page-writeback: fix the calculation of the oldest_jif in wb_kupdate()
[linux-2.6.git] / mm / page-writeback.c
1 /*
2  * mm/page-writeback.c
3  *
4  * Copyright (C) 2002, Linus Torvalds.
5  * Copyright (C) 2007 Red Hat, Inc., Peter Zijlstra <pzijlstr@redhat.com>
6  *
7  * Contains functions related to writing back dirty pages at the
8  * address_space level.
9  *
10  * 10Apr2002    Andrew Morton
11  *              Initial version
12  */
13
14 #include <linux/kernel.h>
15 #include <linux/module.h>
16 #include <linux/spinlock.h>
17 #include <linux/fs.h>
18 #include <linux/mm.h>
19 #include <linux/swap.h>
20 #include <linux/slab.h>
21 #include <linux/pagemap.h>
22 #include <linux/writeback.h>
23 #include <linux/init.h>
24 #include <linux/backing-dev.h>
25 #include <linux/task_io_accounting_ops.h>
26 #include <linux/blkdev.h>
27 #include <linux/mpage.h>
28 #include <linux/rmap.h>
29 #include <linux/percpu.h>
30 #include <linux/notifier.h>
31 #include <linux/smp.h>
32 #include <linux/sysctl.h>
33 #include <linux/cpu.h>
34 #include <linux/syscalls.h>
35 #include <linux/buffer_head.h>
36 #include <linux/pagevec.h>
37
38 /*
39  * The maximum number of pages to writeout in a single bdflush/kupdate
40  * operation.  We do this so we don't hold I_SYNC against an inode for
41  * enormous amounts of time, which would block a userspace task which has
42  * been forced to throttle against that inode.  Also, the code reevaluates
43  * the dirty each time it has written this many pages.
44  */
45 #define MAX_WRITEBACK_PAGES     1024
46
47 /*
48  * After a CPU has dirtied this many pages, balance_dirty_pages_ratelimited
49  * will look to see if it needs to force writeback or throttling.
50  */
51 static long ratelimit_pages = 32;
52
53 /*
54  * When balance_dirty_pages decides that the caller needs to perform some
55  * non-background writeback, this is how many pages it will attempt to write.
56  * It should be somewhat larger than RATELIMIT_PAGES to ensure that reasonably
57  * large amounts of I/O are submitted.
58  */
59 static inline long sync_writeback_pages(void)
60 {
61         return ratelimit_pages + ratelimit_pages / 2;
62 }
63
64 /* The following parameters are exported via /proc/sys/vm */
65
66 /*
67  * Start background writeback (via pdflush) at this percentage
68  */
69 int dirty_background_ratio = 10;
70
71 /*
72  * dirty_background_bytes starts at 0 (disabled) so that it is a function of
73  * dirty_background_ratio * the amount of dirtyable memory
74  */
75 unsigned long dirty_background_bytes;
76
77 /*
78  * free highmem will not be subtracted from the total free memory
79  * for calculating free ratios if vm_highmem_is_dirtyable is true
80  */
81 int vm_highmem_is_dirtyable;
82
83 /*
84  * The generator of dirty data starts writeback at this percentage
85  */
86 int vm_dirty_ratio = 20;
87
88 /*
89  * vm_dirty_bytes starts at 0 (disabled) so that it is a function of
90  * vm_dirty_ratio * the amount of dirtyable memory
91  */
92 unsigned long vm_dirty_bytes;
93
94 /*
95  * The interval between `kupdate'-style writebacks
96  */
97 unsigned int dirty_writeback_interval = 5 * 100; /* centiseconds */
98
99 /*
100  * The longest time for which data is allowed to remain dirty
101  */
102 unsigned int dirty_expire_interval = 30 * 100; /* centiseconds */
103
104 /*
105  * Flag that makes the machine dump writes/reads and block dirtyings.
106  */
107 int block_dump;
108
109 /*
110  * Flag that puts the machine in "laptop mode". Doubles as a timeout in jiffies:
111  * a full sync is triggered after this time elapses without any disk activity.
112  */
113 int laptop_mode;
114
115 EXPORT_SYMBOL(laptop_mode);
116
117 /* End of sysctl-exported parameters */
118
119
120 static void background_writeout(unsigned long _min_pages);
121
122 /*
123  * Scale the writeback cache size proportional to the relative writeout speeds.
124  *
125  * We do this by keeping a floating proportion between BDIs, based on page
126  * writeback completions [end_page_writeback()]. Those devices that write out
127  * pages fastest will get the larger share, while the slower will get a smaller
128  * share.
129  *
130  * We use page writeout completions because we are interested in getting rid of
131  * dirty pages. Having them written out is the primary goal.
132  *
133  * We introduce a concept of time, a period over which we measure these events,
134  * because demand can/will vary over time. The length of this period itself is
135  * measured in page writeback completions.
136  *
137  */
138 static struct prop_descriptor vm_completions;
139 static struct prop_descriptor vm_dirties;
140
141 /*
142  * couple the period to the dirty_ratio:
143  *
144  *   period/2 ~ roundup_pow_of_two(dirty limit)
145  */
146 static int calc_period_shift(void)
147 {
148         unsigned long dirty_total;
149
150         if (vm_dirty_bytes)
151                 dirty_total = vm_dirty_bytes / PAGE_SIZE;
152         else
153                 dirty_total = (vm_dirty_ratio * determine_dirtyable_memory()) /
154                                 100;
155         return 2 + ilog2(dirty_total - 1);
156 }
157
158 /*
159  * update the period when the dirty threshold changes.
160  */
161 static void update_completion_period(void)
162 {
163         int shift = calc_period_shift();
164         prop_change_shift(&vm_completions, shift);
165         prop_change_shift(&vm_dirties, shift);
166 }
167
168 int dirty_background_ratio_handler(struct ctl_table *table, int write,
169                 struct file *filp, void __user *buffer, size_t *lenp,
170                 loff_t *ppos)
171 {
172         int ret;
173
174         ret = proc_dointvec_minmax(table, write, filp, buffer, lenp, ppos);
175         if (ret == 0 && write)
176                 dirty_background_bytes = 0;
177         return ret;
178 }
179
180 int dirty_background_bytes_handler(struct ctl_table *table, int write,
181                 struct file *filp, void __user *buffer, size_t *lenp,
182                 loff_t *ppos)
183 {
184         int ret;
185
186         ret = proc_doulongvec_minmax(table, write, filp, buffer, lenp, ppos);
187         if (ret == 0 && write)
188                 dirty_background_ratio = 0;
189         return ret;
190 }
191
192 int dirty_ratio_handler(struct ctl_table *table, int write,
193                 struct file *filp, void __user *buffer, size_t *lenp,
194                 loff_t *ppos)
195 {
196         int old_ratio = vm_dirty_ratio;
197         int ret;
198
199         ret = proc_dointvec_minmax(table, write, filp, buffer, lenp, ppos);
200         if (ret == 0 && write && vm_dirty_ratio != old_ratio) {
201                 update_completion_period();
202                 vm_dirty_bytes = 0;
203         }
204         return ret;
205 }
206
207
208 int dirty_bytes_handler(struct ctl_table *table, int write,
209                 struct file *filp, void __user *buffer, size_t *lenp,
210                 loff_t *ppos)
211 {
212         unsigned long old_bytes = vm_dirty_bytes;
213         int ret;
214
215         ret = proc_doulongvec_minmax(table, write, filp, buffer, lenp, ppos);
216         if (ret == 0 && write && vm_dirty_bytes != old_bytes) {
217                 update_completion_period();
218                 vm_dirty_ratio = 0;
219         }
220         return ret;
221 }
222
223 /*
224  * Increment the BDI's writeout completion count and the global writeout
225  * completion count. Called from test_clear_page_writeback().
