[PATCH] Represent laptop_mode as jiffies internally
[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 __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_interval = 5 * HZ;
79
80 /*
81  * The longest number of centiseconds for which data is allowed to remain dirty
82  */
83 int dirty_expire_interval = 30 * HZ;
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". Doubles as a timeout in jiffies:
92  * a full sync is triggered after this time elapses without any disk activity.
93  */
94 int laptop_mode;
95
96 EXPORT_SYMBOL(laptop_mode);
97
98 /* End of sysctl-exported parameters */
99
100
101 static void background_writeout(unsigned long _min_pages);
102
103 struct writeback_state
104 {
105         unsigned long nr_dirty;
106         unsigned long nr_unstable;
107         unsigned long nr_mapped;
108         unsigned long nr_writeback;
109 };
110
111 static void get_writeback_state(struct writeback_state *wbs)
112 {
113         wbs->nr_dirty = read_page_state(nr_dirty);
114         wbs->nr_unstable = read_page_state(nr_unstable);
115         wbs->nr_mapped = read_page_state(nr_mapped);
116         wbs->nr_writeback = read_page_state(nr_writeback);
117 }
118
119 /*
120  * Work out the current dirty-memory clamping and background writeout
121  * thresholds.
122  *
123  * The main aim here is to lower them aggressively if there is a lot of mapped
124  * memory around.  To avoid stressing page reclaim with lots of unreclaimable
125  * pages.  It is better to clamp down on writers than to start swapping, and
126  * performing lots of scanning.
127  *
128  * We only allow 1/2 of the currently-unmapped memory to be dirtied.
129  *
130  * We don't permit the clamping level to fall below 5% - that is getting rather
131  * excessive.
132  *
133  * We make sure that the background writeout level is below the adjusted
134  * clamping level.
135  */
136 static void
137 get_dirty_limits(struct writeback_state *wbs, long *pbackground, long *pdirty,
138                 struct address_space *mapping)
139 {
140         int background_ratio;           /* Percentages */
141         int dirty_ratio;
142         int unmapped_ratio;
143         long background;
144         long dirty;
145         unsigned long available_memory = total_pages;
146         struct task_struct *tsk;
147
148         get_writeback_state(wbs);
149
150 #ifdef CONFIG_HIGHMEM
151         /*
152          * If this mapping can only allocate from low memory,
153          * we exclude high memory from our count.
154          */
155         if (mapping && !(mapping_gfp_mask(mapping) & __GFP_HIGHMEM))
156                 available_memory -= totalhigh_pages;
157 #endif
158
159
160         unmapped_ratio = 100 - (wbs->nr_mapped * 100) / total_pages;
161
162         dirty_ratio = vm_dirty_ratio;
163         if (dirty_ratio > unmapped_ratio / 2)
164                 dirty_ratio = unmapped_ratio / 2;
165
166         if (dirty_ratio < 5)
167                 dirty_ratio = 5;
168
169         background_ratio = dirty_background_ratio;
170         if (background_ratio >= dirty_ratio)
171                 background_ratio = dirty_ratio / 2;
172
173         background = (background_ratio * available_memory) / 100;
174         dirty = (dirty_ratio * available_memory) / 100;
175         tsk = current;
176         if (tsk->flags & PF_LESS_THROTTLE || rt_task(tsk)) {
177                 background += background / 4;
178                 dirty += dirty / 4;
179         }
180         *pbackground = background;
181         *pdirty = dirty;
182 }
183
184 /*
185  * balance_dirty_pages() must be called by processes which are generating dirty
186  * data.  It looks at the number of dirty pages in the machine and will force
187  * the caller to perform writeback if the system is over `vm_dirty_ratio'.
188  * If we're over `background_thresh' then pdflush is woken to perform some
189  * writeout.
