writeback: Add a 'reason' to wb_writeback_work
[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/module.h>
16 #include <linux/spinlock.h>
17 #include <linux/fs.h>
18 #include <linux/mm.h>
19 #include <linux/swap.h>
20 #include <linux/slab.h>
21 #include <linux/pagemap.h>
22 #include <linux/writeback.h>
23 #include <linux/init.h>
24 #include <linux/backing-dev.h>
25 #include <linux/task_io_accounting_ops.h>
26 #include <linux/blkdev.h>
27 #include <linux/mpage.h>
28 #include <linux/rmap.h>
29 #include <linux/percpu.h>
30 #include <linux/notifier.h>
31 #include <linux/smp.h>
32 #include <linux/sysctl.h>
33 #include <linux/cpu.h>
34 #include <linux/syscalls.h>
35 #include <linux/buffer_head.h>
36 #include <linux/pagevec.h>
37 #include <trace/events/writeback.h>
38
39 /*
40  * Sleep at most 200ms at a time in balance_dirty_pages().
41  */
42 #define MAX_PAUSE               max(HZ/5, 1)
43
44 /*
45  * Estimate write bandwidth at 200ms intervals.
46  */
47 #define BANDWIDTH_INTERVAL      max(HZ/5, 1)
48
49 #define RATELIMIT_CALC_SHIFT    10
50
51 /*
52  * After a CPU has dirtied this many pages, balance_dirty_pages_ratelimited
53  * will look to see if it needs to force writeback or throttling.
54  */
55 static long ratelimit_pages = 32;
56
57 /* The following parameters are exported via /proc/sys/vm */
58
59 /*
60  * Start background writeback (via writeback threads) at this percentage
61  */
62 int dirty_background_ratio = 10;
63
64 /*
65  * dirty_background_bytes starts at 0 (disabled) so that it is a function of
66  * dirty_background_ratio * the amount of dirtyable memory
67  */
68 unsigned long dirty_background_bytes;
69
70 /*
71  * free highmem will not be subtracted from the total free memory
72  * for calculating free ratios if vm_highmem_is_dirtyable is true
73  */
74 int vm_highmem_is_dirtyable;
75
76 /*
77  * The generator of dirty data starts writeback at this percentage
78  */
79 int vm_dirty_ratio = 20;
80
81 /*
82  * vm_dirty_bytes starts at 0 (disabled) so that it is a function of
83  * vm_dirty_ratio * the amount of dirtyable memory
84  */
85 unsigned long vm_dirty_bytes;
86
87 /*
88  * The interval between `kupdate'-style writebacks
89  */
90 unsigned int dirty_writeback_interval = 5 * 100; /* centiseconds */
91
92 /*
93  * The longest time for which data is allowed to remain dirty
94  */
95 unsigned int dirty_expire_interval = 30 * 100; /* centiseconds */
96
97 /*
98  * Flag that makes the machine dump writes/reads and block dirtyings.
99  */
100 int block_dump;
101
102 /*
103  * Flag that puts the machine in "laptop mode". Doubles as a timeout in jiffies:
104  * a full sync is triggered after this time elapses without any disk activity.
105  */
106 int laptop_mode;
107
108 EXPORT_SYMBOL(laptop_mode);
109
110 /* End of sysctl-exported parameters */
111
112 unsigned long global_dirty_limit;
113
114 /*
115  * Scale the writeback cache size proportional to the relative writeout speeds.
116  *
117  * We do this by keeping a floating proportion between BDIs, based on page
118  * writeback completions [end_page_writeback()]. Those devices that write out
119  * pages fastest will get the larger share, while the slower will get a smaller
120  * share.
121  *
122  * We use page writeout completions because we are interested in getting rid of
123  * dirty pages. Having them written out is the primary goal.
124  *
125  * We introduce a concept of time, a period over which we measure these events,
126  * because demand can/will vary over time. The length of this period itself is
127  * measured in page writeback completions.
