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page-writeback.c
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1 /*
2  * mm/page-writeback.c
3  *
4  * Copyright (C) 2002, Linus Torvalds.
5  * Copyright (C) 2007 Red Hat, Inc., Peter Zijlstra <[email protected]>
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>
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  */
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  */
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 
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  */
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  */
116 
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 
197  struct zone *z =
198  &NODE_DATA(node)->node_zones[ZONE_HIGHMEM];
199 
200  x += zone_page_state(z, NR_FREE_PAGES) +
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 
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() -
227 
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 
251  available_memory = global_dirtyable_memory();
252 
253  if (vm_dirty_bytes)
255  else
256  dirty = (vm_dirty_ratio * available_memory) / 100;
257 
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 
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 
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)
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 
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 
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)
348  return ret;
349 }
350 
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)
360  return ret;
361 }
362 
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) {
373  vm_dirty_bytes = 0;
374  }
375  return ret;
376 }
377 
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) {
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 
425 {
426  unsigned long flags;
427 
428  local_irq_save(flags);
429  __bdi_writeout_inc(bdi);
430  local_irq_restore(flags);
431 }
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) /
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 }
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 
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:
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 
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 {
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)))
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) >>
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);
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)
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 
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 }
1497 
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;
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  */
1532  void __user *buffer, size_t *length, loff_t *ppos)
1533 {
1534  proc_dointvec(table, write, buffer, length, ppos);
1535  return 0;
1536 }
1537 
1538 #ifdef CONFIG_BLOCK
1539 void laptop_mode_timer_fn(unsigned long data)
1540 {
1541  struct request_queue *q = (struct request_queue *)data;
1542  int nr_pages = global_page_state(NR_FILE_DIRTY) +
1543  global_page_state(NR_UNSTABLE_NFS);
1544 
1545  /*
1546  * We want to write everything out, not just down to the dirty
1547  * threshold
1548  */
1549  if (bdi_has_dirty_io(&q->backing_dev_info))
1550  bdi_start_writeback(&q->backing_dev_info, nr_pages,
1552 }
1553 
1554 /*
1555  * We've spun up the disk and we're in laptop mode: schedule writeback
1556  * of all dirty data a few seconds from now. If the flush is already scheduled
1557  * then push it back - the user is still using the disk.
1558  */
1559 void laptop_io_completion(struct backing_dev_info *info)
1560 {
1561  mod_timer(&info->laptop_mode_wb_timer, jiffies + laptop_mode);
1562 }
1563 
1564 /*
1565  * We're in laptop mode and we've just synced. The sync's writes will have
1566  * caused another writeback to be scheduled by laptop_io_completion.
1567  * Nothing needs to be written back anymore, so we unschedule the writeback.
1568  */
1569 void laptop_sync_completion(void)
1570 {
1571  struct backing_dev_info *bdi;
1572 
1573  rcu_read_lock();
1574 
1575  list_for_each_entry_rcu(bdi, &bdi_list, bdi_list)
1577 
1578  rcu_read_unlock();
1579 }
1580 #endif
1581 
1582 /*
1583  * If ratelimit_pages is too high then we can get into dirty-data overload
1584  * if a large number of processes all perform writes at the same time.
1585  * If it is too low then SMP machines will call the (expensive)
1586  * get_writeback_state too often.
1587  *
1588  * Here we set ratelimit_pages to a level which ensures that when all CPUs are
1589  * dirtying in parallel, we cannot go more than 3% (1/32) over the dirty memory
1590  * thresholds.
1591  */
1592 
1594 {
1595  unsigned long background_thresh;
1596  unsigned long dirty_thresh;
1597  global_dirty_limits(&background_thresh, &dirty_thresh);
1598  global_dirty_limit = dirty_thresh;
1599  ratelimit_pages = dirty_thresh / (num_online_cpus() * 32);
1600  if (ratelimit_pages < 16)
1601  ratelimit_pages = 16;
1602 }
1603 
1604 static int __cpuinit
1605 ratelimit_handler(struct notifier_block *self, unsigned long action,
1606  void *hcpu)
1607 {
1608 
1609  switch (action & ~CPU_TASKS_FROZEN) {
1610  case CPU_ONLINE:
1611  case CPU_DEAD:
1613  return NOTIFY_OK;
1614  default:
1615  return NOTIFY_DONE;
1616  }
1617 }
1618 
1619 static struct notifier_block __cpuinitdata ratelimit_nb = {
1620  .notifier_call = ratelimit_handler,
1621  .next = NULL,
1622 };
1623 
1624 /*
1625  * Called early on to tune the page writeback dirty limits.
