4 * Copyright (C) 2002, Linus Torvalds.
5 * Copyright (C) 2007 Red Hat, Inc., Peter Zijlstra
7 * Contains functions related to writing back dirty pages at the
10 * 10Apr2002 Andrew Morton
14 #include <linux/kernel.h>
15 #include <linux/export.h>
16 #include <linux/spinlock.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/sched/signal.h>
40 #include <linux/mm_inline.h>
41 #include <trace/events/writeback.h>
46 * Sleep at most 200ms at a time in balance_dirty_pages().
48 #define MAX_PAUSE max(HZ/5, 1)
51 * Try to keep balance_dirty_pages() call intervals higher than this many pages
52 * by raising pause time to max_pause when falls below it.
54 #define DIRTY_POLL_THRESH (128 >> (PAGE_SHIFT - 10))
57 * Estimate write bandwidth at 200ms intervals.
59 #define BANDWIDTH_INTERVAL max(HZ/5, 1)
61 #define RATELIMIT_CALC_SHIFT 10
64 * After a CPU has dirtied this many pages, balance_dirty_pages_ratelimited
65 * will look to see if it needs to force writeback or throttling.
67 static long ratelimit_pages = 32;
69 /* The following parameters are exported via /proc/sys/vm */
72 * Start background writeback (via writeback threads) at this percentage
74 int dirty_background_ratio = 10;
77 * dirty_background_bytes starts at 0 (disabled) so that it is a function of
78 * dirty_background_ratio * the amount of dirtyable memory
80 unsigned long dirty_background_bytes;
83 * free highmem will not be subtracted from the total free memory
84 * for calculating free ratios if vm_highmem_is_dirtyable is true
86 int vm_highmem_is_dirtyable;
89 * The generator of dirty data starts writeback at this percentage
91 int vm_dirty_ratio = 20;
94 * vm_dirty_bytes starts at 0 (disabled) so that it is a function of
95 * vm_dirty_ratio * the amount of dirtyable memory
97 unsigned long vm_dirty_bytes;
100 * The interval between `kupdate'-style writebacks
102 unsigned int dirty_writeback_interval = 5 * 100; /* centiseconds */
104 EXPORT_SYMBOL_GPL(dirty_writeback_interval);
107 * The longest time for which data is allowed to remain dirty
109 unsigned int dirty_expire_interval = 30 * 100; /* centiseconds */
112 * Flag that makes the machine dump writes/reads and block dirtyings.
117 * Flag that puts the machine in "laptop mode". Doubles as a timeout in jiffies:
118 * a full sync is triggered after this time elapses without any disk activity.
122 EXPORT_SYMBOL(laptop_mode);
124 /* End of sysctl-exported parameters */
126 struct wb_domain global_wb_domain;
128 /* consolidated parameters for balance_dirty_pages() and its subroutines */
129 struct dirty_throttle_control {
130 #ifdef CONFIG_CGROUP_WRITEBACK
131 struct wb_domain *dom;
132 struct dirty_throttle_control *gdtc; /* only set in memcg dtc's */
134 struct bdi_writeback *wb;
135 struct fprop_local_percpu *wb_completions;
137 unsigned long avail; /* dirtyable */
138 unsigned long dirty; /* file_dirty + write + nfs */
139 unsigned long thresh; /* dirty threshold */
140 unsigned long bg_thresh; /* dirty background threshold */
142 unsigned long wb_dirty; /* per-wb counterparts */
143 unsigned long wb_thresh;
144 unsigned long wb_bg_thresh;
146 unsigned long pos_ratio;
150 * Length of period for aging writeout fractions of bdis. This is an
151 * arbitrarily chosen number. The longer the period, the slower fractions will
152 * reflect changes in current writeout rate.
154 #define VM_COMPLETIONS_PERIOD_LEN (3*HZ)
156 #ifdef CONFIG_CGROUP_WRITEBACK
158 #define GDTC_INIT(__wb) .wb = (__wb), \
159 .dom = &global_wb_domain, \
160 .wb_completions = &(__wb)->completions
162 #define GDTC_INIT_NO_WB .dom = &global_wb_domain
164 #define MDTC_INIT(__wb, __gdtc) .wb = (__wb), \
165 .dom = mem_cgroup_wb_domain(__wb), \
166 .wb_completions = &(__wb)->memcg_completions, \
169 static bool mdtc_valid(struct dirty_throttle_control *dtc)
174 static struct wb_domain *dtc_dom(struct dirty_throttle_control *dtc)
179 static struct dirty_throttle_control *mdtc_gdtc(struct dirty_throttle_control *mdtc)
184 static struct fprop_local_percpu *wb_memcg_completions(struct bdi_writeback *wb)
186 return &wb->memcg_completions;
189 static void wb_min_max_ratio(struct bdi_writeback *wb,
190 unsigned long *minp, unsigned long *maxp)
192 unsigned long this_bw = wb->avg_write_bandwidth;
193 unsigned long tot_bw = atomic_long_read(&wb->bdi->tot_write_bandwidth);
194 unsigned long long min = wb->bdi->min_ratio;
195 unsigned long long max = wb->bdi->max_ratio;
198 * @wb may already be clean by the time control reaches here and
199 * the total may not include its bw.
201 if (this_bw < tot_bw) {
216 #else /* CONFIG_CGROUP_WRITEBACK */
218 #define GDTC_INIT(__wb) .wb = (__wb), \
219 .wb_completions = &(__wb)->completions
220 #define GDTC_INIT_NO_WB
221 #define MDTC_INIT(__wb, __gdtc)
223 static bool mdtc_valid(struct dirty_throttle_control *dtc)
228 static struct wb_domain *dtc_dom(struct dirty_throttle_control *dtc)
230 return &global_wb_domain;
233 static struct dirty_throttle_control *mdtc_gdtc(struct dirty_throttle_control *mdtc)
238 static struct fprop_local_percpu *wb_memcg_completions(struct bdi_writeback *wb)
243 static void wb_min_max_ratio(struct bdi_writeback *wb,
244 unsigned long *minp, unsigned long *maxp)
246 *minp = wb->bdi->min_ratio;
247 *maxp = wb->bdi->max_ratio;
250 #endif /* CONFIG_CGROUP_WRITEBACK */
253 * In a memory zone, there is a certain amount of pages we consider
254 * available for the page cache, which is essentially the number of
255 * free and reclaimable pages, minus some zone reserves to protect
256 * lowmem and the ability to uphold the zone's watermarks without
257 * requiring writeback.
259 * This number of dirtyable pages is the base value of which the
260 * user-configurable dirty ratio is the effictive number of pages that
261 * are allowed to be actually dirtied. Per individual zone, or
262 * globally by using the sum of dirtyable pages over all zones.
264 * Because the user is allowed to specify the dirty limit globally as
265 * absolute number of bytes, calculating the per-zone dirty limit can
266 * require translating the configured limit into a percentage of
267 * global dirtyable memory first.
271 * node_dirtyable_memory - number of dirtyable pages in a node
274 * Returns the node's number of pages potentially available for dirty
275 * page cache. This is the base value for the per-node dirty limits.
277 static unsigned long node_dirtyable_memory(struct pglist_data *pgdat)
279 unsigned long nr_pages = 0;
282 for (z = 0; z < MAX_NR_ZONES; z++) {
283 struct zone *zone = pgdat->node_zones + z;
285 if (!populated_zone(zone))
288 nr_pages += zone_page_state(zone, NR_FREE_PAGES);
292 * Pages reserved for the kernel should not be considered
293 * dirtyable, to prevent a situation where reclaim has to
294 * clean pages in order to balance the zones.
296 nr_pages -= min(nr_pages, pgdat->totalreserve_pages);
298 nr_pages += node_page_state(pgdat, NR_INACTIVE_FILE);
299 nr_pages += node_page_state(pgdat, NR_ACTIVE_FILE);
304 static unsigned long highmem_dirtyable_memory(unsigned long total)
306 #ifdef CONFIG_HIGHMEM
311 for_each_node_state(node, N_HIGH_MEMORY) {
312 for (i = ZONE_NORMAL + 1; i < MAX_NR_ZONES; i++) {
314 unsigned long nr_pages;
316 if (!is_highmem_idx(i))
319 z = &NODE_DATA(node)->node_zones[i];
320 if (!populated_zone(z))
323 nr_pages = zone_page_state(z, NR_FREE_PAGES);
324 /* watch for underflows */
325 nr_pages -= min(nr_pages, high_wmark_pages(z));
326 nr_pages += zone_page_state(z, NR_ZONE_INACTIVE_FILE);
327 nr_pages += zone_page_state(z, NR_ZONE_ACTIVE_FILE);
333 * Unreclaimable memory (kernel memory or anonymous memory
334 * without swap) can bring down the dirtyable pages below
335 * the zone's dirty balance reserve and the above calculation
336 * will underflow. However we still want to add in nodes
337 * which are below threshold (negative values) to get a more
338 * accurate calculation but make sure that the total never
345 * Make sure that the number of highmem pages is never larger
346 * than the number of the total dirtyable memory. This can only
347 * occur in very strange VM situations but we want to make sure
348 * that this does not occur.
350 return min(x, total);
357 * global_dirtyable_memory - number of globally dirtyable pages
359 * Returns the global number of pages potentially available for dirty
360 * page cache. This is the base value for the global dirty limits.
362 static unsigned long global_dirtyable_memory(void)
366 x = global_zone_page_state(NR_FREE_PAGES);
368 * Pages reserved for the kernel should not be considered
369 * dirtyable, to prevent a situation where reclaim has to
370 * clean pages in order to balance the zones.
372 x -= min(x, totalreserve_pages);
374 x += global_node_page_state(NR_INACTIVE_FILE);
375 x += global_node_page_state(NR_ACTIVE_FILE);
377 if (!vm_highmem_is_dirtyable)
378 x -= highmem_dirtyable_memory(x);
380 return x + 1; /* Ensure that we never return 0 */
384 * domain_dirty_limits - calculate thresh and bg_thresh for a wb_domain
385 * @dtc: dirty_throttle_control of interest
387 * Calculate @dtc->thresh and ->bg_thresh considering
388 * vm_dirty_{bytes|ratio} and dirty_background_{bytes|ratio}. The caller
389 * must ensure that @dtc->avail is set before calling this function. The
390 * dirty limits will be lifted by 1/4 for PF_LESS_THROTTLE (ie. nfsd) and
393 static void domain_dirty_limits(struct dirty_throttle_control *dtc)
395 const unsigned long available_memory = dtc->avail;
396 struct dirty_throttle_control *gdtc = mdtc_gdtc(dtc);
397 unsigned long bytes = vm_dirty_bytes;
398 unsigned long bg_bytes = dirty_background_bytes;
399 /* convert ratios to per-PAGE_SIZE for higher precision */
400 unsigned long ratio = (vm_dirty_ratio * PAGE_SIZE) / 100;
401 unsigned long bg_ratio = (dirty_background_ratio * PAGE_SIZE) / 100;
402 unsigned long thresh;
403 unsigned long bg_thresh;
404 struct task_struct *tsk;
406 /* gdtc is !NULL iff @dtc is for memcg domain */
408 unsigned long global_avail = gdtc->avail;
411 * The byte settings can't be applied directly to memcg
412 * domains. Convert them to ratios by scaling against
413 * globally available memory. As the ratios are in
414 * per-PAGE_SIZE, they can be obtained by dividing bytes by
418 ratio = min(DIV_ROUND_UP(bytes, global_avail),
421 bg_ratio = min(DIV_ROUND_UP(bg_bytes, global_avail),
423 bytes = bg_bytes = 0;
427 thresh = DIV_ROUND_UP(bytes, PAGE_SIZE);
429 thresh = (ratio * available_memory) / PAGE_SIZE;
432 bg_thresh = DIV_ROUND_UP(bg_bytes, PAGE_SIZE);
434 bg_thresh = (bg_ratio * available_memory) / PAGE_SIZE;
436 if (bg_thresh >= thresh)
437 bg_thresh = thresh / 2;
439 if (tsk->flags & PF_LESS_THROTTLE || rt_task(tsk)) {
440 bg_thresh += bg_thresh / 4 + global_wb_domain.dirty_limit / 32;
441 thresh += thresh / 4 + global_wb_domain.dirty_limit / 32;
443 dtc->thresh = thresh;
444 dtc->bg_thresh = bg_thresh;
446 /* we should eventually report the domain in the TP */
448 trace_global_dirty_state(bg_thresh, thresh);
452 * global_dirty_limits - background-writeback and dirty-throttling thresholds
453 * @pbackground: out parameter for bg_thresh
454 * @pdirty: out parameter for thresh
456 * Calculate bg_thresh and thresh for global_wb_domain. See
457 * domain_dirty_limits() for details.
