4 * Copyright (C) 2002, Linus Torvalds.
5 * Copyright (C) 2007 Red Hat, Inc., Peter Zijlstra <pzijlstr@redhat.com>
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/mm_inline.h>
40 #include <trace/events/writeback.h>
45 * Sleep at most 200ms at a time in balance_dirty_pages().
47 #define MAX_PAUSE max(HZ/5, 1)
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.
53 #define DIRTY_POLL_THRESH (128 >> (PAGE_SHIFT - 10))
56 * Estimate write bandwidth at 200ms intervals.
58 #define BANDWIDTH_INTERVAL max(HZ/5, 1)
60 #define RATELIMIT_CALC_SHIFT 10
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.
66 static long ratelimit_pages
= 32;
68 /* The following parameters are exported via /proc/sys/vm */
71 * Start background writeback (via writeback threads) at this percentage
73 int dirty_background_ratio
= 10;
76 * dirty_background_bytes starts at 0 (disabled) so that it is a function of
77 * dirty_background_ratio * the amount of dirtyable memory
79 unsigned long dirty_background_bytes
;
82 * free highmem will not be subtracted from the total free memory
83 * for calculating free ratios if vm_highmem_is_dirtyable is true
85 int vm_highmem_is_dirtyable
;
88 * The generator of dirty data starts writeback at this percentage
90 int vm_dirty_ratio
= 20;
93 * vm_dirty_bytes starts at 0 (disabled) so that it is a function of
94 * vm_dirty_ratio * the amount of dirtyable memory
96 unsigned long vm_dirty_bytes
;
99 * The interval between `kupdate'-style writebacks
101 unsigned int dirty_writeback_interval
= 5 * 100; /* centiseconds */
103 EXPORT_SYMBOL_GPL(dirty_writeback_interval
);
106 * The longest time for which data is allowed to remain dirty
108 unsigned int dirty_expire_interval
= 30 * 100; /* centiseconds */
111 * Flag that makes the machine dump writes/reads and block dirtyings.
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.
121 EXPORT_SYMBOL(laptop_mode
);
123 /* End of sysctl-exported parameters */
125 struct wb_domain global_wb_domain
;
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 */
133 struct bdi_writeback
*wb
;
134 struct fprop_local_percpu
*wb_completions
;
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 */
141 unsigned long wb_dirty
; /* per-wb counterparts */
142 unsigned long wb_thresh
;
143 unsigned long wb_bg_thresh
;
145 unsigned long pos_ratio
;
148 #define DTC_INIT_COMMON(__wb) .wb = (__wb), \
149 .wb_completions = &(__wb)->completions
152 * Length of period for aging writeout fractions of bdis. This is an
153 * arbitrarily chosen number. The longer the period, the slower fractions will
154 * reflect changes in current writeout rate.
156 #define VM_COMPLETIONS_PERIOD_LEN (3*HZ)
158 #ifdef CONFIG_CGROUP_WRITEBACK
160 #define GDTC_INIT(__wb) .dom = &global_wb_domain, \
161 DTC_INIT_COMMON(__wb)
162 #define GDTC_INIT_NO_WB .dom = &global_wb_domain
164 static struct wb_domain
*dtc_dom(struct dirty_throttle_control
*dtc
)
169 static struct dirty_throttle_control
*mdtc_gdtc(struct dirty_throttle_control
*mdtc
)
174 static void wb_min_max_ratio(struct bdi_writeback
*wb
,
175 unsigned long *minp
, unsigned long *maxp
)
177 unsigned long this_bw
= wb
->avg_write_bandwidth
;
178 unsigned long tot_bw
= atomic_long_read(&wb
->bdi
->tot_write_bandwidth
);
179 unsigned long long min
= wb
->bdi
->min_ratio
;
180 unsigned long long max
= wb
->bdi
->max_ratio
;
183 * @wb may already be clean by the time control reaches here and
184 * the total may not include its bw.
186 if (this_bw
< tot_bw
) {
201 #else /* CONFIG_CGROUP_WRITEBACK */
203 #define GDTC_INIT(__wb) DTC_INIT_COMMON(__wb)
204 #define GDTC_INIT_NO_WB
206 static struct wb_domain
*dtc_dom(struct dirty_throttle_control
*dtc
)
208 return &global_wb_domain
;
211 static struct dirty_throttle_control
*mdtc_gdtc(struct dirty_throttle_control
*mdtc
)
216 static void wb_min_max_ratio(struct bdi_writeback
*wb
,
217 unsigned long *minp
, unsigned long *maxp
)
219 *minp
= wb
->bdi
->min_ratio
;
220 *maxp
= wb
->bdi
->max_ratio
;
223 #endif /* CONFIG_CGROUP_WRITEBACK */
226 * In a memory zone, there is a certain amount of pages we consider
227 * available for the page cache, which is essentially the number of
228 * free and reclaimable pages, minus some zone reserves to protect
229 * lowmem and the ability to uphold the zone's watermarks without
230 * requiring writeback.
232 * This number of dirtyable pages is the base value of which the
233 * user-configurable dirty ratio is the effictive number of pages that
234 * are allowed to be actually dirtied. Per individual zone, or
235 * globally by using the sum of dirtyable pages over all zones.
237 * Because the user is allowed to specify the dirty limit globally as
238 * absolute number of bytes, calculating the per-zone dirty limit can
239 * require translating the configured limit into a percentage of
240 * global dirtyable memory first.
244 * zone_dirtyable_memory - number of dirtyable pages in a zone
247 * Returns the zone's number of pages potentially available for dirty
248 * page cache. This is the base value for the per-zone dirty limits.
250 static unsigned long zone_dirtyable_memory(struct zone
*zone
)
252 unsigned long nr_pages
;
254 nr_pages
= zone_page_state(zone
, NR_FREE_PAGES
);
255 nr_pages
-= min(nr_pages
, zone
->dirty_balance_reserve
);
257 nr_pages
+= zone_page_state(zone
, NR_INACTIVE_FILE
);
258 nr_pages
+= zone_page_state(zone
, NR_ACTIVE_FILE
);
263 static unsigned long highmem_dirtyable_memory(unsigned long total
)
265 #ifdef CONFIG_HIGHMEM
269 for_each_node_state(node
, N_HIGH_MEMORY
) {
270 struct zone
*z
= &NODE_DATA(node
)->node_zones
[ZONE_HIGHMEM
];
272 x
+= zone_dirtyable_memory(z
);
275 * Unreclaimable memory (kernel memory or anonymous memory
276 * without swap) can bring down the dirtyable pages below
277 * the zone's dirty balance reserve and the above calculation
278 * will underflow. However we still want to add in nodes
279 * which are below threshold (negative values) to get a more
280 * accurate calculation but make sure that the total never
287 * Make sure that the number of highmem pages is never larger
288 * than the number of the total dirtyable memory. This can only
289 * occur in very strange VM situations but we want to make sure
290 * that this does not occur.
292 return min(x
, total
);
299 * global_dirtyable_memory - number of globally dirtyable pages
301 * Returns the global number of pages potentially available for dirty
302 * page cache. This is the base value for the global dirty limits.
304 static unsigned long global_dirtyable_memory(void)
308 x
= global_page_state(NR_FREE_PAGES
);
309 x
-= min(x
, dirty_balance_reserve
);
311 x
+= global_page_state(NR_INACTIVE_FILE
);
312 x
+= global_page_state(NR_ACTIVE_FILE
);
314 if (!vm_highmem_is_dirtyable
)
315 x
-= highmem_dirtyable_memory(x
);
317 return x
+ 1; /* Ensure that we never return 0 */
321 * domain_dirty_limits - calculate thresh and bg_thresh for a wb_domain
322 * @dtc: dirty_throttle_control of interest
324 * Calculate @dtc->thresh and ->bg_thresh considering
325 * vm_dirty_{bytes|ratio} and dirty_background_{bytes|ratio}. The caller
326 * must ensure that @dtc->avail is set before calling this function. The
327 * dirty limits will be lifted by 1/4 for PF_LESS_THROTTLE (ie. nfsd) and
330 static void domain_dirty_limits(struct dirty_throttle_control
*dtc
)
332 const unsigned long available_memory
= dtc
->avail
;
333 struct dirty_throttle_control
*gdtc
= mdtc_gdtc(dtc
);
334 unsigned long bytes
= vm_dirty_bytes
;
335 unsigned long bg_bytes
= dirty_background_bytes
;
336 unsigned long ratio
= vm_dirty_ratio
;
337 unsigned long bg_ratio
= dirty_background_ratio
;
338 unsigned long thresh
;
339 unsigned long bg_thresh
;
340 struct task_struct
*tsk
;
342 /* gdtc is !NULL iff @dtc is for memcg domain */
344 unsigned long global_avail
= gdtc
->avail
;
347 * The byte settings can't be applied directly to memcg
348 * domains. Convert them to ratios by scaling against
349 * globally available memory.
352 ratio
= min(DIV_ROUND_UP(bytes
, PAGE_SIZE
) * 100 /
353 global_avail
, 100UL);
355 bg_ratio
= min(DIV_ROUND_UP(bg_bytes
, PAGE_SIZE
) * 100 /
356 global_avail
, 100UL);
357 bytes
= bg_bytes
= 0;
361 thresh
= DIV_ROUND_UP(bytes
, PAGE_SIZE
);
363 thresh
= (ratio
* available_memory
) / 100;
366 bg_thresh
= DIV_ROUND_UP(bg_bytes
, PAGE_SIZE
);
368 bg_thresh
= (bg_ratio
* available_memory
) / 100;
370 if (bg_thresh
>= thresh
)
371 bg_thresh
= thresh
/ 2;
373 if (tsk
->flags
& PF_LESS_THROTTLE
|| rt_task(tsk
)) {
374 bg_thresh
+= bg_thresh
/ 4;
375 thresh
+= thresh
/ 4;
377 dtc
->thresh
= thresh
;
378 dtc
->bg_thresh
= bg_thresh
;
380 /* we should eventually report the domain in the TP */
382 trace_global_dirty_state(bg_thresh
, thresh
);
386 * global_dirty_limits - background-writeback and dirty-throttling thresholds
387 * @pbackground: out parameter for bg_thresh
388 * @pdirty: out parameter for thresh
390 * Calculate bg_thresh and thresh for global_wb_domain. See
391 * domain_dirty_limits() for details.
393 void global_dirty_limits(unsigned long *pbackground
, unsigned long *pdirty
)
395 struct dirty_throttle_control gdtc
= { GDTC_INIT_NO_WB
};
397 gdtc
.avail
= global_dirtyable_memory();
398 domain_dirty_limits(&gdtc
);
400 *pbackground
= gdtc
.bg_thresh
;
401 *pdirty
= gdtc
.thresh
;
405 * zone_dirty_limit - maximum number of dirty pages allowed in a zone
408 * Returns the maximum number of dirty pages allowed in a zone, based
409 * on the zone's dirtyable memory.