190  */
191 static void balance_dirty_pages(struct address_space *mapping)
192 {
193         struct writeback_state wbs;
194         long nr_reclaimable;
195         long background_thresh;
196         long dirty_thresh;
197         unsigned long pages_written = 0;
198         unsigned long write_chunk = sync_writeback_pages();
199
200         struct backing_dev_info *bdi = mapping->backing_dev_info;
201
202         for (;;) {
203                 struct writeback_control wbc = {
204                         .bdi            = bdi,
205                         .sync_mode      = WB_SYNC_NONE,
206                         .older_than_this = NULL,
207                         .nr_to_write    = write_chunk,
208                 };
209
210                 get_dirty_limits(&wbs, &background_thresh,
211                                         &dirty_thresh, mapping);
212                 nr_reclaimable = wbs.nr_dirty + wbs.nr_unstable;
213                 if (nr_reclaimable + wbs.nr_writeback <= dirty_thresh)
214                         break;
215
216                 if (!dirty_exceeded)
217                         dirty_exceeded = 1;
218
219                 /* Note: nr_reclaimable denotes nr_dirty + nr_unstable.
220                  * Unstable writes are a feature of certain networked
221                  * filesystems (i.e. NFS) in which data may have been
222                  * written to the server's write cache, but has not yet
223                  * been flushed to permanent storage.
224                  */
225                 if (nr_reclaimable) {
226                         writeback_inodes(&wbc);
227                         get_dirty_limits(&wbs, &background_thresh,
228                                         &dirty_thresh, mapping);
229                         nr_reclaimable = wbs.nr_dirty + wbs.nr_unstable;
230                         if (nr_reclaimable + wbs.nr_writeback <= dirty_thresh)
231                                 break;
232                         pages_written += write_chunk - wbc.nr_to_write;
233                         if (pages_written >= write_chunk)
234                                 break;          /* We've done our duty */
235                 }
236                 blk_congestion_wait(WRITE, HZ/10);
237         }
238
239         if (nr_reclaimable + wbs.nr_writeback <= dirty_thresh && dirty_exceeded)
240                 dirty_exceeded = 0;
241
242         if (writeback_in_progress(bdi))
243                 return;         /* pdflush is already working this queue */
244
245         /*
246          * In laptop mode, we wait until hitting the higher threshold before
247          * starting background writeout, and then write out all the way down
248          * to the lower threshold.  So slow writers cause minimal disk activity.
249          *
250          * In normal mode, we start background writeout at the lower
251          * background_thresh, to keep the amount of dirty memory low.
252          */
253         if ((laptop_mode && pages_written) ||
254              (!laptop_mode && (nr_reclaimable > background_thresh)))
255                 pdflush_operation(background_writeout, 0);
256 }
257
258 /**
259  * balance_dirty_pages_ratelimited - balance dirty memory state
260  * @mapping: address_space which was dirtied
261  *
262  * Processes which are dirtying memory should call in here once for each page
263  * which was newly dirtied.  The function will periodically check the system's
264  * dirty state and will initiate writeback if needed.
265  *
266  * On really big machines, get_writeback_state is expensive, so try to avoid
267  * calling it too often (ratelimiting).  But once we're over the dirty memory
268  * limit we decrease the ratelimiting by a lot, to prevent individual processes
269  * from overshooting the limit by (ratelimit_pages) each.
270  */
271 void balance_dirty_pages_ratelimited(struct address_space *mapping)
272 {
273         static DEFINE_PER_CPU(int, ratelimits) = 0;
274         long ratelimit;
275
276         ratelimit = ratelimit_pages;
277         if (dirty_exceeded)
278                 ratelimit = 8;
279
280         /*
281          * Check the rate limiting. Also, we do not want to throttle real-time
282          * tasks in balance_dirty_pages(). Period.
283          */
284         if (get_cpu_var(ratelimits)++ >= ratelimit) {
285                 __get_cpu_var(ratelimits) = 0;
286                 put_cpu_var(ratelimits);
287                 balance_dirty_pages(mapping);
288                 return;
289         }
290         put_cpu_var(ratelimits);
291 }
292 EXPORT_SYMBOL(balance_dirty_pages_ratelimited);
293
294 void throttle_vm_writeout(void)
295 {
296         struct writeback_state wbs;
297         long background_thresh;
298         long dirty_thresh;
299
300         for ( ; ; ) {
301                 get_dirty_limits(&wbs, &background_thresh, &dirty_thresh, NULL);
302
303                 /*
304                  * Boost the allowable dirty threshold a bit for page
305                  * allocators so they don't get DoS'ed by heavy writers
306                  */
307                 dirty_thresh += dirty_thresh / 10;      /* wheeee... */
308
309                 if (wbs.nr_unstable + wbs.nr_writeback <= dirty_thresh)
310                         break;
311                 blk_congestion_wait(WRITE, HZ/10);
312         }
313 }
314
315
316 /*
317  * writeback at least _min_pages, and keep writing until the amount of dirty
318  * memory is less than the background threshold, or until we're all clean.
