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Linus Torvalds1da177e2005-04-16 15:20:36 -07001/*
2 * mm/page-writeback.c.
3 *
4 * Copyright (C) 2002, Linus Torvalds.
5 *
6 * Contains functions related to writing back dirty pages at the
7 * address_space level.
8 *
9 * 10Apr2002 akpm@zip.com.au
10 * Initial version
11 */
12
13#include <linux/kernel.h>
14#include <linux/module.h>
15#include <linux/spinlock.h>
16#include <linux/fs.h>
17#include <linux/mm.h>
18#include <linux/swap.h>
19#include <linux/slab.h>
20#include <linux/pagemap.h>
21#include <linux/writeback.h>
22#include <linux/init.h>
23#include <linux/backing-dev.h>
24#include <linux/blkdev.h>
25#include <linux/mpage.h>
26#include <linux/percpu.h>
27#include <linux/notifier.h>
28#include <linux/smp.h>
29#include <linux/sysctl.h>
30#include <linux/cpu.h>
31#include <linux/syscalls.h>
32
33/*
34 * The maximum number of pages to writeout in a single bdflush/kupdate
35 * operation. We do this so we don't hold I_LOCK against an inode for
36 * enormous amounts of time, which would block a userspace task which has
37 * been forced to throttle against that inode. Also, the code reevaluates
38 * the dirty each time it has written this many pages.
39 */
40#define MAX_WRITEBACK_PAGES 1024
41
42/*
43 * After a CPU has dirtied this many pages, balance_dirty_pages_ratelimited
44 * will look to see if it needs to force writeback or throttling.
45 */
46static long ratelimit_pages = 32;
47
48static long total_pages; /* The total number of pages in the machine. */
49static int dirty_exceeded; /* Dirty mem may be over limit */
50
51/*
52 * When balance_dirty_pages decides that the caller needs to perform some
53 * non-background writeback, this is how many pages it will attempt to write.
54 * It should be somewhat larger than RATELIMIT_PAGES to ensure that reasonably
55 * large amounts of I/O are submitted.
56 */
57static inline long sync_writeback_pages(void)
58{
59 return ratelimit_pages + ratelimit_pages / 2;
60}
61
62/* The following parameters are exported via /proc/sys/vm */
63
64/*
65 * Start background writeback (via pdflush) at this percentage
66 */
67int dirty_background_ratio = 10;
68
69/*
70 * The generator of dirty data starts writeback at this percentage
71 */
72int vm_dirty_ratio = 40;
73
74/*
75 * The interval between `kupdate'-style writebacks, in centiseconds
76 * (hundredths of a second)
77 */
78int dirty_writeback_centisecs = 5 * 100;
79
80/*
81 * The longest number of centiseconds for which data is allowed to remain dirty
82 */
83int dirty_expire_centisecs = 30 * 100;
84
85/*
86 * Flag that makes the machine dump writes/reads and block dirtyings.
87 */
88int block_dump;
89
90/*
91 * Flag that puts the machine in "laptop mode".
92 */
93int laptop_mode;
94
95EXPORT_SYMBOL(laptop_mode);
96
97/* End of sysctl-exported parameters */
98
99
100static void background_writeout(unsigned long _min_pages);
101
102struct writeback_state
103{
104 unsigned long nr_dirty;
105 unsigned long nr_unstable;
106 unsigned long nr_mapped;
107 unsigned long nr_writeback;
108};
109
110static void get_writeback_state(struct writeback_state *wbs)
111{
112 wbs->nr_dirty = read_page_state(nr_dirty);
113 wbs->nr_unstable = read_page_state(nr_unstable);
114 wbs->nr_mapped = read_page_state(nr_mapped);
115 wbs->nr_writeback = read_page_state(nr_writeback);
116}
117
118/*
119 * Work out the current dirty-memory clamping and background writeout
120 * thresholds.
121 *
122 * The main aim here is to lower them aggressively if there is a lot of mapped
123 * memory around. To avoid stressing page reclaim with lots of unreclaimable
124 * pages. It is better to clamp down on writers than to start swapping, and
125 * performing lots of scanning.
126 *
127 * We only allow 1/2 of the currently-unmapped memory to be dirtied.
128 *
129 * We don't permit the clamping level to fall below 5% - that is getting rather
130 * excessive.
