[PATCH] rename wakeup_bdflush to wakeup_pdflush
[linux-2.6.git] / mm / page-writeback.c
1 /*
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  */
46 static long ratelimit_pages = 32;
47
48 static long total_pages;        /* The total number of pages in the machine. */
49 static 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  */
57 static 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  */
67 int dirty_background_ratio = 10;
68
69 /*
70  * The generator of dirty data starts writeback at this percentage
71  */
72 int vm_dirty_ratio = 40;
73
74 /*
75  * The interval between `kupdate'-style writebacks, in centiseconds
76  * (hundredths of a second)
77  */
78 int dirty_writeback_centisecs = 5 * 100;
79
80 /*
81  * The longest number of centiseconds for which data is allowed to remain dirty
82  */
83 int dirty_expire_centisecs = 30 * 100;
84
85 /*
86  * Flag that makes the machine dump writes/reads and block dirtyings.
87  */
88 int block_dump;
89
90 /*
91  * Flag that puts the machine in "laptop mode".
92  */
93 int laptop_mode;
94
95 EXPORT_SYMBOL(laptop_mode);
96
97 /* End of sysctl-exported parameters */
98
99
100 static void background_writeout(unsigned long _min_pages);
101
102 struct 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
110 static 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  */
135 static void
136 get_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  */
190 static 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
258  * @mapping: address_space which was dirtied
259  *
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  */
269 void 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 }
290 EXPORT_SYMBOL(balance_dirty_pages_ratelimited);
291
292 void 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  */
318 static 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  */
357 int wakeup_pdflush(long nr_pages)
358 {
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
368 static void wb_timer_fn(unsigned long unused);
369 static void laptop_timer_fn(unsigned long unused);
370
371 static struct timer_list wb_timer =
372                         TIMER_INITIALIZER(wb_timer_fn, 0, 0);
373 static struct timer_list laptop_mode_wb_timer =
374                         TIMER_INITIALIZER(laptop_timer_fn, 0, 0);
375
376 /*
377  * Periodic writeback of "old" data.
378  *
379  * Define "old": the first time one of an inode's pages is dirtied, we mark the
380  * dirtying-time in the inode's address_space.  So this periodic writeback code
381  * just walks the superblock inode list, writing back any inodes which are
382  * older than a specific point in time.
383  *
384  * Try to run once per dirty_writeback_centisecs.  But if a writeback event
385  * takes longer than a dirty_writeback_centisecs interval, then leave a
386  * one-second gap.
387  *
388  * older_than_this takes precedence over nr_to_write.  So we'll only write back
389  * all dirty pages if they are all attached to "old" mappings.
390  */
391 static void wb_kupdate(unsigned long arg)
392 {
393         unsigned long oldest_jif;
394         unsigned long start_jif;
395         unsigned long next_jif;
396         long nr_to_write;
397         struct writeback_state wbs;
398         struct writeback_control wbc = {
399                 .bdi            = NULL,
400                 .sync_mode      = WB_SYNC_NONE,
401                 .older_than_this = &oldest_jif,
402                 .nr_to_write    = 0,
403                 .nonblocking    = 1,
404                 .for_kupdate    = 1,
405         };
406
407         sync_supers();
408
409         get_writeback_state(&wbs);
410         oldest_jif = jiffies - (dirty_expire_centisecs * HZ) / 100;
411         start_jif = jiffies;
412         next_jif = start_jif + (dirty_writeback_centisecs * HZ) / 100;
413         nr_to_write = wbs.nr_dirty + wbs.nr_unstable +
414                         (inodes_stat.nr_inodes - inodes_stat.nr_unused);
415         while (nr_to_write > 0) {
416                 wbc.encountered_congestion = 0;
417                 wbc.nr_to_write = MAX_WRITEBACK_PAGES;
418                 writeback_inodes(&wbc);
419                 if (wbc.nr_to_write > 0) {
420                         if (wbc.encountered_congestion)
421                                 blk_congestion_wait(WRITE, HZ/10);
422                         else
423                                 break;  /* All the old data is written */
424                 }
425                 nr_to_write -= MAX_WRITEBACK_PAGES - wbc.nr_to_write;
426         }
427         if (time_before(next_jif, jiffies + HZ))
428                 next_jif = jiffies + HZ;
429         if (dirty_writeback_centisecs)
430                 mod_timer(&wb_timer, next_jif);
431 }
432
433 /*
434  * sysctl handler for /proc/sys/vm/dirty_writeback_centisecs
435  */
436 int dirty_writeback_centisecs_handler(ctl_table *table, int write,
437                 struct file *file, void __user *buffer, size_t *length, loff_t *ppos)
438 {
439         proc_dointvec(table, write, file, buffer, length, ppos);
440         if (dirty_writeback_centisecs) {
441                 mod_timer(&wb_timer,
442                         jiffies + (dirty_writeback_centisecs * HZ) / 100);
443         } else {
444                 del_timer(&wb_timer);
445         }
446         return 0;
447 }
448
449 static void wb_timer_fn(unsigned long unused)
450 {
451         if (pdflush_operation(wb_kupdate, 0) < 0)
452                 mod_timer(&wb_timer, jiffies + HZ); /* delay 1 second */
453 }
454
455 static void laptop_flush(unsigned long unused)
456 {
457         sys_sync();
458 }
459
460 static void laptop_timer_fn(unsigned long unused)
461 {
462         pdflush_operation(laptop_flush, 0);
463 }
464
465 /*
466  * We've spun up the disk and we're in laptop mode: schedule writeback
467  * of all dirty data a few seconds from now.  If the flush is already scheduled
468  * then push it back - the user is still using the disk.
