[PATCH] rt2x00: Make *_beacon_update static
[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/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, int page_mkwrite)
278 {
279         if (set_page_dirty(page) || page_mkwrite) {
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, jiffies + dirty_writeback_interval);
484         else
485                 del_timer(&wb_timer);
486         return 0;
487 }
488
489 static void wb_timer_fn(unsigned long unused)
490 {
491         if (pdflush_operation(wb_kupdate, 0) < 0)
492                 mod_timer(&wb_timer, jiffies + HZ); /* delay 1 second */
493 }
494
495 static void laptop_flush(unsigned long unused)
496 {
497         sys_sync();
498 }
499
500 static void laptop_timer_fn(unsigned long unused)
501 {
502         pdflush_operation(laptop_flush, 0);
503 }
504
505 /*
506  * We've spun up the disk and we're in laptop mode: schedule writeback
507  * of all dirty data a few seconds from now.  If the flush is already scheduled
508  * then push it back - the user is still using the disk.
509  */
510 void laptop_io_completion(void)
511 {
512         mod_timer(&laptop_mode_wb_timer, jiffies + laptop_mode);
513 }
514
515 /*
516  * We're in laptop mode and we've just synced. The sync's writes will have
517  * caused another writeback to be scheduled by laptop_io_completion.
518  * Nothing needs to be written back anymore, so we unschedule the writeback.
519  */
520 void laptop_sync_completion(void)
521 {
522         del_timer(&laptop_mode_wb_timer);
523 }
524
525 /*
526  * If ratelimit_pages is too high then we can get into dirty-data overload
527  * if a large number of processes all perform writes at the same time.
528  * If it is too low then SMP machines will call the (expensive)
529  * get_writeback_state too often.
530  *
531  * Here we set ratelimit_pages to a level which ensures that when all CPUs are
532  * dirtying in parallel, we cannot go more than 3% (1/32) over the dirty memory
533  * thresholds before writeback cuts in.
534  *
535  * But the limit should not be set too high.  Because it also controls the
536  * amount of memory which the balance_dirty_pages() caller has to write back.
537  * If this is too large then the caller will block on the IO queue all the
538  * time.  So limit it to four megabytes - the balance_dirty_pages() caller
539  * will write six megabyte chunks, max.
540  */
541
542 void writeback_set_ratelimit(void)
543 {
544         ratelimit_pages = vm_total_pages / (num_online_cpus() * 32);
545         if (ratelimit_pages < 16)
546                 ratelimit_pages = 16;
547         if (ratelimit_pages * PAGE_CACHE_SIZE > 4096 * 1024)
548                 ratelimit_pages = (4096 * 1024) / PAGE_CACHE_SIZE;
549 }
550
551 static int __cpuinit
552 ratelimit_handler(struct notifier_block *self, unsigned long u, void *v)
553 {
554         writeback_set_ratelimit();
555         return NOTIFY_DONE;
556 }
557
558 static struct notifier_block __cpuinitdata ratelimit_nb = {
559         .notifier_call  = ratelimit_handler,
560         .next           = NULL,
561 };
562
563 /*
564  * Called early on to tune the page writeback dirty limits.
565  *
566  * We used to scale dirty pages according to how total memory
567  * related to pages that could be allocated for buffers (by
568  * comparing nr_free_buffer_pages() to vm_total_pages.
569  *
570  * However, that was when we used "dirty_ratio" to scale with
571  * all memory, and we don't do that any more. "dirty_ratio"
572  * is now applied to total non-HIGHPAGE memory (by subtracting
573  * totalhigh_pages from vm_total_pages), and as such we can't
574  * get into the old insane situation any more where we had
575  * large amounts of dirty pages compared to a small amount of
576  * non-HIGHMEM memory.
577  *
578  * But we might still want to scale the dirty_ratio by how
579  * much memory the box has..
580  */
581 void __init page_writeback_init(void)
582 {
583         mod_timer(&wb_timer, jiffies + dirty_writeback_interval);
584         writeback_set_ratelimit();
585         register_cpu_notifier(&ratelimit_nb);
586 }
587
588 /**
589  * write_cache_pages - walk the list of dirty pages of the given address space and write all of them.