131 *
132 * We make sure that the background writeout level is below the adjusted
133 * clamping level.
134 */
135static void
136get_dirty_limits(struct writeback_state *wbs, long *pbackground, long *pdirty,
137 struct address_space *mapping)
138{
139 int background_ratio; /* Percentages */
140 int dirty_ratio;
141 int unmapped_ratio;
142 long background;
143 long dirty;
144 unsigned long available_memory = total_pages;
145 struct task_struct *tsk;
146
147 get_writeback_state(wbs);
148
149#ifdef CONFIG_HIGHMEM
150 /*
151 * If this mapping can only allocate from low memory,
152 * we exclude high memory from our count.
153 */
154 if (mapping && !(mapping_gfp_mask(mapping) & __GFP_HIGHMEM))
155 available_memory -= totalhigh_pages;
156#endif
157
158
159 unmapped_ratio = 100 - (wbs->nr_mapped * 100) / total_pages;
160
161 dirty_ratio = vm_dirty_ratio;
162 if (dirty_ratio > unmapped_ratio / 2)
163 dirty_ratio = unmapped_ratio / 2;
164
165 if (dirty_ratio < 5)
166 dirty_ratio = 5;
167
168 background_ratio = dirty_background_ratio;
169 if (background_ratio >= dirty_ratio)
170 background_ratio = dirty_ratio / 2;
171
172 background = (background_ratio * available_memory) / 100;
173 dirty = (dirty_ratio * available_memory) / 100;
174 tsk = current;
175 if (tsk->flags & PF_LESS_THROTTLE || rt_task(tsk)) {
176 background += background / 4;
177 dirty += dirty / 4;
178 }
179 *pbackground = background;
180 *pdirty = dirty;
181}
182
183/*
184 * balance_dirty_pages() must be called by processes which are generating dirty
185 * data. It looks at the number of dirty pages in the machine and will force
186 * the caller to perform writeback if the system is over `vm_dirty_ratio'.
187 * If we're over `background_thresh' then pdflush is woken to perform some
188 * writeout.
189 */
190static void balance_dirty_pages(struct address_space *mapping)
191{
192 struct writeback_state wbs;
193 long nr_reclaimable;
194 long background_thresh;
195 long dirty_thresh;
196 unsigned long pages_written = 0;
197 unsigned long write_chunk = sync_writeback_pages();
198
199 struct backing_dev_info *bdi = mapping->backing_dev_info;
200
201 for (;;) {
202 struct writeback_control wbc = {
203 .bdi = bdi,
204 .sync_mode = WB_SYNC_NONE,
205 .older_than_this = NULL,
206 .nr_to_write = write_chunk,
207 };
208
209 get_dirty_limits(&wbs, &background_thresh,
210 &dirty_thresh, mapping);
211 nr_reclaimable = wbs.nr_dirty + wbs.nr_unstable;
212 if (nr_reclaimable + wbs.nr_writeback <= dirty_thresh)
213 break;
214
215 dirty_exceeded = 1;
216
217 /* Note: nr_reclaimable denotes nr_dirty + nr_unstable.
218 * Unstable writes are a feature of certain networked
219 * filesystems (i.e. NFS) in which data may have been
220 * written to the server's write cache, but has not yet
221 * been flushed to permanent storage.
222 */
223 if (nr_reclaimable) {
224 writeback_inodes(&wbc);
225 get_dirty_limits(&wbs, &background_thresh,
226 &dirty_thresh, mapping);
227 nr_reclaimable = wbs.nr_dirty + wbs.nr_unstable;
228 if (nr_reclaimable + wbs.nr_writeback <= dirty_thresh)
229 break;
230 pages_written += write_chunk - wbc.nr_to_write;
231 if (pages_written >= write_chunk)
232 break; /* We've done our duty */
233 }
234 blk_congestion_wait(WRITE, HZ/10);
235 }
236
237 if (nr_reclaimable + wbs.nr_writeback <= dirty_thresh)
238 dirty_exceeded = 0;
239
240 if (writeback_in_progress(bdi))
241 return; /* pdflush is already working this queue */
242
243 /*
244 * In laptop mode, we wait until hitting the higher threshold before
245 * starting background writeout, and then write out all the way down
246 * to the lower threshold. So slow writers cause minimal disk activity.
