029dfad5a235753fab2b7f81dda1950e770e9f2d
[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/task_io_accounting_ops.h>
25 #include <linux/blkdev.h>
26 #include <linux/mpage.h>
27 #include <linux/rmap.h>
28 #include <linux/percpu.h>
29 #include <linux/notifier.h>
30 #include <linux/smp.h>
31 #include <linux/sysctl.h>
32 #include <linux/cpu.h>
33 #include <linux/syscalls.h>
34 #include <linux/buffer_head.h>
35 #include <linux/pagevec.h>
36
37 /*
38  * The maximum number of pages to writeout in a single bdflush/kupdate
39  * operation.  We do this so we don't hold I_LOCK against an inode for
40  * enormous amounts of time, which would block a userspace task which has
41  * been forced to throttle against that inode.  Also, the code reevaluates
42  * the dirty each time it has written this many pages.
43  */
44 #define MAX_WRITEBACK_PAGES     1024
45
46 /*
47  * After a CPU has dirtied this many pages, balance_dirty_pages_ratelimited
48  * will look to see if it needs to force writeback or throttling.
49  */
50 static long ratelimit_pages = 32;
51
52 static int dirty_exceeded __cacheline_aligned_in_smp;   /* Dirty mem may be over limit */
53
54 /*
55  * When balance_dirty_pages decides that the caller needs to perform some
56  * non-background writeback, this is how many pages it will attempt to write.
57  * It should be somewhat larger than RATELIMIT_PAGES to ensure that reasonably
58  * large amounts of I/O are submitted.
59  */
60 static inline long sync_writeback_pages(void)
61 {
62         return ratelimit_pages + ratelimit_pages / 2;
63 }
64
65 /* The following parameters are exported via /proc/sys/vm */
66
67 /*
68  * Start background writeback (via pdflush) at this percentage
69  */
70 int dirty_background_ratio = 5;
71
72 /*
73  * The generator of dirty data starts writeback at this percentage
74  */
75 int vm_dirty_ratio = 10;
76
77 /*
78  * The interval between `kupdate'-style writebacks, in jiffies
79  */
80 int dirty_writeback_interval = 5 * HZ;
81
82 /*
83  * The longest number of jiffies for which data is allowed to remain dirty
84  */
85 int dirty_expire_interval = 30 * HZ;
86
87 /*
88  * Flag that makes the machine dump writes/reads and block dirtyings.
89  */
90 int block_dump;
91
92 /*
93  * Flag that puts the machine in "laptop mode". Doubles as a timeout in jiffies:
94  * a full sync is triggered after this time elapses without any disk activity.
95  */
96 int laptop_mode;
97
98 EXPORT_SYMBOL(laptop_mode);
99
100 /* End of sysctl-exported parameters */
101
102
103 static void background_writeout(unsigned long _min_pages);
104
105 /*
106  * Work out the current dirty-memory clamping and background writeout
107  * thresholds.
108  *
109  * The main aim here is to lower them aggressively if there is a lot of mapped
110  * memory around.  To avoid stressing page reclaim with lots of unreclaimable
111  * pages.  It is better to clamp down on writers than to start swapping, and
112  * performing lots of scanning.
113  *
114  * We only allow 1/2 of the currently-unmapped memory to be dirtied.
115  *
116  * We don't permit the clamping level to fall below 5% - that is getting rather
117  * excessive.
118  *
119  * We make sure that the background writeout level is below the adjusted
120  * clamping level.
121  */
122
123 static unsigned long highmem_dirtyable_memory(unsigned long total)
124 {
125 #ifdef CONFIG_HIGHMEM
126         int node;
127         unsigned long x = 0;
128
129         for_each_online_node(node) {
130                 struct zone *z =
131                         &NODE_DATA(node)->node_zones[ZONE_HIGHMEM];
132
133                 x += zone_page_state(z, NR_FREE_PAGES)
134                         + zone_page_state(z, NR_INACTIVE)
135                         + zone_page_state(z, NR_ACTIVE);
136         }
137         /*
138          * Make sure that the number of highmem pages is never larger
139          * than the number of the total dirtyable memory. This can only
140          * occur in very strange VM situations but we want to make sure
141          * that this does not occur.
