_ratio = pos_ratio_polynom(setpoint, dtc->dirty, limit);
931
932 /*
933 * The strictlimit feature is a tool preventing mistrusted filesystems
934 * from growing a large number of dirty pages before throttling. For
935 * such filesystems balance_dirty_pages always checks wb counters
936 * against wb limits. Even if global "nr_dirty" is under "freerun".
937 * This is especially important for fuse which sets bdi->max_ratio to
938 * 1% by default. Without strictlimit feature, fuse writeback may
939 * consume arbitrary amount of RAM because it is accounted in
940 * NR_WRITEBACK_TEMP which is not involved in calculating "nr_dirty".
941 *
942 * Here, in wb_position_ratio(), we calculate pos_ratio based on
943 * two values: wb_dirty and wb_thresh. Let's consider an example:
944 * total amount of RAM is 16GB, bdi->max_ratio is equal to 1%, global
945 * limits are set by default to 10% and 20% (background and throttle).
946 * Then wb_thresh is 1% of 20% of 16GB. This amounts to ~8K pages.
947 * wb_calc_thresh(wb, bg_thresh) is about ~4K pages. wb_setpoint is
948 * about ~6K pages (as the average of background and throttle wb
949 * limits). The 3rd order polynomial will provide positive feedback if
950 * wb_dirty is under wb_setpoint and vice versa.
951 *
952 * Note, that we cannot use global counters in these calculations
953 * because we want to throttle process writing to a strictlimit wb
954 * much earlier than global "freerun" is reached (~23MB vs. ~2.3GB
955 * in the example above).
956 */
957 if (unlikely(wb->bdi->capabilities & BDI_CAP_STRICTLIMIT)) {
958 long long wb_pos_ratio;
959
960 if (dtc->wb_dirty < 8) {
961 dtc->pos_ratio = min_t(long long, pos_ratio * 2,
962 2 << RATELIMIT_CALC_SHIFT);
963 return;
964 }
965
966 if (dtc->wb_dirty >= wb_thresh)
967 return;
968
969 wb_setpoint = dirty_freerun_ceiling(wb_thresh,
970 dtc->wb_bg_thresh);
971
972 if (wb_setpoint == 0 || wb_setpoint == wb_thresh)
973 return;
974
975 wb_pos_ratio = pos_ratio_polynom(wb_setpoint, dtc->wb_dirty,
976 wb_thresh);
977
978 /*
979 * Typically, for strictlimit case, wb_setpoint << setpoint
980 * and pos_ratio >> wb_pos_ratio. In the other words global
981 * state ("dirty") is not limiting factor and we have to
982 * make decision based on wb counters. But there is an
983 * important case when global pos_ratio should get precedence:
984 * global limits are exceeded (e.g. due to activities on other
985 * wb's) while given strictlimit wb is below limit.
986 *
987 * "pos_ratio * wb_pos_ratio" would work for the case above,
988 * but it would look too non-natural for the case of all
989 * activity in the system coming from a single strictlimit wb
990 * with bdi->max_ratio == 100%.
991 *
992 * Note that min() below somewhat changes the dynamics of the
993 * control system. Normally, pos_ratio value can be well over 3
994 * (when globally we are at freerun and wb is well below wb
995 * setpoint). Now the maximum pos_ratio in the same situation
996 * is 2. We might want to tweak this if we observe the control
997 * system is too slow to adapt.
998 */
999 dtc->pos_ratio = min(pos_ratio, wb_pos_ratio);
1000 return;
1001 }
1002
1003 /*
1004 * We have computed basic pos_ratio above based on global situation. If
1005 * the wb is over/under its share of dirty pages, we want to scale
1006 * pos_ratio further down/up. That is done by the following mechanism.
1007 */
1008
1009 /*
1010 * wb setpoint
1011 *
1012 * f(wb_dirty) := 1.0 + k * (wb_dirty - wb_setpoint)
1013 *
1014 * x_intercept - wb_dirty
1015 * := --------------------------
1016 * x_intercept - wb_setpoint
1017 *
1018 * The main wb control line is a linear function that subjects to
1019 *
1020 * (1) f(wb_setpoint) = 1.0
1021 * (2) k = - 1 / (8 * write_bw) (in single wb case)
1022 * or equally: x_intercept = wb_setpoint + 8 * write_bw
1023 *
1024 * For single wb case, the dirty pages are observed to fluctuate
1025 * regularly within range
1026 * [wb_setpoint - write_bw/2, wb_setpoint + write_bw/2]
1027 * for various filesystems, where (2) can yield in a reasonable 12.5%
1028 * fluctuation range for pos_ratio.
1029 *
1030 * For JBOD case, wb_thresh (not wb_dirty!) could fluctuate up to its
1031 * own size, so move the slope over accordingly and choose a slope that
1032 * yields 100% pos_ratio fluctuation on suddenly doubled wb_thresh.
1033 */
1034 if (unlikely(wb_thresh > dtc->thresh))
1035 wb_thresh = dtc->thresh;
1036 /*
1037 * It's very possible that wb_thresh is close to 0 not because the
1038 * device is slow, but that it has remained inactive for long time.
1039 * Honour such devices a reasonable good (hopefully IO efficient)
1040 * threshold, so that the occasional writes won't be blocked and active
1041 * writes can rampup the threshold quickly.
1042 */
1043 wb_thresh = max(wb_thresh, (limit - dtc->dirty) / 8);
1044 /*
1045 * scale global setpoint to wb's:
1046 * wb_setpoint = setpoint * wb_thresh / thresh
1047 */
1048 x = div_u64((u64)wb_thresh << 16, dtc->thresh | 1);
1049 wb_setpoint = setpoint * (u64)x >> 16;
1050 /*
1051 * Use span=(8*write_bw) in single wb case as indicated by
1052 * (thresh - wb_thresh ~= 0) and transit to wb_thresh in JBOD case.
1053 *
1054 * wb_thresh thresh - wb_thresh
1055 * span = --------- * (8 * write_bw) + ------------------ * wb_thresh
1056 * thresh thresh
1057 */
1058 span = (dtc->thresh - wb_thresh + 8 * write_bw) * (u64)x >> 16;
1059 x_intercept = wb_setpoint + span;
1060
1061 if (dtc->wb_dirty < x_intercept - span / 4) {
1062 pos_ratio = div64_u64(pos_ratio * (x_intercept - dtc->wb_dirty),
1063 (x_intercept - wb_setpoint) | 1);
1064 } else
1065 pos_ratio /= 4;
1066
1067 /*
1068 * wb reserve area, safeguard against dirty pool underrun and disk idle
1069 * It may push the desired control point of global dirty pages higher
1070 * than setpoint.
1071 */
1072 x_intercept = wb_thresh / 2;
1073 if (dtc->wb_dirty < x_intercept) {
1074 if (dtc->wb_dirty > x_intercept / 8)
1075 pos_ratio = div_u64(pos_ratio * x_intercept,
1076 dtc->wb_dirty);
1077 else
1078 pos_ratio *= 8;
1079 }
1080
1081 dtc->pos_ratio = pos_ratio;
1082 }
1083
1084 static void wb_update_write_bandwidth(struct bdi_writeback *wb,
1085 unsigned long elapsed,
1086 unsigned long written)
1087 {
1088 const unsigned long period = roundup_pow_of_two(3 * HZ);
1089 unsigned long avg = wb->avg_write_bandwidth;
1090 unsigned long old = wb->write_bandwidth;
1091 u64 bw;
1092
1093 /*
1094 * bw = written * HZ / elapsed
1095 *
1096 * bw * elapsed + write_bandwidth * (period - elapsed)
1097 * write_bandwidth = ---------------------------------------------------
1098 * period
1099 *
1100 * @written may have decreased due to account_page_redirty().
1101 * Avoid underflowing @bw calculation.
1102 */
1103 bw = written - min(written, wb->written_stamp);
1104 bw *= HZ;
1105 if (unlikely(elapsed > period)) {
1106 do_div(bw, elapsed);
1107 avg = bw;
1108 goto out;
1109 }
1110 bw += (u64)wb->write_bandwidth * (period - elapsed);
1111 bw >>= ilog2(period);
1112
1113 /*
1114 * one more level of smoothing, for filtering out sudden spikes
1115 */
1116 if (avg > old && old >= (unsigned long)bw)
1117 avg -= (avg - old) >> 3;
1118
1119 if (avg < old && old <= (unsigned long)bw)
1120 avg += (old - avg) >> 3;
1121
1122 out:
1123 /* keep avg > 0 to guarantee that tot > 0 if there are dirty wbs */
1124 avg = max(avg, 1LU);
1125 if (wb_has_dirty_io(wb)) {
1126 long delta = avg - wb->avg_write_bandwidth;
1127 WARN_ON_ONCE(atomic_long_add_return(delta,
1128 &wb->bdi->tot_write_bandwidth) <= 0);
1129 }
1130 wb->write_bandwidth = bw;
1131 wb->avg_write_bandwidth = avg;
1132 }
1133
1134 static void update_dirty_limit(struct dirty_throttle_control *dtc)
1135 {
1136 struct wb_domain *dom = dtc_dom(dtc);
1137 unsigned long thresh = dtc->thresh;
1138 unsigned long limit = dom->dirty_limit;
1139
1140 /*
1141 * Follow up in one step.
1142 */
1143 if (limit < thresh) {
1144 limit = thresh;
1145 goto update;
1146 }
1147
1148 /*
1149 * Follow down slowly. Use the higher one as the target, because thresh
1150 * may drop below dirty. This is exactly the reason to introduce
1151 * dom->dirty_limit which is guaranteed to lie above the dirty pages.