1626  *
1627  * We used to scale dirty pages according to how total memory
1628  * related to pages that could be allocated for buffers (by
1629  * comparing nr_free_buffer_pages() to vm_total_pages.
1630  *
1631  * However, that was when we used "dirty_ratio" to scale with
1632  * all memory, and we don't do that any more. "dirty_ratio"
1633  * is now applied to total non-HIGHPAGE memory (by subtracting
1634  * totalhigh_pages from vm_total_pages), and as such we can't
1635  * get into the old insane situation any more where we had
1636  * large amounts of dirty pages compared to a small amount of
1637  * non-HIGHMEM memory.
1638  *
1639  * But we might still want to scale the dirty_ratio by how
1640  * much memory the box has..
1641  */
1643 {
1645  register_cpu_notifier(&ratelimit_nb);
1646 
1647  fprop_global_init(&writeout_completions);
1648 }
1649 
1664 /*
1665  * We tag pages in batches of WRITEBACK_TAG_BATCH to reduce tree_lock latency.
1666  */
1669 {
1670 #define WRITEBACK_TAG_BATCH 4096
1671  unsigned long tagged;
1672 
1673  do {
1674  spin_lock_irq(&mapping->tree_lock);
1675  tagged = radix_tree_range_tag_if_tagged(&mapping->page_tree,
1676  &start, end, WRITEBACK_TAG_BATCH,
1678  spin_unlock_irq(&mapping->tree_lock);
1680  cond_resched();
1681  /* We check 'start' to handle wrapping when end == ~0UL */
1682  } while (tagged >= WRITEBACK_TAG_BATCH && start);
1683 }
1685 
1708 int write_cache_pages(struct address_space *mapping,
1709  struct writeback_control *wbc, writepage_t writepage,
1710  void *data)
1711 {
1712  int ret = 0;
1713  int done = 0;
1714  struct pagevec pvec;
1715  int nr_pages;
1717  pgoff_t index;
1718  pgoff_t end; /* Inclusive */
1719  pgoff_t done_index;
1720  int cycled;
1721  int range_whole = 0;
1722  int tag;
1723 
1724  pagevec_init(&pvec, 0);
1725  if (wbc->range_cyclic) {
1726  writeback_index = mapping->writeback_index; /* prev offset */
1727  index = writeback_index;
1728  if (index == 0)
1729  cycled = 1;
1730  else
1731  cycled = 0;
1732  end = -1;
1733  } else {
1734  index = wbc->range_start >> PAGE_CACHE_SHIFT;
1735  end = wbc->range_end >> PAGE_CACHE_SHIFT;
1736  if (wbc->range_start == 0 && wbc->range_end == LLONG_MAX)
1737  range_whole = 1;
1738  cycled = 1; /* ignore range_cyclic tests */
1739  }
1740  if (wbc->sync_mode == WB_SYNC_ALL || wbc->tagged_writepages)
1741  tag = PAGECACHE_TAG_TOWRITE;
1742  else
1743  tag = PAGECACHE_TAG_DIRTY;
1744 retry:
1745  if (wbc->sync_mode == WB_SYNC_ALL || wbc->tagged_writepages)
1746  tag_pages_for_writeback(mapping, index, end);
1747  done_index = index;
1748  while (!done && (index <= end)) {
1749  int i;
1750 
1751  nr_pages = pagevec_lookup_tag(&pvec, mapping, &index, tag,
1752  min(end - index, (pgoff_t)PAGEVEC_SIZE-1) + 1);
1753  if (nr_pages == 0)
1754  break;
1755 
1756  for (i = 0; i < nr_pages; i++) {
1757  struct page *page = pvec.pages[i];
1758 
1759  /*
1760  * At this point, the page may be truncated or
1761  * invalidated (changing page->mapping to NULL), or
1762  * even swizzled back from swapper_space to tmpfs file
1763  * mapping. However, page->index will not change
1764  * because we have a reference on the page.
