mm: memcg: only check for PageSwapCache when uncharging anon
[linux-3.10.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/export.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> /* __set_page_dirty_buffers */
36 #include <linux/pagevec.h>
37 #include <linux/timer.h>
38 #include <trace/events/writeback.h>
39
40 /*
41  * Sleep at most 200ms at a time in balance_dirty_pages().
42  */
43 #define MAX_PAUSE               max(HZ/5, 1)
44
45 /*
46  * Try to keep balance_dirty_pages() call intervals higher than this many pages
47  * by raising pause time to max_pause when falls below it.
48  */
49 #define DIRTY_POLL_THRESH       (128 >> (PAGE_SHIFT - 10))
50
51 /*
52  * Estimate write bandwidth at 200ms intervals.
53  */
54 #define BANDWIDTH_INTERVAL      max(HZ/5, 1)
55
56 #define RATELIMIT_CALC_SHIFT    10
57
58 /*
59  * After a CPU has dirtied this many pages, balance_dirty_pages_ratelimited
60  * will look to see if it needs to force writeback or throttling.
61  */
62 static long ratelimit_pages = 32;
63
64 /* The following parameters are exported via /proc/sys/vm */
65
66 /*
67  * Start background writeback (via writeback threads) 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 EXPORT_SYMBOL_GPL(dirty_writeback_interval);
100
101 /*
102  * The longest time for which data is allowed to remain dirty
103  */
104 unsigned int dirty_expire_interval = 30 * 100; /* centiseconds */
105
106 /*
107  * Flag that makes the machine dump writes/reads and block dirtyings.
108  */
109 int block_dump;
110
111 /*
112  * Flag that puts the machine in "laptop mode". Doubles as a timeout in jiffies:
113  * a full sync is triggered after this time elapses without any disk activity.
114  */
115 int laptop_mode;
116
117 EXPORT_SYMBOL(laptop_mode);
118
119 /* End of sysctl-exported parameters */
120
121 unsigned long global_dirty_limit;
122
123 /*
124  * Scale the writeback cache size proportional to the relative writeout speeds.
125  *
126  * We do this by keeping a floating proportion between BDIs, based on page
127  * writeback completions [end_page_writeback()]. Those devices that write out
128  * pages fastest will get the larger share, while the slower will get a smaller
129  * share.
130  *
131  * We use page writeout completions because we are interested in getting rid of
132  * dirty pages. Having them written out is the primary goal.
133  *
134  * We introduce a concept of time, a period over which we measure these events,
135  * because demand can/will vary over time. The length of this period itself is
136  * measured in page writeback completions.
137  *
138  */
139 static struct fprop_global writeout_completions;
140
141 static void writeout_period(unsigned long t);
142 /* Timer for aging of writeout_completions */
143 static struct timer_list writeout_period_timer =
144                 TIMER_DEFERRED_INITIALIZER(writeout_period, 0, 0);
145 static unsigned long writeout_period_time = 0;
146
147 /*
148  * Length of period for aging writeout fractions of bdis. This is an
149  * arbitrarily chosen number. The longer the period, the slower fractions will
150  * reflect changes in current writeout rate.
151  */
152 #define VM_COMPLETIONS_PERIOD_LEN (3*HZ)
153
154 /*
155  * Work out the current dirty-memory clamping and background writeout
156  * thresholds.
157  *
158  * The main aim here is to lower them aggressively if there is a lot of mapped
159  * memory around.  To avoid stressing page reclaim with lots of unreclaimable
160  * pages.  It is better to clamp down on writers than to start swapping, and
161  * performing lots of scanning.
162  *
163  * We only allow 1/2 of the currently-unmapped memory to be dirtied.
164  *
165  * We don't permit the clamping level to fall below 5% - that is getting rather
166  * excessive.
167  *
168  * We make sure that the background writeout level is below the adjusted
169  * clamping level.
170  */
171
172 /*
173  * In a memory zone, there is a certain amount of pages we consider
174  * available for the page cache, which is essentially the number of
175  * free and reclaimable pages, minus some zone reserves to protect
176  * lowmem and the ability to uphold the zone's watermarks without
177  * requiring writeback.
178  *
179  * This number of dirtyable pages is the base value of which the
180  * user-configurable dirty ratio is the effictive number of pages that
181  * are allowed to be actually dirtied.  Per individual zone, or
182  * globally by using the sum of dirtyable pages over all zones.
183  *
184  * Because the user is allowed to specify the dirty limit globally as
185  * absolute number of bytes, calculating the per-zone dirty limit can
186  * require translating the configured limit into a percentage of
187  * global dirtyable memory first.
188  */
189
190 static unsigned long highmem_dirtyable_memory(unsigned long total)
191 {
192 #ifdef CONFIG_HIGHMEM
193         int node;
194         unsigned long x = 0;
195
196         for_each_node_state(node, N_HIGH_MEMORY) {
197                 struct zone *z =
198                         &NODE_DATA(node)->node_zones[ZONE_HIGHMEM];
199
200                 x += zone_page_state(z, NR_FREE_PAGES) +
201                      zone_reclaimable_pages(z) - z->dirty_balance_reserve;
202         }
203         /*
204          * Make sure that the number of highmem pages is never larger
205          * than the number of the total dirtyable memory. This can only
206          * occur in very strange VM situations but we want to make sure
207          * that this does not occur.
208          */
209         return min(x, total);
210 #else
211         return 0;
212 #endif
213 }
214
215 /**
216  * global_dirtyable_memory - number of globally dirtyable pages
217  *
218  * Returns the global number of pages potentially available for dirty
219  * page cache.  This is the base value for the global dirty limits.
220  */
221 static unsigned long global_dirtyable_memory(void)
222 {
223         unsigned long x;
224
225         x = global_page_state(NR_FREE_PAGES) + global_reclaimable_pages() -
226             dirty_balance_reserve;
227
228         if (!vm_highmem_is_dirtyable)
229                 x -= highmem_dirtyable_memory(x);
230
231         return x + 1;   /* Ensure that we never return 0 */
232 }
233
234 /*
235  * global_dirty_limits - background-writeback and dirty-throttling thresholds
236  *
237  * Calculate the dirty thresholds based on sysctl parameters
238  * - vm.dirty_background_ratio  or  vm.dirty_background_bytes
239  * - vm.dirty_ratio             or  vm.dirty_bytes
240  * The dirty limits will be lifted by 1/4 for PF_LESS_THROTTLE (ie. nfsd) and
241  * real-time tasks.
242  */
243 void global_dirty_limits(unsigned long *pbackground, unsigned long *pdirty)
244 {
245         unsigned long background;
246         unsigned long dirty;
247         unsigned long uninitialized_var(available_memory);
248         struct task_struct *tsk;
249
250         if (!vm_dirty_bytes || !dirty_background_bytes)
251                 available_memory = global_dirtyable_memory();
252
253         if (vm_dirty_bytes)
254                 dirty = DIV_ROUND_UP(vm_dirty_bytes, PAGE_SIZE);
255         else
256                 dirty = (vm_dirty_ratio * available_memory) / 100;
257
258         if (dirty_background_bytes)
259                 background = DIV_ROUND_UP(dirty_background_bytes, PAGE_SIZE);
260         else
261                 background = (dirty_background_ratio * available_memory) / 100;
262
263         if (background >= dirty)
264                 background = dirty / 2;
265         tsk = current;
266         if (tsk->flags & PF_LESS_THROTTLE || rt_task(tsk)) {
267                 background += background / 4;
268                 dirty += dirty / 4;
269         }
270         *pbackground = background;
271         *pdirty = dirty;
272         trace_global_dirty_state(background, dirty);
273 }
274
275 /**
276  * zone_dirtyable_memory - number of dirtyable pages in a zone
277  * @zone: the zone
278  *
279  * Returns the zone's number of pages potentially available for dirty
280  * page cache.  This is the base value for the per-zone dirty limits.
281  */
282 static unsigned long zone_dirtyable_memory(struct zone *zone)
283 {
284         /*
285          * The effective global number of dirtyable pages may exclude
286          * highmem as a big-picture measure to keep the ratio between
287          * dirty memory and lowmem reasonable.
288          *
289          * But this function is purely about the individual zone and a
290          * highmem zone can hold its share of dirty pages, so we don't
291          * care about vm_highmem_is_dirtyable here.
292          */
293         return zone_page_state(zone, NR_FREE_PAGES) +
294                zone_reclaimable_pages(zone) -
295                zone->dirty_balance_reserve;
296 }
297
298 /**
299  * zone_dirty_limit - maximum number of dirty pages allowed in a zone
300  * @zone: the zone
301  *
302  * Returns the maximum number of dirty pages allowed in a zone, based
303  * on the zone's dirtyable memory.
304  */
305 static unsigned long zone_dirty_limit(struct zone *zone)
306 {
307         unsigned long zone_memory = zone_dirtyable_memory(zone);
308         struct task_struct *tsk = current;
309         unsigned long dirty;
310
311         if (vm_dirty_bytes)
312                 dirty = DIV_ROUND_UP(vm_dirty_bytes, PAGE_SIZE) *
313                         zone_memory / global_dirtyable_memory();
314         else
315                 dirty = vm_dirty_ratio * zone_memory / 100;
316
317         if (tsk->flags & PF_LESS_THROTTLE || rt_task(tsk))
318                 dirty += dirty / 4;
319
320         return dirty;
321 }
322
323 /**
324  * zone_dirty_ok - tells whether a zone is within its dirty limits
325  * @zone: the zone to check
326  *
327  * Returns %true when the dirty pages in @zone are within the zone's
328  * dirty limit, %false if the limit is exceeded.
329  */
330 bool zone_dirty_ok(struct zone *zone)
331 {
332         unsigned long limit = zone_dirty_limit(zone);
333
334         return zone_page_state(zone, NR_FILE_DIRTY) +
335                zone_page_state(zone, NR_UNSTABLE_NFS) +
336                zone_page_state(zone, NR_WRITEBACK) <= limit;
337 }
338
339 int dirty_background_ratio_handler(struct ctl_table *table, int write,
340                 void __user *buffer, size_t *lenp,
341                 loff_t *ppos)
342 {
343         int ret;
344
345         ret = proc_dointvec_minmax(table, write, buffer, lenp, ppos);
346         if (ret == 0 && write)
347                 dirty_background_bytes = 0;
348         return ret;
349 }
350
351 int dirty_background_bytes_handler(struct ctl_table *table, int write,
352                 void __user *buffer, size_t *lenp,
353                 loff_t *ppos)
354 {
355         int ret;
356
357         ret = proc_doulongvec_minmax(table, write, buffer, lenp, ppos);
358         if (ret == 0 && write)
359                 dirty_background_ratio = 0;
360         return ret;
361 }
362
363 int dirty_ratio_handler(struct ctl_table *table, int write,
364                 void __user *buffer, size_t *lenp,
365                 loff_t *ppos)
366 {
367         int old_ratio = vm_dirty_ratio;
368         int ret;
369
370         ret = proc_dointvec_minmax(table, write, buffer, lenp, ppos);
371         if (ret == 0 && write && vm_dirty_ratio != old_ratio) {
372                 writeback_set_ratelimit();
373                 vm_dirty_bytes = 0;
374         }
375         return ret;
376 }
377
378 int dirty_bytes_handler(struct ctl_table *table, int write,
379                 void __user *buffer, size_t *lenp,
380                 loff_t *ppos)
381 {
382         unsigned long old_bytes = vm_dirty_bytes;
383         int ret;
384
385         ret = proc_doulongvec_minmax(table, write, buffer, lenp, ppos);
386         if (ret == 0 && write && vm_dirty_bytes != old_bytes) {
387                 writeback_set_ratelimit();
388                 vm_dirty_ratio = 0;
389         }
390         return ret;
391 }
392
393 static unsigned long wp_next_time(unsigned long cur_time)
394 {
395         cur_time += VM_COMPLETIONS_PERIOD_LEN;
396         /* 0 has a special meaning... */
397         if (!cur_time)
398                 return 1;
399         return cur_time;
400 }
401
402 /*
403  * Increment the BDI's writeout completion count and the global writeout
404  * completion count. Called from test_clear_page_writeback().
