[PATCH] slab: fix kernel-doc warnings
[linux-2.6] / 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 __cacheline_aligned_in_smp;   /* 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                 if (!dirty_exceeded)
216                         dirty_exceeded = 1;
217
218                 /* Note: nr_reclaimable denotes nr_dirty + nr_unstable.
219                  * Unstable writes are a feature of certain networked
220                  * filesystems (i.e. NFS) in which data may have been
221                  * written to the server's write cache, but has not yet
222                  * been flushed to permanent storage.
223                  */
224                 if (nr_reclaimable) {
225                         writeback_inodes(&wbc);
226                         get_dirty_limits(&wbs, &background_thresh,
227                                         &dirty_thresh, mapping);
228                         nr_reclaimable = wbs.nr_dirty + wbs.nr_unstable;
229                         if (nr_reclaimable + wbs.nr_writeback <= dirty_thresh)
230                                 break;
231                         pages_written += write_chunk - wbc.nr_to_write;
232                         if (pages_written >= write_chunk)
233                                 break;          /* We've done our duty */
234                 }
235                 blk_congestion_wait(WRITE, HZ/10);
236         }
237
238         if (nr_reclaimable + wbs.nr_writeback <= dirty_thresh && dirty_exceeded)
239                 dirty_exceeded = 0;
240
241         if (writeback_in_progress(bdi))
242                 return;         /* pdflush is already working this queue */
243
244         /*
245          * In laptop mode, we wait until hitting the higher threshold before
246          * starting background writeout, and then write out all the way down
247          * to the lower threshold.  So slow writers cause minimal disk activity.
248          *
249          * In normal mode, we start background writeout at the lower
250          * background_thresh, to keep the amount of dirty memory low.
251          */
252         if ((laptop_mode && pages_written) ||
253              (!laptop_mode && (nr_reclaimable > background_thresh)))
254                 pdflush_operation(background_writeout, 0);
255 }
256
257 /**
258  * balance_dirty_pages_ratelimited - balance dirty memory state
259  * @mapping: address_space which was dirtied
260  *
261  * Processes which are dirtying memory should call in here once for each page
262  * which was newly dirtied.  The function will periodically check the system's
263  * dirty state and will initiate writeback if needed.
264  *
265  * On really big machines, get_writeback_state is expensive, so try to avoid
266  * calling it too often (ratelimiting).  But once we're over the dirty memory
267  * limit we decrease the ratelimiting by a lot, to prevent individual processes
268  * from overshooting the limit by (ratelimit_pages) each.
269  */
270 void balance_dirty_pages_ratelimited(struct address_space *mapping)
271 {
272         static DEFINE_PER_CPU(int, ratelimits) = 0;
273         long ratelimit;
274
275         ratelimit = ratelimit_pages;
276         if (dirty_exceeded)
277                 ratelimit = 8;
278
279         /*
280          * Check the rate limiting. Also, we do not want to throttle real-time
281          * tasks in balance_dirty_pages(). Period.
282          */
283         if (get_cpu_var(ratelimits)++ >= ratelimit) {
284                 __get_cpu_var(ratelimits) = 0;
285                 put_cpu_var(ratelimits);
286                 balance_dirty_pages(mapping);
287                 return;
288         }
289         put_cpu_var(ratelimits);
290 }
291 EXPORT_SYMBOL(balance_dirty_pages_ratelimited);
292
293 void throttle_vm_writeout(void)
294 {
295         struct writeback_state wbs;
296         long background_thresh;
297         long dirty_thresh;
298
299         for ( ; ; ) {
300                 get_dirty_limits(&wbs, &background_thresh, &dirty_thresh, NULL);
301
302                 /*
303                  * Boost the allowable dirty threshold a bit for page
304                  * allocators so they don't get DoS'ed by heavy writers
305                  */
306                 dirty_thresh += dirty_thresh / 10;      /* wheeee... */
307
308                 if (wbs.nr_unstable + wbs.nr_writeback <= dirty_thresh)
309                         break;
310                 blk_congestion_wait(WRITE, HZ/10);
311         }
312 }
313
314
315 /*
316  * writeback at least _min_pages, and keep writing until the amount of dirty
317  * memory is less than the background threshold, or until we're all clean.