1765  */
1766  if (page->index > end) {
1767  /*
1768  * can't be range_cyclic (1st pass) because
1769  * end == -1 in that case.
1770  */
1771  done = 1;
1772  break;
1773  }
1774 
1775  done_index = page->index;
1776 
1777  lock_page(page);
1778 
1779  /*
1780  * Page truncated or invalidated. We can freely skip it
1781  * then, even for data integrity operations: the page
1782  * has disappeared concurrently, so there could be no
1783  * real expectation of this data interity operation
1784  * even if there is now a new, dirty page at the same
1785  * pagecache address.
1786  */
1787  if (unlikely(page->mapping != mapping)) {
1788 continue_unlock:
1789  unlock_page(page);
1790  continue;
1791  }
1792 
1793  if (!PageDirty(page)) {
1794  /* someone wrote it for us */
1795  goto continue_unlock;
1796  }
1797 
1798  if (PageWriteback(page)) {
1799  if (wbc->sync_mode != WB_SYNC_NONE)
1800  wait_on_page_writeback(page);
1801  else
1802  goto continue_unlock;
1803  }
1804 
1805  BUG_ON(PageWriteback(page));
1806  if (!clear_page_dirty_for_io(page))
1807  goto continue_unlock;
1808 
1809  trace_wbc_writepage(wbc, mapping->backing_dev_info);
1810  ret = (*writepage)(page, wbc, data);
1811  if (unlikely(ret)) {
1812  if (ret == AOP_WRITEPAGE_ACTIVATE) {
1813  unlock_page(page);
1814  ret = 0;
1815  } else {
1816  /*
1817  * done_index is set past this page,
1818  * so media errors will not choke
1819  * background writeout for the entire
1820  * file. This has consequences for
1821  * range_cyclic semantics (ie. it may
1822  * not be suitable for data integrity
1823  * writeout).
1824  */
1825  done_index = page->index + 1;
1826  done = 1;
1827  break;
1828  }
1829  }
1830 
1831  /*
1832  * We stop writing back only if we are not doing
1833  * integrity sync. In case of integrity sync we have to
1834  * keep going until we have written all the pages
1835  * we tagged for writeback prior to entering this loop.
1836  */
1837  if (--wbc->nr_to_write <= 0 &&
1838  wbc->sync_mode == WB_SYNC_NONE) {
1839  done = 1;
1840  break;
1841  }
1842  }
1843  pagevec_release(&pvec);
1844  cond_resched();
1845  }
1846  if (!cycled && !done) {
1847  /*
1848  * range_cyclic:
1849  * We hit the last page and there is more work to be done: wrap
1850  * back to the start of the file
1851  */
1852  cycled = 1;
1853  index = 0;
1854  end = writeback_index - 1;
1855  goto retry;
1856  }
1857  if (wbc->range_cyclic || (range_whole && wbc->nr_to_write > 0))
1858  mapping->writeback_index = done_index;
1859 
1860  return ret;
1861 }
1863 
1864 /*
1865  * Function used by generic_writepages to call the real writepage
1866  * function and set the mapping flags on error
1867  */
1868 static int __writepage(struct page *page, struct writeback_control *wbc,
1869  void *data)
1870 {
1871  struct address_space *mapping = data;
1872  int ret = mapping->a_ops->writepage(page, wbc);
1873  mapping_set_error(mapping, ret);
1874  return ret;
1875 }
1876 
1885 int generic_writepages(struct address_space *mapping,
1886  struct writeback_control *wbc)
1887 {
1888  struct blk_plug plug;
1889  int ret;
1890 
1891  /* deal with chardevs and other special file */
1892  if (!mapping->a_ops->writepage)
1893  return 0;
1894 
1895  blk_start_plug(&plug);
1896  ret = write_cache_pages(mapping, wbc, __writepage, mapping);
1897  blk_finish_plug(&plug);
1898  return ret;
1899 }
1900 
1902 
1903 int do_writepages(struct address_space *mapping, struct writeback_control *wbc)
1904 {
1905  int ret;
1906 
1907  if (wbc->nr_to_write <= 0)
1908  return 0;
1909  if (mapping->a_ops->writepages)
1910  ret = mapping->a_ops->writepages(mapping, wbc);
1911  else
1912  ret = generic_writepages(mapping, wbc);
1913  return ret;
1914 }
1915 
1925 int write_one_page(struct page *page, int wait)
1926 {
1927  struct address_space *mapping = page->mapping;
1928  int ret = 0;
1929  struct writeback_control wbc = {
1931  .nr_to_write = 1,
1932  };
1933 
1934  BUG_ON(!PageLocked(page));
1935 
1936  if (wait)
1937  wait_on_page_writeback(page);
1938 
1939  if (clear_page_dirty_for_io(page)) {
1940  page_cache_get(page);
1941  ret = mapping->a_ops->writepage(page, &wbc);
1942  if (ret == 0 && wait) {
1943  wait_on_page_writeback(page);
1944  if (PageError(page))
1945  ret = -EIO;
1946  }
1947  page_cache_release(page);
1948  } else {
1949  unlock_page(page);
1950  }
1951  return ret;
1952 }
1954 
1955 /*
1956  * For address_spaces which do not use buffers nor write back.