226  */
227 static inline void __bdi_writeout_inc(struct backing_dev_info *bdi)
228 {
229         __prop_inc_percpu_max(&vm_completions, &bdi->completions,
230                               bdi->max_prop_frac);
231 }
232
233 void bdi_writeout_inc(struct backing_dev_info *bdi)
234 {
235         unsigned long flags;
236
237         local_irq_save(flags);
238         __bdi_writeout_inc(bdi);
239         local_irq_restore(flags);
240 }
241 EXPORT_SYMBOL_GPL(bdi_writeout_inc);
242
243 void task_dirty_inc(struct task_struct *tsk)
244 {
245         prop_inc_single(&vm_dirties, &tsk->dirties);
246 }
247
248 /*
249  * Obtain an accurate fraction of the BDI's portion.
250  */
251 static void bdi_writeout_fraction(struct backing_dev_info *bdi,
252                 long *numerator, long *denominator)
253 {
254         if (bdi_cap_writeback_dirty(bdi)) {
255                 prop_fraction_percpu(&vm_completions, &bdi->completions,
256                                 numerator, denominator);
257         } else {
258                 *numerator = 0;
259                 *denominator = 1;
260         }
261 }
262
263 /*
264  * Clip the earned share of dirty pages to that which is actually available.
265  * This avoids exceeding the total dirty_limit when the floating averages
266  * fluctuate too quickly.
267  */
268 static void
269 clip_bdi_dirty_limit(struct backing_dev_info *bdi, long dirty, long *pbdi_dirty)
270 {
271         long avail_dirty;
272
273         avail_dirty = dirty -
274                 (global_page_state(NR_FILE_DIRTY) +
275                  global_page_state(NR_WRITEBACK) +
276                  global_page_state(NR_UNSTABLE_NFS) +
277                  global_page_state(NR_WRITEBACK_TEMP));
278
279         if (avail_dirty < 0)
280                 avail_dirty = 0;
281
282         avail_dirty += bdi_stat(bdi, BDI_RECLAIMABLE) +
283                 bdi_stat(bdi, BDI_WRITEBACK);
284
285         *pbdi_dirty = min(*pbdi_dirty, avail_dirty);
286 }
287
288 static inline void task_dirties_fraction(struct task_struct *tsk,
289                 long *numerator, long *denominator)
290 {
291         prop_fraction_single(&vm_dirties, &tsk->dirties,
292                                 numerator, denominator);
293 }
294
295 /*
296  * scale the dirty limit
297  *
298  * task specific dirty limit:
299  *
300  *   dirty -= (dirty/8) * p_{t}
301  */
302 static void task_dirty_limit(struct task_struct *tsk, long *pdirty)
303 {
304         long numerator, denominator;
305         long dirty = *pdirty;
306         u64 inv = dirty >> 3;
307
308         task_dirties_fraction(tsk, &numerator, &denominator);
309         inv *= numerator;
310         do_div(inv, denominator);
311
312         dirty -= inv;
313         if (dirty < *pdirty/2)
314                 dirty = *pdirty/2;
315
316         *pdirty = dirty;
317 }
318
319 /*
320  *
321  */
322 static DEFINE_SPINLOCK(bdi_lock);
323 static unsigned int bdi_min_ratio;
324
325 int bdi_set_min_ratio(struct backing_dev_info *bdi, unsigned int min_ratio)
326 {
327         int ret = 0;
328         unsigned long flags;
329
330         spin_lock_irqsave(&bdi_lock, flags);
331         if (min_ratio > bdi->max_ratio) {
332                 ret = -EINVAL;
333         } else {
334                 min_ratio -= bdi->min_ratio;
335                 if (bdi_min_ratio + min_ratio < 100) {
336                         bdi_min_ratio += min_ratio;
337                         bdi->min_ratio += min_ratio;
338                 } else {
339                         ret = -EINVAL;
340                 }
341         }
342         spin_unlock_irqrestore(&bdi_lock, flags);
343
344         return ret;
345 }
346
347 int bdi_set_max_ratio(struct backing_dev_info *bdi, unsigned max_ratio)
348 {
349         unsigned long flags;
350         int ret = 0;
351
352         if (max_ratio > 100)
353                 return -EINVAL;
354
355         spin_lock_irqsave(&bdi_lock, flags);
356         if (bdi->min_ratio > max_ratio) {
357                 ret = -EINVAL;
358         } else {
359                 bdi->max_ratio = max_ratio;
360                 bdi->max_prop_frac = (PROP_FRAC_BASE * max_ratio) / 100;
361         }
362         spin_unlock_irqrestore(&bdi_lock, flags);
363
364         return ret;
365 }
366 EXPORT_SYMBOL(bdi_set_max_ratio);
367
368 /*
369  * Work out the current dirty-memory clamping and background writeout
370  * thresholds.
371  *
372  * The main aim here is to lower them aggressively if there is a lot of mapped
373  * memory around.  To avoid stressing page reclaim with lots of unreclaimable
374  * pages.  It is better to clamp down on writers than to start swapping, and
375  * performing lots of scanning.
376  *
377  * We only allow 1/2 of the currently-unmapped memory to be dirtied.
378  *
379  * We don't permit the clamping level to fall below 5% - that is getting rather
380  * excessive.
381  *
382  * We make sure that the background writeout level is below the adjusted
383  * clamping level.
384  */
385
386 static unsigned long highmem_dirtyable_memory(unsigned long total)
387 {
388 #ifdef CONFIG_HIGHMEM
389         int node;
390         unsigned long x = 0;
391
392         for_each_node_state(node, N_HIGH_MEMORY) {
393                 struct zone *z =
394                         &NODE_DATA(node)->node_zones[ZONE_HIGHMEM];
395
396                 x += zone_page_state(z, NR_FREE_PAGES) + zone_lru_pages(z);
397         }
398         /*
399          * Make sure that the number of highmem pages is never larger
400          * than the number of the total dirtyable memory. This can only
401          * occur in very strange VM situations but we want to make sure
402          * that this does not occur.