1152 */
1153 thresh = max(thresh, dtc->dirty);
1154 if (limit > thresh) {
1155 limit -= (limit - thresh) >> 5;
1156 goto update;
1157 }
1158 return;
1159 update:
1160 dom->dirty_limit = limit;
1161 }
1162
1163 static void domain_update_bandwidth(struct dirty_throttle_control *dtc,
1164 unsigned long now)
1165 {
1166 struct wb_domain *dom = dtc_dom(dtc);
1167
1168 /*
1169 * check locklessly first to optimize away locking for the most time
1170 */
1171 if (time_before(now, dom->dirty_limit_tstamp + BANDWIDTH_INTERVAL))
1172 return;
1173
1174 spin_lock(&dom->lock);
1175 if (time_after_eq(now, dom->dirty_limit_tstamp + BANDWIDTH_INTERVAL)) {
1176 update_dirty_limit(dtc);
1177 dom->dirty_limit_tstamp = now;
1178 }
1179 spin_unlock(&dom->lock);
1180 }
1181
1182 /*
1183 * Maintain wb->dirty_ratelimit, the base dirty throttle rate.
1184 *
1185 * Normal wb tasks will be curbed at or below it in long term.
1186 * Obviously it should be around (write_bw / N) when there are N dd tasks.
1187 */
1188 static void wb_update_dirty_ratelimit(struct dirty_throttle_control *dtc,
1189 unsigned long dirtied,
1190 unsigned long elapsed)
1191 {
1192 struct bdi_writeback *wb = dtc->wb;
1193 unsigned long dirty = dtc->dirty;
1194 unsigned long freerun = dirty_freerun_ceiling(dtc->thresh, dtc->bg_thresh);
1195 unsigned long limit = hard_dirty_limit(dtc_dom(dtc), dtc->thresh);
1196 unsigned long setpoint = (freerun + limit) / 2;
1197 unsigned long write_bw = wb->avg_write_bandwidth;
1198 unsigned long dirty_ratelimit = wb->dirty_ratelimit;
1199 unsigned long dirty_rate;
1200 unsigned long task_ratelimit;
1201 unsigned long balanced_dirty_ratelimit;
1202 unsigned long step;
1203 unsigned long x;
1204 unsigned long shift;
1205
1206 /*
1207 * The dirty rate will match the writeout rate in long term, except
1208 * when dirty pages are truncated by userspace or re-dirtied by FS.
1209 */
1210 dirty_rate = (dirtied - wb->dirtied_stamp) * HZ / elapsed;
1211
1212 /*
1213 * task_ratelimit reflects each dd's dirty rate for the past 200ms.
1214 */
1215 task_ratelimit = (u64)dirty_ratelimit *
1216 dtc->pos_ratio >> RATELIMIT_CALC_SHIFT;
1217 task_ratelimit++; /* it helps rampup dirty_ratelimit from tiny values */
1218
1219 /*
1220 * A linear estimation of the "balanced" throttle rate. The theory is,
1221 * if there are N dd tasks, each throttled at task_ratelimit, the wb's
1222 * dirty_rate will be measured to be (N * task_ratelimit). So the below
1223 * formula will yield the balanced rate limit (write_bw / N).
1224 *
1225 * Note that the expanded form is not a pure rate feedback:
1226 * rate_(i+1) = rate_(i) * (write_bw / dirty_rate) (1)
1227 * but also takes pos_ratio into account:
1228 * rate_(i+1) = rate_(i) * (write_bw / dirty_rate) * pos_ratio (2)
1229 *
1230 * (1) is not realistic because pos_ratio also takes part in balancing
1231 * the dirty rate. Consider the state
1232 * pos_ratio = 0.5 (3)
1233 * rate = 2 * (write_bw / N) (4)
1234 * If (1) is used, it will stuck in that state! Because each dd will
1235 * be throttled at
1236 * task_ratelimit = pos_ratio * rate = (write_bw / N) (5)
1237 * yielding
1238 * dirty_rate = N * task_ratelimit = write_bw (6)
1239 * put (6) into (1) we get
1240 * rate_(i+1) = rate_(i) (7)
1241 *
1242 * So we end up using (2) to always keep
1243 * rate_(i+1) ~= (write_bw / N) (8)
1244 * regardless of the value of pos_ratio. As long as (8) is satisfied,
1245 * pos_ratio is able to drive itself to 1.0, which is not only where
1246 * the dirty count meet the setpoint, but also where the slope of
1247 * pos_ratio is most flat and hence task_ratelimit is least fluctuated.
1248 */
1249 balanced_dirty_ratelimit = div_u64((u64)task_ratelimit * write_bw,
1250 dirty_rate | 1);
1251 /*
1252 * balanced_dirty_ratelimit ~= (write_bw / N) <= write_bw
1253 */
1254 if (unlikely(balanced_dirty_ratelimit > write_bw))
1255 balanced_dirty_ratelimit = write_bw;
1256
1257 /*
1258 * We could safely do this and return immediately:
1259 *
1260 * wb->dirty_ratelimit = balanced_dirty_ratelimit;
1261 *
1262 * However to get a more stable dirty_ratelimit, the below elaborated
1263 * code makes use of task_ratelimit to filter out singular points and
1264 * limit the step size.
1265 *
1266 * The below code essentially only uses the relative value of
1267 *
1268 * task_ratelimit - dirty_ratelimit
1269 * = (pos_ratio - 1) * dirty_ratelimit
1270 *
1271 * which reflects the direction and size of dirty position error.
1272 */
1273
1274 /*
1275 * dirty_ratelimit will follow balanced_dirty_ratelimit iff
1276 * task_ratelimit is on the same side of dirty_ratelimit, too.
1277 * For example, when
1278 * - dirty_ratelimit > balanced_dirty_ratelimit
1279 * - dirty_ratelimit > task_ratelimit (dirty pages are above setpoint)
1280 * lowering dirty_ratelimit will help meet both the position and rate
1281 * control targets. Otherwise, don't update dirty_ratelimit if it will
1282 * only help meet the rate target. After all, what the users ultimately
1283 * feel and care are stable dirty rate and small position error.
1284 *
1285 * |task_ratelimit - dirty_ratelimit| is used to limit the step size
1286 * and filter out the singular points of balanced_dirty_ratelimit. Which
1287 * keeps jumping around randomly and can even leap far away at times
1288 * due to the small 200ms estimation period of dirty_rate (we want to
1289 * keep that period small to reduce time lags).
1290 */
1291 step = 0;
1292
1293 /*
1294 * For strictlimit case, calculations above were based on wb counters
1295 * and limits (starting from pos_ratio = wb_position_ratio() and up to
1296 * balanced_dirty_ratelimit = task_ratelimit * write_bw / dirty_rate).
1297 * Hence, to calculate "step" properly, we have to use wb_dirty as
1298 * "dirty" and wb_setpoint as "setpoint".
1299 *
1300 * We rampup dirty_ratelimit forcibly if wb_dirty is low because
1301 * it's possible that wb_thresh is close to zero due to inactivity
1302 * of backing device.
1303 */
1304 if (unlikely(wb->bdi->capabilities & BDI_CAP_STRICTLIMIT)) {
1305 dirty = dtc->wb_dirty;
1306 if (dtc->wb_dirty < 8)
1307 setpoint = dtc->wb_dirty + 1;
1308 else
1309 setpoint = (dtc->wb_thresh + dtc->wb_bg_thresh) / 2;
1310 }
1311
1312 if (dirty < setpoint) {
1313 x = min3(wb->balanced_dirty_ratelimit,
1314 balanced_dirty_ratelimit, task_ratelimit);
1315 if (dirty_ratelimit < x)
1316 step = x - dirty_ratelimit;
1317 } else {
1318 x = max3(wb->balanced_dirty_ratelimit,
1319 balanced_dirty_ratelimit, task_ratelimit);
1320 if (dirty_ratelimit > x)
1321 step = dirty_ratelimit - x;
1322 }
1323
1324 /*
1325 * Don't pursue 100% rate matching. It's impossible since the balanced
1326 * rate itself is constantly fluctuating. So decrease the track speed
1327 * when it gets close to the target. Helps eliminate pointless tremors.
1328 */
1329 shift = dirty_ratelimit / (2 * step + 1);
1330 if (shift < BITS_PER_LONG)
1331 step = DIV_ROUND_UP(step >> shift, 8);
1332 else
1333 step = 0;
1334
1335 if (dirty_ratelimit < balanced_dirty_ratelimit)
1336 dirty_ratelimit += step;
1337 else
1338 dirty_ratelimit -= step;
1339
1340 wb->dirty_ratelimit = max(dirty_ratelimit, 1UL);
1341 wb->balanced_dirty_ratelimit = balanced_dirty_ratelimit;
1342
1343 trace_bdi_dirty_ratelimit(wb, dirty_rate, task_ratelimit);
1344 }
1345
1346 static void __wb_update_bandwidth(struct dirty_throttle_control *gdtc,
1347 struct dirty_throttle_control *mdtc,
1348 unsigned long start_time,
1349 bool update_ratelimit)
1350 {
1351 struct bdi_writeback *wb = gdtc->wb;
1352 unsigned long now = jiffies;
1353 unsigned long elapsed = now - wb->bw_time_stamp;
1354 unsigned long dirtied;
1355 unsigned long written;
1356
1357 lockdep_assert_held(&wb->list_lock);
1358
1359 /*
1360 * rate-limit, only update once every 200ms.
1361 */
1362 if (elapsed < BANDWIDTH_INTERVAL)
1363 return;
1364
1365 dirtied = percpu_counter_read(&wb->stat[WB_DIRTIED]);
1366 written = percpu_counter_read(&wb->stat[WB_WRITTEN]);
1367
1368 /*
1369 * Skip quiet periods when disk bandwidth is under-utilized.
1370 * (at least 1s idle time between two flusher runs)
1371 */
1372 if (elapsed > HZ && time_before(wb->bw_time_stamp, start_time))
1373 goto snapshot;
1374
1375 if (update_ratelimit) {
1376 domain_update_bandwidth(gdtc, now);
1377 wb_update_dirty_ratelimit(gdtc, dirtied, elapsed);
1378
1379 /*
1380 * @mdtc is always NULL if !CGROUP_WRITEBACK but the
1381 * compiler has no way to figure that out. Help it.
