tmpfs: copy truncate_inode_pages_range
[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 #include <trace/events/writeback.h>
38
39 /*
40  * Sleep at most 200ms at a time in balance_dirty_pages().
41  */
42 #define MAX_PAUSE               max(HZ/5, 1)
43
44 /*
45  * Estimate write bandwidth at 200ms intervals.
46  */
47 #define BANDWIDTH_INTERVAL      max(HZ/5, 1)
48
49 /*
50  * After a CPU has dirtied this many pages, balance_dirty_pages_ratelimited
51  * will look to see if it needs to force writeback or throttling.
52  */
53 static long ratelimit_pages = 32;
54
55 /*
56  * When balance_dirty_pages decides that the caller needs to perform some
57  * non-background writeback, this is how many pages it will attempt to write.
58  * It should be somewhat larger than dirtied pages to ensure that reasonably
59  * large amounts of I/O are submitted.
60  */
61 static inline long sync_writeback_pages(unsigned long dirtied)
62 {
63         if (dirtied < ratelimit_pages)
64                 dirtied = ratelimit_pages;
65
66         return dirtied + dirtied / 2;
67 }
68
69 /* The following parameters are exported via /proc/sys/vm */
70
71 /*
72  * Start background writeback (via writeback threads) at this percentage
73  */
74 int dirty_background_ratio = 10;
75
76 /*
77  * dirty_background_bytes starts at 0 (disabled) so that it is a function of
78  * dirty_background_ratio * the amount of dirtyable memory
79  */
80 unsigned long dirty_background_bytes;
81
82 /*
83  * free highmem will not be subtracted from the total free memory
84  * for calculating free ratios if vm_highmem_is_dirtyable is true
85  */
86 int vm_highmem_is_dirtyable;
87
88 /*
89  * The generator of dirty data starts writeback at this percentage
90  */
91 int vm_dirty_ratio = 20;
92
93 /*
94  * vm_dirty_bytes starts at 0 (disabled) so that it is a function of
95  * vm_dirty_ratio * the amount of dirtyable memory
96  */
97 unsigned long vm_dirty_bytes;
98
99 /*
100  * The interval between `kupdate'-style writebacks
101  */
102 unsigned int dirty_writeback_interval = 5 * 100; /* centiseconds */
103
104 /*
105  * The longest time for which data is allowed to remain dirty
106  */
107 unsigned int dirty_expire_interval = 30 * 100; /* centiseconds */
108
109 /*
110  * Flag that makes the machine dump writes/reads and block dirtyings.
111  */
112 int block_dump;
113
114 /*
115  * Flag that puts the machine in "laptop mode". Doubles as a timeout in jiffies:
116  * a full sync is triggered after this time elapses without any disk activity.
117  */
118 int laptop_mode;
119
120 EXPORT_SYMBOL(laptop_mode);
121
122 /* End of sysctl-exported parameters */
123
124 unsigned long global_dirty_limit;
125
126 /*
127  * Scale the writeback cache size proportional to the relative writeout speeds.
128  *
129  * We do this by keeping a floating proportion between BDIs, based on page
130  * writeback completions [end_page_writeback()]. Those devices that write out
131  * pages fastest will get the larger share, while the slower will get a smaller
132  * share.
133  *
134  * We use page writeout completions because we are interested in getting rid of
135  * dirty pages. Having them written out is the primary goal.
136  *
137  * We introduce a concept of time, a period over which we measure these events,
138  * because demand can/will vary over time. The length of this period itself is
139  * measured in page writeback completions.
140  *
141  */
142 static struct prop_descriptor vm_completions;
143 static struct prop_descriptor vm_dirties;
144
145 /*
146  * couple the period to the dirty_ratio:
147  *
148  *   period/2 ~ roundup_pow_of_two(dirty limit)
149  */
150 static int calc_period_shift(void)
151 {
152         unsigned long dirty_total;
153
154         if (vm_dirty_bytes)
155                 dirty_total = vm_dirty_bytes / PAGE_SIZE;
156         else
157                 dirty_total = (vm_dirty_ratio * determine_dirtyable_memory()) /
158                                 100;
159         return 2 + ilog2(dirty_total - 1);
160 }
161
162 /*
163  * update the period when the dirty threshold changes.
164  */
165 static void update_completion_period(void)
166 {
167         int shift = calc_period_shift();
168         prop_change_shift(&vm_completions, shift);
169         prop_change_shift(&vm_dirties, shift);
170 }
171
172 int dirty_background_ratio_handler(struct ctl_table *table, int write,
173                 void __user *buffer, size_t *lenp,
174                 loff_t *ppos)
175 {
176         int ret;
177
178         ret = proc_dointvec_minmax(table, write, buffer, lenp, ppos);
179         if (ret == 0 && write)
180                 dirty_background_bytes = 0;
181         return ret;
182 }
183
184 int dirty_background_bytes_handler(struct ctl_table *table, int write,
185                 void __user *buffer, size_t *lenp,
186                 loff_t *ppos)
187 {
188         int ret;
189
190         ret = proc_doulongvec_minmax(table, write, buffer, lenp, ppos);
191         if (ret == 0 && write)
192                 dirty_background_ratio = 0;
193         return ret;
194 }
195
196 int dirty_ratio_handler(struct ctl_table *table, int write,
197                 void __user *buffer, size_t *lenp,
198                 loff_t *ppos)
199 {
200         int old_ratio = vm_dirty_ratio;
201         int ret;
202
203         ret = proc_dointvec_minmax(table, write, buffer, lenp, ppos);
204         if (ret == 0 && write && vm_dirty_ratio != old_ratio) {
205                 update_completion_period();
206                 vm_dirty_bytes = 0;
207         }
208         return ret;
209 }
210
211
212 int dirty_bytes_handler(struct ctl_table *table, int write,
213                 void __user *buffer, size_t *lenp,
214                 loff_t *ppos)
215 {
216         unsigned long old_bytes = vm_dirty_bytes;
217         int ret;
218
219         ret = proc_doulongvec_minmax(table, write, buffer, lenp, ppos);
220         if (ret == 0 && write && vm_dirty_bytes != old_bytes) {
221                 update_completion_period();
222                 vm_dirty_ratio = 0;
223         }
224         return ret;
225 }
226
227 /*
228  * Increment the BDI's writeout completion count and the global writeout
229  * completion count. Called from test_clear_page_writeback().
230  */
231 static inline void __bdi_writeout_inc(struct backing_dev_info *bdi)
232 {
233         __inc_bdi_stat(bdi, BDI_WRITTEN);
234         __prop_inc_percpu_max(&vm_completions, &bdi->completions,
235                               bdi->max_prop_frac);
236 }
237
238 void bdi_writeout_inc(struct backing_dev_info *bdi)
239 {
240         unsigned long flags;
241
242         local_irq_save(flags);
243         __bdi_writeout_inc(bdi);
244         local_irq_restore(flags);
245 }
246 EXPORT_SYMBOL_GPL(bdi_writeout_inc);
247
248 void task_dirty_inc(struct task_struct *tsk)
249 {
250         prop_inc_single(&vm_dirties, &tsk->dirties);
251 }
252
253 /*
254  * Obtain an accurate fraction of the BDI's portion.