411 static unsigned long zone_dirty_limit(struct zone
*zone
)
413 unsigned long zone_memory
= zone_dirtyable_memory(zone
);
414 struct task_struct
*tsk
= current
;
418 dirty
= DIV_ROUND_UP(vm_dirty_bytes
, PAGE_SIZE
) *
419 zone_memory
/ global_dirtyable_memory();
421 dirty
= vm_dirty_ratio
* zone_memory
/ 100;
423 if (tsk
->flags
& PF_LESS_THROTTLE
|| rt_task(tsk
))
430 * zone_dirty_ok - tells whether a zone is within its dirty limits
431 * @zone: the zone to check
433 * Returns %true when the dirty pages in @zone are within the zone's
434 * dirty limit, %false if the limit is exceeded.
436 bool zone_dirty_ok(struct zone
*zone
)
438 unsigned long limit
= zone_dirty_limit(zone
);
440 return zone_page_state(zone
, NR_FILE_DIRTY
) +
441 zone_page_state(zone
, NR_UNSTABLE_NFS
) +
442 zone_page_state(zone
, NR_WRITEBACK
) <= limit
;
445 int dirty_background_ratio_handler(struct ctl_table
*table
, int write
,
446 void __user
*buffer
, size_t *lenp
,
451 ret
= proc_dointvec_minmax(table
, write
, buffer
, lenp
, ppos
);
452 if (ret
== 0 && write
)
453 dirty_background_bytes
= 0;
457 int dirty_background_bytes_handler(struct ctl_table
*table
, int write
,
458 void __user
*buffer
, size_t *lenp
,
463 ret
= proc_doulongvec_minmax(table
, write
, buffer
, lenp
, ppos
);
464 if (ret
== 0 && write
)
465 dirty_background_ratio
= 0;
469 int dirty_ratio_handler(struct ctl_table
*table
, int write
,
470 void __user
*buffer
, size_t *lenp
,
473 int old_ratio
= vm_dirty_ratio
;
476 ret
= proc_dointvec_minmax(table
, write
, buffer
, lenp
, ppos
);
477 if (ret
== 0 && write
&& vm_dirty_ratio
!= old_ratio
) {
478 writeback_set_ratelimit();
484 int dirty_bytes_handler(struct ctl_table
*table
, int write
,
485 void __user
*buffer
, size_t *lenp
,
488 unsigned long old_bytes
= vm_dirty_bytes
;
491 ret
= proc_doulongvec_minmax(table
, write
, buffer
, lenp
, ppos
);
492 if (ret
== 0 && write
&& vm_dirty_bytes
!= old_bytes
) {
493 writeback_set_ratelimit();
499 static unsigned long wp_next_time(unsigned long cur_time
)
501 cur_time
+= VM_COMPLETIONS_PERIOD_LEN
;
502 /* 0 has a special meaning... */
508 static void wb_domain_writeout_inc(struct wb_domain
*dom
,
509 struct fprop_local_percpu
*completions
,
510 unsigned int max_prop_frac
)
512 __fprop_inc_percpu_max(&dom
->completions
, completions
,
514 /* First event after period switching was turned off? */
515 if (!unlikely(dom
->period_time
)) {
517 * We can race with other __bdi_writeout_inc calls here but
518 * it does not cause any harm since the resulting time when
519 * timer will fire and what is in writeout_period_time will be
522 dom
->period_time
= wp_next_time(jiffies
);
523 mod_timer(&dom
->period_timer
, dom
->period_time
);
528 * Increment @wb's writeout completion count and the global writeout
529 * completion count. Called from test_clear_page_writeback().
531 static inline void __wb_writeout_inc(struct bdi_writeback
*wb
)
533 __inc_wb_stat(wb
, WB_WRITTEN
);
534 wb_domain_writeout_inc(&global_wb_domain
, &wb
->completions
,
535 wb
->bdi
->max_prop_frac
);
538 void wb_writeout_inc(struct bdi_writeback
*wb
)
542 local_irq_save(flags
);
543 __wb_writeout_inc(wb
);
544 local_irq_restore(flags
);
546 EXPORT_SYMBOL_GPL(wb_writeout_inc
);
549 * On idle system, we can be called long after we scheduled because we use
550 * deferred timers so count with missed periods.
552 static void writeout_period(unsigned long t
)
554 struct wb_domain
*dom
= (void *)t
;
555 int miss_periods
= (jiffies
- dom
->period_time
) /
556 VM_COMPLETIONS_PERIOD_LEN
;
558 if (fprop_new_period(&dom
->completions
, miss_periods
+ 1)) {
559 dom
->period_time
= wp_next_time(dom
->period_time
+
560 miss_periods
* VM_COMPLETIONS_PERIOD_LEN
);
561 mod_timer(&dom
->period_timer
, dom
->period_time
);
564 * Aging has zeroed all fractions. Stop wasting CPU on period
567 dom
->period_time
= 0;
571 int wb_domain_init(struct wb_domain
*dom
, gfp_t gfp
)
573 memset(dom
, 0, sizeof(*dom
));
575 spin_lock_init(&dom
->lock
);
577 init_timer_deferrable(&dom
->period_timer
);
578 dom
->period_timer
.function
= writeout_period
;
579 dom
->period_timer
.data
= (unsigned long)dom
;
581 dom
->dirty_limit_tstamp
= jiffies
;
583 return fprop_global_init(&dom
->completions
, gfp
);
587 * bdi_min_ratio keeps the sum of the minimum dirty shares of all
588 * registered backing devices, which, for obvious reasons, can not
591 static unsigned int bdi_min_ratio
;
593 int bdi_set_min_ratio(struct backing_dev_info
*bdi
, unsigned int min_ratio
)
597 spin_lock_bh(&bdi_lock
);
598 if (min_ratio
> bdi
->max_ratio
) {
601 min_ratio
-= bdi
->min_ratio
;
602 if (bdi_min_ratio
+ min_ratio
< 100) {
603 bdi_min_ratio
+= min_ratio
;
604 bdi
->min_ratio
+= min_ratio
;
609 spin_unlock_bh(&bdi_lock
);
614 int bdi_set_max_ratio(struct backing_dev_info
*bdi
, unsigned max_ratio
)
621 spin_lock_bh(&bdi_lock
);
622 if (bdi
->min_ratio
> max_ratio
) {
625 bdi
->max_ratio
= max_ratio
;
626 bdi
->max_prop_frac
= (FPROP_FRAC_BASE
* max_ratio
) / 100;
628 spin_unlock_bh(&bdi_lock
);
632 EXPORT_SYMBOL(bdi_set_max_ratio
);
634 static unsigned long dirty_freerun_ceiling(unsigned long thresh
,
635 unsigned long bg_thresh
)
637 return (thresh
+ bg_thresh
) / 2;
640 static unsigned long hard_dirty_limit(struct wb_domain
*dom
,
641 unsigned long thresh
)
643 return max(thresh
, dom
->dirty_limit
);
647 * __wb_calc_thresh - @wb's share of dirty throttling threshold
648 * @dtc: dirty_throttle_context of interest
650 * Returns @wb's dirty limit in pages. The term "dirty" in the context of
651 * dirty balancing includes all PG_dirty, PG_writeback and NFS unstable pages.
653 * Note that balance_dirty_pages() will only seriously take it as a hard limit
654 * when sleeping max_pause per page is not enough to keep the dirty pages under
655 * control. For example, when the device is completely stalled due to some error
656 * conditions, or when there are 1000 dd tasks writing to a slow 10MB/s USB key.
657 * In the other normal situations, it acts more gently by throttling the tasks
658 * more (rather than completely block them) when the wb dirty pages go high.
660 * It allocates high/low dirty limits to fast/slow devices, in order to prevent
661 * - starving fast devices
662 * - piling up dirty pages (that will take long time to sync) on slow devices
664 * The wb's share of dirty limit will be adapting to its throughput and
665 * bounded by the bdi->min_ratio and/or bdi->max_ratio parameters, if set.
667 static unsigned long __wb_calc_thresh(struct dirty_throttle_control
*dtc
)
669 struct wb_domain
*dom
= dtc_dom(dtc
);
670 unsigned long thresh
= dtc
->thresh
;
672 long numerator
, denominator
;
673 unsigned long wb_min_ratio
, wb_max_ratio
;
676 * Calculate this BDI's share of the thresh ratio.
678 fprop_fraction_percpu(&dom
->completions
, dtc
->wb_completions
,
679 &numerator
, &denominator
);
681 wb_thresh
= (thresh
* (100 - bdi_min_ratio
)) / 100;
682 wb_thresh
*= numerator
;
683 do_div(wb_thresh
, denominator
);
685 wb_min_max_ratio(dtc
->wb
, &wb_min_ratio
, &wb_max_ratio
);
687 wb_thresh
+= (thresh
* wb_min_ratio
) / 100;
688 if (wb_thresh
> (thresh
* wb_max_ratio
) / 100)
689 wb_thresh
= thresh
* wb_max_ratio
/ 100;
694 unsigned long wb_calc_thresh(struct bdi_writeback
*wb
, unsigned long thresh
)
696 struct dirty_throttle_control gdtc
= { GDTC_INIT(wb
),
698 return __wb_calc_thresh(&gdtc
);
703 * f(dirty) := 1.0 + (----------------)
706 * it's a 3rd order polynomial that subjects to
708 * (1) f(freerun) = 2.0 => rampup dirty_ratelimit reasonably fast
709 * (2) f(setpoint) = 1.0 => the balance point
710 * (3) f(limit) = 0 => the hard limit
711 * (4) df/dx <= 0 => negative feedback control
712 * (5) the closer to setpoint, the smaller |df/dx| (and the reverse)
713 * => fast response on large errors; small oscillation near setpoint
715 static long long pos_ratio_polynom(unsigned long setpoint
,
722 x
= div64_s64(((s64
)setpoint
- (s64
)dirty
) << RATELIMIT_CALC_SHIFT
,
723 limit
- setpoint
+ 1);
725 pos_ratio
= pos_ratio
* x
>> RATELIMIT_CALC_SHIFT
;
726 pos_ratio
= pos_ratio
* x
>> RATELIMIT_CALC_SHIFT
;
727 pos_ratio
+= 1 << RATELIMIT_CALC_SHIFT
;
729 return clamp(pos_ratio
, 0LL, 2LL << RATELIMIT_CALC_SHIFT
);
733 * Dirty position control.
735 * (o) global/bdi setpoints
737 * We want the dirty pages be balanced around the global/wb setpoints.
738 * When the number of dirty pages is higher/lower than the setpoint, the
739 * dirty position control ratio (and hence task dirty ratelimit) will be
740 * decreased/increased to bring the dirty pages back to the setpoint.
742 * pos_ratio = 1 << RATELIMIT_CALC_SHIFT
744 * if (dirty < setpoint) scale up pos_ratio
745 * if (dirty > setpoint) scale down pos_ratio
747 * if (wb_dirty < wb_setpoint) scale up pos_ratio
748 * if (wb_dirty > wb_setpoint) scale down pos_ratio
750 * task_ratelimit = dirty_ratelimit * pos_ratio >> RATELIMIT_CALC_SHIFT
752 * (o) global control line
756 * | |<===== global dirty control scope ======>|
764 * 1.0 ................................*
770 * 0 +------------.------------------.----------------------*------------->
771 * freerun^ setpoint^ limit^ dirty pages
773 * (o) wb control line
781 * | * |<=========== span ============>|
782 * 1.0 .......................*
794 * 1/4 ...............................................* * * * * * * * * * * *
798 * 0 +----------------------.-------------------------------.------------->
799 * wb_setpoint^ x_intercept^
801 * The wb control line won't drop below pos_ratio=1/4, so that wb_dirty can
802 * be smoothly throttled down to normal if it starts high in situations like
803 * - start writing to a slow SD card and a fast disk at the same time. The SD
804 * card's wb_dirty may rush to many times higher than wb_setpoint.