403          */
404         return min(x, total);
405 #else
406         return 0;
407 #endif
408 }
409
410 /**
411  * determine_dirtyable_memory - amount of memory that may be used
412  *
413  * Returns the numebr of pages that can currently be freed and used
414  * by the kernel for direct mappings.
415  */
416 unsigned long determine_dirtyable_memory(void)
417 {
418         unsigned long x;
419
420         x = global_page_state(NR_FREE_PAGES) + global_lru_pages();
421
422         if (!vm_highmem_is_dirtyable)
423                 x -= highmem_dirtyable_memory(x);
424
425         return x + 1;   /* Ensure that we never return 0 */
426 }
427
428 void
429 get_dirty_limits(unsigned long *pbackground, unsigned long *pdirty,
430                  unsigned long *pbdi_dirty, struct backing_dev_info *bdi)
431 {
432         unsigned long background;
433         unsigned long dirty;
434         unsigned long available_memory = determine_dirtyable_memory();
435         struct task_struct *tsk;
436
437         if (vm_dirty_bytes)
438                 dirty = DIV_ROUND_UP(vm_dirty_bytes, PAGE_SIZE);
439         else {
440                 int dirty_ratio;
441
442                 dirty_ratio = vm_dirty_ratio;
443                 if (dirty_ratio < 5)
444                         dirty_ratio = 5;
445                 dirty = (dirty_ratio * available_memory) / 100;
446         }
447
448         if (dirty_background_bytes)
449                 background = DIV_ROUND_UP(dirty_background_bytes, PAGE_SIZE);
450         else
451                 background = (dirty_background_ratio * available_memory) / 100;
452
453         if (background >= dirty)
454                 background = dirty / 2;
455         tsk = current;
456         if (tsk->flags & PF_LESS_THROTTLE || rt_task(tsk)) {
457                 background += background / 4;
458                 dirty += dirty / 4;
459         }
460         *pbackground = background;
461         *pdirty = dirty;
462
463         if (bdi) {
464                 u64 bdi_dirty;
465                 long numerator, denominator;
466
467                 /*
468                  * Calculate this BDI's share of the dirty ratio.
469                  */
470                 bdi_writeout_fraction(bdi, &numerator, &denominator);
471
472                 bdi_dirty = (dirty * (100 - bdi_min_ratio)) / 100;
473                 bdi_dirty *= numerator;
474                 do_div(bdi_dirty, denominator);
475                 bdi_dirty += (dirty * bdi->min_ratio) / 100;
476                 if (bdi_dirty > (dirty * bdi->max_ratio) / 100)
477                         bdi_dirty = dirty * bdi->max_ratio / 100;
478
479                 *pbdi_dirty = bdi_dirty;
480                 clip_bdi_dirty_limit(bdi, dirty, pbdi_dirty);
481                 task_dirty_limit(current, pbdi_dirty);
482         }
483 }
484
485 /*
486  * balance_dirty_pages() must be called by processes which are generating dirty
487  * data.  It looks at the number of dirty pages in the machine and will force
488  * the caller to perform writeback if the system is over `vm_dirty_ratio'.
489  * If we're over `background_thresh' then pdflush is woken to perform some
490  * writeout.
491  */
492 static void balance_dirty_pages(struct address_space *mapping)
493 {
494         long nr_reclaimable, bdi_nr_reclaimable;
495         long nr_writeback, bdi_nr_writeback;
496         unsigned long background_thresh;
497         unsigned long dirty_thresh;
498         unsigned long bdi_thresh;
499         unsigned long pages_written = 0;
500         unsigned long write_chunk = sync_writeback_pages();
501
502         struct backing_dev_info *bdi = mapping->backing_dev_info;
503
504         for (;;) {
505                 struct writeback_control wbc = {
506                         .bdi            = bdi,
507                         .sync_mode      = WB_SYNC_NONE,
508                         .older_than_this = NULL,
509                         .nr_to_write    = write_chunk,
510                         .range_cyclic   = 1,
511                 };
512
513                 get_dirty_limits(&background_thresh, &dirty_thresh,
514                                 &bdi_thresh, bdi);
515
516                 nr_reclaimable = global_page_state(NR_FILE_DIRTY) +
517                                         global_page_state(NR_UNSTABLE_NFS);
518                 nr_writeback = global_page_state(NR_WRITEBACK);
519
520                 bdi_nr_reclaimable = bdi_stat(bdi, BDI_RECLAIMABLE);
521                 bdi_nr_writeback = bdi_stat(bdi, BDI_WRITEBACK);
522
523                 if (bdi_nr_reclaimable + bdi_nr_writeback <= bdi_thresh)
524                         break;
525
526                 /*
527                  * Throttle it only when the background writeback cannot
528                  * catch-up. This avoids (excessively) small writeouts
529                  * when the bdi limits are ramping up.
530                  */
531                 if (nr_reclaimable + nr_writeback <
532                                 (background_thresh + dirty_thresh) / 2)
533                         break;
534
535                 if (!bdi->dirty_exceeded)
536                         bdi->dirty_exceeded = 1;
537
538                 /* Note: nr_reclaimable denotes nr_dirty + nr_unstable.
539                  * Unstable writes are a feature of certain networked
540                  * filesystems (i.e. NFS) in which data may have been
541                  * written to the server's write cache, but has not yet
542                  * been flushed to permanent storage.
543                  */
544                 if (bdi_nr_reclaimable) {
545                         writeback_inodes(&wbc);
546                         pages_written += write_chunk - wbc.nr_to_write;
547                         get_dirty_limits(&background_thresh, &dirty_thresh,
548                                        &bdi_thresh, bdi);
549                 }
550
551                 /*
552                  * In order to avoid the stacked BDI deadlock we need
553                  * to ensure we accurately count the 'dirty' pages when
554                  * the threshold is low.
555                  *
556                  * Otherwise it would be possible to get thresh+n pages
557                  * reported dirty, even though there are thresh-m pages
558                  * actually dirty; with m+n sitting in the percpu
559                  * deltas.