1382 */
1383 if (IS_ENABLED(CONFIG_CGROUP_WRITEBACK) && mdtc) {
1384 domain_update_bandwidth(mdtc, now);
1385 wb_update_dirty_ratelimit(mdtc, dirtied, elapsed);
1386 }
1387 }
1388 wb_update_write_bandwidth(wb, elapsed, written);
1389
1390 snapshot:
1391 wb->dirtied_stamp = dirtied;
1392 wb->written_stamp = written;
1393 wb->bw_time_stamp = now;
1394 }
1395
1396 void wb_update_bandwidth(struct bdi_writeback *wb, unsigned long start_time)
1397 {
1398 struct dirty_throttle_control gdtc = { GDTC_INIT(wb) };
1399
1400 __wb_update_bandwidth(&gdtc, NULL, start_time, false);
1401 }
1402
1403 /*
1404 * After a task dirtied this many pages, balance_dirty_pages_ratelimited()
1405 * will look to see if it needs to start dirty throttling.
1406 *
1407 * If dirty_poll_interval is too low, big NUMA machines will call the expensive
1408 * global_page_state() too often. So scale it near-sqrt to the safety margin
1409 * (the number of pages we may dirty without exceeding the dirty limits).
1410 */
1411 static unsigned long dirty_poll_interval(unsigned long dirty,
1412 unsigned long thresh)
1413 {
1414 if (thresh > dirty)
1415 return 1UL << (ilog2(thresh - dirty) >> 1);
1416
1417 return 1;
1418 }
1419
1420 static unsigned long wb_max_pause(struct bdi_writeback *wb,
1421 unsigned long wb_dirty)
1422 {
1423 unsigned long bw = wb->avg_write_bandwidth;
1424 unsigned long t;
1425
1426 /*
1427 * Limit pause time for small memory systems. If sleeping for too long
1428 * time, a small pool of dirty/writeback pages may go empty and disk go
1429 * idle.
1430 *
1431 * 8 serves as the safety ratio.
1432 */
1433 t = wb_dirty / (1 + bw / roundup_pow_of_two(1 + HZ / 8));
1434 t++;
1435
1436 return min_t(unsigned long, t, MAX_PAUSE);
1437 }
1438
1439 static long wb_min_pause(struct bdi_writeback *wb,
1440 long max_pause,
1441 unsigned long task_ratelimit,
1442 unsigned long dirty_ratelimit,
1443 int *nr_dirtied_pause)
1444 {
1445 long hi = ilog2(wb->avg_write_bandwidth);
1446 long lo = ilog2(wb->dirty_ratelimit);
1447 long t; /* target pause */
1448 long pause; /* estimated next pause */
1449 int pages; /* target nr_dirtied_pause */
1450
1451 /* target for 10ms pause on 1-dd case */
1452 t = max(1, HZ / 100);
1453
1454 /*
1455 * Scale up pause time for concurrent dirtiers in order to reduce CPU
1456 * overheads.
1457 *
1458 * (N * 10ms) on 2^N concurrent tasks.
1459 */
1460 if (hi > lo)
1461 t += (hi - lo) * (10 * HZ) / 1024;
1462
1463 /*
1464 * This is a bit convoluted. We try to base the next nr_dirtied_pause
1465 * on the much more stable dirty_ratelimit. However the next pause time
1466 * will be computed based on task_ratelimit and the two rate limits may
1467 * depart considerably at some time. Especially if task_ratelimit goes
1468 * below dirty_ratelimit/2 and the target pause is max_pause, the next
1469 * pause time will be max_pause*2 _trimmed down_ to max_pause. As a
1470 * result task_ratelimit won't be executed faithfully, which could
1471 * eventually bring down dirty_ratelimit.
1472 *
1473 * We apply two rules to fix it up:
1474 * 1) try to estimate the next pause time and if necessary, use a lower
1475 * nr_dirtied_pause so as not to exceed max_pause. When this happens,
1476 * nr_dirtied_pause will be "dancing" with task_ratelimit.
1477 * 2) limit the target pause time to max_pause/2, so that the normal
1478 * small fluctuations of task_ratelimit won't trigger rule (1) and
1479 * nr_dirtied_pause will remain as stable as dirty_ratelimit.
1480 */
1481 t = min(t, 1 + max_pause / 2);
1482 pages = dirty_ratelimit * t / roundup_pow_of_two(HZ);
1483
1484 /*
1485 * Tiny nr_dirtied_pause is found to hurt I/O performance in the test
1486 * case fio-mmap-randwrite-64k, which does 16*{sync read, async write}.
1487 * When the 16 consecutive reads are often interrupted by some dirty
1488 * throttling pause during the async writes, cfq will go into idles
1489 * (deadline is fine). So push nr_dirtied_pause as high as possible
1490 * until reaches DIRTY_POLL_THRESH=32 pages.
1491 */
1492 if (pages < DIRTY_POLL_THRESH) {
1493 t = max_pause;
1494 pages = dirty_ratelimit * t / roundup_pow_of_two(HZ);
1495 if (pages > DIRTY_POLL_THRESH) {
1496 pages = DIRTY_POLL_THRESH;
1497 t = HZ * DIRTY_POLL_THRESH / dirty_ratelimit;
1498 }
1499 }
1500
1501 pause = HZ * pages / (task_ratelimit + 1);
1502 if (pause > max_pause) {
1503 t = max_pause;
1504 pages = task_ratelimit * t / roundup_pow_of_two(HZ);
1505 }
1506
1507 *nr_dirtied_pause = pages;
1508 /*
1509 * The minimal pause time will normally be half the target pause time.
1510 */
1511 return pages >= DIRTY_POLL_THRESH ? 1 + t / 2 : t;
1512 }
1513
1514 static inline void wb_dirty_limits(struct dirty_throttle_control *dtc)
1515 {
1516 struct bdi_writeback *wb = dtc->wb;
1517 unsigned long wb_reclaimable;
1518
1519 /*
1520 * wb_thresh is not treated as some limiting factor as
1521 * dirty_thresh, due to reasons
1522 * - in JBOD setup, wb_thresh can fluctuate a lot
1523 * - in a system with HDD and USB key, the USB key may somehow
1524 * go into state (wb_dirty >> wb_thresh) either because
1525 * wb_dirty starts high, or because wb_thresh drops low.
1526 * In this case we don't want to hard throttle the USB key
1527 * dirtiers for 100 seconds until wb_dirty drops under
1528 * wb_thresh. Instead the auxiliary wb control line in
1529 * wb_position_ratio() will let the dirtier task progress
1530 * at some rate <= (write_bw / 2) for bringing down wb_dirty.
1531 */
1532 dtc->wb_thresh = __wb_calc_thresh(dtc);
1533 dtc->wb_bg_thresh = dtc->thresh ?
1534 div_u64((u64)dtc->wb_thresh * dtc->bg_thresh, dtc->thresh) : 0;
1535
1536 /*
1537 * In order to avoid the stacked BDI deadlock we need
1538 * to ensure we accurately count the 'dirty' pages when
1539 * the threshold is low.
1540 *
1541 * Otherwise it would be possible to get thresh+n pages
1542 * reported dirty, even though there are thresh-m pages
1543 * actually dirty; with m+n sitting in the percpu
1544 * deltas.
1545 */
1546 if (dtc->wb_thresh < 2 * wb_stat_error(wb)) {
1547 wb_reclaimable = wb_stat_sum(wb, WB_RECLAIMABLE);
1548 dtc->wb_dirty = wb_reclaimable + wb_stat_sum(wb, WB_WRITEBACK);
1549 } else {
1550 wb_reclaimable = wb_stat(wb, WB_RECLAIMABLE);
1551 dtc->wb_dirty = wb_reclaimable + wb_stat(wb, WB_WRITEBACK);
1552 }
1553 }
1554
1555 /*
1556 * balance_dirty_pages() must be called by processes which are generating dirty
1557 * data. It looks at the number of dirty pages in the machine and will force
1558 * the caller to wait once crossing the (background_thresh + dirty_thresh) / 2.
1559 * If we're over `background_thresh' then the writeback threads are woken to
1560 * perform some writeout.
1561 */
1562 static void balance_dirty_pages(struct address_space *mapping,
1563 struct bdi_writeback *wb,
1564 unsigned long pages_dirtied)
1565 {
1566 struct dirty_throttle_control gdtc_stor = { GDTC_INIT(wb) };
1567 struct dirty_throttle_control mdtc_stor = { MDTC_INIT(wb, &gdtc_stor) };
1568 struct dirty_throttle_control * const gdtc = &gdtc_stor;
1569 struct dirty_throttle_control * const mdtc = mdtc_valid(&mdtc_stor) ?
1570 &mdtc_stor : NULL;
1571 struct dirty_throttle_control *sdtc;
1572 unsigned long nr_reclaimable; /* = file_dirty + unstable_nfs */
1573 long period;
1574 long pause;
1575 long max_pause;
1576 long min_pause;
1577 int nr_dirtied_pause;
1578 bool dirty_exceeded = false;
1579 unsigned long task_ratelimit;
1580 unsigned long dirty_ratelimit;
1581 struct backing_dev_info *bdi = wb->bdi;
1582 bool strictlimit = bdi->capabilities & BDI_CAP_STRICTLIMIT;
1583 unsigned long start_time = jiffies;
1584
1585 for (;;) {
1586 unsigned long now = jiffies;
1587 unsigned long dirty, thresh, bg_thresh;
1588 unsigned long m_dirty = 0; /* stop bogus uninit warnings */
1589 unsigned long m_thresh = 0;
1590 unsigned long m_bg_thresh = 0;
1591
1592 /*
1593 * Unstable writes are a feature of certain networked
1594 * filesystems (i.e. NFS) in which data may have been
1595 * written to the server's write cache, but has not yet
1596 * been flushed to permanent storage.