805 * - the wb dirty thresh drops quickly due to change of JBOD workload
807 static void wb_position_ratio(struct dirty_throttle_control
*dtc
)
809 struct bdi_writeback
*wb
= dtc
->wb
;
810 unsigned long write_bw
= wb
->avg_write_bandwidth
;
811 unsigned long freerun
= dirty_freerun_ceiling(dtc
->thresh
, dtc
->bg_thresh
);
812 unsigned long limit
= hard_dirty_limit(dtc_dom(dtc
), dtc
->thresh
);
813 unsigned long wb_thresh
= dtc
->wb_thresh
;
814 unsigned long x_intercept
;
815 unsigned long setpoint
; /* dirty pages' target balance point */
816 unsigned long wb_setpoint
;
818 long long pos_ratio
; /* for scaling up/down the rate limit */
823 if (unlikely(dtc
->dirty
>= limit
))
829 * See comment for pos_ratio_polynom().
831 setpoint
= (freerun
+ limit
) / 2;
832 pos_ratio
= pos_ratio_polynom(setpoint
, dtc
->dirty
, limit
);
835 * The strictlimit feature is a tool preventing mistrusted filesystems
836 * from growing a large number of dirty pages before throttling. For
837 * such filesystems balance_dirty_pages always checks wb counters
838 * against wb limits. Even if global "nr_dirty" is under "freerun".
839 * This is especially important for fuse which sets bdi->max_ratio to
840 * 1% by default. Without strictlimit feature, fuse writeback may
841 * consume arbitrary amount of RAM because it is accounted in
842 * NR_WRITEBACK_TEMP which is not involved in calculating "nr_dirty".
844 * Here, in wb_position_ratio(), we calculate pos_ratio based on
845 * two values: wb_dirty and wb_thresh. Let's consider an example:
846 * total amount of RAM is 16GB, bdi->max_ratio is equal to 1%, global
847 * limits are set by default to 10% and 20% (background and throttle).
848 * Then wb_thresh is 1% of 20% of 16GB. This amounts to ~8K pages.
849 * wb_calc_thresh(wb, bg_thresh) is about ~4K pages. wb_setpoint is
850 * about ~6K pages (as the average of background and throttle wb
851 * limits). The 3rd order polynomial will provide positive feedback if
852 * wb_dirty is under wb_setpoint and vice versa.
854 * Note, that we cannot use global counters in these calculations
855 * because we want to throttle process writing to a strictlimit wb
856 * much earlier than global "freerun" is reached (~23MB vs. ~2.3GB
857 * in the example above).
859 if (unlikely(wb
->bdi
->capabilities
& BDI_CAP_STRICTLIMIT
)) {
860 long long wb_pos_ratio
;
862 if (dtc
->wb_dirty
< 8) {
863 dtc
->pos_ratio
= min_t(long long, pos_ratio
* 2,
864 2 << RATELIMIT_CALC_SHIFT
);
868 if (dtc
->wb_dirty
>= wb_thresh
)
871 wb_setpoint
= dirty_freerun_ceiling(wb_thresh
,
874 if (wb_setpoint
== 0 || wb_setpoint
== wb_thresh
)
877 wb_pos_ratio
= pos_ratio_polynom(wb_setpoint
, dtc
->wb_dirty
,
881 * Typically, for strictlimit case, wb_setpoint << setpoint
882 * and pos_ratio >> wb_pos_ratio. In the other words global
883 * state ("dirty") is not limiting factor and we have to
884 * make decision based on wb counters. But there is an
885 * important case when global pos_ratio should get precedence:
886 * global limits are exceeded (e.g. due to activities on other
887 * wb's) while given strictlimit wb is below limit.
889 * "pos_ratio * wb_pos_ratio" would work for the case above,
890 * but it would look too non-natural for the case of all
891 * activity in the system coming from a single strictlimit wb
892 * with bdi->max_ratio == 100%.
894 * Note that min() below somewhat changes the dynamics of the
895 * control system. Normally, pos_ratio value can be well over 3
896 * (when globally we are at freerun and wb is well below wb
897 * setpoint). Now the maximum pos_ratio in the same situation
898 * is 2. We might want to tweak this if we observe the control
899 * system is too slow to adapt.
901 dtc
->pos_ratio
= min(pos_ratio
, wb_pos_ratio
);
906 * We have computed basic pos_ratio above based on global situation. If
907 * the wb is over/under its share of dirty pages, we want to scale
908 * pos_ratio further down/up. That is done by the following mechanism.
914 * f(wb_dirty) := 1.0 + k * (wb_dirty - wb_setpoint)
916 * x_intercept - wb_dirty
917 * := --------------------------
918 * x_intercept - wb_setpoint
920 * The main wb control line is a linear function that subjects to
922 * (1) f(wb_setpoint) = 1.0
923 * (2) k = - 1 / (8 * write_bw) (in single wb case)
924 * or equally: x_intercept = wb_setpoint + 8 * write_bw
926 * For single wb case, the dirty pages are observed to fluctuate
927 * regularly within range
928 * [wb_setpoint - write_bw/2, wb_setpoint + write_bw/2]
929 * for various filesystems, where (2) can yield in a reasonable 12.5%
930 * fluctuation range for pos_ratio.
932 * For JBOD case, wb_thresh (not wb_dirty!) could fluctuate up to its
933 * own size, so move the slope over accordingly and choose a slope that
934 * yields 100% pos_ratio fluctuation on suddenly doubled wb_thresh.
936 if (unlikely(wb_thresh
> dtc
->thresh
))
937 wb_thresh
= dtc
->thresh
;
939 * It's very possible that wb_thresh is close to 0 not because the
940 * device is slow, but that it has remained inactive for long time.
941 * Honour such devices a reasonable good (hopefully IO efficient)
942 * threshold, so that the occasional writes won't be blocked and active
943 * writes can rampup the threshold quickly.
945 wb_thresh
= max(wb_thresh
, (limit
- dtc
->dirty
) / 8);
947 * scale global setpoint to wb's:
948 * wb_setpoint = setpoint * wb_thresh / thresh
950 x
= div_u64((u64
)wb_thresh
<< 16, dtc
->thresh
+ 1);
951 wb_setpoint
= setpoint
* (u64
)x
>> 16;
953 * Use span=(8*write_bw) in single wb case as indicated by
954 * (thresh - wb_thresh ~= 0) and transit to wb_thresh in JBOD case.
956 * wb_thresh thresh - wb_thresh
957 * span = --------- * (8 * write_bw) + ------------------ * wb_thresh
960 span
= (dtc
->thresh
- wb_thresh
+ 8 * write_bw
) * (u64
)x
>> 16;
961 x_intercept
= wb_setpoint
+ span
;
963 if (dtc
->wb_dirty
< x_intercept
- span
/ 4) {
964 pos_ratio
= div64_u64(pos_ratio
* (x_intercept
- dtc
->wb_dirty
),
965 x_intercept
- wb_setpoint
+ 1);
970 * wb reserve area, safeguard against dirty pool underrun and disk idle
971 * It may push the desired control point of global dirty pages higher
974 x_intercept
= wb_thresh
/ 2;
975 if (dtc
->wb_dirty
< x_intercept
) {
976 if (dtc
->wb_dirty
> x_intercept
/ 8)
977 pos_ratio
= div_u64(pos_ratio
* x_intercept
,
983 dtc
->pos_ratio
= pos_ratio
;
986 static void wb_update_write_bandwidth(struct bdi_writeback
*wb
,
987 unsigned long elapsed
,
988 unsigned long written
)
990 const unsigned long period
= roundup_pow_of_two(3 * HZ
);
991 unsigned long avg
= wb
->avg_write_bandwidth
;
992 unsigned long old
= wb
->write_bandwidth
;
996 * bw = written * HZ / elapsed
998 * bw * elapsed + write_bandwidth * (period - elapsed)
999 * write_bandwidth = ---------------------------------------------------
1002 * @written may have decreased due to account_page_redirty().
1003 * Avoid underflowing @bw calculation.
1005 bw
= written
- min(written
, wb
->written_stamp
);
1007 if (unlikely(elapsed
> period
)) {
1008 do_div(bw
, elapsed
);
1012 bw
+= (u64
)wb
->write_bandwidth
* (period
- elapsed
);
1013 bw
>>= ilog2(period
);
1016 * one more level of smoothing, for filtering out sudden spikes
1018 if (avg
> old
&& old
>= (unsigned long)bw
)
1019 avg
-= (avg
- old
) >> 3;
1021 if (avg
< old
&& old
<= (unsigned long)bw
)
1022 avg
+= (old
- avg
) >> 3;
1025 /* keep avg > 0 to guarantee that tot > 0 if there are dirty wbs */
1026 avg
= max(avg
, 1LU);
1027 if (wb_has_dirty_io(wb
)) {
1028 long delta
= avg
- wb
->avg_write_bandwidth
;
1029 WARN_ON_ONCE(atomic_long_add_return(delta
,
1030 &wb
->bdi
->tot_write_bandwidth
) <= 0);
1032 wb
->write_bandwidth
= bw
;
1033 wb
->avg_write_bandwidth
= avg
;
1036 static void update_dirty_limit(struct dirty_throttle_control
*dtc
)
1038 struct wb_domain
*dom
= dtc_dom(dtc
);
1039 unsigned long thresh
= dtc
->thresh
;
1040 unsigned long limit
= dom
->dirty_limit
;
1043 * Follow up in one step.
1045 if (limit
< thresh
) {
1051 * Follow down slowly. Use the higher one as the target, because thresh
1052 * may drop below dirty. This is exactly the reason to introduce
1053 * dom->dirty_limit which is guaranteed to lie above the dirty pages.
1055 thresh
= max(thresh
, dtc
->dirty
);
1056 if (limit
> thresh
) {
1057 limit
-= (limit
- thresh
) >> 5;
1062 dom
->dirty_limit
= limit
;
1065 static void domain_update_bandwidth(struct dirty_throttle_control
*dtc
,
1068 struct wb_domain
*dom
= dtc_dom(dtc
);
1071 * check locklessly first to optimize away locking for the most time
1073 if (time_before(now
, dom
->dirty_limit_tstamp
+ BANDWIDTH_INTERVAL
))
1076 spin_lock(&dom
->lock
);
1077 if (time_after_eq(now
, dom
->dirty_limit_tstamp
+ BANDWIDTH_INTERVAL
)) {
1078 update_dirty_limit(dtc
);
1079 dom
->dirty_limit_tstamp
= now
;
1081 spin_unlock(&dom
->lock
);
1085 * Maintain wb->dirty_ratelimit, the base dirty throttle rate.