469  */
470 void laptop_io_completion(void)
471 {
472         mod_timer(&laptop_mode_wb_timer, jiffies + laptop_mode * HZ);
473 }
474
475 /*
476  * We're in laptop mode and we've just synced. The sync's writes will have
477  * caused another writeback to be scheduled by laptop_io_completion.
478  * Nothing needs to be written back anymore, so we unschedule the writeback.
479  */
480 void laptop_sync_completion(void)
481 {
482         del_timer(&laptop_mode_wb_timer);
483 }
484
485 /*
486  * If ratelimit_pages is too high then we can get into dirty-data overload
487  * if a large number of processes all perform writes at the same time.
488  * If it is too low then SMP machines will call the (expensive)
489  * get_writeback_state too often.
490  *
491  * Here we set ratelimit_pages to a level which ensures that when all CPUs are
492  * dirtying in parallel, we cannot go more than 3% (1/32) over the dirty memory
493  * thresholds before writeback cuts in.
494  *
495  * But the limit should not be set too high.  Because it also controls the
496  * amount of memory which the balance_dirty_pages() caller has to write back.
497  * If this is too large then the caller will block on the IO queue all the
498  * time.  So limit it to four megabytes - the balance_dirty_pages() caller
499  * will write six megabyte chunks, max.
500  */
501
502 static void set_ratelimit(void)
503 {
504         ratelimit_pages = total_pages / (num_online_cpus() * 32);
505         if (ratelimit_pages < 16)
506                 ratelimit_pages = 16;
507         if (ratelimit_pages * PAGE_CACHE_SIZE > 4096 * 1024)
508                 ratelimit_pages = (4096 * 1024) / PAGE_CACHE_SIZE;
509 }
510
511 static int
512 ratelimit_handler(struct notifier_block *self, unsigned long u, void *v)
513 {
514         set_ratelimit();
515         return 0;
516 }
517
518 static struct notifier_block ratelimit_nb = {
519         .notifier_call  = ratelimit_handler,
520         .next           = NULL,
521 };
522
523 /*
524  * If the machine has a large highmem:lowmem ratio then scale back the default
525  * dirty memory thresholds: allowing too much dirty highmem pins an excessive
526  * number of buffer_heads.
527  */
528 void __init page_writeback_init(void)
529 {
530         long buffer_pages = nr_free_buffer_pages();
531         long correction;
532
533         total_pages = nr_free_pagecache_pages();
534
535         correction = (100 * 4 * buffer_pages) / total_pages;
536
537         if (correction < 100) {
538                 dirty_background_ratio *= correction;
539                 dirty_background_ratio /= 100;
540                 vm_dirty_ratio *= correction;
541                 vm_dirty_ratio /= 100;
542
543                 if (dirty_background_ratio <= 0)
544                         dirty_background_ratio = 1;
545                 if (vm_dirty_ratio <= 0)
546                         vm_dirty_ratio = 1;
547         }
548         mod_timer(&wb_timer, jiffies + (dirty_writeback_centisecs * HZ) / 100);
549         set_ratelimit();
550         register_cpu_notifier(&ratelimit_nb);
551 }
552
553 int do_writepages(struct address_space *mapping, struct writeback_control *wbc)
554 {
555         if (wbc->nr_to_write <= 0)
556                 return 0;
557         if (mapping->a_ops->writepages)
558                 return mapping->a_ops->writepages(mapping, wbc);
559         return generic_writepages(mapping, wbc);
560 }
561
562 /**
563  * write_one_page - write out a single page and optionally wait on I/O
564  *
565  * @page: the page to write
566  * @wait: if true, wait on writeout
567  *
568  * The page must be locked by the caller and will be unlocked upon return.