247 *
248 * In normal mode, we start background writeout at the lower
249 * background_thresh, to keep the amount of dirty memory low.
250 */
251 if ((laptop_mode && pages_written) ||
252 (!laptop_mode && (nr_reclaimable > background_thresh)))
253 pdflush_operation(background_writeout, 0);
254}
255
256/**
257 * balance_dirty_pages_ratelimited - balance dirty memory state
Martin Waitz67be2dd2005-05-01 08:59:26 -0700258 * @mapping: address_space which was dirtied
Linus Torvalds1da177e2005-04-16 15:20:36 -0700259 *
260 * Processes which are dirtying memory should call in here once for each page
261 * which was newly dirtied. The function will periodically check the system's
262 * dirty state and will initiate writeback if needed.
263 *
264 * On really big machines, get_writeback_state is expensive, so try to avoid
265 * calling it too often (ratelimiting). But once we're over the dirty memory
266 * limit we decrease the ratelimiting by a lot, to prevent individual processes
267 * from overshooting the limit by (ratelimit_pages) each.
268 */
269void balance_dirty_pages_ratelimited(struct address_space *mapping)
270{
271 static DEFINE_PER_CPU(int, ratelimits) = 0;
272 long ratelimit;
273
274 ratelimit = ratelimit_pages;
275 if (dirty_exceeded)
276 ratelimit = 8;
277
278 /*
279 * Check the rate limiting. Also, we do not want to throttle real-time
280 * tasks in balance_dirty_pages(). Period.
281 */
282 if (get_cpu_var(ratelimits)++ >= ratelimit) {
283 __get_cpu_var(ratelimits) = 0;
284 put_cpu_var(ratelimits);
285 balance_dirty_pages(mapping);
286 return;
287 }
288 put_cpu_var(ratelimits);
289}
290EXPORT_SYMBOL(balance_dirty_pages_ratelimited);
291
292void throttle_vm_writeout(void)
293{
294 struct writeback_state wbs;
295 long background_thresh;
296 long dirty_thresh;
297
298 for ( ; ; ) {
299 get_dirty_limits(&wbs, &background_thresh, &dirty_thresh, NULL);
300
301 /*
302 * Boost the allowable dirty threshold a bit for page
303 * allocators so they don't get DoS'ed by heavy writers
304 */
305 dirty_thresh += dirty_thresh / 10; /* wheeee... */
306
307 if (wbs.nr_unstable + wbs.nr_writeback <= dirty_thresh)
308 break;
309 blk_congestion_wait(WRITE, HZ/10);
310 }
311}
312
313
314/*
315 * writeback at least _min_pages, and keep writing until the amount of dirty
316 * memory is less than the background threshold, or until we're all clean.
317 */
318static void background_writeout(unsigned long _min_pages)
319{
320 long min_pages = _min_pages;
321 struct writeback_control wbc = {
322 .bdi = NULL,
323 .sync_mode = WB_SYNC_NONE,
324 .older_than_this = NULL,
325 .nr_to_write = 0,
326 .nonblocking = 1,
327 };
328
329 for ( ; ; ) {
330 struct writeback_state wbs;
331 long background_thresh;
332 long dirty_thresh;
333
334 get_dirty_limits(&wbs, &background_thresh, &dirty_thresh, NULL);
335 if (wbs.nr_dirty + wbs.nr_unstable < background_thresh
336 && min_pages <= 0)
337 break;
338 wbc.encountered_congestion = 0;
339 wbc.nr_to_write = MAX_WRITEBACK_PAGES;
340 wbc.pages_skipped = 0;
341 writeback_inodes(&wbc);
342 min_pages -= MAX_WRITEBACK_PAGES - wbc.nr_to_write;
343 if (wbc.nr_to_write > 0 || wbc.pages_skipped > 0) {
344 /* Wrote less than expected */
345 blk_congestion_wait(WRITE, HZ/10);
346 if (!wbc.encountered_congestion)
347 break;
348 }
349 }
350}
351
352/*
353 * Start writeback of `nr_pages' pages. If `nr_pages' is zero, write back
354 * the whole world. Returns 0 if a pdflush thread was dispatched. Returns
355 * -1 if all pdflush threads were busy.