318  */
319 static void background_writeout(unsigned long _min_pages)
320 {
321         long min_pages = _min_pages;
322         struct writeback_control wbc = {
323                 .bdi            = NULL,
324                 .sync_mode      = WB_SYNC_NONE,
325                 .older_than_this = NULL,
326                 .nr_to_write    = 0,
327                 .nonblocking    = 1,
328         };
329
330         for ( ; ; ) {
331                 struct writeback_state wbs;
332                 long background_thresh;
333                 long dirty_thresh;
334
335                 get_dirty_limits(&wbs, &background_thresh, &dirty_thresh, NULL);
336                 if (wbs.nr_dirty + wbs.nr_unstable < background_thresh
337                                 && min_pages <= 0)
338                         break;
339                 wbc.encountered_congestion = 0;
340                 wbc.nr_to_write = MAX_WRITEBACK_PAGES;
341                 wbc.pages_skipped = 0;
342                 writeback_inodes(&wbc);
343                 min_pages -= MAX_WRITEBACK_PAGES - wbc.nr_to_write;
344                 if (wbc.nr_to_write > 0 || wbc.pages_skipped > 0) {
345                         /* Wrote less than expected */
346                         blk_congestion_wait(WRITE, HZ/10);
347                         if (!wbc.encountered_congestion)
348                                 break;
349                 }
350         }
351 }
352
353 /*
354  * Start writeback of `nr_pages' pages.  If `nr_pages' is zero, write back
355  * the whole world.  Returns 0 if a pdflush thread was dispatched.  Returns
356  * -1 if all pdflush threads were busy.
357  */
358 int wakeup_pdflush(long nr_pages)
359 {
360         if (nr_pages == 0) {
361                 struct writeback_state wbs;
362
363                 get_writeback_state(&wbs);
364                 nr_pages = wbs.nr_dirty + wbs.nr_unstable;
365         }
366         return pdflush_operation(background_writeout, nr_pages);
367 }
368
369 static void wb_timer_fn(unsigned long unused);
370 static void laptop_timer_fn(unsigned long unused);
371
372 static DEFINE_TIMER(wb_timer, wb_timer_fn, 0, 0);
373 static DEFINE_TIMER(laptop_mode_wb_timer, laptop_timer_fn, 0, 0);
374
375 /*
376  * Periodic writeback of "old" data.
377  *
378  * Define "old": the first time one of an inode's pages is dirtied, we mark the
379  * dirtying-time in the inode's address_space.  So this periodic writeback code
380  * just walks the superblock inode list, writing back any inodes which are
381  * older than a specific point in time.
382  *
383  * Try to run once per dirty_writeback_centisecs.  But if a writeback event
384  * takes longer than a dirty_writeback_centisecs interval, then leave a
385  * one-second gap.
386  *
387  * older_than_this takes precedence over nr_to_write.  So we'll only write back
388  * all dirty pages if they are all attached to "old" mappings.
389  */
390 static void wb_kupdate(unsigned long arg)
391 {
392         unsigned long oldest_jif;
393         unsigned long start_jif;
394         unsigned long next_jif;
395         long nr_to_write;
396         struct writeback_state wbs;
397         struct writeback_control wbc = {
398                 .bdi            = NULL,
399                 .sync_mode      = WB_SYNC_NONE,
400                 .older_than_this = &oldest_jif,
401                 .nr_to_write    = 0,
402                 .nonblocking    = 1,
403                 .for_kupdate    = 1,
404         };
405
406         sync_supers();
407
408         get_writeback_state(&wbs);
409         oldest_jif = jiffies - (dirty_expire_centisecs * HZ) / 100;
410         start_jif = jiffies;
411         next_jif = start_jif + (dirty_writeback_centisecs * HZ) / 100;
412         nr_to_write = wbs.nr_dirty + wbs.nr_unstable +
413                         (inodes_stat.nr_inodes - inodes_stat.nr_unused);
414         while (nr_to_write > 0) {
415                 wbc.encountered_congestion = 0;
416                 wbc.nr_to_write = MAX_WRITEBACK_PAGES;
417                 writeback_inodes(&wbc);
418                 if (wbc.nr_to_write > 0) {
419                         if (wbc.encountered_congestion)
420                                 blk_congestion_wait(WRITE, HZ/10);
421                         else
422                                 break;  /* All the old data is written */
423                 }
424                 nr_to_write -= MAX_WRITEBACK_PAGES - wbc.nr_to_write;
425         }
426         if (time_before(next_jif, jiffies + HZ))
427                 next_jif = jiffies + HZ;
428         if (dirty_writeback_centisecs)
429                 mod_timer(&wb_timer, next_jif);
430 }
431
432 /*
433  * sysctl handler for /proc/sys/vm/dirty_writeback_centisecs
434  */
435 int dirty_writeback_centisecs_handler(ctl_table *table, int write,
436                 struct file *file, void __user *buffer, size_t *length, loff_t *ppos)
437 {
438         proc_dointvec(table, write, file, buffer, length, ppos);
439         if (dirty_writeback_centisecs) {
440                 mod_timer(&wb_timer,
441                         jiffies + (dirty_writeback_centisecs * HZ) / 100);
442         } else {
443                 del_timer(&wb_timer);
444         }
445         return 0;
446 }
447
448 static void wb_timer_fn(unsigned long unused)
449 {
450         if (pdflush_operation(wb_kupdate, 0) < 0)
451                 mod_timer(&wb_timer, jiffies + HZ); /* delay 1 second */
452 }
453
454 static void laptop_flush(unsigned long unused)
455 {
456         sys_sync();
457 }
458
459 static void laptop_timer_fn(unsigned long unused)
460 {
461         pdflush_operation(laptop_flush, 0);
462 }
463
464 /*
465  * We've spun up the disk and we're in laptop mode: schedule writeback
466  * of all dirty data a few seconds from now.  If the flush is already scheduled
467  * then push it back - the user is still using the disk.
