nfsd4: typo logical vs bitwise negate for want_mask
[linux-btrfs-devel.git] / mm / page-writeback.c
blobd1960744f881d34fe3f1c3412d717db86b8e5478
1 /*
2 * mm/page-writeback.c
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
8 * address_space level.
10 * 10Apr2002 Andrew Morton
11 * Initial version
14 #include <linux/kernel.h>
15 #include <linux/module.h>
16 #include <linux/spinlock.h>
17 #include <linux/fs.h>
18 #include <linux/mm.h>
19 #include <linux/swap.h>
20 #include <linux/slab.h>
21 #include <linux/pagemap.h>
22 #include <linux/writeback.h>
23 #include <linux/init.h>
24 #include <linux/backing-dev.h>
25 #include <linux/task_io_accounting_ops.h>
26 #include <linux/blkdev.h>
27 #include <linux/mpage.h>
28 #include <linux/rmap.h>
29 #include <linux/percpu.h>
30 #include <linux/notifier.h>
31 #include <linux/smp.h>
32 #include <linux/sysctl.h>
33 #include <linux/cpu.h>
34 #include <linux/syscalls.h>
35 #include <linux/buffer_head.h>
36 #include <linux/pagevec.h>
37 #include <trace/events/writeback.h>
40 * Sleep at most 200ms at a time in balance_dirty_pages().
42 #define MAX_PAUSE max(HZ/5, 1)
45 * Estimate write bandwidth at 200ms intervals.
47 #define BANDWIDTH_INTERVAL max(HZ/5, 1)
50 * After a CPU has dirtied this many pages, balance_dirty_pages_ratelimited
51 * will look to see if it needs to force writeback or throttling.
53 static long ratelimit_pages = 32;
56 * When balance_dirty_pages decides that the caller needs to perform some
57 * non-background writeback, this is how many pages it will attempt to write.
58 * It should be somewhat larger than dirtied pages to ensure that reasonably
59 * large amounts of I/O are submitted.
61 static inline long sync_writeback_pages(unsigned long dirtied)
63 if (dirtied < ratelimit_pages)
64 dirtied = ratelimit_pages;
66 return dirtied + dirtied / 2;
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 */
105 * The longest time for which data is allowed to remain dirty
107 unsigned int dirty_expire_interval = 30 * 100; /* centiseconds */
110 * Flag that makes the machine dump writes/reads and block dirtyings.
112 int block_dump;
115 * Flag that puts the machine in "laptop mode". Doubles as a timeout in jiffies:
116 * a full sync is triggered after this time elapses without any disk activity.
118 int laptop_mode;
120 EXPORT_SYMBOL(laptop_mode);
122 /* End of sysctl-exported parameters */
124 unsigned long global_dirty_limit;
127 * Scale the writeback cache size proportional to the relative writeout speeds.
129 * We do this by keeping a floating proportion between BDIs, based on page
130 * writeback completions [end_page_writeback()]. Those devices that write out
131 * pages fastest will get the larger share, while the slower will get a smaller
132 * share.
134 * We use page writeout completions because we are interested in getting rid of
135 * dirty pages. Having them written out is the primary goal.
137 * We introduce a concept of time, a period over which we measure these events,
138 * because demand can/will vary over time. The length of this period itself is
139 * measured in page writeback completions.
142 static struct prop_descriptor vm_completions;
143 static struct prop_descriptor vm_dirties;
146 * couple the period to the dirty_ratio:
148 * period/2 ~ roundup_pow_of_two(dirty limit)
150 static int calc_period_shift(void)
152 unsigned long dirty_total;
154 if (vm_dirty_bytes)
155 dirty_total = vm_dirty_bytes / PAGE_SIZE;
156 else
157 dirty_total = (vm_dirty_ratio * determine_dirtyable_memory()) /
158 100;
159 return 2 + ilog2(dirty_total - 1);
163 * update the period when the dirty threshold changes.
165 static void update_completion_period(void)
167 int shift = calc_period_shift();
168 prop_change_shift(&vm_completions, shift);
169 prop_change_shift(&vm_dirties, shift);
172 int dirty_background_ratio_handler(struct ctl_table *table, int write,
173 void __user *buffer, size_t *lenp,
174 loff_t *ppos)
176 int ret;
178 ret = proc_dointvec_minmax(table, write, buffer, lenp, ppos);
179 if (ret == 0 && write)
180 dirty_background_bytes = 0;
181 return ret;
184 int dirty_background_bytes_handler(struct ctl_table *table, int write,
185 void __user *buffer, size_t *lenp,
186 loff_t *ppos)
188 int ret;
190 ret = proc_doulongvec_minmax(table, write, buffer, lenp, ppos);
191 if (ret == 0 && write)
192 dirty_background_ratio = 0;
193 return ret;
196 int dirty_ratio_handler(struct ctl_table *table, int write,
197 void __user *buffer, size_t *lenp,
198 loff_t *ppos)
200 int old_ratio = vm_dirty_ratio;
201 int ret;
203 ret = proc_dointvec_minmax(table, write, buffer, lenp, ppos);
204 if (ret == 0 && write && vm_dirty_ratio != old_ratio) {
205 update_completion_period();
206 vm_dirty_bytes = 0;
208 return ret;
212 int dirty_bytes_handler(struct ctl_table *table, int write,
213 void __user *buffer, size_t *lenp,
214 loff_t *ppos)
216 unsigned long old_bytes = vm_dirty_bytes;
217 int ret;
219 ret = proc_doulongvec_minmax(table, write, buffer, lenp, ppos);
220 if (ret == 0 && write && vm_dirty_bytes != old_bytes) {
221 update_completion_period();
222 vm_dirty_ratio = 0;
224 return ret;
228 * Increment the BDI's writeout completion count and the global writeout
229 * completion count. Called from test_clear_page_writeback().
231 static inline void __bdi_writeout_inc(struct backing_dev_info *bdi)
233 __inc_bdi_stat(bdi, BDI_WRITTEN);
234 __prop_inc_percpu_max(&vm_completions, &bdi->completions,
235 bdi->max_prop_frac);
238 void bdi_writeout_inc(struct backing_dev_info *bdi)
240 unsigned long flags;
242 local_irq_save(flags);
243 __bdi_writeout_inc(bdi);
244 local_irq_restore(flags);
246 EXPORT_SYMBOL_GPL(bdi_writeout_inc);
248 void task_dirty_inc(struct task_struct *tsk)
250 prop_inc_single(&vm_dirties, &tsk->dirties);
254 * Obtain an accurate fraction of the BDI's portion.