459 void global_dirty_limits(unsigned long *pbackground, unsigned long *pdirty)
461 struct dirty_throttle_control gdtc = { GDTC_INIT_NO_WB };
463 gdtc.avail = global_dirtyable_memory();
464 domain_dirty_limits(&gdtc);
466 *pbackground = gdtc.bg_thresh;
467 *pdirty = gdtc.thresh;
471 * node_dirty_limit - maximum number of dirty pages allowed in a node
474 * Returns the maximum number of dirty pages allowed in a node, based
475 * on the node's dirtyable memory.
477 static unsigned long node_dirty_limit(struct pglist_data *pgdat)
479 unsigned long node_memory = node_dirtyable_memory(pgdat);
480 struct task_struct *tsk = current;
484 dirty = DIV_ROUND_UP(vm_dirty_bytes, PAGE_SIZE) *
485 node_memory / global_dirtyable_memory();
487 dirty = vm_dirty_ratio * node_memory / 100;
489 if (tsk->flags & PF_LESS_THROTTLE || rt_task(tsk))
496 * node_dirty_ok - tells whether a node is within its dirty limits
497 * @pgdat: the node to check
499 * Returns %true when the dirty pages in @pgdat are within the node's
500 * dirty limit, %false if the limit is exceeded.
502 bool node_dirty_ok(struct pglist_data *pgdat)
504 unsigned long limit = node_dirty_limit(pgdat);
505 unsigned long nr_pages = 0;
507 nr_pages += node_page_state(pgdat, NR_FILE_DIRTY);
508 nr_pages += node_page_state(pgdat, NR_UNSTABLE_NFS);
509 nr_pages += node_page_state(pgdat, NR_WRITEBACK);
511 return nr_pages <= limit;
514 int dirty_background_ratio_handler(struct ctl_table *table, int write,
515 void __user *buffer, size_t *lenp,
520 ret = proc_dointvec_minmax(table, write, buffer, lenp, ppos);
521 if (ret == 0 && write)
522 dirty_background_bytes = 0;
526 int dirty_background_bytes_handler(struct ctl_table *table, int write,
527 void __user *buffer, size_t *lenp,
532 ret = proc_doulongvec_minmax(table, write, buffer, lenp, ppos);
533 if (ret == 0 && write)
534 dirty_background_ratio = 0;
538 int dirty_ratio_handler(struct ctl_table *table, int write,
539 void __user *buffer, size_t *lenp,
542 int old_ratio = vm_dirty_ratio;
545 ret = proc_dointvec_minmax(table, write, buffer, lenp, ppos);
546 if (ret == 0 && write && vm_dirty_ratio != old_ratio) {
547 writeback_set_ratelimit();
553 int dirty_bytes_handler(struct ctl_table *table, int write,
554 void __user *buffer, size_t *lenp,
557 unsigned long old_bytes = vm_dirty_bytes;
560 ret = proc_doulongvec_minmax(table, write, buffer, lenp, ppos);
561 if (ret == 0 && write && vm_dirty_bytes != old_bytes) {
562 writeback_set_ratelimit();
568 static unsigned long wp_next_time(unsigned long cur_time)
570 cur_time += VM_COMPLETIONS_PERIOD_LEN;
571 /* 0 has a special meaning... */
577 static void wb_domain_writeout_inc(struct wb_domain *dom,
578 struct fprop_local_percpu *completions,
579 unsigned int max_prop_frac)
581 __fprop_inc_percpu_max(&dom->completions, completions,
583 /* First event after period switching was turned off? */
584 if (unlikely(!dom->period_time)) {
586 * We can race with other __bdi_writeout_inc calls here but
587 * it does not cause any harm since the resulting time when
588 * timer will fire and what is in writeout_period_time will be
591 dom->period_time = wp_next_time(jiffies);
592 mod_timer(&dom->period_timer, dom->period_time);
597 * Increment @wb's writeout completion count and the global writeout
598 * completion count. Called from test_clear_page_writeback().
600 static inline void __wb_writeout_inc(struct bdi_writeback *wb)
602 struct wb_domain *cgdom;
604 inc_wb_stat(wb, WB_WRITTEN);
605 wb_domain_writeout_inc(&global_wb_domain, &wb->completions,
606 wb->bdi->max_prop_frac);
608 cgdom = mem_cgroup_wb_domain(wb);
610 wb_domain_writeout_inc(cgdom, wb_memcg_completions(wb),
611 wb->bdi->max_prop_frac);
614 void wb_writeout_inc(struct bdi_writeback *wb)
618 local_irq_save(flags);
619 __wb_writeout_inc(wb);
620 local_irq_restore(flags);
622 EXPORT_SYMBOL_GPL(wb_writeout_inc);
625 * On idle system, we can be called long after we scheduled because we use
626 * deferred timers so count with missed periods.
628 static void writeout_period(struct timer_list *t)
630 struct wb_domain *dom = from_timer(dom, t, period_timer);
631 int miss_periods = (jiffies - dom->period_time) /
632 VM_COMPLETIONS_PERIOD_LEN;
634 if (fprop_new_period(&dom->completions, miss_periods + 1)) {
635 dom->period_time = wp_next_time(dom->period_time +
636 miss_periods * VM_COMPLETIONS_PERIOD_LEN);
637 mod_timer(&dom->period_timer, dom->period_time);
640 * Aging has zeroed all fractions. Stop wasting CPU on period
643 dom->period_time = 0;
647 int wb_domain_init(struct wb_domain *dom, gfp_t gfp)
649 memset(dom, 0, sizeof(*dom));
651 spin_lock_init(&dom->lock);
653 timer_setup(&dom->period_timer, writeout_period, TIMER_DEFERRABLE);
655 dom->dirty_limit_tstamp = jiffies;
657 return fprop_global_init(&dom->completions, gfp);
660 #ifdef CONFIG_CGROUP_WRITEBACK
661 void wb_domain_exit(struct wb_domain *dom)
663 del_timer_sync(&dom->period_timer);
664 fprop_global_destroy(&dom->completions);
669 * bdi_min_ratio keeps the sum of the minimum dirty shares of all
670 * registered backing devices, which, for obvious reasons, can not
673 static unsigned int bdi_min_ratio;
675 int bdi_set_min_ratio(struct backing_dev_info *bdi, unsigned int min_ratio)
679 spin_lock_bh(&bdi_lock);
680 if (min_ratio > bdi->max_ratio) {
683 min_ratio -= bdi->min_ratio;
684 if (bdi_min_ratio + min_ratio < 100) {
685 bdi_min_ratio += min_ratio;
686 bdi->min_ratio += min_ratio;
691 spin_unlock_bh(&bdi_lock);
696 int bdi_set_max_ratio(struct backing_dev_info *bdi, unsigned max_ratio)
703 spin_lock_bh(&bdi_lock);
704 if (bdi->min_ratio > max_ratio) {
707 bdi->max_ratio = max_ratio;
708 bdi->max_prop_frac = (FPROP_FRAC_BASE * max_ratio) / 100;
710 spin_unlock_bh(&bdi_lock);
714 EXPORT_SYMBOL(bdi_set_max_ratio);
716 static unsigned long dirty_freerun_ceiling(unsigned long thresh,
717 unsigned long bg_thresh)
719 return (thresh + bg_thresh) / 2;
722 static unsigned long hard_dirty_limit(struct wb_domain *dom,
723 unsigned long thresh)
725 return max(thresh, dom->dirty_limit);
729 * Memory which can be further allocated to a memcg domain is capped by
730 * system-wide clean memory excluding the amount being used in the domain.
732 static void mdtc_calc_avail(struct dirty_throttle_control *mdtc,
733 unsigned long filepages, unsigned long headroom)
735 struct dirty_throttle_control *gdtc = mdtc_gdtc(mdtc);
736 unsigned long clean = filepages - min(filepages, mdtc->dirty);
737 unsigned long global_clean = gdtc->avail - min(gdtc->avail, gdtc->dirty);
738 unsigned long other_clean = global_clean - min(global_clean, clean);
740 mdtc->avail = filepages + min(headroom, other_clean);
744 * __wb_calc_thresh - @wb's share of dirty throttling threshold
745 * @dtc: dirty_throttle_context of interest
747 * Returns @wb's dirty limit in pages. The term "dirty" in the context of
748 * dirty balancing includes all PG_dirty, PG_writeback and NFS unstable pages.
750 * Note that balance_dirty_pages() will only seriously take it as a hard limit
751 * when sleeping max_pause per page is not enough to keep the dirty pages under
752 * control. For example, when the device is completely stalled due to some error
753 * conditions, or when there are 1000 dd tasks writing to a slow 10MB/s USB key.
754 * In the other normal situations, it acts more gently by throttling the tasks
755 * more (rather than completely block them) when the wb dirty pages go high.
757 * It allocates high/low dirty limits to fast/slow devices, in order to prevent
758 * - starving fast devices
759 * - piling up dirty pages (that will take long time to sync) on slow devices
761 * The wb's share of dirty limit will be adapting to its throughput and
762 * bounded by the bdi->min_ratio and/or bdi->max_ratio parameters, if set.
764 static unsigned long __wb_calc_thresh(struct dirty_throttle_control *dtc)
766 struct wb_domain *dom = dtc_dom(dtc);
767 unsigned long thresh = dtc->thresh;
769 long numerator, denominator;
770 unsigned long wb_min_ratio, wb_max_ratio;
773 * Calculate this BDI's share of the thresh ratio.
775 fprop_fraction_percpu(&dom->completions, dtc->wb_completions,
776 &numerator, &denominator);
778 wb_thresh = (thresh * (100 - bdi_min_ratio)) / 100;
779 wb_thresh *= numerator;
780 do_div(wb_thresh, denominator);
782 wb_min_max_ratio(dtc->wb, &wb_min_ratio, &wb_max_ratio);
784 wb_thresh += (thresh * wb_min_ratio) / 100;
785 if (wb_thresh > (thresh * wb_max_ratio) / 100)
786 wb_thresh = thresh * wb_max_ratio / 100;
791 unsigned long wb_calc_thresh(struct bdi_writeback *wb, unsigned long thresh)
793 struct dirty_throttle_control gdtc = { GDTC_INIT(wb),
795 return __wb_calc_thresh(&gdtc);
800 * f(dirty) := 1.0 + (----------------)
803 * it's a 3rd order polynomial that subjects to
805 * (1) f(freerun) = 2.0 => rampup dirty_ratelimit reasonably fast
806 * (2) f(setpoint) = 1.0 => the balance point
807 * (3) f(limit) = 0 => the hard limit
808 * (4) df/dx <= 0 => negative feedback control
809 * (5) the closer to setpoint, the smaller |df/dx| (and the reverse)
810 * => fast response on large errors; small oscillation near setpoint
812 static long long pos_ratio_polynom(unsigned long setpoint,
819 x = div64_s64(((s64)setpoint - (s64)dirty) << RATELIMIT_CALC_SHIFT,
820 (limit - setpoint) | 1);
822 pos_ratio = pos_ratio * x >> RATELIMIT_CALC_SHIFT;
823 pos_ratio = pos_ratio * x >> RATELIMIT_CALC_SHIFT;
824 pos_ratio += 1 << RATELIMIT_CALC_SHIFT;
826 return clamp(pos_ratio, 0LL, 2LL << RATELIMIT_CALC_SHIFT);
830 * Dirty position control.
