Merge branch 'master'
[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;      /* 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 DEFINE_TIMER(wb_timer, wb_timer_fn, 0, 0);
372 static DEFINE_TIMER(laptop_mode_wb_timer, laptop_timer_fn, 0, 0);
373
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  */
389 static 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  */
434 int 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
447 static 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
453 static void laptop_flush(unsigned long unused)
454 {
455         sys_sync();
456 }
457
458 static 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  */
468 void 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  */
478 void 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
500 static 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
509 static int
510 ratelimit_handler(struct notifier_block *self, unsigned long u, void *v)
511 {
512         set_ratelimit();
513         return 0;
514 }
515
516 static 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  */
526 void __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
551 int 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  *
563  * @page: the page to write
564  * @wait: if true, wait on writeout
565  *
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  */
570 int 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 }
598 EXPORT_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  */
615 int __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 }
643 EXPORT_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  */
650 int redirty_page_for_writepage(struct writeback_control *wbc, struct page *page)
651 {
652         wbc->pages_skipped++;
653         return __set_page_dirty_nobuffers(page);
654 }
655 EXPORT_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  */
661 int 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 }
675 EXPORT_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  */
687 int 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 }
696 EXPORT_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  */
702 int 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 }
723 EXPORT_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  */
739 int 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 }
753 EXPORT_SYMBOL(clear_page_dirty_for_io);
754
755 int 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
776 int 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 }
801 EXPORT_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  */
807 int 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 }
817 EXPORT_SYMBOL(mapping_tagged);