drm/radeon/kms: fix i2c map for rv250/280
[linux-2.6/linux-acpi-2.6/ibm-acpi-2.6.git] / mm / page-writeback.c
blob31f698862420021cc9b1e39e608077d1d468730a
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 * After a CPU has dirtied this many pages, balance_dirty_pages_ratelimited
41 * will look to see if it needs to force writeback or throttling.
43 static long ratelimit_pages = 32;
46 * When balance_dirty_pages decides that the caller needs to perform some
47 * non-background writeback, this is how many pages it will attempt to write.
48 * It should be somewhat larger than dirtied pages to ensure that reasonably
49 * large amounts of I/O are submitted.
51 static inline long sync_writeback_pages(unsigned long dirtied)
53 if (dirtied < ratelimit_pages)
54 dirtied = ratelimit_pages;
56 return dirtied + dirtied / 2;
59 /* The following parameters are exported via /proc/sys/vm */
62 * Start background writeback (via writeback threads) at this percentage
64 int dirty_background_ratio = 10;
67 * dirty_background_bytes starts at 0 (disabled) so that it is a function of
68 * dirty_background_ratio * the amount of dirtyable memory
70 unsigned long dirty_background_bytes;
73 * free highmem will not be subtracted from the total free memory
74 * for calculating free ratios if vm_highmem_is_dirtyable is true
76 int vm_highmem_is_dirtyable;
79 * The generator of dirty data starts writeback at this percentage
81 int vm_dirty_ratio = 20;
84 * vm_dirty_bytes starts at 0 (disabled) so that it is a function of
85 * vm_dirty_ratio * the amount of dirtyable memory
87 unsigned long vm_dirty_bytes;
90 * The interval between `kupdate'-style writebacks
92 unsigned int dirty_writeback_interval = 5 * 100; /* centiseconds */
95 * The longest time for which data is allowed to remain dirty
97 unsigned int dirty_expire_interval = 30 * 100; /* centiseconds */
100 * Flag that makes the machine dump writes/reads and block dirtyings.
102 int block_dump;
105 * Flag that puts the machine in "laptop mode". Doubles as a timeout in jiffies:
106 * a full sync is triggered after this time elapses without any disk activity.
108 int laptop_mode;
110 EXPORT_SYMBOL(laptop_mode);
112 /* End of sysctl-exported parameters */
116 * Scale the writeback cache size proportional to the relative writeout speeds.
118 * We do this by keeping a floating proportion between BDIs, based on page
119 * writeback completions [end_page_writeback()]. Those devices that write out
120 * pages fastest will get the larger share, while the slower will get a smaller
121 * share.
123 * We use page writeout completions because we are interested in getting rid of
124 * dirty pages. Having them written out is the primary goal.
126 * We introduce a concept of time, a period over which we measure these events,
127 * because demand can/will vary over time. The length of this period itself is
128 * measured in page writeback completions.
131 static struct prop_descriptor vm_completions;
132 static struct prop_descriptor vm_dirties;
135 * couple the period to the dirty_ratio:
137 * period/2 ~ roundup_pow_of_two(dirty limit)
139 static int calc_period_shift(void)
141 unsigned long dirty_total;
143 if (vm_dirty_bytes)
144 dirty_total = vm_dirty_bytes / PAGE_SIZE;
145 else
146 dirty_total = (vm_dirty_ratio * determine_dirtyable_memory()) /
147 100;
148 return 2 + ilog2(dirty_total - 1);
152 * update the period when the dirty threshold changes.
154 static void update_completion_period(void)
156 int shift = calc_period_shift();
157 prop_change_shift(&vm_completions, shift);
158 prop_change_shift(&vm_dirties, shift);
161 int dirty_background_ratio_handler(struct ctl_table *table, int write,
162 void __user *buffer, size_t *lenp,
163 loff_t *ppos)
165 int ret;
167 ret = proc_dointvec_minmax(table, write, buffer, lenp, ppos);
168 if (ret == 0 && write)
169 dirty_background_bytes = 0;
170 return ret;
173 int dirty_background_bytes_handler(struct ctl_table *table, int write,
174 void __user *buffer, size_t *lenp,
175 loff_t *ppos)
177 int ret;
179 ret = proc_doulongvec_minmax(table, write, buffer, lenp, ppos);
180 if (ret == 0 && write)
181 dirty_background_ratio = 0;
182 return ret;
185 int dirty_ratio_handler(struct ctl_table *table, int write,
186 void __user *buffer, size_t *lenp,
187 loff_t *ppos)
189 int old_ratio = vm_dirty_ratio;
190 int ret;
192 ret = proc_dointvec_minmax(table, write, buffer, lenp, ppos);
193 if (ret == 0 && write && vm_dirty_ratio != old_ratio) {
194 update_completion_period();
195 vm_dirty_bytes = 0;
197 return ret;
201 int dirty_bytes_handler(struct ctl_table *table, int write,
202 void __user *buffer, size_t *lenp,
203 loff_t *ppos)
205 unsigned long old_bytes = vm_dirty_bytes;
206 int ret;
208 ret = proc_doulongvec_minmax(table, write, buffer, lenp, ppos);
209 if (ret == 0 && write && vm_dirty_bytes != old_bytes) {
210 update_completion_period();
211 vm_dirty_ratio = 0;
213 return ret;
217 * Increment the BDI's writeout completion count and the global writeout
218 * completion count. Called from test_clear_page_writeback().
220 static inline void __bdi_writeout_inc(struct backing_dev_info *bdi)
222 __prop_inc_percpu_max(&vm_completions, &bdi->completions,
223 bdi->max_prop_frac);
226 void bdi_writeout_inc(struct backing_dev_info *bdi)
228 unsigned long flags;
230 local_irq_save(flags);
231 __bdi_writeout_inc(bdi);
232 local_irq_restore(flags);
234 EXPORT_SYMBOL_GPL(bdi_writeout_inc);
236 void task_dirty_inc(struct task_struct *tsk)
238 prop_inc_single(&vm_dirties, &tsk->dirties);
242 * Obtain an accurate fraction of the BDI's portion.