256 static void bdi_writeout_fraction(struct backing_dev_info *bdi,
257 long *numerator, long *denominator)
259 prop_fraction_percpu(&vm_completions, &bdi->completions,
260 numerator, denominator);
263 static inline void task_dirties_fraction(struct task_struct *tsk,
264 long *numerator, long *denominator)
266 prop_fraction_single(&vm_dirties, &tsk->dirties,
267 numerator, denominator);
271 * task_dirty_limit - scale down dirty throttling threshold for one task
273 * task specific dirty limit:
275 * dirty -= (dirty/8) * p_{t}
277 * To protect light/slow dirtying tasks from heavier/fast ones, we start
278 * throttling individual tasks before reaching the bdi dirty limit.
279 * Relatively low thresholds will be allocated to heavy dirtiers. So when
280 * dirty pages grow large, heavy dirtiers will be throttled first, which will
281 * effectively curb the growth of dirty pages. Light dirtiers with high enough
282 * dirty threshold may never get throttled.
284 #define TASK_LIMIT_FRACTION 8
285 static unsigned long task_dirty_limit(struct task_struct *tsk,
286 unsigned long bdi_dirty)
288 long numerator, denominator;
289 unsigned long dirty = bdi_dirty;
290 u64 inv = dirty / TASK_LIMIT_FRACTION;
292 task_dirties_fraction(tsk, &numerator, &denominator);
293 inv *= numerator;
294 do_div(inv, denominator);
296 dirty -= inv;
298 return max(dirty, bdi_dirty/2);
301 /* Minimum limit for any task */
302 static unsigned long task_min_dirty_limit(unsigned long bdi_dirty)
304 return bdi_dirty - bdi_dirty / TASK_LIMIT_FRACTION;
310 static unsigned int bdi_min_ratio;
312 int bdi_set_min_ratio(struct backing_dev_info *bdi, unsigned int min_ratio)
314 int ret = 0;
316 spin_lock_bh(&bdi_lock);
317 if (min_ratio > bdi->max_ratio) {
318 ret = -EINVAL;
319 } else {
320 min_ratio -= bdi->min_ratio;
321 if (bdi_min_ratio + min_ratio < 100) {
322 bdi_min_ratio += min_ratio;
323 bdi->min_ratio += min_ratio;
324 } else {
325 ret = -EINVAL;
328 spin_unlock_bh(&bdi_lock);
330 return ret;
333 int bdi_set_max_ratio(struct backing_dev_info *bdi, unsigned max_ratio)
335 int ret = 0;
337 if (max_ratio > 100)
338 return -EINVAL;
340 spin_lock_bh(&bdi_lock);
341 if (bdi->min_ratio > max_ratio) {
342 ret = -EINVAL;
343 } else {
344 bdi->max_ratio = max_ratio;
345 bdi->max_prop_frac = (PROP_FRAC_BASE * max_ratio) / 100;
347 spin_unlock_bh(&bdi_lock);
349 return ret;
351 EXPORT_SYMBOL(bdi_set_max_ratio);
354 * Work out the current dirty-memory clamping and background writeout
355 * thresholds.
357 * The main aim here is to lower them aggressively if there is a lot of mapped
358 * memory around. To avoid stressing page reclaim with lots of unreclaimable
359 * pages. It is better to clamp down on writers than to start swapping, and
360 * performing lots of scanning.
362 * We only allow 1/2 of the currently-unmapped memory to be dirtied.
364 * We don't permit the clamping level to fall below 5% - that is getting rather
365 * excessive.
367 * We make sure that the background writeout level is below the adjusted
368 * clamping level.
371 static unsigned long highmem_dirtyable_memory(unsigned long total)
373 #ifdef CONFIG_HIGHMEM
374 int node;
375 unsigned long x = 0;
377 for_each_node_state(node, N_HIGH_MEMORY) {
378 struct zone *z =
379 &NODE_DATA(node)->node_zones[ZONE_HIGHMEM];
381 x += zone_page_state(z, NR_FREE_PAGES) +
382 zone_reclaimable_pages(z);
385 * Make sure that the number of highmem pages is never larger
386 * than the number of the total dirtyable memory. This can only
387 * occur in very strange VM situations but we want to make sure
388 * that this does not occur.
390 return min(x, total);
391 #else
392 return 0;
393 #endif
397 * determine_dirtyable_memory - amount of memory that may be used
399 * Returns the numebr of pages that can currently be freed and used
400 * by the kernel for direct mappings.
402 unsigned long determine_dirtyable_memory(void)
404 unsigned long x;
406 x = global_page_state(NR_FREE_PAGES) + global_reclaimable_pages();
408 if (!vm_highmem_is_dirtyable)
409 x -= highmem_dirtyable_memory(x);
411 return x + 1; /* Ensure that we never return 0 */
414 static unsigned long hard_dirty_limit(unsigned long thresh)
416 return max(thresh, global_dirty_limit);
420 * global_dirty_limits - background-writeback and dirty-throttling thresholds
422 * Calculate the dirty thresholds based on sysctl parameters
423 * - vm.dirty_background_ratio or vm.dirty_background_bytes
424 * - vm.dirty_ratio or vm.dirty_bytes
425 * The dirty limits will be lifted by 1/4 for PF_LESS_THROTTLE (ie. nfsd) and
426 * real-time tasks.
428 void global_dirty_limits(unsigned long *pbackground, unsigned long *pdirty)
430 unsigned long background;
431 unsigned long dirty;
432 unsigned long uninitialized_var(available_memory);
433 struct task_struct *tsk;
435 if (!vm_dirty_bytes || !dirty_background_bytes)
436 available_memory = determine_dirtyable_memory();
438 if (vm_dirty_bytes)
439 dirty = DIV_ROUND_UP(vm_dirty_bytes, PAGE_SIZE);
440 else
441 dirty = (vm_dirty_ratio * available_memory) / 100;
443 if (dirty_background_bytes)
444 background = DIV_ROUND_UP(dirty_background_bytes, PAGE_SIZE);
445 else
446 background = (dirty_background_ratio * available_memory) / 100;
448 if (background >= dirty)
449 background = dirty / 2;
450 tsk = current;
451 if (tsk->flags & PF_LESS_THROTTLE || rt_task(tsk)) {
452 background += background / 4;
453 dirty += dirty / 4;
455 *pbackground = background;
456 *pdirty = dirty;
457 trace_global_dirty_state(background, dirty);
461 * bdi_dirty_limit - @bdi's share of dirty throttling threshold
462 * @bdi: the backing_dev_info to query
463 * @dirty: global dirty limit in pages
465 * Returns @bdi's dirty limit in pages. The term "dirty" in the context of
466 * dirty balancing includes all PG_dirty, PG_writeback and NFS unstable pages.
467 * And the "limit" in the name is not seriously taken as hard limit in
468 * balance_dirty_pages().