405  */
406 static inline void __bdi_writeout_inc(struct backing_dev_info *bdi)
407 {
408         __inc_bdi_stat(bdi, BDI_WRITTEN);
409         __fprop_inc_percpu_max(&writeout_completions, &bdi->completions,
410                                bdi->max_prop_frac);
411         /* First event after period switching was turned off? */
412         if (!unlikely(writeout_period_time)) {
413                 /*
414                  * We can race with other __bdi_writeout_inc calls here but
415                  * it does not cause any harm since the resulting time when
416                  * timer will fire and what is in writeout_period_time will be
417                  * roughly the same.
418                  */
419                 writeout_period_time = wp_next_time(jiffies);
420                 mod_timer(&writeout_period_timer, writeout_period_time);
421         }
422 }
423
424 void bdi_writeout_inc(struct backing_dev_info *bdi)
425 {
426         unsigned long flags;
427
428         local_irq_save(flags);
429         __bdi_writeout_inc(bdi);
430         local_irq_restore(flags);
431 }
432 EXPORT_SYMBOL_GPL(bdi_writeout_inc);
433
434 /*
435  * Obtain an accurate fraction of the BDI's portion.
436  */
437 static void bdi_writeout_fraction(struct backing_dev_info *bdi,
438                 long *numerator, long *denominator)
439 {
440         fprop_fraction_percpu(&writeout_completions, &bdi->completions,
441                                 numerator, denominator);
442 }
443
444 /*
445  * On idle system, we can be called long after we scheduled because we use
446  * deferred timers so count with missed periods.
447  */
448 static void writeout_period(unsigned long t)
449 {
450         int miss_periods = (jiffies - writeout_period_time) /
451                                                  VM_COMPLETIONS_PERIOD_LEN;
452
453         if (fprop_new_period(&writeout_completions, miss_periods + 1)) {
454                 writeout_period_time = wp_next_time(writeout_period_time +
455                                 miss_periods * VM_COMPLETIONS_PERIOD_LEN);
456                 mod_timer(&writeout_period_timer, writeout_period_time);
457         } else {
458                 /*
459                  * Aging has zeroed all fractions. Stop wasting CPU on period
460                  * updates.
461                  */
462                 writeout_period_time = 0;
463         }
464 }
465
466 /*
467  * bdi_min_ratio keeps the sum of the minimum dirty shares of all
468  * registered backing devices, which, for obvious reasons, can not
469  * exceed 100%.
470  */
471 static unsigned int bdi_min_ratio;
472
473 int bdi_set_min_ratio(struct backing_dev_info *bdi, unsigned int min_ratio)
474 {
475         int ret = 0;
476
477         spin_lock_bh(&bdi_lock);
478         if (min_ratio > bdi->max_ratio) {
479                 ret = -EINVAL;
480         } else {
481                 min_ratio -= bdi->min_ratio;
482                 if (bdi_min_ratio + min_ratio < 100) {
483                         bdi_min_ratio += min_ratio;
484                         bdi->min_ratio += min_ratio;
485                 } else {
486                         ret = -EINVAL;
487                 }
488         }
489         spin_unlock_bh(&bdi_lock);
490
491         return ret;
492 }
493
494 int bdi_set_max_ratio(struct backing_dev_info *bdi, unsigned max_ratio)
495 {
496         int ret = 0;
497
498         if (max_ratio > 100)
499                 return -EINVAL;
500
501         spin_lock_bh(&bdi_lock);
502         if (bdi->min_ratio > max_ratio) {
503                 ret = -EINVAL;
504         } else {
505                 bdi->max_ratio = max_ratio;
506                 bdi->max_prop_frac = (FPROP_FRAC_BASE * max_ratio) / 100;
507         }
508         spin_unlock_bh(&bdi_lock);
509
510         return ret;
511 }
512 EXPORT_SYMBOL(bdi_set_max_ratio);
513
514 static unsigned long dirty_freerun_ceiling(unsigned long thresh,
515                                            unsigned long bg_thresh)
516 {
517         return (thresh + bg_thresh) / 2;
518 }
519
520 static unsigned long hard_dirty_limit(unsigned long thresh)
521 {
522         return max(thresh, global_dirty_limit);
523 }
524
525 /**
526  * bdi_dirty_limit - @bdi's share of dirty throttling threshold
527  * @bdi: the backing_dev_info to query
528  * @dirty: global dirty limit in pages
529  *
530  * Returns @bdi's dirty limit in pages. The term "dirty" in the context of
531  * dirty balancing includes all PG_dirty, PG_writeback and NFS unstable pages.
532  *
533  * Note that balance_dirty_pages() will only seriously take it as a hard limit
534  * when sleeping max_pause per page is not enough to keep the dirty pages under
535  * control. For example, when the device is completely stalled due to some error
536  * conditions, or when there are 1000 dd tasks writing to a slow 10MB/s USB key.
537  * In the other normal situations, it acts more gently by throttling the tasks
538  * more (rather than completely block them) when the bdi dirty pages go high.
539  *
540  * It allocates high/low dirty limits to fast/slow devices, in order to prevent
541  * - starving fast devices
542  * - piling up dirty pages (that will take long time to sync) on slow devices
543  *
544  * The bdi's share of dirty limit will be adapting to its throughput and
545  * bounded by the bdi->min_ratio and/or bdi->max_ratio parameters, if set.
546  */
547 unsigned long bdi_dirty_limit(struct backing_dev_info *bdi, unsigned long dirty)
548 {
549         u64 bdi_dirty;
550         long numerator, denominator;
551
552         /*
553          * Calculate this BDI's share of the dirty ratio.
554          */
555         bdi_writeout_fraction(bdi, &numerator, &denominator);
556
557         bdi_dirty = (dirty * (100 - bdi_min_ratio)) / 100;
558         bdi_dirty *= numerator;
559         do_div(bdi_dirty, denominator);
560
561         bdi_dirty += (dirty * bdi->min_ratio) / 100;
562         if (bdi_dirty > (dirty * bdi->max_ratio) / 100)
563                 bdi_dirty = dirty * bdi->max_ratio / 100;
564
565         return bdi_dirty;
566 }
567
568 /*
569  * Dirty position control.
570  *
571  * (o) global/bdi setpoints
572  *
573  * We want the dirty pages be balanced around the global/bdi setpoints.
574  * When the number of dirty pages is higher/lower than the setpoint, the
575  * dirty position control ratio (and hence task dirty ratelimit) will be
576  * decreased/increased to bring the dirty pages back to the setpoint.
577  *
578  *     pos_ratio = 1 << RATELIMIT_CALC_SHIFT
579  *
580  *     if (dirty < setpoint) scale up   pos_ratio
581  *     if (dirty > setpoint) scale down pos_ratio
582  *
583  *     if (bdi_dirty < bdi_setpoint) scale up   pos_ratio
584  *     if (bdi_dirty > bdi_setpoint) scale down pos_ratio
585  *
586  *     task_ratelimit = dirty_ratelimit * pos_ratio >> RATELIMIT_CALC_SHIFT
587  *
588  * (o) global control line
589  *
590  *     ^ pos_ratio
591  *     |
592  *     |            |<===== global dirty control scope ======>|
593  * 2.0 .............*
594  *     |            .*
595  *     |            . *
596  *     |            .   *
597  *     |            .     *
598  *     |            .        *
599  *     |            .            *
600  * 1.0 ................................*
601  *     |            .                  .     *
602  *     |            .                  .          *
603  *     |            .                  .              *
604  *     |            .                  .                 *
605  *     |            .                  .                    *
606  *   0 +------------.------------------.----------------------*------------->
607  *           freerun^          setpoint^                 limit^   dirty pages
608  *
609  * (o) bdi control line
610  *
611  *     ^ pos_ratio
612  *     |
613  *     |            *
614  *     |              *
615  *     |                *
616  *     |                  *
617  *     |                    * |<=========== span ============>|
618  * 1.0 .......................*
619  *     |                      . *
620  *     |                      .   *
621  *     |                      .     *
622  *     |                      .       *
623  *     |                      .         *
624  *     |                      .           *
625  *     |                      .             *
626  *     |                      .               *
627  *     |                      .                 *
628  *     |                      .                   *
629  *     |                      .                     *
630  * 1/4 ...............................................* * * * * * * * * * * *
631  *     |                      .                         .
632  *     |                      .                           .
633  *     |                      .                             .
634  *   0 +----------------------.-------------------------------.------------->
635  *                bdi_setpoint^                    x_intercept^
636  *
637  * The bdi control line won't drop below pos_ratio=1/4, so that bdi_dirty can
638  * be smoothly throttled down to normal if it starts high in situations like
639  * - start writing to a slow SD card and a fast disk at the same time. The SD
640  *   card's bdi_dirty may rush to many times higher than bdi_setpoint.