569  *
570  * write_one_page() returns a negative error code if I/O failed.
571  */
572 int write_one_page(struct page *page, int wait)
573 {
574         struct address_space *mapping = page->mapping;
575         int ret = 0;
576         struct writeback_control wbc = {
577                 .sync_mode = WB_SYNC_ALL,
578                 .nr_to_write = 1,
579         };
580
581         BUG_ON(!PageLocked(page));
582
583         if (wait)
584                 wait_on_page_writeback(page);
585
586         if (clear_page_dirty_for_io(page)) {
587                 page_cache_get(page);
588                 ret = mapping->a_ops->writepage(page, &wbc);
589                 if (ret == 0 && wait) {
590                         wait_on_page_writeback(page);
591                         if (PageError(page))
592                                 ret = -EIO;
593                 }
594                 page_cache_release(page);
595         } else {
596                 unlock_page(page);
597         }
598         return ret;
599 }
600 EXPORT_SYMBOL(write_one_page);
601
602 /*
603  * For address_spaces which do not use buffers.  Just tag the page as dirty in
604  * its radix tree.
605  *
606  * This is also used when a single buffer is being dirtied: we want to set the
607  * page dirty in that case, but not all the buffers.  This is a "bottom-up"
608  * dirtying, whereas __set_page_dirty_buffers() is a "top-down" dirtying.
609  *
610  * Most callers have locked the page, which pins the address_space in memory.
611  * But zap_pte_range() does not lock the page, however in that case the
612  * mapping is pinned by the vma's ->vm_file reference.
613  *
614  * We take care to handle the case where the page was truncated from the
615  * mapping by re-checking page_mapping() insode tree_lock.
616  */
617 int __set_page_dirty_nobuffers(struct page *page)
618 {
619         int ret = 0;
620
621         if (!TestSetPageDirty(page)) {
622                 struct address_space *mapping = page_mapping(page);
623                 struct address_space *mapping2;
624
625                 if (mapping) {
626                         write_lock_irq(&mapping->tree_lock);
627                         mapping2 = page_mapping(page);
628                         if (mapping2) { /* Race with truncate? */
629                                 BUG_ON(mapping2 != mapping);
630                                 if (mapping_cap_account_dirty(mapping))
631                                         inc_page_state(nr_dirty);
632                                 radix_tree_tag_set(&mapping->page_tree,
633                                         page_index(page), PAGECACHE_TAG_DIRTY);
634                         }
635                         write_unlock_irq(&mapping->tree_lock);
636                         if (mapping->host) {
637                                 /* !PageAnon && !swapper_space */
638                                 __mark_inode_dirty(mapping->host,
639                                                         I_DIRTY_PAGES);
640                         }
641                 }
642         }
643         return ret;
644 }
645 EXPORT_SYMBOL(__set_page_dirty_nobuffers);
646
647 /*
648  * When a writepage implementation decides that it doesn't want to write this
649  * page for some reason, it should redirty the locked page via
650  * redirty_page_for_writepage() and it should then unlock the page and return 0
651  */
652 int redirty_page_for_writepage(struct writeback_control *wbc, struct page *page)
653 {
654         wbc->pages_skipped++;
655         return __set_page_dirty_nobuffers(page);
656 }
657 EXPORT_SYMBOL(redirty_page_for_writepage);
658
659 /*
660  * If the mapping doesn't provide a set_page_dirty a_op, then
661  * just fall through and assume that it wants buffer_heads.
662  */
663 int fastcall set_page_dirty(struct page *page)
664 {
665         struct address_space *mapping = page_mapping(page);
666
667         if (likely(mapping)) {
668                 int (*spd)(struct page *) = mapping->a_ops->set_page_dirty;
669                 if (spd)
670                         return (*spd)(page);
671                 return __set_page_dirty_buffers(page);
672         }
673         if (!PageDirty(page))
674                 SetPageDirty(page);
675         return 0;
676 }
677 EXPORT_SYMBOL(set_page_dirty);
678
679 /*
680  * set_page_dirty() is racy if the caller has no reference against
681  * page->mapping->host, and if the page is unlocked.  This is because another
682  * CPU could truncate the page off the mapping and then free the mapping.
683  *
684  * Usually, the page _is_ locked, or the caller is a user-space process which
685  * holds a reference on the inode by having an open file.
686  *
687  * In other cases, the page should be locked before running set_page_dirty().