142          */
143         return min(x, total);
144 #else
145         return 0;
146 #endif
147 }
148
149 static unsigned long determine_dirtyable_memory(void)
150 {
151         unsigned long x;
152
153         x = global_page_state(NR_FREE_PAGES)
154                 + global_page_state(NR_INACTIVE)
155                 + global_page_state(NR_ACTIVE);
156         x -= highmem_dirtyable_memory(x);
157         return x + 1;   /* Ensure that we never return 0 */
158 }
159
160 static void
161 get_dirty_limits(long *pbackground, long *pdirty,
162                                         struct address_space *mapping)
163 {
164         int background_ratio;           /* Percentages */
165         int dirty_ratio;
166         int unmapped_ratio;
167         long background;
168         long dirty;
169         unsigned long available_memory = determine_dirtyable_memory();
170         struct task_struct *tsk;
171
172         unmapped_ratio = 100 - ((global_page_state(NR_FILE_MAPPED) +
173                                 global_page_state(NR_ANON_PAGES)) * 100) /
174                                         available_memory;
175
176         dirty_ratio = vm_dirty_ratio;
177         if (dirty_ratio > unmapped_ratio / 2)
178                 dirty_ratio = unmapped_ratio / 2;
179
180         if (dirty_ratio < 5)
181                 dirty_ratio = 5;
182
183         background_ratio = dirty_background_ratio;
184         if (background_ratio >= dirty_ratio)
185                 background_ratio = dirty_ratio / 2;
186
187         background = (background_ratio * available_memory) / 100;
188         dirty = (dirty_ratio * available_memory) / 100;
189         tsk = current;
190         if (tsk->flags & PF_LESS_THROTTLE || rt_task(tsk)) {
191                 background += background / 4;
192                 dirty += dirty / 4;
193         }
194         *pbackground = background;
195         *pdirty = dirty;
196 }
197
198 /*
199  * balance_dirty_pages() must be called by processes which are generating dirty
200  * data.  It looks at the number of dirty pages in the machine and will force
201  * the caller to perform writeback if the system is over `vm_dirty_ratio'.
202  * If we're over `background_thresh' then pdflush is woken to perform some
203  * writeout.
204  */
205 static void balance_dirty_pages(struct address_space *mapping)
206 {
207         long nr_reclaimable;
208         long background_thresh;
209         long dirty_thresh;
210         unsigned long pages_written = 0;
211         unsigned long write_chunk = sync_writeback_pages();
212
213         struct backing_dev_info *bdi = mapping->backing_dev_info;
214
215         for (;;) {
216                 struct writeback_control wbc = {
217                         .bdi            = bdi,
218                         .sync_mode      = WB_SYNC_NONE,
219                         .older_than_this = NULL,
220                         .nr_to_write    = write_chunk,
221                         .range_cyclic   = 1,
222                 };
223
224                 get_dirty_limits(&background_thresh, &dirty_thresh, mapping);
225                 nr_reclaimable = global_page_state(NR_FILE_DIRTY) +
226                                         global_page_state(NR_UNSTABLE_NFS);
227                 if (nr_reclaimable + global_page_state(NR_WRITEBACK) <=
228                         dirty_thresh)
229                                 break;
230
231                 if (!dirty_exceeded)
232                         dirty_exceeded = 1;
233
234                 /* Note: nr_reclaimable denotes nr_dirty + nr_unstable.
235                  * Unstable writes are a feature of certain networked
236                  * filesystems (i.e. NFS) in which data may have been
237                  * written to the server's write cache, but has not yet
238                  * been flushed to permanent storage.
239                  */
240                 if (nr_reclaimable) {
241                         writeback_inodes(&wbc);
242                         get_dirty_limits(&background_thresh,
243                                                 &dirty_thresh, mapping);
244                         nr_reclaimable = global_page_state(NR_FILE_DIRTY) +
245                                         global_page_state(NR_UNSTABLE_NFS);
246                         if (nr_reclaimable +
247                                 global_page_state(NR_WRITEBACK)
248                                         <= dirty_thresh)
249                                                 break;
250                         pages_written += write_chunk - wbc.nr_to_write;
251                         if (pages_written >= write_chunk)
252                                 break;          /* We've done our duty */
253                 }
254                 congestion_wait(WRITE, HZ/10);
255         }
256
257         if (nr_reclaimable + global_page_state(NR_WRITEBACK)
258                 <= dirty_thresh && dirty_exceeded)
259                         dirty_exceeded = 0;
260
261         if (writeback_in_progress(bdi))
262                 return;         /* pdflush is already working this queue */
263
264         /*
265          * In laptop mode, we wait until hitting the higher threshold before
266          * starting background writeout, and then write out all the way down
267          * to the lower threshold.  So slow writers cause minimal disk activity.
268          *
269          * In normal mode, we start background writeout at the lower
270          * background_thresh, to keep the amount of dirty memory low.