590  * @mapping: address space structure to write
591  * @wbc: subtract the number of written pages from *@wbc->nr_to_write
592  * @writepage: function called for each page
593  * @data: data passed to writepage function
594  *
595  * If a page is already under I/O, write_cache_pages() skips it, even
596  * if it's dirty.  This is desirable behaviour for memory-cleaning writeback,
597  * but it is INCORRECT for data-integrity system calls such as fsync().  fsync()
598  * and msync() need to guarantee that all the data which was dirty at the time
599  * the call was made get new I/O started against them.  If wbc->sync_mode is
600  * WB_SYNC_ALL then we were called for data integrity and we must wait for
601  * existing IO to complete.
602  */
603 int write_cache_pages(struct address_space *mapping,
604                       struct writeback_control *wbc, writepage_t writepage,
605                       void *data)
606 {
607         struct backing_dev_info *bdi = mapping->backing_dev_info;
608         int ret = 0;
609         int done = 0;
610         struct pagevec pvec;
611         int nr_pages;
612         pgoff_t index;
613         pgoff_t end;            /* Inclusive */
614         int scanned = 0;
615         int range_whole = 0;
616
617         if (wbc->nonblocking && bdi_write_congested(bdi)) {
618                 wbc->encountered_congestion = 1;
619                 return 0;
620         }
621
622         pagevec_init(&pvec, 0);
623         if (wbc->range_cyclic) {
624                 index = mapping->writeback_index; /* Start from prev offset */
625                 end = -1;
626         } else {
627                 index = wbc->range_start >> PAGE_CACHE_SHIFT;
628                 end = wbc->range_end >> PAGE_CACHE_SHIFT;
629                 if (wbc->range_start == 0 && wbc->range_end == LLONG_MAX)
630                         range_whole = 1;
631                 scanned = 1;
632         }
633 retry:
634         while (!done && (index <= end) &&
635                (nr_pages = pagevec_lookup_tag(&pvec, mapping, &index,
636                                               PAGECACHE_TAG_DIRTY,
637                                               min(end - index, (pgoff_t)PAGEVEC_SIZE-1) + 1))) {
638                 unsigned i;
639
640                 scanned = 1;
641                 for (i = 0; i < nr_pages; i++) {
642                         struct page *page = pvec.pages[i];
643
644                         /*
645                          * At this point we hold neither mapping->tree_lock nor
646                          * lock on the page itself: the page may be truncated or
647                          * invalidated (changing page->mapping to NULL), or even
648                          * swizzled back from swapper_space to tmpfs file
649                          * mapping
650                          */
651                         lock_page(page);
652
653                         if (unlikely(page->mapping != mapping)) {
654                                 unlock_page(page);
655                                 continue;
656                         }
657
658                         if (!wbc->range_cyclic && page->index > end) {
659                                 done = 1;
660                                 unlock_page(page);
661                                 continue;
662                         }
663
664                         if (wbc->sync_mode != WB_SYNC_NONE)
665                                 wait_on_page_writeback(page);
666
667                         if (PageWriteback(page) ||
668                             !clear_page_dirty_for_io(page)) {
669                                 unlock_page(page);
670                                 continue;
671                         }
672
673                         ret = (*writepage)(page, wbc, data);
674
675                         if (unlikely(ret == AOP_WRITEPAGE_ACTIVATE))
676                                 unlock_page(page);
677                         if (ret || (--(wbc->nr_to_write) <= 0))
678                                 done = 1;
679                         if (wbc->nonblocking && bdi_write_congested(bdi)) {
680                                 wbc->encountered_congestion = 1;
681                                 done = 1;
682                         }
683                 }
684                 pagevec_release(&pvec);
685                 cond_resched();
686         }
687         if (!scanned && !done) {
688                 /*
689                  * We hit the last page and there is more work to be done: wrap
690                  * back to the start of the file
691                  */
692                 scanned = 1;
693                 index = 0;
694                 goto retry;
695         }
696         if (wbc->range_cyclic || (range_whole && wbc->nr_to_write > 0))
697                 mapping->writeback_index = index;
698         return ret;
699 }
700 EXPORT_SYMBOL(write_cache_pages);
701
702 /*
703  * Function used by generic_writepages to call the real writepage
704  * function and set the mapping flags on error
705  */
706 static int __writepage(struct page *page, struct writeback_control *wbc,
707                        void *data)
708 {
709         struct address_space *mapping = data;
710         int ret = mapping->a_ops->writepage(page, wbc);
711         mapping_set_error(mapping, ret);
712         return ret;
713 }
714
715 /**
716  * generic_writepages - walk the list of dirty pages of the given address space and writepage() all of them.