356 */
Pekka J Enberg687a21c2005-06-28 20:44:55 -0700357int wakeup_pdflush(long nr_pages)
Linus Torvalds1da177e2005-04-16 15:20:36 -0700358{
359 if (nr_pages == 0) {
360 struct writeback_state wbs;
361
362 get_writeback_state(&wbs);
363 nr_pages = wbs.nr_dirty + wbs.nr_unstable;
364 }
365 return pdflush_operation(background_writeout, nr_pages);
366}
367
368static void wb_timer_fn(unsigned long unused);
369static void laptop_timer_fn(unsigned long unused);
370
Ingo Molnar8d06afa2005-09-09 13:10:40 -0700371static DEFINE_TIMER(wb_timer, wb_timer_fn, 0, 0);
372static DEFINE_TIMER(laptop_mode_wb_timer, laptop_timer_fn, 0, 0);
Linus Torvalds1da177e2005-04-16 15:20:36 -0700373
374/*
375 * Periodic writeback of "old" data.
376 *
377 * Define "old": the first time one of an inode's pages is dirtied, we mark the
378 * dirtying-time in the inode's address_space. So this periodic writeback code
379 * just walks the superblock inode list, writing back any inodes which are
380 * older than a specific point in time.
381 *
382 * Try to run once per dirty_writeback_centisecs. But if a writeback event
383 * takes longer than a dirty_writeback_centisecs interval, then leave a
384 * one-second gap.
385 *
386 * older_than_this takes precedence over nr_to_write. So we'll only write back
387 * all dirty pages if they are all attached to "old" mappings.
388 */
389static void wb_kupdate(unsigned long arg)
390{
391 unsigned long oldest_jif;
392 unsigned long start_jif;
393 unsigned long next_jif;
394 long nr_to_write;
395 struct writeback_state wbs;
396 struct writeback_control wbc = {
397 .bdi = NULL,
398 .sync_mode = WB_SYNC_NONE,
399 .older_than_this = &oldest_jif,
400 .nr_to_write = 0,
401 .nonblocking = 1,
402 .for_kupdate = 1,
403 };
404
405 sync_supers();
406
407 get_writeback_state(&wbs);
408 oldest_jif = jiffies - (dirty_expire_centisecs * HZ) / 100;
409 start_jif = jiffies;
410 next_jif = start_jif + (dirty_writeback_centisecs * HZ) / 100;
411 nr_to_write = wbs.nr_dirty + wbs.nr_unstable +
412 (inodes_stat.nr_inodes - inodes_stat.nr_unused);
413 while (nr_to_write > 0) {
414 wbc.encountered_congestion = 0;
415 wbc.nr_to_write = MAX_WRITEBACK_PAGES;
416 writeback_inodes(&wbc);
417 if (wbc.nr_to_write > 0) {
418 if (wbc.encountered_congestion)
419 blk_congestion_wait(WRITE, HZ/10);
420 else
421 break; /* All the old data is written */
422 }
423 nr_to_write -= MAX_WRITEBACK_PAGES - wbc.nr_to_write;
424 }
425 if (time_before(next_jif, jiffies + HZ))
426 next_jif = jiffies + HZ;
427 if (dirty_writeback_centisecs)
428 mod_timer(&wb_timer, next_jif);
429}
430
431/*
432 * sysctl handler for /proc/sys/vm/dirty_writeback_centisecs
433 */
434int dirty_writeback_centisecs_handler(ctl_table *table, int write,
435 struct file *file, void __user *buffer, size_t *length, loff_t *ppos)
436{
437 proc_dointvec(table, write, file, buffer, length, ppos);
438 if (dirty_writeback_centisecs) {
439 mod_timer(&wb_timer,
440 jiffies + (dirty_writeback_centisecs * HZ) / 100);
441 } else {
442 del_timer(&wb_timer);
443 }
444 return 0;
445}
446
447static void wb_timer_fn(unsigned long unused)
448{
449 if (pdflush_operation(wb_kupdate, 0) < 0)
450 mod_timer(&wb_timer, jiffies + HZ); /* delay 1 second */
451}
452
453static void laptop_flush(unsigned long unused)
454{
455 sys_sync();
456}
457
458static void laptop_timer_fn(unsigned long unused)
459{
460 pdflush_operation(laptop_flush, 0);
461}
462
463/*
464 * We've spun up the disk and we're in laptop mode: schedule writeback
465 * of all dirty data a few seconds from now. If the flush is already scheduled
466 * then push it back - the user is still using the disk.