468  */
469 void laptop_io_completion(void)
470 {
471         mod_timer(&laptop_mode_wb_timer, jiffies + laptop_mode * HZ);
472 }
473
474 /*
475  * We're in laptop mode and we've just synced. The sync's writes will have
476  * caused another writeback to be scheduled by laptop_io_completion.
477  * Nothing needs to be written back anymore, so we unschedule the writeback.
478  */
479 void laptop_sync_completion(void)
480 {
481         del_timer(&laptop_mode_wb_timer);
482 }
483
484 /*
485  * If ratelimit_pages is too high then we can get into dirty-data overload
486  * if a large number of processes all perform writes at the same time.
487  * If it is too low then SMP machines will call the (expensive)
488  * get_writeback_state too often.
489  *
490  * Here we set ratelimit_pages to a level which ensures that when all CPUs are
491  * dirtying in parallel, we cannot go more than 3% (1/32) over the dirty memory
492  * thresholds before writeback cuts in.
493  *
494  * But the limit should not be set too high.  Because it also controls the
495  * amount of memory which the balance_dirty_pages() caller has to write back.
496  * If this is too large then the caller will block on the IO queue all the
497  * time.  So limit it to four megabytes - the balance_dirty_pages() caller
498  * will write six megabyte chunks, max.
499  */
500
501 static void set_ratelimit(void)
502 {
503         ratelimit_pages = total_pages / (num_online_cpus() * 32);
504         if (ratelimit_pages < 16)
505                 ratelimit_pages = 16;
506         if (ratelimit_pages * PAGE_CACHE_SIZE > 4096 * 1024)
507                 ratelimit_pages = (4096 * 1024) / PAGE_CACHE_SIZE;
508 }
509
510 static int
511 ratelimit_handler(struct notifier_block *self, unsigned long u, void *v)
512 {
513         set_ratelimit();
514         return 0;
515 }
516
517 static struct notifier_block ratelimit_nb = {
518         .notifier_call  = ratelimit_handler,
519         .next           = NULL,
520 };
521
522 /*
523  * If the machine has a large highmem:lowmem ratio then scale back the default
524  * dirty memory thresholds: allowing too much dirty highmem pins an excessive
525  * number of buffer_heads.
526  */
527 void __init page_writeback_init(void)
528 {
529         long buffer_pages = nr_free_buffer_pages();
530         long correction;
531
532         total_pages = nr_free_pagecache_pages();
533
534         correction = (100 * 4 * buffer_pages) / total_pages;
535
536         if (correction < 100) {
537                 dirty_background_ratio *= correction;
538                 dirty_background_ratio /= 100;
539                 vm_dirty_ratio *= correction;
540                 vm_dirty_ratio /= 100;
541
542                 if (dirty_background_ratio <= 0)
543                         dirty_background_ratio = 1;
544                 if (vm_dirty_ratio <= 0)
545                         vm_dirty_ratio = 1;
546         }
547         mod_timer(&wb_timer, jiffies + (dirty_writeback_centisecs * HZ) / 100);
548         set_ratelimit();
549         register_cpu_notifier(&ratelimit_nb);
550 }
551
552 int do_writepages(struct address_space *mapping, struct writeback_control *wbc)
553 {
554         int ret;
555
556         if (wbc->nr_to_write <= 0)
557                 return 0;
558         wbc->for_writepages = 1;
559         if (mapping->a_ops->writepages)
560                 ret =  mapping->a_ops->writepages(mapping, wbc);
561         else
562                 ret = generic_writepages(mapping, wbc);
563         wbc->for_writepages = 0;
564         return ret;
565 }
566
567 /**
568  * write_one_page - write out a single page and optionally wait on I/O
569  *
570  * @page: the page to write
571  * @wait: if true, wait on writeout
572  *
573  * The page must be locked by the caller and will be unlocked upon return.