688  */
689 int set_page_dirty_lock(struct page *page)
690 {
691         int ret;
692
693         lock_page(page);
694         ret = set_page_dirty(page);
695         unlock_page(page);
696         return ret;
697 }
698 EXPORT_SYMBOL(set_page_dirty_lock);
699
700 /*
701  * Clear a page's dirty flag, while caring for dirty memory accounting. 
702  * Returns true if the page was previously dirty.
703  */
704 int test_clear_page_dirty(struct page *page)
705 {
706         struct address_space *mapping = page_mapping(page);
707         unsigned long flags;
708
709         if (mapping) {
710                 write_lock_irqsave(&mapping->tree_lock, flags);
711                 if (TestClearPageDirty(page)) {
712                         radix_tree_tag_clear(&mapping->page_tree,
713                                                 page_index(page),
714                                                 PAGECACHE_TAG_DIRTY);
715                         write_unlock_irqrestore(&mapping->tree_lock, flags);
716                         if (mapping_cap_account_dirty(mapping))
717                                 dec_page_state(nr_dirty);
718                         return 1;
719                 }
720                 write_unlock_irqrestore(&mapping->tree_lock, flags);
721                 return 0;
722         }
723         return TestClearPageDirty(page);
724 }
725 EXPORT_SYMBOL(test_clear_page_dirty);
726
727 /*
728  * Clear a page's dirty flag, while caring for dirty memory accounting.
729  * Returns true if the page was previously dirty.
730  *
731  * This is for preparing to put the page under writeout.  We leave the page
732  * tagged as dirty in the radix tree so that a concurrent write-for-sync
733  * can discover it via a PAGECACHE_TAG_DIRTY walk.  The ->writepage
734  * implementation will run either set_page_writeback() or set_page_dirty(),
735  * at which stage we bring the page's dirty flag and radix-tree dirty tag
736  * back into sync.
737  *
738  * This incoherency between the page's dirty flag and radix-tree tag is
739  * unfortunate, but it only exists while the page is locked.
740  */
741 int clear_page_dirty_for_io(struct page *page)
742 {
743         struct address_space *mapping = page_mapping(page);
744
745         if (mapping) {
746                 if (TestClearPageDirty(page)) {
747                         if (mapping_cap_account_dirty(mapping))
748                                 dec_page_state(nr_dirty);
749                         return 1;
750                 }
751                 return 0;
752         }
753         return TestClearPageDirty(page);
754 }
755 EXPORT_SYMBOL(clear_page_dirty_for_io);
756
757 int test_clear_page_writeback(struct page *page)
758 {
759         struct address_space *mapping = page_mapping(page);
760         int ret;
761
762         if (mapping) {
763                 unsigned long flags;
764
765                 write_lock_irqsave(&mapping->tree_lock, flags);
766                 ret = TestClearPageWriteback(page);
767                 if (ret)
768                         radix_tree_tag_clear(&mapping->page_tree,
769                                                 page_index(page),
770                                                 PAGECACHE_TAG_WRITEBACK);
771                 write_unlock_irqrestore(&mapping->tree_lock, flags);
772         } else {
773                 ret = TestClearPageWriteback(page);
774         }
775         return ret;
776 }
777
778 int test_set_page_writeback(struct page *page)
779 {
780         struct address_space *mapping = page_mapping(page);
781         int ret;
782
783         if (mapping) {
784                 unsigned long flags;
785
786                 write_lock_irqsave(&mapping->tree_lock, flags);
787                 ret = TestSetPageWriteback(page);
788                 if (!ret)
789                         radix_tree_tag_set(&mapping->page_tree,
790                                                 page_index(page),
791                                                 PAGECACHE_TAG_WRITEBACK);
792                 if (!PageDirty(page))
793                         radix_tree_tag_clear(&mapping->page_tree,
794                                                 page_index(page),
795                                                 PAGECACHE_TAG_DIRTY);
796                 write_unlock_irqrestore(&mapping->tree_lock, flags);
797         } else {
798                 ret = TestSetPageWriteback(page);
799         }
800         return ret;
801
802 }
803 EXPORT_SYMBOL(test_set_page_writeback);
804
805 /*
806  * Return true if any of the pages in the mapping are marged with the
807  * passed tag.
808  */
809 int mapping_tagged(struct address_space *mapping, int tag)
810 {
811         unsigned long flags;
812         int ret;
813
814         read_lock_irqsave(&mapping->tree_lock, flags);
815         ret = radix_tree_tagged(&mapping->page_tree, tag);
816         read_unlock_irqrestore(&mapping->tree_lock, flags);
817         return ret;
818 }
819 EXPORT_SYMBOL(mapping_tagged);