128  *
129  */
130 static struct prop_descriptor vm_completions;
131 static struct prop_descriptor vm_dirties;
132
133 /*
134  * couple the period to the dirty_ratio:
135  *
136  *   period/2 ~ roundup_pow_of_two(dirty limit)
137  */
138 static int calc_period_shift(void)
139 {
140         unsigned long dirty_total;
141
142         if (vm_dirty_bytes)
143                 dirty_total = vm_dirty_bytes / PAGE_SIZE;
144         else
145                 dirty_total = (vm_dirty_ratio * determine_dirtyable_memory()) /
146                                 100;
147         return 2 + ilog2(dirty_total - 1);
148 }
149
150 /*
151  * update the period when the dirty threshold changes.
152  */
153 static void update_completion_period(void)
154 {
155         int shift = calc_period_shift();
156         prop_change_shift(&vm_completions, shift);
157         prop_change_shift(&vm_dirties, shift);
158
159         writeback_set_ratelimit();
160 }
161
162 int dirty_background_ratio_handler(struct ctl_table *table, int write,
163                 void __user *buffer, size_t *lenp,
164                 loff_t *ppos)
165 {
166         int ret;
167
168         ret = proc_dointvec_minmax(table, write, buffer, lenp, ppos);
169         if (ret == 0 && write)
170                 dirty_background_bytes = 0;
171         return ret;
172 }
173
174 int dirty_background_bytes_handler(struct ctl_table *table, int write,
175                 void __user *buffer, size_t *lenp,
176                 loff_t *ppos)
177 {
178         int ret;
179
180         ret = proc_doulongvec_minmax(table, write, buffer, lenp, ppos);
181         if (ret == 0 && write)
182                 dirty_background_ratio = 0;
183         return ret;
184 }
185
186 int dirty_ratio_handler(struct ctl_table *table, int write,
187                 void __user *buffer, size_t *lenp,
188                 loff_t *ppos)
189 {
190         int old_ratio = vm_dirty_ratio;
191         int ret;
192
193         ret = proc_dointvec_minmax(table, write, buffer, lenp, ppos);
194         if (ret == 0 && write && vm_dirty_ratio != old_ratio) {
195                 update_completion_period();
196                 vm_dirty_bytes = 0;
197         }
198         return ret;
199 }
200
201
202 int dirty_bytes_handler(struct ctl_table *table, int write,
203                 void __user *buffer, size_t *lenp,
204                 loff_t *ppos)
205 {
206         unsigned long old_bytes = vm_dirty_bytes;
207         int ret;
208
209         ret = proc_doulongvec_minmax(table, write, buffer, lenp, ppos);
210         if (ret == 0 && write && vm_dirty_bytes != old_bytes) {
211                 update_completion_period();
212                 vm_dirty_ratio = 0;
213         }
214         return ret;
215 }
216
217 /*
218  * Increment the BDI's writeout completion count and the global writeout
219  * completion count. Called from test_clear_page_writeback().
220  */
221 static inline void __bdi_writeout_inc(struct backing_dev_info *bdi)
222 {
223         __inc_bdi_stat(bdi, BDI_WRITTEN);
224         __prop_inc_percpu_max(&vm_completions, &bdi->completions,
225                               bdi->max_prop_frac);
226 }
227
228 void bdi_writeout_inc(struct backing_dev_info *bdi)
229 {
230         unsigned long flags;
231
232         local_irq_save(flags);
233         __bdi_writeout_inc(bdi);
234         local_irq_restore(flags);
235 }
236 EXPORT_SYMBOL_GPL(bdi_writeout_inc);
237
238 void task_dirty_inc(struct task_struct *tsk)
239 {
240         prop_inc_single(&vm_dirties, &tsk->dirties);
241 }
242
243 /*
244  * Obtain an accurate fraction of the BDI's portion.