271          */
272         if ((laptop_mode && pages_written) ||
273              (!laptop_mode && (nr_reclaimable > background_thresh)))
274                 pdflush_operation(background_writeout, 0);
275 }
276
277 void set_page_dirty_balance(struct page *page)
278 {
279         if (set_page_dirty(page)) {
280                 struct address_space *mapping = page_mapping(page);
281
282                 if (mapping)
283                         balance_dirty_pages_ratelimited(mapping);
284         }
285 }
286
287 /**
288  * balance_dirty_pages_ratelimited_nr - balance dirty memory state
289  * @mapping: address_space which was dirtied
290  * @nr_pages_dirtied: number of pages which the caller has just dirtied
291  *
292  * Processes which are dirtying memory should call in here once for each page
293  * which was newly dirtied.  The function will periodically check the system's
294  * dirty state and will initiate writeback if needed.
295  *
296  * On really big machines, get_writeback_state is expensive, so try to avoid
297  * calling it too often (ratelimiting).  But once we're over the dirty memory
298  * limit we decrease the ratelimiting by a lot, to prevent individual processes
299  * from overshooting the limit by (ratelimit_pages) each.
300  */
301 void balance_dirty_pages_ratelimited_nr(struct address_space *mapping,
302                                         unsigned long nr_pages_dirtied)
303 {
304         static DEFINE_PER_CPU(unsigned long, ratelimits) = 0;
305         unsigned long ratelimit;
306         unsigned long *p;
307
308         ratelimit = ratelimit_pages;
309         if (dirty_exceeded)
310                 ratelimit = 8;
311
312         /*
313          * Check the rate limiting. Also, we do not want to throttle real-time
314          * tasks in balance_dirty_pages(). Period.
315          */
316         preempt_disable();
317         p =  &__get_cpu_var(ratelimits);
318         *p += nr_pages_dirtied;
319         if (unlikely(*p >= ratelimit)) {
320                 *p = 0;
321                 preempt_enable();
322                 balance_dirty_pages(mapping);
323                 return;
324         }
325         preempt_enable();
326 }
327 EXPORT_SYMBOL(balance_dirty_pages_ratelimited_nr);
328
329 void throttle_vm_writeout(gfp_t gfp_mask)
330 {
331         long background_thresh;
332         long dirty_thresh;
333
334         if ((gfp_mask & (__GFP_FS|__GFP_IO)) != (__GFP_FS|__GFP_IO)) {
335                 /*
336                  * The caller might hold locks which can prevent IO completion
337                  * or progress in the filesystem.  So we cannot just sit here
338                  * waiting for IO to complete.
339                  */
340                 congestion_wait(WRITE, HZ/10);
341                 return;
342         }
343
344         for ( ; ; ) {
345                 get_dirty_limits(&background_thresh, &dirty_thresh, NULL);
346
347                 /*
348                  * Boost the allowable dirty threshold a bit for page
349                  * allocators so they don't get DoS'ed by heavy writers
350                  */
351                 dirty_thresh += dirty_thresh / 10;      /* wheeee... */
352
353                 if (global_page_state(NR_UNSTABLE_NFS) +
354                         global_page_state(NR_WRITEBACK) <= dirty_thresh)
355                                 break;
356                 congestion_wait(WRITE, HZ/10);
357         }
358 }
359
360 /*
361  * writeback at least _min_pages, and keep writing until the amount of dirty
362  * memory is less than the background threshold, or until we're all clean.
363  */
364 static void background_writeout(unsigned long _min_pages)
365 {
366         long min_pages = _min_pages;
367         struct writeback_control wbc = {
368                 .bdi            = NULL,
369                 .sync_mode      = WB_SYNC_NONE,
370                 .older_than_this = NULL,
371                 .nr_to_write    = 0,
372                 .nonblocking    = 1,
373                 .range_cyclic   = 1,
374         };
375
376         for ( ; ; ) {
377                 long background_thresh;
378                 long dirty_thresh;
379
380                 get_dirty_limits(&background_thresh, &dirty_thresh, NULL);
381                 if (global_page_state(NR_FILE_DIRTY) +
382                         global_page_state(NR_UNSTABLE_NFS) < background_thresh
383                                 && min_pages <= 0)
384                         break;
385                 wbc.encountered_congestion = 0;
386                 wbc.nr_to_write = MAX_WRITEBACK_PAGES;
387                 wbc.pages_skipped = 0;
388                 writeback_inodes(&wbc);
389                 min_pages -= MAX_WRITEBACK_PAGES - wbc.nr_to_write;
390                 if (wbc.nr_to_write > 0 || wbc.pages_skipped > 0) {
391                         /* Wrote less than expected */
392                         congestion_wait(WRITE, HZ/10);
393                         if (!wbc.encountered_congestion)
394                                 break;
395                 }
396         }
397 }
398
399 /*
400  * Start writeback of `nr_pages' pages.  If `nr_pages' is zero, write back
401  * the whole world.  Returns 0 if a pdflush thread was dispatched.  Returns
402  * -1 if all pdflush threads were busy.