244 static void bdi_writeout_fraction(struct backing_dev_info *bdi,
245 long *numerator, long *denominator)
247 if (bdi_cap_writeback_dirty(bdi)) {
248 prop_fraction_percpu(&vm_completions, &bdi->completions,
249 numerator, denominator);
250 } else {
251 *numerator = 0;
252 *denominator = 1;
256 static inline void task_dirties_fraction(struct task_struct *tsk,
257 long *numerator, long *denominator)
259 prop_fraction_single(&vm_dirties, &tsk->dirties,
260 numerator, denominator);
264 * task_dirty_limit - scale down dirty throttling threshold for one task
266 * task specific dirty limit:
268 * dirty -= (dirty/8) * p_{t}
270 * To protect light/slow dirtying tasks from heavier/fast ones, we start
271 * throttling individual tasks before reaching the bdi dirty limit.
272 * Relatively low thresholds will be allocated to heavy dirtiers. So when
273 * dirty pages grow large, heavy dirtiers will be throttled first, which will
274 * effectively curb the growth of dirty pages. Light dirtiers with high enough
275 * dirty threshold may never get throttled.
277 static unsigned long task_dirty_limit(struct task_struct *tsk,
278 unsigned long bdi_dirty)
280 long numerator, denominator;
281 unsigned long dirty = bdi_dirty;
282 u64 inv = dirty >> 3;
284 task_dirties_fraction(tsk, &numerator, &denominator);
285 inv *= numerator;
286 do_div(inv, denominator);
288 dirty -= inv;
290 return max(dirty, bdi_dirty/2);
296 static unsigned int bdi_min_ratio;
298 int bdi_set_min_ratio(struct backing_dev_info *bdi, unsigned int min_ratio)
300 int ret = 0;
302 spin_lock_bh(&bdi_lock);
303 if (min_ratio > bdi->max_ratio) {
304 ret = -EINVAL;
305 } else {
306 min_ratio -= bdi->min_ratio;
307 if (bdi_min_ratio + min_ratio < 100) {
308 bdi_min_ratio += min_ratio;
309 bdi->min_ratio += min_ratio;
310 } else {
311 ret = -EINVAL;
314 spin_unlock_bh(&bdi_lock);
316 return ret;
319 int bdi_set_max_ratio(struct backing_dev_info *bdi, unsigned max_ratio)
321 int ret = 0;
323 if (max_ratio > 100)
324 return -EINVAL;
326 spin_lock_bh(&bdi_lock);
327 if (bdi->min_ratio > max_ratio) {
328 ret = -EINVAL;
329 } else {
330 bdi->max_ratio = max_ratio;
331 bdi->max_prop_frac = (PROP_FRAC_BASE * max_ratio) / 100;
333 spin_unlock_bh(&bdi_lock);
335 return ret;
337 EXPORT_SYMBOL(bdi_set_max_ratio);
340 * Work out the current dirty-memory clamping and background writeout
341 * thresholds.
343 * The main aim here is to lower them aggressively if there is a lot of mapped
344 * memory around. To avoid stressing page reclaim with lots of unreclaimable
345 * pages. It is better to clamp down on writers than to start swapping, and
346 * performing lots of scanning.
348 * We only allow 1/2 of the currently-unmapped memory to be dirtied.
350 * We don't permit the clamping level to fall below 5% - that is getting rather
351 * excessive.
353 * We make sure that the background writeout level is below the adjusted
354 * clamping level.
357 static unsigned long highmem_dirtyable_memory(unsigned long total)
359 #ifdef CONFIG_HIGHMEM
360 int node;
361 unsigned long x = 0;
363 for_each_node_state(node, N_HIGH_MEMORY) {
364 struct zone *z =
365 &NODE_DATA(node)->node_zones[ZONE_HIGHMEM];
367 x += zone_page_state(z, NR_FREE_PAGES) +
368 zone_reclaimable_pages(z);
371 * Make sure that the number of highmem pages is never larger
372 * than the number of the total dirtyable memory. This can only
373 * occur in very strange VM situations but we want to make sure
374 * that this does not occur.
376 return min(x, total);
377 #else
378 return 0;
379 #endif
383 * determine_dirtyable_memory - amount of memory that may be used
385 * Returns the numebr of pages that can currently be freed and used
386 * by the kernel for direct mappings.
388 unsigned long determine_dirtyable_memory(void)
390 unsigned long x;
392 x = global_page_state(NR_FREE_PAGES) + global_reclaimable_pages();
394 if (!vm_highmem_is_dirtyable)
395 x -= highmem_dirtyable_memory(x);
397 return x + 1; /* Ensure that we never return 0 */
401 * global_dirty_limits - background-writeback and dirty-throttling thresholds
403 * Calculate the dirty thresholds based on sysctl parameters
404 * - vm.dirty_background_ratio or vm.dirty_background_bytes
405 * - vm.dirty_ratio or vm.dirty_bytes
406 * The dirty limits will be lifted by 1/4 for PF_LESS_THROTTLE (ie. nfsd) and
407 * real-time tasks.