717  * @mapping: address space structure to write
718  * @wbc: subtract the number of written pages from *@wbc->nr_to_write
719  *
720  * This is a library function, which implements the writepages()
721  * address_space_operation.
722  */
723 int generic_writepages(struct address_space *mapping,
724                        struct writeback_control *wbc)
725 {
726         /* deal with chardevs and other special file */
727         if (!mapping->a_ops->writepage)
728                 return 0;
729
730         return write_cache_pages(mapping, wbc, __writepage, mapping);
731 }
732
733 EXPORT_SYMBOL(generic_writepages);
734
735 int do_writepages(struct address_space *mapping, struct writeback_control *wbc)
736 {
737         int ret;
738
739         if (wbc->nr_to_write <= 0)
740                 return 0;
741         wbc->for_writepages = 1;
742         if (mapping->a_ops->writepages)
743                 ret = mapping->a_ops->writepages(mapping, wbc);
744         else
745                 ret = generic_writepages(mapping, wbc);
746         wbc->for_writepages = 0;
747         return ret;
748 }
749
750 /**
751  * write_one_page - write out a single page and optionally wait on I/O
752  * @page: the page to write
753  * @wait: if true, wait on writeout
754  *
755  * The page must be locked by the caller and will be unlocked upon return.
756  *
757  * write_one_page() returns a negative error code if I/O failed.
758  */
759 int write_one_page(struct page *page, int wait)
760 {
761         struct address_space *mapping = page->mapping;
762         int ret = 0;
763         struct writeback_control wbc = {
764                 .sync_mode = WB_SYNC_ALL,
765                 .nr_to_write = 1,
766         };
767
768         BUG_ON(!PageLocked(page));
769
770         if (wait)
771                 wait_on_page_writeback(page);
772
773         if (clear_page_dirty_for_io(page)) {
774                 page_cache_get(page);
775                 ret = mapping->a_ops->writepage(page, &wbc);
776                 if (ret == 0 && wait) {
777                         wait_on_page_writeback(page);
778                         if (PageError(page))
779                                 ret = -EIO;
780                 }
781                 page_cache_release(page);
782         } else {
783                 unlock_page(page);
784         }
785         return ret;
786 }
787 EXPORT_SYMBOL(write_one_page);
788
789 /*
790  * For address_spaces which do not use buffers nor write back.
791  */
792 int __set_page_dirty_no_writeback(struct page *page)
793 {
794         if (!PageDirty(page))
795                 SetPageDirty(page);
796         return 0;
797 }
798
799 /*
800  * For address_spaces which do not use buffers.  Just tag the page as dirty in
801  * its radix tree.
802  *
803  * This is also used when a single buffer is being dirtied: we want to set the
804  * page dirty in that case, but not all the buffers.  This is a "bottom-up"
805  * dirtying, whereas __set_page_dirty_buffers() is a "top-down" dirtying.
806  *
807  * Most callers have locked the page, which pins the address_space in memory.
808  * But zap_pte_range() does not lock the page, however in that case the
809  * mapping is pinned by the vma's ->vm_file reference.
810  *
811  * We take care to handle the case where the page was truncated from the
812  * mapping by re-checking page_mapping() insode tree_lock.