574  *
575  * write_one_page() returns a negative error code if I/O failed.
576  */
577 int write_one_page(struct page *page, int wait)
578 {
579         struct address_space *mapping = page->mapping;
580         int ret = 0;
581         struct writeback_control wbc = {
582                 .sync_mode = WB_SYNC_ALL,
583                 .nr_to_write = 1,
584         };
585
586         BUG_ON(!PageLocked(page));
587
588         if (wait)
589                 wait_on_page_writeback(page);
590
591         if (clear_page_dirty_for_io(page)) {
592                 page_cache_get(page);
593                 ret = mapping->a_ops->writepage(page, &wbc);
594                 if (ret == 0 && wait) {
595                         wait_on_page_writeback(page);
596                         if (PageError(page))
597                                 ret = -EIO;
598                 }
599                 page_cache_release(page);
600         } else {
601                 unlock_page(page);
602         }
603         return ret;
604 }
605 EXPORT_SYMBOL(write_one_page);
606
607 /*
608  * For address_spaces which do not use buffers.  Just tag the page as dirty in
609  * its radix tree.
610  *
611  * This is also used when a single buffer is being dirtied: we want to set the
612  * page dirty in that case, but not all the buffers.  This is a "bottom-up"
613  * dirtying, whereas __set_page_dirty_buffers() is a "top-down" dirtying.
614  *
615  * Most callers have locked the page, which pins the address_space in memory.
616  * But zap_pte_range() does not lock the page, however in that case the
617  * mapping is pinned by the vma's ->vm_file reference.
618  *
619  * We take care to handle the case where the page was truncated from the
620  * mapping by re-checking page_mapping() insode tree_lock.
621  */
622 int __set_page_dirty_nobuffers(struct page *page)
623 {
624         int ret = 0;
625
626         if (!TestSetPageDirty(page)) {
627                 struct address_space *mapping = page_mapping(page);
628                 struct address_space *mapping2;
629
630                 if (mapping) {
631                         write_lock_irq(&mapping->tree_lock);
632                         mapping2 = page_mapping(page);
633                         if (mapping2) { /* Race with truncate? */
634                                 BUG_ON(mapping2 != mapping);
635                                 if (mapping_cap_account_dirty(mapping))
636                                         inc_page_state(nr_dirty);
637                                 radix_tree_tag_set(&mapping->page_tree,
638                                         page_index(page), PAGECACHE_TAG_DIRTY);
639                         }
640                         write_unlock_irq(&mapping->tree_lock);
641                         if (mapping->host) {
642                                 /* !PageAnon && !swapper_space */
643                                 __mark_inode_dirty(mapping->host,
644                                                         I_DIRTY_PAGES);
645                         }
646                 }
647         }
648         return ret;
649 }
650 EXPORT_SYMBOL(__set_page_dirty_nobuffers);
651
652 /*
653  * When a writepage implementation decides that it doesn't want to write this
654  * page for some reason, it should redirty the locked page via
655  * redirty_page_for_writepage() and it should then unlock the page and return 0
656  */
657 int redirty_page_for_writepage(struct writeback_control *wbc, struct page *page)
658 {
659         wbc->pages_skipped++;
660         return __set_page_dirty_nobuffers(page);
661 }
662 EXPORT_SYMBOL(redirty_page_for_writepage);
663
664 /*
665  * If the mapping doesn't provide a set_page_dirty a_op, then
666  * just fall through and assume that it wants buffer_heads.
667  */
668 int fastcall set_page_dirty(struct page *page)
669 {
670         struct address_space *mapping = page_mapping(page);
671
672         if (likely(mapping)) {
673                 int (*spd)(struct page *) = mapping->a_ops->set_page_dirty;
674                 if (spd)
675                         return (*spd)(page);
676                 return __set_page_dirty_buffers(page);
677         }
678         if (!PageDirty(page))
679                 SetPageDirty(page);
680         return 0;
681 }
682 EXPORT_SYMBOL(set_page_dirty);
683
684 /*
685  * set_page_dirty() is racy if the caller has no reference against
686  * page->mapping->host, and if the page is unlocked.  This is because another
687  * CPU could truncate the page off the mapping and then free the mapping.
688  *
689  * Usually, the page _is_ locked, or the caller is a user-space process which
690  * holds a reference on the inode by having an open file.
691  *
692  * In other cases, the page should be locked before running set_page_dirty().