409 void global_dirty_limits(unsigned long *pbackground, unsigned long *pdirty)
411 unsigned long background;
412 unsigned long dirty;
413 unsigned long uninitialized_var(available_memory);
414 struct task_struct *tsk;
416 if (!vm_dirty_bytes || !dirty_background_bytes)
417 available_memory = determine_dirtyable_memory();
419 if (vm_dirty_bytes)
420 dirty = DIV_ROUND_UP(vm_dirty_bytes, PAGE_SIZE);
421 else
422 dirty = (vm_dirty_ratio * available_memory) / 100;
424 if (dirty_background_bytes)
425 background = DIV_ROUND_UP(dirty_background_bytes, PAGE_SIZE);
426 else
427 background = (dirty_background_ratio * available_memory) / 100;
429 if (background >= dirty)
430 background = dirty / 2;
431 tsk = current;
432 if (tsk->flags & PF_LESS_THROTTLE || rt_task(tsk)) {
433 background += background / 4;
434 dirty += dirty / 4;
436 *pbackground = background;
437 *pdirty = dirty;
441 * bdi_dirty_limit - @bdi's share of dirty throttling threshold
443 * Allocate high/low dirty limits to fast/slow devices, in order to prevent
444 * - starving fast devices
445 * - piling up dirty pages (that will take long time to sync) on slow devices
447 * The bdi's share of dirty limit will be adapting to its throughput and
448 * bounded by the bdi->min_ratio and/or bdi->max_ratio parameters, if set.
450 unsigned long bdi_dirty_limit(struct backing_dev_info *bdi, unsigned long dirty)
452 u64 bdi_dirty;
453 long numerator, denominator;
456 * Calculate this BDI's share of the dirty ratio.
458 bdi_writeout_fraction(bdi, &numerator, &denominator);
460 bdi_dirty = (dirty * (100 - bdi_min_ratio)) / 100;
461 bdi_dirty *= numerator;
462 do_div(bdi_dirty, denominator);
464 bdi_dirty += (dirty * bdi->min_ratio) / 100;
465 if (bdi_dirty > (dirty * bdi->max_ratio) / 100)
466 bdi_dirty = dirty * bdi->max_ratio / 100;
468 return bdi_dirty;
472 * balance_dirty_pages() must be called by processes which are generating dirty
473 * data. It looks at the number of dirty pages in the machine and will force
474 * the caller to perform writeback if the system is over `vm_dirty_ratio'.
475 * If we're over `background_thresh' then the writeback threads are woken to
476 * perform some writeout.
478 static void balance_dirty_pages(struct address_space *mapping,
479 unsigned long write_chunk)
481 long nr_reclaimable, bdi_nr_reclaimable;
482 long nr_writeback, bdi_nr_writeback;
483 unsigned long background_thresh;
484 unsigned long dirty_thresh;
485 unsigned long bdi_thresh;
486 unsigned long pages_written = 0;
487 unsigned long pause = 1;
488 bool dirty_exceeded = false;
489 struct backing_dev_info *bdi = mapping->backing_dev_info;
491 for (;;) {
492 struct writeback_control wbc = {
493 .sync_mode = WB_SYNC_NONE,
494 .older_than_this = NULL,
495 .nr_to_write = write_chunk,
496 .range_cyclic = 1,
499 nr_reclaimable = global_page_state(NR_FILE_DIRTY) +
500 global_page_state(NR_UNSTABLE_NFS);
501 nr_writeback = global_page_state(NR_WRITEBACK);
503 global_dirty_limits(&background_thresh, &dirty_thresh);
506 * Throttle it only when the background writeback cannot
507 * catch-up. This avoids (excessively) small writeouts
508 * when the bdi limits are ramping up.
510 if (nr_reclaimable + nr_writeback <=
511 (background_thresh + dirty_thresh) / 2)
512 break;
514 bdi_thresh = bdi_dirty_limit(bdi, dirty_thresh);
515 bdi_thresh = task_dirty_limit(current, bdi_thresh);
518 * In order to avoid the stacked BDI deadlock we need
519 * to ensure we accurately count the 'dirty' pages when
520 * the threshold is low.
522 * Otherwise it would be possible to get thresh+n pages
523 * reported dirty, even though there are thresh-m pages
524 * actually dirty; with m+n sitting in the percpu
525 * deltas.
527 if (bdi_thresh < 2*bdi_stat_error(bdi)) {
528 bdi_nr_reclaimable = bdi_stat_sum(bdi, BDI_RECLAIMABLE);
529 bdi_nr_writeback = bdi_stat_sum(bdi, BDI_WRITEBACK);
530 } else {
531 bdi_nr_reclaimable = bdi_stat(bdi, BDI_RECLAIMABLE);
532 bdi_nr_writeback = bdi_stat(bdi, BDI_WRITEBACK);
536 * The bdi thresh is somehow "soft" limit derived from the
537 * global "hard" limit. The former helps to prevent heavy IO
538 * bdi or process from holding back light ones; The latter is
539 * the last resort safeguard.
541 dirty_exceeded =
542 (bdi_nr_reclaimable + bdi_nr_writeback > bdi_thresh)
543 || (nr_reclaimable + nr_writeback > dirty_thresh);
545 if (!dirty_exceeded)
546 break;
548 if (!bdi->dirty_exceeded)
549 bdi->dirty_exceeded = 1;
551 /* Note: nr_reclaimable denotes nr_dirty + nr_unstable.
552 * Unstable writes are a feature of certain networked
553 * filesystems (i.e. NFS) in which data may have been
554 * written to the server's write cache, but has not yet
555 * been flushed to permanent storage.
556 * Only move pages to writeback if this bdi is over its
557 * threshold otherwise wait until the disk writes catch
558 * up.
560 trace_wbc_balance_dirty_start(&wbc, bdi);
561 if (bdi_nr_reclaimable > bdi_thresh) {
562 writeback_inodes_wb(&bdi->wb, &wbc);
563 pages_written += write_chunk - wbc.nr_to_write;
564 trace_wbc_balance_dirty_written(&wbc, bdi);
565 if (pages_written >= write_chunk)
566 break; /* We've done our duty */
568 trace_wbc_balance_dirty_wait(&wbc, bdi);
569 __set_current_state(TASK_UNINTERRUPTIBLE);
570 io_schedule_timeout(pause);
573 * Increase the delay for each loop, up to our previous
574 * default of taking a 100ms nap.