1597 */
1598 nr_reclaimable = global_node_page_state(NR_FILE_DIRTY) +
1599 global_node_page_state(NR_UNSTABLE_NFS);
1600 gdtc->avail = global_dirtyable_memory();
1601 gdtc->dirty = nr_reclaimable + global_node_page_state(NR_WRITEBACK);
1602
1603 domain_dirty_limits(gdtc);
1604
1605 if (unlikely(strictlimit)) {
1606 wb_dirty_limits(gdtc);
1607
1608 dirty = gdtc->wb_dirty;
1609 thresh = gdtc->wb_thresh;
1610 bg_thresh = gdtc->wb_bg_thresh;
1611 } else {
1612 dirty = gdtc->dirty;
1613 thresh = gdtc->thresh;
1614 bg_thresh = gdtc->bg_thresh;
1615 }
1616
1617 if (mdtc) {
1618 unsigned long filepages, headroom, writeback;
1619
1620 /*
1621 * If @wb belongs to !root memcg, repeat the same
1622 * basic calculations for the memcg domain.
1623 */
1624 mem_cgroup_wb_stats(wb, &filepages, &headroom,
1625 &mdtc->dirty, &writeback);
1626 mdtc->dirty += writeback;
1627 mdtc_calc_avail(mdtc, filepages, headroom);
1628
1629 domain_dirty_limits(mdtc);
1630
1631 if (unlikely(strictlimit)) {
1632 wb_dirty_limits(mdtc);
1633 m_dirty = mdtc->wb_dirty;
1634 m_thresh = mdtc->wb_thresh;
1635 m_bg_thresh = mdtc->wb_bg_thresh;
1636 } else {
1637 m_dirty = mdtc->dirty;
1638 m_thresh = mdtc->thresh;
1639 m_bg_thresh = mdtc->bg_thresh;
1640 }
1641 }
1642
1643 /*
1644 * Throttle it only when the background writeback cannot
1645 * catch-up. This avoids (excessively) small writeouts
1646 * when the wb limits are ramping up in case of !strictlimit.
1647 *
1648 * In strictlimit case make decision based on the wb counters
1649 * and limits. Small writeouts when the wb limits are ramping
1650 * up are the price we consciously pay for strictlimit-ing.
1651 *
1652 * If memcg domain is in effect, @dirty should be under
1653 * both global and memcg freerun ceilings.
1654 */
1655 if (dirty <= dirty_freerun_ceiling(thresh, bg_thresh) &&
1656 (!mdtc ||
1657 m_dirty <= dirty_freerun_ceiling(m_thresh, m_bg_thresh))) {
1658 unsigned long intv = dirty_poll_interval(dirty, thresh);
1659 unsigned long m_intv = ULONG_MAX;
1660
1661 current->dirty_paused_when = now;
1662 current->nr_dirtied = 0;
1663 if (mdtc)
1664 m_intv = dirty_poll_interval(m_dirty, m_thresh);
1665 current->nr_dirtied_pause = min(intv, m_intv);
1666 break;
1667 }
1668
1669 if (unlikely(!writeback_in_progress(wb)))
1670 wb_start_background_writeback(wb);
1671
1672 /*
1673 * Calculate global domain's pos_ratio and select the
1674 * global dtc by default.
1675 */
1676 if (!strictlimit)
1677 wb_dirty_limits(gdtc);
1678
1679 dirty_exceeded = (gdtc->wb_dirty > gdtc->wb_thresh) &&
1680 ((gdtc->dirty > gdtc->thresh) || strictlimit);
1681
1682 wb_position_ratio(gdtc);
1683 sdtc = gdtc;
1684
1685 if (mdtc) {
1686 /*
1687 * If memcg domain is in effect, calculate its
1688 * pos_ratio. @wb should satisfy constraints from
1689 * both global and memcg domains. Choose the one
1690 * w/ lower pos_ratio.
1691 */
1692 if (!strictlimit)
1693 wb_dirty_limits(mdtc);
1694
1695 dirty_exceeded |= (mdtc->wb_dirty > mdtc->wb_thresh) &&
1696 ((mdtc->dirty > mdtc->thresh) || strictlimit);
1697
1698 wb_position_ratio(mdtc);
1699 if (mdtc->pos_ratio < gdtc->pos_ratio)
1700 sdtc = mdtc;
1701 }
1702
1703 if (dirty_exceeded && !wb->dirty_exceeded)
1704 wb->dirty_exceeded = 1;
1705
1706 if (time_is_before_jiffies(wb->bw_time_stamp +
1707 BANDWIDTH_INTERVAL)) {
1708 spin_lock(&wb->list_lock);
1709 __wb_update_bandwidth(gdtc, mdtc, start_time, true);
1710 spin_unlock(&wb->list_lock);
1711 }
1712
1713 /* throttle according to the chosen dtc */
1714 dirty_ratelimit = wb->dirty_ratelimit;
1715 task_ratelimit = ((u64)dirty_ratelimit * sdtc->pos_ratio) >>
1716 RATELIMIT_CALC_SHIFT;
1717 max_pause = wb_max_pause(wb, sdtc->wb_dirty);
1718 min_pause = wb_min_pause(wb, max_pause,
1719 task_ratelimit, dirty_ratelimit,
1720 &nr_dirtied_pause);
1721
1722 if (unlikely(task_ratelimit == 0)) {
1723 period = max_pause;
1724 pause = max_pause;
1725 goto pause;
1726 }
1727 period = HZ * pages_dirtied / task_ratelimit;
1728 pause = period;
1729 if (current->dirty_paused_when)
1730 pause -= now - current->dirty_paused_when;
1731 /*
1732 * For less than 1s think time (ext3/4 may block the dirtier
1733 * for up to 800ms from time to time on 1-HDD; so does xfs,
1734 * however at much less frequency), try to compensate it in
1735 * future periods by updating the virtual time; otherwise just
1736 * do a reset, as it may be a light dirtier.
1737 */
1738 if (pause < min_pause) {
1739 trace_balance_dirty_pages(wb,
1740 sdtc->thresh,
1741 sdtc->bg_thresh,
1742 sdtc->dirty,
1743 sdtc->wb_thresh,
1744 sdtc->wb_dirty,
1745 dirty_ratelimit,
1746 task_ratelimit,
1747 pages_dirtied,
1748 period,
1749 min(pause, 0L),
1750 start_time);
1751 if (pause < -HZ) {
1752 current->dirty_paused_when = now;
1753 current->nr_dirtied = 0;
1754 } else if (period) {
1755 current->dirty_paused_when += period;
1756 current->nr_dirtied = 0;
1757 } else if (current->nr_dirtied_pause <= pages_dirtied)
1758 current->nr_dirtied_pause += pages_dirtied;
1759 break;
1760 }
1761 if (unlikely(pause > max_pause)) {
1762 /* for occasional dropped task_ratelimit */
1763 now += min(pause - max_pause, max_pause);
1764 pause = max_pause;
1765 }
1766
1767 pause:
1768 trace_balance_dirty_pages(wb,
1769 sdtc->thresh,
1770 sdtc->bg_thresh,
1771 sdtc->dirty,
1772 sdtc->wb_thresh,
1773 sdtc->wb_dirty,
1774 dirty_ratelimit,
1775 task_ratelimit,
1776 pages_dirtied,
1777 period,
1778 pause,
1779 start_time);
1780 __set_current_state(TASK_KILLABLE);
1781 io_schedule_timeout(pause);
1782
1783 current->dirty_paused_when = now + pause;
1784 current->nr_dirtied = 0;
1785 current->nr_dirtied_pause = nr_dirtied_pause;
1786
1787 /*
1788 * This is typically equal to (dirty < thresh) and can also
1789 * keep "1000+ dd on a slow USB stick" under control.
1790 */
1791 if (task_ratelimit)
1792 break;
1793
1794 /*
1795 * In the case of an unresponding NFS server and the NFS dirty
1796 * pages exceeds dirty_thresh, give the other good wb's a pipe
1797 * to go through, so that tasks on them still remain responsive.
1798 *
1799 * In theory 1 page is enough to keep the comsumer-producer
1800 * pipe going: the flusher cleans 1 page => the task dirties 1
1801 * more page. However wb_dirty has accounting errors. So use
1802 * the larger and more IO friendly wb_stat_error.
1803 */
1804 if (sdtc->wb_dirty <= wb_stat_error(wb))
1805 break;
1806
1807 if (fatal_signal_pending(current))
1808 break;
1809 }
1810
1811 if (!dirty_exceeded && wb->dirty_exceeded)
1812 wb->dirty_exceeded = 0;
1813
1814 if (writeback_in_progress(wb))
1815 return;
1816
1817 /*
1818 * In laptop mode, we wait until hitting the higher threshold before
1819 * starting background writeout, and then write out all the way down
1820 * to the lower threshold. So slow writers cause minimal disk activity.
1821 *
1822 * In normal mode, we start background writeout at the lower
1823 * background_thresh, to keep the amount of dirty memory low.
1824 */
1825 if (laptop_mode)
1826 return;
1827
1828 if (nr_reclaimable > gdtc->bg_thresh)
1829 wb_start_background_writeback(wb);
1830 }
1831
1832 static DEFINE_PER_CPU(int, bdp_ratelimits);
1833
1834 /*
1835 * Normal tasks are throttled by
1836 * loop {
1837 * dirty tsk->nr_dirtied_pause pages;
1838 * take a snap in balance_dirty_pages();
1839 * }
1840 * However there is a worst case. If every task exit immediately when dirtied
1841 * (tsk->nr_dirtied_pause - 1) pages, balance_dirty_pages() will never be
1842 * called to throttle the page dirties. The solution is to save the not yet
1843 * throttled page dirties in dirty_throttle_leaks on task exit and charge them
1844 * randomly into the running tasks. This works well for the above worst case,
1845 * as the new task will pick up and accumulate the old task's leaked dirty
1846 * count and eventually get throttled.
1847 */
1848 DEFINE_PER_CPU(int, dirty_throttle_leaks) = 0;
1849
1850 /**
1851 * balance_dirty_pages_ratelimited - balance dirty memory state
1852 * @mapping: address_space which was dirtied
1853 *
1854 * Processes which are dirtying memory should call in here once for each page
1855 * which was newly dirtied. The function will periodically check the system's
1856 * dirty state and will initiate writeback if needed.