832 * (o) global/bdi setpoints
834 * We want the dirty pages be balanced around the global/wb setpoints.
835 * When the number of dirty pages is higher/lower than the setpoint, the
836 * dirty position control ratio (and hence task dirty ratelimit) will be
837 * decreased/increased to bring the dirty pages back to the setpoint.
839 * pos_ratio = 1 << RATELIMIT_CALC_SHIFT
841 * if (dirty < setpoint) scale up pos_ratio
842 * if (dirty > setpoint) scale down pos_ratio
844 * if (wb_dirty < wb_setpoint) scale up pos_ratio
845 * if (wb_dirty > wb_setpoint) scale down pos_ratio
847 * task_ratelimit = dirty_ratelimit * pos_ratio >> RATELIMIT_CALC_SHIFT
849 * (o) global control line
853 * | |<===== global dirty control scope ======>|
861 * 1.0 ................................*
867 * 0 +------------.------------------.----------------------*------------->
868 * freerun^ setpoint^ limit^ dirty pages
870 * (o) wb control line
878 * | * |<=========== span ============>|
879 * 1.0 .......................*
891 * 1/4 ...............................................* * * * * * * * * * * *
895 * 0 +----------------------.-------------------------------.------------->
896 * wb_setpoint^ x_intercept^
898 * The wb control line won't drop below pos_ratio=1/4, so that wb_dirty can
899 * be smoothly throttled down to normal if it starts high in situations like
900 * - start writing to a slow SD card and a fast disk at the same time. The SD
901 * card's wb_dirty may rush to many times higher than wb_setpoint.
902 * - the wb dirty thresh drops quickly due to change of JBOD workload
904 static void wb_position_ratio(struct dirty_throttle_control *dtc)
906 struct bdi_writeback *wb = dtc->wb;
907 unsigned long write_bw = wb->avg_write_bandwidth;
908 unsigned long freerun = dirty_freerun_ceiling(dtc->thresh, dtc->bg_thresh);
909 unsigned long limit = hard_dirty_limit(dtc_dom(dtc), dtc->thresh);
910 unsigned long wb_thresh = dtc->wb_thresh;
911 unsigned long x_intercept;
912 unsigned long setpoint; /* dirty pages' target balance point */
913 unsigned long wb_setpoint;
915 long long pos_ratio; /* for scaling up/down the rate limit */
920 if (unlikely(dtc->dirty >= limit))
926 * See comment for pos_ratio_polynom().
928 setpoint = (freerun + limit) / 2;
929 pos_ratio = pos_ratio_polynom(setpoint, dtc->dirty, limit);
932 * The strictlimit feature is a tool preventing mistrusted filesystems
933 * from growing a large number of dirty pages before throttling. For
934 * such filesystems balance_dirty_pages always checks wb counters
935 * against wb limits. Even if global "nr_dirty" is under "freerun".
936 * This is especially important for fuse which sets bdi->max_ratio to
937 * 1% by default. Without strictlimit feature, fuse writeback may
938 * consume arbitrary amount of RAM because it is accounted in
939 * NR_WRITEBACK_TEMP which is not involved in calculating "nr_dirty".
941 * Here, in wb_position_ratio(), we calculate pos_ratio based on
942 * two values: wb_dirty and wb_thresh. Let's consider an example:
943 * total amount of RAM is 16GB, bdi->max_ratio is equal to 1%, global
944 * limits are set by default to 10% and 20% (background and throttle).
945 * Then wb_thresh is 1% of 20% of 16GB. This amounts to ~8K pages.
946 * wb_calc_thresh(wb, bg_thresh) is about ~4K pages. wb_setpoint is
947 * about ~6K pages (as the average of background and throttle wb
948 * limits). The 3rd order polynomial will provide positive feedback if
949 * wb_dirty is under wb_setpoint and vice versa.
951 * Note, that we cannot use global counters in these calculations
952 * because we want to throttle process writing to a strictlimit wb
953 * much earlier than global "freerun" is reached (~23MB vs. ~2.3GB
954 * in the example above).
956 if (unlikely(wb->bdi->capabilities & BDI_CAP_STRICTLIMIT)) {
957 long long wb_pos_ratio;
959 if (dtc->wb_dirty < 8) {
960 dtc->pos_ratio = min_t(long long, pos_ratio * 2,
961 2 << RATELIMIT_CALC_SHIFT);
965 if (dtc->wb_dirty >= wb_thresh)
968 wb_setpoint = dirty_freerun_ceiling(wb_thresh,
971 if (wb_setpoint == 0 || wb_setpoint == wb_thresh)
974 wb_pos_ratio = pos_ratio_polynom(wb_setpoint, dtc->wb_dirty,
978 * Typically, for strictlimit case, wb_setpoint << setpoint
979 * and pos_ratio >> wb_pos_ratio. In the other words global
980 * state ("dirty") is not limiting factor and we have to
981 * make decision based on wb counters. But there is an
982 * important case when global pos_ratio should get precedence:
983 * global limits are exceeded (e.g. due to activities on other
984 * wb's) while given strictlimit wb is below limit.
986 * "pos_ratio * wb_pos_ratio" would work for the case above,
987 * but it would look too non-natural for the case of all
988 * activity in the system coming from a single strictlimit wb
989 * with bdi->max_ratio == 100%.
991 * Note that min() below somewhat changes the dynamics of the
992 * control system. Normally, pos_ratio value can be well over 3
993 * (when globally we are at freerun and wb is well below wb
994 * setpoint). Now the maximum pos_ratio in the same situation
995 * is 2. We might want to tweak this if we observe the control
996 * system is too slow to adapt.
998 dtc->pos_ratio = min(pos_ratio, wb_pos_ratio);
1003 * We have computed basic pos_ratio above based on global situation. If
1004 * the wb is over/under its share of dirty pages, we want to scale
1005 * pos_ratio further down/up. That is done by the following mechanism.
1011 * f(wb_dirty) := 1.0 + k * (wb_dirty - wb_setpoint)
1013 * x_intercept - wb_dirty
1014 * := --------------------------
1015 * x_intercept - wb_setpoint
1017 * The main wb control line is a linear function that subjects to
1019 * (1) f(wb_setpoint) = 1.0
1020 * (2) k = - 1 / (8 * write_bw) (in single wb case)
1021 * or equally: x_intercept = wb_setpoint + 8 * write_bw
1023 * For single wb case, the dirty pages are observed to fluctuate
1024 * regularly within range
1025 * [wb_setpoint - write_bw/2, wb_setpoint + write_bw/2]
1026 * for various filesystems, where (2) can yield in a reasonable 12.5%
1027 * fluctuation range for pos_ratio.
1029 * For JBOD case, wb_thresh (not wb_dirty!) could fluctuate up to its
1030 * own size, so move the slope over accordingly and choose a slope that
1031 * yields 100% pos_ratio fluctuation on suddenly doubled wb_thresh.
1033 if (unlikely(wb_thresh > dtc->thresh))
1034 wb_thresh = dtc->thresh;
1036 * It's very possible that wb_thresh is close to 0 not because the
1037 * device is slow, but that it has remained inactive for long time.
1038 * Honour such devices a reasonable good (hopefully IO efficient)
1039 * threshold, so that the occasional writes won't be blocked and active
1040 * writes can rampup the threshold quickly.
1042 wb_thresh = max(wb_thresh, (limit - dtc->dirty) / 8);
1044 * scale global setpoint to wb's:
1045 * wb_setpoint = setpoint * wb_thresh / thresh
1047 x = div_u64((u64)wb_thresh << 16, dtc->thresh | 1);
1048 wb_setpoint = setpoint * (u64)x >> 16;
1050 * Use span=(8*write_bw) in single wb case as indicated by
1051 * (thresh - wb_thresh ~= 0) and transit to wb_thresh in JBOD case.
1053 * wb_thresh thresh - wb_thresh
1054 * span = --------- * (8 * write_bw) + ------------------ * wb_thresh
1057 span = (dtc->thresh - wb_thresh + 8 * write_bw) * (u64)x >> 16;
1058 x_intercept = wb_setpoint + span;
1060 if (dtc->wb_dirty < x_intercept - span / 4) {
1061 pos_ratio = div64_u64(pos_ratio * (x_intercept - dtc->wb_dirty),
1062 (x_intercept - wb_setpoint) | 1);
1067 * wb reserve area, safeguard against dirty pool underrun and disk idle
1068 * It may push the desired control point of global dirty pages higher
1071 x_intercept = wb_thresh / 2;
1072 if (dtc->wb_dirty < x_intercept) {
1073 if (dtc->wb_dirty > x_intercept / 8)
1074 pos_ratio = div_u64(pos_ratio * x_intercept,
1080 dtc->pos_ratio = pos_ratio;
1083 static void wb_update_write_bandwidth(struct bdi_writeback *wb,
1084 unsigned long elapsed,
1085 unsigned long written)
1087 const unsigned long period = roundup_pow_of_two(3 * HZ);
1088 unsigned long avg = wb->avg_write_bandwidth;
1089 unsigned long old = wb->write_bandwidth;
1093 * bw = written * HZ / elapsed
1095 * bw * elapsed + write_bandwidth * (period - elapsed)
1096 * write_bandwidth = ---------------------------------------------------
1099 * @written may have decreased due to account_page_redirty().
1100 * Avoid underflowing @bw calculation.
1102 bw = written - min(written, wb->written_stamp);
1104 if (unlikely(elapsed > period)) {
1105 do_div(bw, elapsed);
1109 bw += (u64)wb->write_bandwidth * (period - elapsed);
1110 bw >>= ilog2(period);
1113 * one more level of smoothing, for filtering out sudden spikes
1115 if (avg > old && old >= (unsigned long)bw)
1116 avg -= (avg - old) >> 3;
1118 if (avg < old && old <= (unsigned long)bw)
1119 avg += (old - avg) >> 3;
1122 /* keep avg > 0 to guarantee that tot > 0 if there are dirty wbs */
1123 avg = max(avg, 1LU);
1124 if (wb_has_dirty_io(wb)) {
1125 long delta = avg - wb->avg_write_bandwidth;
1126 WARN_ON_ONCE(atomic_long_add_return(delta,
1127 &wb->bdi->tot_write_bandwidth) <= 0);
1129 wb->write_bandwidth = bw;
1130 wb->avg_write_bandwidth = avg;
1133 static void update_dirty_limit(struct dirty_throttle_control *dtc)
1135 struct wb_domain *dom = dtc_dom(dtc);
1136 unsigned long thresh = dtc->thresh;
1137 unsigned long limit = dom->dirty_limit;
1140 * Follow up in one step.
1142 if (limit < thresh) {
1148 * Follow down slowly. Use the higher one as the target, because thresh
1149 * may drop below dirty. This is exactly the reason to introduce
1150 * dom->dirty_limit which is guaranteed to lie above the dirty pages.