467 */
468void laptop_io_completion(void)
469{
470 mod_timer(&laptop_mode_wb_timer, jiffies + laptop_mode * HZ);
471}
472
473/*
474 * We're in laptop mode and we've just synced. The sync's writes will have
475 * caused another writeback to be scheduled by laptop_io_completion.
476 * Nothing needs to be written back anymore, so we unschedule the writeback.
477 */
478void laptop_sync_completion(void)
479{
480 del_timer(&laptop_mode_wb_timer);
481}
482
483/*
484 * If ratelimit_pages is too high then we can get into dirty-data overload
485 * if a large number of processes all perform writes at the same time.
486 * If it is too low then SMP machines will call the (expensive)
487 * get_writeback_state too often.
488 *
489 * Here we set ratelimit_pages to a level which ensures that when all CPUs are
490 * dirtying in parallel, we cannot go more than 3% (1/32) over the dirty memory
491 * thresholds before writeback cuts in.
492 *
493 * But the limit should not be set too high. Because it also controls the
494 * amount of memory which the balance_dirty_pages() caller has to write back.
495 * If this is too large then the caller will block on the IO queue all the
496 * time. So limit it to four megabytes - the balance_dirty_pages() caller
497 * will write six megabyte chunks, max.
498 */
499
500static void set_ratelimit(void)
501{
502 ratelimit_pages = total_pages / (num_online_cpus() * 32);
503 if (ratelimit_pages < 16)
504 ratelimit_pages = 16;
505 if (ratelimit_pages * PAGE_CACHE_SIZE > 4096 * 1024)
506 ratelimit_pages = (4096 * 1024) / PAGE_CACHE_SIZE;
507}
508
509static int
510ratelimit_handler(struct notifier_block *self, unsigned long u, void *v)
511{
512 set_ratelimit();
513 return 0;
514}
515
516static struct notifier_block ratelimit_nb = {
517 .notifier_call = ratelimit_handler,
518 .next = NULL,
519};
520
521/*
522 * If the machine has a large highmem:lowmem ratio then scale back the default
523 * dirty memory thresholds: allowing too much dirty highmem pins an excessive
524 * number of buffer_heads.
525 */
526void __init page_writeback_init(void)
527{
528 long buffer_pages = nr_free_buffer_pages();
529 long correction;
530
531 total_pages = nr_free_pagecache_pages();
532
533 correction = (100 * 4 * buffer_pages) / total_pages;
534
535 if (correction < 100) {
536 dirty_background_ratio *= correction;
537 dirty_background_ratio /= 100;
538 vm_dirty_ratio *= correction;
539 vm_dirty_ratio /= 100;
540
541 if (dirty_background_ratio <= 0)
542 dirty_background_ratio = 1;
543 if (vm_dirty_ratio <= 0)
544 vm_dirty_ratio = 1;
545 }
546 mod_timer(&wb_timer, jiffies + (dirty_writeback_centisecs * HZ) / 100);
547 set_ratelimit();
548 register_cpu_notifier(&ratelimit_nb);
549}
550
551int do_writepages(struct address_space *mapping, struct writeback_control *wbc)
552{
553 if (wbc->nr_to_write <= 0)
554 return 0;
555 if (mapping->a_ops->writepages)
556 return mapping->a_ops->writepages(mapping, wbc);
557 return generic_writepages(mapping, wbc);
558}
559
560/**
561 * write_one_page - write out a single page and optionally wait on I/O
562 *
Martin Waitz67be2dd2005-05-01 08:59:26 -0700563 * @page: the page to write
564 * @wait: if true, wait on writeout
Linus Torvalds1da177e2005-04-16 15:20:36 -0700565 *
566 * The page must be locked by the caller and will be unlocked upon return.
567 *
568 * write_one_page() returns a negative error code if I/O failed.