641  * - the bdi dirty thresh drops quickly due to change of JBOD workload
642  */
643 static unsigned long bdi_position_ratio(struct backing_dev_info *bdi,
644                                         unsigned long thresh,
645                                         unsigned long bg_thresh,
646                                         unsigned long dirty,
647                                         unsigned long bdi_thresh,
648                                         unsigned long bdi_dirty)
649 {
650         unsigned long write_bw = bdi->avg_write_bandwidth;
651         unsigned long freerun = dirty_freerun_ceiling(thresh, bg_thresh);
652         unsigned long limit = hard_dirty_limit(thresh);
653         unsigned long x_intercept;
654         unsigned long setpoint;         /* dirty pages' target balance point */
655         unsigned long bdi_setpoint;
656         unsigned long span;
657         long long pos_ratio;            /* for scaling up/down the rate limit */
658         long x;
659
660         if (unlikely(dirty >= limit))
661                 return 0;
662
663         /*
664          * global setpoint
665          *
666          *                           setpoint - dirty 3
667          *        f(dirty) := 1.0 + (----------------)
668          *                           limit - setpoint
669          *
670          * it's a 3rd order polynomial that subjects to
671          *
672          * (1) f(freerun)  = 2.0 => rampup dirty_ratelimit reasonably fast
673          * (2) f(setpoint) = 1.0 => the balance point
674          * (3) f(limit)    = 0   => the hard limit
675          * (4) df/dx      <= 0   => negative feedback control
676          * (5) the closer to setpoint, the smaller |df/dx| (and the reverse)
677          *     => fast response on large errors; small oscillation near setpoint
678          */
679         setpoint = (freerun + limit) / 2;
680         x = div_s64((setpoint - dirty) << RATELIMIT_CALC_SHIFT,
681                     limit - setpoint + 1);
682         pos_ratio = x;
683         pos_ratio = pos_ratio * x >> RATELIMIT_CALC_SHIFT;
684         pos_ratio = pos_ratio * x >> RATELIMIT_CALC_SHIFT;
685         pos_ratio += 1 << RATELIMIT_CALC_SHIFT;
686
687         /*
688          * We have computed basic pos_ratio above based on global situation. If
689          * the bdi is over/under its share of dirty pages, we want to scale
690          * pos_ratio further down/up. That is done by the following mechanism.
691          */
692
693         /*
694          * bdi setpoint
695          *
696          *        f(bdi_dirty) := 1.0 + k * (bdi_dirty - bdi_setpoint)
697          *
698          *                        x_intercept - bdi_dirty
699          *                     := --------------------------
700          *                        x_intercept - bdi_setpoint
701          *
702          * The main bdi control line is a linear function that subjects to
703          *
704          * (1) f(bdi_setpoint) = 1.0
705          * (2) k = - 1 / (8 * write_bw)  (in single bdi case)
706          *     or equally: x_intercept = bdi_setpoint + 8 * write_bw
707          *
708          * For single bdi case, the dirty pages are observed to fluctuate
709          * regularly within range
710          *        [bdi_setpoint - write_bw/2, bdi_setpoint + write_bw/2]
711          * for various filesystems, where (2) can yield in a reasonable 12.5%
712          * fluctuation range for pos_ratio.
713          *
714          * For JBOD case, bdi_thresh (not bdi_dirty!) could fluctuate up to its
715          * own size, so move the slope over accordingly and choose a slope that
716          * yields 100% pos_ratio fluctuation on suddenly doubled bdi_thresh.
717          */
718         if (unlikely(bdi_thresh > thresh))
719                 bdi_thresh = thresh;
720         /*
721          * It's very possible that bdi_thresh is close to 0 not because the
722          * device is slow, but that it has remained inactive for long time.
723          * Honour such devices a reasonable good (hopefully IO efficient)
724          * threshold, so that the occasional writes won't be blocked and active
725          * writes can rampup the threshold quickly.
726          */
727         bdi_thresh = max(bdi_thresh, (limit - dirty) / 8);
728         /*
729          * scale global setpoint to bdi's:
730          *      bdi_setpoint = setpoint * bdi_thresh / thresh
731          */
732         x = div_u64((u64)bdi_thresh << 16, thresh + 1);
733         bdi_setpoint = setpoint * (u64)x >> 16;
734         /*
735          * Use span=(8*write_bw) in single bdi case as indicated by
736          * (thresh - bdi_thresh ~= 0) and transit to bdi_thresh in JBOD case.
737          *
738          *        bdi_thresh                    thresh - bdi_thresh
739          * span = ---------- * (8 * write_bw) + ------------------- * bdi_thresh
740          *          thresh                            thresh
741          */
742         span = (thresh - bdi_thresh + 8 * write_bw) * (u64)x >> 16;
743         x_intercept = bdi_setpoint + span;
744
745         if (bdi_dirty < x_intercept - span / 4) {
746                 pos_ratio = div_u64(pos_ratio * (x_intercept - bdi_dirty),
747                                     x_intercept - bdi_setpoint + 1);
748         } else
749                 pos_ratio /= 4;
750
751         /*
752          * bdi reserve area, safeguard against dirty pool underrun and disk idle
753          * It may push the desired control point of global dirty pages higher
754          * than setpoint.
755          */
756         x_intercept = bdi_thresh / 2;
757         if (bdi_dirty < x_intercept) {
758                 if (bdi_dirty > x_intercept / 8)
759                         pos_ratio = div_u64(pos_ratio * x_intercept, bdi_dirty);
760                 else
761                         pos_ratio *= 8;
762         }
763
764         return pos_ratio;
765 }
766
767 static void bdi_update_write_bandwidth(struct backing_dev_info *bdi,
768                                        unsigned long elapsed,
769                                        unsigned long written)
770 {
771         const unsigned long period = roundup_pow_of_two(3 * HZ);
772         unsigned long avg = bdi->avg_write_bandwidth;
773         unsigned long old = bdi->write_bandwidth;
774         u64 bw;
775
776         /*
777          * bw = written * HZ / elapsed
778          *
779          *                   bw * elapsed + write_bandwidth * (period - elapsed)
780          * write_bandwidth = ---------------------------------------------------
781          *                                          period
782          */
783         bw = written - bdi->written_stamp;
784         bw *= HZ;
785         if (unlikely(elapsed > period)) {
786                 do_div(bw, elapsed);
787                 avg = bw;
788                 goto out;
789         }
790         bw += (u64)bdi->write_bandwidth * (period - elapsed);
791         bw >>= ilog2(period);
792
793         /*
794          * one more level of smoothing, for filtering out sudden spikes
795          */
796         if (avg > old && old >= (unsigned long)bw)
797                 avg -= (avg - old) >> 3;
798
799         if (avg < old && old <= (unsigned long)bw)
800                 avg += (old - avg) >> 3;
801
802 out:
803         bdi->write_bandwidth = bw;
804         bdi->avg_write_bandwidth = avg;
805 }
806
807 /*
808  * The global dirtyable memory and dirty threshold could be suddenly knocked
809  * down by a large amount (eg. on the startup of KVM in a swapless system).
810  * This may throw the system into deep dirty exceeded state and throttle
811  * heavy/light dirtiers alike. To retain good responsiveness, maintain
812  * global_dirty_limit for tracking slowly down to the knocked down dirty
813  * threshold.
814  */
815 static void update_dirty_limit(unsigned long thresh, unsigned long dirty)
816 {
817         unsigned long limit = global_dirty_limit;
818
819         /*
820          * Follow up in one step.
821          */
822         if (limit < thresh) {
823                 limit = thresh;
824                 goto update;
825         }
826
827         /*
828          * Follow down slowly. Use the higher one as the target, because thresh
829          * may drop below dirty. This is exactly the reason to introduce
830          * global_dirty_limit which is guaranteed to lie above the dirty pages.
831          */
832         thresh = max(thresh, dirty);
833         if (limit > thresh) {
834                 limit -= (limit - thresh) >> 5;
835                 goto update;
836         }
837         return;
838 update:
839         global_dirty_limit = limit;
840 }
841
842 static void global_update_bandwidth(unsigned long thresh,
843                                     unsigned long dirty,
844                                     unsigned long now)
845 {
846         static DEFINE_SPINLOCK(dirty_lock);
847         static unsigned long update_time;
848
849         /*
850          * check locklessly first to optimize away locking for the most time
851          */
852         if (time_before(now, update_time + BANDWIDTH_INTERVAL))
853                 return;
854
855         spin_lock(&dirty_lock);
856         if (time_after_eq(now, update_time + BANDWIDTH_INTERVAL)) {
857                 update_dirty_limit(thresh, dirty);
858                 update_time = now;
859         }
860         spin_unlock(&dirty_lock);
861 }
862
863 /*
864  * Maintain bdi->dirty_ratelimit, the base dirty throttle rate.
865  *
866  * Normal bdi tasks will be curbed at or below it in long term.
867  * Obviously it should be around (write_bw / N) when there are N dd tasks.
868  */
869 static void bdi_update_dirty_ratelimit(struct backing_dev_info *bdi,
870                                        unsigned long thresh,
871                                        unsigned long bg_thresh,
872                                        unsigned long dirty,
873                                        unsigned long bdi_thresh,
874                                        unsigned long bdi_dirty,
875                                        unsigned long dirtied,
876                                        unsigned long elapsed)
877 {
878         unsigned long freerun = dirty_freerun_ceiling(thresh, bg_thresh);
879         unsigned long limit = hard_dirty_limit(thresh);
880         unsigned long setpoint = (freerun + limit) / 2;
881         unsigned long write_bw = bdi->avg_write_bandwidth;
882         unsigned long dirty_ratelimit = bdi->dirty_ratelimit;
883         unsigned long dirty_rate;
884         unsigned long task_ratelimit;
885         unsigned long balanced_dirty_ratelimit;
886         unsigned long pos_ratio;
887         unsigned long step;
888         unsigned long x;
889
890         /*
891          * The dirty rate will match the writeout rate in long term, except
892          * when dirty pages are truncated by userspace or re-dirtied by FS.
893          */
894         dirty_rate = (dirtied - bdi->dirtied_stamp) * HZ / elapsed;
895
896         pos_ratio = bdi_position_ratio(bdi, thresh, bg_thresh, dirty,
897                                        bdi_thresh, bdi_dirty);
898         /*
899          * task_ratelimit reflects each dd's dirty rate for the past 200ms.
900          */
901         task_ratelimit = (u64)dirty_ratelimit *
902                                         pos_ratio >> RATELIMIT_CALC_SHIFT;
903         task_ratelimit++; /* it helps rampup dirty_ratelimit from tiny values */
904
905         /*
906          * A linear estimation of the "balanced" throttle rate. The theory is,
907          * if there are N dd tasks, each throttled at task_ratelimit, the bdi's
908          * dirty_rate will be measured to be (N * task_ratelimit). So the below
909          * formula will yield the balanced rate limit (write_bw / N).
910          *
911          * Note that the expanded form is not a pure rate feedback:
912          *      rate_(i+1) = rate_(i) * (write_bw / dirty_rate)              (1)
913          * but also takes pos_ratio into account:
914          *      rate_(i+1) = rate_(i) * (write_bw / dirty_rate) * pos_ratio  (2)
915          *
916          * (1) is not realistic because pos_ratio also takes part in balancing
917          * the dirty rate.  Consider the state
918          *      pos_ratio = 0.5                                              (3)
919          *      rate = 2 * (write_bw / N)                                    (4)
920          * If (1) is used, it will stuck in that state! Because each dd will
921          * be throttled at
922          *      task_ratelimit = pos_ratio * rate = (write_bw / N)           (5)
923          * yielding
924          *      dirty_rate = N * task_ratelimit = write_bw                   (6)
925          * put (6) into (1) we get
926          *      rate_(i+1) = rate_(i)                                        (7)
927          *
928          * So we end up using (2) to always keep
929          *      rate_(i+1) ~= (write_bw / N)                                 (8)
930          * regardless of the value of pos_ratio. As long as (8) is satisfied,
931          * pos_ratio is able to drive itself to 1.0, which is not only where
932          * the dirty count meet the setpoint, but also where the slope of
933          * pos_ratio is most flat and hence task_ratelimit is least fluctuated.