1857 *
1858 * On really big machines, get_writeback_state is expensive, so try to avoid
1859 * calling it too often (ratelimiting). But once we're over the dirty memory
1860 * limit we decrease the ratelimiting by a lot, to prevent individual processes
1861 * from overshooting the limit by (ratelimit_pages) each.
1862 */
1863 void balance_dirty_pages_ratelimited(struct address_space *mapping)
1864 {
1865 struct inode *inode = mapping->host;
1866 struct backing_dev_info *bdi = inode_to_bdi(inode);
1867 struct bdi_writeback *wb = NULL;
1868 int ratelimit;
1869 int *p;
1870
1871 if (!bdi_cap_account_dirty(bdi))
1872 return;
1873
1874 if (inode_cgwb_enabled(inode))
1875 wb = wb_get_create_current(bdi, GFP_KERNEL);
1876 if (!wb)
1877 wb = &bdi->wb;
1878
1879 ratelimit = current->nr_dirtied_pause;
1880 if (wb->dirty_exceeded)
1881 ratelimit = min(ratelimit, 32 >> (PAGE_SHIFT - 10));
1882
1883 preempt_disable();
1884 /*
1885 * This prevents one CPU to accumulate too many dirtied pages without
1886 * calling into balance_dirty_pages(), which can happen when there are
1887 * 1000+ tasks, all of them start dirtying pages at exactly the same
1888 * time, hence all honoured too large initial task->nr_dirtied_pause.
1889 */
1890 p = this_cpu_ptr(&bdp_ratelimits);
1891 if (unlikely(current->nr_dirtied >= ratelimit))
1892 *p = 0;
1893 else if (unlikely(*p >= ratelimit_pages)) {
1894 *p = 0;
1895 ratelimit = 0;
1896 }
1897 /*
1898 * Pick up the dirtied pages by the exited tasks. This avoids lots of
1899 * short-lived tasks (eg. gcc invocations in a kernel build) escaping
1900 * the dirty throttling and livelock other long-run dirtiers.
1901 */
1902 p = this_cpu_ptr(&dirty_throttle_leaks);
1903 if (*p > 0 && current->nr_dirtied < ratelimit) {
1904 unsigned long nr_pages_dirtied;
1905 nr_pages_dirtied = min(*p, ratelimit - current->nr_dirtied);
1906 *p -= nr_pages_dirtied;
1907 current->nr_dirtied += nr_pages_dirtied;
1908 }
1909 preempt_enable();
1910
1911 if (unlikely(current->nr_dirtied >= ratelimit))
1912 balance_dirty_pages(mapping, wb, current->nr_dirtied);
1913
1914 wb_put(wb);
1915 }
1916 EXPORT_SYMBOL(balance_dirty_pages_ratelimited);
1917
1918 /**
1919 * wb_over_bg_thresh - does @wb need to be written back?
1920 * @wb: bdi_writeback of interest
1921 *
1922 * Determines whether background writeback should keep writing @wb or it's
1923 * clean enough. Returns %true if writeback should continue.
1924 */
1925 bool wb_over_bg_thresh(struct bdi_writeback *wb)
1926 {
1927 struct dirty_throttle_control gdtc_stor = { GDTC_INIT(wb) };
1928 struct dirty_throttle_control mdtc_stor = { MDTC_INIT(wb, &gdtc_stor) };
1929 struct dirty_throttle_control * const gdtc = &gdtc_stor;
1930 struct dirty_throttle_control * const mdtc = mdtc_valid(&mdtc_stor) ?
1931 &mdtc_stor : NULL;
1932
1933 /*
1934 * Similar to balance_dirty_pages() but ignores pages being written
1935 * as we're trying to decide whether to put more under writeback.
1936 */
1937 gdtc->avail = global_dirtyable_memory();
1938 gdtc->dirty = global_node_page_state(NR_FILE_DIRTY) +
1939 global_node_page_state(NR_UNSTABLE_NFS);
1940 domain_dirty_limits(gdtc);
1941
1942 if (gdtc->dirty > gdtc->bg_thresh)
1943 return true;
1944
1945 if (wb_stat(wb, WB_RECLAIMABLE) >
1946 wb_calc_thresh(gdtc->wb, gdtc->bg_thresh))
1947 return true;
1948
1949 if (mdtc) {
1950 unsigned long filepages, headroom, writeback;
1951
1952 mem_cgroup_wb_stats(wb, &filepages, &headroom, &mdtc->dirty,
1953 &writeback);
1954 mdtc_calc_avail(mdtc, filepages, headroom);
1955 domain_dirty_limits(mdtc); /* ditto, ignore writeback */
1956
1957 if (mdtc->dirty > mdtc->bg_thresh)
1958 return true;
1959
1960 if (wb_stat(wb, WB_RECLAIMABLE) >
1961 wb_calc_thresh(mdtc->wb, mdtc->bg_thresh))
1962 return true;
1963 }
1964
1965 return false;
1966 }
1967
1968 void throttle_vm_writeout(gfp_t gfp_mask)
1969 {
1970 unsigned long background_thresh;
1971 unsigned long dirty_thresh;
1972
1973 for ( ; ; ) {
1974 global_dirty_limits(&background_thresh, &dirty_thresh);
1975 dirty_thresh = hard_dirty_limit(&global_wb_domain, dirty_thresh);
1976
1977 /*
1978 * Boost the allowable dirty threshold a bit for page
1979 * allocators so they don't get DoS'ed by heavy writers
1980 */
1981 dirty_thresh += dirty_thresh / 10; /* wheeee... */
1982
1983 if (global_node_page_state(NR_UNSTABLE_NFS) +
1984 global_node_page_state(NR_WRITEBACK) <= dirty_thresh)
1985 break;
1986 congestion_wait(BLK_RW_ASYNC, HZ/10);
1987
1988 /*
1989 * The caller might hold locks which can prevent IO completion
1990 * or progress in the filesystem. So we cannot just sit here
1991 * waiting for IO to complete.
1992 */
1993 if ((gfp_mask & (__GFP_FS|__GFP_IO)) != (__GFP_FS|__GFP_IO))
1994 break;
1995 }
1996 }
1997
1998 /*
1999 * sysctl handler for /proc/sys/vm/dirty_writeback_centisecs
2000 */
2001 int dirty_writeback_centisecs_handler(struct ctl_table *table, int write,
2002 void __user *buffer, size_t *length, loff_t *ppos)
2003 {
2004 proc_dointvec(table, write, buffer, length, ppos);
2005 return 0;
2006 }
2007
2008 #ifdef CONFIG_BLOCK
2009 void laptop_mode_timer_fn(unsigned long data)
2010 {
2011 struct request_queue *q = (struct request_queue *)data;
2012 int nr_pages = global_node_page_state(NR_FILE_DIRTY) +
2013 global_node_page_state(NR_UNSTABLE_NFS);
2014 struct bdi_writeback *wb;
2015
2016 /*
2017 * We want to write everything out, not just down to the dirty
2018 * threshold
2019 */
2020 if (!bdi_has_dirty_io(&q->backing_dev_info))
2021 return;
2022
2023 rcu_read_lock();
2024 list_for_each_entry_rcu(wb, &q->backing_dev_info.wb_list, bdi_node)
2025 if (wb_has_dirty_io(wb))
2026 wb_start_writeback(wb, nr_pages, true,
2027 WB_REASON_LAPTOP_TIMER);
2028 rcu_read_unlock();
2029 }
2030
2031 /*
2032 * We've spun up the disk and we're in laptop mode: schedule writeback
2033 * of all dirty data a few seconds from now. If the flush is already scheduled
2034 * then push it back - the user is still using the disk.
2035 */
2036 void laptop_io_completion(struct backing_dev_info *info)
2037 {
2038 mod_timer(&info->laptop_mode_wb_timer, jiffies + laptop_mode);
2039 }
2040
2041 /*
2042 * We're in laptop mode and we've just synced. The sync's writes will have
2043 * caused another writeback to be scheduled by laptop_io_completion.
2044 * Nothing needs to be written back anymore, so we unschedule the writeback.
2045 */
2046 void laptop_sync_completion(void)
2047 {
2048 struct backing_dev_info *bdi;
2049
2050 rcu_read_lock();
2051
2052 list_for_each_entry_rcu(bdi, &bdi_list, bdi_list)
2053 del_timer(&bdi->laptop_mode_wb_timer);
2054
2055 rcu_read_unlock();
2056 }
2057 #endif
2058
2059 /*
2060 * If ratelimit_pages is too high then we can get into dirty-data overload
2061 * if a large number of processes all perform writes at the same time.
2062 * If it is too low then SMP machines will call the (expensive)
2063 * get_writeback_state too often.
2064 *
2065 * Here we set ratelimit_pages to a level which ensures that when all CPUs are
2066 * dirtying in parallel, we cannot go more than 3% (1/32) over the dirty memory
2067 * thresholds.
2068 */
2069
2070 void writeback_set_ratelimit(void)
2071 {
2072 struct wb_domain *dom = &global_wb_domain;
2073 unsigned long background_thresh;
2074 unsigned long dirty_thresh;
2075
2076 global_dirty_limits(&background_thresh, &dirty_thresh);
2077 dom->dirty_limit = dirty_thresh;
2078 ratelimit_pages = dirty_thresh / (num_online_cpus() * 32);
2079 if (ratelimit_pages < 16)
2080 ratelimit_pages = 16;
2081 }
2082
2083 static int
2084 ratelimit_handler(struct notifier_block *self, unsigned long action,
2085 void *hcpu)
2086 {
2087
2088 switch (action & ~CPU_TASKS_FROZEN) {
2089 case CPU_ONLINE:
2090 case CPU_DEAD:
2091 writeback_set_ratelimit();
2092 return NOTIFY_OK;
2093 default:
2094 return NOTIFY_DONE;
2095 }
2096 }
2097
2098 static struct notifier_block ratelimit_nb = {
2099 .notifier_call = ratelimit_handler,
2100 .next = NULL,
2101 };
2102
2103 /*
2104 * Called early on to tune the page writeback dirty limits.