1152 thresh = max(thresh, dtc->dirty);
1153 if (limit > thresh) {
1154 limit -= (limit - thresh) >> 5;
1159 dom->dirty_limit = limit;
1162 static void domain_update_bandwidth(struct dirty_throttle_control *dtc,
1165 struct wb_domain *dom = dtc_dom(dtc);
1168 * check locklessly first to optimize away locking for the most time
1170 if (time_before(now, dom->dirty_limit_tstamp + BANDWIDTH_INTERVAL))
1173 spin_lock(&dom->lock);
1174 if (time_after_eq(now, dom->dirty_limit_tstamp + BANDWIDTH_INTERVAL)) {
1175 update_dirty_limit(dtc);
1176 dom->dirty_limit_tstamp = now;
1178 spin_unlock(&dom->lock);
1182 * Maintain wb->dirty_ratelimit, the base dirty throttle rate.
1184 * Normal wb tasks will be curbed at or below it in long term.
1185 * Obviously it should be around (write_bw / N) when there are N dd tasks.
1187 static void wb_update_dirty_ratelimit(struct dirty_throttle_control *dtc,
1188 unsigned long dirtied,
1189 unsigned long elapsed)
1191 struct bdi_writeback *wb = dtc->wb;
1192 unsigned long dirty = dtc->dirty;
1193 unsigned long freerun = dirty_freerun_ceiling(dtc->thresh, dtc->bg_thresh);
1194 unsigned long limit = hard_dirty_limit(dtc_dom(dtc), dtc->thresh);
1195 unsigned long setpoint = (freerun + limit) / 2;
1196 unsigned long write_bw = wb->avg_write_bandwidth;
1197 unsigned long dirty_ratelimit = wb->dirty_ratelimit;
1198 unsigned long dirty_rate;
1199 unsigned long task_ratelimit;
1200 unsigned long balanced_dirty_ratelimit;
1203 unsigned long shift;
1206 * The dirty rate will match the writeout rate in long term, except
1207 * when dirty pages are truncated by userspace or re-dirtied by FS.
1209 dirty_rate = (dirtied - wb->dirtied_stamp) * HZ / elapsed;
1212 * task_ratelimit reflects each dd's dirty rate for the past 200ms.
1214 task_ratelimit = (u64)dirty_ratelimit *
1215 dtc->pos_ratio >> RATELIMIT_CALC_SHIFT;
1216 task_ratelimit++; /* it helps rampup dirty_ratelimit from tiny values */
1219 * A linear estimation of the "balanced" throttle rate. The theory is,
1220 * if there are N dd tasks, each throttled at task_ratelimit, the wb's
1221 * dirty_rate will be measured to be (N * task_ratelimit). So the below
1222 * formula will yield the balanced rate limit (write_bw / N).
1224 * Note that the expanded form is not a pure rate feedback:
1225 * rate_(i+1) = rate_(i) * (write_bw / dirty_rate) (1)
1226 * but also takes pos_ratio into account:
1227 * rate_(i+1) = rate_(i) * (write_bw / dirty_rate) * pos_ratio (2)
1229 * (1) is not realistic because pos_ratio also takes part in balancing
1230 * the dirty rate. Consider the state
1231 * pos_ratio = 0.5 (3)
1232 * rate = 2 * (write_bw / N) (4)
1233 * If (1) is used, it will stuck in that state! Because each dd will
1235 * task_ratelimit = pos_ratio * rate = (write_bw / N) (5)
1237 * dirty_rate = N * task_ratelimit = write_bw (6)
1238 * put (6) into (1) we get
1239 * rate_(i+1) = rate_(i) (7)
1241 * So we end up using (2) to always keep
1242 * rate_(i+1) ~= (write_bw / N) (8)
1243 * regardless of the value of pos_ratio. As long as (8) is satisfied,
1244 * pos_ratio is able to drive itself to 1.0, which is not only where
1245 * the dirty count meet the setpoint, but also where the slope of
1246 * pos_ratio is most flat and hence task_ratelimit is least fluctuated.
1248 balanced_dirty_ratelimit = div_u64((u64)task_ratelimit * write_bw,
1251 * balanced_dirty_ratelimit ~= (write_bw / N) <= write_bw
1253 if (unlikely(balanced_dirty_ratelimit > write_bw))
1254 balanced_dirty_ratelimit = write_bw;
1257 * We could safely do this and return immediately:
1259 * wb->dirty_ratelimit = balanced_dirty_ratelimit;
1261 * However to get a more stable dirty_ratelimit, the below elaborated
1262 * code makes use of task_ratelimit to filter out singular points and
1263 * limit the step size.
1265 * The below code essentially only uses the relative value of
1267 * task_ratelimit - dirty_ratelimit
1268 * = (pos_ratio - 1) * dirty_ratelimit
1270 * which reflects the direction and size of dirty position error.
1274 * dirty_ratelimit will follow balanced_dirty_ratelimit iff
1275 * task_ratelimit is on the same side of dirty_ratelimit, too.
1277 * - dirty_ratelimit > balanced_dirty_ratelimit
1278 * - dirty_ratelimit > task_ratelimit (dirty pages are above setpoint)
1279 * lowering dirty_ratelimit will help meet both the position and rate
1280 * control targets. Otherwise, don't update dirty_ratelimit if it will
1281 * only help meet the rate target. After all, what the users ultimately
1282 * feel and care are stable dirty rate and small position error.
1284 * |task_ratelimit - dirty_ratelimit| is used to limit the step size
1285 * and filter out the singular points of balanced_dirty_ratelimit. Which
1286 * keeps jumping around randomly and can even leap far away at times
1287 * due to the small 200ms estimation period of dirty_rate (we want to
1288 * keep that period small to reduce time lags).
1293 * For strictlimit case, calculations above were based on wb counters
1294 * and limits (starting from pos_ratio = wb_position_ratio() and up to
1295 * balanced_dirty_ratelimit = task_ratelimit * write_bw / dirty_rate).
1296 * Hence, to calculate "step" properly, we have to use wb_dirty as
1297 * "dirty" and wb_setpoint as "setpoint".
1299 * We rampup dirty_ratelimit forcibly if wb_dirty is low because
1300 * it's possible that wb_thresh is close to zero due to inactivity
1301 * of backing device.
1303 if (unlikely(wb->bdi->capabilities & BDI_CAP_STRICTLIMIT)) {
1304 dirty = dtc->wb_dirty;
1305 if (dtc->wb_dirty < 8)
1306 setpoint = dtc->wb_dirty + 1;
1308 setpoint = (dtc->wb_thresh + dtc->wb_bg_thresh) / 2;
1311 if (dirty < setpoint) {
1312 x = min3(wb->balanced_dirty_ratelimit,
1313 balanced_dirty_ratelimit, task_ratelimit);
1314 if (dirty_ratelimit < x)
1315 step = x - dirty_ratelimit;
1317 x = max3(wb->balanced_dirty_ratelimit,
1318 balanced_dirty_ratelimit, task_ratelimit);
1319 if (dirty_ratelimit > x)
1320 step = dirty_ratelimit - x;
1324 * Don't pursue 100% rate matching. It's impossible since the balanced
1325 * rate itself is constantly fluctuating. So decrease the track speed
1326 * when it gets close to the target. Helps eliminate pointless tremors.
1328 shift = dirty_ratelimit / (2 * step + 1);
1329 if (shift < BITS_PER_LONG)
1330 step = DIV_ROUND_UP(step >> shift, 8);
1334 if (dirty_ratelimit < balanced_dirty_ratelimit)
1335 dirty_ratelimit += step;
1337 dirty_ratelimit -= step;
1339 wb->dirty_ratelimit = max(dirty_ratelimit, 1UL);
1340 wb->balanced_dirty_ratelimit = balanced_dirty_ratelimit;
1342 trace_bdi_dirty_ratelimit(wb, dirty_rate, task_ratelimit);
1345 static void __wb_update_bandwidth(struct dirty_throttle_control *gdtc,
1346 struct dirty_throttle_control *mdtc,
1347 unsigned long start_time,
1348 bool update_ratelimit)
1350 struct bdi_writeback *wb = gdtc->wb;
1351 unsigned long now = jiffies;
1352 unsigned long elapsed = now - wb->bw_time_stamp;
1353 unsigned long dirtied;
1354 unsigned long written;
1356 lockdep_assert_held(&wb->list_lock);
1359 * rate-limit, only update once every 200ms.
1361 if (elapsed < BANDWIDTH_INTERVAL)
1364 dirtied = percpu_counter_read(&wb->stat[WB_DIRTIED]);
1365 written = percpu_counter_read(&wb->stat[WB_WRITTEN]);
1368 * Skip quiet periods when disk bandwidth is under-utilized.
1369 * (at least 1s idle time between two flusher runs)
1371 if (elapsed > HZ && time_before(wb->bw_time_stamp, start_time))
1374 if (update_ratelimit) {
1375 domain_update_bandwidth(gdtc, now);
1376 wb_update_dirty_ratelimit(gdtc, dirtied, elapsed);
1379 * @mdtc is always NULL if !CGROUP_WRITEBACK but the
1380 * compiler has no way to figure that out. Help it.
1382 if (IS_ENABLED(CONFIG_CGROUP_WRITEBACK) && mdtc) {
1383 domain_update_bandwidth(mdtc, now);
1384 wb_update_dirty_ratelimit(mdtc, dirtied, elapsed);
1387 wb_update_write_bandwidth(wb, elapsed, written);
1390 wb->dirtied_stamp = dirtied;
1391 wb->written_stamp = written;
1392 wb->bw_time_stamp = now;
1395 void wb_update_bandwidth(struct bdi_writeback *wb, unsigned long start_time)
1397 struct dirty_throttle_control gdtc = { GDTC_INIT(wb) };
1399 __wb_update_bandwidth(&gdtc, NULL, start_time, false);
1403 * After a task dirtied this many pages, balance_dirty_pages_ratelimited()
1404 * will look to see if it needs to start dirty throttling.
1406 * If dirty_poll_interval is too low, big NUMA machines will call the expensive
1407 * global_zone_page_state() too often. So scale it near-sqrt to the safety margin
1408 * (the number of pages we may dirty without exceeding the dirty limits).
1410 static unsigned long dirty_poll_interval(unsigned long dirty,
1411 unsigned long thresh)
1414 return 1UL << (ilog2(thresh - dirty) >> 1);
1419 static unsigned long wb_max_pause(struct bdi_writeback *wb,
1420 unsigned long wb_dirty)
1422 unsigned long bw = wb->avg_write_bandwidth;
1426 * Limit pause time for small memory systems. If sleeping for too long
1427 * time, a small pool of dirty/writeback pages may go empty and disk go
1430 * 8 serves as the safety ratio.
1432 t = wb_dirty / (1 + bw / roundup_pow_of_two(1 + HZ / 8));
1435 return min_t(unsigned long, t, MAX_PAUSE);
1438 static long wb_min_pause(struct bdi_writeback *wb,
1440 unsigned long task_ratelimit,
1441 unsigned long dirty_ratelimit,
1442 int *nr_dirtied_pause)
1444 long hi = ilog2(wb->avg_write_bandwidth);
1445 long lo = ilog2(wb->dirty_ratelimit);
1446 long t; /* target pause */
1447 long pause; /* estimated next pause */
1448 int pages; /* target nr_dirtied_pause */
1450 /* target for 10ms pause on 1-dd case */
1451 t = max(1, HZ / 100);
1454 * Scale up pause time for concurrent dirtiers in order to reduce CPU
1457 * (N * 10ms) on 2^N concurrent tasks.