934          */
935         balanced_dirty_ratelimit = div_u64((u64)task_ratelimit * write_bw,
936                                            dirty_rate | 1);
937         /*
938          * balanced_dirty_ratelimit ~= (write_bw / N) <= write_bw
939          */
940         if (unlikely(balanced_dirty_ratelimit > write_bw))
941                 balanced_dirty_ratelimit = write_bw;
942
943         /*
944          * We could safely do this and return immediately:
945          *
946          *      bdi->dirty_ratelimit = balanced_dirty_ratelimit;
947          *
948          * However to get a more stable dirty_ratelimit, the below elaborated
949          * code makes use of task_ratelimit to filter out singular points and
950          * limit the step size.
951          *
952          * The below code essentially only uses the relative value of
953          *
954          *      task_ratelimit - dirty_ratelimit
955          *      = (pos_ratio - 1) * dirty_ratelimit
956          *
957          * which reflects the direction and size of dirty position error.
958          */
959
960         /*
961          * dirty_ratelimit will follow balanced_dirty_ratelimit iff
962          * task_ratelimit is on the same side of dirty_ratelimit, too.
963          * For example, when
964          * - dirty_ratelimit > balanced_dirty_ratelimit
965          * - dirty_ratelimit > task_ratelimit (dirty pages are above setpoint)
966          * lowering dirty_ratelimit will help meet both the position and rate
967          * control targets. Otherwise, don't update dirty_ratelimit if it will
968          * only help meet the rate target. After all, what the users ultimately
969          * feel and care are stable dirty rate and small position error.
970          *
971          * |task_ratelimit - dirty_ratelimit| is used to limit the step size
972          * and filter out the singular points of balanced_dirty_ratelimit. Which
973          * keeps jumping around randomly and can even leap far away at times
974          * due to the small 200ms estimation period of dirty_rate (we want to
975          * keep that period small to reduce time lags).
976          */
977         step = 0;
978         if (dirty < setpoint) {
979                 x = min(bdi->balanced_dirty_ratelimit,
980                          min(balanced_dirty_ratelimit, task_ratelimit));
981                 if (dirty_ratelimit < x)
982                         step = x - dirty_ratelimit;
983         } else {
984                 x = max(bdi->balanced_dirty_ratelimit,
985                          max(balanced_dirty_ratelimit, task_ratelimit));
986                 if (dirty_ratelimit > x)
987                         step = dirty_ratelimit - x;
988         }
989
990         /*
991          * Don't pursue 100% rate matching. It's impossible since the balanced
992          * rate itself is constantly fluctuating. So decrease the track speed
993          * when it gets close to the target. Helps eliminate pointless tremors.
994          */
995         step >>= dirty_ratelimit / (2 * step + 1);
996         /*
997          * Limit the tracking speed to avoid overshooting.
998          */
999         step = (step + 7) / 8;
1000
1001         if (dirty_ratelimit < balanced_dirty_ratelimit)
1002                 dirty_ratelimit += step;
1003         else
1004                 dirty_ratelimit -= step;
1005
1006         bdi->dirty_ratelimit = max(dirty_ratelimit, 1UL);
1007         bdi->balanced_dirty_ratelimit = balanced_dirty_ratelimit;
1008
1009         trace_bdi_dirty_ratelimit(bdi, dirty_rate, task_ratelimit);
1010 }
1011
1012 void __bdi_update_bandwidth(struct backing_dev_info *bdi,
1013                             unsigned long thresh,
1014                             unsigned long bg_thresh,
1015                             unsigned long dirty,
1016                             unsigned long bdi_thresh,
1017                             unsigned long bdi_dirty,
1018                             unsigned long start_time)
1019 {
1020         unsigned long now = jiffies;
1021         unsigned long elapsed = now - bdi->bw_time_stamp;
1022         unsigned long dirtied;
1023         unsigned long written;
1024
1025         /*
1026          * rate-limit, only update once every 200ms.
1027          */
1028         if (elapsed < BANDWIDTH_INTERVAL)
1029                 return;
1030
1031         dirtied = percpu_counter_read(&bdi->bdi_stat[BDI_DIRTIED]);
1032         written = percpu_counter_read(&bdi->bdi_stat[BDI_WRITTEN]);
1033
1034         /*
1035          * Skip quiet periods when disk bandwidth is under-utilized.
1036          * (at least 1s idle time between two flusher runs)
1037          */
1038         if (elapsed > HZ && time_before(bdi->bw_time_stamp, start_time))
1039                 goto snapshot;
1040
1041         if (thresh) {
1042                 global_update_bandwidth(thresh, dirty, now);
1043                 bdi_update_dirty_ratelimit(bdi, thresh, bg_thresh, dirty,
1044                                            bdi_thresh, bdi_dirty,
1045                                            dirtied, elapsed);
1046         }
1047         bdi_update_write_bandwidth(bdi, elapsed, written);
1048
1049 snapshot:
1050         bdi->dirtied_stamp = dirtied;
1051         bdi->written_stamp = written;
1052         bdi->bw_time_stamp = now;
1053 }
1054
1055 static void bdi_update_bandwidth(struct backing_dev_info *bdi,
1056                                  unsigned long thresh,
1057                                  unsigned long bg_thresh,
1058                                  unsigned long dirty,
1059                                  unsigned long bdi_thresh,
1060                                  unsigned long bdi_dirty,
1061                                  unsigned long start_time)
1062 {
1063         if (time_is_after_eq_jiffies(bdi->bw_time_stamp + BANDWIDTH_INTERVAL))
1064                 return;
1065         spin_lock(&bdi->wb.list_lock);
1066         __bdi_update_bandwidth(bdi, thresh, bg_thresh, dirty,
1067                                bdi_thresh, bdi_dirty, start_time);
1068         spin_unlock(&bdi->wb.list_lock);
1069 }
1070
1071 /*
1072  * After a task dirtied this many pages, balance_dirty_pages_ratelimited_nr()
1073  * will look to see if it needs to start dirty throttling.
1074  *
1075  * If dirty_poll_interval is too low, big NUMA machines will call the expensive
1076  * global_page_state() too often. So scale it near-sqrt to the safety margin
1077  * (the number of pages we may dirty without exceeding the dirty limits).
1078  */
1079 static unsigned long dirty_poll_interval(unsigned long dirty,
1080                                          unsigned long thresh)
1081 {
1082         if (thresh > dirty)
1083                 return 1UL << (ilog2(thresh - dirty) >> 1);
1084
1085         return 1;
1086 }
1087
1088 static long bdi_max_pause(struct backing_dev_info *bdi,
1089                           unsigned long bdi_dirty)
1090 {
1091         long bw = bdi->avg_write_bandwidth;
1092         long t;
1093
1094         /*
1095          * Limit pause time for small memory systems. If sleeping for too long
1096          * time, a small pool of dirty/writeback pages may go empty and disk go
1097          * idle.
1098          *
1099          * 8 serves as the safety ratio.
1100          */
1101         t = bdi_dirty / (1 + bw / roundup_pow_of_two(1 + HZ / 8));
1102         t++;
1103
1104         return min_t(long, t, MAX_PAUSE);
1105 }
1106
1107 static long bdi_min_pause(struct backing_dev_info *bdi,
1108                           long max_pause,
1109                           unsigned long task_ratelimit,
1110                           unsigned long dirty_ratelimit,
1111                           int *nr_dirtied_pause)
1112 {
1113         long hi = ilog2(bdi->avg_write_bandwidth);
1114         long lo = ilog2(bdi->dirty_ratelimit);
1115         long t;         /* target pause */
1116         long pause;     /* estimated next pause */
1117         int pages;      /* target nr_dirtied_pause */
1118
1119         /* target for 10ms pause on 1-dd case */
1120         t = max(1, HZ / 100);
1121
1122         /*
1123          * Scale up pause time for concurrent dirtiers in order to reduce CPU
1124          * overheads.
1125          *
1126          * (N * 10ms) on 2^N concurrent tasks.
1127          */
1128         if (hi > lo)
1129                 t += (hi - lo) * (10 * HZ) / 1024;
1130
1131         /*
1132          * This is a bit convoluted. We try to base the next nr_dirtied_pause
1133          * on the much more stable dirty_ratelimit. However the next pause time
1134          * will be computed based on task_ratelimit and the two rate limits may
1135          * depart considerably at some time. Especially if task_ratelimit goes
1136          * below dirty_ratelimit/2 and the target pause is max_pause, the next
1137          * pause time will be max_pause*2 _trimmed down_ to max_pause.  As a
1138          * result task_ratelimit won't be executed faithfully, which could
1139          * eventually bring down dirty_ratelimit.
1140          *
1141          * We apply two rules to fix it up:
1142          * 1) try to estimate the next pause time and if necessary, use a lower
1143          *    nr_dirtied_pause so as not to exceed max_pause. When this happens,
1144          *    nr_dirtied_pause will be "dancing" with task_ratelimit.
1145          * 2) limit the target pause time to max_pause/2, so that the normal
1146          *    small fluctuations of task_ratelimit won't trigger rule (1) and
1147          *    nr_dirtied_pause will remain as stable as dirty_ratelimit.
1148          */
1149         t = min(t, 1 + max_pause / 2);
1150         pages = dirty_ratelimit * t / roundup_pow_of_two(HZ);
1151
1152         /*
1153          * Tiny nr_dirtied_pause is found to hurt I/O performance in the test
1154          * case fio-mmap-randwrite-64k, which does 16*{sync read, async write}.
1155          * When the 16 consecutive reads are often interrupted by some dirty
1156          * throttling pause during the async writes, cfq will go into idles
1157          * (deadline is fine). So push nr_dirtied_pause as high as possible
1158          * until reaches DIRTY_POLL_THRESH=32 pages.
1159          */
1160         if (pages < DIRTY_POLL_THRESH) {
1161                 t = max_pause;
1162                 pages = dirty_ratelimit * t / roundup_pow_of_two(HZ);
1163                 if (pages > DIRTY_POLL_THRESH) {
1164                         pages = DIRTY_POLL_THRESH;
1165                         t = HZ * DIRTY_POLL_THRESH / dirty_ratelimit;
1166                 }
1167         }
1168
1169         pause = HZ * pages / (task_ratelimit + 1);
1170         if (pause > max_pause) {
1171                 t = max_pause;
1172                 pages = task_ratelimit * t / roundup_pow_of_two(HZ);
1173         }
1174
1175         *nr_dirtied_pause = pages;
1176         /*
1177          * The minimal pause time will normally be half the target pause time.
1178          */
1179         return pages >= DIRTY_POLL_THRESH ? 1 + t / 2 : t;
1180 }
1181
1182 /*
1183  * balance_dirty_pages() must be called by processes which are generating dirty
1184  * data.  It looks at the number of dirty pages in the machine and will force
1185  * the caller to wait once crossing the (background_thresh + dirty_thresh) / 2.
1186  * If we're over `background_thresh' then the writeback threads are woken to
1187  * perform some writeout.