245  */
246 static void bdi_writeout_fraction(struct backing_dev_info *bdi,
247                 long *numerator, long *denominator)
248 {
249         prop_fraction_percpu(&vm_completions, &bdi->completions,
250                                 numerator, denominator);
251 }
252
253 /*
254  *
255  */
256 static unsigned int bdi_min_ratio;
257
258 int bdi_set_min_ratio(struct backing_dev_info *bdi, unsigned int min_ratio)
259 {
260         int ret = 0;
261
262         spin_lock_bh(&bdi_lock);
263         if (min_ratio > bdi->max_ratio) {
264                 ret = -EINVAL;
265         } else {
266                 min_ratio -= bdi->min_ratio;
267                 if (bdi_min_ratio + min_ratio < 100) {
268                         bdi_min_ratio += min_ratio;
269                         bdi->min_ratio += min_ratio;
270                 } else {
271                         ret = -EINVAL;
272                 }
273         }
274         spin_unlock_bh(&bdi_lock);
275
276         return ret;
277 }
278
279 int bdi_set_max_ratio(struct backing_dev_info *bdi, unsigned max_ratio)
280 {
281         int ret = 0;
282
283         if (max_ratio > 100)
284                 return -EINVAL;
285
286         spin_lock_bh(&bdi_lock);
287         if (bdi->min_ratio > max_ratio) {
288                 ret = -EINVAL;
289         } else {
290                 bdi->max_ratio = max_ratio;
291                 bdi->max_prop_frac = (PROP_FRAC_BASE * max_ratio) / 100;
292         }
293         spin_unlock_bh(&bdi_lock);
294
295         return ret;
296 }
297 EXPORT_SYMBOL(bdi_set_max_ratio);
298
299 /*
300  * Work out the current dirty-memory clamping and background writeout
301  * thresholds.
302  *
303  * The main aim here is to lower them aggressively if there is a lot of mapped
304  * memory around.  To avoid stressing page reclaim with lots of unreclaimable
305  * pages.  It is better to clamp down on writers than to start swapping, and
306  * performing lots of scanning.
307  *
308  * We only allow 1/2 of the currently-unmapped memory to be dirtied.
309  *
310  * We don't permit the clamping level to fall below 5% - that is getting rather
311  * excessive.
312  *
313  * We make sure that the background writeout level is below the adjusted
314  * clamping level.
315  */
316
317 static unsigned long highmem_dirtyable_memory(unsigned long total)
318 {
319 #ifdef CONFIG_HIGHMEM
320         int node;
321         unsigned long x = 0;
322
323         for_each_node_state(node, N_HIGH_MEMORY) {
324                 struct zone *z =
325                         &NODE_DATA(node)->node_zones[ZONE_HIGHMEM];
326
327                 x += zone_page_state(z, NR_FREE_PAGES) +
328                      zone_reclaimable_pages(z);
329         }
330         /*
331          * Make sure that the number of highmem pages is never larger
332          * than the number of the total dirtyable memory. This can only
333          * occur in very strange VM situations but we want to make sure
334          * that this does not occur.
335          */
336         return min(x, total);
337 #else
338         return 0;
339 #endif
340 }
341
342 /**
343  * determine_dirtyable_memory - amount of memory that may be used
344  *
345  * Returns the numebr of pages that can currently be freed and used
346  * by the kernel for direct mappings.
347  */
348 unsigned long determine_dirtyable_memory(void)
349 {
350         unsigned long x;
351
352         x = global_page_state(NR_FREE_PAGES) + global_reclaimable_pages();
353
354         if (!vm_highmem_is_dirtyable)
355                 x -= highmem_dirtyable_memory(x);
356
357         return x + 1;   /* Ensure that we never return 0 */
358 }
359
360 static unsigned long dirty_freerun_ceiling(unsigned long thresh,
361                                            unsigned long bg_thresh)
362 {
363         return (thresh + bg_thresh) / 2;
364 }
365
366 static unsigned long hard_dirty_limit(unsigned long thresh)
367 {
368         return max(thresh, global_dirty_limit);
369 }
370
371 /*
372  * global_dirty_limits - background-writeback and dirty-throttling thresholds
373  *
374  * Calculate the dirty thresholds based on sysctl parameters
375  * - vm.dirty_background_ratio  or  vm.dirty_background_bytes
376  * - vm.dirty_ratio             or  vm.dirty_bytes
377  * The dirty limits will be lifted by 1/4 for PF_LESS_THROTTLE (ie. nfsd) and
378  * real-time tasks.