1460 t += (hi - lo) * (10 * HZ) / 1024;
1463 * This is a bit convoluted. We try to base the next nr_dirtied_pause
1464 * on the much more stable dirty_ratelimit. However the next pause time
1465 * will be computed based on task_ratelimit and the two rate limits may
1466 * depart considerably at some time. Especially if task_ratelimit goes
1467 * below dirty_ratelimit/2 and the target pause is max_pause, the next
1468 * pause time will be max_pause*2 _trimmed down_ to max_pause. As a
1469 * result task_ratelimit won't be executed faithfully, which could
1470 * eventually bring down dirty_ratelimit.
1472 * We apply two rules to fix it up:
1473 * 1) try to estimate the next pause time and if necessary, use a lower
1474 * nr_dirtied_pause so as not to exceed max_pause. When this happens,
1475 * nr_dirtied_pause will be "dancing" with task_ratelimit.
1476 * 2) limit the target pause time to max_pause/2, so that the normal
1477 * small fluctuations of task_ratelimit won't trigger rule (1) and
1478 * nr_dirtied_pause will remain as stable as dirty_ratelimit.
1480 t = min(t, 1 + max_pause / 2);
1481 pages = dirty_ratelimit * t / roundup_pow_of_two(HZ);
1484 * Tiny nr_dirtied_pause is found to hurt I/O performance in the test
1485 * case fio-mmap-randwrite-64k, which does 16*{sync read, async write}.
1486 * When the 16 consecutive reads are often interrupted by some dirty
1487 * throttling pause during the async writes, cfq will go into idles
1488 * (deadline is fine). So push nr_dirtied_pause as high as possible
1489 * until reaches DIRTY_POLL_THRESH=32 pages.
1491 if (pages < DIRTY_POLL_THRESH) {
1493 pages = dirty_ratelimit * t / roundup_pow_of_two(HZ);
1494 if (pages > DIRTY_POLL_THRESH) {
1495 pages = DIRTY_POLL_THRESH;
1496 t = HZ * DIRTY_POLL_THRESH / dirty_ratelimit;
1500 pause = HZ * pages / (task_ratelimit + 1);
1501 if (pause > max_pause) {
1503 pages = task_ratelimit * t / roundup_pow_of_two(HZ);
1506 *nr_dirtied_pause = pages;
1508 * The minimal pause time will normally be half the target pause time.
1510 return pages >= DIRTY_POLL_THRESH ? 1 + t / 2 : t;
1513 static inline void wb_dirty_limits(struct dirty_throttle_control *dtc)
1515 struct bdi_writeback *wb = dtc->wb;
1516 unsigned long wb_reclaimable;
1519 * wb_thresh is not treated as some limiting factor as
1520 * dirty_thresh, due to reasons
1521 * - in JBOD setup, wb_thresh can fluctuate a lot
1522 * - in a system with HDD and USB key, the USB key may somehow
1523 * go into state (wb_dirty >> wb_thresh) either because
1524 * wb_dirty starts high, or because wb_thresh drops low.
1525 * In this case we don't want to hard throttle the USB key
1526 * dirtiers for 100 seconds until wb_dirty drops under
1527 * wb_thresh. Instead the auxiliary wb control line in
1528 * wb_position_ratio() will let the dirtier task progress
1529 * at some rate <= (write_bw / 2) for bringing down wb_dirty.
1531 dtc->wb_thresh = __wb_calc_thresh(dtc);
1532 dtc->wb_bg_thresh = dtc->thresh ?
1533 div_u64((u64)dtc->wb_thresh * dtc->bg_thresh, dtc->thresh) : 0;
1536 * In order to avoid the stacked BDI deadlock we need
1537 * to ensure we accurately count the 'dirty' pages when
1538 * the threshold is low.
1540 * Otherwise it would be possible to get thresh+n pages
1541 * reported dirty, even though there are thresh-m pages
1542 * actually dirty; with m+n sitting in the percpu
1545 if (dtc->wb_thresh < 2 * wb_stat_error()) {
1546 wb_reclaimable = wb_stat_sum(wb, WB_RECLAIMABLE);
1547 dtc->wb_dirty = wb_reclaimable + wb_stat_sum(wb, WB_WRITEBACK);
1549 wb_reclaimable = wb_stat(wb, WB_RECLAIMABLE);
1550 dtc->wb_dirty = wb_reclaimable + wb_stat(wb, WB_WRITEBACK);
1555 * balance_dirty_pages() must be called by processes which are generating dirty
1556 * data. It looks at the number of dirty pages in the machine and will force
1557 * the caller to wait once crossing the (background_thresh + dirty_thresh) / 2.
1558 * If we're over `background_thresh' then the writeback threads are woken to
1559 * perform some writeout.
1561 static void balance_dirty_pages(struct bdi_writeback *wb,
1562 unsigned long pages_dirtied)
1564 struct dirty_throttle_control gdtc_stor = { GDTC_INIT(wb) };
1565 struct dirty_throttle_control mdtc_stor = { MDTC_INIT(wb, &gdtc_stor) };
1566 struct dirty_throttle_control * const gdtc = &gdtc_stor;
1567 struct dirty_throttle_control * const mdtc = mdtc_valid(&mdtc_stor) ?
1569 struct dirty_throttle_control *sdtc;
1570 unsigned long nr_reclaimable; /* = file_dirty + unstable_nfs */
1575 int nr_dirtied_pause;
1576 bool dirty_exceeded = false;
1577 unsigned long task_ratelimit;
1578 unsigned long dirty_ratelimit;
1579 struct backing_dev_info *bdi = wb->bdi;
1580 bool strictlimit = bdi->capabilities & BDI_CAP_STRICTLIMIT;
1581 unsigned long start_time = jiffies;
1584 unsigned long now = jiffies;
1585 unsigned long dirty, thresh, bg_thresh;
1586 unsigned long m_dirty = 0; /* stop bogus uninit warnings */
1587 unsigned long m_thresh = 0;
1588 unsigned long m_bg_thresh = 0;
1591 * Unstable writes are a feature of certain networked
1592 * filesystems (i.e. NFS) in which data may have been
1593 * written to the server's write cache, but has not yet
1594 * been flushed to permanent storage.
1596 nr_reclaimable = global_node_page_state(NR_FILE_DIRTY) +
1597 global_node_page_state(NR_UNSTABLE_NFS);
1598 gdtc->avail = global_dirtyable_memory();
1599 gdtc->dirty = nr_reclaimable + global_node_page_state(NR_WRITEBACK);
1601 domain_dirty_limits(gdtc);
1603 if (unlikely(strictlimit)) {
1604 wb_dirty_limits(gdtc);
1606 dirty = gdtc->wb_dirty;
1607 thresh = gdtc->wb_thresh;
1608 bg_thresh = gdtc->wb_bg_thresh;
1610 dirty = gdtc->dirty;
1611 thresh = gdtc->thresh;
1612 bg_thresh = gdtc->bg_thresh;
1616 unsigned long filepages, headroom, writeback;
1619 * If @wb belongs to !root memcg, repeat the same
1620 * basic calculations for the memcg domain.
1622 mem_cgroup_wb_stats(wb, &filepages, &headroom,
1623 &mdtc->dirty, &writeback);
1624 mdtc->dirty += writeback;
1625 mdtc_calc_avail(mdtc, filepages, headroom);
1627 domain_dirty_limits(mdtc);
1629 if (unlikely(strictlimit)) {
1630 wb_dirty_limits(mdtc);
1631 m_dirty = mdtc->wb_dirty;
1632 m_thresh = mdtc->wb_thresh;
1633 m_bg_thresh = mdtc->wb_bg_thresh;
1635 m_dirty = mdtc->dirty;
1636 m_thresh = mdtc->thresh;
1637 m_bg_thresh = mdtc->bg_thresh;
1642 * Throttle it only when the background writeback cannot
1643 * catch-up. This avoids (excessively) small writeouts
1644 * when the wb limits are ramping up in case of !strictlimit.
1646 * In strictlimit case make decision based on the wb counters
1647 * and limits. Small writeouts when the wb limits are ramping
1648 * up are the price we consciously pay for strictlimit-ing.
1650 * If memcg domain is in effect, @dirty should be under
1651 * both global and memcg freerun ceilings.
1653 if (dirty <= dirty_freerun_ceiling(thresh, bg_thresh) &&
1655 m_dirty <= dirty_freerun_ceiling(m_thresh, m_bg_thresh))) {
1656 unsigned long intv = dirty_poll_interval(dirty, thresh);
1657 unsigned long m_intv = ULONG_MAX;
1659 current->dirty_paused_when = now;
1660 current->nr_dirtied = 0;
1662 m_intv = dirty_poll_interval(m_dirty, m_thresh);
1663 current->nr_dirtied_pause = min(intv, m_intv);
1667 if (unlikely(!writeback_in_progress(wb)))
1668 wb_start_background_writeback(wb);
1671 * Calculate global domain's pos_ratio and select the
1672 * global dtc by default.
1675 wb_dirty_limits(gdtc);
1677 dirty_exceeded = (gdtc->wb_dirty > gdtc->wb_thresh) &&
1678 ((gdtc->dirty > gdtc->thresh) || strictlimit);
1680 wb_position_ratio(gdtc);
1685 * If memcg domain is in effect, calculate its
1686 * pos_ratio. @wb should satisfy constraints from
1687 * both global and memcg domains. Choose the one
1688 * w/ lower pos_ratio.
1691 wb_dirty_limits(mdtc);
1693 dirty_exceeded |= (mdtc->wb_dirty > mdtc->wb_thresh) &&
1694 ((mdtc->dirty > mdtc->thresh) || strictlimit);
1696 wb_position_ratio(mdtc);
1697 if (mdtc->pos_ratio < gdtc->pos_ratio)
1701 if (dirty_exceeded && !wb->dirty_exceeded)
1702 wb->dirty_exceeded = 1;
1704 if (time_is_before_jiffies(wb->bw_time_stamp +
1705 BANDWIDTH_INTERVAL)) {
1706 spin_lock(&wb->list_lock);
1707 __wb_update_bandwidth(gdtc, mdtc, start_time, true);
1708 spin_unlock(&wb->list_lock);
1711 /* throttle according to the chosen dtc */
1712 dirty_ratelimit = wb->dirty_ratelimit;
1713 task_ratelimit = ((u64)dirty_ratelimit * sdtc->pos_ratio) >>
1714 RATELIMIT_CALC_SHIFT;
1715 max_pause = wb_max_pause(wb, sdtc->wb_dirty);
1716 min_pause = wb_min_pause(wb, max_pause,
1717 task_ratelimit, dirty_ratelimit,
1720 if (unlikely(task_ratelimit == 0)) {
1725 period = HZ * pages_dirtied / task_ratelimit;
1727 if (current->dirty_paused_when)
1728 pause -= now - current->dirty_paused_when;
1730 * For less than 1s think time (ext3/4 may block the dirtier
1731 * for up to 800ms from time to time on 1-HDD; so does xfs,
1732 * however at much less frequency), try to compensate it in
1733 * future periods by updating the virtual time; otherwise just
1734 * do a reset, as it may be a light dirtier.