1957  */
1958 int __set_page_dirty_no_writeback(struct page *page)
1959 {
1960  if (!PageDirty(page))
1961  return !TestSetPageDirty(page);
1962  return 0;
1963 }
1964 
1965 /*
1966  * Helper function for set_page_dirty family.
1967  * NOTE: This relies on being atomic wrt interrupts.
1968  */
1969 void account_page_dirtied(struct page *page, struct address_space *mapping)
1970 {
1971  if (mapping_cap_account_dirty(mapping)) {
1972  __inc_zone_page_state(page, NR_FILE_DIRTY);
1973  __inc_zone_page_state(page, NR_DIRTIED);
1974  __inc_bdi_stat(mapping->backing_dev_info, BDI_RECLAIMABLE);
1975  __inc_bdi_stat(mapping->backing_dev_info, BDI_DIRTIED);
1976  task_io_account_write(PAGE_CACHE_SIZE);
1977  current->nr_dirtied++;
1978  this_cpu_inc(bdp_ratelimits);
1979  }
1980 }
1982 
1983 /*
1984  * Helper function for set_page_writeback family.
1985  * NOTE: Unlike account_page_dirtied this does not rely on being atomic
1986  * wrt interrupts.
1987  */
1988 void account_page_writeback(struct page *page)
1989 {
1991 }
1993 
1994 /*
1995  * For address_spaces which do not use buffers. Just tag the page as dirty in
1996  * its radix tree.
1997  *
1998  * This is also used when a single buffer is being dirtied: we want to set the
1999  * page dirty in that case, but not all the buffers. This is a "bottom-up"
2000  * dirtying, whereas __set_page_dirty_buffers() is a "top-down" dirtying.
2001  *
2002  * Most callers have locked the page, which pins the address_space in memory.
2003  * But zap_pte_range() does not lock the page, however in that case the
2004  * mapping is pinned by the vma's ->vm_file reference.
2005  *
2006  * We take care to handle the case where the page was truncated from the
2007  * mapping by re-checking page_mapping() inside tree_lock.
2008  */
2009 int __set_page_dirty_nobuffers(struct page *page)
2010 {
2011  if (!TestSetPageDirty(page)) {
2012  struct address_space *mapping = page_mapping(page);
2013  struct address_space *mapping2;
2014 
2015  if (!mapping)
2016  return 1;
2017 
2018  spin_lock_irq(&mapping->tree_lock);
2019  mapping2 = page_mapping(page);
2020  if (mapping2) { /* Race with truncate? */
2021  BUG_ON(mapping2 != mapping);
2022  WARN_ON_ONCE(!PagePrivate(page) && !PageUptodate(page));
2023  account_page_dirtied(page, mapping);
2024  radix_tree_tag_set(&mapping->page_tree,
2025  page_index(page), PAGECACHE_TAG_DIRTY);
2026  }
2027  spin_unlock_irq(&mapping->tree_lock);
2028  if (mapping->host) {
2029  /* !PageAnon && !swapper_space */
2031  }
2032  return 1;
2033  }
2034  return 0;
2035 }
2037 
2038 /*
2039  * Call this whenever redirtying a page, to de-account the dirty counters
2040  * (NR_DIRTIED, BDI_DIRTIED, tsk->nr_dirtied), so that they match the written
2041  * counters (NR_WRITTEN, BDI_WRITTEN) in long term. The mismatches will lead to
2042  * systematic errors in balanced_dirty_ratelimit and the dirty pages position
2043  * control.