576 pause <<= 1;
577 if (pause > HZ / 10)
578 pause = HZ / 10;
581 if (!dirty_exceeded && bdi->dirty_exceeded)
582 bdi->dirty_exceeded = 0;
584 if (writeback_in_progress(bdi))
585 return;
588 * In laptop mode, we wait until hitting the higher threshold before
589 * starting background writeout, and then write out all the way down
590 * to the lower threshold. So slow writers cause minimal disk activity.
592 * In normal mode, we start background writeout at the lower
593 * background_thresh, to keep the amount of dirty memory low.
595 if ((laptop_mode && pages_written) ||
596 (!laptop_mode && (nr_reclaimable > background_thresh)))
597 bdi_start_background_writeback(bdi);
600 void set_page_dirty_balance(struct page *page, int page_mkwrite)
602 if (set_page_dirty(page) || page_mkwrite) {
603 struct address_space *mapping = page_mapping(page);
605 if (mapping)
606 balance_dirty_pages_ratelimited(mapping);
610 static DEFINE_PER_CPU(unsigned long, bdp_ratelimits) = 0;
613 * balance_dirty_pages_ratelimited_nr - balance dirty memory state
614 * @mapping: address_space which was dirtied
615 * @nr_pages_dirtied: number of pages which the caller has just dirtied
617 * Processes which are dirtying memory should call in here once for each page
618 * which was newly dirtied. The function will periodically check the system's
619 * dirty state and will initiate writeback if needed.
621 * On really big machines, get_writeback_state is expensive, so try to avoid
622 * calling it too often (ratelimiting). But once we're over the dirty memory
623 * limit we decrease the ratelimiting by a lot, to prevent individual processes
624 * from overshooting the limit by (ratelimit_pages) each.
626 void balance_dirty_pages_ratelimited_nr(struct address_space *mapping,
627 unsigned long nr_pages_dirtied)
629 unsigned long ratelimit;
630 unsigned long *p;
632 ratelimit = ratelimit_pages;
633 if (mapping->backing_dev_info->dirty_exceeded)
634 ratelimit = 8;
637 * Check the rate limiting. Also, we do not want to throttle real-time
638 * tasks in balance_dirty_pages(). Period.
640 preempt_disable();
641 p = &__get_cpu_var(bdp_ratelimits);
642 *p += nr_pages_dirtied;
643 if (unlikely(*p >= ratelimit)) {
644 ratelimit = sync_writeback_pages(*p);
645 *p = 0;
646 preempt_enable();
647 balance_dirty_pages(mapping, ratelimit);
648 return;
650 preempt_enable();
652 EXPORT_SYMBOL(balance_dirty_pages_ratelimited_nr);
654 void throttle_vm_writeout(gfp_t gfp_mask)
656 unsigned long background_thresh;
657 unsigned long dirty_thresh;
659 for ( ; ; ) {
660 global_dirty_limits(&background_thresh, &dirty_thresh);
663 * Boost the allowable dirty threshold a bit for page
664 * allocators so they don't get DoS'ed by heavy writers
666 dirty_thresh += dirty_thresh / 10; /* wheeee... */
668 if (global_page_state(NR_UNSTABLE_NFS) +
669 global_page_state(NR_WRITEBACK) <= dirty_thresh)
670 break;
671 congestion_wait(BLK_RW_ASYNC, HZ/10);
674 * The caller might hold locks which can prevent IO completion
675 * or progress in the filesystem. So we cannot just sit here
676 * waiting for IO to complete.
678 if ((gfp_mask & (__GFP_FS|__GFP_IO)) != (__GFP_FS|__GFP_IO))
679 break;
684 * sysctl handler for /proc/sys/vm/dirty_writeback_centisecs
686 int dirty_writeback_centisecs_handler(ctl_table *table, int write,
687 void __user *buffer, size_t *length, loff_t *ppos)
689 proc_dointvec(table, write, buffer, length, ppos);
690 bdi_arm_supers_timer();
691 return 0;
694 #ifdef CONFIG_BLOCK
695 void laptop_mode_timer_fn(unsigned long data)
697 struct request_queue *q = (struct request_queue *)data;
698 int nr_pages = global_page_state(NR_FILE_DIRTY) +
699 global_page_state(NR_UNSTABLE_NFS);
702 * We want to write everything out, not just down to the dirty
703 * threshold
705 if (bdi_has_dirty_io(&q->backing_dev_info))
706 bdi_start_writeback(&q->backing_dev_info, nr_pages);
710 * We've spun up the disk and we're in laptop mode: schedule writeback
711 * of all dirty data a few seconds from now. If the flush is already scheduled
712 * then push it back - the user is still using the disk.
714 void laptop_io_completion(struct backing_dev_info *info)
716 mod_timer(&info->laptop_mode_wb_timer, jiffies + laptop_mode);
720 * We're in laptop mode and we've just synced. The sync's writes will have
721 * caused another writeback to be scheduled by laptop_io_completion.
722 * Nothing needs to be written back anymore, so we unschedule the writeback.
724 void laptop_sync_completion(void)
726 struct backing_dev_info *bdi;
728 rcu_read_lock();
730 list_for_each_entry_rcu(bdi, &bdi_list, bdi_list)
731 del_timer(&bdi->laptop_mode_wb_timer);
733 rcu_read_unlock();
735 #endif
738 * If ratelimit_pages is too high then we can get into dirty-data overload
739 * if a large number of processes all perform writes at the same time.
740 * If it is too low then SMP machines will call the (expensive)
741 * get_writeback_state too often.