560                  */
561                 if (bdi_thresh < 2*bdi_stat_error(bdi)) {
562                         bdi_nr_reclaimable = bdi_stat_sum(bdi, BDI_RECLAIMABLE);
563                         bdi_nr_writeback = bdi_stat_sum(bdi, BDI_WRITEBACK);
564                 } else if (bdi_nr_reclaimable) {
565                         bdi_nr_reclaimable = bdi_stat(bdi, BDI_RECLAIMABLE);
566                         bdi_nr_writeback = bdi_stat(bdi, BDI_WRITEBACK);
567                 }
568
569                 if (bdi_nr_reclaimable + bdi_nr_writeback <= bdi_thresh)
570                         break;
571                 if (pages_written >= write_chunk)
572                         break;          /* We've done our duty */
573
574                 congestion_wait(WRITE, HZ/10);
575         }
576
577         if (bdi_nr_reclaimable + bdi_nr_writeback < bdi_thresh &&
578                         bdi->dirty_exceeded)
579                 bdi->dirty_exceeded = 0;
580
581         if (writeback_in_progress(bdi))
582                 return;         /* pdflush is already working this queue */
583
584         /*
585          * In laptop mode, we wait until hitting the higher threshold before
586          * starting background writeout, and then write out all the way down
587          * to the lower threshold.  So slow writers cause minimal disk activity.
588          *
589          * In normal mode, we start background writeout at the lower
590          * background_thresh, to keep the amount of dirty memory low.
591          */
592         if ((laptop_mode && pages_written) ||
593                         (!laptop_mode && (global_page_state(NR_FILE_DIRTY)
594                                           + global_page_state(NR_UNSTABLE_NFS)
595                                           > background_thresh)))
596                 pdflush_operation(background_writeout, 0);
597 }
598
599 void set_page_dirty_balance(struct page *page, int page_mkwrite)
600 {
601         if (set_page_dirty(page) || page_mkwrite) {
602                 struct address_space *mapping = page_mapping(page);
603
604                 if (mapping)
605                         balance_dirty_pages_ratelimited(mapping);
606         }
607 }
608
609 /**
610  * balance_dirty_pages_ratelimited_nr - balance dirty memory state
611  * @mapping: address_space which was dirtied
612  * @nr_pages_dirtied: number of pages which the caller has just dirtied
613  *
614  * Processes which are dirtying memory should call in here once for each page
615  * which was newly dirtied.  The function will periodically check the system's
616  * dirty state and will initiate writeback if needed.
617  *
618  * On really big machines, get_writeback_state is expensive, so try to avoid
619  * calling it too often (ratelimiting).  But once we're over the dirty memory
620  * limit we decrease the ratelimiting by a lot, to prevent individual processes
621  * from overshooting the limit by (ratelimit_pages) each.
622  */
623 void balance_dirty_pages_ratelimited_nr(struct address_space *mapping,
624                                         unsigned long nr_pages_dirtied)
625 {
626         static DEFINE_PER_CPU(unsigned long, ratelimits) = 0;
627         unsigned long ratelimit;
628         unsigned long *p;
629
630         ratelimit = ratelimit_pages;
631         if (mapping->backing_dev_info->dirty_exceeded)
632                 ratelimit = 8;
633
634         /*
635          * Check the rate limiting. Also, we do not want to throttle real-time
636          * tasks in balance_dirty_pages(). Period.
637          */
638         preempt_disable();
639         p =  &__get_cpu_var(ratelimits);
640         *p += nr_pages_dirtied;
641         if (unlikely(*p >= ratelimit)) {
642                 *p = 0;
643                 preempt_enable();
644                 balance_dirty_pages(mapping);
645                 return;
646         }
647         preempt_enable();
648 }
649 EXPORT_SYMBOL(balance_dirty_pages_ratelimited_nr);
650
651 void throttle_vm_writeout(gfp_t gfp_mask)
652 {
653         unsigned long background_thresh;
654         unsigned long dirty_thresh;
655
656         for ( ; ; ) {
657                 get_dirty_limits(&background_thresh, &dirty_thresh, NULL, NULL);
658
659                 /*
660                  * Boost the allowable dirty threshold a bit for page
661                  * allocators so they don't get DoS'ed by heavy writers
662                  */
663                 dirty_thresh += dirty_thresh / 10;      /* wheeee... */
664
665                 if (global_page_state(NR_UNSTABLE_NFS) +
666                         global_page_state(NR_WRITEBACK) <= dirty_thresh)
667                                 break;
668                 congestion_wait(WRITE, HZ/10);
669
670                 /*
671                  * The caller might hold locks which can prevent IO completion
672                  * or progress in the filesystem.  So we cannot just sit here
673                  * waiting for IO to complete.
674                  */
675                 if ((gfp_mask & (__GFP_FS|__GFP_IO)) != (__GFP_FS|__GFP_IO))
676                         break;
677         }
678 }
679
680 /*
681  * writeback at least _min_pages, and keep writing until the amount of dirty
682  * memory is less than the background threshold, or until we're all clean.
683  */
684 static void background_writeout(unsigned long _min_pages)
685 {
686         long min_pages = _min_pages;
687         struct writeback_control wbc = {
688                 .bdi            = NULL,
689                 .sync_mode      = WB_SYNC_NONE,
690                 .older_than_this = NULL,
691                 .nr_to_write    = 0,
692                 .nonblocking    = 1,
693                 .range_cyclic   = 1,
694         };
695
696         for ( ; ; ) {
697                 unsigned long background_thresh;
698                 unsigned long dirty_thresh;
699
700                 get_dirty_limits(&background_thresh, &dirty_thresh, NULL, NULL);
701                 if (global_page_state(NR_FILE_DIRTY) +
702                         global_page_state(NR_UNSTABLE_NFS) < background_thresh
703                                 && min_pages <= 0)
704                         break;
705                 wbc.more_io = 0;
706                 wbc.encountered_congestion = 0;
707                 wbc.nr_to_write = MAX_WRITEBACK_PAGES;
708                 wbc.pages_skipped = 0;
709                 writeback_inodes(&wbc);
710                 min_pages -= MAX_WRITEBACK_PAGES - wbc.nr_to_write;
711                 if (wbc.nr_to_write > 0 || wbc.pages_skipped > 0) {
712                         /* Wrote less than expected */
713                         if (wbc.encountered_congestion || wbc.more_io)
714                                 congestion_wait(WRITE, HZ/10);
715                         else
716                                 break;
717                 }
718         }
719 }
720
721 /*
722  * Start writeback of `nr_pages' pages.  If `nr_pages' is zero, write back
723  * the whole world.  Returns 0 if a pdflush thread was dispatched.  Returns
724  * -1 if all pdflush threads were busy.
725  */
726 int wakeup_pdflush(long nr_pages)
727 {
728         if (nr_pages == 0)
729                 nr_pages = global_page_state(NR_FILE_DIRTY) +
730                                 global_page_state(NR_UNSTABLE_NFS);
731         return pdflush_operation(background_writeout, nr_pages);
732 }
733
734 static void wb_timer_fn(unsigned long unused);
735 static void laptop_timer_fn(unsigned long unused);
736
737 static DEFINE_TIMER(wb_timer, wb_timer_fn, 0, 0);
738 static DEFINE_TIMER(laptop_mode_wb_timer, laptop_timer_fn, 0, 0);
739
740 /*
741  * Periodic writeback of "old" data.