2044  */
2045 void account_page_redirty(struct page *page)
2046 {
2047  struct address_space *mapping = page->mapping;
2048  if (mapping && mapping_cap_account_dirty(mapping)) {
2049  current->nr_dirtied--;
2051  dec_bdi_stat(mapping->backing_dev_info, BDI_DIRTIED);
2052  }
2053 }
2055 
2056 /*
2057  * When a writepage implementation decides that it doesn't want to write this
2058  * page for some reason, it should redirty the locked page via
2059  * redirty_page_for_writepage() and it should then unlock the page and return 0
2060  */
2061 int redirty_page_for_writepage(struct writeback_control *wbc, struct page *page)
2062 {
2063  wbc->pages_skipped++;
2064  account_page_redirty(page);
2065  return __set_page_dirty_nobuffers(page);
2066 }
2068 
2069 /*
2070  * Dirty a page.
2071  *
2072  * For pages with a mapping this should be done under the page lock
2073  * for the benefit of asynchronous memory errors who prefer a consistent
2074  * dirty state. This rule can be broken in some special cases,
2075  * but should be better not to.
2076  *
2077  * If the mapping doesn't provide a set_page_dirty a_op, then
2078  * just fall through and assume that it wants buffer_heads.
2079  */
2080 int set_page_dirty(struct page *page)
2081 {
2082  struct address_space *mapping = page_mapping(page);
2083 
2084  if (likely(mapping)) {
2085  int (*spd)(struct page *) = mapping->a_ops->set_page_dirty;
2086  /*
2087  * readahead/lru_deactivate_page could remain
2088  * PG_readahead/PG_reclaim due to race with end_page_writeback
2089  * About readahead, if the page is written, the flags would be
2090  * reset. So no problem.
2091  * About lru_deactivate_page, if the page is redirty, the flag
2092  * will be reset. So no problem. but if the page is used by readahead
2093  * it will confuse readahead and make it restart the size rampup
2094  * process. But it's a trivial problem.
2095  */
2096  ClearPageReclaim(page);
2097 #ifdef CONFIG_BLOCK
2098  if (!spd)
2100 #endif
2101  return (*spd)(page);
2102  }
2103  if (!PageDirty(page)) {
2104  if (!TestSetPageDirty(page))
2105  return 1;
2106  }
2107  return 0;
2108 }
2110 
2111 /*
2112  * set_page_dirty() is racy if the caller has no reference against
2113  * page->mapping->host, and if the page is unlocked. This is because another
2114  * CPU could truncate the page off the mapping and then free the mapping.
2115  *
2116  * Usually, the page _is_ locked, or the caller is a user-space process which
2117  * holds a reference on the inode by having an open file.
2118  *
2119  * In other cases, the page should be locked before running set_page_dirty().
2120  */
2121 int set_page_dirty_lock(struct page *page)
2122 {
2123  int ret;
2124 
2125  lock_page(page);
2126  ret = set_page_dirty(page);
2127  unlock_page(page);
2128  return ret;
2129 }
2131 
2132 /*
2133  * Clear a page's dirty flag, while caring for dirty memory accounting.
2134  * Returns true if the page was previously dirty.
2135  *
2136  * This is for preparing to put the page under writeout. We leave the page
2137  * tagged as dirty in the radix tree so that a concurrent write-for-sync
2138  * can discover it via a PAGECACHE_TAG_DIRTY walk. The ->writepage
2139  * implementation will run either set_page_writeback() or set_page_dirty(),
2140  * at which stage we bring the page's dirty flag and radix-tree dirty tag
2141  * back into sync.
2142  *
2143  * This incoherency between the page's dirty flag and radix-tree tag is
2144  * unfortunate, but it only exists while the page is locked.