813  */
814 int __set_page_dirty_nobuffers(struct page *page)
815 {
816         if (!TestSetPageDirty(page)) {
817                 struct address_space *mapping = page_mapping(page);
818                 struct address_space *mapping2;
819
820                 if (!mapping)
821                         return 1;
822
823                 write_lock_irq(&mapping->tree_lock);
824                 mapping2 = page_mapping(page);
825                 if (mapping2) { /* Race with truncate? */
826                         BUG_ON(mapping2 != mapping);
827                         WARN_ON_ONCE(!PagePrivate(page) && !PageUptodate(page));
828                         if (mapping_cap_account_dirty(mapping)) {
829                                 __inc_zone_page_state(page, NR_FILE_DIRTY);
830                                 task_io_account_write(PAGE_CACHE_SIZE);
831                         }
832                         radix_tree_tag_set(&mapping->page_tree,
833                                 page_index(page), PAGECACHE_TAG_DIRTY);
834                 }
835                 write_unlock_irq(&mapping->tree_lock);
836                 if (mapping->host) {
837                         /* !PageAnon && !swapper_space */
838                         __mark_inode_dirty(mapping->host, I_DIRTY_PAGES);
839                 }
840                 return 1;
841         }
842         return 0;
843 }
844 EXPORT_SYMBOL(__set_page_dirty_nobuffers);
845
846 /*
847  * When a writepage implementation decides that it doesn't want to write this
848  * page for some reason, it should redirty the locked page via
849  * redirty_page_for_writepage() and it should then unlock the page and return 0
850  */
851 int redirty_page_for_writepage(struct writeback_control *wbc, struct page *page)
852 {
853         wbc->pages_skipped++;
854         return __set_page_dirty_nobuffers(page);
855 }
856 EXPORT_SYMBOL(redirty_page_for_writepage);
857
858 /*
859  * If the mapping doesn't provide a set_page_dirty a_op, then
860  * just fall through and assume that it wants buffer_heads.
861  */
862 int fastcall set_page_dirty(struct page *page)
863 {
864         struct address_space *mapping = page_mapping(page);
865
866         if (likely(mapping)) {
867                 int (*spd)(struct page *) = mapping->a_ops->set_page_dirty;
868 #ifdef CONFIG_BLOCK
869                 if (!spd)
870                         spd = __set_page_dirty_buffers;
871 #endif
872                 return (*spd)(page);
873         }
874         if (!PageDirty(page)) {
875                 if (!TestSetPageDirty(page))
876                         return 1;
877         }
878         return 0;
879 }
880 EXPORT_SYMBOL(set_page_dirty);
881
882 /*
883  * set_page_dirty() is racy if the caller has no reference against
884  * page->mapping->host, and if the page is unlocked.  This is because another
885  * CPU could truncate the page off the mapping and then free the mapping.
886  *
887  * Usually, the page _is_ locked, or the caller is a user-space process which
888  * holds a reference on the inode by having an open file.
889  *
890  * In other cases, the page should be locked before running set_page_dirty().
891  */
892 int set_page_dirty_lock(struct page *page)
893 {
894         int ret;
895
896         lock_page_nosync(page);
897         ret = set_page_dirty(page);
898         unlock_page(page);
899         return ret;
900 }
901 EXPORT_SYMBOL(set_page_dirty_lock);
902
903 /*
904  * Clear a page's dirty flag, while caring for dirty memory accounting.
905  * Returns true if the page was previously dirty.
906  *
907  * This is for preparing to put the page under writeout.  We leave the page
908  * tagged as dirty in the radix tree so that a concurrent write-for-sync
909  * can discover it via a PAGECACHE_TAG_DIRTY walk.  The ->writepage
910  * implementation will run either set_page_writeback() or set_page_dirty(),
911  * at which stage we bring the page's dirty flag and radix-tree dirty tag
912  * back into sync.
913  *
914  * This incoherency between the page's dirty flag and radix-tree tag is
915  * unfortunate, but it only exists while the page is locked.
916  */
917 int clear_page_dirty_for_io(struct page *page)
918 {
919         struct address_space *mapping = page_mapping(page);
920
921         BUG_ON(!PageLocked(page));
922
923         ClearPageReclaim(page);
924         if (mapping && mapping_cap_account_dirty(mapping)) {
925                 /*
926                  * Yes, Virginia, this is indeed insane.