569 */
570int write_one_page(struct page *page, int wait)
571{
572 struct address_space *mapping = page->mapping;
573 int ret = 0;
574 struct writeback_control wbc = {
575 .sync_mode = WB_SYNC_ALL,
576 .nr_to_write = 1,
577 };
578
579 BUG_ON(!PageLocked(page));
580
581 if (wait)
582 wait_on_page_writeback(page);
583
584 if (clear_page_dirty_for_io(page)) {
585 page_cache_get(page);
586 ret = mapping->a_ops->writepage(page, &wbc);
587 if (ret == 0 && wait) {
588 wait_on_page_writeback(page);
589 if (PageError(page))
590 ret = -EIO;
591 }
592 page_cache_release(page);
593 } else {
594 unlock_page(page);
595 }
596 return ret;
597}
598EXPORT_SYMBOL(write_one_page);
599
600/*
601 * For address_spaces which do not use buffers. Just tag the page as dirty in
602 * its radix tree.
603 *
604 * This is also used when a single buffer is being dirtied: we want to set the
605 * page dirty in that case, but not all the buffers. This is a "bottom-up"
606 * dirtying, whereas __set_page_dirty_buffers() is a "top-down" dirtying.
607 *
608 * Most callers have locked the page, which pins the address_space in memory.
609 * But zap_pte_range() does not lock the page, however in that case the
610 * mapping is pinned by the vma's ->vm_file reference.
611 *
612 * We take care to handle the case where the page was truncated from the
613 * mapping by re-checking page_mapping() insode tree_lock.
614 */
615int __set_page_dirty_nobuffers(struct page *page)
616{
617 int ret = 0;
618
619 if (!TestSetPageDirty(page)) {
620 struct address_space *mapping = page_mapping(page);
621 struct address_space *mapping2;
622
623 if (mapping) {
624 write_lock_irq(&mapping->tree_lock);
625 mapping2 = page_mapping(page);
626 if (mapping2) { /* Race with truncate? */
627 BUG_ON(mapping2 != mapping);
628 if (mapping_cap_account_dirty(mapping))
629 inc_page_state(nr_dirty);
630 radix_tree_tag_set(&mapping->page_tree,
631 page_index(page), PAGECACHE_TAG_DIRTY);
632 }
633 write_unlock_irq(&mapping->tree_lock);
634 if (mapping->host) {
635 /* !PageAnon && !swapper_space */
636 __mark_inode_dirty(mapping->host,
637 I_DIRTY_PAGES);
638 }
639 }
640 }
641 return ret;
642}
643EXPORT_SYMBOL(__set_page_dirty_nobuffers);
644
645/*
646 * When a writepage implementation decides that it doesn't want to write this
647 * page for some reason, it should redirty the locked page via
648 * redirty_page_for_writepage() and it should then unlock the page and return 0
649 */
650int redirty_page_for_writepage(struct writeback_control *wbc, struct page *page)
651{
652 wbc->pages_skipped++;
653 return __set_page_dirty_nobuffers(page);
654}
655EXPORT_SYMBOL(redirty_page_for_writepage);
656
657/*
658 * If the mapping doesn't provide a set_page_dirty a_op, then
659 * just fall through and assume that it wants buffer_heads.
660 */
661int fastcall set_page_dirty(struct page *page)
662{
663 struct address_space *mapping = page_mapping(page);
664
665 if (likely(mapping)) {
666 int (*spd)(struct page *) = mapping->a_ops->set_page_dirty;
667 if (spd)
668 return (*spd)(page);
669 return __set_page_dirty_buffers(page);
670 }
671 if (!PageDirty(page))
672 SetPageDirty(page);
673 return 0;
674}
675EXPORT_SYMBOL(set_page_dirty);
676
677/*
678 * set_page_dirty() is racy if the caller has no reference against
679 * page->mapping->host, and if the page is unlocked. This is because another
680 * CPU could truncate the page off the mapping and then free the mapping.
681 *
682 * Usually, the page _is_ locked, or the caller is a user-space process which
683 * holds a reference on the inode by having an open file.
684 *
685 * In other cases, the page should be locked before running set_page_dirty().
686 */
687int set_page_dirty_lock(struct page *page)
688{
689 int ret;
690
691 lock_page(page);
692 ret = set_page_dirty(page);
693 unlock_page(page);
694 return ret;
695}
696EXPORT_SYMBOL(set_page_dirty_lock);
697
698/*
699 * Clear a page's dirty flag, while caring for dirty memory accounting.