2145  */
2146 int clear_page_dirty_for_io(struct page *page)
2147 {
2148  struct address_space *mapping = page_mapping(page);
2149 
2150  BUG_ON(!PageLocked(page));
2151 
2152  if (mapping && mapping_cap_account_dirty(mapping)) {
2153  /*
2154  * Yes, Virginia, this is indeed insane.
2155  *
2156  * We use this sequence to make sure that
2157  * (a) we account for dirty stats properly
2158  * (b) we tell the low-level filesystem to
2159  * mark the whole page dirty if it was
2160  * dirty in a pagetable. Only to then
2161  * (c) clean the page again and return 1 to
2162  * cause the writeback.
2163  *
2164  * This way we avoid all nasty races with the
2165  * dirty bit in multiple places and clearing
2166  * them concurrently from different threads.
2167  *
2168  * Note! Normally the "set_page_dirty(page)"
2169  * has no effect on the actual dirty bit - since
2170  * that will already usually be set. But we
2171  * need the side effects, and it can help us
2172  * avoid races.
2173  *
2174  * We basically use the page "master dirty bit"
2175  * as a serialization point for all the different
2176  * threads doing their things.
2177  */
2178  if (page_mkclean(page))
2179  set_page_dirty(page);
2180  /*
2181  * We carefully synchronise fault handlers against
2182  * installing a dirty pte and marking the page dirty
2183  * at this point. We do this by having them hold the
2184  * page lock at some point after installing their
2185  * pte, but before marking the page dirty.
2186  * Pages are always locked coming in here, so we get
2187  * the desired exclusion. See mm/memory.c:do_wp_page()
2188  * for more comments.
2189  */
2190  if (TestClearPageDirty(page)) {
2192  dec_bdi_stat(mapping->backing_dev_info,
2193  BDI_RECLAIMABLE);
2194  return 1;
2195  }
2196  return 0;
2197  }
2198  return TestClearPageDirty(page);
2199 }
2201 
2202 int test_clear_page_writeback(struct page *page)
2203 {
2204  struct address_space *mapping = page_mapping(page);
2205  int ret;
2206 
2207  if (mapping) {
2208  struct backing_dev_info *bdi = mapping->backing_dev_info;
2209  unsigned long flags;
2210 
2211  spin_lock_irqsave(&mapping->tree_lock, flags);
2212  ret = TestClearPageWriteback(page);
2213  if (ret) {
2214  radix_tree_tag_clear(&mapping->page_tree,
2215  page_index(page),
2217  if (bdi_cap_account_writeback(bdi)) {
2218  __dec_bdi_stat(bdi, BDI_WRITEBACK);
2219  __bdi_writeout_inc(bdi);
2220  }
2221  }
2222  spin_unlock_irqrestore(&mapping->tree_lock, flags);
2223  } else {
2224  ret = TestClearPageWriteback(page);
2225  }
2226  if (ret) {
2229  }
2230  return ret;
2231 }
2232 
2233 int test_set_page_writeback(struct page *page)
2234 {
2235  struct address_space *mapping = page_mapping(page);
2236  int ret;
2237 
2238  if (mapping) {
2239  struct backing_dev_info *bdi = mapping->backing_dev_info;
2240  unsigned long flags;
2241 
2242  spin_lock_irqsave(&mapping->tree_lock, flags);
2243  ret = TestSetPageWriteback(page);
2244  if (!ret) {
2245  radix_tree_tag_set(&mapping->page_tree,
2246  page_index(page),
2248  if (bdi_cap_account_writeback(bdi))
2249  __inc_bdi_stat(bdi, BDI_WRITEBACK);
2250  }
2251  if (!PageDirty(page))
2252  radix_tree_tag_clear(&mapping->page_tree,
2253  page_index(page),
2255  radix_tree_tag_clear(&mapping->page_tree,
2256  page_index(page),
2258  spin_unlock_irqrestore(&mapping->tree_lock, flags);
2259  } else {
2260  ret = TestSetPageWriteback(page);
2261  }
2262  if (!ret)
2263  account_page_writeback(page);
2264  return ret;
2265 
2266 }
2268 
2269 /*
2270  * Return true if any of the pages in the mapping are marked with the
2271  * passed tag.
2272  */
2273 int mapping_tagged(struct address_space *mapping, int tag)
2274 {
2275  return radix_tree_tagged(&mapping->page_tree, tag);
2276 }