1188  */
1189 static void balance_dirty_pages(struct address_space *mapping,
1190                                 unsigned long pages_dirtied)
1191 {
1192         unsigned long nr_reclaimable;   /* = file_dirty + unstable_nfs */
1193         unsigned long bdi_reclaimable;
1194         unsigned long nr_dirty;  /* = file_dirty + writeback + unstable_nfs */
1195         unsigned long bdi_dirty;
1196         unsigned long freerun;
1197         unsigned long background_thresh;
1198         unsigned long dirty_thresh;
1199         unsigned long bdi_thresh;
1200         long period;
1201         long pause;
1202         long max_pause;
1203         long min_pause;
1204         int nr_dirtied_pause;
1205         bool dirty_exceeded = false;
1206         unsigned long task_ratelimit;
1207         unsigned long dirty_ratelimit;
1208         unsigned long pos_ratio;
1209         struct backing_dev_info *bdi = mapping->backing_dev_info;
1210         unsigned long start_time = jiffies;
1211
1212         for (;;) {
1213                 unsigned long now = jiffies;
1214
1215                 /*
1216                  * Unstable writes are a feature of certain networked
1217                  * filesystems (i.e. NFS) in which data may have been
1218                  * written to the server's write cache, but has not yet
1219                  * been flushed to permanent storage.
1220                  */
1221                 nr_reclaimable = global_page_state(NR_FILE_DIRTY) +
1222                                         global_page_state(NR_UNSTABLE_NFS);
1223                 nr_dirty = nr_reclaimable + global_page_state(NR_WRITEBACK);
1224
1225                 global_dirty_limits(&background_thresh, &dirty_thresh);
1226
1227                 /*
1228                  * Throttle it only when the background writeback cannot
1229                  * catch-up. This avoids (excessively) small writeouts
1230                  * when the bdi limits are ramping up.
1231                  */
1232                 freerun = dirty_freerun_ceiling(dirty_thresh,
1233                                                 background_thresh);
1234                 if (nr_dirty <= freerun) {
1235                         current->dirty_paused_when = now;
1236                         current->nr_dirtied = 0;
1237                         current->nr_dirtied_pause =
1238                                 dirty_poll_interval(nr_dirty, dirty_thresh);
1239                         break;
1240                 }
1241
1242                 if (unlikely(!writeback_in_progress(bdi)))
1243                         bdi_start_background_writeback(bdi);
1244
1245                 /*
1246                  * bdi_thresh is not treated as some limiting factor as
1247                  * dirty_thresh, due to reasons
1248                  * - in JBOD setup, bdi_thresh can fluctuate a lot
1249                  * - in a system with HDD and USB key, the USB key may somehow
1250                  *   go into state (bdi_dirty >> bdi_thresh) either because
1251                  *   bdi_dirty starts high, or because bdi_thresh drops low.
1252                  *   In this case we don't want to hard throttle the USB key
1253                  *   dirtiers for 100 seconds until bdi_dirty drops under
1254                  *   bdi_thresh. Instead the auxiliary bdi control line in
1255                  *   bdi_position_ratio() will let the dirtier task progress
1256                  *   at some rate <= (write_bw / 2) for bringing down bdi_dirty.
1257                  */
1258                 bdi_thresh = bdi_dirty_limit(bdi, dirty_thresh);
1259
1260                 /*
1261                  * In order to avoid the stacked BDI deadlock we need
1262                  * to ensure we accurately count the 'dirty' pages when
1263                  * the threshold is low.
1264                  *
1265                  * Otherwise it would be possible to get thresh+n pages
1266                  * reported dirty, even though there are thresh-m pages
1267                  * actually dirty; with m+n sitting in the percpu
1268                  * deltas.
1269                  */
1270                 if (bdi_thresh < 2 * bdi_stat_error(bdi)) {
1271                         bdi_reclaimable = bdi_stat_sum(bdi, BDI_RECLAIMABLE);
1272                         bdi_dirty = bdi_reclaimable +
1273                                     bdi_stat_sum(bdi, BDI_WRITEBACK);
1274                 } else {
1275                         bdi_reclaimable = bdi_stat(bdi, BDI_RECLAIMABLE);
1276                         bdi_dirty = bdi_reclaimable +
1277                                     bdi_stat(bdi, BDI_WRITEBACK);
1278                 }
1279
1280                 dirty_exceeded = (bdi_dirty > bdi_thresh) &&
1281                                   (nr_dirty > dirty_thresh);
1282                 if (dirty_exceeded && !bdi->dirty_exceeded)
1283                         bdi->dirty_exceeded = 1;
1284
1285                 bdi_update_bandwidth(bdi, dirty_thresh, background_thresh,
1286                                      nr_dirty, bdi_thresh, bdi_dirty,
1287                                      start_time);
1288
1289                 dirty_ratelimit = bdi->dirty_ratelimit;
1290                 pos_ratio = bdi_position_ratio(bdi, dirty_thresh,
1291                                                background_thresh, nr_dirty,
1292                                                bdi_thresh, bdi_dirty);
1293                 task_ratelimit = ((u64)dirty_ratelimit * pos_ratio) >>
1294                                                         RATELIMIT_CALC_SHIFT;
1295                 max_pause = bdi_max_pause(bdi, bdi_dirty);
1296                 min_pause = bdi_min_pause(bdi, max_pause,
1297                                           task_ratelimit, dirty_ratelimit,
1298                                           &nr_dirtied_pause);
1299
1300                 if (unlikely(task_ratelimit == 0)) {
1301                         period = max_pause;
1302                         pause = max_pause;
1303                         goto pause;
1304                 }
1305                 period = HZ * pages_dirtied / task_ratelimit;
1306                 pause = period;
1307                 if (current->dirty_paused_when)
1308                         pause -= now - current->dirty_paused_when;
1309                 /*
1310                  * For less than 1s think time (ext3/4 may block the dirtier
1311                  * for up to 800ms from time to time on 1-HDD; so does xfs,
1312                  * however at much less frequency), try to compensate it in
1313                  * future periods by updating the virtual time; otherwise just
1314                  * do a reset, as it may be a light dirtier.
1315                  */
1316                 if (pause < min_pause) {
1317                         trace_balance_dirty_pages(bdi,
1318                                                   dirty_thresh,
1319                                                   background_thresh,
1320                                                   nr_dirty,
1321                                                   bdi_thresh,
1322                                                   bdi_dirty,
1323                                                   dirty_ratelimit,
1324                                                   task_ratelimit,
1325                                                   pages_dirtied,
1326                                                   period,
1327                                                   min(pause, 0L),
1328                                                   start_time);
1329                         if (pause < -HZ) {
1330                                 current->dirty_paused_when = now;
1331                                 current->nr_dirtied = 0;
1332                         } else if (period) {
1333                                 current->dirty_paused_when += period;
1334                                 current->nr_dirtied = 0;
1335                         } else if (current->nr_dirtied_pause <= pages_dirtied)
1336                                 current->nr_dirtied_pause += pages_dirtied;
1337                         break;
1338                 }
1339                 if (unlikely(pause > max_pause)) {
1340                         /* for occasional dropped task_ratelimit */
1341                         now += min(pause - max_pause, max_pause);
1342                         pause = max_pause;
1343                 }
1344
1345 pause:
1346                 trace_balance_dirty_pages(bdi,
1347                                           dirty_thresh,
1348                                           background_thresh,
1349                                           nr_dirty,
1350                                           bdi_thresh,
1351                                           bdi_dirty,
1352                                           dirty_ratelimit,
1353                                           task_ratelimit,
1354                                           pages_dirtied,
1355                                           period,
1356                                           pause,
1357                                           start_time);
1358                 __set_current_state(TASK_KILLABLE);
1359                 io_schedule_timeout(pause);
1360
1361                 current->dirty_paused_when = now + pause;
1362                 current->nr_dirtied = 0;
1363                 current->nr_dirtied_pause = nr_dirtied_pause;
1364
1365                 /*
1366                  * This is typically equal to (nr_dirty < dirty_thresh) and can
1367                  * also keep "1000+ dd on a slow USB stick" under control.
1368                  */
1369                 if (task_ratelimit)
1370                         break;
1371
1372                 /*
1373                  * In the case of an unresponding NFS server and the NFS dirty
1374                  * pages exceeds dirty_thresh, give the other good bdi's a pipe
1375                  * to go through, so that tasks on them still remain responsive.
1376                  *
1377                  * In theory 1 page is enough to keep the comsumer-producer
1378                  * pipe going: the flusher cleans 1 page => the task dirties 1
1379                  * more page. However bdi_dirty has accounting errors.  So use
1380                  * the larger and more IO friendly bdi_stat_error.
1381                  */
1382                 if (bdi_dirty <= bdi_stat_error(bdi))
1383                         break;
1384
1385                 if (fatal_signal_pending(current))
1386                         break;
1387         }
1388
1389         if (!dirty_exceeded && bdi->dirty_exceeded)
1390                 bdi->dirty_exceeded = 0;
1391
1392         if (writeback_in_progress(bdi))
1393                 return;
1394
1395         /*
1396          * In laptop mode, we wait until hitting the higher threshold before
1397          * starting background writeout, and then write out all the way down
1398          * to the lower threshold.  So slow writers cause minimal disk activity.
1399          *
1400          * In normal mode, we start background writeout at the lower
1401          * background_thresh, to keep the amount of dirty memory low.
1402          */
1403         if (laptop_mode)
1404                 return;
1405
1406         if (nr_reclaimable > background_thresh)
1407                 bdi_start_background_writeback(bdi);
1408 }
1409
1410 void set_page_dirty_balance(struct page *page, int page_mkwrite)
1411 {
1412         if (set_page_dirty(page) || page_mkwrite) {
1413                 struct address_space *mapping = page_mapping(page);
1414
1415                 if (mapping)
1416                         balance_dirty_pages_ratelimited(mapping);
1417         }
1418 }
1419
1420 static DEFINE_PER_CPU(int, bdp_ratelimits);
1421
1422 /*
1423  * Normal tasks are throttled by
1424  *      loop {
1425  *              dirty tsk->nr_dirtied_pause pages;
1426  *              take a snap in balance_dirty_pages();
1427  *      }
1428  * However there is a worst case. If every task exit immediately when dirtied
1429  * (tsk->nr_dirtied_pause - 1) pages, balance_dirty_pages() will never be
1430  * called to throttle the page dirties. The solution is to save the not yet
1431  * throttled page dirties in dirty_throttle_leaks on task exit and charge them
1432  * randomly into the running tasks. This works well for the above worst case,
1433  * as the new task will pick up and accumulate the old task's leaked dirty
1434  * count and eventually get throttled.
1435  */
1436 DEFINE_PER_CPU(int, dirty_throttle_leaks) = 0;
1437
1438 /**
1439  * balance_dirty_pages_ratelimited_nr - balance dirty memory state
1440  * @mapping: address_space which was dirtied
1441  * @nr_pages_dirtied: number of pages which the caller has just dirtied
1442  *
1443  * Processes which are dirtying memory should call in here once for each page
1444  * which was newly dirtied.  The function will periodically check the system's
1445  * dirty state and will initiate writeback if needed.