2105 *
2106 * We used to scale dirty pages according to how total memory
2107 * related to pages that could be allocated for buffers (by
2108 * comparing nr_free_buffer_pages() to vm_total_pages.
2109 *
2110 * However, that was when we used "dirty_ratio" to scale with
2111 * all memory, and we don't do that any more. "dirty_ratio"
2112 * is now applied to total non-HIGHPAGE memory (by subtracting
2113 * totalhigh_pages from vm_total_pages), and as such we can't
2114 * get into the old insane situation any more where we had
2115 * large amounts of dirty pages compared to a small amount of
2116 * non-HIGHMEM memory.
2117 *
2118 * But we might still want to scale the dirty_ratio by how
2119 * much memory the box has..
2120 */
2121 void __init page_writeback_init(void)
2122 {
2123 BUG_ON(wb_domain_init(&global_wb_domain, GFP_KERNEL));
2124
2125 writeback_set_ratelimit();
2126 register_cpu_notifier(&ratelimit_nb);
2127 }
2128
2129 /**
2130 * tag_pages_for_writeback - tag pages to be written by write_cache_pages
2131 * @mapping: address space structure to write
2132 * @start: starting page index
2133 * @end: ending page index (inclusive)
2134 *
2135 * This function scans the page range from @start to @end (inclusive) and tags
2136 * all pages that have DIRTY tag set with a special TOWRITE tag. The idea is
2137 * that write_cache_pages (or whoever calls this function) will then use
2138 * TOWRITE tag to identify pages eligible for writeback. This mechanism is
2139 * used to avoid livelocking of writeback by a process steadily creating new
2140 * dirty pages in the file (thus it is important for this function to be quick
2141 * so that it can tag pages faster than a dirtying process can create them).
2142 */
2143 /*
2144 * We tag pages in batches of WRITEBACK_TAG_BATCH to reduce tree_lock latency.
2145 */
2146 void tag_pages_for_writeback(struct address_space *mapping,
2147 pgoff_t start, pgoff_t end)
2148 {
2149 #define WRITEBACK_TAG_BATCH 4096
2150 unsigned long tagged;
2151
2152 do {
2153 spin_lock_irq(&mapping->tree_lock);
2154 tagged = radix_tree_range_tag_if_tagged(&mapping->page_tree,
2155 &start, end, WRITEBACK_TAG_BATCH,
2156 PAGECACHE_TAG_DIRTY, PAGECACHE_TAG_TOWRITE);
2157 spin_unlock_irq(&mapping->tree_lock);
2158 WARN_ON_ONCE(tagged > WRITEBACK_TAG_BATCH);
2159 cond_resched();
2160 /* We check 'start' to handle wrapping when end == ~0UL */
2161 } while (tagged >= WRITEBACK_TAG_BATCH && start);
2162 }
2163 EXPORT_SYMBOL(tag_pages_for_writeback);
2164
2165 /**
2166 * write_cache_pages - walk the list of dirty pages of the given address space and write all of them.
2167 * @mapping: address space structure to write
2168 * @wbc: subtract the number of written pages from *@wbc->nr_to_write
2169 * @writepage: function called for each page
2170 * @data: data passed to writepage function
2171 *
2172 * If a page is already under I/O, write_cache_pages() skips it, even
2173 * if it's dirty. This is desirable behaviour for memory-cleaning writeback,
2174 * but it is INCORRECT for data-integrity system calls such as fsync(). fsync()
2175 * and msync() need to guarantee that all the data which was dirty at the time
2176 * the call was made get new I/O started against them. If wbc->sync_mode is
2177 * WB_SYNC_ALL then we were called for data integrity and we must wait for
2178 * existing IO to complete.
2179 *
2180 * To avoid livelocks (when other process dirties new pages), we first tag
2181 * pages which should be written back with TOWRITE tag and only then start
2182 * writing them. For data-integrity sync we have to be careful so that we do
2183 * not miss some pages (e.g., because some other process has cleared TOWRITE
2184 * tag we set). The rule we follow is that TOWRITE tag can be cleared only
2185 * by the process clearing the DIRTY tag (and submitting the page for IO).
2186 */
2187 int write_cache_pages(struct address_space *mapping,
2188 struct writeback_control *wbc, writepage_t writepage,
2189 void *data)
2190 {
2191 int ret = 0;
2192 int done = 0;
2193 struct pagevec pvec;
2194 int nr_pages;
2195 pgoff_t uninitialized_var(writeback_index);
2196 pgoff_t index;
2197 pgoff_t end; /* Inclusive */
2198 pgoff_t done_index;
2199 int cycled;
2200 int range_whole = 0;
2201 int tag;
2202
2203 pagevec_init(&pvec, 0);
2204 if (wbc->range_cyclic) {
2205 writeback_index = mapping->writeback_index; /* prev offset */
2206 index = writeback_index;
2207 if (index == 0)
2208 cycled = 1;
2209 else
2210 cycled = 0;
2211 end = -1;
2212 } else {
2213 index = wbc->range_start >> PAGE_SHIFT;
2214 end = wbc->range_end >> PAGE_SHIFT;
2215 if (wbc->range_start == 0 && wbc->range_end == LLONG_MAX)
2216 range_whole = 1;
2217 cycled = 1; /* ignore range_cyclic tests */
2218 }
2219 if (wbc->sync_mode == WB_SYNC_ALL || wbc->tagged_writepages)
2220 tag = PAGECACHE_TAG_TOWRITE;
2221 else
2222 tag = PAGECACHE_TAG_DIRTY;
2223 retry:
2224 if (wbc->sync_mode == WB_SYNC_ALL || wbc->tagged_writepages)
2225 tag_pages_for_writeback(mapping, index, end);
2226 done_index = index;
2227 while (!done && (index <= end)) {
2228 int i;
2229
2230 nr_pages = pagevec_lookup_tag(&pvec, mapping, &index, tag,
2231 min(end - index, (pgoff_t)PAGEVEC_SIZE-1) + 1);
2232 if (nr_pages == 0)
2233 break;
2234
2235 for (i = 0; i < nr_pages; i++) {
2236 struct page *page = pvec.pages[i];
2237
2238 /*
2239 * At this point, the page may be truncated or
2240 * invalidated (changing page->mapping to NULL), or
2241 * even swizzled back from swapper_space to tmpfs file
2242 * mapping. However, page->index will not change
2243 * because we have a reference on the page.
2244 */
2245 if (page->index > end) {
2246 /*
2247 * can't be range_cyclic (1st pass) because
2248 * end == -1 in that case.
2249 */
2250 done = 1;
2251 break;
2252 }
2253
2254 done_index = page->index;
2255
2256 lock_page(page);
2257
2258 /*
2259 * Page truncated or invalidated. We can freely skip it
2260 * then, even for data integrity operations: the page
2261 * has disappeared concurrently, so there could be no
2262 * real expectation of this data interity operation
2263 * even if there is now a new, dirty page at the same
2264 * pagecache address.
2265 */
2266 if (unlikely(page->mapping != mapping)) {
2267 continue_unlock:
2268 unlock_page(page);
2269 continue;
2270 }
2271
2272 if (!PageDirty(page)) {
2273 /* someone wrote it for us */
2274 goto continue_unlock;
2275 }
2276
2277 if (PageWriteback(page)) {
2278 if (wbc->sync_mode != WB_SYNC_NONE)
2279 wait_on_page_writeback(page);
2280 else
2281 goto continue_unlock;
2282 }
2283
2284 BUG_ON(PageWriteback(page));
2285 if (!clear_page_dirty_for_io(page))
2286 goto continue_unlock;
2287
2288 trace_wbc_writepage(wbc, inode_to_bdi(mapping->host));
2289 ret = (*writepage)(page, wbc, data);
2290 if (unlikely(ret)) {
2291 if (ret == AOP_WRITEPAGE_ACTIVATE) {
2292 unlock_page(page);
2293 ret = 0;
2294 } else {
2295 /*
2296 * done_index is set past this page,
2297 * so media errors will not choke
2298 * background writeout for the entire
2299 * file. This has consequences for
2300 * range_cyclic semantics (ie. it may
2301 * not be suitable for data integrity
2302 * writeout).
2303 */
2304 done_index = page->index + 1;
2305 done = 1;
2306 break;
2307 }
2308 }
2309
2310 /*
2311 * We stop writing back only if we are not doing
2312 * integrity sync. In case of integrity sync we have to
2313 * keep going until we have written all the pages
2314 * we tagged for writeback prior to entering this loop.
2315 */
2316 if (--wbc->nr_to_write <= 0 &&
2317 wbc->sync_mode == WB_SYNC_NONE) {
2318 done = 1;
2319 break;
2320 }
2321 }
2322 pagevec_release(&pvec);
2323 cond_resched();
2324 }
2325 if (!cycled && !done) {
2326 /*
2327 * range_cyclic:
2328 * We hit the last page and there is more work to be done: wrap
2329 * back to the start of the file
2330 */
2331 cycled = 1;
2332 index = 0;
2333 end = writeback_index - 1;
2334 goto retry;
2335 }
2336 if (wbc->range_cyclic || (range_whole && wbc->nr_to_write > 0))
2337 mapping->writeback_index = done_index;
2338
2339 return ret;
2340 }
2341 EXPORT_SYMBOL(write_cache_pages);
2342
2343 /*
2344 * Function used by generic_writepages to call the real writepage
2345 * function and set the mapping flags on error
2346 */
2347 static int __writepage(struct page *page, struct writeback_control *wbc,
2348 void *data)
2349 {
2350 struct address_space *mapping = data;
2351 int ret = mapping->a_ops->writepage(page, wbc);
2352 mapping_set_error(mapping, ret);
2353 return ret;
2354 }
2355
2356 /**
2357 * generic_writepages - walk the list of dirty pages of the given address space and writepage() all of them.
2358 * @mapping: address space structure to write
2359 * @wbc: subtract the number of written pages from *@wbc->nr_to_write
2360 *
2361 * This is a library function, which implements the writepages()
2362 * address_space_operation.