1087 * Normal wb tasks will be curbed at or below it in long term.
1088 * Obviously it should be around (write_bw / N) when there are N dd tasks.
1090 static void wb_update_dirty_ratelimit(struct dirty_throttle_control
*dtc
,
1091 unsigned long dirtied
,
1092 unsigned long elapsed
)
1094 struct bdi_writeback
*wb
= dtc
->wb
;
1095 unsigned long dirty
= dtc
->dirty
;
1096 unsigned long freerun
= dirty_freerun_ceiling(dtc
->thresh
, dtc
->bg_thresh
);
1097 unsigned long limit
= hard_dirty_limit(dtc_dom(dtc
), dtc
->thresh
);
1098 unsigned long setpoint
= (freerun
+ limit
) / 2;
1099 unsigned long write_bw
= wb
->avg_write_bandwidth
;
1100 unsigned long dirty_ratelimit
= wb
->dirty_ratelimit
;
1101 unsigned long dirty_rate
;
1102 unsigned long task_ratelimit
;
1103 unsigned long balanced_dirty_ratelimit
;
1108 * The dirty rate will match the writeout rate in long term, except
1109 * when dirty pages are truncated by userspace or re-dirtied by FS.
1111 dirty_rate
= (dirtied
- wb
->dirtied_stamp
) * HZ
/ elapsed
;
1114 * task_ratelimit reflects each dd's dirty rate for the past 200ms.
1116 task_ratelimit
= (u64
)dirty_ratelimit
*
1117 dtc
->pos_ratio
>> RATELIMIT_CALC_SHIFT
;
1118 task_ratelimit
++; /* it helps rampup dirty_ratelimit from tiny values */
1121 * A linear estimation of the "balanced" throttle rate. The theory is,
1122 * if there are N dd tasks, each throttled at task_ratelimit, the wb's
1123 * dirty_rate will be measured to be (N * task_ratelimit). So the below
1124 * formula will yield the balanced rate limit (write_bw / N).
1126 * Note that the expanded form is not a pure rate feedback:
1127 * rate_(i+1) = rate_(i) * (write_bw / dirty_rate) (1)
1128 * but also takes pos_ratio into account:
1129 * rate_(i+1) = rate_(i) * (write_bw / dirty_rate) * pos_ratio (2)
1131 * (1) is not realistic because pos_ratio also takes part in balancing
1132 * the dirty rate. Consider the state
1133 * pos_ratio = 0.5 (3)
1134 * rate = 2 * (write_bw / N) (4)
1135 * If (1) is used, it will stuck in that state! Because each dd will
1137 * task_ratelimit = pos_ratio * rate = (write_bw / N) (5)
1139 * dirty_rate = N * task_ratelimit = write_bw (6)
1140 * put (6) into (1) we get
1141 * rate_(i+1) = rate_(i) (7)
1143 * So we end up using (2) to always keep
1144 * rate_(i+1) ~= (write_bw / N) (8)
1145 * regardless of the value of pos_ratio. As long as (8) is satisfied,
1146 * pos_ratio is able to drive itself to 1.0, which is not only where
1147 * the dirty count meet the setpoint, but also where the slope of
1148 * pos_ratio is most flat and hence task_ratelimit is least fluctuated.
1150 balanced_dirty_ratelimit
= div_u64((u64
)task_ratelimit
* write_bw
,
1153 * balanced_dirty_ratelimit ~= (write_bw / N) <= write_bw
1155 if (unlikely(balanced_dirty_ratelimit
> write_bw
))
1156 balanced_dirty_ratelimit
= write_bw
;
1159 * We could safely do this and return immediately:
1161 * wb->dirty_ratelimit = balanced_dirty_ratelimit;
1163 * However to get a more stable dirty_ratelimit, the below elaborated
1164 * code makes use of task_ratelimit to filter out singular points and
1165 * limit the step size.
1167 * The below code essentially only uses the relative value of
1169 * task_ratelimit - dirty_ratelimit
1170 * = (pos_ratio - 1) * dirty_ratelimit
1172 * which reflects the direction and size of dirty position error.
1176 * dirty_ratelimit will follow balanced_dirty_ratelimit iff
1177 * task_ratelimit is on the same side of dirty_ratelimit, too.
1179 * - dirty_ratelimit > balanced_dirty_ratelimit
1180 * - dirty_ratelimit > task_ratelimit (dirty pages are above setpoint)
1181 * lowering dirty_ratelimit will help meet both the position and rate
1182 * control targets. Otherwise, don't update dirty_ratelimit if it will
1183 * only help meet the rate target. After all, what the users ultimately
1184 * feel and care are stable dirty rate and small position error.
1186 * |task_ratelimit - dirty_ratelimit| is used to limit the step size
1187 * and filter out the singular points of balanced_dirty_ratelimit. Which
1188 * keeps jumping around randomly and can even leap far away at times
1189 * due to the small 200ms estimation period of dirty_rate (we want to
1190 * keep that period small to reduce time lags).
1195 * For strictlimit case, calculations above were based on wb counters
1196 * and limits (starting from pos_ratio = wb_position_ratio() and up to
1197 * balanced_dirty_ratelimit = task_ratelimit * write_bw / dirty_rate).
1198 * Hence, to calculate "step" properly, we have to use wb_dirty as
1199 * "dirty" and wb_setpoint as "setpoint".
1201 * We rampup dirty_ratelimit forcibly if wb_dirty is low because
1202 * it's possible that wb_thresh is close to zero due to inactivity
1203 * of backing device.
1205 if (unlikely(wb
->bdi
->capabilities
& BDI_CAP_STRICTLIMIT
)) {
1206 dirty
= dtc
->wb_dirty
;
1207 if (dtc
->wb_dirty
< 8)
1208 setpoint
= dtc
->wb_dirty
+ 1;
1210 setpoint
= (dtc
->wb_thresh
+ dtc
->wb_bg_thresh
) / 2;
1213 if (dirty
< setpoint
) {
1214 x
= min3(wb
->balanced_dirty_ratelimit
,
1215 balanced_dirty_ratelimit
, task_ratelimit
);
1216 if (dirty_ratelimit
< x
)
1217 step
= x
- dirty_ratelimit
;
1219 x
= max3(wb
->balanced_dirty_ratelimit
,
1220 balanced_dirty_ratelimit
, task_ratelimit
);
1221 if (dirty_ratelimit
> x
)
1222 step
= dirty_ratelimit
- x
;
1226 * Don't pursue 100% rate matching. It's impossible since the balanced
1227 * rate itself is constantly fluctuating. So decrease the track speed
1228 * when it gets close to the target. Helps eliminate pointless tremors.
1230 step
>>= dirty_ratelimit
/ (2 * step
+ 1);
1232 * Limit the tracking speed to avoid overshooting.
1234 step
= (step
+ 7) / 8;
1236 if (dirty_ratelimit
< balanced_dirty_ratelimit
)
1237 dirty_ratelimit
+= step
;
1239 dirty_ratelimit
-= step
;
1241 wb
->dirty_ratelimit
= max(dirty_ratelimit
, 1UL);
1242 wb
->balanced_dirty_ratelimit
= balanced_dirty_ratelimit
;
1244 trace_bdi_dirty_ratelimit(wb
->bdi
, dirty_rate
, task_ratelimit
);
1247 static void __wb_update_bandwidth(struct dirty_throttle_control
*dtc
,
1248 unsigned long start_time
,
1249 bool update_ratelimit
)
1251 struct bdi_writeback
*wb
= dtc
->wb
;
1252 unsigned long now
= jiffies
;
1253 unsigned long elapsed
= now
- wb
->bw_time_stamp
;
1254 unsigned long dirtied
;
1255 unsigned long written
;
1257 lockdep_assert_held(&wb
->list_lock
);
1260 * rate-limit, only update once every 200ms.
1262 if (elapsed
< BANDWIDTH_INTERVAL
)
1265 dirtied
= percpu_counter_read(&wb
->stat
[WB_DIRTIED
]);
1266 written
= percpu_counter_read(&wb
->stat
[WB_WRITTEN
]);
1269 * Skip quiet periods when disk bandwidth is under-utilized.
1270 * (at least 1s idle time between two flusher runs)
1272 if (elapsed
> HZ
&& time_before(wb
->bw_time_stamp
, start_time
))
1275 if (update_ratelimit
) {
1276 domain_update_bandwidth(dtc
, now
);
1277 wb_update_dirty_ratelimit(dtc
, dirtied
, elapsed
);
1279 wb_update_write_bandwidth(wb
, elapsed
, written
);
1282 wb
->dirtied_stamp
= dirtied
;
1283 wb
->written_stamp
= written
;
1284 wb
->bw_time_stamp
= now
;
1287 void wb_update_bandwidth(struct bdi_writeback
*wb
, unsigned long start_time
)
1289 struct dirty_throttle_control gdtc
= { GDTC_INIT(wb
) };
1291 __wb_update_bandwidth(&gdtc
, start_time
, false);
1295 * After a task dirtied this many pages, balance_dirty_pages_ratelimited()
1296 * will look to see if it needs to start dirty throttling.
1298 * If dirty_poll_interval is too low, big NUMA machines will call the expensive
1299 * global_page_state() too often. So scale it near-sqrt to the safety margin
1300 * (the number of pages we may dirty without exceeding the dirty limits).
1302 static unsigned long dirty_poll_interval(unsigned long dirty
,
1303 unsigned long thresh
)
1306 return 1UL << (ilog2(thresh
- dirty
) >> 1);
1311 static unsigned long wb_max_pause(struct bdi_writeback
*wb
,
1312 unsigned long wb_dirty
)
1314 unsigned long bw
= wb
->avg_write_bandwidth
;
1318 * Limit pause time for small memory systems. If sleeping for too long
1319 * time, a small pool of dirty/writeback pages may go empty and disk go
1322 * 8 serves as the safety ratio.
1324 t
= wb_dirty
/ (1 + bw
/ roundup_pow_of_two(1 + HZ
/ 8));
1327 return min_t(unsigned long, t
, MAX_PAUSE
);
1330 static long wb_min_pause(struct bdi_writeback
*wb
,
1332 unsigned long task_ratelimit
,
1333 unsigned long dirty_ratelimit
,
1334 int *nr_dirtied_pause
)
1336 long hi
= ilog2(wb
->avg_write_bandwidth
);
1337 long lo
= ilog2(wb
->dirty_ratelimit
);
1338 long t
; /* target pause */
1339 long pause
; /* estimated next pause */
1340 int pages
; /* target nr_dirtied_pause */
1342 /* target for 10ms pause on 1-dd case */
1343 t
= max(1, HZ
/ 100);
1346 * Scale up pause time for concurrent dirtiers in order to reduce CPU
1349 * (N * 10ms) on 2^N concurrent tasks.