470 * It allocates high/low dirty limits to fast/slow devices, in order to prevent
471 * - starving fast devices
472 * - piling up dirty pages (that will take long time to sync) on slow devices
474 * The bdi's share of dirty limit will be adapting to its throughput and
475 * bounded by the bdi->min_ratio and/or bdi->max_ratio parameters, if set.
477 unsigned long bdi_dirty_limit(struct backing_dev_info *bdi, unsigned long dirty)
479 u64 bdi_dirty;
480 long numerator, denominator;
483 * Calculate this BDI's share of the dirty ratio.
485 bdi_writeout_fraction(bdi, &numerator, &denominator);
487 bdi_dirty = (dirty * (100 - bdi_min_ratio)) / 100;
488 bdi_dirty *= numerator;
489 do_div(bdi_dirty, denominator);
491 bdi_dirty += (dirty * bdi->min_ratio) / 100;
492 if (bdi_dirty > (dirty * bdi->max_ratio) / 100)
493 bdi_dirty = dirty * bdi->max_ratio / 100;
495 return bdi_dirty;
498 static void bdi_update_write_bandwidth(struct backing_dev_info *bdi,
499 unsigned long elapsed,
500 unsigned long written)
502 const unsigned long period = roundup_pow_of_two(3 * HZ);
503 unsigned long avg = bdi->avg_write_bandwidth;
504 unsigned long old = bdi->write_bandwidth;
505 u64 bw;
508 * bw = written * HZ / elapsed
510 * bw * elapsed + write_bandwidth * (period - elapsed)
511 * write_bandwidth = ---------------------------------------------------
512 * period
514 bw = written - bdi->written_stamp;
515 bw *= HZ;
516 if (unlikely(elapsed > period)) {
517 do_div(bw, elapsed);
518 avg = bw;
519 goto out;
521 bw += (u64)bdi->write_bandwidth * (period - elapsed);
522 bw >>= ilog2(period);
525 * one more level of smoothing, for filtering out sudden spikes
527 if (avg > old && old >= (unsigned long)bw)
528 avg -= (avg - old) >> 3;
530 if (avg < old && old <= (unsigned long)bw)
531 avg += (old - avg) >> 3;
533 out:
534 bdi->write_bandwidth = bw;
535 bdi->avg_write_bandwidth = avg;
539 * The global dirtyable memory and dirty threshold could be suddenly knocked
540 * down by a large amount (eg. on the startup of KVM in a swapless system).
541 * This may throw the system into deep dirty exceeded state and throttle
542 * heavy/light dirtiers alike. To retain good responsiveness, maintain
543 * global_dirty_limit for tracking slowly down to the knocked down dirty
544 * threshold.
546 static void update_dirty_limit(unsigned long thresh, unsigned long dirty)
548 unsigned long limit = global_dirty_limit;
551 * Follow up in one step.
553 if (limit < thresh) {
554 limit = thresh;
555 goto update;
559 * Follow down slowly. Use the higher one as the target, because thresh
560 * may drop below dirty. This is exactly the reason to introduce
561 * global_dirty_limit which is guaranteed to lie above the dirty pages.
563 thresh = max(thresh, dirty);
564 if (limit > thresh) {
565 limit -= (limit - thresh) >> 5;
566 goto update;
568 return;
569 update:
570 global_dirty_limit = limit;
573 static void global_update_bandwidth(unsigned long thresh,
574 unsigned long dirty,
575 unsigned long now)
577 static DEFINE_SPINLOCK(dirty_lock);
578 static unsigned long update_time;
581 * check locklessly first to optimize away locking for the most time
583 if (time_before(now, update_time + BANDWIDTH_INTERVAL))
584 return;
586 spin_lock(&dirty_lock);
587 if (time_after_eq(now, update_time + BANDWIDTH_INTERVAL)) {
588 update_dirty_limit(thresh, dirty);
589 update_time = now;
591 spin_unlock(&dirty_lock);
594 void __bdi_update_bandwidth(struct backing_dev_info *bdi,
595 unsigned long thresh,
596 unsigned long dirty,
597 unsigned long bdi_thresh,
598 unsigned long bdi_dirty,
599 unsigned long start_time)
601 unsigned long now = jiffies;
602 unsigned long elapsed = now - bdi->bw_time_stamp;
603 unsigned long written;
606 * rate-limit, only update once every 200ms.
608 if (elapsed < BANDWIDTH_INTERVAL)
609 return;
611 written = percpu_counter_read(&bdi->bdi_stat[BDI_WRITTEN]);
614 * Skip quiet periods when disk bandwidth is under-utilized.
615 * (at least 1s idle time between two flusher runs)
617 if (elapsed > HZ && time_before(bdi->bw_time_stamp, start_time))
618 goto snapshot;
620 if (thresh)
621 global_update_bandwidth(thresh, dirty, now);
623 bdi_update_write_bandwidth(bdi, elapsed, written);
625 snapshot:
626 bdi->written_stamp = written;
627 bdi->bw_time_stamp = now;
630 static void bdi_update_bandwidth(struct backing_dev_info *bdi,
631 unsigned long thresh,
632 unsigned long dirty,
633 unsigned long bdi_thresh,
634 unsigned long bdi_dirty,
635 unsigned long start_time)
637 if (time_is_after_eq_jiffies(bdi->bw_time_stamp + BANDWIDTH_INTERVAL))
638 return;
639 spin_lock(&bdi->wb.list_lock);
640 __bdi_update_bandwidth(bdi, thresh, dirty, bdi_thresh, bdi_dirty,
641 start_time);
642 spin_unlock(&bdi->wb.list_lock);
646 * balance_dirty_pages() must be called by processes which are generating dirty
647 * data. It looks at the number of dirty pages in the machine and will force
648 * the caller to perform writeback if the system is over `vm_dirty_ratio'.
649 * If we're over `background_thresh' then the writeback threads are woken to
650 * perform some writeout.
652 static void balance_dirty_pages(struct address_space *mapping,
653 unsigned long write_chunk)
655 unsigned long nr_reclaimable, bdi_nr_reclaimable;
656 unsigned long nr_dirty; /* = file_dirty + writeback + unstable_nfs */
657 unsigned long bdi_dirty;
658 unsigned long background_thresh;
659 unsigned long dirty_thresh;
660 unsigned long bdi_thresh;
661 unsigned long task_bdi_thresh;
662 unsigned long min_task_bdi_thresh;
663 unsigned long pages_written = 0;
664 unsigned long pause = 1;
665 bool dirty_exceeded = false;
666 bool clear_dirty_exceeded = true;
667 struct backing_dev_info *bdi = mapping->backing_dev_info;
668 unsigned long start_time = jiffies;
670 for (;;) {
671 nr_reclaimable = global_page_state(NR_FILE_DIRTY) +
672 global_page_state(NR_UNSTABLE_NFS);
673 nr_dirty = nr_reclaimable + global_page_state(NR_WRITEBACK);
675 global_dirty_limits(&background_thresh, &dirty_thresh);
678 * Throttle it only when the background writeback cannot
679 * catch-up. This avoids (excessively) small writeouts
680 * when the bdi limits are ramping up.