693  */
694 int set_page_dirty_lock(struct page *page)
695 {
696         int ret;
697
698         lock_page(page);
699         ret = set_page_dirty(page);
700         unlock_page(page);
701         return ret;
702 }
703 EXPORT_SYMBOL(set_page_dirty_lock);
704
705 /*
706  * Clear a page's dirty flag, while caring for dirty memory accounting. 
707  * Returns true if the page was previously dirty.
708  */
709 int test_clear_page_dirty(struct page *page)
710 {
711         struct address_space *mapping = page_mapping(page);
712         unsigned long flags;
713
714         if (mapping) {
715                 write_lock_irqsave(&mapping->tree_lock, flags);
716                 if (TestClearPageDirty(page)) {
717                         radix_tree_tag_clear(&mapping->page_tree,
718                                                 page_index(page),
719                                                 PAGECACHE_TAG_DIRTY);
720                         write_unlock_irqrestore(&mapping->tree_lock, flags);
721                         if (mapping_cap_account_dirty(mapping))
722                                 dec_page_state(nr_dirty);
723                         return 1;
724                 }
725                 write_unlock_irqrestore(&mapping->tree_lock, flags);
726                 return 0;
727         }
728         return TestClearPageDirty(page);
729 }
730 EXPORT_SYMBOL(test_clear_page_dirty);
731
732 /*
733  * Clear a page's dirty flag, while caring for dirty memory accounting.
734  * Returns true if the page was previously dirty.
735  *
736  * This is for preparing to put the page under writeout.  We leave the page
737  * tagged as dirty in the radix tree so that a concurrent write-for-sync
738  * can discover it via a PAGECACHE_TAG_DIRTY walk.  The ->writepage
739  * implementation will run either set_page_writeback() or set_page_dirty(),
740  * at which stage we bring the page's dirty flag and radix-tree dirty tag
741  * back into sync.
742  *
743  * This incoherency between the page's dirty flag and radix-tree tag is
744  * unfortunate, but it only exists while the page is locked.
745  */
746 int clear_page_dirty_for_io(struct page *page)
747 {
748         struct address_space *mapping = page_mapping(page);
749
750         if (mapping) {
751                 if (TestClearPageDirty(page)) {
752                         if (mapping_cap_account_dirty(mapping))
753                                 dec_page_state(nr_dirty);
754                         return 1;
755                 }
756                 return 0;
757         }
758         return TestClearPageDirty(page);
759 }
760 EXPORT_SYMBOL(clear_page_dirty_for_io);
761
762 int test_clear_page_writeback(struct page *page)
763 {
764         struct address_space *mapping = page_mapping(page);
765         int ret;
766
767         if (mapping) {
768                 unsigned long flags;
769
770                 write_lock_irqsave(&mapping->tree_lock, flags);
771                 ret = TestClearPageWriteback(page);
772                 if (ret)
773                         radix_tree_tag_clear(&mapping->page_tree,
774                                                 page_index(page),
775                                                 PAGECACHE_TAG_WRITEBACK);
776                 write_unlock_irqrestore(&mapping->tree_lock, flags);
777         } else {
778                 ret = TestClearPageWriteback(page);
779         }
780         return ret;
781 }
782
783 int test_set_page_writeback(struct page *page)
784 {
785         struct address_space *mapping = page_mapping(page);
786         int ret;
787
788         if (mapping) {
789                 unsigned long flags;
790
791                 write_lock_irqsave(&mapping->tree_lock, flags);
792                 ret = TestSetPageWriteback(page);
793                 if (!ret)
794                         radix_tree_tag_set(&mapping->page_tree,
795                                                 page_index(page),
796                                                 PAGECACHE_TAG_WRITEBACK);
797                 if (!PageDirty(page))
798                         radix_tree_tag_clear(&mapping->page_tree,
799                                                 page_index(page),
800                                                 PAGECACHE_TAG_DIRTY);
801                 write_unlock_irqrestore(&mapping->tree_lock, flags);
802         } else {
803                 ret = TestSetPageWriteback(page);
804         }
805         return ret;
806
807 }
808 EXPORT_SYMBOL(test_set_page_writeback);
809
810 /*
811  * Return true if any of the pages in the mapping are marged with the
812  * passed tag.
813  */
814 int mapping_tagged(struct address_space *mapping, int tag)
815 {
816         unsigned long flags;
817         int ret;
818
819         read_lock_irqsave(&mapping->tree_lock, flags);
820         ret = radix_tree_tagged(&mapping->page_tree, tag);
821         read_unlock_irqrestore(&mapping->tree_lock, flags);
822         return ret;
823 }
824 EXPORT_SYMBOL(mapping_tagged);