1446  *
1447  * On really big machines, get_writeback_state is expensive, so try to avoid
1448  * calling it too often (ratelimiting).  But once we're over the dirty memory
1449  * limit we decrease the ratelimiting by a lot, to prevent individual processes
1450  * from overshooting the limit by (ratelimit_pages) each.
1451  */
1452 void balance_dirty_pages_ratelimited_nr(struct address_space *mapping,
1453                                         unsigned long nr_pages_dirtied)
1454 {
1455         struct backing_dev_info *bdi = mapping->backing_dev_info;
1456         int ratelimit;
1457         int *p;
1458
1459         if (!bdi_cap_account_dirty(bdi))
1460                 return;
1461
1462         ratelimit = current->nr_dirtied_pause;
1463         if (bdi->dirty_exceeded)
1464                 ratelimit = min(ratelimit, 32 >> (PAGE_SHIFT - 10));
1465
1466         preempt_disable();
1467         /*
1468          * This prevents one CPU to accumulate too many dirtied pages without
1469          * calling into balance_dirty_pages(), which can happen when there are
1470          * 1000+ tasks, all of them start dirtying pages at exactly the same
1471          * time, hence all honoured too large initial task->nr_dirtied_pause.
1472          */
1473         p =  &__get_cpu_var(bdp_ratelimits);
1474         if (unlikely(current->nr_dirtied >= ratelimit))
1475                 *p = 0;
1476         else if (unlikely(*p >= ratelimit_pages)) {
1477                 *p = 0;
1478                 ratelimit = 0;
1479         }
1480         /*
1481          * Pick up the dirtied pages by the exited tasks. This avoids lots of
1482          * short-lived tasks (eg. gcc invocations in a kernel build) escaping
1483          * the dirty throttling and livelock other long-run dirtiers.
1484          */
1485         p = &__get_cpu_var(dirty_throttle_leaks);
1486         if (*p > 0 && current->nr_dirtied < ratelimit) {
1487                 nr_pages_dirtied = min(*p, ratelimit - current->nr_dirtied);
1488                 *p -= nr_pages_dirtied;
1489                 current->nr_dirtied += nr_pages_dirtied;
1490         }
1491         preempt_enable();
1492
1493         if (unlikely(current->nr_dirtied >= ratelimit))
1494                 balance_dirty_pages(mapping, current->nr_dirtied);
1495 }
1496 EXPORT_SYMBOL(balance_dirty_pages_ratelimited_nr);
1497
1498 void throttle_vm_writeout(gfp_t gfp_mask)
1499 {
1500         unsigned long background_thresh;
1501         unsigned long dirty_thresh;
1502
1503         for ( ; ; ) {
1504                 global_dirty_limits(&background_thresh, &dirty_thresh);
1505                 dirty_thresh = hard_dirty_limit(dirty_thresh);
1506
1507                 /*
1508                  * Boost the allowable dirty threshold a bit for page
1509                  * allocators so they don't get DoS'ed by heavy writers
1510                  */
1511                 dirty_thresh += dirty_thresh / 10;      /* wheeee... */
1512
1513                 if (global_page_state(NR_UNSTABLE_NFS) +
1514                         global_page_state(NR_WRITEBACK) <= dirty_thresh)
1515                                 break;
1516                 congestion_wait(BLK_RW_ASYNC, HZ/10);
1517
1518                 /*
1519                  * The caller might hold locks which can prevent IO completion
1520                  * or progress in the filesystem.  So we cannot just sit here
1521                  * waiting for IO to complete.
1522                  */
1523                 if ((gfp_mask & (__GFP_FS|__GFP_IO)) != (__GFP_FS|__GFP_IO))
1524                         break;
1525         }
1526 }
1527
1528 /*
1529  * sysctl handler for /proc/sys/vm/dirty_writeback_centisecs
1530  */
1531 int dirty_writeback_centisecs_handler(ctl_table *table, int write,
1532         void __user *buffer, size_t *length, loff_t *ppos)
1533 {
1534         proc_dointvec(table, write, buffer, length, ppos);
1535         bdi_arm_supers_timer();
1536         return 0;
1537 }
1538
1539 #ifdef CONFIG_BLOCK
1540 void laptop_mode_timer_fn(unsigned long data)
1541 {
1542         struct request_queue *q = (struct request_queue *)data;
1543         int nr_pages = global_page_state(NR_FILE_DIRTY) +
1544                 global_page_state(NR_UNSTABLE_NFS);
1545
1546         /*
1547          * We want to write everything out, not just down to the dirty
1548          * threshold
1549          */
1550         if (bdi_has_dirty_io(&q->backing_dev_info))
1551                 bdi_start_writeback(&q->backing_dev_info, nr_pages,
1552                                         WB_REASON_LAPTOP_TIMER);
1553 }
1554
1555 /*
1556  * We've spun up the disk and we're in laptop mode: schedule writeback
1557  * of all dirty data a few seconds from now.  If the flush is already scheduled
1558  * then push it back - the user is still using the disk.
1559  */
1560 void laptop_io_completion(struct backing_dev_info *info)
1561 {
1562         mod_timer(&info->laptop_mode_wb_timer, jiffies + laptop_mode);
1563 }
1564
1565 /*
1566  * We're in laptop mode and we've just synced. The sync's writes will have
1567  * caused another writeback to be scheduled by laptop_io_completion.
1568  * Nothing needs to be written back anymore, so we unschedule the writeback.
1569  */
1570 void laptop_sync_completion(void)
1571 {
1572         struct backing_dev_info *bdi;
1573
1574         rcu_read_lock();
1575
1576         list_for_each_entry_rcu(bdi, &bdi_list, bdi_list)
1577                 del_timer(&bdi->laptop_mode_wb_timer);
1578
1579         rcu_read_unlock();
1580 }
1581 #endif
1582
1583 /*
1584  * If ratelimit_pages is too high then we can get into dirty-data overload
1585  * if a large number of processes all perform writes at the same time.
1586  * If it is too low then SMP machines will call the (expensive)
1587  * get_writeback_state too often.
1588  *
1589  * Here we set ratelimit_pages to a level which ensures that when all CPUs are
1590  * dirtying in parallel, we cannot go more than 3% (1/32) over the dirty memory
1591  * thresholds.
1592  */
1593
1594 void writeback_set_ratelimit(void)
1595 {
1596         unsigned long background_thresh;
1597         unsigned long dirty_thresh;
1598         global_dirty_limits(&background_thresh, &dirty_thresh);
1599         global_dirty_limit = dirty_thresh;
1600         ratelimit_pages = dirty_thresh / (num_online_cpus() * 32);
1601         if (ratelimit_pages < 16)
1602                 ratelimit_pages = 16;
1603 }
1604
1605 static int __cpuinit
1606 ratelimit_handler(struct notifier_block *self, unsigned long u, void *v)
1607 {
1608         writeback_set_ratelimit();
1609         return NOTIFY_DONE;
1610 }
1611
1612 static struct notifier_block __cpuinitdata ratelimit_nb = {
1613         .notifier_call  = ratelimit_handler,
1614         .next           = NULL,
1615 };
1616
1617 /*
1618  * Called early on to tune the page writeback dirty limits.
1619  *
1620  * We used to scale dirty pages according to how total memory
1621  * related to pages that could be allocated for buffers (by
1622  * comparing nr_free_buffer_pages() to vm_total_pages.
1623  *
1624  * However, that was when we used "dirty_ratio" to scale with
1625  * all memory, and we don't do that any more. "dirty_ratio"
1626  * is now applied to total non-HIGHPAGE memory (by subtracting
1627  * totalhigh_pages from vm_total_pages), and as such we can't
1628  * get into the old insane situation any more where we had
1629  * large amounts of dirty pages compared to a small amount of
1630  * non-HIGHMEM memory.
1631  *
1632  * But we might still want to scale the dirty_ratio by how
1633  * much memory the box has..
1634  */
1635 void __init page_writeback_init(void)
1636 {
1637         writeback_set_ratelimit();
1638         register_cpu_notifier(&ratelimit_nb);
1639
1640         fprop_global_init(&writeout_completions);
1641 }
1642
1643 /**
1644  * tag_pages_for_writeback - tag pages to be written by write_cache_pages
1645  * @mapping: address space structure to write
1646  * @start: starting page index
1647  * @end: ending page index (inclusive)
1648  *
1649  * This function scans the page range from @start to @end (inclusive) and tags
1650  * all pages that have DIRTY tag set with a special TOWRITE tag. The idea is
1651  * that write_cache_pages (or whoever calls this function) will then use
1652  * TOWRITE tag to identify pages eligible for writeback.  This mechanism is
1653  * used to avoid livelocking of writeback by a process steadily creating new
1654  * dirty pages in the file (thus it is important for this function to be quick
1655  * so that it can tag pages faster than a dirtying process can create them).
1656  */
1657 /*
1658  * We tag pages in batches of WRITEBACK_TAG_BATCH to reduce tree_lock latency.
1659  */
1660 void tag_pages_for_writeback(struct address_space *mapping,
1661                              pgoff_t start, pgoff_t end)
1662 {
1663 #define WRITEBACK_TAG_BATCH 4096
1664         unsigned long tagged;
1665
1666         do {
1667                 spin_lock_irq(&mapping->tree_lock);
1668                 tagged = radix_tree_range_tag_if_tagged(&mapping->page_tree,
1669                                 &start, end, WRITEBACK_TAG_BATCH,
1670                                 PAGECACHE_TAG_DIRTY, PAGECACHE_TAG_TOWRITE);
1671                 spin_unlock_irq(&mapping->tree_lock);
1672                 WARN_ON_ONCE(tagged > WRITEBACK_TAG_BATCH);
1673                 cond_resched();
1674                 /* We check 'start' to handle wrapping when end == ~0UL */
1675         } while (tagged >= WRITEBACK_TAG_BATCH && start);
1676 }
1677 EXPORT_SYMBOL(tag_pages_for_writeback);
1678
1679 /**
1680  * write_cache_pages - walk the list of dirty pages of the given address space and write all of them.
1681  * @mapping: address space structure to write
1682  * @wbc: subtract the number of written pages from *@wbc->nr_to_write
1683  * @writepage: function called for each page
1684  * @data: data passed to writepage function
1685  *
1686  * If a page is already under I/O, write_cache_pages() skips it, even
1687  * if it's dirty.  This is desirable behaviour for memory-cleaning writeback,
1688  * but it is INCORRECT for data-integrity system calls such as fsync().  fsync()
1689  * and msync() need to guarantee that all the data which was dirty at the time
1690  * the call was made get new I/O started against them.  If wbc->sync_mode is
1691  * WB_SYNC_ALL then we were called for data integrity and we must wait for
1692  * existing IO to complete.