403  */
404 int wakeup_pdflush(long nr_pages)
405 {
406         if (nr_pages == 0)
407                 nr_pages = global_page_state(NR_FILE_DIRTY) +
408                                 global_page_state(NR_UNSTABLE_NFS);
409         return pdflush_operation(background_writeout, nr_pages);
410 }
411
412 static void wb_timer_fn(unsigned long unused);
413 static void laptop_timer_fn(unsigned long unused);
414
415 static DEFINE_TIMER(wb_timer, wb_timer_fn, 0, 0);
416 static DEFINE_TIMER(laptop_mode_wb_timer, laptop_timer_fn, 0, 0);
417
418 /*
419  * Periodic writeback of "old" data.
420  *
421  * Define "old": the first time one of an inode's pages is dirtied, we mark the
422  * dirtying-time in the inode's address_space.  So this periodic writeback code
423  * just walks the superblock inode list, writing back any inodes which are
424  * older than a specific point in time.
425  *
426  * Try to run once per dirty_writeback_interval.  But if a writeback event
427  * takes longer than a dirty_writeback_interval interval, then leave a
428  * one-second gap.
429  *
430  * older_than_this takes precedence over nr_to_write.  So we'll only write back
431  * all dirty pages if they are all attached to "old" mappings.
432  */
433 static void wb_kupdate(unsigned long arg)
434 {
435         unsigned long oldest_jif;
436         unsigned long start_jif;
437         unsigned long next_jif;
438         long nr_to_write;
439         struct writeback_control wbc = {
440                 .bdi            = NULL,
441                 .sync_mode      = WB_SYNC_NONE,
442                 .older_than_this = &oldest_jif,
443                 .nr_to_write    = 0,
444                 .nonblocking    = 1,
445                 .for_kupdate    = 1,
446                 .range_cyclic   = 1,
447         };
448
449         sync_supers();
450
451         oldest_jif = jiffies - dirty_expire_interval;
452         start_jif = jiffies;
453         next_jif = start_jif + dirty_writeback_interval;
454         nr_to_write = global_page_state(NR_FILE_DIRTY) +
455                         global_page_state(NR_UNSTABLE_NFS) +
456                         (inodes_stat.nr_inodes - inodes_stat.nr_unused);
457         while (nr_to_write > 0) {
458                 wbc.encountered_congestion = 0;
459                 wbc.nr_to_write = MAX_WRITEBACK_PAGES;
460                 writeback_inodes(&wbc);
461                 if (wbc.nr_to_write > 0) {
462                         if (wbc.encountered_congestion)
463                                 congestion_wait(WRITE, HZ/10);
464                         else
465                                 break;  /* All the old data is written */
466                 }
467                 nr_to_write -= MAX_WRITEBACK_PAGES - wbc.nr_to_write;
468         }
469         if (time_before(next_jif, jiffies + HZ))
470                 next_jif = jiffies + HZ;
471         if (dirty_writeback_interval)
472                 mod_timer(&wb_timer, next_jif);
473 }
474
475 /*
476  * sysctl handler for /proc/sys/vm/dirty_writeback_centisecs
477  */
478 int dirty_writeback_centisecs_handler(ctl_table *table, int write,
479                 struct file *file, void __user *buffer, size_t *length, loff_t *ppos)
480 {
481         proc_dointvec_userhz_jiffies(table, write, file, buffer, length, ppos);
482         if (dirty_writeback_interval) {
483                 mod_timer(&wb_timer,
484                         jiffies + dirty_writeback_interval);
485                 } else {
486                 del_timer(&wb_timer);
487         }
488         return 0;
489 }
490
491 static void wb_timer_fn(unsigned long unused)
492 {
493         if (pdflush_operation(wb_kupdate, 0) < 0)
494                 mod_timer(&wb_timer, jiffies + HZ); /* delay 1 second */
495 }
496
497 static void laptop_flush(unsigned long unused)
498 {
499         sys_sync();
500 }
501
502 static void laptop_timer_fn(unsigned long unused)
503 {
504         pdflush_operation(laptop_flush, 0);
505 }
506
507 /*
508  * We've spun up the disk and we're in laptop mode: schedule writeback
509  * of all dirty data a few seconds from now.  If the flush is already scheduled
510  * then push it back - the user is still using the disk.