682 if (nr_dirty <= (background_thresh + dirty_thresh) / 2)
683 break;
685 bdi_thresh = bdi_dirty_limit(bdi, dirty_thresh);
686 min_task_bdi_thresh = task_min_dirty_limit(bdi_thresh);
687 task_bdi_thresh = task_dirty_limit(current, bdi_thresh);
690 * In order to avoid the stacked BDI deadlock we need
691 * to ensure we accurately count the 'dirty' pages when
692 * the threshold is low.
694 * Otherwise it would be possible to get thresh+n pages
695 * reported dirty, even though there are thresh-m pages
696 * actually dirty; with m+n sitting in the percpu
697 * deltas.
699 if (task_bdi_thresh < 2 * bdi_stat_error(bdi)) {
700 bdi_nr_reclaimable = bdi_stat_sum(bdi, BDI_RECLAIMABLE);
701 bdi_dirty = bdi_nr_reclaimable +
702 bdi_stat_sum(bdi, BDI_WRITEBACK);
703 } else {
704 bdi_nr_reclaimable = bdi_stat(bdi, BDI_RECLAIMABLE);
705 bdi_dirty = bdi_nr_reclaimable +
706 bdi_stat(bdi, BDI_WRITEBACK);
710 * The bdi thresh is somehow "soft" limit derived from the
711 * global "hard" limit. The former helps to prevent heavy IO
712 * bdi or process from holding back light ones; The latter is
713 * the last resort safeguard.
715 dirty_exceeded = (bdi_dirty > task_bdi_thresh) ||
716 (nr_dirty > dirty_thresh);
717 clear_dirty_exceeded = (bdi_dirty <= min_task_bdi_thresh) &&
718 (nr_dirty <= dirty_thresh);
720 if (!dirty_exceeded)
721 break;
723 if (!bdi->dirty_exceeded)
724 bdi->dirty_exceeded = 1;
726 bdi_update_bandwidth(bdi, dirty_thresh, nr_dirty,
727 bdi_thresh, bdi_dirty, start_time);
729 /* Note: nr_reclaimable denotes nr_dirty + nr_unstable.
730 * Unstable writes are a feature of certain networked
731 * filesystems (i.e. NFS) in which data may have been
732 * written to the server's write cache, but has not yet
733 * been flushed to permanent storage.
734 * Only move pages to writeback if this bdi is over its
735 * threshold otherwise wait until the disk writes catch
736 * up.
738 trace_balance_dirty_start(bdi);
739 if (bdi_nr_reclaimable > task_bdi_thresh) {
740 pages_written += writeback_inodes_wb(&bdi->wb,
741 write_chunk);
742 trace_balance_dirty_written(bdi, pages_written);
743 if (pages_written >= write_chunk)
744 break; /* We've done our duty */
746 __set_current_state(TASK_UNINTERRUPTIBLE);
747 io_schedule_timeout(pause);
748 trace_balance_dirty_wait(bdi);
750 dirty_thresh = hard_dirty_limit(dirty_thresh);
752 * max-pause area. If dirty exceeded but still within this
753 * area, no need to sleep for more than 200ms: (a) 8 pages per
754 * 200ms is typically more than enough to curb heavy dirtiers;
755 * (b) the pause time limit makes the dirtiers more responsive.
757 if (nr_dirty < dirty_thresh +
758 dirty_thresh / DIRTY_MAXPAUSE_AREA &&
759 time_after(jiffies, start_time + MAX_PAUSE))
760 break;
762 * pass-good area. When some bdi gets blocked (eg. NFS server
763 * not responding), or write bandwidth dropped dramatically due
764 * to concurrent reads, or dirty threshold suddenly dropped and
765 * the dirty pages cannot be brought down anytime soon (eg. on
766 * slow USB stick), at least let go of the good bdi's.
768 if (nr_dirty < dirty_thresh +
769 dirty_thresh / DIRTY_PASSGOOD_AREA &&
770 bdi_dirty < bdi_thresh)
771 break;
774 * Increase the delay for each loop, up to our previous
775 * default of taking a 100ms nap.
777 pause <<= 1;
778 if (pause > HZ / 10)
779 pause = HZ / 10;
782 /* Clear dirty_exceeded flag only when no task can exceed the limit */
783 if (clear_dirty_exceeded && bdi->dirty_exceeded)
784 bdi->dirty_exceeded = 0;
786 if (writeback_in_progress(bdi))
787 return;
790 * In laptop mode, we wait until hitting the higher threshold before
791 * starting background writeout, and then write out all the way down
792 * to the lower threshold. So slow writers cause minimal disk activity.
794 * In normal mode, we start background writeout at the lower
795 * background_thresh, to keep the amount of dirty memory low.
797 if ((laptop_mode && pages_written) ||
798 (!laptop_mode && (nr_reclaimable > background_thresh)))
799 bdi_start_background_writeback(bdi);
802 void set_page_dirty_balance(struct page *page, int page_mkwrite)
804 if (set_page_dirty(page) || page_mkwrite) {
805 struct address_space *mapping = page_mapping(page);
807 if (mapping)
808 balance_dirty_pages_ratelimited(mapping);
812 static DEFINE_PER_CPU(unsigned long, bdp_ratelimits) = 0;
815 * balance_dirty_pages_ratelimited_nr - balance dirty memory state
816 * @mapping: address_space which was dirtied
817 * @nr_pages_dirtied: number of pages which the caller has just dirtied
819 * Processes which are dirtying memory should call in here once for each page
820 * which was newly dirtied. The function will periodically check the system's
821 * dirty state and will initiate writeback if needed.
823 * On really big machines, get_writeback_state is expensive, so try to avoid
824 * calling it too often (ratelimiting). But once we're over the dirty memory
825 * limit we decrease the ratelimiting by a lot, to prevent individual processes
826 * from overshooting the limit by (ratelimit_pages) each.
828 void balance_dirty_pages_ratelimited_nr(struct address_space *mapping,
829 unsigned long nr_pages_dirtied)
831 struct backing_dev_info *bdi = mapping->backing_dev_info;
832 unsigned long ratelimit;
833 unsigned long *p;
835 if (!bdi_cap_account_dirty(bdi))
836 return;
838 ratelimit = ratelimit_pages;
839 if (mapping->backing_dev_info->dirty_exceeded)
840 ratelimit = 8;
843 * Check the rate limiting. Also, we do not want to throttle real-time
844 * tasks in balance_dirty_pages(). Period.