379  */
380 void global_dirty_limits(unsigned long *pbackground, unsigned long *pdirty)
381 {
382         unsigned long background;
383         unsigned long dirty;
384         unsigned long uninitialized_var(available_memory);
385         struct task_struct *tsk;
386
387         if (!vm_dirty_bytes || !dirty_background_bytes)
388                 available_memory = determine_dirtyable_memory();
389
390         if (vm_dirty_bytes)
391                 dirty = DIV_ROUND_UP(vm_dirty_bytes, PAGE_SIZE);
392         else
393                 dirty = (vm_dirty_ratio * available_memory) / 100;
394
395         if (dirty_background_bytes)
396                 background = DIV_ROUND_UP(dirty_background_bytes, PAGE_SIZE);
397         else
398                 background = (dirty_background_ratio * available_memory) / 100;
399
400         if (background >= dirty)
401                 background = dirty / 2;
402         tsk = current;
403         if (tsk->flags & PF_LESS_THROTTLE || rt_task(tsk)) {
404                 background += background / 4;
405                 dirty += dirty / 4;
406         }
407         *pbackground = background;
408         *pdirty = dirty;
409         trace_global_dirty_state(background, dirty);
410 }
411
412 /**
413  * bdi_dirty_limit - @bdi's share of dirty throttling threshold
414  * @bdi: the backing_dev_info to query
415  * @dirty: global dirty limit in pages
416  *
417  * Returns @bdi's dirty limit in pages. The term "dirty" in the context of
418  * dirty balancing includes all PG_dirty, PG_writeback and NFS unstable pages.
419  * And the "limit" in the name is not seriously taken as hard limit in
420  * balance_dirty_pages().
421  *
422  * It allocates high/low dirty limits to fast/slow devices, in order to prevent
423  * - starving fast devices
424  * - piling up dirty pages (that will take long time to sync) on slow devices
425  *
426  * The bdi's share of dirty limit will be adapting to its throughput and
427  * bounded by the bdi->min_ratio and/or bdi->max_ratio parameters, if set.
428  */
429 unsigned long bdi_dirty_limit(struct backing_dev_info *bdi, unsigned long dirty)
430 {
431         u64 bdi_dirty;
432         long numerator, denominator;
433
434         /*
435          * Calculate this BDI's share of the dirty ratio.
436          */
437         bdi_writeout_fraction(bdi, &numerator, &denominator);
438
439         bdi_dirty = (dirty * (100 - bdi_min_ratio)) / 100;
440         bdi_dirty *= numerator;
441         do_div(bdi_dirty, denominator);
442
443         bdi_dirty += (dirty * bdi->min_ratio) / 100;
444         if (bdi_dirty > (dirty * bdi->max_ratio) / 100)
445                 bdi_dirty = dirty * bdi->max_ratio / 100;
446
447         return bdi_dirty;
448 }
449
450 /*
451  * Dirty position control.
452  *
453  * (o) global/bdi setpoints
454  *
455  * We want the dirty pages be balanced around the global/bdi setpoints.
456  * When the number of dirty pages is higher/lower than the setpoint, the
457  * dirty position control ratio (and hence task dirty ratelimit) will be
458  * decreased/increased to bring the dirty pages back to the setpoint.