255  */
256 static void bdi_writeout_fraction(struct backing_dev_info *bdi,
257                 long *numerator, long *denominator)
258 {
259         prop_fraction_percpu(&vm_completions, &bdi->completions,
260                                 numerator, denominator);
261 }
262
263 static inline void task_dirties_fraction(struct task_struct *tsk,
264                 long *numerator, long *denominator)
265 {
266         prop_fraction_single(&vm_dirties, &tsk->dirties,
267                                 numerator, denominator);
268 }
269
270 /*
271  * task_dirty_limit - scale down dirty throttling threshold for one task
272  *
273  * task specific dirty limit:
274  *
275  *   dirty -= (dirty/8) * p_{t}
276  *
277  * To protect light/slow dirtying tasks from heavier/fast ones, we start
278  * throttling individual tasks before reaching the bdi dirty limit.
279  * Relatively low thresholds will be allocated to heavy dirtiers. So when
280  * dirty pages grow large, heavy dirtiers will be throttled first, which will
281  * effectively curb the growth of dirty pages. Light dirtiers with high enough
282  * dirty threshold may never get throttled.
283  */
284 #define TASK_LIMIT_FRACTION 8
285 static unsigned long task_dirty_limit(struct task_struct *tsk,
286                                        unsigned long bdi_dirty)
287 {
288         long numerator, denominator;
289         unsigned long dirty = bdi_dirty;
290         u64 inv = dirty / TASK_LIMIT_FRACTION;
291
292         task_dirties_fraction(tsk, &numerator, &denominator);
293         inv *= numerator;
294         do_div(inv, denominator);
295
296         dirty -= inv;
297
298         return max(dirty, bdi_dirty/2);
299 }
300
301 /* Minimum limit for any task */
302 static unsigned long task_min_dirty_limit(unsigned long bdi_dirty)
303 {
304         return bdi_dirty - bdi_dirty / TASK_LIMIT_FRACTION;
305 }
306
307 /*
308  *
309  */
310 static unsigned int bdi_min_ratio;
311
312 int bdi_set_min_ratio(struct backing_dev_info *bdi, unsigned int min_ratio)
313 {
314         int ret = 0;
315
316         spin_lock_bh(&bdi_lock);
317         if (min_ratio > bdi->max_ratio) {
318                 ret = -EINVAL;
319         } else {
320                 min_ratio -= bdi->min_ratio;
321                 if (bdi_min_ratio + min_ratio < 100) {
322                         bdi_min_ratio += min_ratio;
323                         bdi->min_ratio += min_ratio;
324                 } else {
325                         ret = -EINVAL;
326                 }
327         }
328         spin_unlock_bh(&bdi_lock);
329
330         return ret;
331 }
332
333 int bdi_set_max_ratio(struct backing_dev_info *bdi, unsigned max_ratio)
334 {
335         int ret = 0;
336
337         if (max_ratio > 100)
338                 return -EINVAL;
339
340         spin_lock_bh(&bdi_lock);
341         if (bdi->min_ratio > max_ratio) {
342                 ret = -EINVAL;
343         } else {
344                 bdi->max_ratio = max_ratio;
345                 bdi->max_prop_frac = (PROP_FRAC_BASE * max_ratio) / 100;
346         }
347         spin_unlock_bh(&bdi_lock);
348
349         return ret;
350 }
351 EXPORT_SYMBOL(bdi_set_max_ratio);
352
353 /*
354  * Work out the current dirty-memory clamping and background writeout
355  * thresholds.
356  *
357  * The main aim here is to lower them aggressively if there is a lot of mapped
358  * memory around.  To avoid stressing page reclaim with lots of unreclaimable
359  * pages.  It is better to clamp down on writers than to start swapping, and
360  * performing lots of scanning.
361  *
362  * We only allow 1/2 of the currently-unmapped memory to be dirtied.
363  *
364  * We don't permit the clamping level to fall below 5% - that is getting rather
365  * excessive.
366  *
367  * We make sure that the background writeout level is below the adjusted
368  * clamping level.
369  */
370
371 static unsigned long highmem_dirtyable_memory(unsigned long total)
372 {
373 #ifdef CONFIG_HIGHMEM
374         int node;
375         unsigned long x = 0;
376
377         for_each_node_state(node, N_HIGH_MEMORY) {
378                 struct zone *z =
379                         &NODE_DATA(node)->node_zones[ZONE_HIGHMEM];
380
381                 x += zone_page_state(z, NR_FREE_PAGES) +
382                      zone_reclaimable_pages(z);
383         }
384         /*
385          * Make sure that the number of highmem pages is never larger
386          * than the number of the total dirtyable memory. This can only
387          * occur in very strange VM situations but we want to make sure
388          * that this does not occur.
389          */
390         return min(x, total);
391 #else
392         return 0;
393 #endif
394 }
395
396 /**
397  * determine_dirtyable_memory - amount of memory that may be used
398  *
399  * Returns the numebr of pages that can currently be freed and used
400  * by the kernel for direct mappings.
401  */
402 unsigned long determine_dirtyable_memory(void)
403 {
404         unsigned long x;
405
406         x = global_page_state(NR_FREE_PAGES) + global_reclaimable_pages();
407
408         if (!vm_highmem_is_dirtyable)
409                 x -= highmem_dirtyable_memory(x);
410
411         return x + 1;   /* Ensure that we never return 0 */
412 }
413
414 static unsigned long hard_dirty_limit(unsigned long thresh)
415 {
416         return max(thresh, global_dirty_limit);
417 }
418
419 /*
420  * global_dirty_limits - background-writeback and dirty-throttling thresholds
421  *
422  * Calculate the dirty thresholds based on sysctl parameters
423  * - vm.dirty_background_ratio  or  vm.dirty_background_bytes
424  * - vm.dirty_ratio             or  vm.dirty_bytes
425  * The dirty limits will be lifted by 1/4 for PF_LESS_THROTTLE (ie. nfsd) and
426  * real-time tasks.
427  */
428 void global_dirty_limits(unsigned long *pbackground, unsigned long *pdirty)
429 {
430         unsigned long background;
431         unsigned long dirty;
432         unsigned long uninitialized_var(available_memory);
433         struct task_struct *tsk;
434
435         if (!vm_dirty_bytes || !dirty_background_bytes)
436                 available_memory = determine_dirtyable_memory();
437
438         if (vm_dirty_bytes)
439                 dirty = DIV_ROUND_UP(vm_dirty_bytes, PAGE_SIZE);
440         else
441                 dirty = (vm_dirty_ratio * available_memory) / 100;
442
443         if (dirty_background_bytes)
444                 background = DIV_ROUND_UP(dirty_background_bytes, PAGE_SIZE);
445         else
446                 background = (dirty_background_ratio * available_memory) / 100;
447
448         if (background >= dirty)
449                 background = dirty / 2;
450         tsk = current;
451         if (tsk->flags & PF_LESS_THROTTLE || rt_task(tsk)) {
452                 background += background / 4;
453                 dirty += dirty / 4;
454         }
455         *pbackground = background;
456         *pdirty = dirty;
457         trace_global_dirty_state(background, dirty);
458 }
459
460 /**
461  * bdi_dirty_limit - @bdi's share of dirty throttling threshold
462  * @bdi: the backing_dev_info to query
463  * @dirty: global dirty limit in pages
464  *
465  * Returns @bdi's dirty limit in pages. The term "dirty" in the context of
466  * dirty balancing includes all PG_dirty, PG_writeback and NFS unstable pages.
467  * And the "limit" in the name is not seriously taken as hard limit in
468  * balance_dirty_pages().
469  *
470  * It allocates high/low dirty limits to fast/slow devices, in order to prevent
471  * - starving fast devices
472  * - piling up dirty pages (that will take long time to sync) on slow devices
473  *
474  * The bdi's share of dirty limit will be adapting to its throughput and
475  * bounded by the bdi->min_ratio and/or bdi->max_ratio parameters, if set.