743 * Here we set ratelimit_pages to a level which ensures that when all CPUs are
744 * dirtying in parallel, we cannot go more than 3% (1/32) over the dirty memory
745 * thresholds before writeback cuts in.
747 * But the limit should not be set too high. Because it also controls the
748 * amount of memory which the balance_dirty_pages() caller has to write back.
749 * If this is too large then the caller will block on the IO queue all the
750 * time. So limit it to four megabytes - the balance_dirty_pages() caller
751 * will write six megabyte chunks, max.
754 void writeback_set_ratelimit(void)
756 ratelimit_pages = vm_total_pages / (num_online_cpus() * 32);
757 if (ratelimit_pages < 16)
758 ratelimit_pages = 16;
759 if (ratelimit_pages * PAGE_CACHE_SIZE > 4096 * 1024)
760 ratelimit_pages = (4096 * 1024) / PAGE_CACHE_SIZE;
763 static int __cpuinit
764 ratelimit_handler(struct notifier_block *self, unsigned long u, void *v)
766 writeback_set_ratelimit();
767 return NOTIFY_DONE;
770 static struct notifier_block __cpuinitdata ratelimit_nb = {
771 .notifier_call = ratelimit_handler,
772 .next = NULL,
776 * Called early on to tune the page writeback dirty limits.
778 * We used to scale dirty pages according to how total memory
779 * related to pages that could be allocated for buffers (by
780 * comparing nr_free_buffer_pages() to vm_total_pages.
782 * However, that was when we used "dirty_ratio" to scale with
783 * all memory, and we don't do that any more. "dirty_ratio"
784 * is now applied to total non-HIGHPAGE memory (by subtracting
785 * totalhigh_pages from vm_total_pages), and as such we can't
786 * get into the old insane situation any more where we had
787 * large amounts of dirty pages compared to a small amount of
788 * non-HIGHMEM memory.
790 * But we might still want to scale the dirty_ratio by how
791 * much memory the box has..
793 void __init page_writeback_init(void)
795 int shift;
797 writeback_set_ratelimit();
798 register_cpu_notifier(&ratelimit_nb);
800 shift = calc_period_shift();
801 prop_descriptor_init(&vm_completions, shift);
802 prop_descriptor_init(&vm_dirties, shift);
806 * tag_pages_for_writeback - tag pages to be written by write_cache_pages
807 * @mapping: address space structure to write
808 * @start: starting page index
809 * @end: ending page index (inclusive)
811 * This function scans the page range from @start to @end (inclusive) and tags
812 * all pages that have DIRTY tag set with a special TOWRITE tag. The idea is
813 * that write_cache_pages (or whoever calls this function) will then use
814 * TOWRITE tag to identify pages eligible for writeback. This mechanism is
815 * used to avoid livelocking of writeback by a process steadily creating new
816 * dirty pages in the file (thus it is important for this function to be quick
817 * so that it can tag pages faster than a dirtying process can create them).
820 * We tag pages in batches of WRITEBACK_TAG_BATCH to reduce tree_lock latency.
822 void tag_pages_for_writeback(struct address_space *mapping,
823 pgoff_t start, pgoff_t end)
825 #define WRITEBACK_TAG_BATCH 4096
826 unsigned long tagged;
828 do {
829 spin_lock_irq(&mapping->tree_lock);
830 tagged = radix_tree_range_tag_if_tagged(&mapping->page_tree,
831 &start, end, WRITEBACK_TAG_BATCH,
832 PAGECACHE_TAG_DIRTY, PAGECACHE_TAG_TOWRITE);
833 spin_unlock_irq(&mapping->tree_lock);
834 WARN_ON_ONCE(tagged > WRITEBACK_TAG_BATCH);
835 cond_resched();
836 /* We check 'start' to handle wrapping when end == ~0UL */
837 } while (tagged >= WRITEBACK_TAG_BATCH && start);
839 EXPORT_SYMBOL(tag_pages_for_writeback);
842 * write_cache_pages - walk the list of dirty pages of the given address space and write all of them.
843 * @mapping: address space structure to write
844 * @wbc: subtract the number of written pages from *@wbc->nr_to_write
845 * @writepage: function called for each page
846 * @data: data passed to writepage function
848 * If a page is already under I/O, write_cache_pages() skips it, even
849 * if it's dirty. This is desirable behaviour for memory-cleaning writeback,
850 * but it is INCORRECT for data-integrity system calls such as fsync(). fsync()
851 * and msync() need to guarantee that all the data which was dirty at the time
852 * the call was made get new I/O started against them. If wbc->sync_mode is
853 * WB_SYNC_ALL then we were called for data integrity and we must wait for
854 * existing IO to complete.
856 * To avoid livelocks (when other process dirties new pages), we first tag
857 * pages which should be written back with TOWRITE tag and only then start
858 * writing them. For data-integrity sync we have to be careful so that we do
859 * not miss some pages (e.g., because some other process has cleared TOWRITE
860 * tag we set). The rule we follow is that TOWRITE tag can be cleared only
861 * by the process clearing the DIRTY tag (and submitting the page for IO).