319  */
320 static void background_writeout(unsigned long _min_pages)
321 {
322         long min_pages = _min_pages;
323         struct writeback_control wbc = {
324                 .bdi            = NULL,
325                 .sync_mode      = WB_SYNC_NONE,
326                 .older_than_this = NULL,
327                 .nr_to_write    = 0,
328                 .nonblocking    = 1,
329         };
330
331         for ( ; ; ) {
332                 struct writeback_state wbs;
333                 long background_thresh;
334                 long dirty_thresh;
335
336                 get_dirty_limits(&wbs, &background_thresh, &dirty_thresh, NULL);
337                 if (wbs.nr_dirty + wbs.nr_unstable < background_thresh
338                                 && min_pages <= 0)
339                         break;
340                 wbc.encountered_congestion = 0;
341                 wbc.nr_to_write = MAX_WRITEBACK_PAGES;
342                 wbc.pages_skipped = 0;
343                 writeback_inodes(&wbc);
344                 min_pages -= MAX_WRITEBACK_PAGES - wbc.nr_to_write;
345                 if (wbc.nr_to_write > 0 || wbc.pages_skipped > 0) {
346                         /* Wrote less than expected */
347                         blk_congestion_wait(WRITE, HZ/10);
348                         if (!wbc.encountered_congestion)
349                                 break;
350                 }
351         }
352 }
353
354 /*
355  * Start writeback of `nr_pages' pages.  If `nr_pages' is zero, write back
356  * the whole world.  Returns 0 if a pdflush thread was dispatched.  Returns
357  * -1 if all pdflush threads were busy.
358  */
359 int wakeup_pdflush(long nr_pages)
360 {
361         if (nr_pages == 0) {
362                 struct writeback_state wbs;
363
364                 get_writeback_state(&wbs);
365                 nr_pages = wbs.nr_dirty + wbs.nr_unstable;
366         }
367         return pdflush_operation(background_writeout, nr_pages);
368 }
369
370 static void wb_timer_fn(unsigned long unused);
371 static void laptop_timer_fn(unsigned long unused);
372
373 static DEFINE_TIMER(wb_timer, wb_timer_fn, 0, 0);
374 static DEFINE_TIMER(laptop_mode_wb_timer, 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_interval.  But if a writeback event
385  * takes longer than a dirty_writeback_interval 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_interval;
411         start_jif = jiffies;
412         next_jif = start_jif + dirty_writeback_interval;
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_interval)
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_userhz_jiffies(table, write, file, buffer, length, ppos);
440         if (dirty_writeback_interval) {
441                 mod_timer(&wb_timer,
442                         jiffies + dirty_writeback_interval);
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);
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_interval);
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         int ret;
556
557         if (wbc->nr_to_write <= 0)
558                 return 0;
559         wbc->for_writepages = 1;
560         if (mapping->a_ops->writepages)
561                 ret =  mapping->a_ops->writepages(mapping, wbc);
562         else
563                 ret = generic_writepages(mapping, wbc);
564         wbc->for_writepages = 0;
565         return ret;
566 }
567
568 /**
569  * write_one_page - write out a single page and optionally wait on I/O
570  *
571  * @page: the page to write
572  * @wait: if true, wait on writeout
573  *
574  * The page must be locked by the caller and will be unlocked upon return.
575  *
576  * write_one_page() returns a negative error code if I/O failed.
577  */
578 int write_one_page(struct page *page, int wait)
579 {
580         struct address_space *mapping = page->mapping;
581         int ret = 0;
582         struct writeback_control wbc = {
583                 .sync_mode = WB_SYNC_ALL,
584                 .nr_to_write = 1,
585         };
586
587         BUG_ON(!PageLocked(page));
588
589         if (wait)
590                 wait_on_page_writeback(page);
591
592         if (clear_page_dirty_for_io(page)) {
593                 page_cache_get(page);
594                 ret = mapping->a_ops->writepage(page, &wbc);
595                 if (ret == 0 && wait) {
596                         wait_on_page_writeback(page);
597                         if (PageError(page))
598                                 ret = -EIO;
599                 }
600                 page_cache_release(page);
601         } else {
602                 unlock_page(page);
603         }
604         return ret;
605 }
606 EXPORT_SYMBOL(write_one_page);
607
608 /*
609  * For address_spaces which do not use buffers.  Just tag the page as dirty in
610  * its radix tree.