742  *
743  * Define "old": the first time one of an inode's pages is dirtied, we mark the
744  * dirtying-time in the inode's address_space.  So this periodic writeback code
745  * just walks the superblock inode list, writing back any inodes which are
746  * older than a specific point in time.
747  *
748  * Try to run once per dirty_writeback_interval.  But if a writeback event
749  * takes longer than a dirty_writeback_interval interval, then leave a
750  * one-second gap.
751  *
752  * older_than_this takes precedence over nr_to_write.  So we'll only write back
753  * all dirty pages if they are all attached to "old" mappings.
754  */
755 static void wb_kupdate(unsigned long arg)
756 {
757         unsigned long oldest_jif;
758         unsigned long start_jif;
759         unsigned long next_jif;
760         long nr_to_write;
761         struct writeback_control wbc = {
762                 .bdi            = NULL,
763                 .sync_mode      = WB_SYNC_NONE,
764                 .older_than_this = &oldest_jif,
765                 .nr_to_write    = 0,
766                 .nonblocking    = 1,
767                 .for_kupdate    = 1,
768                 .range_cyclic   = 1,
769         };
770
771         sync_supers();
772
773         oldest_jif = jiffies - msecs_to_jiffies(dirty_expire_interval * 10);
774         start_jif = jiffies;
775         next_jif = start_jif + msecs_to_jiffies(dirty_writeback_interval * 10);
776         nr_to_write = global_page_state(NR_FILE_DIRTY) +
777                         global_page_state(NR_UNSTABLE_NFS) +
778                         (inodes_stat.nr_inodes - inodes_stat.nr_unused);
779         while (nr_to_write > 0) {
780                 wbc.more_io = 0;
781                 wbc.encountered_congestion = 0;
782                 wbc.nr_to_write = MAX_WRITEBACK_PAGES;
783                 writeback_inodes(&wbc);
784                 if (wbc.nr_to_write > 0) {
785                         if (wbc.encountered_congestion || wbc.more_io)
786                                 congestion_wait(WRITE, HZ/10);
787                         else
788                                 break;  /* All the old data is written */
789                 }
790                 nr_to_write -= MAX_WRITEBACK_PAGES - wbc.nr_to_write;
791         }
792         if (time_before(next_jif, jiffies + HZ))
793                 next_jif = jiffies + HZ;
794         if (dirty_writeback_interval)
795                 mod_timer(&wb_timer, next_jif);
796 }
797
798 /*
799  * sysctl handler for /proc/sys/vm/dirty_writeback_centisecs
800  */
801 int dirty_writeback_centisecs_handler(ctl_table *table, int write,
802         struct file *file, void __user *buffer, size_t *length, loff_t *ppos)
803 {
804         proc_dointvec(table, write, file, buffer, length, ppos);
805         if (dirty_writeback_interval)
806                 mod_timer(&wb_timer, jiffies +
807                         msecs_to_jiffies(dirty_writeback_interval * 10));
808         else
809                 del_timer(&wb_timer);
810         return 0;
811 }
812
813 static void wb_timer_fn(unsigned long unused)
814 {
815         if (pdflush_operation(wb_kupdate, 0) < 0)
816                 mod_timer(&wb_timer, jiffies + HZ); /* delay 1 second */
817 }
818
819 static void laptop_flush(unsigned long unused)
820 {
821         sys_sync();
822 }
823
824 static void laptop_timer_fn(unsigned long unused)
825 {
826         pdflush_operation(laptop_flush, 0);
827 }
828
829 /*
830  * We've spun up the disk and we're in laptop mode: schedule writeback
831  * of all dirty data a few seconds from now.  If the flush is already scheduled
832  * then push it back - the user is still using the disk.
833  */
834 void laptop_io_completion(void)
835 {
836         mod_timer(&laptop_mode_wb_timer, jiffies + laptop_mode);
837 }
838
839 /*
840  * We're in laptop mode and we've just synced. The sync's writes will have
841  * caused another writeback to be scheduled by laptop_io_completion.
842  * Nothing needs to be written back anymore, so we unschedule the writeback.
843  */
844 void laptop_sync_completion(void)
845 {
846         del_timer(&laptop_mode_wb_timer);
847 }
848
849 /*
850  * If ratelimit_pages is too high then we can get into dirty-data overload
851  * if a large number of processes all perform writes at the same time.
852  * If it is too low then SMP machines will call the (expensive)
853  * get_writeback_state too often.
854  *
855  * Here we set ratelimit_pages to a level which ensures that when all CPUs are
856  * dirtying in parallel, we cannot go more than 3% (1/32) over the dirty memory
857  * thresholds before writeback cuts in.
858  *
859  * But the limit should not be set too high.  Because it also controls the
860  * amount of memory which the balance_dirty_pages() caller has to write back.
861  * If this is too large then the caller will block on the IO queue all the
862  * time.  So limit it to four megabytes - the balance_dirty_pages() caller
863  * will write six megabyte chunks, max.
864  */
865
866 void writeback_set_ratelimit(void)
867 {
868         ratelimit_pages = vm_total_pages / (num_online_cpus() * 32);
869         if (ratelimit_pages < 16)
870                 ratelimit_pages = 16;
871         if (ratelimit_pages * PAGE_CACHE_SIZE > 4096 * 1024)
872                 ratelimit_pages = (4096 * 1024) / PAGE_CACHE_SIZE;
873 }
874
875 static int __cpuinit
876 ratelimit_handler(struct notifier_block *self, unsigned long u, void *v)
877 {
878         writeback_set_ratelimit();
879         return NOTIFY_DONE;
880 }
881
882 static struct notifier_block __cpuinitdata ratelimit_nb = {
883         .notifier_call  = ratelimit_handler,
884         .next           = NULL,
885 };
886
887 /*
888  * Called early on to tune the page writeback dirty limits.
889  *
890  * We used to scale dirty pages according to how total memory
891  * related to pages that could be allocated for buffers (by
892  * comparing nr_free_buffer_pages() to vm_total_pages.
893  *
894  * However, that was when we used "dirty_ratio" to scale with
895  * all memory, and we don't do that any more. "dirty_ratio"
896  * is now applied to total non-HIGHPAGE memory (by subtracting
897  * totalhigh_pages from vm_total_pages), and as such we can't
898  * get into the old insane situation any more where we had
899  * large amounts of dirty pages compared to a small amount of
900  * non-HIGHMEM memory.
901  *
902  * But we might still want to scale the dirty_ratio by how
903  * much memory the box has..
904  */
905 void __init page_writeback_init(void)
906 {
907         int shift;
908
909         mod_timer(&wb_timer,
910                   jiffies + msecs_to_jiffies(dirty_writeback_interval * 10));
911         writeback_set_ratelimit();
912         register_cpu_notifier(&ratelimit_nb);
913
914         shift = calc_period_shift();
915         prop_descriptor_init(&vm_completions, shift);
916         prop_descriptor_init(&vm_dirties, shift);
917 }
918
919 /**
920  * write_cache_pages - walk the list of dirty pages of the given address space and write all of them.