476  */
477 unsigned long bdi_dirty_limit(struct backing_dev_info *bdi, unsigned long dirty)
478 {
479         u64 bdi_dirty;
480         long numerator, denominator;
481
482         /*
483          * Calculate this BDI's share of the dirty ratio.
484          */
485         bdi_writeout_fraction(bdi, &numerator, &denominator);
486
487         bdi_dirty = (dirty * (100 - bdi_min_ratio)) / 100;
488         bdi_dirty *= numerator;
489         do_div(bdi_dirty, denominator);
490
491         bdi_dirty += (dirty * bdi->min_ratio) / 100;
492         if (bdi_dirty > (dirty * bdi->max_ratio) / 100)
493                 bdi_dirty = dirty * bdi->max_ratio / 100;
494
495         return bdi_dirty;
496 }
497
498 static void bdi_update_write_bandwidth(struct backing_dev_info *bdi,
499                                        unsigned long elapsed,
500                                        unsigned long written)
501 {
502         const unsigned long period = roundup_pow_of_two(3 * HZ);
503         unsigned long avg = bdi->avg_write_bandwidth;
504         unsigned long old = bdi->write_bandwidth;
505         u64 bw;
506
507         /*
508          * bw = written * HZ / elapsed
509          *
510          *                   bw * elapsed + write_bandwidth * (period - elapsed)
511          * write_bandwidth = ---------------------------------------------------
512          *                                          period
513          */
514         bw = written - bdi->written_stamp;
515         bw *= HZ;
516         if (unlikely(elapsed > period)) {
517                 do_div(bw, elapsed);
518                 avg = bw;
519                 goto out;
520         }
521         bw += (u64)bdi->write_bandwidth * (period - elapsed);
522         bw >>= ilog2(period);
523
524         /*
525          * one more level of smoothing, for filtering out sudden spikes
526          */
527         if (avg > old && old >= (unsigned long)bw)
528                 avg -= (avg - old) >> 3;
529
530         if (avg < old && old <= (unsigned long)bw)
531                 avg += (old - avg) >> 3;
532
533 out:
534         bdi->write_bandwidth = bw;
535         bdi->avg_write_bandwidth = avg;
536 }
537
538 /*
539  * The global dirtyable memory and dirty threshold could be suddenly knocked
540  * down by a large amount (eg. on the startup of KVM in a swapless system).
541  * This may throw the system into deep dirty exceeded state and throttle
542  * heavy/light dirtiers alike. To retain good responsiveness, maintain
543  * global_dirty_limit for tracking slowly down to the knocked down dirty
544  * threshold.
545  */
546 static void update_dirty_limit(unsigned long thresh, unsigned long dirty)
547 {
548         unsigned long limit = global_dirty_limit;
549
550         /*
551          * Follow up in one step.
552          */
553         if (limit < thresh) {
554                 limit = thresh;
555                 goto update;
556         }
557
558         /*
559          * Follow down slowly. Use the higher one as the target, because thresh
560          * may drop below dirty. This is exactly the reason to introduce
561          * global_dirty_limit which is guaranteed to lie above the dirty pages.
562          */
563         thresh = max(thresh, dirty);
564         if (limit > thresh) {
565                 limit -= (limit - thresh) >> 5;
566                 goto update;
567         }
568         return;
569 update:
570         global_dirty_limit = limit;
571 }
572
573 static void global_update_bandwidth(unsigned long thresh,
574                                     unsigned long dirty,
575                                     unsigned long now)
576 {
577         static DEFINE_SPINLOCK(dirty_lock);
578         static unsigned long update_time;
579
580         /*
581          * check locklessly first to optimize away locking for the most time
582          */
583         if (time_before(now, update_time + BANDWIDTH_INTERVAL))
584                 return;
585
586         spin_lock(&dirty_lock);
587         if (time_after_eq(now, update_time + BANDWIDTH_INTERVAL)) {
588                 update_dirty_limit(thresh, dirty);
589                 update_time = now;
590         }
591         spin_unlock(&dirty_lock);
592 }
593
594 void __bdi_update_bandwidth(struct backing_dev_info *bdi,
595                             unsigned long thresh,
596                             unsigned long dirty,
597                             unsigned long bdi_thresh,
598                             unsigned long bdi_dirty,
599                             unsigned long start_time)
600 {
601         unsigned long now = jiffies;
602         unsigned long elapsed = now - bdi->bw_time_stamp;
603         unsigned long written;
604
605         /*
606          * rate-limit, only update once every 200ms.
607          */
608         if (elapsed < BANDWIDTH_INTERVAL)
609                 return;
610
611         written = percpu_counter_read(&bdi->bdi_stat[BDI_WRITTEN]);
612
613         /*
614          * Skip quiet periods when disk bandwidth is under-utilized.
615          * (at least 1s idle time between two flusher runs)
616          */
617         if (elapsed > HZ && time_before(bdi->bw_time_stamp, start_time))
618                 goto snapshot;
619
620         if (thresh)
621                 global_update_bandwidth(thresh, dirty, now);
622
623         bdi_update_write_bandwidth(bdi, elapsed, written);
624
625 snapshot:
626         bdi->written_stamp = written;
627         bdi->bw_time_stamp = now;
628 }
629
630 static void bdi_update_bandwidth(struct backing_dev_info *bdi,
631                                  unsigned long thresh,
632                                  unsigned long dirty,
633                                  unsigned long bdi_thresh,
634                                  unsigned long bdi_dirty,
635                                  unsigned long start_time)
636 {
637         if (time_is_after_eq_jiffies(bdi->bw_time_stamp + BANDWIDTH_INTERVAL))
638                 return;
639         spin_lock(&bdi->wb.list_lock);
640         __bdi_update_bandwidth(bdi, thresh, dirty, bdi_thresh, bdi_dirty,
641                                start_time);
642         spin_unlock(&bdi->wb.list_lock);
643 }
644
645 /*
646  * balance_dirty_pages() must be called by processes which are generating dirty
647  * data.  It looks at the number of dirty pages in the machine and will force
648  * the caller to perform writeback if the system is over `vm_dirty_ratio'.
649  * If we're over `background_thresh' then the writeback threads are woken to
650  * perform some writeout.
651  */
652 static void balance_dirty_pages(struct address_space *mapping,
653                                 unsigned long write_chunk)
654 {
655         unsigned long nr_reclaimable, bdi_nr_reclaimable;
656         unsigned long nr_dirty;  /* = file_dirty + writeback + unstable_nfs */
657         unsigned long bdi_dirty;
658         unsigned long background_thresh;
659         unsigned long dirty_thresh;
660         unsigned long bdi_thresh;
661         unsigned long task_bdi_thresh;
662         unsigned long min_task_bdi_thresh;
663         unsigned long pages_written = 0;
664         unsigned long pause = 1;
665         bool dirty_exceeded = false;
666         bool clear_dirty_exceeded = true;
667         struct backing_dev_info *bdi = mapping->backing_dev_info;
668         unsigned long start_time = jiffies;
669
670         for (;;) {
671                 nr_reclaimable = global_page_state(NR_FILE_DIRTY) +
672                                         global_page_state(NR_UNSTABLE_NFS);
673                 nr_dirty = nr_reclaimable + global_page_state(NR_WRITEBACK);
674
675                 global_dirty_limits(&background_thresh, &dirty_thresh);
676
677                 /*
678                  * Throttle it only when the background writeback cannot
679                  * catch-up. This avoids (excessively) small writeouts
680                  * when the bdi limits are ramping up.