1352 t
+= (hi
- lo
) * (10 * HZ
) / 1024;
1355 * This is a bit convoluted. We try to base the next nr_dirtied_pause
1356 * on the much more stable dirty_ratelimit. However the next pause time
1357 * will be computed based on task_ratelimit and the two rate limits may
1358 * depart considerably at some time. Especially if task_ratelimit goes
1359 * below dirty_ratelimit/2 and the target pause is max_pause, the next
1360 * pause time will be max_pause*2 _trimmed down_ to max_pause. As a
1361 * result task_ratelimit won't be executed faithfully, which could
1362 * eventually bring down dirty_ratelimit.
1364 * We apply two rules to fix it up:
1365 * 1) try to estimate the next pause time and if necessary, use a lower
1366 * nr_dirtied_pause so as not to exceed max_pause. When this happens,
1367 * nr_dirtied_pause will be "dancing" with task_ratelimit.
1368 * 2) limit the target pause time to max_pause/2, so that the normal
1369 * small fluctuations of task_ratelimit won't trigger rule (1) and
1370 * nr_dirtied_pause will remain as stable as dirty_ratelimit.
1372 t
= min(t
, 1 + max_pause
/ 2);
1373 pages
= dirty_ratelimit
* t
/ roundup_pow_of_two(HZ
);
1376 * Tiny nr_dirtied_pause is found to hurt I/O performance in the test
1377 * case fio-mmap-randwrite-64k, which does 16*{sync read, async write}.
1378 * When the 16 consecutive reads are often interrupted by some dirty
1379 * throttling pause during the async writes, cfq will go into idles
1380 * (deadline is fine). So push nr_dirtied_pause as high as possible
1381 * until reaches DIRTY_POLL_THRESH=32 pages.
1383 if (pages
< DIRTY_POLL_THRESH
) {
1385 pages
= dirty_ratelimit
* t
/ roundup_pow_of_two(HZ
);
1386 if (pages
> DIRTY_POLL_THRESH
) {
1387 pages
= DIRTY_POLL_THRESH
;
1388 t
= HZ
* DIRTY_POLL_THRESH
/ dirty_ratelimit
;
1392 pause
= HZ
* pages
/ (task_ratelimit
+ 1);
1393 if (pause
> max_pause
) {
1395 pages
= task_ratelimit
* t
/ roundup_pow_of_two(HZ
);
1398 *nr_dirtied_pause
= pages
;
1400 * The minimal pause time will normally be half the target pause time.
1402 return pages
>= DIRTY_POLL_THRESH
? 1 + t
/ 2 : t
;
1405 static inline void wb_dirty_limits(struct dirty_throttle_control
*dtc
)
1407 struct bdi_writeback
*wb
= dtc
->wb
;
1408 unsigned long wb_reclaimable
;
1411 * wb_thresh is not treated as some limiting factor as
1412 * dirty_thresh, due to reasons
1413 * - in JBOD setup, wb_thresh can fluctuate a lot
1414 * - in a system with HDD and USB key, the USB key may somehow
1415 * go into state (wb_dirty >> wb_thresh) either because
1416 * wb_dirty starts high, or because wb_thresh drops low.
1417 * In this case we don't want to hard throttle the USB key
1418 * dirtiers for 100 seconds until wb_dirty drops under
1419 * wb_thresh. Instead the auxiliary wb control line in
1420 * wb_position_ratio() will let the dirtier task progress
1421 * at some rate <= (write_bw / 2) for bringing down wb_dirty.
1423 dtc
->wb_thresh
= __wb_calc_thresh(dtc
);
1424 dtc
->wb_bg_thresh
= dtc
->thresh
?
1425 div_u64((u64
)dtc
->wb_thresh
* dtc
->bg_thresh
, dtc
->thresh
) : 0;
1428 * In order to avoid the stacked BDI deadlock we need
1429 * to ensure we accurately count the 'dirty' pages when
1430 * the threshold is low.
1432 * Otherwise it would be possible to get thresh+n pages
1433 * reported dirty, even though there are thresh-m pages
1434 * actually dirty; with m+n sitting in the percpu
1437 if (dtc
->wb_thresh
< 2 * wb_stat_error(wb
)) {
1438 wb_reclaimable
= wb_stat_sum(wb
, WB_RECLAIMABLE
);
1439 dtc
->wb_dirty
= wb_reclaimable
+ wb_stat_sum(wb
, WB_WRITEBACK
);
1441 wb_reclaimable
= wb_stat(wb
, WB_RECLAIMABLE
);
1442 dtc
->wb_dirty
= wb_reclaimable
+ wb_stat(wb
, WB_WRITEBACK
);
1447 * balance_dirty_pages() must be called by processes which are generating dirty
1448 * data. It looks at the number of dirty pages in the machine and will force
1449 * the caller to wait once crossing the (background_thresh + dirty_thresh) / 2.
1450 * If we're over `background_thresh' then the writeback threads are woken to
1451 * perform some writeout.
1453 static void balance_dirty_pages(struct address_space
*mapping
,
1454 struct bdi_writeback
*wb
,
1455 unsigned long pages_dirtied
)
1457 struct dirty_throttle_control gdtc_stor
= { GDTC_INIT(wb
) };
1458 struct dirty_throttle_control
* const gdtc
= &gdtc_stor
;
1459 unsigned long nr_reclaimable
; /* = file_dirty + unstable_nfs */
1464 int nr_dirtied_pause
;
1465 bool dirty_exceeded
= false;
1466 unsigned long task_ratelimit
;
1467 unsigned long dirty_ratelimit
;
1468 struct backing_dev_info
*bdi
= wb
->bdi
;
1469 bool strictlimit
= bdi
->capabilities
& BDI_CAP_STRICTLIMIT
;
1470 unsigned long start_time
= jiffies
;
1473 unsigned long now
= jiffies
;
1474 unsigned long dirty
, thresh
, bg_thresh
;
1477 * Unstable writes are a feature of certain networked
1478 * filesystems (i.e. NFS) in which data may have been
1479 * written to the server's write cache, but has not yet
1480 * been flushed to permanent storage.
1482 nr_reclaimable
= global_page_state(NR_FILE_DIRTY
) +
1483 global_page_state(NR_UNSTABLE_NFS
);
1484 gdtc
->avail
= global_dirtyable_memory();
1485 gdtc
->dirty
= nr_reclaimable
+ global_page_state(NR_WRITEBACK
);
1487 domain_dirty_limits(gdtc
);
1489 if (unlikely(strictlimit
)) {
1490 wb_dirty_limits(gdtc
);
1492 dirty
= gdtc
->wb_dirty
;
1493 thresh
= gdtc
->wb_thresh
;
1494 bg_thresh
= gdtc
->wb_bg_thresh
;
1496 dirty
= gdtc
->dirty
;
1497 thresh
= gdtc
->thresh
;
1498 bg_thresh
= gdtc
->bg_thresh
;
1502 * Throttle it only when the background writeback cannot
1503 * catch-up. This avoids (excessively) small writeouts
1504 * when the wb limits are ramping up in case of !strictlimit.
1506 * In strictlimit case make decision based on the wb counters
1507 * and limits. Small writeouts when the wb limits are ramping
1508 * up are the price we consciously pay for strictlimit-ing.
1510 if (dirty
<= dirty_freerun_ceiling(thresh
, bg_thresh
)) {
1511 current
->dirty_paused_when
= now
;
1512 current
->nr_dirtied
= 0;
1513 current
->nr_dirtied_pause
=
1514 dirty_poll_interval(dirty
, thresh
);
1518 if (unlikely(!writeback_in_progress(wb
)))
1519 wb_start_background_writeback(wb
);
1522 wb_dirty_limits(gdtc
);
1524 dirty_exceeded
= (gdtc
->wb_dirty
> gdtc
->wb_thresh
) &&
1525 ((gdtc
->dirty
> gdtc
->thresh
) || strictlimit
);
1527 wb_position_ratio(gdtc
);
1529 if (dirty_exceeded
&& !wb
->dirty_exceeded
)
1530 wb
->dirty_exceeded
= 1;
1532 if (time_is_before_jiffies(wb
->bw_time_stamp
+
1533 BANDWIDTH_INTERVAL
)) {
1534 spin_lock(&wb
->list_lock
);
1535 __wb_update_bandwidth(gdtc
, start_time
, true);
1536 spin_unlock(&wb
->list_lock
);
1539 dirty_ratelimit
= wb
->dirty_ratelimit
;
1540 task_ratelimit
= ((u64
)dirty_ratelimit
* gdtc
->pos_ratio
) >>
1541 RATELIMIT_CALC_SHIFT
;
1542 max_pause
= wb_max_pause(wb
, gdtc
->wb_dirty
);
1543 min_pause
= wb_min_pause(wb
, max_pause
,
1544 task_ratelimit
, dirty_ratelimit
,
1547 if (unlikely(task_ratelimit
== 0)) {
1552 period
= HZ
* pages_dirtied
/ task_ratelimit
;
1554 if (current
->dirty_paused_when
)
1555 pause
-= now
- current
->dirty_paused_when
;
1557 * For less than 1s think time (ext3/4 may block the dirtier
1558 * for up to 800ms from time to time on 1-HDD; so does xfs,
1559 * however at much less frequency), try to compensate it in
1560 * future periods by updating the virtual time; otherwise just
1561 * do a reset, as it may be a light dirtier.
1563 if (pause
< min_pause
) {
1564 trace_balance_dirty_pages(bdi
,
1577 current
->dirty_paused_when
= now
;
1578 current
->nr_dirtied
= 0;
1579 } else if (period
) {
1580 current
->dirty_paused_when
+= period
;
1581 current
->nr_dirtied
= 0;
1582 } else if (current
->nr_dirtied_pause
<= pages_dirtied
)
1583 current
->nr_dirtied_pause
+= pages_dirtied
;
1586 if (unlikely(pause
> max_pause
)) {
1587 /* for occasional dropped task_ratelimit */
1588 now
+= min(pause
- max_pause
, max_pause
);
1593 trace_balance_dirty_pages(bdi
,
1605 __set_current_state(TASK_KILLABLE
);
1606 io_schedule_timeout(pause
);
1608 current
->dirty_paused_when
= now
+ pause
;
1609 current
->nr_dirtied
= 0;
1610 current
->nr_dirtied_pause
= nr_dirtied_pause
;
1613 * This is typically equal to (dirty < thresh) and can also
1614 * keep "1000+ dd on a slow USB stick" under control.
1620 * In the case of an unresponding NFS server and the NFS dirty
1621 * pages exceeds dirty_thresh, give the other good wb's a pipe
1622 * to go through, so that tasks on them still remain responsive.
1624 * In theory 1 page is enough to keep the comsumer-producer
1625 * pipe going: the flusher cleans 1 page => the task dirties 1
1626 * more page. However wb_dirty has accounting errors. So use
1627 * the larger and more IO friendly wb_stat_error.
1629 if (gdtc
->wb_dirty
<= wb_stat_error(wb
))
1632 if (fatal_signal_pending(current
))
1636 if (!dirty_exceeded
&& wb
->dirty_exceeded
)
1637 wb
->dirty_exceeded
= 0;
1639 if (writeback_in_progress(wb
))
1643 * In laptop mode, we wait until hitting the higher threshold before
1644 * starting background writeout, and then write out all the way down
1645 * to the lower threshold. So slow writers cause minimal disk activity.