511  */
512 void laptop_io_completion(void)
513 {
514         mod_timer(&laptop_mode_wb_timer, jiffies + laptop_mode);
515 }
516
517 /*
518  * We're in laptop mode and we've just synced. The sync's writes will have
519  * caused another writeback to be scheduled by laptop_io_completion.
520  * Nothing needs to be written back anymore, so we unschedule the writeback.
521  */
522 void laptop_sync_completion(void)
523 {
524         del_timer(&laptop_mode_wb_timer);
525 }
526
527 /*
528  * If ratelimit_pages is too high then we can get into dirty-data overload
529  * if a large number of processes all perform writes at the same time.
530  * If it is too low then SMP machines will call the (expensive)
531  * get_writeback_state too often.
532  *
533  * Here we set ratelimit_pages to a level which ensures that when all CPUs are
534  * dirtying in parallel, we cannot go more than 3% (1/32) over the dirty memory
535  * thresholds before writeback cuts in.
536  *
537  * But the limit should not be set too high.  Because it also controls the
538  * amount of memory which the balance_dirty_pages() caller has to write back.
539  * If this is too large then the caller will block on the IO queue all the
540  * time.  So limit it to four megabytes - the balance_dirty_pages() caller
541  * will write six megabyte chunks, max.
542  */
543
544 void writeback_set_ratelimit(void)
545 {
546         ratelimit_pages = vm_total_pages / (num_online_cpus() * 32);
547         if (ratelimit_pages < 16)
548                 ratelimit_pages = 16;
549         if (ratelimit_pages * PAGE_CACHE_SIZE > 4096 * 1024)
550                 ratelimit_pages = (4096 * 1024) / PAGE_CACHE_SIZE;
551 }
552
553 static int __cpuinit
554 ratelimit_handler(struct notifier_block *self, unsigned long u, void *v)
555 {
556         writeback_set_ratelimit();
557         return NOTIFY_DONE;
558 }
559
560 static struct notifier_block __cpuinitdata ratelimit_nb = {
561         .notifier_call  = ratelimit_handler,
562         .next           = NULL,
563 };
564
565 /*
566  * Called early on to tune the page writeback dirty limits.
567  *
568  * We used to scale dirty pages according to how total memory
569  * related to pages that could be allocated for buffers (by
570  * comparing nr_free_buffer_pages() to vm_total_pages.
571  *
572  * However, that was when we used "dirty_ratio" to scale with
573  * all memory, and we don't do that any more. "dirty_ratio"
574  * is now applied to total non-HIGHPAGE memory (by subtracting
575  * totalhigh_pages from vm_total_pages), and as such we can't
576  * get into the old insane situation any more where we had
577  * large amounts of dirty pages compared to a small amount of
578  * non-HIGHMEM memory.
579  *
580  * But we might still want to scale the dirty_ratio by how
581  * much memory the box has..
582  */
583 void __init page_writeback_init(void)
584 {
585         mod_timer(&wb_timer, jiffies + dirty_writeback_interval);
586         writeback_set_ratelimit();
587         register_cpu_notifier(&ratelimit_nb);
588 }
589
590 /**
591  * generic_writepages - walk the list of dirty pages of the given address space and writepage() all of them.
592  * @mapping: address space structure to write
593  * @wbc: subtract the number of written pages from *@wbc->nr_to_write
594  *
595  * This is a library function, which implements the writepages()
596  * address_space_operation.
597  *
598  * If a page is already under I/O, generic_writepages() skips it, even
599  * if it's dirty.  This is desirable behaviour for memory-cleaning writeback,
600  * but it is INCORRECT for data-integrity system calls such as fsync().  fsync()
601  * and msync() need to guarantee that all the data which was dirty at the time
602  * the call was made get new I/O started against them.  If wbc->sync_mode is
603  * WB_SYNC_ALL then we were called for data integrity and we must wait for
604  * existing IO to complete.
605  *
606  * Derived from mpage_writepages() - if you fix this you should check that
607  * also!