681                  */
682                 if (nr_dirty <= (background_thresh + dirty_thresh) / 2)
683                         break;
684
685                 bdi_thresh = bdi_dirty_limit(bdi, dirty_thresh);
686                 min_task_bdi_thresh = task_min_dirty_limit(bdi_thresh);
687                 task_bdi_thresh = task_dirty_limit(current, bdi_thresh);
688
689                 /*
690                  * In order to avoid the stacked BDI deadlock we need
691                  * to ensure we accurately count the 'dirty' pages when
692                  * the threshold is low.
693                  *
694                  * Otherwise it would be possible to get thresh+n pages
695                  * reported dirty, even though there are thresh-m pages
696                  * actually dirty; with m+n sitting in the percpu
697                  * deltas.
698                  */
699                 if (task_bdi_thresh < 2 * bdi_stat_error(bdi)) {
700                         bdi_nr_reclaimable = bdi_stat_sum(bdi, BDI_RECLAIMABLE);
701                         bdi_dirty = bdi_nr_reclaimable +
702                                     bdi_stat_sum(bdi, BDI_WRITEBACK);
703                 } else {
704                         bdi_nr_reclaimable = bdi_stat(bdi, BDI_RECLAIMABLE);
705                         bdi_dirty = bdi_nr_reclaimable +
706                                     bdi_stat(bdi, BDI_WRITEBACK);
707                 }
708
709                 /*
710                  * The bdi thresh is somehow "soft" limit derived from the
711                  * global "hard" limit. The former helps to prevent heavy IO
712                  * bdi or process from holding back light ones; The latter is
713                  * the last resort safeguard.
714                  */
715                 dirty_exceeded = (bdi_dirty > task_bdi_thresh) ||
716                                   (nr_dirty > dirty_thresh);
717                 clear_dirty_exceeded = (bdi_dirty <= min_task_bdi_thresh) &&
718                                         (nr_dirty <= dirty_thresh);
719
720                 if (!dirty_exceeded)
721                         break;
722
723                 if (!bdi->dirty_exceeded)
724                         bdi->dirty_exceeded = 1;
725
726                 bdi_update_bandwidth(bdi, dirty_thresh, nr_dirty,
727                                      bdi_thresh, bdi_dirty, start_time);
728
729                 /* Note: nr_reclaimable denotes nr_dirty + nr_unstable.
730                  * Unstable writes are a feature of certain networked
731                  * filesystems (i.e. NFS) in which data may have been
732                  * written to the server's write cache, but has not yet
733                  * been flushed to permanent storage.
734                  * Only move pages to writeback if this bdi is over its
735                  * threshold otherwise wait until the disk writes catch
736                  * up.
737                  */
738                 trace_balance_dirty_start(bdi);
739                 if (bdi_nr_reclaimable > task_bdi_thresh) {
740                         pages_written += writeback_inodes_wb(&bdi->wb,
741                                                              write_chunk);
742                         trace_balance_dirty_written(bdi, pages_written);
743                         if (pages_written >= write_chunk)
744                                 break;          /* We've done our duty */
745                 }
746                 __set_current_state(TASK_UNINTERRUPTIBLE);
747                 io_schedule_timeout(pause);
748                 trace_balance_dirty_wait(bdi);
749
750                 dirty_thresh = hard_dirty_limit(dirty_thresh);
751                 /*
752                  * max-pause area. If dirty exceeded but still within this
753                  * area, no need to sleep for more than 200ms: (a) 8 pages per
754                  * 200ms is typically more than enough to curb heavy dirtiers;
755                  * (b) the pause time limit makes the dirtiers more responsive.
756                  */
757                 if (nr_dirty < dirty_thresh +
758                                dirty_thresh / DIRTY_MAXPAUSE_AREA &&
759                     time_after(jiffies, start_time + MAX_PAUSE))
760                         break;
761                 /*
762                  * pass-good area. When some bdi gets blocked (eg. NFS server
763                  * not responding), or write bandwidth dropped dramatically due
764                  * to concurrent reads, or dirty threshold suddenly dropped and
765                  * the dirty pages cannot be brought down anytime soon (eg. on
766                  * slow USB stick), at least let go of the good bdi's.
767                  */
768                 if (nr_dirty < dirty_thresh +
769                                dirty_thresh / DIRTY_PASSGOOD_AREA &&
770                     bdi_dirty < bdi_thresh)
771                         break;
772
773                 /*
774                  * Increase the delay for each loop, up to our previous
775                  * default of taking a 100ms nap.
776                  */
777                 pause <<= 1;
778                 if (pause > HZ / 10)
779                         pause = HZ / 10;
780         }
781
782         /* Clear dirty_exceeded flag only when no task can exceed the limit */
783         if (clear_dirty_exceeded && bdi->dirty_exceeded)
784                 bdi->dirty_exceeded = 0;
785
786         if (writeback_in_progress(bdi))
787                 return;
788
789         /*
790          * In laptop mode, we wait until hitting the higher threshold before
791          * starting background writeout, and then write out all the way down
792          * to the lower threshold.  So slow writers cause minimal disk activity.
793          *
794          * In normal mode, we start background writeout at the lower
795          * background_thresh, to keep the amount of dirty memory low.
796          */
797         if ((laptop_mode && pages_written) ||
798             (!laptop_mode && (nr_reclaimable > background_thresh)))
799                 bdi_start_background_writeback(bdi);
800 }
801
802 void set_page_dirty_balance(struct page *page, int page_mkwrite)
803 {
804         if (set_page_dirty(page) || page_mkwrite) {
805                 struct address_space *mapping = page_mapping(page);
806
807                 if (mapping)
808                         balance_dirty_pages_ratelimited(mapping);
809         }
810 }
811
812 static DEFINE_PER_CPU(unsigned long, bdp_ratelimits) = 0;
813
814 /**
815  * balance_dirty_pages_ratelimited_nr - balance dirty memory state
816  * @mapping: address_space which was dirtied
817  * @nr_pages_dirtied: number of pages which the caller has just dirtied
818  *
819  * Processes which are dirtying memory should call in here once for each page
820  * which was newly dirtied.  The function will periodically check the system's
821  * dirty state and will initiate writeback if needed.
822  *
823  * On really big machines, get_writeback_state is expensive, so try to avoid
824  * calling it too often (ratelimiting).  But once we're over the dirty memory
825  * limit we decrease the ratelimiting by a lot, to prevent individual processes
826  * from overshooting the limit by (ratelimit_pages) each.
827  */
828 void balance_dirty_pages_ratelimited_nr(struct address_space *mapping,
829                                         unsigned long nr_pages_dirtied)
830 {
831         struct backing_dev_info *bdi = mapping->backing_dev_info;
832         unsigned long ratelimit;
833         unsigned long *p;
834
835         if (!bdi_cap_account_dirty(bdi))
836                 return;
837
838         ratelimit = ratelimit_pages;
839         if (mapping->backing_dev_info->dirty_exceeded)
840                 ratelimit = 8;
841
842         /*
843          * Check the rate limiting. Also, we do not want to throttle real-time
844          * tasks in balance_dirty_pages(). Period.