1647 * In normal mode, we start background writeout at the lower
1648 * background_thresh, to keep the amount of dirty memory low.
1653 if (nr_reclaimable
> gdtc
->bg_thresh
)
1654 wb_start_background_writeback(wb
);
1657 static DEFINE_PER_CPU(int, bdp_ratelimits
);
1660 * Normal tasks are throttled by
1662 * dirty tsk->nr_dirtied_pause pages;
1663 * take a snap in balance_dirty_pages();
1665 * However there is a worst case. If every task exit immediately when dirtied
1666 * (tsk->nr_dirtied_pause - 1) pages, balance_dirty_pages() will never be
1667 * called to throttle the page dirties. The solution is to save the not yet
1668 * throttled page dirties in dirty_throttle_leaks on task exit and charge them
1669 * randomly into the running tasks. This works well for the above worst case,
1670 * as the new task will pick up and accumulate the old task's leaked dirty
1671 * count and eventually get throttled.
1673 DEFINE_PER_CPU(int, dirty_throttle_leaks
) = 0;
1676 * balance_dirty_pages_ratelimited - balance dirty memory state
1677 * @mapping: address_space which was dirtied
1679 * Processes which are dirtying memory should call in here once for each page
1680 * which was newly dirtied. The function will periodically check the system's
1681 * dirty state and will initiate writeback if needed.
1683 * On really big machines, get_writeback_state is expensive, so try to avoid
1684 * calling it too often (ratelimiting). But once we're over the dirty memory
1685 * limit we decrease the ratelimiting by a lot, to prevent individual processes
1686 * from overshooting the limit by (ratelimit_pages) each.
1688 void balance_dirty_pages_ratelimited(struct address_space
*mapping
)
1690 struct inode
*inode
= mapping
->host
;
1691 struct backing_dev_info
*bdi
= inode_to_bdi(inode
);
1692 struct bdi_writeback
*wb
= NULL
;
1696 if (!bdi_cap_account_dirty(bdi
))
1699 if (inode_cgwb_enabled(inode
))
1700 wb
= wb_get_create_current(bdi
, GFP_KERNEL
);
1704 ratelimit
= current
->nr_dirtied_pause
;
1705 if (wb
->dirty_exceeded
)
1706 ratelimit
= min(ratelimit
, 32 >> (PAGE_SHIFT
- 10));
1710 * This prevents one CPU to accumulate too many dirtied pages without
1711 * calling into balance_dirty_pages(), which can happen when there are
1712 * 1000+ tasks, all of them start dirtying pages at exactly the same
1713 * time, hence all honoured too large initial task->nr_dirtied_pause.
1715 p
= this_cpu_ptr(&bdp_ratelimits
);
1716 if (unlikely(current
->nr_dirtied
>= ratelimit
))
1718 else if (unlikely(*p
>= ratelimit_pages
)) {
1723 * Pick up the dirtied pages by the exited tasks. This avoids lots of
1724 * short-lived tasks (eg. gcc invocations in a kernel build) escaping
1725 * the dirty throttling and livelock other long-run dirtiers.
1727 p
= this_cpu_ptr(&dirty_throttle_leaks
);
1728 if (*p
> 0 && current
->nr_dirtied
< ratelimit
) {
1729 unsigned long nr_pages_dirtied
;
1730 nr_pages_dirtied
= min(*p
, ratelimit
- current
->nr_dirtied
);
1731 *p
-= nr_pages_dirtied
;
1732 current
->nr_dirtied
+= nr_pages_dirtied
;
1736 if (unlikely(current
->nr_dirtied
>= ratelimit
))
1737 balance_dirty_pages(mapping
, wb
, current
->nr_dirtied
);
1741 EXPORT_SYMBOL(balance_dirty_pages_ratelimited
);
1743 void throttle_vm_writeout(gfp_t gfp_mask
)
1745 unsigned long background_thresh
;
1746 unsigned long dirty_thresh
;
1749 global_dirty_limits(&background_thresh
, &dirty_thresh
);
1750 dirty_thresh
= hard_dirty_limit(&global_wb_domain
, dirty_thresh
);
1753 * Boost the allowable dirty threshold a bit for page
1754 * allocators so they don't get DoS'ed by heavy writers
1756 dirty_thresh
+= dirty_thresh
/ 10; /* wheeee... */
1758 if (global_page_state(NR_UNSTABLE_NFS
) +
1759 global_page_state(NR_WRITEBACK
) <= dirty_thresh
)
1761 congestion_wait(BLK_RW_ASYNC
, HZ
/10);
1764 * The caller might hold locks which can prevent IO completion
1765 * or progress in the filesystem. So we cannot just sit here
1766 * waiting for IO to complete.
1768 if ((gfp_mask
& (__GFP_FS
|__GFP_IO
)) != (__GFP_FS
|__GFP_IO
))
1774 * sysctl handler for /proc/sys/vm/dirty_writeback_centisecs
1776 int dirty_writeback_centisecs_handler(struct ctl_table
*table
, int write
,
1777 void __user
*buffer
, size_t *length
, loff_t
*ppos
)
1779 proc_dointvec(table
, write
, buffer
, length
, ppos
);
1784 void laptop_mode_timer_fn(unsigned long data
)
1786 struct request_queue
*q
= (struct request_queue
*)data
;
1787 int nr_pages
= global_page_state(NR_FILE_DIRTY
) +
1788 global_page_state(NR_UNSTABLE_NFS
);
1789 struct bdi_writeback
*wb
;
1790 struct wb_iter iter
;
1793 * We want to write everything out, not just down to the dirty
1796 if (!bdi_has_dirty_io(&q
->backing_dev_info
))
1799 bdi_for_each_wb(wb
, &q
->backing_dev_info
, &iter
, 0)
1800 if (wb_has_dirty_io(wb
))
1801 wb_start_writeback(wb
, nr_pages
, true,
1802 WB_REASON_LAPTOP_TIMER
);
1806 * We've spun up the disk and we're in laptop mode: schedule writeback
1807 * of all dirty data a few seconds from now. If the flush is already scheduled
1808 * then push it back - the user is still using the disk.
1810 void laptop_io_completion(struct backing_dev_info
*info
)
1812 mod_timer(&info
->laptop_mode_wb_timer
, jiffies
+ laptop_mode
);
1816 * We're in laptop mode and we've just synced. The sync's writes will have
1817 * caused another writeback to be scheduled by laptop_io_completion.
1818 * Nothing needs to be written back anymore, so we unschedule the writeback.
1820 void laptop_sync_completion(void)
1822 struct backing_dev_info
*bdi
;
1826 list_for_each_entry_rcu(bdi
, &bdi_list
, bdi_list
)
1827 del_timer(&bdi
->laptop_mode_wb_timer
);
1834 * If ratelimit_pages is too high then we can get into dirty-data overload
1835 * if a large number of processes all perform writes at the same time.
1836 * If it is too low then SMP machines will call the (expensive)
1837 * get_writeback_state too often.
1839 * Here we set ratelimit_pages to a level which ensures that when all CPUs are
1840 * dirtying in parallel, we cannot go more than 3% (1/32) over the dirty memory
1844 void writeback_set_ratelimit(void)
1846 struct wb_domain
*dom
= &global_wb_domain
;
1847 unsigned long background_thresh
;
1848 unsigned long dirty_thresh
;
1850 global_dirty_limits(&background_thresh
, &dirty_thresh
);
1851 dom
->dirty_limit
= dirty_thresh
;
1852 ratelimit_pages
= dirty_thresh
/ (num_online_cpus() * 32);
1853 if (ratelimit_pages
< 16)
1854 ratelimit_pages
= 16;
1858 ratelimit_handler(struct notifier_block
*self
, unsigned long action
,
1862 switch (action
& ~CPU_TASKS_FROZEN
) {
1865 writeback_set_ratelimit();
1872 static struct notifier_block ratelimit_nb
= {
1873 .notifier_call
= ratelimit_handler
,
1878 * Called early on to tune the page writeback dirty limits.
1880 * We used to scale dirty pages according to how total memory
1881 * related to pages that could be allocated for buffers (by
1882 * comparing nr_free_buffer_pages() to vm_total_pages.
1884 * However, that was when we used "dirty_ratio" to scale with
1885 * all memory, and we don't do that any more. "dirty_ratio"
1886 * is now applied to total non-HIGHPAGE memory (by subtracting
1887 * totalhigh_pages from vm_total_pages), and as such we can't
1888 * get into the old insane situation any more where we had
1889 * large amounts of dirty pages compared to a small amount of
1890 * non-HIGHMEM memory.
1892 * But we might still want to scale the dirty_ratio by how
1893 * much memory the box has..
1895 void __init
page_writeback_init(void)
1897 writeback_set_ratelimit();
1898 register_cpu_notifier(&ratelimit_nb
);
1900 BUG_ON(wb_domain_init(&global_wb_domain
, GFP_KERNEL
));
1904 * tag_pages_for_writeback - tag pages to be written by write_cache_pages
1905 * @mapping: address space structure to write
1906 * @start: starting page index
1907 * @end: ending page index (inclusive)
1909 * This function scans the page range from @start to @end (inclusive) and tags
1910 * all pages that have DIRTY tag set with a special TOWRITE tag. The idea is
1911 * that write_cache_pages (or whoever calls this function) will then use
1912 * TOWRITE tag to identify pages eligible for writeback. This mechanism is
1913 * used to avoid livelocking of writeback by a process steadily creating new
1914 * dirty pages in the file (thus it is important for this function to be quick
1915 * so that it can tag pages faster than a dirtying process can create them).
1918 * We tag pages in batches of WRITEBACK_TAG_BATCH to reduce tree_lock latency.
1920 void tag_pages_for_writeback(struct address_space
*mapping
,
1921 pgoff_t start
, pgoff_t end
)
1923 #define WRITEBACK_TAG_BATCH 4096
1924 unsigned long tagged
;
1927 spin_lock_irq(&mapping
->tree_lock
);
1928 tagged
= radix_tree_range_tag_if_tagged(&mapping
->page_tree
,
1929 &start
, end
, WRITEBACK_TAG_BATCH
,
1930 PAGECACHE_TAG_DIRTY
, PAGECACHE_TAG_TOWRITE
);
1931 spin_unlock_irq(&mapping
->tree_lock
);
1932 WARN_ON_ONCE(tagged
> WRITEBACK_TAG_BATCH
);
1934 /* We check 'start' to handle wrapping when end == ~0UL */
1935 } while (tagged
>= WRITEBACK_TAG_BATCH
&& start
);
1937 EXPORT_SYMBOL(tag_pages_for_writeback
);
1940 * write_cache_pages - walk the list of dirty pages of the given address space and write all of them.
1941 * @mapping: address space structure to write
1942 * @wbc: subtract the number of written pages from *@wbc->nr_to_write
1943 * @writepage: function called for each page
1944 * @data: data passed to writepage function
1946 * If a page is already under I/O, write_cache_pages() skips it, even
1947 * if it's dirty. This is desirable behaviour for memory-cleaning writeback,
1948 * but it is INCORRECT for data-integrity system calls such as fsync(). fsync()
1949 * and msync() need to guarantee that all the data which was dirty at the time
1950 * the call was made get new I/O started against them. If wbc->sync_mode is
1951 * WB_SYNC_ALL then we were called for data integrity and we must wait for
1952 * existing IO to complete.