2363 */
2364 int generic_writepages(struct address_space *mapping,
2365 struct writeback_control *wbc)
2366 {
2367 struct blk_plug plug;
2368 int ret;
2369
2370 /* deal with chardevs and other special file */
2371 if (!mapping->a_ops->writepage)
2372 return 0;
2373
2374 blk_start_plug(&plug);
2375 ret = write_cache_pages(mapping, wbc, __writepage, mapping);
2376 blk_finish_plug(&plug);
2377 return ret;
2378 }
2379
2380 EXPORT_SYMBOL(generic_writepages);
2381
2382 int do_writepages(struct address_space *mapping, struct writeback_control *wbc)
2383 {
2384 int ret;
2385
2386 if (wbc->nr_to_write <= 0)
2387 return 0;
2388 if (mapping->a_ops->writepages)
2389 ret = mapping->a_ops->writepages(mapping, wbc);
2390 else
2391 ret = generic_writepages(mapping, wbc);
2392 return ret;
2393 }
2394
2395 /**
2396 * write_one_page - write out a single page and optionally wait on I/O
2397 * @page: the page to write
2398 * @wait: if true, wait on writeout
2399 *
2400 * The page must be locked by the caller and will be unlocked upon return.
2401 *
2402 * write_one_page() returns a negative error code if I/O failed.
2403 */
2404 int write_one_page(struct page *page, int wait)
2405 {
2406 struct address_space *mapping = page->mapping;
2407 int ret = 0;
2408 struct writeback_control wbc = {
2409 .sync_mode = WB_SYNC_ALL,
2410 .nr_to_write = 1,
2411 };
2412
2413 BUG_ON(!PageLocked(page));
2414
2415 if (wait)
2416 wait_on_page_writeback(page);
2417
2418 if (clear_page_dirty_for_io(page)) {
2419 get_page(page);
2420 ret = mapping->a_ops->writepage(page, &wbc);
2421 if (ret == 0 && wait) {
2422 wait_on_page_writeback(page);
2423 if (PageError(page))
2424 ret = -EIO;
2425 }
2426 put_page(page);
2427 } else {
2428 unlock_page(page);
2429 }
2430 return ret;
2431 }
2432 EXPORT_SYMBOL(write_one_page);
2433
2434 /*
2435 * For address_spaces which do not use buffers nor write back.
2436 */
2437 int __set_page_dirty_no_writeback(struct page *page)
2438 {
2439 if (!PageDirty(page))
2440 return !TestSetPageDirty(page);
2441 return 0;
2442 }
2443
2444 /*
2445 * Helper function for set_page_dirty family.
2446 *
2447 * Caller must hold lock_page_memcg().
2448 *
2449 * NOTE: This relies on being atomic wrt interrupts.
2450 */
2451 void account_page_dirtied(struct page *page, struct address_space *mapping)
2452 {
2453 struct inode *inode = mapping->host;
2454
2455 trace_writeback_dirty_page(page, mapping);
2456
2457 if (mapping_cap_account_dirty(mapping)) {
2458 struct bdi_writeback *wb;
2459
2460 inode_attach_wb(inode, page);
2461 wb = inode_to_wb(inode);
2462
2463 mem_cgroup_inc_page_stat(page, MEM_CGROUP_STAT_DIRTY);
2464 __inc_node_page_state(page, NR_FILE_DIRTY);
2465 __inc_zone_page_state(page, NR_ZONE_WRITE_PENDING);
2466 __inc_node_page_state(page, NR_DIRTIED);
2467 __inc_wb_stat(wb, WB_RECLAIMABLE);
2468 __inc_wb_stat(wb, WB_DIRTIED);
2469 task_io_account_write(PAGE_SIZE);
2470 current->nr_dirtied++;
2471 this_cpu_inc(bdp_ratelimits);
2472 }
2473 }
2474 EXPORT_SYMBOL(account_page_dirtied);
2475
2476 /*
2477 * Helper function for deaccounting dirty page without writeback.
2478 *
2479 * Caller must hold lock_page_memcg().
2480 */
2481 void account_page_cleaned(struct page *page, struct address_space *mapping,
2482 struct bdi_writeback *wb)
2483 {
2484 if (mapping_cap_account_dirty(mapping)) {
2485 mem_cgroup_dec_page_stat(page, MEM_CGROUP_STAT_DIRTY);
2486 dec_node_page_state(page, NR_FILE_DIRTY);
2487 dec_zone_page_state(page, NR_ZONE_WRITE_PENDING);
2488 dec_wb_stat(wb, WB_RECLAIMABLE);
2489 task_io_account_cancelled_write(PAGE_SIZE);
2490 }
2491 }
2492
2493 /*
2494 * For address_spaces which do not use buffers. Just tag the page as dirty in
2495 * its radix tree.
2496 *
2497 * This is also used when a single buffer is being dirtied: we want to set the
2498 * page dirty in that case, but not all the buffers. This is a "bottom-up"
2499 * dirtying, whereas __set_page_dirty_buffers() is a "top-down" dirtying.
2500 *
2501 * The caller must ensure this doesn't race with truncation. Most will simply
2502 * hold the page lock, but e.g. zap_pte_range() calls with the page mapped and
2503 * the pte lock held, which also locks out truncation.
2504 */
2505 int __set_page_dirty_nobuffers(struct page *page)
2506 {
2507 lock_page_memcg(page);
2508 if (!TestSetPageDirty(page)) {
2509 struct address_space *mapping = page_mapping(page);
2510 unsigned long flags;
2511
2512 if (!mapping) {
2513 unlock_page_memcg(page);
2514 return 1;
2515 }
2516
2517 spin_lock_irqsave(&mapping->tree_lock, flags);
2518 BUG_ON(page_mapping(page) != mapping);
2519 WARN_ON_ONCE(!PagePrivate(page) && !PageUptodate(page));
2520 account_page_dirtied(page, mapping);
2521 radix_tree_tag_set(&mapping->page_tree, page_index(page),
2522 PAGECACHE_TAG_DIRTY);
2523 spin_unlock_irqrestore(&mapping->tree_lock, flags);
2524 unlock_page_memcg(page);
2525
2526 if (mapping->host) {
2527 /* !PageAnon && !swapper_space */
2528 __mark_inode_dirty(mapping->host, I_DIRTY_PAGES);
2529 }
2530 return 1;
2531 }
2532 unlock_page_memcg(page);
2533 return 0;
2534 }
2535 EXPORT_SYMBOL(__set_page_dirty_nobuffers);
2536
2537 /*
2538 * Call this whenever redirtying a page, to de-account the dirty counters
2539 * (NR_DIRTIED, BDI_DIRTIED, tsk->nr_dirtied), so that they match the written
2540 * counters (NR_WRITTEN, BDI_WRITTEN) in long term. The mismatches will lead to
2541 * systematic errors in balanced_dirty_ratelimit and the dirty pages position
2542 * control.
2543 */
2544 void account_page_redirty(struct page *page)
2545 {
2546 struct address_space *mapping = page->mapping;
2547
2548 if (mapping && mapping_cap_account_dirty(mapping)) {
2549 struct inode *inode = mapping->host;
2550 struct bdi_writeback *wb;
2551 bool locked;
2552
2553 wb = unlocked_inode_to_wb_begin(inode, &locked);
2554 current->nr_dirtied--;
2555 dec_node_page_state(page, NR_DIRTIED);
2556 dec_wb_stat(wb, WB_DIRTIED);
2557 unlocked_inode_to_wb_end(inode, locked);
2558 }
2559 }
2560 EXPORT_SYMBOL(account_page_redirty);
2561
2562 /*
2563 * When a writepage implementation decides that it doesn't want to write this
2564 * page for some reason, it should redirty the locked page via
2565 * redirty_page_for_writepage() and it should then unlock the page and return 0
2566 */
2567 int redirty_page_for_writepage(struct writeback_control *wbc, struct page *page)
2568 {
2569 int ret;
2570
2571 wbc->pages_skipped++;
2572 ret = __set_page_dirty_nobuffers(page);
2573 account_page_redirty(page);
2574 return ret;
2575 }
2576 EXPORT_SYMBOL(redirty_page_for_writepage);
2577
2578 /*
2579 * Dirty a page.
2580 *
2581 * For pages with a mapping this should be done under the page lock
2582 * for the benefit of asynchronous memory errors who prefer a consistent
2583 * dirty state. This rule can be broken in some special cases,
2584 * but should be better not to.
2585 *
2586 * If the mapping doesn't provide a set_page_dirty a_op, then
2587 * just fall through and assume that it wants buffer_heads.
2588 */
2589 int set_page_dirty(struct page *page)
2590 {
2591 struct address_space *mapping = page_mapping(page);
2592
2593 page = compound_head(page);
2594 if (likely(mapping)) {
2595 int (*spd)(struct page *) = mapping->a_ops->set_page_dirty;
2596 /*
2597 * readahead/lru_deactivate_page could remain
2598 * PG_readahead/PG_reclaim due to race with end_page_writeback
2599 * About readahead, if the page is written, the flags would be
2600 * reset. So no problem.
2601 * About lru_deactivate_page, if the page is redirty, the flag
2602 * will be reset. So no problem. but if the page is used by readahead
2603 * it will confuse readahead and make it restart the size rampup
2604 * process. But it's a trivial problem.
2605 */
2606 if (PageReclaim(page))
2607 ClearPageReclaim(page);
2608 #ifdef CONFIG_BLOCK
2609 if (!spd)
2610 spd = __set_page_dirty_buffers;
2611 #endif
2612 return (*spd)(page);
2613 }
2614 if (!PageDirty(page)) {
2615 if (!TestSetPageDirty(page))
2616 return 1;
2617 }
2618 return 0;
2619 }
2620 EXPORT_SYMBOL(set_page_dirty);
2621
2622 /*
2623 * set_page_dirty() is racy if the caller has no reference against
2624 * page->mapping->host, and if the page is unlocked. This is because another
2625 * CPU could truncate the page off the mapping and then free the mapping.