608  */
609 int generic_writepages(struct address_space *mapping,
610                        struct writeback_control *wbc)
611 {
612         struct backing_dev_info *bdi = mapping->backing_dev_info;
613         int ret = 0;
614         int done = 0;
615         int (*writepage)(struct page *page, struct writeback_control *wbc);
616         struct pagevec pvec;
617         int nr_pages;
618         pgoff_t index;
619         pgoff_t end;            /* Inclusive */
620         int scanned = 0;
621         int range_whole = 0;
622
623         if (wbc->nonblocking && bdi_write_congested(bdi)) {
624                 wbc->encountered_congestion = 1;
625                 return 0;
626         }
627
628         writepage = mapping->a_ops->writepage;
629
630         /* deal with chardevs and other special file */
631         if (!writepage)
632                 return 0;
633
634         pagevec_init(&pvec, 0);
635         if (wbc->range_cyclic) {
636                 index = mapping->writeback_index; /* Start from prev offset */
637                 end = -1;
638         } else {
639                 index = wbc->range_start >> PAGE_CACHE_SHIFT;
640                 end = wbc->range_end >> PAGE_CACHE_SHIFT;
641                 if (wbc->range_start == 0 && wbc->range_end == LLONG_MAX)
642                         range_whole = 1;
643                 scanned = 1;
644         }
645 retry:
646         while (!done && (index <= end) &&
647                (nr_pages = pagevec_lookup_tag(&pvec, mapping, &index,
648                                               PAGECACHE_TAG_DIRTY,
649                                               min(end - index, (pgoff_t)PAGEVEC_SIZE-1) + 1))) {
650                 unsigned i;
651
652                 scanned = 1;
653                 for (i = 0; i < nr_pages; i++) {
654                         struct page *page = pvec.pages[i];
655
656                         /*
657                          * At this point we hold neither mapping->tree_lock nor
658                          * lock on the page itself: the page may be truncated or
659                          * invalidated (changing page->mapping to NULL), or even
660                          * swizzled back from swapper_space to tmpfs file
661                          * mapping
662                          */
663                         lock_page(page);
664
665                         if (unlikely(page->mapping != mapping)) {
666                                 unlock_page(page);
667                                 continue;
668                         }
669
670                         if (!wbc->range_cyclic && page->index > end) {
671                                 done = 1;
672                                 unlock_page(page);
673                                 continue;
674                         }
675
676                         if (wbc->sync_mode != WB_SYNC_NONE)
677                                 wait_on_page_writeback(page);
678
679                         if (PageWriteback(page) ||
680                             !clear_page_dirty_for_io(page)) {
681                                 unlock_page(page);
682                                 continue;
683                         }
684
685                         ret = (*writepage)(page, wbc);
686                         if (ret) {
687                                 if (ret == -ENOSPC)
688                                         set_bit(AS_ENOSPC, &mapping->flags);
689                                 else
690                                         set_bit(AS_EIO, &mapping->flags);
691                         }
692
693                         if (unlikely(ret == AOP_WRITEPAGE_ACTIVATE))
694                                 unlock_page(page);
695                         if (ret || (--(wbc->nr_to_write) <= 0))
696                                 done = 1;
697                         if (wbc->nonblocking && bdi_write_congested(bdi)) {
698                                 wbc->encountered_congestion = 1;
699                                 done = 1;
700                         }
701                 }
702                 pagevec_release(&pvec);
703                 cond_resched();
704         }
705         if (!scanned && !done) {
706                 /*
707                  * We hit the last page and there is more work to be done: wrap
708                  * back to the start of the file
709                  */
710                 scanned = 1;
711                 index = 0;
712                 goto retry;
713         }
714         if (wbc->range_cyclic || (range_whole && wbc->nr_to_write > 0))
715                 mapping->writeback_index = index;
716         return ret;
717 }
718
719 EXPORT_SYMBOL(generic_writepages);
720
721 int do_writepages(struct address_space *mapping, struct writeback_control *wbc)
722 {
723         int ret;
724
725         if (wbc->nr_to_write <= 0)
726                 return 0;
727         wbc->for_writepages = 1;
728         if (mapping->a_ops->writepages)
729                 ret = mapping->a_ops->writepages(mapping, wbc);
730         else
731                 ret = generic_writepages(mapping, wbc);
732         wbc->for_writepages = 0;
733         return ret;
734 }
735
736 /**
737  * write_one_page - write out a single page and optionally wait on I/O
738  * @page: the page to write
739  * @wait: if true, wait on writeout
740  *
741  * The page must be locked by the caller and will be unlocked upon return.
742  *
743  * write_one_page() returns a negative error code if I/O failed.
744  */
745 int write_one_page(struct page *page, int wait)
746 {
747         struct address_space *mapping = page->mapping;
748         int ret = 0;
749         struct writeback_control wbc = {
750                 .sync_mode = WB_SYNC_ALL,
751                 .nr_to_write = 1,
752         };
753
754         BUG_ON(!PageLocked(page));
755
756         if (wait)
757                 wait_on_page_writeback(page);
758
759         if (clear_page_dirty_for_io(page)) {
760                 page_cache_get(page);
761                 ret = mapping->a_ops->writepage(page, &wbc);
762                 if (ret == 0 && wait) {
763                         wait_on_page_writeback(page);
764                         if (PageError(page))
765                                 ret = -EIO;
766                 }
767                 page_cache_release(page);
768         } else {
769                 unlock_page(page);
770         }
771         return ret;
772 }
773 EXPORT_SYMBOL(write_one_page);
774
775 /*
776  * For address_spaces which do not use buffers nor write back.