1954 * To avoid livelocks (when other process dirties new pages), we first tag
1955 * pages which should be written back with TOWRITE tag and only then start
1956 * writing them. For data-integrity sync we have to be careful so that we do
1957 * not miss some pages (e.g., because some other process has cleared TOWRITE
1958 * tag we set). The rule we follow is that TOWRITE tag can be cleared only
1959 * by the process clearing the DIRTY tag (and submitting the page for IO).
1961 int write_cache_pages(struct address_space
*mapping
,
1962 struct writeback_control
*wbc
, writepage_t writepage
,
1967 struct pagevec pvec
;
1969 pgoff_t
uninitialized_var(writeback_index
);
1971 pgoff_t end
; /* Inclusive */
1974 int range_whole
= 0;
1977 pagevec_init(&pvec
, 0);
1978 if (wbc
->range_cyclic
) {
1979 writeback_index
= mapping
->writeback_index
; /* prev offset */
1980 index
= writeback_index
;
1987 index
= wbc
->range_start
>> PAGE_CACHE_SHIFT
;
1988 end
= wbc
->range_end
>> PAGE_CACHE_SHIFT
;
1989 if (wbc
->range_start
== 0 && wbc
->range_end
== LLONG_MAX
)
1991 cycled
= 1; /* ignore range_cyclic tests */
1993 if (wbc
->sync_mode
== WB_SYNC_ALL
|| wbc
->tagged_writepages
)
1994 tag
= PAGECACHE_TAG_TOWRITE
;
1996 tag
= PAGECACHE_TAG_DIRTY
;
1998 if (wbc
->sync_mode
== WB_SYNC_ALL
|| wbc
->tagged_writepages
)
1999 tag_pages_for_writeback(mapping
, index
, end
);
2001 while (!done
&& (index
<= end
)) {
2004 nr_pages
= pagevec_lookup_tag(&pvec
, mapping
, &index
, tag
,
2005 min(end
- index
, (pgoff_t
)PAGEVEC_SIZE
-1) + 1);
2009 for (i
= 0; i
< nr_pages
; i
++) {
2010 struct page
*page
= pvec
.pages
[i
];
2013 * At this point, the page may be truncated or
2014 * invalidated (changing page->mapping to NULL), or
2015 * even swizzled back from swapper_space to tmpfs file
2016 * mapping. However, page->index will not change
2017 * because we have a reference on the page.
2019 if (page
->index
> end
) {
2021 * can't be range_cyclic (1st pass) because
2022 * end == -1 in that case.
2028 done_index
= page
->index
;
2033 * Page truncated or invalidated. We can freely skip it
2034 * then, even for data integrity operations: the page
2035 * has disappeared concurrently, so there could be no
2036 * real expectation of this data interity operation
2037 * even if there is now a new, dirty page at the same
2038 * pagecache address.
2040 if (unlikely(page
->mapping
!= mapping
)) {
2046 if (!PageDirty(page
)) {
2047 /* someone wrote it for us */
2048 goto continue_unlock
;
2051 if (PageWriteback(page
)) {
2052 if (wbc
->sync_mode
!= WB_SYNC_NONE
)
2053 wait_on_page_writeback(page
);
2055 goto continue_unlock
;
2058 BUG_ON(PageWriteback(page
));
2059 if (!clear_page_dirty_for_io(page
))
2060 goto continue_unlock
;
2062 trace_wbc_writepage(wbc
, inode_to_bdi(mapping
->host
));
2063 ret
= (*writepage
)(page
, wbc
, data
);
2064 if (unlikely(ret
)) {
2065 if (ret
== AOP_WRITEPAGE_ACTIVATE
) {
2070 * done_index is set past this page,
2071 * so media errors will not choke
2072 * background writeout for the entire
2073 * file. This has consequences for
2074 * range_cyclic semantics (ie. it may
2075 * not be suitable for data integrity
2078 done_index
= page
->index
+ 1;
2085 * We stop writing back only if we are not doing
2086 * integrity sync. In case of integrity sync we have to
2087 * keep going until we have written all the pages
2088 * we tagged for writeback prior to entering this loop.
2090 if (--wbc
->nr_to_write
<= 0 &&
2091 wbc
->sync_mode
== WB_SYNC_NONE
) {
2096 pagevec_release(&pvec
);
2099 if (!cycled
&& !done
) {
2102 * We hit the last page and there is more work to be done: wrap
2103 * back to the start of the file
2107 end
= writeback_index
- 1;
2110 if (wbc
->range_cyclic
|| (range_whole
&& wbc
->nr_to_write
> 0))
2111 mapping
->writeback_index
= done_index
;
2115 EXPORT_SYMBOL(write_cache_pages
);
2118 * Function used by generic_writepages to call the real writepage
2119 * function and set the mapping flags on error
2121 static int __writepage(struct page
*page
, struct writeback_control
*wbc
,
2124 struct address_space
*mapping
= data
;
2125 int ret
= mapping
->a_ops
->writepage(page
, wbc
);
2126 mapping_set_error(mapping
, ret
);
2131 * generic_writepages - walk the list of dirty pages of the given address space and writepage() all of them.
2132 * @mapping: address space structure to write
2133 * @wbc: subtract the number of written pages from *@wbc->nr_to_write
2135 * This is a library function, which implements the writepages()
2136 * address_space_operation.
2138 int generic_writepages(struct address_space
*mapping
,
2139 struct writeback_control
*wbc
)
2141 struct blk_plug plug
;
2144 /* deal with chardevs and other special file */
2145 if (!mapping
->a_ops
->writepage
)
2148 blk_start_plug(&plug
);
2149 ret
= write_cache_pages(mapping
, wbc
, __writepage
, mapping
);
2150 blk_finish_plug(&plug
);
2154 EXPORT_SYMBOL(generic_writepages
);
2156 int do_writepages(struct address_space
*mapping
, struct writeback_control
*wbc
)
2160 if (wbc
->nr_to_write
<= 0)
2162 if (mapping
->a_ops
->writepages
)
2163 ret
= mapping
->a_ops
->writepages(mapping
, wbc
);
2165 ret
= generic_writepages(mapping
, wbc
);
2170 * write_one_page - write out a single page and optionally wait on I/O
2171 * @page: the page to write
2172 * @wait: if true, wait on writeout
2174 * The page must be locked by the caller and will be unlocked upon return.
2176 * write_one_page() returns a negative error code if I/O failed.
2178 int write_one_page(struct page
*page
, int wait
)
2180 struct address_space
*mapping
= page
->mapping
;
2182 struct writeback_control wbc
= {
2183 .sync_mode
= WB_SYNC_ALL
,
2187 BUG_ON(!PageLocked(page
));
2190 wait_on_page_writeback(page
);
2192 if (clear_page_dirty_for_io(page
)) {
2193 page_cache_get(page
);
2194 ret
= mapping
->a_ops
->writepage(page
, &wbc
);
2195 if (ret
== 0 && wait
) {
2196 wait_on_page_writeback(page
);
2197 if (PageError(page
))
2200 page_cache_release(page
);
2206 EXPORT_SYMBOL(write_one_page
);
2209 * For address_spaces which do not use buffers nor write back.
2211 int __set_page_dirty_no_writeback(struct page
*page
)
2213 if (!PageDirty(page
))
2214 return !TestSetPageDirty(page
);
2219 * Helper function for set_page_dirty family.
2221 * Caller must hold mem_cgroup_begin_page_stat().
2223 * NOTE: This relies on being atomic wrt interrupts.
2225 void account_page_dirtied(struct page
*page
, struct address_space
*mapping
,
2226 struct mem_cgroup
*memcg
)
2228 struct inode
*inode
= mapping
->host
;
2230 trace_writeback_dirty_page(page
, mapping
);
2232 if (mapping_cap_account_dirty(mapping
)) {
2233 struct bdi_writeback
*wb
;
2235 inode_attach_wb(inode
, page
);
2236 wb
= inode_to_wb(inode
);
2238 mem_cgroup_inc_page_stat(memcg
, MEM_CGROUP_STAT_DIRTY
);
2239 __inc_zone_page_state(page
, NR_FILE_DIRTY
);
2240 __inc_zone_page_state(page
, NR_DIRTIED
);
2241 __inc_wb_stat(wb
, WB_RECLAIMABLE
);
2242 __inc_wb_stat(wb
, WB_DIRTIED
);
2243 task_io_account_write(PAGE_CACHE_SIZE
);
2244 current
->nr_dirtied
++;
2245 this_cpu_inc(bdp_ratelimits
);
2248 EXPORT_SYMBOL(account_page_dirtied
);
2251 * Helper function for deaccounting dirty page without writeback.
2253 * Caller must hold mem_cgroup_begin_page_stat().
2255 void account_page_cleaned(struct page
*page
, struct address_space
*mapping
,
2256 struct mem_cgroup
*memcg
)
2258 if (mapping_cap_account_dirty(mapping
)) {
2259 mem_cgroup_dec_page_stat(memcg
, MEM_CGROUP_STAT_DIRTY
);
2260 dec_zone_page_state(page
, NR_FILE_DIRTY
);
2261 dec_wb_stat(inode_to_wb(mapping
->host
), WB_RECLAIMABLE
);
2262 task_io_account_cancelled_write(PAGE_CACHE_SIZE
);
2267 * For address_spaces which do not use buffers. Just tag the page as dirty in
2270 * This is also used when a single buffer is being dirtied: we want to set the
2271 * page dirty in that case, but not all the buffers. This is a "bottom-up"
2272 * dirtying, whereas __set_page_dirty_buffers() is a "top-down" dirtying.
2274 * The caller must ensure this doesn't race with truncation. Most will simply
2275 * hold the page lock, but e.g. zap_pte_range() calls with the page mapped and
2276 * the pte lock held, which also locks out truncation.