921  * @mapping: address space structure to write
922  * @wbc: subtract the number of written pages from *@wbc->nr_to_write
923  * @writepage: function called for each page
924  * @data: data passed to writepage function
925  *
926  * If a page is already under I/O, write_cache_pages() skips it, even
927  * if it's dirty.  This is desirable behaviour for memory-cleaning writeback,
928  * but it is INCORRECT for data-integrity system calls such as fsync().  fsync()
929  * and msync() need to guarantee that all the data which was dirty at the time
930  * the call was made get new I/O started against them.  If wbc->sync_mode is
931  * WB_SYNC_ALL then we were called for data integrity and we must wait for
932  * existing IO to complete.
933  */
934 int write_cache_pages(struct address_space *mapping,
935                       struct writeback_control *wbc, writepage_t writepage,
936                       void *data)
937 {
938         struct backing_dev_info *bdi = mapping->backing_dev_info;
939         int ret = 0;
940         int done = 0;
941         struct pagevec pvec;
942         int nr_pages;
943         pgoff_t uninitialized_var(writeback_index);
944         pgoff_t index;
945         pgoff_t end;            /* Inclusive */
946         pgoff_t done_index;
947         int cycled;
948         int range_whole = 0;
949         long nr_to_write = wbc->nr_to_write;
950
951         if (wbc->nonblocking && bdi_write_congested(bdi)) {
952                 wbc->encountered_congestion = 1;
953                 return 0;
954         }
955
956         pagevec_init(&pvec, 0);
957         if (wbc->range_cyclic) {
958                 writeback_index = mapping->writeback_index; /* prev offset */
959                 index = writeback_index;
960                 if (index == 0)
961                         cycled = 1;
962                 else
963                         cycled = 0;
964                 end = -1;
965         } else {
966                 index = wbc->range_start >> PAGE_CACHE_SHIFT;
967                 end = wbc->range_end >> PAGE_CACHE_SHIFT;
968                 if (wbc->range_start == 0 && wbc->range_end == LLONG_MAX)
969                         range_whole = 1;
970                 cycled = 1; /* ignore range_cyclic tests */
971         }
972 retry:
973         done_index = index;
974         while (!done && (index <= end)) {
975                 int i;
976
977                 nr_pages = pagevec_lookup_tag(&pvec, mapping, &index,
978                               PAGECACHE_TAG_DIRTY,
979                               min(end - index, (pgoff_t)PAGEVEC_SIZE-1) + 1);
980                 if (nr_pages == 0)
981                         break;
982
983                 for (i = 0; i < nr_pages; i++) {
984                         struct page *page = pvec.pages[i];
985
986                         /*
987                          * At this point, the page may be truncated or
988                          * invalidated (changing page->mapping to NULL), or
989                          * even swizzled back from swapper_space to tmpfs file
990                          * mapping. However, page->index will not change
991                          * because we have a reference on the page.
992                          */
993                         if (page->index > end) {
994                                 /*
995                                  * can't be range_cyclic (1st pass) because
996                                  * end == -1 in that case.
997                                  */
998                                 done = 1;
999                                 break;
1000                         }
1001
1002                         done_index = page->index + 1;
1003
1004                         lock_page(page);
1005
1006                         /*
1007                          * Page truncated or invalidated. We can freely skip it
1008                          * then, even for data integrity operations: the page
1009                          * has disappeared concurrently, so there could be no
1010                          * real expectation of this data interity operation
1011                          * even if there is now a new, dirty page at the same
1012                          * pagecache address.
1013                          */
1014                         if (unlikely(page->mapping != mapping)) {
1015 continue_unlock:
1016                                 unlock_page(page);
1017                                 continue;
1018                         }
1019
1020                         if (!PageDirty(page)) {
1021                                 /* someone wrote it for us */
1022                                 goto continue_unlock;
1023                         }
1024
1025                         if (PageWriteback(page)) {
1026                                 if (wbc->sync_mode != WB_SYNC_NONE)
1027                                         wait_on_page_writeback(page);
1028                                 else
1029                                         goto continue_unlock;
1030                         }
1031
1032                         BUG_ON(PageWriteback(page));
1033                         if (!clear_page_dirty_for_io(page))
1034                                 goto continue_unlock;
1035
1036                         ret = (*writepage)(page, wbc, data);
1037                         if (unlikely(ret)) {
1038                                 if (ret == AOP_WRITEPAGE_ACTIVATE) {
1039                                         unlock_page(page);
1040                                         ret = 0;
1041                                 } else {
1042                                         /*
1043                                          * done_index is set past this page,
1044                                          * so media errors will not choke
1045                                          * background writeout for the entire
1046                                          * file. This has consequences for
1047                                          * range_cyclic semantics (ie. it may
1048                                          * not be suitable for data integrity
1049                                          * writeout).
1050                                          */
1051                                         done = 1;
1052                                         break;
1053                                 }
1054                         }
1055
1056                         if (nr_to_write > 0) {
1057                                 nr_to_write--;
1058                                 if (nr_to_write == 0 &&
1059                                     wbc->sync_mode == WB_SYNC_NONE) {
1060                                         /*
1061                                          * We stop writing back only if we are
1062                                          * not doing integrity sync. In case of
1063                                          * integrity sync we have to keep going
1064                                          * because someone may be concurrently
1065                                          * dirtying pages, and we might have
1066                                          * synced a lot of newly appeared dirty
1067                                          * pages, but have not synced all of the
1068                                          * old dirty pages.
1069                                          */
1070                                         done = 1;
1071                                         break;
1072                                 }
1073                         }
1074
1075                         if (wbc->nonblocking && bdi_write_congested(bdi)) {
1076                                 wbc->encountered_congestion = 1;
1077                                 done = 1;
1078                                 break;
1079                         }
1080                 }
1081                 pagevec_release(&pvec);
1082                 cond_resched();
1083         }
1084         if (!cycled && !done) {
1085                 /*
1086                  * range_cyclic:
1087                  * We hit the last page and there is more work to be done: wrap
1088                  * back to the start of the file
1089                  */
1090                 cycled = 1;
1091                 index = 0;
1092                 end = writeback_index - 1;
1093                 goto retry;
1094         }
1095         if (!wbc->no_nrwrite_index_update) {
1096                 if (wbc->range_cyclic || (range_whole && nr_to_write > 0))
1097                         mapping->writeback_index = done_index;
1098                 wbc->nr_to_write = nr_to_write;
1099         }
1100
1101         return ret;
1102 }
1103 EXPORT_SYMBOL(write_cache_pages);
1104
1105 /*
1106  * Function used by generic_writepages to call the real writepage
1107  * function and set the mapping flags on error
1108  */
1109 static int __writepage(struct page *page, struct writeback_control *wbc,
1110                        void *data)
1111 {
1112         struct address_space *mapping = data;
1113         int ret = mapping->a_ops->writepage(page, wbc);
1114         mapping_set_error(mapping, ret);
1115         return ret;
1116 }
1117
1118 /**
1119  * generic_writepages - walk the list of dirty pages of the given address space and writepage() all of them.