777  */
778 int __set_page_dirty_no_writeback(struct page *page)
779 {
780         if (!PageDirty(page))
781                 SetPageDirty(page);
782         return 0;
783 }
784
785 /*
786  * For address_spaces which do not use buffers.  Just tag the page as dirty in
787  * its radix tree.
788  *
789  * This is also used when a single buffer is being dirtied: we want to set the
790  * page dirty in that case, but not all the buffers.  This is a "bottom-up"
791  * dirtying, whereas __set_page_dirty_buffers() is a "top-down" dirtying.
792  *
793  * Most callers have locked the page, which pins the address_space in memory.
794  * But zap_pte_range() does not lock the page, however in that case the
795  * mapping is pinned by the vma's ->vm_file reference.
796  *
797  * We take care to handle the case where the page was truncated from the
798  * mapping by re-checking page_mapping() insode tree_lock.
799  */
800 int __set_page_dirty_nobuffers(struct page *page)
801 {
802         if (!TestSetPageDirty(page)) {
803                 struct address_space *mapping = page_mapping(page);
804                 struct address_space *mapping2;
805
806                 if (!mapping)
807                         return 1;
808
809                 write_lock_irq(&mapping->tree_lock);
810                 mapping2 = page_mapping(page);
811                 if (mapping2) { /* Race with truncate? */
812                         BUG_ON(mapping2 != mapping);
813                         if (mapping_cap_account_dirty(mapping)) {
814                                 __inc_zone_page_state(page, NR_FILE_DIRTY);
815                                 task_io_account_write(PAGE_CACHE_SIZE);
816                         }
817                         radix_tree_tag_set(&mapping->page_tree,
818                                 page_index(page), PAGECACHE_TAG_DIRTY);
819                 }
820                 write_unlock_irq(&mapping->tree_lock);
821                 if (mapping->host) {
822                         /* !PageAnon && !swapper_space */
823                         __mark_inode_dirty(mapping->host, I_DIRTY_PAGES);
824                 }
825                 return 1;
826         }
827         return 0;
828 }
829 EXPORT_SYMBOL(__set_page_dirty_nobuffers);
830
831 /*
832  * When a writepage implementation decides that it doesn't want to write this
833  * page for some reason, it should redirty the locked page via
834  * redirty_page_for_writepage() and it should then unlock the page and return 0
835  */
836 int redirty_page_for_writepage(struct writeback_control *wbc, struct page *page)
837 {
838         wbc->pages_skipped++;
839         return __set_page_dirty_nobuffers(page);
840 }
841 EXPORT_SYMBOL(redirty_page_for_writepage);
842
843 /*
844  * If the mapping doesn't provide a set_page_dirty a_op, then
845  * just fall through and assume that it wants buffer_heads.
846  */
847 int fastcall set_page_dirty(struct page *page)
848 {
849         struct address_space *mapping = page_mapping(page);
850
851         if (likely(mapping)) {
852                 int (*spd)(struct page *) = mapping->a_ops->set_page_dirty;
853 #ifdef CONFIG_BLOCK
854                 if (!spd)
855                         spd = __set_page_dirty_buffers;
856 #endif
857                 return (*spd)(page);
858         }
859         if (!PageDirty(page)) {
860                 if (!TestSetPageDirty(page))
861                         return 1;
862         }
863         return 0;
864 }
865 EXPORT_SYMBOL(set_page_dirty);
866
867 /*
868  * set_page_dirty() is racy if the caller has no reference against
869  * page->mapping->host, and if the page is unlocked.  This is because another
870  * CPU could truncate the page off the mapping and then free the mapping.
871  *
872  * Usually, the page _is_ locked, or the caller is a user-space process which
873  * holds a reference on the inode by having an open file.
874  *
875  * In other cases, the page should be locked before running set_page_dirty().
876  */
877 int set_page_dirty_lock(struct page *page)
878 {
879         int ret;
880
881         lock_page_nosync(page);
882         ret = set_page_dirty(page);
883         unlock_page(page);
884         return ret;
885 }
886 EXPORT_SYMBOL(set_page_dirty_lock);
887
888 /*
889  * Clear a page's dirty flag, while caring for dirty memory accounting.