2278 int __set_page_dirty_nobuffers(struct page
*page
)
2280 struct mem_cgroup
*memcg
;
2282 memcg
= mem_cgroup_begin_page_stat(page
);
2283 if (!TestSetPageDirty(page
)) {
2284 struct address_space
*mapping
= page_mapping(page
);
2285 unsigned long flags
;
2288 mem_cgroup_end_page_stat(memcg
);
2292 spin_lock_irqsave(&mapping
->tree_lock
, flags
);
2293 BUG_ON(page_mapping(page
) != mapping
);
2294 WARN_ON_ONCE(!PagePrivate(page
) && !PageUptodate(page
));
2295 account_page_dirtied(page
, mapping
, memcg
);
2296 radix_tree_tag_set(&mapping
->page_tree
, page_index(page
),
2297 PAGECACHE_TAG_DIRTY
);
2298 spin_unlock_irqrestore(&mapping
->tree_lock
, flags
);
2299 mem_cgroup_end_page_stat(memcg
);
2301 if (mapping
->host
) {
2302 /* !PageAnon && !swapper_space */
2303 __mark_inode_dirty(mapping
->host
, I_DIRTY_PAGES
);
2307 mem_cgroup_end_page_stat(memcg
);
2310 EXPORT_SYMBOL(__set_page_dirty_nobuffers
);
2313 * Call this whenever redirtying a page, to de-account the dirty counters
2314 * (NR_DIRTIED, BDI_DIRTIED, tsk->nr_dirtied), so that they match the written
2315 * counters (NR_WRITTEN, BDI_WRITTEN) in long term. The mismatches will lead to
2316 * systematic errors in balanced_dirty_ratelimit and the dirty pages position
2319 void account_page_redirty(struct page
*page
)
2321 struct address_space
*mapping
= page
->mapping
;
2323 if (mapping
&& mapping_cap_account_dirty(mapping
)) {
2324 struct bdi_writeback
*wb
= inode_to_wb(mapping
->host
);
2326 current
->nr_dirtied
--;
2327 dec_zone_page_state(page
, NR_DIRTIED
);
2328 dec_wb_stat(wb
, WB_DIRTIED
);
2331 EXPORT_SYMBOL(account_page_redirty
);
2334 * When a writepage implementation decides that it doesn't want to write this
2335 * page for some reason, it should redirty the locked page via
2336 * redirty_page_for_writepage() and it should then unlock the page and return 0
2338 int redirty_page_for_writepage(struct writeback_control
*wbc
, struct page
*page
)
2342 wbc
->pages_skipped
++;
2343 ret
= __set_page_dirty_nobuffers(page
);
2344 account_page_redirty(page
);
2347 EXPORT_SYMBOL(redirty_page_for_writepage
);
2352 * For pages with a mapping this should be done under the page lock
2353 * for the benefit of asynchronous memory errors who prefer a consistent
2354 * dirty state. This rule can be broken in some special cases,
2355 * but should be better not to.
2357 * If the mapping doesn't provide a set_page_dirty a_op, then
2358 * just fall through and assume that it wants buffer_heads.
2360 int set_page_dirty(struct page
*page
)
2362 struct address_space
*mapping
= page_mapping(page
);
2364 if (likely(mapping
)) {
2365 int (*spd
)(struct page
*) = mapping
->a_ops
->set_page_dirty
;
2367 * readahead/lru_deactivate_page could remain
2368 * PG_readahead/PG_reclaim due to race with end_page_writeback
2369 * About readahead, if the page is written, the flags would be
2370 * reset. So no problem.
2371 * About lru_deactivate_page, if the page is redirty, the flag
2372 * will be reset. So no problem. but if the page is used by readahead
2373 * it will confuse readahead and make it restart the size rampup
2374 * process. But it's a trivial problem.
2376 if (PageReclaim(page
))
2377 ClearPageReclaim(page
);
2380 spd
= __set_page_dirty_buffers
;
2382 return (*spd
)(page
);
2384 if (!PageDirty(page
)) {
2385 if (!TestSetPageDirty(page
))
2390 EXPORT_SYMBOL(set_page_dirty
);
2393 * set_page_dirty() is racy if the caller has no reference against
2394 * page->mapping->host, and if the page is unlocked. This is because another
2395 * CPU could truncate the page off the mapping and then free the mapping.
2397 * Usually, the page _is_ locked, or the caller is a user-space process which
2398 * holds a reference on the inode by having an open file.
2400 * In other cases, the page should be locked before running set_page_dirty().
2402 int set_page_dirty_lock(struct page
*page
)
2407 ret
= set_page_dirty(page
);
2411 EXPORT_SYMBOL(set_page_dirty_lock
);
2414 * This cancels just the dirty bit on the kernel page itself, it does NOT
2415 * actually remove dirty bits on any mmap's that may be around. It also
2416 * leaves the page tagged dirty, so any sync activity will still find it on
2417 * the dirty lists, and in particular, clear_page_dirty_for_io() will still
2418 * look at the dirty bits in the VM.
2420 * Doing this should *normally* only ever be done when a page is truncated,
2421 * and is not actually mapped anywhere at all. However, fs/buffer.c does
2422 * this when it notices that somebody has cleaned out all the buffers on a
2423 * page without actually doing it through the VM. Can you say "ext3 is
2424 * horribly ugly"? Thought you could.
2426 void cancel_dirty_page(struct page
*page
)
2428 struct address_space
*mapping
= page_mapping(page
);
2430 if (mapping_cap_account_dirty(mapping
)) {
2431 struct mem_cgroup
*memcg
;
2433 memcg
= mem_cgroup_begin_page_stat(page
);
2435 if (TestClearPageDirty(page
))
2436 account_page_cleaned(page
, mapping
, memcg
);
2438 mem_cgroup_end_page_stat(memcg
);
2440 ClearPageDirty(page
);
2443 EXPORT_SYMBOL(cancel_dirty_page
);
2446 * Clear a page's dirty flag, while caring for dirty memory accounting.
2447 * Returns true if the page was previously dirty.
2449 * This is for preparing to put the page under writeout. We leave the page
2450 * tagged as dirty in the radix tree so that a concurrent write-for-sync
2451 * can discover it via a PAGECACHE_TAG_DIRTY walk. The ->writepage
2452 * implementation will run either set_page_writeback() or set_page_dirty(),
2453 * at which stage we bring the page's dirty flag and radix-tree dirty tag
2456 * This incoherency between the page's dirty flag and radix-tree tag is
2457 * unfortunate, but it only exists while the page is locked.
2459 int clear_page_dirty_for_io(struct page
*page
)
2461 struct address_space
*mapping
= page_mapping(page
);
2462 struct mem_cgroup
*memcg
;
2465 BUG_ON(!PageLocked(page
));
2467 if (mapping
&& mapping_cap_account_dirty(mapping
)) {
2469 * Yes, Virginia, this is indeed insane.
2471 * We use this sequence to make sure that
2472 * (a) we account for dirty stats properly
2473 * (b) we tell the low-level filesystem to
2474 * mark the whole page dirty if it was
2475 * dirty in a pagetable. Only to then
2476 * (c) clean the page again and return 1 to
2477 * cause the writeback.
2479 * This way we avoid all nasty races with the
2480 * dirty bit in multiple places and clearing
2481 * them concurrently from different threads.
2483 * Note! Normally the "set_page_dirty(page)"
2484 * has no effect on the actual dirty bit - since
2485 * that will already usually be set. But we
2486 * need the side effects, and it can help us
2489 * We basically use the page "master dirty bit"
2490 * as a serialization point for all the different
2491 * threads doing their things.
2493 if (page_mkclean(page
))
2494 set_page_dirty(page
);
2496 * We carefully synchronise fault handlers against
2497 * installing a dirty pte and marking the page dirty
2498 * at this point. We do this by having them hold the
2499 * page lock while dirtying the page, and pages are
2500 * always locked coming in here, so we get the desired
2503 memcg
= mem_cgroup_begin_page_stat(page
);
2504 if (TestClearPageDirty(page
)) {
2505 mem_cgroup_dec_page_stat(memcg
, MEM_CGROUP_STAT_DIRTY
);
2506 dec_zone_page_state(page
, NR_FILE_DIRTY
);
2507 dec_wb_stat(inode_to_wb(mapping
->host
), WB_RECLAIMABLE
);
2510 mem_cgroup_end_page_stat(memcg
);
2513 return TestClearPageDirty(page
);
2515 EXPORT_SYMBOL(clear_page_dirty_for_io
);
2517 int test_clear_page_writeback(struct page
*page
)
2519 struct address_space
*mapping
= page_mapping(page
);
2520 struct mem_cgroup
*memcg
;
2523 memcg
= mem_cgroup_begin_page_stat(page
);
2525 struct inode
*inode
= mapping
->host
;
2526 struct backing_dev_info
*bdi
= inode_to_bdi(inode
);
2527 unsigned long flags
;
2529 spin_lock_irqsave(&mapping
->tree_lock
, flags
);
2530 ret
= TestClearPageWriteback(page
);
2532 radix_tree_tag_clear(&mapping
->page_tree
,
2534 PAGECACHE_TAG_WRITEBACK
);
2535 if (bdi_cap_account_writeback(bdi
)) {
2536 struct bdi_writeback
*wb
= inode_to_wb(inode
);
2538 __dec_wb_stat(wb
, WB_WRITEBACK
);
2539 __wb_writeout_inc(wb
);
2542 spin_unlock_irqrestore(&mapping
->tree_lock
, flags
);
2544 ret
= TestClearPageWriteback(page
);
2547 mem_cgroup_dec_page_stat(memcg
, MEM_CGROUP_STAT_WRITEBACK
);
2548 dec_zone_page_state(page
, NR_WRITEBACK
);
2549 inc_zone_page_state(page
, NR_WRITTEN
);
2551 mem_cgroup_end_page_stat(memcg
);
2555 int __test_set_page_writeback(struct page
*page
, bool keep_write
)
2557 struct address_space
*mapping
= page_mapping(page
);
2558 struct mem_cgroup
*memcg
;
2561 memcg
= mem_cgroup_begin_page_stat(page
);
2563 struct inode
*inode
= mapping
->host
;
2564 struct backing_dev_info
*bdi
= inode_to_bdi(inode
);
2565 unsigned long flags
;
2567 spin_lock_irqsave(&mapping
->tree_lock
, flags
);
2568 ret
= TestSetPageWriteback(page
);
2570 radix_tree_tag_set(&mapping
->page_tree
,
2572 PAGECACHE_TAG_WRITEBACK
);
2573 if (bdi_cap_account_writeback(bdi
))
2574 __inc_wb_stat(inode_to_wb(inode
), WB_WRITEBACK
);
2576 if (!PageDirty(page
))
2577 radix_tree_tag_clear(&mapping
->page_tree
,
2579 PAGECACHE_TAG_DIRTY
);
2581 radix_tree_tag_clear(&mapping
->page_tree
,
2583 PAGECACHE_TAG_TOWRITE
);
2584 spin_unlock_irqrestore(&mapping
->tree_lock
, flags
);
2586 ret
= TestSetPageWriteback(page
);
2589 mem_cgroup_inc_page_stat(memcg
, MEM_CGROUP_STAT_WRITEBACK
);
2590 inc_zone_page_state(page
, NR_WRITEBACK
);
2592 mem_cgroup_end_page_stat(memcg
);
2596 EXPORT_SYMBOL(__test_set_page_writeback
);
2599 * Return true if any of the pages in the mapping are marked with the
2602 int mapping_tagged(struct address_space
*mapping
, int tag
)
2604 return radix_tree_tagged(&mapping
->page_tree
, tag
);
2606 EXPORT_SYMBOL(mapping_tagged
);
2609 * wait_for_stable_page() - wait for writeback to finish, if necessary.
2610 * @page: The page to wait on.
2612 * This function determines if the given page is related to a backing device
2613 * that requires page contents to be held stable during writeback. If so, then
2614 * it will wait for any pending writeback to complete.
2616 void wait_for_stable_page(struct page
*page
)
2618 if (bdi_cap_stable_pages_required(inode_to_bdi(page
->mapping
->host
)))
2619 wait_on_page_writeback(page
);
2621 EXPORT_SYMBOL_GPL(wait_for_stable_page
);