846 preempt_disable();
847 p = &__get_cpu_var(bdp_ratelimits);
848 *p += nr_pages_dirtied;
849 if (unlikely(*p >= ratelimit)) {
850 ratelimit = sync_writeback_pages(*p);
851 *p = 0;
852 preempt_enable();
853 balance_dirty_pages(mapping, ratelimit);
854 return;
856 preempt_enable();
858 EXPORT_SYMBOL(balance_dirty_pages_ratelimited_nr);
860 void throttle_vm_writeout(gfp_t gfp_mask)
862 unsigned long background_thresh;
863 unsigned long dirty_thresh;
865 for ( ; ; ) {
866 global_dirty_limits(&background_thresh, &dirty_thresh);
869 * Boost the allowable dirty threshold a bit for page
870 * allocators so they don't get DoS'ed by heavy writers
872 dirty_thresh += dirty_thresh / 10; /* wheeee... */
874 if (global_page_state(NR_UNSTABLE_NFS) +
875 global_page_state(NR_WRITEBACK) <= dirty_thresh)
876 break;
877 congestion_wait(BLK_RW_ASYNC, HZ/10);
880 * The caller might hold locks which can prevent IO completion
881 * or progress in the filesystem. So we cannot just sit here
882 * waiting for IO to complete.
884 if ((gfp_mask & (__GFP_FS|__GFP_IO)) != (__GFP_FS|__GFP_IO))
885 break;
890 * sysctl handler for /proc/sys/vm/dirty_writeback_centisecs
892 int dirty_writeback_centisecs_handler(ctl_table *table, int write,
893 void __user *buffer, size_t *length, loff_t *ppos)
895 proc_dointvec(table, write, buffer, length, ppos);
896 bdi_arm_supers_timer();
897 return 0;
900 #ifdef CONFIG_BLOCK
901 void laptop_mode_timer_fn(unsigned long data)
903 struct request_queue *q = (struct request_queue *)data;
904 int nr_pages = global_page_state(NR_FILE_DIRTY) +
905 global_page_state(NR_UNSTABLE_NFS);
908 * We want to write everything out, not just down to the dirty
909 * threshold
911 if (bdi_has_dirty_io(&q->backing_dev_info))
912 bdi_start_writeback(&q->backing_dev_info, nr_pages);
916 * We've spun up the disk and we're in laptop mode: schedule writeback
917 * of all dirty data a few seconds from now. If the flush is already scheduled
918 * then push it back - the user is still using the disk.
920 void laptop_io_completion(struct backing_dev_info *info)
922 mod_timer(&info->laptop_mode_wb_timer, jiffies + laptop_mode);
926 * We're in laptop mode and we've just synced. The sync's writes will have
927 * caused another writeback to be scheduled by laptop_io_completion.
928 * Nothing needs to be written back anymore, so we unschedule the writeback.
930 void laptop_sync_completion(void)
932 struct backing_dev_info *bdi;
934 rcu_read_lock();
936 list_for_each_entry_rcu(bdi, &bdi_list, bdi_list)
937 del_timer(&bdi->laptop_mode_wb_timer);
939 rcu_read_unlock();
941 #endif
944 * If ratelimit_pages is too high then we can get into dirty-data overload
945 * if a large number of processes all perform writes at the same time.
946 * If it is too low then SMP machines will call the (expensive)
947 * get_writeback_state too often.
949 * Here we set ratelimit_pages to a level which ensures that when all CPUs are
950 * dirtying in parallel, we cannot go more than 3% (1/32) over the dirty memory
951 * thresholds before writeback cuts in.
953 * But the limit should not be set too high. Because it also controls the
954 * amount of memory which the balance_dirty_pages() caller has to write back.
955 * If this is too large then the caller will block on the IO queue all the
956 * time. So limit it to four megabytes - the balance_dirty_pages() caller
957 * will write six megabyte chunks, max.
960 void writeback_set_ratelimit(void)
962 ratelimit_pages = vm_total_pages / (num_online_cpus() * 32);
963 if (ratelimit_pages < 16)
964 ratelimit_pages = 16;
965 if (ratelimit_pages * PAGE_CACHE_SIZE > 4096 * 1024)
966 ratelimit_pages = (4096 * 1024) / PAGE_CACHE_SIZE;
969 static int __cpuinit
970 ratelimit_handler(struct notifier_block *self, unsigned long u, void *v)
972 writeback_set_ratelimit();
973 return NOTIFY_DONE;
976 static struct notifier_block __cpuinitdata ratelimit_nb = {
977 .notifier_call = ratelimit_handler,
978 .next = NULL,
982 * Called early on to tune the page writeback dirty limits.
984 * We used to scale dirty pages according to how total memory
985 * related to pages that could be allocated for buffers (by
986 * comparing nr_free_buffer_pages() to vm_total_pages.
988 * However, that was when we used "dirty_ratio" to scale with
989 * all memory, and we don't do that any more. "dirty_ratio"
990 * is now applied to total non-HIGHPAGE memory (by subtracting
991 * totalhigh_pages from vm_total_pages), and as such we can't
992 * get into the old insane situation any more where we had
993 * large amounts of dirty pages compared to a small amount of
994 * non-HIGHMEM memory.
996 * But we might still want to scale the dirty_ratio by how
997 * much memory the box has..
999 void __init page_writeback_init(void)
1001 int shift;
1003 writeback_set_ratelimit();
1004 register_cpu_notifier(&ratelimit_nb);
1006 shift = calc_period_shift();
1007 prop_descriptor_init(&vm_completions, shift);
1008 prop_descriptor_init(&vm_dirties, shift);
1012 * tag_pages_for_writeback - tag pages to be written by write_cache_pages
1013 * @mapping: address space structure to write
1014 * @start: starting page index
1015 * @end: ending page index (inclusive)
1017 * This function scans the page range from @start to @end (inclusive) and tags
1018 * all pages that have DIRTY tag set with a special TOWRITE tag. The idea is
1019 * that write_cache_pages (or whoever calls this function) will then use
1020 * TOWRITE tag to identify pages eligible for writeback. This mechanism is
1021 * used to avoid livelocking of writeback by a process steadily creating new
1022 * dirty pages in the file (thus it is important for this function to be quick
1023 * so that it can tag pages faster than a dirtying process can create them).
1026 * We tag pages in batches of WRITEBACK_TAG_BATCH to reduce tree_lock latency.