1736 if (pause < min_pause) {
1737 trace_balance_dirty_pages(wb,
1750 current->dirty_paused_when = now;
1751 current->nr_dirtied = 0;
1752 } else if (period) {
1753 current->dirty_paused_when += period;
1754 current->nr_dirtied = 0;
1755 } else if (current->nr_dirtied_pause <= pages_dirtied)
1756 current->nr_dirtied_pause += pages_dirtied;
1759 if (unlikely(pause > max_pause)) {
1760 /* for occasional dropped task_ratelimit */
1761 now += min(pause - max_pause, max_pause);
1766 trace_balance_dirty_pages(wb,
1778 __set_current_state(TASK_KILLABLE);
1779 wb->dirty_sleep = now;
1780 io_schedule_timeout(pause);
1782 current->dirty_paused_when = now + pause;
1783 current->nr_dirtied = 0;
1784 current->nr_dirtied_pause = nr_dirtied_pause;
1787 * This is typically equal to (dirty < thresh) and can also
1788 * keep "1000+ dd on a slow USB stick" under control.
1794 * In the case of an unresponding NFS server and the NFS dirty
1795 * pages exceeds dirty_thresh, give the other good wb's a pipe
1796 * to go through, so that tasks on them still remain responsive.
1798 * In theory 1 page is enough to keep the consumer-producer
1799 * pipe going: the flusher cleans 1 page => the task dirties 1
1800 * more page. However wb_dirty has accounting errors. So use
1801 * the larger and more IO friendly wb_stat_error.
1803 if (sdtc->wb_dirty <= wb_stat_error())
1806 if (fatal_signal_pending(current))
1810 if (!dirty_exceeded && wb->dirty_exceeded)
1811 wb->dirty_exceeded = 0;
1813 if (writeback_in_progress(wb))
1817 * In laptop mode, we wait until hitting the higher threshold before
1818 * starting background writeout, and then write out all the way down
1819 * to the lower threshold. So slow writers cause minimal disk activity.
1821 * In normal mode, we start background writeout at the lower
1822 * background_thresh, to keep the amount of dirty memory low.
1827 if (nr_reclaimable > gdtc->bg_thresh)
1828 wb_start_background_writeback(wb);
1831 static DEFINE_PER_CPU(int, bdp_ratelimits);
1834 * Normal tasks are throttled by
1836 * dirty tsk->nr_dirtied_pause pages;
1837 * take a snap in balance_dirty_pages();
1839 * However there is a worst case. If every task exit immediately when dirtied
1840 * (tsk->nr_dirtied_pause - 1) pages, balance_dirty_pages() will never be
1841 * called to throttle the page dirties. The solution is to save the not yet
1842 * throttled page dirties in dirty_throttle_leaks on task exit and charge them
1843 * randomly into the running tasks. This works well for the above worst case,
1844 * as the new task will pick up and accumulate the old task's leaked dirty
1845 * count and eventually get throttled.
1847 DEFINE_PER_CPU(int, dirty_throttle_leaks) = 0;
1850 * balance_dirty_pages_ratelimited - balance dirty memory state
1851 * @mapping: address_space which was dirtied
1853 * Processes which are dirtying memory should call in here once for each page
1854 * which was newly dirtied. The function will periodically check the system's
1855 * dirty state and will initiate writeback if needed.
1857 * On really big machines, get_writeback_state is expensive, so try to avoid
1858 * calling it too often (ratelimiting). But once we're over the dirty memory
1859 * limit we decrease the ratelimiting by a lot, to prevent individual processes
1860 * from overshooting the limit by (ratelimit_pages) each.
1862 void balance_dirty_pages_ratelimited(struct address_space *mapping)
1864 struct inode *inode = mapping->host;
1865 struct backing_dev_info *bdi = inode_to_bdi(inode);
1866 struct bdi_writeback *wb = NULL;
1870 if (!bdi_cap_account_dirty(bdi))
1873 if (inode_cgwb_enabled(inode))
1874 wb = wb_get_create_current(bdi, GFP_KERNEL);
1878 ratelimit = current->nr_dirtied_pause;
1879 if (wb->dirty_exceeded)
1880 ratelimit = min(ratelimit, 32 >> (PAGE_SHIFT - 10));
1884 * This prevents one CPU to accumulate too many dirtied pages without
1885 * calling into balance_dirty_pages(), which can happen when there are
1886 * 1000+ tasks, all of them start dirtying pages at exactly the same
1887 * time, hence all honoured too large initial task->nr_dirtied_pause.
1889 p = this_cpu_ptr(&bdp_ratelimits);
1890 if (unlikely(current->nr_dirtied >= ratelimit))
1892 else if (unlikely(*p >= ratelimit_pages)) {
1897 * Pick up the dirtied pages by the exited tasks. This avoids lots of
1898 * short-lived tasks (eg. gcc invocations in a kernel build) escaping
1899 * the dirty throttling and livelock other long-run dirtiers.
1901 p = this_cpu_ptr(&dirty_throttle_leaks);
1902 if (*p > 0 && current->nr_dirtied < ratelimit) {
1903 unsigned long nr_pages_dirtied;
1904 nr_pages_dirtied = min(*p, ratelimit - current->nr_dirtied);
1905 *p -= nr_pages_dirtied;
1906 current->nr_dirtied += nr_pages_dirtied;
1910 if (unlikely(current->nr_dirtied >= ratelimit))
1911 balance_dirty_pages(wb, current->nr_dirtied);
1915 EXPORT_SYMBOL(balance_dirty_pages_ratelimited);
1918 * wb_over_bg_thresh - does @wb need to be written back?
1919 * @wb: bdi_writeback of interest
1921 * Determines whether background writeback should keep writing @wb or it's
1922 * clean enough. Returns %true if writeback should continue.
1924 bool wb_over_bg_thresh(struct bdi_writeback *wb)
1926 struct dirty_throttle_control gdtc_stor = { GDTC_INIT(wb) };
1927 struct dirty_throttle_control mdtc_stor = { MDTC_INIT(wb, &gdtc_stor) };
1928 struct dirty_throttle_control * const gdtc = &gdtc_stor;
1929 struct dirty_throttle_control * const mdtc = mdtc_valid(&mdtc_stor) ?
1933 * Similar to balance_dirty_pages() but ignores pages being written
1934 * as we're trying to decide whether to put more under writeback.
1936 gdtc->avail = global_dirtyable_memory();
1937 gdtc->dirty = global_node_page_state(NR_FILE_DIRTY) +
1938 global_node_page_state(NR_UNSTABLE_NFS);
1939 domain_dirty_limits(gdtc);
1941 if (gdtc->dirty > gdtc->bg_thresh)
1944 if (wb_stat(wb, WB_RECLAIMABLE) >
1945 wb_calc_thresh(gdtc->wb, gdtc->bg_thresh))
1949 unsigned long filepages, headroom, writeback;
1951 mem_cgroup_wb_stats(wb, &filepages, &headroom, &mdtc->dirty,
1953 mdtc_calc_avail(mdtc, filepages, headroom);
1954 domain_dirty_limits(mdtc); /* ditto, ignore writeback */
1956 if (mdtc->dirty > mdtc->bg_thresh)
1959 if (wb_stat(wb, WB_RECLAIMABLE) >
1960 wb_calc_thresh(mdtc->wb, mdtc->bg_thresh))
1968 * sysctl handler for /proc/sys/vm/dirty_writeback_centisecs
1970 int dirty_writeback_centisecs_handler(struct ctl_table *table, int write,
1971 void __user *buffer, size_t *length, loff_t *ppos)
1973 unsigned int old_interval = dirty_writeback_interval;
1976 ret = proc_dointvec(table, write, buffer, length, ppos);
1979 * Writing 0 to dirty_writeback_interval will disable periodic writeback
1980 * and a different non-zero value will wakeup the writeback threads.
1981 * wb_wakeup_delayed() would be more appropriate, but it's a pain to
1982 * iterate over all bdis and wbs.
1983 * The reason we do this is to make the change take effect immediately.
1985 if (!ret && write && dirty_writeback_interval &&
1986 dirty_writeback_interval != old_interval)
1987 wakeup_flusher_threads(WB_REASON_PERIODIC);
1993 void laptop_mode_timer_fn(struct timer_list *t)
1995 struct backing_dev_info *backing_dev_info =
1996 from_timer(backing_dev_info, t, laptop_mode_wb_timer);
1998 wakeup_flusher_threads_bdi(backing_dev_info, WB_REASON_LAPTOP_TIMER);
2002 * We've spun up the disk and we're in laptop mode: schedule writeback
2003 * of all dirty data a few seconds from now. If the flush is already scheduled
2004 * then push it back - the user is still using the disk.
2006 void laptop_io_completion(struct backing_dev_info *info)
2008 mod_timer(&info->laptop_mode_wb_timer, jiffies + laptop_mode);
2012 * We're in laptop mode and we've just synced. The sync's writes will have
2013 * caused another writeback to be scheduled by laptop_io_completion.
2014 * Nothing needs to be written back anymore, so we unschedule the writeback.
2016 void laptop_sync_completion(void)
2018 struct backing_dev_info *bdi;
2022 list_for_each_entry_rcu(bdi, &bdi_list, bdi_list)
2023 del_timer(&bdi->laptop_mode_wb_timer);
2030 * If ratelimit_pages is too high then we can get into dirty-data overload
2031 * if a large number of processes all perform writes at the same time.
2032 * If it is too low then SMP machines will call the (expensive)
2033 * get_writeback_state too often.
2035 * Here we set ratelimit_pages to a level which ensures that when all CPUs are
2036 * dirtying in parallel, we cannot go more than 3% (1/32) over the dirty memory
2040 void writeback_set_ratelimit(void)
2042 struct wb_domain *dom = &global_wb_domain;
2043 unsigned long background_thresh;
2044 unsigned long dirty_thresh;
2046 global_dirty_limits(&background_thresh, &dirty_thresh);
2047 dom->dirty_limit = dirty_thresh;
2048 ratelimit_pages = dirty_thresh / (num_online_cpus() * 32);
2049 if (ratelimit_pages < 16)
2050 ratelimit_pages = 16;
2053 static int page_writeback_cpu_online(unsigned int cpu)
2055 writeback_set_ratelimit();
2060 * Called early on to tune the page writeback dirty limits.
2062 * We used to scale dirty pages according to how total memory
2063 * related to pages that could be allocated for buffers (by
2064 * comparing nr_free_buffer_pages() to vm_total_pages.
2066 * However, that was when we used "dirty_ratio" to scale with
2067 * all memory, and we don't do that any more. "dirty_ratio"
2068 * is now applied to total non-HIGHPAGE memory (by subtracting
2069 * totalhigh_pages from vm_total_pages), and as such we can't
2070 * get into the old insane situation any more where we had
2071 * large amounts of dirty pages compared to a small amount of
2072 * non-HIGHMEM memory.
2074 * But we might still want to scale the dirty_ratio by how
2075 * much memory the box has..
2077 void __init page_writeback_init(void)
2079 BUG_ON(wb_domain_init(&global_wb_domain, GFP_KERNEL));
2081 cpuhp_setup_state(CPUHP_AP_ONLINE_DYN, "mm/writeback:online",
2082 page_writeback_cpu_online, NULL);
2083 cpuhp_setup_state(CPUHP_MM_WRITEBACK_DEAD, "mm/writeback:dead", NULL,
2084 page_writeback_cpu_online);
2088 * tag_pages_for_writeback - tag pages to be written by write_cache_pages
2089 * @mapping: address space structure to write
2090 * @start: starting page index
2091 * @end: ending page index (inclusive)
2093 * This function scans the page range from @start to @end (inclusive) and tags
2094 * all pages that have DIRTY tag set with a special TOWRITE tag. The idea is
2095 * that write_cache_pages (or whoever calls this function) will then use
2096 * TOWRITE tag to identify pages eligible for writeback. This mechanism is
2097 * used to avoid livelocking of writeback by a process steadily creating new
2098 * dirty pages in the file (thus it is important for this function to be quick
2099 * so that it can tag pages faster than a dirtying process can create them).