927                  *
928                  * We use this sequence to make sure that
929                  *  (a) we account for dirty stats properly
930                  *  (b) we tell the low-level filesystem to
931                  *      mark the whole page dirty if it was
932                  *      dirty in a pagetable. Only to then
933                  *  (c) clean the page again and return 1 to
934                  *      cause the writeback.
935                  *
936                  * This way we avoid all nasty races with the
937                  * dirty bit in multiple places and clearing
938                  * them concurrently from different threads.
939                  *
940                  * Note! Normally the "set_page_dirty(page)"
941                  * has no effect on the actual dirty bit - since
942                  * that will already usually be set. But we
943                  * need the side effects, and it can help us
944                  * avoid races.
945                  *
946                  * We basically use the page "master dirty bit"
947                  * as a serialization point for all the different
948                  * threads doing their things.
949                  */
950                 if (page_mkclean(page))
951                         set_page_dirty(page);
952                 /*
953                  * We carefully synchronise fault handlers against
954                  * installing a dirty pte and marking the page dirty
955                  * at this point. We do this by having them hold the
956                  * page lock at some point after installing their
957                  * pte, but before marking the page dirty.
958                  * Pages are always locked coming in here, so we get
959                  * the desired exclusion. See mm/memory.c:do_wp_page()
960                  * for more comments.
961                  */
962                 if (TestClearPageDirty(page)) {
963                         dec_zone_page_state(page, NR_FILE_DIRTY);
964                         return 1;
965                 }
966                 return 0;
967         }
968         return TestClearPageDirty(page);
969 }
970 EXPORT_SYMBOL(clear_page_dirty_for_io);
971
972 int test_clear_page_writeback(struct page *page)
973 {
974         struct address_space *mapping = page_mapping(page);
975         int ret;
976
977         if (mapping) {
978                 unsigned long flags;
979
980                 write_lock_irqsave(&mapping->tree_lock, flags);
981                 ret = TestClearPageWriteback(page);
982                 if (ret)
983                         radix_tree_tag_clear(&mapping->page_tree,
984                                                 page_index(page),
985                                                 PAGECACHE_TAG_WRITEBACK);
986                 write_unlock_irqrestore(&mapping->tree_lock, flags);
987         } else {
988                 ret = TestClearPageWriteback(page);
989         }
990         if (ret)
991                 dec_zone_page_state(page, NR_WRITEBACK);
992         return ret;
993 }
994
995 int test_set_page_writeback(struct page *page)
996 {
997         struct address_space *mapping = page_mapping(page);
998         int ret;
999
1000         if (mapping) {
1001                 unsigned long flags;
1002
1003                 write_lock_irqsave(&mapping->tree_lock, flags);
1004                 ret = TestSetPageWriteback(page);
1005                 if (!ret)
1006                         radix_tree_tag_set(&mapping->page_tree,
1007                                                 page_index(page),
1008                                                 PAGECACHE_TAG_WRITEBACK);
1009                 if (!PageDirty(page))
1010                         radix_tree_tag_clear(&mapping->page_tree,
1011                                                 page_index(page),
1012                                                 PAGECACHE_TAG_DIRTY);
1013                 write_unlock_irqrestore(&mapping->tree_lock, flags);
1014         } else {
1015                 ret = TestSetPageWriteback(page);
1016         }
1017         if (!ret)
1018                 inc_zone_page_state(page, NR_WRITEBACK);
1019         return ret;
1020
1021 }
1022 EXPORT_SYMBOL(test_set_page_writeback);
1023
1024 /*
1025  * Return true if any of the pages in the mapping are marged with the
1026  * passed tag.
1027  */
1028 int mapping_tagged(struct address_space *mapping, int tag)
1029 {
1030         unsigned long flags;
1031         int ret;
1032
1033         read_lock_irqsave(&mapping->tree_lock, flags);
1034         ret = radix_tree_tagged(&mapping->page_tree, tag);
1035         read_unlock_irqrestore(&mapping->tree_lock, flags);
1036         return ret;
1037 }
1038 EXPORT_SYMBOL(mapping_tagged);