1028 void tag_pages_for_writeback(struct address_space *mapping,
1029 pgoff_t start, pgoff_t end)
1031 #define WRITEBACK_TAG_BATCH 4096
1032 unsigned long tagged;
1034 do {
1035 spin_lock_irq(&mapping->tree_lock);
1036 tagged = radix_tree_range_tag_if_tagged(&mapping->page_tree,
1037 &start, end, WRITEBACK_TAG_BATCH,
1038 PAGECACHE_TAG_DIRTY, PAGECACHE_TAG_TOWRITE);
1039 spin_unlock_irq(&mapping->tree_lock);
1040 WARN_ON_ONCE(tagged > WRITEBACK_TAG_BATCH);
1041 cond_resched();
1042 /* We check 'start' to handle wrapping when end == ~0UL */
1043 } while (tagged >= WRITEBACK_TAG_BATCH && start);
1045 EXPORT_SYMBOL(tag_pages_for_writeback);
1048 * write_cache_pages - walk the list of dirty pages of the given address space and write all of them.
1049 * @mapping: address space structure to write
1050 * @wbc: subtract the number of written pages from *@wbc->nr_to_write
1051 * @writepage: function called for each page
1052 * @data: data passed to writepage function
1054 * If a page is already under I/O, write_cache_pages() skips it, even
1055 * if it's dirty. This is desirable behaviour for memory-cleaning writeback,
1056 * but it is INCORRECT for data-integrity system calls such as fsync(). fsync()
1057 * and msync() need to guarantee that all the data which was dirty at the time
1058 * the call was made get new I/O started against them. If wbc->sync_mode is
1059 * WB_SYNC_ALL then we were called for data integrity and we must wait for
1060 * existing IO to complete.
1062 * To avoid livelocks (when other process dirties new pages), we first tag
1063 * pages which should be written back with TOWRITE tag and only then start
1064 * writing them. For data-integrity sync we have to be careful so that we do
1065 * not miss some pages (e.g., because some other process has cleared TOWRITE
1066 * tag we set). The rule we follow is that TOWRITE tag can be cleared only
1067 * by the process clearing the DIRTY tag (and submitting the page for IO).
1069 int write_cache_pages(struct address_space *mapping,
1070 struct writeback_control *wbc, writepage_t writepage,
1071 void *data)
1073 int ret = 0;
1074 int done = 0;
1075 struct pagevec pvec;
1076 int nr_pages;
1077 pgoff_t uninitialized_var(writeback_index);
1078 pgoff_t index;
1079 pgoff_t end; /* Inclusive */
1080 pgoff_t done_index;
1081 int cycled;
1082 int range_whole = 0;
1083 int tag;
1085 pagevec_init(&pvec, 0);
1086 if (wbc->range_cyclic) {
1087 writeback_index = mapping->writeback_index; /* prev offset */
1088 index = writeback_index;
1089 if (index == 0)
1090 cycled = 1;
1091 else
1092 cycled = 0;
1093 end = -1;
1094 } else {
1095 index = wbc->range_start >> PAGE_CACHE_SHIFT;
1096 end = wbc->range_end >> PAGE_CACHE_SHIFT;
1097 if (wbc->range_start == 0 && wbc->range_end == LLONG_MAX)
1098 range_whole = 1;
1099 cycled = 1; /* ignore range_cyclic tests */
1101 if (wbc->sync_mode == WB_SYNC_ALL || wbc->tagged_writepages)
1102 tag = PAGECACHE_TAG_TOWRITE;
1103 else
1104 tag = PAGECACHE_TAG_DIRTY;
1105 retry:
1106 if (wbc->sync_mode == WB_SYNC_ALL || wbc->tagged_writepages)
1107 tag_pages_for_writeback(mapping, index, end);
1108 done_index = index;
1109 while (!done && (index <= end)) {
1110 int i;
1112 nr_pages = pagevec_lookup_tag(&pvec, mapping, &index, tag,
1113 min(end - index, (pgoff_t)PAGEVEC_SIZE-1) + 1);
1114 if (nr_pages == 0)
1115 break;
1117 for (i = 0; i < nr_pages; i++) {
1118 struct page *page = pvec.pages[i];
1121 * At this point, the page may be truncated or
1122 * invalidated (changing page->mapping to NULL), or
1123 * even swizzled back from swapper_space to tmpfs file
1124 * mapping. However, page->index will not change
1125 * because we have a reference on the page.
1127 if (page->index > end) {
1129 * can't be range_cyclic (1st pass) because
1130 * end == -1 in that case.
1132 done = 1;
1133 break;
1136 done_index = page->index;
1138 lock_page(page);
1141 * Page truncated or invalidated. We can freely skip it
1142 * then, even for data integrity operations: the page
1143 * has disappeared concurrently, so there could be no
1144 * real expectation of this data interity operation
1145 * even if there is now a new, dirty page at the same
1146 * pagecache address.
1148 if (unlikely(page->mapping != mapping)) {
1149 continue_unlock:
1150 unlock_page(page);
1151 continue;
1154 if (!PageDirty(page)) {
1155 /* someone wrote it for us */
1156 goto continue_unlock;
1159 if (PageWriteback(page)) {
1160 if (wbc->sync_mode != WB_SYNC_NONE)
1161 wait_on_page_writeback(page);
1162 else
1163 goto continue_unlock;
1166 BUG_ON(PageWriteback(page));
1167 if (!clear_page_dirty_for_io(page))
1168 goto continue_unlock;
1170 trace_wbc_writepage(wbc, mapping->backing_dev_info);
1171 ret = (*writepage)(page, wbc, data);
1172 if (unlikely(ret)) {
1173 if (ret == AOP_WRITEPAGE_ACTIVATE) {
1174 unlock_page(page);
1175 ret = 0;
1176 } else {
1178 * done_index is set past this page,
1179 * so media errors will not choke
1180 * background writeout for the entire
1181 * file. This has consequences for
1182 * range_cyclic semantics (ie. it may
1183 * not be suitable for data integrity
1184 * writeout).
1186 done_index = page->index + 1;
1187 done = 1;
1188 break;
1193 * We stop writing back only if we are not doing
1194 * integrity sync. In case of integrity sync we have to
1195 * keep going until we have written all the pages
1196 * we tagged for writeback prior to entering this loop.
1198 if (--wbc->nr_to_write <= 0 &&
1199 wbc->sync_mode == WB_SYNC_NONE) {
1200 done = 1;
1201 break;
1204 pagevec_release(&pvec);
1205 cond_resched();
1207 if (!cycled && !done) {
1209 * range_cyclic:
1210 * We hit the last page and there is more work to be done: wrap
1211 * back to the start of the file
1213 cycled = 1;
1214 index = 0;
1215 end = writeback_index - 1;
1216 goto retry;
1218 if (wbc->range_cyclic || (range_whole && wbc->nr_to_write > 0))
1219 mapping->writeback_index = done_index;
1221 return ret;
1223 EXPORT_SYMBOL(write_cache_pages);
1226 * Function used by generic_writepages to call the real writepage
1227 * function and set the mapping flags on error
1229 static int __writepage(struct page *page, struct writeback_control *wbc,
1230 void *data)
1232 struct address_space *mapping = data;
1233 int ret = mapping->a_ops->writepage(page, wbc);
1234 mapping_set_error(mapping, ret);
1235 return ret;
1239 * generic_writepages - walk the list of dirty pages of the given address space and writepage() all of them.