1693  *
1694  * To avoid livelocks (when other process dirties new pages), we first tag
1695  * pages which should be written back with TOWRITE tag and only then start
1696  * writing them. For data-integrity sync we have to be careful so that we do
1697  * not miss some pages (e.g., because some other process has cleared TOWRITE
1698  * tag we set). The rule we follow is that TOWRITE tag can be cleared only
1699  * by the process clearing the DIRTY tag (and submitting the page for IO).
1700  */
1701 int write_cache_pages(struct address_space *mapping,
1702                       struct writeback_control *wbc, writepage_t writepage,
1703                       void *data)
1704 {
1705         int ret = 0;
1706         int done = 0;
1707         struct pagevec pvec;
1708         int nr_pages;
1709         pgoff_t uninitialized_var(writeback_index);
1710         pgoff_t index;
1711         pgoff_t end;            /* Inclusive */
1712         pgoff_t done_index;
1713         int cycled;
1714         int range_whole = 0;
1715         int tag;
1716
1717         pagevec_init(&pvec, 0);
1718         if (wbc->range_cyclic) {
1719                 writeback_index = mapping->writeback_index; /* prev offset */
1720                 index = writeback_index;
1721                 if (index == 0)
1722                         cycled = 1;
1723                 else
1724                         cycled = 0;
1725                 end = -1;
1726         } else {
1727                 index = wbc->range_start >> PAGE_CACHE_SHIFT;
1728                 end = wbc->range_end >> PAGE_CACHE_SHIFT;
1729                 if (wbc->range_start == 0 && wbc->range_end == LLONG_MAX)
1730                         range_whole = 1;
1731                 cycled = 1; /* ignore range_cyclic tests */
1732         }
1733         if (wbc->sync_mode == WB_SYNC_ALL || wbc->tagged_writepages)
1734                 tag = PAGECACHE_TAG_TOWRITE;
1735         else
1736                 tag = PAGECACHE_TAG_DIRTY;
1737 retry:
1738         if (wbc->sync_mode == WB_SYNC_ALL || wbc->tagged_writepages)
1739                 tag_pages_for_writeback(mapping, index, end);
1740         done_index = index;
1741         while (!done && (index <= end)) {
1742                 int i;
1743
1744                 nr_pages = pagevec_lookup_tag(&pvec, mapping, &index, tag,
1745                               min(end - index, (pgoff_t)PAGEVEC_SIZE-1) + 1);
1746                 if (nr_pages == 0)
1747                         break;
1748
1749                 for (i = 0; i < nr_pages; i++) {
1750                         struct page *page = pvec.pages[i];
1751
1752                         /*
1753                          * At this point, the page may be truncated or
1754                          * invalidated (changing page->mapping to NULL), or
1755                          * even swizzled back from swapper_space to tmpfs file
1756                          * mapping. However, page->index will not change
1757                          * because we have a reference on the page.
1758                          */
1759                         if (page->index > end) {
1760                                 /*
1761                                  * can't be range_cyclic (1st pass) because
1762                                  * end == -1 in that case.
1763                                  */
1764                                 done = 1;
1765                                 break;
1766                         }
1767
1768                         done_index = page->index;
1769
1770                         lock_page(page);
1771
1772                         /*
1773                          * Page truncated or invalidated. We can freely skip it
1774                          * then, even for data integrity operations: the page
1775                          * has disappeared concurrently, so there could be no
1776                          * real expectation of this data interity operation
1777                          * even if there is now a new, dirty page at the same
1778                          * pagecache address.
1779                          */
1780                         if (unlikely(page->mapping != mapping)) {
1781 continue_unlock:
1782                                 unlock_page(page);
1783                                 continue;
1784                         }
1785
1786                         if (!PageDirty(page)) {
1787                                 /* someone wrote it for us */
1788                                 goto continue_unlock;
1789                         }
1790
1791                         if (PageWriteback(page)) {
1792                                 if (wbc->sync_mode != WB_SYNC_NONE)
1793                                         wait_on_page_writeback(page);
1794                                 else
1795                                         goto continue_unlock;
1796                         }
1797
1798                         BUG_ON(PageWriteback(page));
1799                         if (!clear_page_dirty_for_io(page))
1800                                 goto continue_unlock;
1801
1802                         trace_wbc_writepage(wbc, mapping->backing_dev_info);
1803                         ret = (*writepage)(page, wbc, data);
1804                         if (unlikely(ret)) {
1805                                 if (ret == AOP_WRITEPAGE_ACTIVATE) {
1806                                         unlock_page(page);
1807                                         ret = 0;
1808                                 } else {
1809                                         /*
1810                                          * done_index is set past this page,
1811                                          * so media errors will not choke
1812                                          * background writeout for the entire
1813                                          * file. This has consequences for
1814                                          * range_cyclic semantics (ie. it may
1815                                          * not be suitable for data integrity
1816                                          * writeout).
1817                                          */
1818                                         done_index = page->index + 1;
1819                                         done = 1;
1820                                         break;
1821                                 }
1822                         }
1823
1824                         /*
1825                          * We stop writing back only if we are not doing
1826                          * integrity sync. In case of integrity sync we have to
1827                          * keep going until we have written all the pages
1828                          * we tagged for writeback prior to entering this loop.
1829                          */
1830                         if (--wbc->nr_to_write <= 0 &&
1831                             wbc->sync_mode == WB_SYNC_NONE) {
1832                                 done = 1;
1833                                 break;
1834                         }
1835                 }
1836                 pagevec_release(&pvec);
1837                 cond_resched();
1838         }
1839         if (!cycled && !done) {
1840                 /*
1841                  * range_cyclic:
1842                  * We hit the last page and there is more work to be done: wrap
1843                  * back to the start of the file
1844                  */
1845                 cycled = 1;
1846                 index = 0;
1847                 end = writeback_index - 1;
1848                 goto retry;
1849         }
1850         if (wbc->range_cyclic || (range_whole && wbc->nr_to_write > 0))
1851                 mapping->writeback_index = done_index;
1852
1853         return ret;
1854 }
1855 EXPORT_SYMBOL(write_cache_pages);
1856
1857 /*
1858  * Function used by generic_writepages to call the real writepage
1859  * function and set the mapping flags on error
1860  */
1861 static int __writepage(struct page *page, struct writeback_control *wbc,
1862                        void *data)
1863 {
1864         struct address_space *mapping = data;
1865         int ret = mapping->a_ops->writepage(page, wbc);
1866         mapping_set_error(mapping, ret);
1867         return ret;
1868 }
1869
1870 /**
1871  * generic_writepages - walk the list of dirty pages of the given address space and writepage() all of them.
1872  * @mapping: address space structure to write
1873  * @wbc: subtract the number of written pages from *@wbc->nr_to_write
1874  *
1875  * This is a library function, which implements the writepages()
1876  * address_space_operation.
1877  */
1878 int generic_writepages(struct address_space *mapping,
1879                        struct writeback_control *wbc)
1880 {
1881         struct blk_plug plug;
1882         int ret;
1883
1884         /* deal with chardevs and other special file */
1885         if (!mapping->a_ops->writepage)
1886                 return 0;
1887
1888         blk_start_plug(&plug);
1889         ret = write_cache_pages(mapping, wbc, __writepage, mapping);
1890         blk_finish_plug(&plug);
1891         return ret;
1892 }
1893
1894 EXPORT_SYMBOL(generic_writepages);
1895
1896 int do_writepages(struct address_space *mapping, struct writeback_control *wbc)
1897 {
1898         int ret;
1899
1900         if (wbc->nr_to_write <= 0)
1901                 return 0;
1902         if (mapping->a_ops->writepages)
1903                 ret = mapping->a_ops->writepages(mapping, wbc);
1904         else
1905                 ret = generic_writepages(mapping, wbc);
1906         return ret;
1907 }
1908
1909 /**
1910  * write_one_page - write out a single page and optionally wait on I/O
1911  * @page: the page to write
1912  * @wait: if true, wait on writeout
1913  *
1914  * The page must be locked by the caller and will be unlocked upon return.
1915  *
1916  * write_one_page() returns a negative error code if I/O failed.
1917  */
1918 int write_one_page(struct page *page, int wait)
1919 {
1920         struct address_space *mapping = page->mapping;
1921         int ret = 0;
1922         struct writeback_control wbc = {
1923                 .sync_mode = WB_SYNC_ALL,
1924                 .nr_to_write = 1,
1925         };
1926
1927         BUG_ON(!PageLocked(page));
1928
1929         if (wait)
1930                 wait_on_page_writeback(page);
1931
1932         if (clear_page_dirty_for_io(page)) {
1933                 page_cache_get(page);
1934                 ret = mapping->a_ops->writepage(page, &wbc);
1935                 if (ret == 0 && wait) {
1936                         wait_on_page_writeback(page);
1937                         if (PageError(page))
1938                                 ret = -EIO;
1939                 }
1940                 page_cache_release(page);
1941         } else {
1942                 unlock_page(page);
1943         }
1944         return ret;
1945 }
1946 EXPORT_SYMBOL(write_one_page);
1947
1948 /*
1949  * For address_spaces which do not use buffers nor write back.
1950  */
1951 int __set_page_dirty_no_writeback(struct page *page)
1952 {
1953         if (!PageDirty(page))
1954                 return !TestSetPageDirty(page);
1955         return 0;
1956 }
1957
1958 /*
1959  * Helper function for set_page_dirty family.
1960  * NOTE: This relies on being atomic wrt interrupts.
1961  */
1962 void account_page_dirtied(struct page *page, struct address_space *mapping)
1963 {
1964         if (mapping_cap_account_dirty(mapping)) {
1965                 __inc_zone_page_state(page, NR_FILE_DIRTY);
1966                 __inc_zone_page_state(page, NR_DIRTIED);
1967                 __inc_bdi_stat(mapping->backing_dev_info, BDI_RECLAIMABLE);
1968                 __inc_bdi_stat(mapping->backing_dev_info, BDI_DIRTIED);
1969                 task_io_account_write(PAGE_CACHE_SIZE);
1970                 current->nr_dirtied++;
1971                 this_cpu_inc(bdp_ratelimits);
1972         }
1973 }
1974 EXPORT_SYMBOL(account_page_dirtied);
1975
1976 /*
1977  * Helper function for set_page_writeback family.
1978  * NOTE: Unlike account_page_dirtied this does not rely on being atomic
1979  * wrt interrupts.
1980  */
1981 void account_page_writeback(struct page *page)
1982 {
1983         inc_zone_page_state(page, NR_WRITEBACK);
1984 }
1985 EXPORT_SYMBOL(account_page_writeback);
1986
1987 /*
1988  * For address_spaces which do not use buffers.  Just tag the page as dirty in
1989  * its radix tree.
1990  *
1991  * This is also used when a single buffer is being dirtied: we want to set the
1992  * page dirty in that case, but not all the buffers.  This is a "bottom-up"
1993  * dirtying, whereas __set_page_dirty_buffers() is a "top-down" dirtying.
1994  *
1995  * Most callers have locked the page, which pins the address_space in memory.
1996  * But zap_pte_range() does not lock the page, however in that case the
1997  * mapping is pinned by the vma's ->vm_file reference.