611  *
612  * This is also used when a single buffer is being dirtied: we want to set the
613  * page dirty in that case, but not all the buffers.  This is a "bottom-up"
614  * dirtying, whereas __set_page_dirty_buffers() is a "top-down" dirtying.
615  *
616  * Most callers have locked the page, which pins the address_space in memory.
617  * But zap_pte_range() does not lock the page, however in that case the
618  * mapping is pinned by the vma's ->vm_file reference.
619  *
620  * We take care to handle the case where the page was truncated from the
621  * mapping by re-checking page_mapping() insode tree_lock.
622  */
623 int __set_page_dirty_nobuffers(struct page *page)
624 {
625         int ret = 0;
626
627         if (!TestSetPageDirty(page)) {
628                 struct address_space *mapping = page_mapping(page);
629                 struct address_space *mapping2;
630
631                 if (mapping) {
632                         write_lock_irq(&mapping->tree_lock);
633                         mapping2 = page_mapping(page);
634                         if (mapping2) { /* Race with truncate? */
635                                 BUG_ON(mapping2 != mapping);
636                                 if (mapping_cap_account_dirty(mapping))
637                                         inc_page_state(nr_dirty);
638                                 radix_tree_tag_set(&mapping->page_tree,
639                                         page_index(page), PAGECACHE_TAG_DIRTY);
640                         }
641                         write_unlock_irq(&mapping->tree_lock);
642                         if (mapping->host) {
643                                 /* !PageAnon && !swapper_space */
644                                 __mark_inode_dirty(mapping->host,
645                                                         I_DIRTY_PAGES);
646                         }
647                 }
648         }
649         return ret;
650 }
651 EXPORT_SYMBOL(__set_page_dirty_nobuffers);
652
653 /*
654  * When a writepage implementation decides that it doesn't want to write this
655  * page for some reason, it should redirty the locked page via
656  * redirty_page_for_writepage() and it should then unlock the page and return 0
657  */
658 int redirty_page_for_writepage(struct writeback_control *wbc, struct page *page)
659 {
660         wbc->pages_skipped++;
661         return __set_page_dirty_nobuffers(page);
662 }
663 EXPORT_SYMBOL(redirty_page_for_writepage);
664
665 /*
666  * If the mapping doesn't provide a set_page_dirty a_op, then
667  * just fall through and assume that it wants buffer_heads.
668  */
669 int fastcall set_page_dirty(struct page *page)
670 {
671         struct address_space *mapping = page_mapping(page);
672
673         if (likely(mapping)) {
674                 int (*spd)(struct page *) = mapping->a_ops->set_page_dirty;
675                 if (spd)
676                         return (*spd)(page);
677                 return __set_page_dirty_buffers(page);
678         }
679         if (!PageDirty(page))
680                 SetPageDirty(page);
681         return 0;
682 }
683 EXPORT_SYMBOL(set_page_dirty);
684
685 /*
686  * set_page_dirty() is racy if the caller has no reference against
687  * page->mapping->host, and if the page is unlocked.  This is because another
688  * CPU could truncate the page off the mapping and then free the mapping.
689  *
690  * Usually, the page _is_ locked, or the caller is a user-space process which
691  * holds a reference on the inode by having an open file.
692  *
693  * In other cases, the page should be locked before running set_page_dirty().
694  */
695 int set_page_dirty_lock(struct page *page)
696 {
697         int ret;
698
699         lock_page(page);
700         ret = set_page_dirty(page);
701         unlock_page(page);
702         return ret;
703 }
704 EXPORT_SYMBOL(set_page_dirty_lock);
705
706 /*
707  * Clear a page's dirty flag, while caring for dirty memory accounting. 
708  * Returns true if the page was previously dirty.