1240 * @mapping: address space structure to write
1241 * @wbc: subtract the number of written pages from *@wbc->nr_to_write
1243 * This is a library function, which implements the writepages()
1244 * address_space_operation.
1246 int generic_writepages(struct address_space *mapping,
1247 struct writeback_control *wbc)
1249 struct blk_plug plug;
1250 int ret;
1252 /* deal with chardevs and other special file */
1253 if (!mapping->a_ops->writepage)
1254 return 0;
1256 blk_start_plug(&plug);
1257 ret = write_cache_pages(mapping, wbc, __writepage, mapping);
1258 blk_finish_plug(&plug);
1259 return ret;
1262 EXPORT_SYMBOL(generic_writepages);
1264 int do_writepages(struct address_space *mapping, struct writeback_control *wbc)
1266 int ret;
1268 if (wbc->nr_to_write <= 0)
1269 return 0;
1270 if (mapping->a_ops->writepages)
1271 ret = mapping->a_ops->writepages(mapping, wbc);
1272 else
1273 ret = generic_writepages(mapping, wbc);
1274 return ret;
1278 * write_one_page - write out a single page and optionally wait on I/O
1279 * @page: the page to write
1280 * @wait: if true, wait on writeout
1282 * The page must be locked by the caller and will be unlocked upon return.
1284 * write_one_page() returns a negative error code if I/O failed.
1286 int write_one_page(struct page *page, int wait)
1288 struct address_space *mapping = page->mapping;
1289 int ret = 0;
1290 struct writeback_control wbc = {
1291 .sync_mode = WB_SYNC_ALL,
1292 .nr_to_write = 1,
1295 BUG_ON(!PageLocked(page));
1297 if (wait)
1298 wait_on_page_writeback(page);
1300 if (clear_page_dirty_for_io(page)) {
1301 page_cache_get(page);
1302 ret = mapping->a_ops->writepage(page, &wbc);
1303 if (ret == 0 && wait) {
1304 wait_on_page_writeback(page);
1305 if (PageError(page))
1306 ret = -EIO;
1308 page_cache_release(page);
1309 } else {
1310 unlock_page(page);
1312 return ret;
1314 EXPORT_SYMBOL(write_one_page);
1317 * For address_spaces which do not use buffers nor write back.
1319 int __set_page_dirty_no_writeback(struct page *page)
1321 if (!PageDirty(page))
1322 return !TestSetPageDirty(page);
1323 return 0;
1327 * Helper function for set_page_dirty family.
1328 * NOTE: This relies on being atomic wrt interrupts.
1330 void account_page_dirtied(struct page *page, struct address_space *mapping)
1332 if (mapping_cap_account_dirty(mapping)) {
1333 __inc_zone_page_state(page, NR_FILE_DIRTY);
1334 __inc_zone_page_state(page, NR_DIRTIED);
1335 __inc_bdi_stat(mapping->backing_dev_info, BDI_RECLAIMABLE);
1336 task_dirty_inc(current);
1337 task_io_account_write(PAGE_CACHE_SIZE);
1340 EXPORT_SYMBOL(account_page_dirtied);
1343 * Helper function for set_page_writeback family.
1344 * NOTE: Unlike account_page_dirtied this does not rely on being atomic
1345 * wrt interrupts.
1347 void account_page_writeback(struct page *page)
1349 inc_zone_page_state(page, NR_WRITEBACK);
1351 EXPORT_SYMBOL(account_page_writeback);
1354 * For address_spaces which do not use buffers. Just tag the page as dirty in
1355 * its radix tree.
1357 * This is also used when a single buffer is being dirtied: we want to set the
1358 * page dirty in that case, but not all the buffers. This is a "bottom-up"
1359 * dirtying, whereas __set_page_dirty_buffers() is a "top-down" dirtying.
1361 * Most callers have locked the page, which pins the address_space in memory.
1362 * But zap_pte_range() does not lock the page, however in that case the
1363 * mapping is pinned by the vma's ->vm_file reference.
1365 * We take care to handle the case where the page was truncated from the
1366 * mapping by re-checking page_mapping() inside tree_lock.
1368 int __set_page_dirty_nobuffers(struct page *page)
1370 if (!TestSetPageDirty(page)) {
1371 struct address_space *mapping = page_mapping(page);
1372 struct address_space *mapping2;
1374 if (!mapping)
1375 return 1;
1377 spin_lock_irq(&mapping->tree_lock);
1378 mapping2 = page_mapping(page);
1379 if (mapping2) { /* Race with truncate? */
1380 BUG_ON(mapping2 != mapping);
1381 WARN_ON_ONCE(!PagePrivate(page) && !PageUptodate(page));
1382 account_page_dirtied(page, mapping);
1383 radix_tree_tag_set(&mapping->page_tree,
1384 page_index(page), PAGECACHE_TAG_DIRTY);
1386 spin_unlock_irq(&mapping->tree_lock);
1387 if (mapping->host) {
1388 /* !PageAnon && !swapper_space */
1389 __mark_inode_dirty(mapping->host, I_DIRTY_PAGES);
1391 return 1;
1393 return 0;
1395 EXPORT_SYMBOL(__set_page_dirty_nobuffers);
1398 * When a writepage implementation decides that it doesn't want to write this
1399 * page for some reason, it should redirty the locked page via
1400 * redirty_page_for_writepage() and it should then unlock the page and return 0
1402 int redirty_page_for_writepage(struct writeback_control *wbc, struct page *page)
1404 wbc->pages_skipped++;
1405 return __set_page_dirty_nobuffers(page);
1407 EXPORT_SYMBOL(redirty_page_for_writepage);
1410 * Dirty a page.
1412 * For pages with a mapping this should be done under the page lock
1413 * for the benefit of asynchronous memory errors who prefer a consistent
1414 * dirty state. This rule can be broken in some special cases,
1415 * but should be better not to.
1417 * If the mapping doesn't provide a set_page_dirty a_op, then
1418 * just fall through and assume that it wants buffer_heads.