1120  * @mapping: address space structure to write
1121  * @wbc: subtract the number of written pages from *@wbc->nr_to_write
1122  *
1123  * This is a library function, which implements the writepages()
1124  * address_space_operation.
1125  */
1126 int generic_writepages(struct address_space *mapping,
1127                        struct writeback_control *wbc)
1128 {
1129         /* deal with chardevs and other special file */
1130         if (!mapping->a_ops->writepage)
1131                 return 0;
1132
1133         return write_cache_pages(mapping, wbc, __writepage, mapping);
1134 }
1135
1136 EXPORT_SYMBOL(generic_writepages);
1137
1138 int do_writepages(struct address_space *mapping, struct writeback_control *wbc)
1139 {
1140         int ret;
1141
1142         if (wbc->nr_to_write <= 0)
1143                 return 0;
1144         wbc->for_writepages = 1;
1145         if (mapping->a_ops->writepages)
1146                 ret = mapping->a_ops->writepages(mapping, wbc);
1147         else
1148                 ret = generic_writepages(mapping, wbc);
1149         wbc->for_writepages = 0;
1150         return ret;
1151 }
1152
1153 /**
1154  * write_one_page - write out a single page and optionally wait on I/O
1155  * @page: the page to write
1156  * @wait: if true, wait on writeout
1157  *
1158  * The page must be locked by the caller and will be unlocked upon return.
1159  *
1160  * write_one_page() returns a negative error code if I/O failed.
1161  */
1162 int write_one_page(struct page *page, int wait)
1163 {
1164         struct address_space *mapping = page->mapping;
1165         int ret = 0;
1166         struct writeback_control wbc = {
1167                 .sync_mode = WB_SYNC_ALL,
1168                 .nr_to_write = 1,
1169         };
1170
1171         BUG_ON(!PageLocked(page));
1172
1173         if (wait)
1174                 wait_on_page_writeback(page);
1175
1176         if (clear_page_dirty_for_io(page)) {
1177                 page_cache_get(page);
1178                 ret = mapping->a_ops->writepage(page, &wbc);
1179                 if (ret == 0 && wait) {
1180                         wait_on_page_writeback(page);
1181                         if (PageError(page))
1182                                 ret = -EIO;
1183                 }
1184                 page_cache_release(page);
1185         } else {
1186                 unlock_page(page);
1187         }
1188         return ret;
1189 }
1190 EXPORT_SYMBOL(write_one_page);
1191
1192 /*
1193  * For address_spaces which do not use buffers nor write back.
1194  */
1195 int __set_page_dirty_no_writeback(struct page *page)
1196 {
1197         if (!PageDirty(page))
1198                 SetPageDirty(page);
1199         return 0;
1200 }
1201
1202 /*
1203  * Helper function for set_page_dirty family.
1204  * NOTE: This relies on being atomic wrt interrupts.
1205  */
1206 void account_page_dirtied(struct page *page, struct address_space *mapping)
1207 {
1208         if (mapping_cap_account_dirty(mapping)) {
1209                 __inc_zone_page_state(page, NR_FILE_DIRTY);
1210                 __inc_bdi_stat(mapping->backing_dev_info, BDI_RECLAIMABLE);
1211                 task_dirty_inc(current);
1212                 task_io_account_write(PAGE_CACHE_SIZE);
1213         }
1214 }
1215
1216 /*
1217  * For address_spaces which do not use buffers.  Just tag the page as dirty in
1218  * its radix tree.
1219  *
1220  * This is also used when a single buffer is being dirtied: we want to set the
1221  * page dirty in that case, but not all the buffers.  This is a "bottom-up"
1222  * dirtying, whereas __set_page_dirty_buffers() is a "top-down" dirtying.
1223  *
1224  * Most callers have locked the page, which pins the address_space in memory.
1225  * But zap_pte_range() does not lock the page, however in that case the
1226  * mapping is pinned by the vma's ->vm_file reference.
1227  *
1228  * We take care to handle the case where the page was truncated from the
1229  * mapping by re-checking page_mapping() inside tree_lock.
1230  */
1231 int __set_page_dirty_nobuffers(struct page *page)
1232 {
1233         if (!TestSetPageDirty(page)) {
1234                 struct address_space *mapping = page_mapping(page);
1235                 struct address_space *mapping2;
1236
1237                 if (!mapping)
1238                         return 1;
1239
1240                 spin_lock_irq(&mapping->tree_lock);
1241                 mapping2 = page_mapping(page);
1242                 if (mapping2) { /* Race with truncate? */
1243                         BUG_ON(mapping2 != mapping);
1244                         WARN_ON_ONCE(!PagePrivate(page) && !PageUptodate(page));
1245                         account_page_dirtied(page, mapping);
1246                         radix_tree_tag_set(&mapping->page_tree,
1247                                 page_index(page), PAGECACHE_TAG_DIRTY);
1248                 }
1249                 spin_unlock_irq(&mapping->tree_lock);
1250                 if (mapping->host) {
1251                         /* !PageAnon && !swapper_space */
1252                         __mark_inode_dirty(mapping->host, I_DIRTY_PAGES);
1253                 }
1254                 return 1;
1255         }
1256         return 0;
1257 }
1258 EXPORT_SYMBOL(__set_page_dirty_nobuffers);
1259
1260 /*
1261  * When a writepage implementation decides that it doesn't want to write this
1262  * page for some reason, it should redirty the locked page via
1263  * redirty_page_for_writepage() and it should then unlock the page and return 0
1264  */
1265 int redirty_page_for_writepage(struct writeback_control *wbc, struct page *page)
1266 {
1267         wbc->pages_skipped++;
1268         return __set_page_dirty_nobuffers(page);
1269 }
1270 EXPORT_SYMBOL(redirty_page_for_writepage);
1271
1272 /*
1273  * If the mapping doesn't provide a set_page_dirty a_op, then
1274  * just fall through and assume that it wants buffer_heads.
1275  */
1276 int set_page_dirty(struct page *page)
1277 {
1278         struct address_space *mapping = page_mapping(page);
1279
1280         if (likely(mapping)) {
1281                 int (*spd)(struct page *) = mapping->a_ops->set_page_dirty;
1282 #ifdef CONFIG_BLOCK
1283                 if (!spd)
1284                         spd = __set_page_dirty_buffers;
1285 #endif
1286                 return (*spd)(page);
1287         }
1288         if (!PageDirty(page)) {
1289                 if (!TestSetPageDirty(page))
1290                         return 1;
1291         }
1292         return 0;
1293 }
1294 EXPORT_SYMBOL(set_page_dirty);
1295
1296 /*
1297  * set_page_dirty() is racy if the caller has no reference against
1298  * page->mapping->host, and if the page is unlocked.  This is because another
1299  * CPU could truncate the page off the mapping and then free the mapping.