2102 * We tag pages in batches of WRITEBACK_TAG_BATCH to reduce the i_pages lock
2105 void tag_pages_for_writeback(struct address_space *mapping,
2106 pgoff_t start, pgoff_t end)
2108 #define WRITEBACK_TAG_BATCH 4096
2109 unsigned long tagged = 0;
2110 struct radix_tree_iter iter;
2113 xa_lock_irq(&mapping->i_pages);
2114 radix_tree_for_each_tagged(slot, &mapping->i_pages, &iter, start,
2115 PAGECACHE_TAG_DIRTY) {
2116 if (iter.index > end)
2118 radix_tree_iter_tag_set(&mapping->i_pages, &iter,
2119 PAGECACHE_TAG_TOWRITE);
2121 if ((tagged % WRITEBACK_TAG_BATCH) != 0)
2123 slot = radix_tree_iter_resume(slot, &iter);
2124 xa_unlock_irq(&mapping->i_pages);
2126 xa_lock_irq(&mapping->i_pages);
2128 xa_unlock_irq(&mapping->i_pages);
2130 EXPORT_SYMBOL(tag_pages_for_writeback);
2133 * write_cache_pages - walk the list of dirty pages of the given address space and write all of them.
2134 * @mapping: address space structure to write
2135 * @wbc: subtract the number of written pages from *@wbc->nr_to_write
2136 * @writepage: function called for each page
2137 * @data: data passed to writepage function
2139 * If a page is already under I/O, write_cache_pages() skips it, even
2140 * if it's dirty. This is desirable behaviour for memory-cleaning writeback,
2141 * but it is INCORRECT for data-integrity system calls such as fsync(). fsync()
2142 * and msync() need to guarantee that all the data which was dirty at the time
2143 * the call was made get new I/O started against them. If wbc->sync_mode is
2144 * WB_SYNC_ALL then we were called for data integrity and we must wait for
2145 * existing IO to complete.
2147 * To avoid livelocks (when other process dirties new pages), we first tag
2148 * pages which should be written back with TOWRITE tag and only then start
2149 * writing them. For data-integrity sync we have to be careful so that we do
2150 * not miss some pages (e.g., because some other process has cleared TOWRITE
2151 * tag we set). The rule we follow is that TOWRITE tag can be cleared only
2152 * by the process clearing the DIRTY tag (and submitting the page for IO).
2154 int write_cache_pages(struct address_space *mapping,
2155 struct writeback_control *wbc, writepage_t writepage,
2160 struct pagevec pvec;
2162 pgoff_t uninitialized_var(writeback_index);
2164 pgoff_t end; /* Inclusive */
2167 int range_whole = 0;
2170 pagevec_init(&pvec);
2171 if (wbc->range_cyclic) {
2172 writeback_index = mapping->writeback_index; /* prev offset */
2173 index = writeback_index;
2180 index = wbc->range_start >> PAGE_SHIFT;
2181 end = wbc->range_end >> PAGE_SHIFT;
2182 if (wbc->range_start == 0 && wbc->range_end == LLONG_MAX)
2184 cycled = 1; /* ignore range_cyclic tests */
2186 if (wbc->sync_mode == WB_SYNC_ALL || wbc->tagged_writepages)
2187 tag = PAGECACHE_TAG_TOWRITE;
2189 tag = PAGECACHE_TAG_DIRTY;
2191 if (wbc->sync_mode == WB_SYNC_ALL || wbc->tagged_writepages)
2192 tag_pages_for_writeback(mapping, index, end);
2194 while (!done && (index <= end)) {
2197 nr_pages = pagevec_lookup_range_tag(&pvec, mapping, &index, end,
2202 for (i = 0; i < nr_pages; i++) {
2203 struct page *page = pvec.pages[i];
2205 done_index = page->index;
2210 * Page truncated or invalidated. We can freely skip it
2211 * then, even for data integrity operations: the page
2212 * has disappeared concurrently, so there could be no
2213 * real expectation of this data interity operation
2214 * even if there is now a new, dirty page at the same
2215 * pagecache address.
2217 if (unlikely(page->mapping != mapping)) {
2223 if (!PageDirty(page)) {
2224 /* someone wrote it for us */
2225 goto continue_unlock;
2228 if (PageWriteback(page)) {
2229 if (wbc->sync_mode != WB_SYNC_NONE)
2230 wait_on_page_writeback(page);
2232 goto continue_unlock;
2235 BUG_ON(PageWriteback(page));
2236 if (!clear_page_dirty_for_io(page))
2237 goto continue_unlock;
2239 trace_wbc_writepage(wbc, inode_to_bdi(mapping->host));
2240 ret = (*writepage)(page, wbc, data);
2241 if (unlikely(ret)) {
2242 if (ret == AOP_WRITEPAGE_ACTIVATE) {
2247 * done_index is set past this page,
2248 * so media errors will not choke
2249 * background writeout for the entire
2250 * file. This has consequences for
2251 * range_cyclic semantics (ie. it may
2252 * not be suitable for data integrity
2255 done_index = page->index + 1;
2262 * We stop writing back only if we are not doing
2263 * integrity sync. In case of integrity sync we have to
2264 * keep going until we have written all the pages
2265 * we tagged for writeback prior to entering this loop.
2267 if (--wbc->nr_to_write <= 0 &&
2268 wbc->sync_mode == WB_SYNC_NONE) {
2273 pagevec_release(&pvec);
2276 if (!cycled && !done) {
2279 * We hit the last page and there is more work to be done: wrap
2280 * back to the start of the file
2284 end = writeback_index - 1;
2287 if (wbc->range_cyclic || (range_whole && wbc->nr_to_write > 0))
2288 mapping->writeback_index = done_index;
2292 EXPORT_SYMBOL(write_cache_pages);
2295 * Function used by generic_writepages to call the real writepage
2296 * function and set the mapping flags on error
2298 static int __writepage(struct page *page, struct writeback_control *wbc,
2301 struct address_space *mapping = data;
2302 int ret = mapping->a_ops->writepage(page, wbc);
2303 mapping_set_error(mapping, ret);
2308 * generic_writepages - walk the list of dirty pages of the given address space and writepage() all of them.
2309 * @mapping: address space structure to write
2310 * @wbc: subtract the number of written pages from *@wbc->nr_to_write
2312 * This is a library function, which implements the writepages()
2313 * address_space_operation.
2315 int generic_writepages(struct address_space *mapping,
2316 struct writeback_control *wbc)
2318 struct blk_plug plug;
2321 /* deal with chardevs and other special file */
2322 if (!mapping->a_ops->writepage)
2325 blk_start_plug(&plug);
2326 ret = write_cache_pages(mapping, wbc, __writepage, mapping);
2327 blk_finish_plug(&plug);
2331 EXPORT_SYMBOL(generic_writepages);
2333 int do_writepages(struct address_space *mapping, struct writeback_control *wbc)
2337 if (wbc->nr_to_write <= 0)
2340 if (mapping->a_ops->writepages)
2341 ret = mapping->a_ops->writepages(mapping, wbc);
2343 ret = generic_writepages(mapping, wbc);
2344 if ((ret != -ENOMEM) || (wbc->sync_mode != WB_SYNC_ALL))
2347 congestion_wait(BLK_RW_ASYNC, HZ/50);
2353 * write_one_page - write out a single page and wait on I/O
2354 * @page: the page to write
2356 * The page must be locked by the caller and will be unlocked upon return.
2358 * Note that the mapping's AS_EIO/AS_ENOSPC flags will be cleared when this
2361 int write_one_page(struct page *page)
2363 struct address_space *mapping = page->mapping;
2365 struct writeback_control wbc = {
2366 .sync_mode = WB_SYNC_ALL,
2370 BUG_ON(!PageLocked(page));
2372 wait_on_page_writeback(page);
2374 if (clear_page_dirty_for_io(page)) {
2376 ret = mapping->a_ops->writepage(page, &wbc);
2378 wait_on_page_writeback(page);
2385 ret = filemap_check_errors(mapping);
2388 EXPORT_SYMBOL(write_one_page);
2391 * For address_spaces which do not use buffers nor write back.
2393 int __set_page_dirty_no_writeback(struct page *page)
2395 if (!PageDirty(page))
2396 return !TestSetPageDirty(page);
2401 * Helper function for set_page_dirty family.
2403 * Caller must hold lock_page_memcg().
2405 * NOTE: This relies on being atomic wrt interrupts.
2407 void account_page_dirtied(struct page *page, struct address_space *mapping)
2409 struct inode *inode = mapping->host;
2411 trace_writeback_dirty_page(page, mapping);
2413 if (mapping_cap_account_dirty(mapping)) {
2414 struct bdi_writeback *wb;
2416 inode_attach_wb(inode, page);
2417 wb = inode_to_wb(inode);
2419 __inc_lruvec_page_state(page, NR_FILE_DIRTY);
2420 __inc_zone_page_state(page, NR_ZONE_WRITE_PENDING);
2421 __inc_node_page_state(page, NR_DIRTIED);
2422 inc_wb_stat(wb, WB_RECLAIMABLE);
2423 inc_wb_stat(wb, WB_DIRTIED);
2424 task_io_account_write(PAGE_SIZE);
2425 current->nr_dirtied++;
2426 this_cpu_inc(bdp_ratelimits);
2429 EXPORT_SYMBOL(account_page_dirtied);
2432 * Helper function for deaccounting dirty page without writeback.
2434 * Caller must hold lock_page_memcg().
2436 void account_page_cleaned(struct page *page, struct address_space *mapping,
2437 struct bdi_writeback *wb)
2439 if (mapping_cap_account_dirty(mapping)) {
2440 dec_lruvec_page_state(page, NR_FILE_DIRTY);
2441 dec_zone_page_state(page, NR_ZONE_WRITE_PENDING);
2442 dec_wb_stat(wb, WB_RECLAIMABLE);
2443 task_io_account_cancelled_write(PAGE_SIZE);
2448 * For address_spaces which do not use buffers. Just tag the page as dirty in
2451 * This is also used when a single buffer is being dirtied: we want to set the
2452 * page dirty in that case, but not all the buffers. This is a "bottom-up"
2453 * dirtying, whereas __set_page_dirty_buffers() is a "top-down" dirtying.
2455 * The caller must ensure this doesn't race with truncation. Most will simply
2456 * hold the page lock, but e.g. zap_pte_range() calls with the page mapped and
2457 * the pte lock held, which also locks out truncation.