890  * Returns true if the page was previously dirty.
891  *
892  * This is for preparing to put the page under writeout.  We leave the page
893  * tagged as dirty in the radix tree so that a concurrent write-for-sync
894  * can discover it via a PAGECACHE_TAG_DIRTY walk.  The ->writepage
895  * implementation will run either set_page_writeback() or set_page_dirty(),
896  * at which stage we bring the page's dirty flag and radix-tree dirty tag
897  * back into sync.
898  *
899  * This incoherency between the page's dirty flag and radix-tree tag is
900  * unfortunate, but it only exists while the page is locked.
901  */
902 int clear_page_dirty_for_io(struct page *page)
903 {
904         struct address_space *mapping = page_mapping(page);
905
906         if (mapping && mapping_cap_account_dirty(mapping)) {
907                 /*
908                  * Yes, Virginia, this is indeed insane.
909                  *
910                  * We use this sequence to make sure that
911                  *  (a) we account for dirty stats properly
912                  *  (b) we tell the low-level filesystem to
913                  *      mark the whole page dirty if it was
914                  *      dirty in a pagetable. Only to then
915                  *  (c) clean the page again and return 1 to
916                  *      cause the writeback.
917                  *
918                  * This way we avoid all nasty races with the
919                  * dirty bit in multiple places and clearing
920                  * them concurrently from different threads.
921                  *
922                  * Note! Normally the "set_page_dirty(page)"
923                  * has no effect on the actual dirty bit - since
924                  * that will already usually be set. But we
925                  * need the side effects, and it can help us
926                  * avoid races.
927                  *
928                  * We basically use the page "master dirty bit"
929                  * as a serialization point for all the different
930                  * threads doing their things.
931                  *
932                  * FIXME! We still have a race here: if somebody
933                  * adds the page back to the page tables in
934                  * between the "page_mkclean()" and the "TestClearPageDirty()",
935                  * we might have it mapped without the dirty bit set.
936                  */
937                 if (page_mkclean(page))
938                         set_page_dirty(page);
939                 if (TestClearPageDirty(page)) {
940                         dec_zone_page_state(page, NR_FILE_DIRTY);
941                         return 1;
942                 }
943                 return 0;
944         }
945         return TestClearPageDirty(page);
946 }
947 EXPORT_SYMBOL(clear_page_dirty_for_io);
948
949 int test_clear_page_writeback(struct page *page)
950 {
951         struct address_space *mapping = page_mapping(page);
952         int ret;
953
954         if (mapping) {
955                 unsigned long flags;
956
957                 write_lock_irqsave(&mapping->tree_lock, flags);
958                 ret = TestClearPageWriteback(page);
959                 if (ret)
960                         radix_tree_tag_clear(&mapping->page_tree,
961                                                 page_index(page),
962                                                 PAGECACHE_TAG_WRITEBACK);
963                 write_unlock_irqrestore(&mapping->tree_lock, flags);
964         } else {
965                 ret = TestClearPageWriteback(page);
966         }
967         return ret;
968 }
969
970 int test_set_page_writeback(struct page *page)
971 {
972         struct address_space *mapping = page_mapping(page);
973         int ret;
974
975         if (mapping) {
976                 unsigned long flags;
977
978                 write_lock_irqsave(&mapping->tree_lock, flags);
979                 ret = TestSetPageWriteback(page);
980                 if (!ret)
981                         radix_tree_tag_set(&mapping->page_tree,
982                                                 page_index(page),
983                                                 PAGECACHE_TAG_WRITEBACK);
984                 if (!PageDirty(page))
985                         radix_tree_tag_clear(&mapping->page_tree,
986                                                 page_index(page),
987                                                 PAGECACHE_TAG_DIRTY);
988                 write_unlock_irqrestore(&mapping->tree_lock, flags);
989         } else {
990                 ret = TestSetPageWriteback(page);
991         }
992         return ret;
993
994 }
995 EXPORT_SYMBOL(test_set_page_writeback);
996
997 /*
998  * Return true if any of the pages in the mapping are marged with the
999  * passed tag.
1000  */
1001 int mapping_tagged(struct address_space *mapping, int tag)
1002 {
1003         unsigned long flags;
1004         int ret;
1005
1006         read_lock_irqsave(&mapping->tree_lock, flags);
1007         ret = radix_tree_tagged(&mapping->page_tree, tag);
1008         read_unlock_irqrestore(&mapping->tree_lock, flags);
1009         return ret;
1010 }
1011 EXPORT_SYMBOL(mapping_tagged);