2626 *
2627 * Usually, the page _is_ locked, or the caller is a user-space process which
2628 * holds a reference on the inode by having an open file.
2629 *
2630 * In other cases, the page should be locked before running set_page_dirty().
2631 */
2632 int set_page_dirty_lock(struct page *page)
2633 {
2634 int ret;
2635
2636 lock_page(page);
2637 ret = set_page_dirty(page);
2638 unlock_page(page);
2639 return ret;
2640 }
2641 EXPORT_SYMBOL(set_page_dirty_lock);
2642
2643 /*
2644 * This cancels just the dirty bit on the kernel page itself, it does NOT
2645 * actually remove dirty bits on any mmap's that may be around. It also
2646 * leaves the page tagged dirty, so any sync activity will still find it on
2647 * the dirty lists, and in particular, clear_page_dirty_for_io() will still
2648 * look at the dirty bits in the VM.
2649 *
2650 * Doing this should *normally* only ever be done when a page is truncated,
2651 * and is not actually mapped anywhere at all. However, fs/buffer.c does
2652 * this when it notices that somebody has cleaned out all the buffers on a
2653 * page without actually doing it through the VM. Can you say "ext3 is
2654 * horribly ugly"? Thought you could.
2655 */
2656 void cancel_dirty_page(struct page *page)
2657 {
2658 struct address_space *mapping = page_mapping(page);
2659
2660 if (mapping_cap_account_dirty(mapping)) {
2661 struct inode *inode = mapping->host;
2662 struct bdi_writeback *wb;
2663 bool locked;
2664
2665 lock_page_memcg(page);
2666 wb = unlocked_inode_to_wb_begin(inode, &locked);
2667
2668 if (TestClearPageDirty(page))
2669 account_page_cleaned(page, mapping, wb);
2670
2671 unlocked_inode_to_wb_end(inode, locked);
2672 unlock_page_memcg(page);
2673 } else {
2674 ClearPageDirty(page);
2675 }
2676 }
2677 EXPORT_SYMBOL(cancel_dirty_page);
2678
2679 /*
2680 * Clear a page's dirty flag, while caring for dirty memory accounting.
2681 * Returns true if the page was previously dirty.
2682 *
2683 * This is for preparing to put the page under writeout. We leave the page
2684 * tagged as dirty in the radix tree so that a concurrent write-for-sync
2685 * can discover it via a PAGECACHE_TAG_DIRTY walk. The ->writepage
2686 * implementation will run either set_page_writeback() or set_page_dirty(),
2687 * at which stage we bring the page's dirty flag and radix-tree dirty tag
2688 * back into sync.
2689 *
2690 * This incoherency between the page's dirty flag and radix-tree tag is
2691 * unfortunate, but it only exists while the page is locked.
2692 */
2693 int clear_page_dirty_for_io(struct page *page)
2694 {
2695 struct address_space *mapping = page_mapping(page);
2696 int ret = 0;
2697
2698 BUG_ON(!PageLocked(page));
2699
2700 if (mapping && mapping_cap_account_dirty(mapping)) {
2701 struct inode *inode = mapping->host;
2702 struct bdi_writeback *wb;
2703 bool locked;
2704
2705 /*
2706 * Yes, Virginia, this is indeed insane.
2707 *
2708 * We use this sequence to make sure that
2709 * (a) we account for dirty stats properly
2710 * (b) we tell the low-level filesystem to
2711 * mark the whole page dirty if it was
2712 * dirty in a pagetable. Only to then
2713 * (c) clean the page again and return 1 to
2714 * cause the writeback.
2715 *
2716 * This way we avoid all nasty races with the
2717 * dirty bit in multiple places and clearing
2718 * them concurrently from different threads.
2719 *
2720 * Note! Normally the "set_page_dirty(page)"
2721 * has no effect on the actual dirty bit - since
2722 * that will already usually be set. But we
2723 * need the side effects, and it can help us
2724 * avoid races.
2725 *
2726 * We basically use the page "master dirty bit"
2727 * as a serialization point for all the different
2728 * threads doing their things.
2729 */
2730 if (page_mkclean(page))
2731 set_page_dirty(page);
2732 /*
2733 * We carefully synchronise fault handlers against
2734 * installing a dirty pte and marking the page dirty
2735 * at this point. We do this by having them hold the
2736 * page lock while dirtying the page, and pages are
2737 * always locked coming in here, so we get the desired
2738 * exclusion.
2739 */
2740 wb = unlocked_inode_to_wb_begin(inode, &locked);
2741 if (TestClearPageDirty(page)) {
2742 mem_cgroup_dec_page_stat(page, MEM_CGROUP_STAT_DIRTY);
2743 dec_node_page_state(page, NR_FILE_DIRTY);
2744 dec_zone_page_state(page, NR_ZONE_WRITE_PENDING);
2745 dec_wb_stat(wb, WB_RECLAIMABLE);
2746 ret = 1;
2747 }
2748 unlocked_inode_to_wb_end(inode, locked);
2749 return ret;
2750 }
2751 return TestClearPageDirty(page);
2752 }
2753 EXPORT_SYMBOL(clear_page_dirty_for_io);
2754
2755 int test_clear_page_writeback(struct page *page)
2756 {
2757 struct address_space *mapping = page_mapping(page);
2758 int ret;
2759
2760 lock_page_memcg(page);
2761 if (mapping) {
2762 struct inode *inode = mapping->host;
2763 struct backing_dev_info *bdi = inode_to_bdi(inode);
2764 unsigned long flags;
2765
2766 spin_lock_irqsave(&mapping->tree_lock, flags);
2767 ret = TestClearPageWriteback(page);
2768 if (ret) {
2769 radix_tree_tag_clear(&mapping->page_tree,
2770 page_index(page),
2771 PAGECACHE_TAG_WRITEBACK);
2772 if (bdi_cap_account_writeback(bdi)) {
2773 struct bdi_writeback *wb = inode_to_wb(inode);
2774
2775 __dec_wb_stat(wb, WB_WRITEBACK);
2776 __wb_writeout_inc(wb);
2777 }
2778 }
2779
2780 if (mapping->host && !mapping_tagged(mapping,
2781 PAGECACHE_TAG_WRITEBACK))
2782 sb_clear_inode_writeback(mapping->host);
2783
2784 spin_unlock_irqrestore(&mapping->tree_lock, flags);
2785 } else {
2786 ret = TestClearPageWriteback(page);
2787 }
2788 if (ret) {
2789 mem_cgroup_dec_page_stat(page, MEM_CGROUP_STAT_WRITEBACK);
2790 dec_node_page_state(page, NR_WRITEBACK);
2791 dec_zone_page_state(page, NR_ZONE_WRITE_PENDING);
2792 inc_node_page_state(page, NR_WRITTEN);
2793 }
2794 unlock_page_memcg(page);
2795 return ret;
2796 }
2797
2798 int __test_set_page_writeback(struct page *page, bool keep_write)
2799 {
2800 struct address_space *mapping = page_mapping(page);
2801 int ret;
2802
2803 lock_page_memcg(page);
2804 if (mapping) {
2805 struct inode *inode = mapping->host;
2806 struct backing_dev_info *bdi = inode_to_bdi(inode);
2807 unsigned long flags;
2808
2809 spin_lock_irqsave(&mapping->tree_lock, flags);
2810 ret = TestSetPageWriteback(page);
2811 if (!ret) {
2812 bool on_wblist;
2813
2814 on_wblist = mapping_tagged(mapping,
2815 PAGECACHE_TAG_WRITEBACK);
2816
2817 radix_tree_tag_set(&mapping->page_tree,
2818 page_index(page),
2819 PAGECACHE_TAG_WRITEBACK);
2820 if (bdi_cap_account_writeback(bdi))
2821 __inc_wb_stat(inode_to_wb(inode), WB_WRITEBACK);
2822
2823 /*
2824 * We can come through here when swapping anonymous
2825 * pages, so we don't necessarily have an inode to track
2826 * for sync.
2827 */
2828 if (mapping->host && !on_wblist)
2829 sb_mark_inode_writeback(mapping->host);
2830 }
2831 if (!PageDirty(page))
2832 radix_tree_tag_clear(&mapping->page_tree,
2833 page_index(page),
2834 PAGECACHE_TAG_DIRTY);
2835 if (!keep_write)
2836 radix_tree_tag_clear(&mapping->page_tree,
2837 page_index(page),
2838 PAGECACHE_TAG_TOWRITE);
2839 spin_unlock_irqrestore(&mapping->tree_lock, flags);
2840 } else {
2841 ret = TestSetPageWriteback(page);
2842 }
2843 if (!ret) {
2844 mem_cgroup_inc_page_stat(page, MEM_CGROUP_STAT_WRITEBACK);
2845 inc_node_page_state(page, NR_WRITEBACK);
2846 inc_zone_page_state(page, NR_ZONE_WRITE_PENDING);
2847 }
2848 unlock_page_memcg(page);
2849 return ret;
2850
2851 }
2852 EXPORT_SYMBOL(__test_set_page_writeback);
2853
2854 /*
2855 * Return true if any of the pages in the mapping are marked with the
2856 * passed tag.
2857 */
2858 int mapping_tagged(struct address_space *mapping, int tag)
2859 {
2860 return radix_tree_tagged(&mapping->page_tree, tag);
2861 }
2862 EXPORT_SYMBOL(mapping_tagged);
2863
2864 /**
2865 * wait_for_stable_page() - wait for writeback to finish, if necessary.
2866 * @page: The page to wait on.
2867 *
2868 * This function determines if the given page is related to a backing device
2869 * that requires page contents to be held stable during writeback. If so, then
2870 * it will wait for any pending writeback to complete.
2871 */
2872 void wait_for_stable_page(struct page *page)
2873 {
2874 if (bdi_cap_stable_pages_required(inode_to_bdi(page->mapping->host)))
2875 wait_on_page_writeback(page);
2876 }
2877 EXPORT_SYMBOL_GPL(wait_for_stable_page);