845          */
846         preempt_disable();
847         p =  &__get_cpu_var(bdp_ratelimits);
848         *p += nr_pages_dirtied;
849         if (unlikely(*p >= ratelimit)) {
850                 ratelimit = sync_writeback_pages(*p);
851                 *p = 0;
852                 preempt_enable();
853                 balance_dirty_pages(mapping, ratelimit);
854                 return;
855         }
856         preempt_enable();
857 }
858 EXPORT_SYMBOL(balance_dirty_pages_ratelimited_nr);
859
860 void throttle_vm_writeout(gfp_t gfp_mask)
861 {
862         unsigned long background_thresh;
863         unsigned long dirty_thresh;
864
865         for ( ; ; ) {
866                 global_dirty_limits(&background_thresh, &dirty_thresh);
867
868                 /*
869                  * Boost the allowable dirty threshold a bit for page
870                  * allocators so they don't get DoS'ed by heavy writers
871                  */
872                 dirty_thresh += dirty_thresh / 10;      /* wheeee... */
873
874                 if (global_page_state(NR_UNSTABLE_NFS) +
875                         global_page_state(NR_WRITEBACK) <= dirty_thresh)
876                                 break;
877                 congestion_wait(BLK_RW_ASYNC, HZ/10);
878
879                 /*
880                  * The caller might hold locks which can prevent IO completion
881                  * or progress in the filesystem.  So we cannot just sit here
882                  * waiting for IO to complete.
883                  */
884                 if ((gfp_mask & (__GFP_FS|__GFP_IO)) != (__GFP_FS|__GFP_IO))
885                         break;
886         }
887 }
888
889 /*
890  * sysctl handler for /proc/sys/vm/dirty_writeback_centisecs
891  */
892 int dirty_writeback_centisecs_handler(ctl_table *table, int write,
893         void __user *buffer, size_t *length, loff_t *ppos)
894 {
895         proc_dointvec(table, write, buffer, length, ppos);
896         bdi_arm_supers_timer();
897         return 0;
898 }
899
900 #ifdef CONFIG_BLOCK
901 void laptop_mode_timer_fn(unsigned long data)
902 {
903         struct request_queue *q = (struct request_queue *)data;
904         int nr_pages = global_page_state(NR_FILE_DIRTY) +
905                 global_page_state(NR_UNSTABLE_NFS);
906
907         /*
908          * We want to write everything out, not just down to the dirty
909          * threshold
910          */
911         if (bdi_has_dirty_io(&q->backing_dev_info))
912                 bdi_start_writeback(&q->backing_dev_info, nr_pages);
913 }
914
915 /*
916  * We've spun up the disk and we're in laptop mode: schedule writeback
917  * of all dirty data a few seconds from now.  If the flush is already scheduled
918  * then push it back - the user is still using the disk.
919  */
920 void laptop_io_completion(struct backing_dev_info *info)
921 {
922         mod_timer(&info->laptop_mode_wb_timer, jiffies + laptop_mode);
923 }
924
925 /*
926  * We're in laptop mode and we've just synced. The sync's writes will have
927  * caused another writeback to be scheduled by laptop_io_completion.
928  * Nothing needs to be written back anymore, so we unschedule the writeback.
929  */
930 void laptop_sync_completion(void)
931 {
932         struct backing_dev_info *bdi;
933
934         rcu_read_lock();
935
936         list_for_each_entry_rcu(bdi, &bdi_list, bdi_list)
937                 del_timer(&bdi->laptop_mode_wb_timer);
938
939         rcu_read_unlock();
940 }
941 #endif
942
943 /*
944  * If ratelimit_pages is too high then we can get into dirty-data overload
945  * if a large number of processes all perform writes at the same time.
946  * If it is too low then SMP machines will call the (expensive)
947  * get_writeback_state too often.
948  *
949  * Here we set ratelimit_pages to a level which ensures that when all CPUs are
950  * dirtying in parallel, we cannot go more than 3% (1/32) over the dirty memory
951  * thresholds before writeback cuts in.
952  *
953  * But the limit should not be set too high.  Because it also controls the
954  * amount of memory which the balance_dirty_pages() caller has to write back.
955  * If this is too large then the caller will block on the IO queue all the
956  * time.  So limit it to four megabytes - the balance_dirty_pages() caller
957  * will write six megabyte chunks, max.
958  */
959
960 void writeback_set_ratelimit(void)
961 {
962         ratelimit_pages = vm_total_pages / (num_online_cpus() * 32);
963         if (ratelimit_pages < 16)
964                 ratelimit_pages = 16;
965         if (ratelimit_pages * PAGE_CACHE_SIZE > 4096 * 1024)
966                 ratelimit_pages = (4096 * 1024) / PAGE_CACHE_SIZE;
967 }
968
969 static int __cpuinit
970 ratelimit_handler(struct notifier_block *self, unsigned long u, void *v)
971 {
972         writeback_set_ratelimit();
973         return NOTIFY_DONE;
974 }
975
976 static struct notifier_block __cpuinitdata ratelimit_nb = {
977         .notifier_call  = ratelimit_handler,
978         .next           = NULL,
979 };
980
981 /*
982  * Called early on to tune the page writeback dirty limits.
983  *
984  * We used to scale dirty pages according to how total memory
985  * related to pages that could be allocated for buffers (by
986  * comparing nr_free_buffer_pages() to vm_total_pages.
987  *
988  * However, that was when we used "dirty_ratio" to scale with
989  * all memory, and we don't do that any more. "dirty_ratio"
990  * is now applied to total non-HIGHPAGE memory (by subtracting
991  * totalhigh_pages from vm_total_pages), and as such we can't
992  * get into the old insane situation any more where we had
993  * large amounts of dirty pages compared to a small amount of
994  * non-HIGHMEM memory.
995  *
996  * But we might still want to scale the dirty_ratio by how
997  * much memory the box has..
998  */
999 void __init page_writeback_init(void)
1000 {
1001         int shift;
1002
1003         writeback_set_ratelimit();
1004         register_cpu_notifier(&ratelimit_nb);
1005
1006         shift = calc_period_shift();
1007         prop_descriptor_init(&vm_completions, shift);
1008         prop_descriptor_init(&vm_dirties, shift);
1009 }
1010
1011 /**
1012  * tag_pages_for_writeback - tag pages to be written by write_cache_pages
1013  * @mapping: address space structure to write
1014  * @start: starting page index
1015  * @end: ending page index (inclusive)
1016  *
1017  * This function scans the page range from @start to @end (inclusive) and tags
1018  * all pages that have DIRTY tag set with a special TOWRITE tag. The idea is
1019  * that write_cache_pages (or whoever calls this function) will then use
1020  * TOWRITE tag to identify pages eligible for writeback.  This mechanism is
1021  * used to avoid livelocking of writeback by a process steadily creating new
1022  * dirty pages in the file (thus it is important for this function to be quick
1023  * so that it can tag pages faster than a dirtying process can create them).
1024  */
1025 /*
1026  * We tag pages in batches of WRITEBACK_TAG_BATCH to reduce tree_lock latency.
1027  */
1028 void tag_pages_for_writeback(struct address_space *mapping,
1029                              pgoff_t start, pgoff_t end)
1030 {
1031 #define WRITEBACK_TAG_BATCH 4096
1032         unsigned long tagged;
1033
1034         do {
1035                 spin_lock_irq(&mapping->tree_lock);
1036                 tagged = radix_tree_range_tag_if_tagged(&mapping->page_tree,
1037                                 &start, end, WRITEBACK_TAG_BATCH,
1038                                 PAGECACHE_TAG_DIRTY, PAGECACHE_TAG_TOWRITE);
1039                 spin_unlock_irq(&mapping->tree_lock);
1040                 WARN_ON_ONCE(tagged > WRITEBACK_TAG_BATCH);
1041                 cond_resched();
1042                 /* We check 'start' to handle wrapping when end == ~0UL */
1043         } while (tagged >= WRITEBACK_TAG_BATCH && start);
1044 }
1045 EXPORT_SYMBOL(tag_pages_for_writeback);
1046
1047 /**
1048  * write_cache_pages - walk the list of dirty pages of the given address space and write all of them.