2459 int __set_page_dirty_nobuffers(struct page *page)
2461 lock_page_memcg(page);
2462 if (!TestSetPageDirty(page)) {
2463 struct address_space *mapping = page_mapping(page);
2464 unsigned long flags;
2467 unlock_page_memcg(page);
2471 xa_lock_irqsave(&mapping->i_pages, flags);
2472 BUG_ON(page_mapping(page) != mapping);
2473 WARN_ON_ONCE(!PagePrivate(page) && !PageUptodate(page));
2474 account_page_dirtied(page, mapping);
2475 radix_tree_tag_set(&mapping->i_pages, page_index(page),
2476 PAGECACHE_TAG_DIRTY);
2477 xa_unlock_irqrestore(&mapping->i_pages, flags);
2478 unlock_page_memcg(page);
2480 if (mapping->host) {
2481 /* !PageAnon && !swapper_space */
2482 __mark_inode_dirty(mapping->host, I_DIRTY_PAGES);
2486 unlock_page_memcg(page);
2489 EXPORT_SYMBOL(__set_page_dirty_nobuffers);
2492 * Call this whenever redirtying a page, to de-account the dirty counters
2493 * (NR_DIRTIED, BDI_DIRTIED, tsk->nr_dirtied), so that they match the written
2494 * counters (NR_WRITTEN, BDI_WRITTEN) in long term. The mismatches will lead to
2495 * systematic errors in balanced_dirty_ratelimit and the dirty pages position
2498 void account_page_redirty(struct page *page)
2500 struct address_space *mapping = page->mapping;
2502 if (mapping && mapping_cap_account_dirty(mapping)) {
2503 struct inode *inode = mapping->host;
2504 struct bdi_writeback *wb;
2505 struct wb_lock_cookie cookie = {};
2507 wb = unlocked_inode_to_wb_begin(inode, &cookie);
2508 current->nr_dirtied--;
2509 dec_node_page_state(page, NR_DIRTIED);
2510 dec_wb_stat(wb, WB_DIRTIED);
2511 unlocked_inode_to_wb_end(inode, &cookie);
2514 EXPORT_SYMBOL(account_page_redirty);
2517 * When a writepage implementation decides that it doesn't want to write this
2518 * page for some reason, it should redirty the locked page via
2519 * redirty_page_for_writepage() and it should then unlock the page and return 0
2521 int redirty_page_for_writepage(struct writeback_control *wbc, struct page *page)
2525 wbc->pages_skipped++;
2526 ret = __set_page_dirty_nobuffers(page);
2527 account_page_redirty(page);
2530 EXPORT_SYMBOL(redirty_page_for_writepage);
2535 * For pages with a mapping this should be done under the page lock
2536 * for the benefit of asynchronous memory errors who prefer a consistent
2537 * dirty state. This rule can be broken in some special cases,
2538 * but should be better not to.
2540 * If the mapping doesn't provide a set_page_dirty a_op, then
2541 * just fall through and assume that it wants buffer_heads.
2543 int set_page_dirty(struct page *page)
2545 struct address_space *mapping = page_mapping(page);
2547 page = compound_head(page);
2548 if (likely(mapping)) {
2549 int (*spd)(struct page *) = mapping->a_ops->set_page_dirty;
2551 * readahead/lru_deactivate_page could remain
2552 * PG_readahead/PG_reclaim due to race with end_page_writeback
2553 * About readahead, if the page is written, the flags would be
2554 * reset. So no problem.
2555 * About lru_deactivate_page, if the page is redirty, the flag
2556 * will be reset. So no problem. but if the page is used by readahead
2557 * it will confuse readahead and make it restart the size rampup
2558 * process. But it's a trivial problem.
2560 if (PageReclaim(page))
2561 ClearPageReclaim(page);
2564 spd = __set_page_dirty_buffers;
2566 return (*spd)(page);
2568 if (!PageDirty(page)) {
2569 if (!TestSetPageDirty(page))
2574 EXPORT_SYMBOL(set_page_dirty);
2577 * set_page_dirty() is racy if the caller has no reference against
2578 * page->mapping->host, and if the page is unlocked. This is because another
2579 * CPU could truncate the page off the mapping and then free the mapping.
2581 * Usually, the page _is_ locked, or the caller is a user-space process which
2582 * holds a reference on the inode by having an open file.
2584 * In other cases, the page should be locked before running set_page_dirty().
2586 int set_page_dirty_lock(struct page *page)
2591 ret = set_page_dirty(page);
2595 EXPORT_SYMBOL(set_page_dirty_lock);
2598 * This cancels just the dirty bit on the kernel page itself, it does NOT
2599 * actually remove dirty bits on any mmap's that may be around. It also
2600 * leaves the page tagged dirty, so any sync activity will still find it on
2601 * the dirty lists, and in particular, clear_page_dirty_for_io() will still
2602 * look at the dirty bits in the VM.
2604 * Doing this should *normally* only ever be done when a page is truncated,
2605 * and is not actually mapped anywhere at all. However, fs/buffer.c does
2606 * this when it notices that somebody has cleaned out all the buffers on a
2607 * page without actually doing it through the VM. Can you say "ext3 is
2608 * horribly ugly"? Thought you could.
2610 void __cancel_dirty_page(struct page *page)
2612 struct address_space *mapping = page_mapping(page);
2614 if (mapping_cap_account_dirty(mapping)) {
2615 struct inode *inode = mapping->host;
2616 struct bdi_writeback *wb;
2617 struct wb_lock_cookie cookie = {};
2619 lock_page_memcg(page);
2620 wb = unlocked_inode_to_wb_begin(inode, &cookie);
2622 if (TestClearPageDirty(page))
2623 account_page_cleaned(page, mapping, wb);
2625 unlocked_inode_to_wb_end(inode, &cookie);
2626 unlock_page_memcg(page);
2628 ClearPageDirty(page);
2631 EXPORT_SYMBOL(__cancel_dirty_page);
2634 * Clear a page's dirty flag, while caring for dirty memory accounting.
2635 * Returns true if the page was previously dirty.
2637 * This is for preparing to put the page under writeout. We leave the page
2638 * tagged as dirty in the radix tree so that a concurrent write-for-sync
2639 * can discover it via a PAGECACHE_TAG_DIRTY walk. The ->writepage
2640 * implementation will run either set_page_writeback() or set_page_dirty(),
2641 * at which stage we bring the page's dirty flag and radix-tree dirty tag
2644 * This incoherency between the page's dirty flag and radix-tree tag is
2645 * unfortunate, but it only exists while the page is locked.
2647 int clear_page_dirty_for_io(struct page *page)
2649 struct address_space *mapping = page_mapping(page);
2652 BUG_ON(!PageLocked(page));
2654 if (mapping && mapping_cap_account_dirty(mapping)) {
2655 struct inode *inode = mapping->host;
2656 struct bdi_writeback *wb;
2657 struct wb_lock_cookie cookie = {};
2660 * Yes, Virginia, this is indeed insane.
2662 * We use this sequence to make sure that
2663 * (a) we account for dirty stats properly
2664 * (b) we tell the low-level filesystem to
2665 * mark the whole page dirty if it was
2666 * dirty in a pagetable. Only to then
2667 * (c) clean the page again and return 1 to
2668 * cause the writeback.
2670 * This way we avoid all nasty races with the
2671 * dirty bit in multiple places and clearing
2672 * them concurrently from different threads.
2674 * Note! Normally the "set_page_dirty(page)"
2675 * has no effect on the actual dirty bit - since
2676 * that will already usually be set. But we
2677 * need the side effects, and it can help us
2680 * We basically use the page "master dirty bit"
2681 * as a serialization point for all the different
2682 * threads doing their things.
2684 if (page_mkclean(page))
2685 set_page_dirty(page);
2687 * We carefully synchronise fault handlers against
2688 * installing a dirty pte and marking the page dirty
2689 * at this point. We do this by having them hold the
2690 * page lock while dirtying the page, and pages are
2691 * always locked coming in here, so we get the desired
2694 wb = unlocked_inode_to_wb_begin(inode, &cookie);
2695 if (TestClearPageDirty(page)) {
2696 dec_lruvec_page_state(page, NR_FILE_DIRTY);
2697 dec_zone_page_state(page, NR_ZONE_WRITE_PENDING);
2698 dec_wb_stat(wb, WB_RECLAIMABLE);
2701 unlocked_inode_to_wb_end(inode, &cookie);
2704 return TestClearPageDirty(page);
2706 EXPORT_SYMBOL(clear_page_dirty_for_io);
2708 int test_clear_page_writeback(struct page *page)
2710 struct address_space *mapping = page_mapping(page);
2711 struct mem_cgroup *memcg;
2712 struct lruvec *lruvec;
2715 memcg = lock_page_memcg(page);
2716 lruvec = mem_cgroup_page_lruvec(page, page_pgdat(page));
2717 if (mapping && mapping_use_writeback_tags(mapping)) {
2718 struct inode *inode = mapping->host;
2719 struct backing_dev_info *bdi = inode_to_bdi(inode);
2720 unsigned long flags;
2722 xa_lock_irqsave(&mapping->i_pages, flags);
2723 ret = TestClearPageWriteback(page);
2725 radix_tree_tag_clear(&mapping->i_pages, page_index(page),
2726 PAGECACHE_TAG_WRITEBACK);
2727 if (bdi_cap_account_writeback(bdi)) {
2728 struct bdi_writeback *wb = inode_to_wb(inode);
2730 dec_wb_stat(wb, WB_WRITEBACK);
2731 __wb_writeout_inc(wb);
2735 if (mapping->host && !mapping_tagged(mapping,
2736 PAGECACHE_TAG_WRITEBACK))
2737 sb_clear_inode_writeback(mapping->host);
2739 xa_unlock_irqrestore(&mapping->i_pages, flags);
2741 ret = TestClearPageWriteback(page);
2744 * NOTE: Page might be free now! Writeback doesn't hold a page
2745 * reference on its own, it relies on truncation to wait for
2746 * the clearing of PG_writeback. The below can only access
2747 * page state that is static across allocation cycles.
2750 dec_lruvec_state(lruvec, NR_WRITEBACK);
2751 dec_zone_page_state(page, NR_ZONE_WRITE_PENDING);
2752 inc_node_page_state(page, NR_WRITTEN);
2754 __unlock_page_memcg(memcg);
2758 int __test_set_page_writeback(struct page *page, bool keep_write)
2760 struct address_space *mapping = page_mapping(page);
2763 lock_page_memcg(page);
2764 if (mapping && mapping_use_writeback_tags(mapping)) {
2765 struct inode *inode = mapping->host;
2766 struct backing_dev_info *bdi = inode_to_bdi(inode);
2767 unsigned long flags;
2769 xa_lock_irqsave(&mapping->i_pages, flags);
2770 ret = TestSetPageWriteback(page);
2774 on_wblist = mapping_tagged(mapping,
2775 PAGECACHE_TAG_WRITEBACK);
2777 radix_tree_tag_set(&mapping->i_pages, page_index(page),
2778 PAGECACHE_TAG_WRITEBACK);
2779 if (bdi_cap_account_writeback(bdi))
2780 inc_wb_stat(inode_to_wb(inode), WB_WRITEBACK);
2783 * We can come through here when swapping anonymous
2784 * pages, so we don't necessarily have an inode to track
2787 if (mapping->host && !on_wblist)
2788 sb_mark_inode_writeback(mapping->host);
2790 if (!PageDirty(page))
2791 radix_tree_tag_clear(&mapping->i_pages, page_index(page),
2792 PAGECACHE_TAG_DIRTY);
2794 radix_tree_tag_clear(&mapping->i_pages, page_index(page),
2795 PAGECACHE_TAG_TOWRITE);
2796 xa_unlock_irqrestore(&mapping->i_pages, flags);
2798 ret = TestSetPageWriteback(page);
2801 inc_lruvec_page_state(page, NR_WRITEBACK);
2802 inc_zone_page_state(page, NR_ZONE_WRITE_PENDING);
2804 unlock_page_memcg(page);
2808 EXPORT_SYMBOL(__test_set_page_writeback);
2811 * Return true if any of the pages in the mapping are marked with the
2814 int mapping_tagged(struct address_space *mapping, int tag)
2816 return radix_tree_tagged(&mapping->i_pages, tag);
2818 EXPORT_SYMBOL(mapping_tagged);
2821 * wait_for_stable_page() - wait for writeback to finish, if necessary.
2822 * @page: The page to wait on.
2824 * This function determines if the given page is related to a backing device
2825 * that requires page contents to be held stable during writeback. If so, then
2826 * it will wait for any pending writeback to complete.
2828 void wait_for_stable_page(struct page *page)
2830 if (bdi_cap_stable_pages_required(inode_to_bdi(page->mapping->host)))
2831 wait_on_page_writeback(page);
2833 EXPORT_SYMBOL_GPL(wait_for_stable_page);