863 int write_cache_pages(struct address_space *mapping,
864 struct writeback_control *wbc, writepage_t writepage,
865 void *data)
867 int ret = 0;
868 int done = 0;
869 struct pagevec pvec;
870 int nr_pages;
871 pgoff_t uninitialized_var(writeback_index);
872 pgoff_t index;
873 pgoff_t end; /* Inclusive */
874 pgoff_t done_index;
875 int cycled;
876 int range_whole = 0;
877 int tag;
879 pagevec_init(&pvec, 0);
880 if (wbc->range_cyclic) {
881 writeback_index = mapping->writeback_index; /* prev offset */
882 index = writeback_index;
883 if (index == 0)
884 cycled = 1;
885 else
886 cycled = 0;
887 end = -1;
888 } else {
889 index = wbc->range_start >> PAGE_CACHE_SHIFT;
890 end = wbc->range_end >> PAGE_CACHE_SHIFT;
891 if (wbc->range_start == 0 && wbc->range_end == LLONG_MAX)
892 range_whole = 1;
893 cycled = 1; /* ignore range_cyclic tests */
895 if (wbc->sync_mode == WB_SYNC_ALL)
896 tag = PAGECACHE_TAG_TOWRITE;
897 else
898 tag = PAGECACHE_TAG_DIRTY;
899 retry:
900 if (wbc->sync_mode == WB_SYNC_ALL)
901 tag_pages_for_writeback(mapping, index, end);
902 done_index = index;
903 while (!done && (index <= end)) {
904 int i;
906 nr_pages = pagevec_lookup_tag(&pvec, mapping, &index, tag,
907 min(end - index, (pgoff_t)PAGEVEC_SIZE-1) + 1);
908 if (nr_pages == 0)
909 break;
911 for (i = 0; i < nr_pages; i++) {
912 struct page *page = pvec.pages[i];
915 * At this point, the page may be truncated or
916 * invalidated (changing page->mapping to NULL), or
917 * even swizzled back from swapper_space to tmpfs file
918 * mapping. However, page->index will not change
919 * because we have a reference on the page.
921 if (page->index > end) {
923 * can't be range_cyclic (1st pass) because
924 * end == -1 in that case.
926 done = 1;
927 break;
930 done_index = page->index;
932 lock_page(page);
935 * Page truncated or invalidated. We can freely skip it
936 * then, even for data integrity operations: the page
937 * has disappeared concurrently, so there could be no
938 * real expectation of this data interity operation
939 * even if there is now a new, dirty page at the same
940 * pagecache address.
942 if (unlikely(page->mapping != mapping)) {
943 continue_unlock:
944 unlock_page(page);
945 continue;
948 if (!PageDirty(page)) {
949 /* someone wrote it for us */
950 goto continue_unlock;
953 if (PageWriteback(page)) {
954 if (wbc->sync_mode != WB_SYNC_NONE)
955 wait_on_page_writeback(page);
956 else
957 goto continue_unlock;
960 BUG_ON(PageWriteback(page));
961 if (!clear_page_dirty_for_io(page))
962 goto continue_unlock;
964 trace_wbc_writepage(wbc, mapping->backing_dev_info);
965 ret = (*writepage)(page, wbc, data);
966 if (unlikely(ret)) {
967 if (ret == AOP_WRITEPAGE_ACTIVATE) {
968 unlock_page(page);
969 ret = 0;
970 } else {
972 * done_index is set past this page,
973 * so media errors will not choke
974 * background writeout for the entire
975 * file. This has consequences for
976 * range_cyclic semantics (ie. it may
977 * not be suitable for data integrity
978 * writeout).
980 done_index = page->index + 1;
981 done = 1;
982 break;
987 * We stop writing back only if we are not doing
988 * integrity sync. In case of integrity sync we have to
989 * keep going until we have written all the pages
990 * we tagged for writeback prior to entering this loop.
992 if (--wbc->nr_to_write <= 0 &&
993 wbc->sync_mode == WB_SYNC_NONE) {
994 done = 1;
995 break;
998 pagevec_release(&pvec);
999 cond_resched();
1001 if (!cycled && !done) {
1003 * range_cyclic:
1004 * We hit the last page and there is more work to be done: wrap
1005 * back to the start of the file
1007 cycled = 1;
1008 index = 0;
1009 end = writeback_index - 1;
1010 goto retry;
1012 if (wbc->range_cyclic || (range_whole && wbc->nr_to_write > 0))
1013 mapping->writeback_index = done_index;
1015 return ret;
1017 EXPORT_SYMBOL(write_cache_pages);
1020 * Function used by generic_writepages to call the real writepage
1021 * function and set the mapping flags on error
1023 static int __writepage(struct page *page, struct writeback_control *wbc,
1024 void *data)
1026 struct address_space *mapping = data;
1027 int ret = mapping->a_ops->writepage(page, wbc);
1028 mapping_set_error(mapping, ret);
1029 return ret;
1033 * generic_writepages - walk the list of dirty pages of the given address space and writepage() all of them.
1034 * @mapping: address space structure to write
1035 * @wbc: subtract the number of written pages from *@wbc->nr_to_write
1037 * This is a library function, which implements the writepages()
1038 * address_space_operation.
1040 int generic_writepages(struct address_space *mapping,
1041 struct writeback_control *wbc)
1043 struct blk_plug plug;
1044 int ret;
1046 /* deal with chardevs and other special file */
1047 if (!mapping->a_ops->writepage)
1048 return 0;
1050 blk_start_plug(&plug);
1051 ret = write_cache_pages(mapping, wbc, __writepage, mapping);
1052 blk_finish_plug(&plug);
1053 return ret;
1056 EXPORT_SYMBOL(generic_writepages);
1058 int do_writepages(struct address_space *mapping, struct writeback_control *wbc)
1060 int ret;
1062 if (wbc->nr_to_write <= 0)
1063 return 0;
1064 if (mapping->a_ops->writepages)
1065 ret = mapping->a_ops->writepages(mapping, wbc);
1066 else
1067 ret = generic_writepages(mapping, wbc);
1068 return ret;
1072 * write_one_page - write out a single page and optionally wait on I/O
1073 * @page: the page to write
1074 * @wait: if true, wait on writeout
1076 * The page must be locked by the caller and will be unlocked upon return.
1078 * write_one_page() returns a negative error code if I/O failed.