1049  * @mapping: address space structure to write
1050  * @wbc: subtract the number of written pages from *@wbc->nr_to_write
1051  * @writepage: function called for each page
1052  * @data: data passed to writepage function
1053  *
1054  * If a page is already under I/O, write_cache_pages() skips it, even
1055  * if it's dirty.  This is desirable behaviour for memory-cleaning writeback,
1056  * but it is INCORRECT for data-integrity system calls such as fsync().  fsync()
1057  * and msync() need to guarantee that all the data which was dirty at the time
1058  * the call was made get new I/O started against them.  If wbc->sync_mode is
1059  * WB_SYNC_ALL then we were called for data integrity and we must wait for
1060  * existing IO to complete.
1061  *
1062  * To avoid livelocks (when other process dirties new pages), we first tag
1063  * pages which should be written back with TOWRITE tag and only then start
1064  * writing them. For data-integrity sync we have to be careful so that we do
1065  * not miss some pages (e.g., because some other process has cleared TOWRITE
1066  * tag we set). The rule we follow is that TOWRITE tag can be cleared only
1067  * by the process clearing the DIRTY tag (and submitting the page for IO).
1068  */
1069 int write_cache_pages(struct address_space *mapping,
1070                       struct writeback_control *wbc, writepage_t writepage,
1071                       void *data)
1072 {
1073         int ret = 0;
1074         int done = 0;
1075         struct pagevec pvec;
1076         int nr_pages;
1077         pgoff_t uninitialized_var(writeback_index);
1078         pgoff_t index;
1079         pgoff_t end;            /* Inclusive */
1080         pgoff_t done_index;
1081         int cycled;
1082         int range_whole = 0;
1083         int tag;
1084
1085         pagevec_init(&pvec, 0);
1086         if (wbc->range_cyclic) {
1087                 writeback_index = mapping->writeback_index; /* prev offset */
1088                 index = writeback_index;
1089                 if (index == 0)
1090                         cycled = 1;
1091                 else
1092                         cycled = 0;
1093                 end = -1;
1094         } else {
1095                 index = wbc->range_start >> PAGE_CACHE_SHIFT;
1096                 end = wbc->range_end >> PAGE_CACHE_SHIFT;
1097                 if (wbc->range_start == 0 && wbc->range_end == LLONG_MAX)
1098                         range_whole = 1;
1099                 cycled = 1; /* ignore range_cyclic tests */
1100         }
1101         if (wbc->sync_mode == WB_SYNC_ALL || wbc->tagged_writepages)
1102                 tag = PAGECACHE_TAG_TOWRITE;
1103         else
1104                 tag = PAGECACHE_TAG_DIRTY;
1105 retry:
1106         if (wbc->sync_mode == WB_SYNC_ALL || wbc->tagged_writepages)
1107                 tag_pages_for_writeback(mapping, index, end);
1108         done_index = index;
1109         while (!done && (index <= end)) {
1110                 int i;
1111
1112                 nr_pages = pagevec_lookup_tag(&pvec, mapping, &index, tag,
1113                               min(end - index, (pgoff_t)PAGEVEC_SIZE-1) + 1);
1114                 if (nr_pages == 0)
1115                         break;
1116
1117                 for (i = 0; i < nr_pages; i++) {
1118                         struct page *page = pvec.pages[i];
1119
1120                         /*
1121                          * At this point, the page may be truncated or
1122                          * invalidated (changing page->mapping to NULL), or
1123                          * even swizzled back from swapper_space to tmpfs file
1124                          * mapping. However, page->index will not change
1125                          * because we have a reference on the page.
1126                          */
1127                         if (page->index > end) {
1128                                 /*
1129                                  * can't be range_cyclic (1st pass) because
1130                                  * end == -1 in that case.
1131                                  */
1132                                 done = 1;
1133                                 break;
1134                         }
1135
1136                         done_index = page->index;
1137
1138                         lock_page(page);
1139
1140                         /*
1141                          * Page truncated or invalidated. We can freely skip it
1142                          * then, even for data integrity operations: the page
1143                          * has disappeared concurrently, so there could be no
1144                          * real expectation of this data interity operation
1145                          * even if there is now a new, dirty page at the same
1146                          * pagecache address.
1147                          */
1148                         if (unlikely(page->mapping != mapping)) {
1149 continue_unlock:
1150                                 unlock_page(page);
1151                                 continue;
1152                         }
1153
1154                         if (!PageDirty(page)) {
1155                                 /* someone wrote it for us */
1156                                 goto continue_unlock;
1157                         }
1158
1159                         if (PageWriteback(page)) {
1160                                 if (wbc->sync_mode != WB_SYNC_NONE)
1161                                         wait_on_page_writeback(page);
1162                                 else
1163                                         goto continue_unlock;
1164                         }
1165
1166                         BUG_ON(PageWriteback(page));
1167                         if (!clear_page_dirty_for_io(page))
1168                                 goto continue_unlock;
1169
1170                         trace_wbc_writepage(wbc, mapping->backing_dev_info);
1171                         ret = (*writepage)(page, wbc, data);
1172                         if (unlikely(ret)) {
1173                                 if (ret == AOP_WRITEPAGE_ACTIVATE) {
1174                                         unlock_page(page);
1175                                         ret = 0;
1176                                 } else {
1177                                         /*
1178                                          * done_index is set past this page,
1179                                          * so media errors will not choke
1180                                          * background writeout for the entire
1181                                          * file. This has consequences for
1182                                          * range_cyclic semantics (ie. it may
1183                                          * not be suitable for data integrity
1184                                          * writeout).
1185                                          */
1186                                         done_index = page->index + 1;
1187                                         done = 1;
1188                                         break;
1189                                 }
1190                         }
1191
1192                         /*
1193                          * We stop writing back only if we are not doing
1194                          * integrity sync. In case of integrity sync we have to
1195                          * keep going until we have written all the pages
1196                          * we tagged for writeback prior to entering this loop.
1197                          */
1198                         if (--wbc->nr_to_write <= 0 &&
1199                             wbc->sync_mode == WB_SYNC_NONE) {
1200                                 done = 1;
1201                                 break;
1202                         }
1203                 }
1204                 pagevec_release(&pvec);
1205                 cond_resched();
1206         }
1207         if (!cycled && !done) {
1208                 /*
1209                  * range_cyclic:
1210                  * We hit the last page and there is more work to be done: wrap
1211                  * back to the start of the file
1212                  */
1213                 cycled = 1;
1214                 index = 0;
1215                 end = writeback_index - 1;
1216                 goto retry;
1217         }
1218         if (wbc->range_cyclic || (range_whole && wbc->nr_to_write > 0))
1219                 mapping->writeback_index = done_index;
1220
1221         return ret;
1222 }
1223 EXPORT_SYMBOL(write_cache_pages);
1224
1225 /*
1226  * Function used by generic_writepages to call the real writepage
1227  * function and set the mapping flags on error
1228  */
1229 static int __writepage(struct page *page, struct writeback_control *wbc,
1230                        void *data)
1231 {
1232         struct address_space *mapping = data;
1233         int ret = mapping->a_ops->writepage(page, wbc);
1234         mapping_set_error(mapping, ret);
1235         return ret;
1236 }
1237
1238 /**
1239  * generic_writepages - walk the list of dirty pages of the given address space and writepage() all of them.