700 * Returns true if the page was previously dirty.
701 */
702int test_clear_page_dirty(struct page *page)
703{
704 struct address_space *mapping = page_mapping(page);
705 unsigned long flags;
706
707 if (mapping) {
708 write_lock_irqsave(&mapping->tree_lock, flags);
709 if (TestClearPageDirty(page)) {
710 radix_tree_tag_clear(&mapping->page_tree,
711 page_index(page),
712 PAGECACHE_TAG_DIRTY);
713 write_unlock_irqrestore(&mapping->tree_lock, flags);
714 if (mapping_cap_account_dirty(mapping))
715 dec_page_state(nr_dirty);
716 return 1;
717 }
718 write_unlock_irqrestore(&mapping->tree_lock, flags);
719 return 0;
720 }
721 return TestClearPageDirty(page);
722}
723EXPORT_SYMBOL(test_clear_page_dirty);
724
725/*
726 * Clear a page's dirty flag, while caring for dirty memory accounting.
727 * Returns true if the page was previously dirty.
728 *
729 * This is for preparing to put the page under writeout. We leave the page
730 * tagged as dirty in the radix tree so that a concurrent write-for-sync
731 * can discover it via a PAGECACHE_TAG_DIRTY walk. The ->writepage
732 * implementation will run either set_page_writeback() or set_page_dirty(),
733 * at which stage we bring the page's dirty flag and radix-tree dirty tag
734 * back into sync.
735 *
736 * This incoherency between the page's dirty flag and radix-tree tag is
737 * unfortunate, but it only exists while the page is locked.
738 */
739int clear_page_dirty_for_io(struct page *page)
740{
741 struct address_space *mapping = page_mapping(page);
742
743 if (mapping) {
744 if (TestClearPageDirty(page)) {
745 if (mapping_cap_account_dirty(mapping))
746 dec_page_state(nr_dirty);
747 return 1;
748 }
749 return 0;
750 }
751 return TestClearPageDirty(page);
752}
Hans Reiser58bb01a2005-11-18 01:10:53 -0800753EXPORT_SYMBOL(clear_page_dirty_for_io);
Linus Torvalds1da177e2005-04-16 15:20:36 -0700754
755int test_clear_page_writeback(struct page *page)
756{
757 struct address_space *mapping = page_mapping(page);
758 int ret;
759
760 if (mapping) {
761 unsigned long flags;
762
763 write_lock_irqsave(&mapping->tree_lock, flags);
764 ret = TestClearPageWriteback(page);
765 if (ret)
766 radix_tree_tag_clear(&mapping->page_tree,
767 page_index(page),
768 PAGECACHE_TAG_WRITEBACK);
769 write_unlock_irqrestore(&mapping->tree_lock, flags);
770 } else {
771 ret = TestClearPageWriteback(page);
772 }
773 return ret;
774}
775
776int test_set_page_writeback(struct page *page)
777{
778 struct address_space *mapping = page_mapping(page);
779 int ret;
780
781 if (mapping) {
782 unsigned long flags;
783
784 write_lock_irqsave(&mapping->tree_lock, flags);
785 ret = TestSetPageWriteback(page);
786 if (!ret)
787 radix_tree_tag_set(&mapping->page_tree,
788 page_index(page),
789 PAGECACHE_TAG_WRITEBACK);
790 if (!PageDirty(page))
791 radix_tree_tag_clear(&mapping->page_tree,
792 page_index(page),
793 PAGECACHE_TAG_DIRTY);
794 write_unlock_irqrestore(&mapping->tree_lock, flags);
795 } else {
796 ret = TestSetPageWriteback(page);
797 }
798 return ret;
799
800}
801EXPORT_SYMBOL(test_set_page_writeback);
802
803/*
804 * Return true if any of the pages in the mapping are marged with the
805 * passed tag.
806 */
807int mapping_tagged(struct address_space *mapping, int tag)
808{
809 unsigned long flags;
810 int ret;
811
812 read_lock_irqsave(&mapping->tree_lock, flags);
813 ret = radix_tree_tagged(&mapping->page_tree, tag);
814 read_unlock_irqrestore(&mapping->tree_lock, flags);
815 return ret;
816}
817EXPORT_SYMBOL(mapping_tagged);