1080 int write_one_page(struct page *page, int wait)
1082 struct address_space *mapping = page->mapping;
1083 int ret = 0;
1084 struct writeback_control wbc = {
1085 .sync_mode = WB_SYNC_ALL,
1086 .nr_to_write = 1,
1089 BUG_ON(!PageLocked(page));
1091 if (wait)
1092 wait_on_page_writeback(page);
1094 if (clear_page_dirty_for_io(page)) {
1095 page_cache_get(page);
1096 ret = mapping->a_ops->writepage(page, &wbc);
1097 if (ret == 0 && wait) {
1098 wait_on_page_writeback(page);
1099 if (PageError(page))
1100 ret = -EIO;
1102 page_cache_release(page);
1103 } else {
1104 unlock_page(page);
1106 return ret;
1108 EXPORT_SYMBOL(write_one_page);
1111 * For address_spaces which do not use buffers nor write back.
1113 int __set_page_dirty_no_writeback(struct page *page)
1115 if (!PageDirty(page))
1116 return !TestSetPageDirty(page);
1117 return 0;
1121 * Helper function for set_page_dirty family.
1122 * NOTE: This relies on being atomic wrt interrupts.
1124 void account_page_dirtied(struct page *page, struct address_space *mapping)
1126 if (mapping_cap_account_dirty(mapping)) {
1127 __inc_zone_page_state(page, NR_FILE_DIRTY);
1128 __inc_zone_page_state(page, NR_DIRTIED);
1129 __inc_bdi_stat(mapping->backing_dev_info, BDI_RECLAIMABLE);
1130 task_dirty_inc(current);
1131 task_io_account_write(PAGE_CACHE_SIZE);
1134 EXPORT_SYMBOL(account_page_dirtied);
1137 * Helper function for set_page_writeback family.
1138 * NOTE: Unlike account_page_dirtied this does not rely on being atomic
1139 * wrt interrupts.
1141 void account_page_writeback(struct page *page)
1143 inc_zone_page_state(page, NR_WRITEBACK);
1144 inc_zone_page_state(page, NR_WRITTEN);
1146 EXPORT_SYMBOL(account_page_writeback);
1149 * For address_spaces which do not use buffers. Just tag the page as dirty in
1150 * its radix tree.
1152 * This is also used when a single buffer is being dirtied: we want to set the
1153 * page dirty in that case, but not all the buffers. This is a "bottom-up"
1154 * dirtying, whereas __set_page_dirty_buffers() is a "top-down" dirtying.
1156 * Most callers have locked the page, which pins the address_space in memory.
1157 * But zap_pte_range() does not lock the page, however in that case the
1158 * mapping is pinned by the vma's ->vm_file reference.
1160 * We take care to handle the case where the page was truncated from the
1161 * mapping by re-checking page_mapping() inside tree_lock.
1163 int __set_page_dirty_nobuffers(struct page *page)
1165 if (!TestSetPageDirty(page)) {
1166 struct address_space *mapping = page_mapping(page);
1167 struct address_space *mapping2;
1169 if (!mapping)
1170 return 1;
1172 spin_lock_irq(&mapping->tree_lock);
1173 mapping2 = page_mapping(page);
1174 if (mapping2) { /* Race with truncate? */
1175 BUG_ON(mapping2 != mapping);
1176 WARN_ON_ONCE(!PagePrivate(page) && !PageUptodate(page));
1177 account_page_dirtied(page, mapping);
1178 radix_tree_tag_set(&mapping->page_tree,
1179 page_index(page), PAGECACHE_TAG_DIRTY);
1181 spin_unlock_irq(&mapping->tree_lock);
1182 if (mapping->host) {
1183 /* !PageAnon && !swapper_space */
1184 __mark_inode_dirty(mapping->host, I_DIRTY_PAGES);
1186 return 1;
1188 return 0;
1190 EXPORT_SYMBOL(__set_page_dirty_nobuffers);
1193 * When a writepage implementation decides that it doesn't want to write this
1194 * page for some reason, it should redirty the locked page via
1195 * redirty_page_for_writepage() and it should then unlock the page and return 0
1197 int redirty_page_for_writepage(struct writeback_control *wbc, struct page *page)
1199 wbc->pages_skipped++;
1200 return __set_page_dirty_nobuffers(page);
1202 EXPORT_SYMBOL(redirty_page_for_writepage);
1205 * Dirty a page.
1207 * For pages with a mapping this should be done under the page lock
1208 * for the benefit of asynchronous memory errors who prefer a consistent
1209 * dirty state. This rule can be broken in some special cases,
1210 * but should be better not to.
1212 * If the mapping doesn't provide a set_page_dirty a_op, then
1213 * just fall through and assume that it wants buffer_heads.
1215 int set_page_dirty(struct page *page)
1217 struct address_space *mapping = page_mapping(page);
1219 if (likely(mapping)) {
1220 int (*spd)(struct page *) = mapping->a_ops->set_page_dirty;
1222 * readahead/lru_deactivate_page could remain
1223 * PG_readahead/PG_reclaim due to race with end_page_writeback
1224 * About readahead, if the page is written, the flags would be
1225 * reset. So no problem.
1226 * About lru_deactivate_page, if the page is redirty, the flag
1227 * will be reset. So no problem. but if the page is used by readahead
1228 * it will confuse readahead and make it restart the size rampup
1229 * process. But it's a trivial problem.
1231 ClearPageReclaim(page);
1232 #ifdef CONFIG_BLOCK
1233 if (!spd)
1234 spd = __set_page_dirty_buffers;
1235 #endif
1236 return (*spd)(page);
1238 if (!PageDirty(page)) {
1239 if (!TestSetPageDirty(page))
1240 return 1;
1242 return 0;
1244 EXPORT_SYMBOL(set_page_dirty);
1247 * set_page_dirty() is racy if the caller has no reference against
1248 * page->mapping->host, and if the page is unlocked. This is because another
1249 * CPU could truncate the page off the mapping and then free the mapping.