1240  * @mapping: address space structure to write
1241  * @wbc: subtract the number of written pages from *@wbc->nr_to_write
1242  *
1243  * This is a library function, which implements the writepages()
1244  * address_space_operation.
1245  */
1246 int generic_writepages(struct address_space *mapping,
1247                        struct writeback_control *wbc)
1248 {
1249         struct blk_plug plug;
1250         int ret;
1251
1252         /* deal with chardevs and other special file */
1253         if (!mapping->a_ops->writepage)
1254                 return 0;
1255
1256         blk_start_plug(&plug);
1257         ret = write_cache_pages(mapping, wbc, __writepage, mapping);
1258         blk_finish_plug(&plug);
1259         return ret;
1260 }
1261
1262 EXPORT_SYMBOL(generic_writepages);
1263
1264 int do_writepages(struct address_space *mapping, struct writeback_control *wbc)
1265 {
1266         int ret;
1267
1268         if (wbc->nr_to_write <= 0)
1269                 return 0;
1270         if (mapping->a_ops->writepages)
1271                 ret = mapping->a_ops->writepages(mapping, wbc);
1272         else
1273                 ret = generic_writepages(mapping, wbc);
1274         return ret;
1275 }
1276
1277 /**
1278  * write_one_page - write out a single page and optionally wait on I/O
1279  * @page: the page to write
1280  * @wait: if true, wait on writeout
1281  *
1282  * The page must be locked by the caller and will be unlocked upon return.
1283  *
1284  * write_one_page() returns a negative error code if I/O failed.
1285  */
1286 int write_one_page(struct page *page, int wait)
1287 {
1288         struct address_space *mapping = page->mapping;
1289         int ret = 0;
1290         struct writeback_control wbc = {
1291                 .sync_mode = WB_SYNC_ALL,
1292                 .nr_to_write = 1,
1293         };
1294
1295         BUG_ON(!PageLocked(page));
1296
1297         if (wait)
1298                 wait_on_page_writeback(page);
1299
1300         if (clear_page_dirty_for_io(page)) {
1301                 page_cache_get(page);
1302                 ret = mapping->a_ops->writepage(page, &wbc);
1303                 if (ret == 0 && wait) {
1304                         wait_on_page_writeback(page);
1305                         if (PageError(page))
1306                                 ret = -EIO;
1307                 }
1308                 page_cache_release(page);
1309         } else {
1310                 unlock_page(page);
1311         }
1312         return ret;
1313 }
1314 EXPORT_SYMBOL(write_one_page);
1315
1316 /*
1317  * For address_spaces which do not use buffers nor write back.
1318  */
1319 int __set_page_dirty_no_writeback(struct page *page)
1320 {
1321         if (!PageDirty(page))
1322                 return !TestSetPageDirty(page);
1323         return 0;
1324 }
1325
1326 /*
1327  * Helper function for set_page_dirty family.
1328  * NOTE: This relies on being atomic wrt interrupts.
1329  */
1330 void account_page_dirtied(struct page *page, struct address_space *mapping)
1331 {
1332         if (mapping_cap_account_dirty(mapping)) {
1333                 __inc_zone_page_state(page, NR_FILE_DIRTY);
1334                 __inc_zone_page_state(page, NR_DIRTIED);
1335                 __inc_bdi_stat(mapping->backing_dev_info, BDI_RECLAIMABLE);
1336                 task_dirty_inc(current);
1337                 task_io_account_write(PAGE_CACHE_SIZE);
1338         }
1339 }
1340 EXPORT_SYMBOL(account_page_dirtied);
1341
1342 /*
1343  * Helper function for set_page_writeback family.
1344  * NOTE: Unlike account_page_dirtied this does not rely on being atomic
1345  * wrt interrupts.
1346  */
1347 void account_page_writeback(struct page *page)
1348 {
1349         inc_zone_page_state(page, NR_WRITEBACK);
1350 }
1351 EXPORT_SYMBOL(account_page_writeback);
1352
1353 /*
1354  * For address_spaces which do not use buffers.  Just tag the page as dirty in
1355  * its radix tree.
1356  *
1357  * This is also used when a single buffer is being dirtied: we want to set the
1358  * page dirty in that case, but not all the buffers.  This is a "bottom-up"
1359  * dirtying, whereas __set_page_dirty_buffers() is a "top-down" dirtying.
1360  *
1361  * Most callers have locked the page, which pins the address_space in memory.
1362  * But zap_pte_range() does not lock the page, however in that case the
1363  * mapping is pinned by the vma's ->vm_file reference.
1364  *
1365  * We take care to handle the case where the page was truncated from the
1366  * mapping by re-checking page_mapping() inside tree_lock.
1367  */
1368 int __set_page_dirty_nobuffers(struct page *page)
1369 {
1370         if (!TestSetPageDirty(page)) {
1371                 struct address_space *mapping = page_mapping(page);
1372                 struct address_space *mapping2;
1373
1374                 if (!mapping)
1375                         return 1;
1376
1377                 spin_lock_irq(&mapping->tree_lock);
1378                 mapping2 = page_mapping(page);
1379                 if (mapping2) { /* Race with truncate? */
1380                         BUG_ON(mapping2 != mapping);
1381                         WARN_ON_ONCE(!PagePrivate(page) && !PageUptodate(page));
1382                         account_page_dirtied(page, mapping);
1383                         radix_tree_tag_set(&mapping->page_tree,
1384                                 page_index(page), PAGECACHE_TAG_DIRTY);
1385                 }
1386                 spin_unlock_irq(&mapping->tree_lock);
1387                 if (mapping->host) {
1388                         /* !PageAnon && !swapper_space */
1389                         __mark_inode_dirty(mapping->host, I_DIRTY_PAGES);
1390                 }
1391                 return 1;
1392         }
1393         return 0;
1394 }
1395 EXPORT_SYMBOL(__set_page_dirty_nobuffers);
1396
1397 /*
1398  * When a writepage implementation decides that it doesn't want to write this
1399  * page for some reason, it should redirty the locked page via
1400  * redirty_page_for_writepage() and it should then unlock the page and return 0
1401  */
1402 int redirty_page_for_writepage(struct writeback_control *wbc, struct page *page)
1403 {
1404         wbc->pages_skipped++;
1405         return __set_page_dirty_nobuffers(page);
1406 }
1407 EXPORT_SYMBOL(redirty_page_for_writepage);
1408
1409 /*
1410  * Dirty a page.
1411  *
1412  * For pages with a mapping this should be done under the page lock
1413  * for the benefit of asynchronous memory errors who prefer a consistent
1414  * dirty state. This rule can be broken in some special cases,
1415  * but should be better not to.
1416  *
1417  * If the mapping doesn't provide a set_page_dirty a_op, then
1418  * just fall through and assume that it wants buffer_heads.
1419  */
1420 int set_page_dirty(struct page *page)
1421 {
1422         struct address_space *mapping = page_mapping(page);
1423
1424         if (likely(mapping)) {
1425                 int (*spd)(struct page *) = mapping->a_ops->set_page_dirty;
1426                 /*
1427                  * readahead/lru_deactivate_page could remain
1428                  * PG_readahead/PG_reclaim due to race with end_page_writeback
1429                  * About readahead, if the page is written, the flags would be
1430                  * reset. So no problem.