709  */
710 int test_clear_page_dirty(struct page *page)
711 {
712         struct address_space *mapping = page_mapping(page);
713         unsigned long flags;
714
715         if (mapping) {
716                 write_lock_irqsave(&mapping->tree_lock, flags);
717                 if (TestClearPageDirty(page)) {
718                         radix_tree_tag_clear(&mapping->page_tree,
719                                                 page_index(page),
720                                                 PAGECACHE_TAG_DIRTY);
721                         write_unlock_irqrestore(&mapping->tree_lock, flags);
722                         if (mapping_cap_account_dirty(mapping))
723                                 dec_page_state(nr_dirty);
724                         return 1;
725                 }
726                 write_unlock_irqrestore(&mapping->tree_lock, flags);
727                 return 0;
728         }
729         return TestClearPageDirty(page);
730 }
731 EXPORT_SYMBOL(test_clear_page_dirty);
732
733 /*
734  * Clear a page's dirty flag, while caring for dirty memory accounting.
735  * Returns true if the page was previously dirty.
736  *
737  * This is for preparing to put the page under writeout.  We leave the page
738  * tagged as dirty in the radix tree so that a concurrent write-for-sync
739  * can discover it via a PAGECACHE_TAG_DIRTY walk.  The ->writepage
740  * implementation will run either set_page_writeback() or set_page_dirty(),
741  * at which stage we bring the page's dirty flag and radix-tree dirty tag
742  * back into sync.
743  *
744  * This incoherency between the page's dirty flag and radix-tree tag is
745  * unfortunate, but it only exists while the page is locked.
746  */
747 int clear_page_dirty_for_io(struct page *page)
748 {
749         struct address_space *mapping = page_mapping(page);
750
751         if (mapping) {
752                 if (TestClearPageDirty(page)) {
753                         if (mapping_cap_account_dirty(mapping))
754                                 dec_page_state(nr_dirty);
755                         return 1;
756                 }
757                 return 0;
758         }
759         return TestClearPageDirty(page);
760 }
761 EXPORT_SYMBOL(clear_page_dirty_for_io);
762
763 int test_clear_page_writeback(struct page *page)
764 {
765         struct address_space *mapping = page_mapping(page);
766         int ret;
767
768         if (mapping) {
769                 unsigned long flags;
770
771                 write_lock_irqsave(&mapping->tree_lock, flags);
772                 ret = TestClearPageWriteback(page);
773                 if (ret)
774                         radix_tree_tag_clear(&mapping->page_tree,
775                                                 page_index(page),
776                                                 PAGECACHE_TAG_WRITEBACK);
777                 write_unlock_irqrestore(&mapping->tree_lock, flags);
778         } else {
779                 ret = TestClearPageWriteback(page);
780         }
781         return ret;
782 }
783
784 int test_set_page_writeback(struct page *page)
785 {
786         struct address_space *mapping = page_mapping(page);
787         int ret;
788
789         if (mapping) {
790                 unsigned long flags;
791
792                 write_lock_irqsave(&mapping->tree_lock, flags);
793                 ret = TestSetPageWriteback(page);
794                 if (!ret)
795                         radix_tree_tag_set(&mapping->page_tree,
796                                                 page_index(page),
797                                                 PAGECACHE_TAG_WRITEBACK);
798                 if (!PageDirty(page))
799                         radix_tree_tag_clear(&mapping->page_tree,
800                                                 page_index(page),
801                                                 PAGECACHE_TAG_DIRTY);
802                 write_unlock_irqrestore(&mapping->tree_lock, flags);
803         } else {
804                 ret = TestSetPageWriteback(page);
805         }
806         return ret;
807
808 }
809 EXPORT_SYMBOL(test_set_page_writeback);
810
811 /*
812  * Return true if any of the pages in the mapping are marged with the
813  * passed tag.
814  */
815 int mapping_tagged(struct address_space *mapping, int tag)
816 {
817         unsigned long flags;
818         int ret;
819
820         read_lock_irqsave(&mapping->tree_lock, flags);
821         ret = radix_tree_tagged(&mapping->page_tree, tag);
822         read_unlock_irqrestore(&mapping->tree_lock, flags);
823         return ret;
824 }
825 EXPORT_SYMBOL(mapping_tagged);