1251 * Usually, the page _is_ locked, or the caller is a user-space process which
1252 * holds a reference on the inode by having an open file.
1254 * In other cases, the page should be locked before running set_page_dirty().
1256 int set_page_dirty_lock(struct page *page)
1258 int ret;
1260 lock_page(page);
1261 ret = set_page_dirty(page);
1262 unlock_page(page);
1263 return ret;
1265 EXPORT_SYMBOL(set_page_dirty_lock);
1268 * Clear a page's dirty flag, while caring for dirty memory accounting.
1269 * Returns true if the page was previously dirty.
1271 * This is for preparing to put the page under writeout. We leave the page
1272 * tagged as dirty in the radix tree so that a concurrent write-for-sync
1273 * can discover it via a PAGECACHE_TAG_DIRTY walk. The ->writepage
1274 * implementation will run either set_page_writeback() or set_page_dirty(),
1275 * at which stage we bring the page's dirty flag and radix-tree dirty tag
1276 * back into sync.
1278 * This incoherency between the page's dirty flag and radix-tree tag is
1279 * unfortunate, but it only exists while the page is locked.
1281 int clear_page_dirty_for_io(struct page *page)
1283 struct address_space *mapping = page_mapping(page);
1285 BUG_ON(!PageLocked(page));
1287 if (mapping && mapping_cap_account_dirty(mapping)) {
1289 * Yes, Virginia, this is indeed insane.
1291 * We use this sequence to make sure that
1292 * (a) we account for dirty stats properly
1293 * (b) we tell the low-level filesystem to
1294 * mark the whole page dirty if it was
1295 * dirty in a pagetable. Only to then
1296 * (c) clean the page again and return 1 to
1297 * cause the writeback.
1299 * This way we avoid all nasty races with the
1300 * dirty bit in multiple places and clearing
1301 * them concurrently from different threads.
1303 * Note! Normally the "set_page_dirty(page)"
1304 * has no effect on the actual dirty bit - since
1305 * that will already usually be set. But we
1306 * need the side effects, and it can help us
1307 * avoid races.
1309 * We basically use the page "master dirty bit"
1310 * as a serialization point for all the different
1311 * threads doing their things.
1313 if (page_mkclean(page))
1314 set_page_dirty(page);
1316 * We carefully synchronise fault handlers against
1317 * installing a dirty pte and marking the page dirty
1318 * at this point. We do this by having them hold the
1319 * page lock at some point after installing their
1320 * pte, but before marking the page dirty.
1321 * Pages are always locked coming in here, so we get
1322 * the desired exclusion. See mm/memory.c:do_wp_page()
1323 * for more comments.
1325 if (TestClearPageDirty(page)) {
1326 dec_zone_page_state(page, NR_FILE_DIRTY);
1327 dec_bdi_stat(mapping->backing_dev_info,
1328 BDI_RECLAIMABLE);
1329 return 1;
1331 return 0;
1333 return TestClearPageDirty(page);
1335 EXPORT_SYMBOL(clear_page_dirty_for_io);
1337 int test_clear_page_writeback(struct page *page)
1339 struct address_space *mapping = page_mapping(page);
1340 int ret;
1342 if (mapping) {
1343 struct backing_dev_info *bdi = mapping->backing_dev_info;
1344 unsigned long flags;
1346 spin_lock_irqsave(&mapping->tree_lock, flags);
1347 ret = TestClearPageWriteback(page);
1348 if (ret) {
1349 radix_tree_tag_clear(&mapping->page_tree,
1350 page_index(page),
1351 PAGECACHE_TAG_WRITEBACK);
1352 if (bdi_cap_account_writeback(bdi)) {
1353 __dec_bdi_stat(bdi, BDI_WRITEBACK);
1354 __bdi_writeout_inc(bdi);
1357 spin_unlock_irqrestore(&mapping->tree_lock, flags);
1358 } else {
1359 ret = TestClearPageWriteback(page);
1361 if (ret)
1362 dec_zone_page_state(page, NR_WRITEBACK);
1363 return ret;
1366 int test_set_page_writeback(struct page *page)
1368 struct address_space *mapping = page_mapping(page);
1369 int ret;
1371 if (mapping) {
1372 struct backing_dev_info *bdi = mapping->backing_dev_info;
1373 unsigned long flags;
1375 spin_lock_irqsave(&mapping->tree_lock, flags);
1376 ret = TestSetPageWriteback(page);
1377 if (!ret) {
1378 radix_tree_tag_set(&mapping->page_tree,
1379 page_index(page),
1380 PAGECACHE_TAG_WRITEBACK);
1381 if (bdi_cap_account_writeback(bdi))
1382 __inc_bdi_stat(bdi, BDI_WRITEBACK);
1384 if (!PageDirty(page))
1385 radix_tree_tag_clear(&mapping->page_tree,
1386 page_index(page),
1387 PAGECACHE_TAG_DIRTY);
1388 radix_tree_tag_clear(&mapping->page_tree,
1389 page_index(page),
1390 PAGECACHE_TAG_TOWRITE);
1391 spin_unlock_irqrestore(&mapping->tree_lock, flags);
1392 } else {
1393 ret = TestSetPageWriteback(page);
1395 if (!ret)
1396 account_page_writeback(page);
1397 return ret;
1400 EXPORT_SYMBOL(test_set_page_writeback);
1403 * Return true if any of the pages in the mapping are marked with the
1404 * passed tag.
1406 int mapping_tagged(struct address_space *mapping, int tag)
1408 int ret;
1409 rcu_read_lock();
1410 ret = radix_tree_tagged(&mapping->page_tree, tag);
1411 rcu_read_unlock();
1412 return ret;
1414 EXPORT_SYMBOL(mapping_tagged);