1431                  * About lru_deactivate_page, if the page is redirty, the flag
1432                  * will be reset. So no problem. but if the page is used by readahead
1433                  * it will confuse readahead and make it restart the size rampup
1434                  * process. But it's a trivial problem.
1435                  */
1436                 ClearPageReclaim(page);
1437 #ifdef CONFIG_BLOCK
1438                 if (!spd)
1439                         spd = __set_page_dirty_buffers;
1440 #endif
1441                 return (*spd)(page);
1442         }
1443         if (!PageDirty(page)) {
1444                 if (!TestSetPageDirty(page))
1445                         return 1;
1446         }
1447         return 0;
1448 }
1449 EXPORT_SYMBOL(set_page_dirty);
1450
1451 /*
1452  * set_page_dirty() is racy if the caller has no reference against
1453  * page->mapping->host, and if the page is unlocked.  This is because another
1454  * CPU could truncate the page off the mapping and then free the mapping.
1455  *
1456  * Usually, the page _is_ locked, or the caller is a user-space process which
1457  * holds a reference on the inode by having an open file.
1458  *
1459  * In other cases, the page should be locked before running set_page_dirty().
1460  */
1461 int set_page_dirty_lock(struct page *page)
1462 {
1463         int ret;
1464
1465         lock_page(page);
1466         ret = set_page_dirty(page);
1467         unlock_page(page);
1468         return ret;
1469 }
1470 EXPORT_SYMBOL(set_page_dirty_lock);
1471
1472 /*
1473  * Clear a page's dirty flag, while caring for dirty memory accounting.
1474  * Returns true if the page was previously dirty.
1475  *
1476  * This is for preparing to put the page under writeout.  We leave the page
1477  * tagged as dirty in the radix tree so that a concurrent write-for-sync
1478  * can discover it via a PAGECACHE_TAG_DIRTY walk.  The ->writepage
1479  * implementation will run either set_page_writeback() or set_page_dirty(),
1480  * at which stage we bring the page's dirty flag and radix-tree dirty tag
1481  * back into sync.
1482  *
1483  * This incoherency between the page's dirty flag and radix-tree tag is
1484  * unfortunate, but it only exists while the page is locked.
1485  */
1486 int clear_page_dirty_for_io(struct page *page)
1487 {
1488         struct address_space *mapping = page_mapping(page);
1489
1490         BUG_ON(!PageLocked(page));
1491
1492         if (mapping && mapping_cap_account_dirty(mapping)) {
1493                 /*
1494                  * Yes, Virginia, this is indeed insane.
1495                  *
1496                  * We use this sequence to make sure that
1497                  *  (a) we account for dirty stats properly
1498                  *  (b) we tell the low-level filesystem to
1499                  *      mark the whole page dirty if it was
1500                  *      dirty in a pagetable. Only to then
1501                  *  (c) clean the page again and return 1 to
1502                  *      cause the writeback.
1503                  *
1504                  * This way we avoid all nasty races with the
1505                  * dirty bit in multiple places and clearing
1506                  * them concurrently from different threads.
1507                  *
1508                  * Note! Normally the "set_page_dirty(page)"
1509                  * has no effect on the actual dirty bit - since
1510                  * that will already usually be set. But we
1511                  * need the side effects, and it can help us
1512                  * avoid races.
1513                  *
1514                  * We basically use the page "master dirty bit"
1515                  * as a serialization point for all the different
1516                  * threads doing their things.
1517                  */
1518                 if (page_mkclean(page))
1519                         set_page_dirty(page);
1520                 /*
1521                  * We carefully synchronise fault handlers against
1522                  * installing a dirty pte and marking the page dirty
1523                  * at this point. We do this by having them hold the
1524                  * page lock at some point after installing their
1525                  * pte, but before marking the page dirty.
1526                  * Pages are always locked coming in here, so we get
1527                  * the desired exclusion. See mm/memory.c:do_wp_page()
1528                  * for more comments.
1529                  */
1530                 if (TestClearPageDirty(page)) {
1531                         dec_zone_page_state(page, NR_FILE_DIRTY);
1532                         dec_bdi_stat(mapping->backing_dev_info,
1533                                         BDI_RECLAIMABLE);
1534                         return 1;
1535                 }
1536                 return 0;
1537         }
1538         return TestClearPageDirty(page);
1539 }
1540 EXPORT_SYMBOL(clear_page_dirty_for_io);
1541
1542 int test_clear_page_writeback(struct page *page)
1543 {
1544         struct address_space *mapping = page_mapping(page);
1545         int ret;
1546
1547         if (mapping) {
1548                 struct backing_dev_info *bdi = mapping->backing_dev_info;
1549                 unsigned long flags;
1550
1551                 spin_lock_irqsave(&mapping->tree_lock, flags);
1552                 ret = TestClearPageWriteback(page);
1553                 if (ret) {
1554                         radix_tree_tag_clear(&mapping->page_tree,
1555                                                 page_index(page),
1556                                                 PAGECACHE_TAG_WRITEBACK);
1557                         if (bdi_cap_account_writeback(bdi)) {
1558                                 __dec_bdi_stat(bdi, BDI_WRITEBACK);
1559                                 __bdi_writeout_inc(bdi);
1560                         }
1561                 }
1562                 spin_unlock_irqrestore(&mapping->tree_lock, flags);
1563         } else {
1564                 ret = TestClearPageWriteback(page);
1565         }
1566         if (ret) {
1567                 dec_zone_page_state(page, NR_WRITEBACK);
1568                 inc_zone_page_state(page, NR_WRITTEN);
1569         }
1570         return ret;
1571 }
1572
1573 int test_set_page_writeback(struct page *page)
1574 {
1575         struct address_space *mapping = page_mapping(page);
1576         int ret;
1577
1578         if (mapping) {
1579                 struct backing_dev_info *bdi = mapping->backing_dev_info;
1580                 unsigned long flags;
1581
1582                 spin_lock_irqsave(&mapping->tree_lock, flags);
1583                 ret = TestSetPageWriteback(page);
1584                 if (!ret) {
1585                         radix_tree_tag_set(&mapping->page_tree,
1586                                                 page_index(page),
1587                                                 PAGECACHE_TAG_WRITEBACK);
1588                         if (bdi_cap_account_writeback(bdi))
1589                                 __inc_bdi_stat(bdi, BDI_WRITEBACK);
1590                 }
1591                 if (!PageDirty(page))
1592                         radix_tree_tag_clear(&mapping->page_tree,
1593                                                 page_index(page),
1594                                                 PAGECACHE_TAG_DIRTY);
1595                 radix_tree_tag_clear(&mapping->page_tree,
1596                                      page_index(page),
1597                                      PAGECACHE_TAG_TOWRITE);
1598                 spin_unlock_irqrestore(&mapping->tree_lock, flags);
1599         } else {
1600                 ret = TestSetPageWriteback(page);
1601         }
1602         if (!ret)
1603                 account_page_writeback(page);
1604         return ret;
1605
1606 }
1607 EXPORT_SYMBOL(test_set_page_writeback);
1608
1609 /*
1610  * Return true if any of the pages in the mapping are marked with the
1611  * passed tag.
1612  */
1613 int mapping_tagged(struct address_space *mapping, int tag)
1614 {
1615         return radix_tree_tagged(&mapping->page_tree, tag);
1616 }
1617 EXPORT_SYMBOL(mapping_tagged);