1420 int set_page_dirty(struct page *page)
1422 struct address_space *mapping = page_mapping(page);
1424 if (likely(mapping)) {
1425 int (*spd)(struct page *) = mapping->a_ops->set_page_dirty;
1427 * readahead/lru_deactivate_page could remain
1428 * PG_readahead/PG_reclaim due to race with end_page_writeback
1429 * About readahead, if the page is written, the flags would be
1430 * reset. So no problem.
1431 * About lru_deactivate_page, if the page is redirty, the flag
1432 * will be reset. So no problem. but if the page is used by readahead
1433 * it will confuse readahead and make it restart the size rampup
1434 * process. But it's a trivial problem.
1436 ClearPageReclaim(page);
1437 #ifdef CONFIG_BLOCK
1438 if (!spd)
1439 spd = __set_page_dirty_buffers;
1440 #endif
1441 return (*spd)(page);
1443 if (!PageDirty(page)) {
1444 if (!TestSetPageDirty(page))
1445 return 1;
1447 return 0;
1449 EXPORT_SYMBOL(set_page_dirty);
1452 * set_page_dirty() is racy if the caller has no reference against
1453 * page->mapping->host, and if the page is unlocked. This is because another
1454 * CPU could truncate the page off the mapping and then free the mapping.
1456 * Usually, the page _is_ locked, or the caller is a user-space process which
1457 * holds a reference on the inode by having an open file.
1459 * In other cases, the page should be locked before running set_page_dirty().
1461 int set_page_dirty_lock(struct page *page)
1463 int ret;
1465 lock_page(page);
1466 ret = set_page_dirty(page);
1467 unlock_page(page);
1468 return ret;
1470 EXPORT_SYMBOL(set_page_dirty_lock);
1473 * Clear a page's dirty flag, while caring for dirty memory accounting.
1474 * Returns true if the page was previously dirty.
1476 * This is for preparing to put the page under writeout. We leave the page
1477 * tagged as dirty in the radix tree so that a concurrent write-for-sync
1478 * can discover it via a PAGECACHE_TAG_DIRTY walk. The ->writepage
1479 * implementation will run either set_page_writeback() or set_page_dirty(),
1480 * at which stage we bring the page's dirty flag and radix-tree dirty tag
1481 * back into sync.
1483 * This incoherency between the page's dirty flag and radix-tree tag is
1484 * unfortunate, but it only exists while the page is locked.
1486 int clear_page_dirty_for_io(struct page *page)
1488 struct address_space *mapping = page_mapping(page);
1490 BUG_ON(!PageLocked(page));
1492 if (mapping && mapping_cap_account_dirty(mapping)) {
1494 * Yes, Virginia, this is indeed insane.
1496 * We use this sequence to make sure that
1497 * (a) we account for dirty stats properly
1498 * (b) we tell the low-level filesystem to
1499 * mark the whole page dirty if it was
1500 * dirty in a pagetable. Only to then
1501 * (c) clean the page again and return 1 to
1502 * cause the writeback.
1504 * This way we avoid all nasty races with the
1505 * dirty bit in multiple places and clearing
1506 * them concurrently from different threads.
1508 * Note! Normally the "set_page_dirty(page)"
1509 * has no effect on the actual dirty bit - since
1510 * that will already usually be set. But we
1511 * need the side effects, and it can help us
1512 * avoid races.
1514 * We basically use the page "master dirty bit"
1515 * as a serialization point for all the different
1516 * threads doing their things.
1518 if (page_mkclean(page))
1519 set_page_dirty(page);
1521 * We carefully synchronise fault handlers against
1522 * installing a dirty pte and marking the page dirty
1523 * at this point. We do this by having them hold the
1524 * page lock at some point after installing their
1525 * pte, but before marking the page dirty.
1526 * Pages are always locked coming in here, so we get
1527 * the desired exclusion. See mm/memory.c:do_wp_page()
1528 * for more comments.
1530 if (TestClearPageDirty(page)) {
1531 dec_zone_page_state(page, NR_FILE_DIRTY);
1532 dec_bdi_stat(mapping->backing_dev_info,
1533 BDI_RECLAIMABLE);
1534 return 1;
1536 return 0;
1538 return TestClearPageDirty(page);
1540 EXPORT_SYMBOL(clear_page_dirty_for_io);
1542 int test_clear_page_writeback(struct page *page)
1544 struct address_space *mapping = page_mapping(page);
1545 int ret;
1547 if (mapping) {
1548 struct backing_dev_info *bdi = mapping->backing_dev_info;
1549 unsigned long flags;
1551 spin_lock_irqsave(&mapping->tree_lock, flags);
1552 ret = TestClearPageWriteback(page);
1553 if (ret) {
1554 radix_tree_tag_clear(&mapping->page_tree,
1555 page_index(page),
1556 PAGECACHE_TAG_WRITEBACK);
1557 if (bdi_cap_account_writeback(bdi)) {
1558 __dec_bdi_stat(bdi, BDI_WRITEBACK);
1559 __bdi_writeout_inc(bdi);
1562 spin_unlock_irqrestore(&mapping->tree_lock, flags);
1563 } else {
1564 ret = TestClearPageWriteback(page);
1566 if (ret) {
1567 dec_zone_page_state(page, NR_WRITEBACK);
1568 inc_zone_page_state(page, NR_WRITTEN);
1570 return ret;
1573 int test_set_page_writeback(struct page *page)
1575 struct address_space *mapping = page_mapping(page);
1576 int ret;
1578 if (mapping) {
1579 struct backing_dev_info *bdi = mapping->backing_dev_info;
1580 unsigned long flags;
1582 spin_lock_irqsave(&mapping->tree_lock, flags);
1583 ret = TestSetPageWriteback(page);
1584 if (!ret) {
1585 radix_tree_tag_set(&mapping->page_tree,
1586 page_index(page),
1587 PAGECACHE_TAG_WRITEBACK);
1588 if (bdi_cap_account_writeback(bdi))
1589 __inc_bdi_stat(bdi, BDI_WRITEBACK);
1591 if (!PageDirty(page))
1592 radix_tree_tag_clear(&mapping->page_tree,
1593 page_index(page),
1594 PAGECACHE_TAG_DIRTY);
1595 radix_tree_tag_clear(&mapping->page_tree,
1596 page_index(page),
1597 PAGECACHE_TAG_TOWRITE);
1598 spin_unlock_irqrestore(&mapping->tree_lock, flags);
1599 } else {
1600 ret = TestSetPageWriteback(page);
1602 if (!ret)
1603 account_page_writeback(page);
1604 return ret;
1607 EXPORT_SYMBOL(test_set_page_writeback);
1610 * Return true if any of the pages in the mapping are marked with the
1611 * passed tag.
1613 int mapping_tagged(struct address_space *mapping, int tag)
1615 return radix_tree_tagged(&mapping->page_tree, tag);
1617 EXPORT_SYMBOL(mapping_tagged);