1998  *
1999  * We take care to handle the case where the page was truncated from the
2000  * mapping by re-checking page_mapping() inside tree_lock.
2001  */
2002 int __set_page_dirty_nobuffers(struct page *page)
2003 {
2004         if (!TestSetPageDirty(page)) {
2005                 struct address_space *mapping = page_mapping(page);
2006                 struct address_space *mapping2;
2007
2008                 if (!mapping)
2009                         return 1;
2010
2011                 spin_lock_irq(&mapping->tree_lock);
2012                 mapping2 = page_mapping(page);
2013                 if (mapping2) { /* Race with truncate? */
2014                         BUG_ON(mapping2 != mapping);
2015                         WARN_ON_ONCE(!PagePrivate(page) && !PageUptodate(page));
2016                         account_page_dirtied(page, mapping);
2017                         radix_tree_tag_set(&mapping->page_tree,
2018                                 page_index(page), PAGECACHE_TAG_DIRTY);
2019                 }
2020                 spin_unlock_irq(&mapping->tree_lock);
2021                 if (mapping->host) {
2022                         /* !PageAnon && !swapper_space */
2023                         __mark_inode_dirty(mapping->host, I_DIRTY_PAGES);
2024                 }
2025                 return 1;
2026         }
2027         return 0;
2028 }
2029 EXPORT_SYMBOL(__set_page_dirty_nobuffers);
2030
2031 /*
2032  * Call this whenever redirtying a page, to de-account the dirty counters
2033  * (NR_DIRTIED, BDI_DIRTIED, tsk->nr_dirtied), so that they match the written
2034  * counters (NR_WRITTEN, BDI_WRITTEN) in long term. The mismatches will lead to
2035  * systematic errors in balanced_dirty_ratelimit and the dirty pages position
2036  * control.
2037  */
2038 void account_page_redirty(struct page *page)
2039 {
2040         struct address_space *mapping = page->mapping;
2041         if (mapping && mapping_cap_account_dirty(mapping)) {
2042                 current->nr_dirtied--;
2043                 dec_zone_page_state(page, NR_DIRTIED);
2044                 dec_bdi_stat(mapping->backing_dev_info, BDI_DIRTIED);
2045         }
2046 }
2047 EXPORT_SYMBOL(account_page_redirty);
2048
2049 /*
2050  * When a writepage implementation decides that it doesn't want to write this
2051  * page for some reason, it should redirty the locked page via
2052  * redirty_page_for_writepage() and it should then unlock the page and return 0
2053  */
2054 int redirty_page_for_writepage(struct writeback_control *wbc, struct page *page)
2055 {
2056         wbc->pages_skipped++;
2057         account_page_redirty(page);
2058         return __set_page_dirty_nobuffers(page);
2059 }
2060 EXPORT_SYMBOL(redirty_page_for_writepage);
2061
2062 /*
2063  * Dirty a page.
2064  *
2065  * For pages with a mapping this should be done under the page lock
2066  * for the benefit of asynchronous memory errors who prefer a consistent
2067  * dirty state. This rule can be broken in some special cases,
2068  * but should be better not to.
2069  *
2070  * If the mapping doesn't provide a set_page_dirty a_op, then
2071  * just fall through and assume that it wants buffer_heads.
2072  */
2073 int set_page_dirty(struct page *page)
2074 {
2075         struct address_space *mapping = page_mapping(page);
2076
2077         if (likely(mapping)) {
2078                 int (*spd)(struct page *) = mapping->a_ops->set_page_dirty;
2079                 /*
2080                  * readahead/lru_deactivate_page could remain
2081                  * PG_readahead/PG_reclaim due to race with end_page_writeback
2082                  * About readahead, if the page is written, the flags would be
2083                  * reset. So no problem.
2084                  * About lru_deactivate_page, if the page is redirty, the flag
2085                  * will be reset. So no problem. but if the page is used by readahead
2086                  * it will confuse readahead and make it restart the size rampup
2087                  * process. But it's a trivial problem.
2088                  */
2089                 ClearPageReclaim(page);
2090 #ifdef CONFIG_BLOCK
2091                 if (!spd)
2092                         spd = __set_page_dirty_buffers;
2093 #endif
2094                 return (*spd)(page);
2095         }
2096         if (!PageDirty(page)) {
2097                 if (!TestSetPageDirty(page))
2098                         return 1;
2099         }
2100         return 0;
2101 }
2102 EXPORT_SYMBOL(set_page_dirty);
2103
2104 /*
2105  * set_page_dirty() is racy if the caller has no reference against
2106  * page->mapping->host, and if the page is unlocked.  This is because another
2107  * CPU could truncate the page off the mapping and then free the mapping.
2108  *
2109  * Usually, the page _is_ locked, or the caller is a user-space process which
2110  * holds a reference on the inode by having an open file.
2111  *
2112  * In other cases, the page should be locked before running set_page_dirty().
2113  */
2114 int set_page_dirty_lock(struct page *page)
2115 {
2116         int ret;
2117
2118         lock_page(page);
2119         ret = set_page_dirty(page);
2120         unlock_page(page);
2121         return ret;
2122 }
2123 EXPORT_SYMBOL(set_page_dirty_lock);
2124
2125 /*
2126  * Clear a page's dirty flag, while caring for dirty memory accounting.
2127  * Returns true if the page was previously dirty.
2128  *
2129  * This is for preparing to put the page under writeout.  We leave the page
2130  * tagged as dirty in the radix tree so that a concurrent write-for-sync
2131  * can discover it via a PAGECACHE_TAG_DIRTY walk.  The ->writepage
2132  * implementation will run either set_page_writeback() or set_page_dirty(),
2133  * at which stage we bring the page's dirty flag and radix-tree dirty tag
2134  * back into sync.
2135  *
2136  * This incoherency between the page's dirty flag and radix-tree tag is
2137  * unfortunate, but it only exists while the page is locked.
2138  */
2139 int clear_page_dirty_for_io(struct page *page)
2140 {
2141         struct address_space *mapping = page_mapping(page);
2142
2143         BUG_ON(!PageLocked(page));
2144
2145         if (mapping && mapping_cap_account_dirty(mapping)) {
2146                 /*
2147                  * Yes, Virginia, this is indeed insane.
2148                  *
2149                  * We use this sequence to make sure that
2150                  *  (a) we account for dirty stats properly
2151                  *  (b) we tell the low-level filesystem to
2152                  *      mark the whole page dirty if it was
2153                  *      dirty in a pagetable. Only to then
2154                  *  (c) clean the page again and return 1 to
2155                  *      cause the writeback.
2156                  *
2157                  * This way we avoid all nasty races with the
2158                  * dirty bit in multiple places and clearing
2159                  * them concurrently from different threads.
2160                  *
2161                  * Note! Normally the "set_page_dirty(page)"
2162                  * has no effect on the actual dirty bit - since
2163                  * that will already usually be set. But we
2164                  * need the side effects, and it can help us
2165                  * avoid races.
2166                  *
2167                  * We basically use the page "master dirty bit"
2168                  * as a serialization point for all the different
2169                  * threads doing their things.
2170                  */
2171                 if (page_mkclean(page))
2172                         set_page_dirty(page);
2173                 /*
2174                  * We carefully synchronise fault handlers against
2175                  * installing a dirty pte and marking the page dirty
2176                  * at this point. We do this by having them hold the
2177                  * page lock at some point after installing their
2178                  * pte, but before marking the page dirty.
2179                  * Pages are always locked coming in here, so we get
2180                  * the desired exclusion. See mm/memory.c:do_wp_page()
2181                  * for more comments.
2182                  */
2183                 if (TestClearPageDirty(page)) {
2184                         dec_zone_page_state(page, NR_FILE_DIRTY);
2185                         dec_bdi_stat(mapping->backing_dev_info,
2186                                         BDI_RECLAIMABLE);
2187                         return 1;
2188                 }
2189                 return 0;
2190         }
2191         return TestClearPageDirty(page);
2192 }
2193 EXPORT_SYMBOL(clear_page_dirty_for_io);
2194
2195 int test_clear_page_writeback(struct page *page)
2196 {
2197         struct address_space *mapping = page_mapping(page);
2198         int ret;
2199
2200         if (mapping) {
2201                 struct backing_dev_info *bdi = mapping->backing_dev_info;
2202                 unsigned long flags;
2203
2204                 spin_lock_irqsave(&mapping->tree_lock, flags);
2205                 ret = TestClearPageWriteback(page);
2206                 if (ret) {
2207                         radix_tree_tag_clear(&mapping->page_tree,
2208                                                 page_index(page),
2209                                                 PAGECACHE_TAG_WRITEBACK);
2210                         if (bdi_cap_account_writeback(bdi)) {
2211                                 __dec_bdi_stat(bdi, BDI_WRITEBACK);
2212                                 __bdi_writeout_inc(bdi);
2213                         }
2214                 }
2215                 spin_unlock_irqrestore(&mapping->tree_lock, flags);
2216         } else {
2217                 ret = TestClearPageWriteback(page);
2218         }
2219         if (ret) {
2220                 dec_zone_page_state(page, NR_WRITEBACK);
2221                 inc_zone_page_state(page, NR_WRITTEN);
2222         }
2223         return ret;
2224 }
2225
2226 int test_set_page_writeback(struct page *page)
2227 {
2228         struct address_space *mapping = page_mapping(page);
2229         int ret;
2230
2231         if (mapping) {
2232                 struct backing_dev_info *bdi = mapping->backing_dev_info;
2233                 unsigned long flags;
2234
2235                 spin_lock_irqsave(&mapping->tree_lock, flags);
2236                 ret = TestSetPageWriteback(page);
2237                 if (!ret) {
2238                         radix_tree_tag_set(&mapping->page_tree,
2239                                                 page_index(page),
2240                                                 PAGECACHE_TAG_WRITEBACK);
2241                         if (bdi_cap_account_writeback(bdi))
2242                                 __inc_bdi_stat(bdi, BDI_WRITEBACK);
2243                 }
2244                 if (!PageDirty(page))
2245                         radix_tree_tag_clear(&mapping->page_tree,
2246                                                 page_index(page),
2247                                                 PAGECACHE_TAG_DIRTY);
2248                 radix_tree_tag_clear(&mapping->page_tree,
2249                                      page_index(page),
2250                                      PAGECACHE_TAG_TOWRITE);
2251                 spin_unlock_irqrestore(&mapping->tree_lock, flags);
2252         } else {
2253                 ret = TestSetPageWriteback(page);
2254         }
2255         if (!ret)
2256                 account_page_writeback(page);
2257         return ret;
2258
2259 }
2260 EXPORT_SYMBOL(test_set_page_writeback);
2261
2262 /*
2263  * Return true if any of the pages in the mapping are marked with the
2264  * passed tag.
2265  */
2266 int mapping_tagged(struct address_space *mapping, int tag)
2267 {
2268         return radix_tree_tagged(&mapping->page_tree, tag);
2269 }
2270 EXPORT_SYMBOL(mapping_tagged);