1300  *
1301  * Usually, the page _is_ locked, or the caller is a user-space process which
1302  * holds a reference on the inode by having an open file.
1303  *
1304  * In other cases, the page should be locked before running set_page_dirty().
1305  */
1306 int set_page_dirty_lock(struct page *page)
1307 {
1308         int ret;
1309
1310         lock_page_nosync(page);
1311         ret = set_page_dirty(page);
1312         unlock_page(page);
1313         return ret;
1314 }
1315 EXPORT_SYMBOL(set_page_dirty_lock);
1316
1317 /*
1318  * Clear a page's dirty flag, while caring for dirty memory accounting.
1319  * Returns true if the page was previously dirty.
1320  *
1321  * This is for preparing to put the page under writeout.  We leave the page
1322  * tagged as dirty in the radix tree so that a concurrent write-for-sync
1323  * can discover it via a PAGECACHE_TAG_DIRTY walk.  The ->writepage
1324  * implementation will run either set_page_writeback() or set_page_dirty(),
1325  * at which stage we bring the page's dirty flag and radix-tree dirty tag
1326  * back into sync.
1327  *
1328  * This incoherency between the page's dirty flag and radix-tree tag is
1329  * unfortunate, but it only exists while the page is locked.
1330  */
1331 int clear_page_dirty_for_io(struct page *page)
1332 {
1333         struct address_space *mapping = page_mapping(page);
1334
1335         BUG_ON(!PageLocked(page));
1336
1337         ClearPageReclaim(page);
1338         if (mapping && mapping_cap_account_dirty(mapping)) {
1339                 /*
1340                  * Yes, Virginia, this is indeed insane.
1341                  *
1342                  * We use this sequence to make sure that
1343                  *  (a) we account for dirty stats properly
1344                  *  (b) we tell the low-level filesystem to
1345                  *      mark the whole page dirty if it was
1346                  *      dirty in a pagetable. Only to then
1347                  *  (c) clean the page again and return 1 to
1348                  *      cause the writeback.
1349                  *
1350                  * This way we avoid all nasty races with the
1351                  * dirty bit in multiple places and clearing
1352                  * them concurrently from different threads.
1353                  *
1354                  * Note! Normally the "set_page_dirty(page)"
1355                  * has no effect on the actual dirty bit - since
1356                  * that will already usually be set. But we
1357                  * need the side effects, and it can help us
1358                  * avoid races.
1359                  *
1360                  * We basically use the page "master dirty bit"
1361                  * as a serialization point for all the different
1362                  * threads doing their things.
1363                  */
1364                 if (page_mkclean(page))
1365                         set_page_dirty(page);
1366                 /*
1367                  * We carefully synchronise fault handlers against
1368                  * installing a dirty pte and marking the page dirty
1369                  * at this point. We do this by having them hold the
1370                  * page lock at some point after installing their
1371                  * pte, but before marking the page dirty.
1372                  * Pages are always locked coming in here, so we get
1373                  * the desired exclusion. See mm/memory.c:do_wp_page()
1374                  * for more comments.
1375                  */
1376                 if (TestClearPageDirty(page)) {
1377                         dec_zone_page_state(page, NR_FILE_DIRTY);
1378                         dec_bdi_stat(mapping->backing_dev_info,
1379                                         BDI_RECLAIMABLE);
1380                         return 1;
1381                 }
1382                 return 0;
1383         }
1384         return TestClearPageDirty(page);
1385 }
1386 EXPORT_SYMBOL(clear_page_dirty_for_io);
1387
1388 int test_clear_page_writeback(struct page *page)
1389 {
1390         struct address_space *mapping = page_mapping(page);
1391         int ret;
1392
1393         if (mapping) {
1394                 struct backing_dev_info *bdi = mapping->backing_dev_info;
1395                 unsigned long flags;
1396
1397                 spin_lock_irqsave(&mapping->tree_lock, flags);
1398                 ret = TestClearPageWriteback(page);
1399                 if (ret) {
1400                         radix_tree_tag_clear(&mapping->page_tree,
1401                                                 page_index(page),
1402                                                 PAGECACHE_TAG_WRITEBACK);
1403                         if (bdi_cap_account_writeback(bdi)) {
1404                                 __dec_bdi_stat(bdi, BDI_WRITEBACK);
1405                                 __bdi_writeout_inc(bdi);
1406                         }
1407                 }
1408                 spin_unlock_irqrestore(&mapping->tree_lock, flags);
1409         } else {
1410                 ret = TestClearPageWriteback(page);
1411         }
1412         if (ret)
1413                 dec_zone_page_state(page, NR_WRITEBACK);
1414         return ret;
1415 }
1416
1417 int test_set_page_writeback(struct page *page)
1418 {
1419         struct address_space *mapping = page_mapping(page);
1420         int ret;
1421
1422         if (mapping) {
1423                 struct backing_dev_info *bdi = mapping->backing_dev_info;
1424                 unsigned long flags;
1425
1426                 spin_lock_irqsave(&mapping->tree_lock, flags);
1427                 ret = TestSetPageWriteback(page);
1428                 if (!ret) {
1429                         radix_tree_tag_set(&mapping->page_tree,
1430                                                 page_index(page),
1431                                                 PAGECACHE_TAG_WRITEBACK);
1432                         if (bdi_cap_account_writeback(bdi))
1433                                 __inc_bdi_stat(bdi, BDI_WRITEBACK);
1434                 }
1435                 if (!PageDirty(page))
1436                         radix_tree_tag_clear(&mapping->page_tree,
1437                                                 page_index(page),
1438                                                 PAGECACHE_TAG_DIRTY);
1439                 spin_unlock_irqrestore(&mapping->tree_lock, flags);
1440         } else {
1441                 ret = TestSetPageWriteback(page);
1442         }
1443         if (!ret)
1444                 inc_zone_page_state(page, NR_WRITEBACK);
1445         return ret;
1446
1447 }
1448 EXPORT_SYMBOL(test_set_page_writeback);
1449
1450 /*
1451  * Return true if any of the pages in the mapping are marked with the
1452  * passed tag.
1453  */
1454 int mapping_tagged(struct address_space *mapping, int tag)
1455 {
1456         int ret;
1457         rcu_read_lock();
1458         ret = radix_tree_tagged(&mapping->page_tree, tag);
1459         rcu_read_unlock();
1460         return ret;
1461 }
1462 EXPORT_SYMBOL(mapping_tagged);