459  *
460  *     pos_ratio = 1 << RATELIMIT_CALC_SHIFT
461  *
462  *     if (dirty < setpoint) scale up   pos_ratio
463  *     if (dirty > setpoint) scale down pos_ratio
464  *
465  *     if (bdi_dirty < bdi_setpoint) scale up   pos_ratio
466  *     if (bdi_dirty > bdi_setpoint) scale down pos_ratio
467  *
468  *     task_ratelimit = dirty_ratelimit * pos_ratio >> RATELIMIT_CALC_SHIFT
469  *
470  * (o) global control line
471  *
472  *     ^ pos_ratio
473  *     |
474  *     |            |<===== global dirty control scope ======>|
475  * 2.0 .............*
476  *     |            .*
477  *     |            . *
478  *     |            .   *
479  *     |            .     *
480  *     |            .        *
481  *     |            .            *
482  * 1.0 ................................*
483  *     |            .                  .     *
484  *     |            .                  .          *
485  *     |            .                  .              *
486  *     |            .                  .                 *
487  *     |            .                  .                    *
488  *   0 +------------.------------------.----------------------*------------->
489  *           freerun^          setpoint^                 limit^   dirty pages
490  *
491  * (o) bdi control line
492  *
493  *     ^ pos_ratio
494  *     |
495  *     |            *
496  *     |              *
497  *     |                *
498  *     |                  *
499  *     |                    * |<=========== span ============>|
500  * 1.0 .......................*
501  *     |                      . *
502  *     |                      .   *
503  *     |                      .     *
504  *     |                      .       *
505  *     |                      .         *
506  *     |                      .           *
507  *     |                      .             *
508  *     |                      .               *
509  *     |                      .                 *
510  *     |                      .                   *
511  *     |                      .                     *
512  * 1/4 ...............................................* * * * * * * * * * * *
513  *     |                      .                         .
514  *     |                      .                           .
515  *     |                      .                             .
516  *   0 +----------------------.-------------------------------.------------->
517  *                bdi_setpoint^                    x_intercept^
518  *
519  * The bdi control line won't drop below pos_ratio=1/4, so that bdi_dirty can
520  * be smoothly throttled down to normal if it starts high in situations like
521  * - start writing to a slow SD card and a fast disk at the same time. The SD
522  *   card's bdi_dirty may rush to many times higher than bdi_setpoint.
523  * - the bdi dirty thresh drops quickly due to change of JBOD workload
524  */
525 static unsigned long bdi_position_ratio(struct backing_dev_info *bdi,
526                                         unsigned long thresh,
527                                         unsigned long bg_thresh,
528                                         unsigned long dirty,
529                                         unsigned long bdi_thresh,
530                                         unsigned long bdi_dirty)
531 {
532         unsigned long write_bw = bdi->avg_write_bandwidth;
533         unsigned long freerun = dirty_freerun_ceiling(thresh, bg_thresh);
534         unsigned long limit = hard_dirty_limit(thresh);
535         unsigned long x_intercept;
536         unsigned long setpoint;         /* dirty pages' target balance point */
537         unsigned long bdi_setpoint;
538         unsigned long span;
539         long long pos_ratio;            /* for scaling up/down the rate limit */
540         long x;
541
542         if (unlikely(dirty >= limit))
543                 return 0;
544
545         /*
546          * global setpoint
547          *
548          *                           setpoint - dirty 3
549          *        f(dirty) := 1.0 + (----------------)
550          *                           limit - setpoint
551          *
552          * it's a 3rd order polynomial that subjects to
553          *
554          * (1) f(freerun)  = 2.0 => rampup dirty_ratelimit reasonably fast
555          * (2) f(setpoint) = 1.0 => the balance point
556          * (3) f(limit)    = 0   => the hard limit
557          * (4) df/dx      <= 0   => negative feedback control
558          * (5) the closer to setpoint, the smaller |df/dx| (and the reverse)
559          *     => fast response on large errors; small oscillation near setpoint
560          */
561         setpoint = (freerun + limit) / 2;
562         x = div_s64((setpoint - dirty) << RATELIMIT_CALC_SHIFT,
563                     limit - setpoint + 1);
564         pos_ratio = x;
565         pos_ratio = pos_ratio * x >> RATELIMIT_CALC_SHIFT;
566         pos_ratio = pos_ratio * x >> RATELIMIT_CALC_SHIFT;
567         pos_ratio += 1 << RATELIMIT_CALC_SHIFT;
568
569         /*
570          * We have computed basic pos_ratio above based on global situation. If
571          * the bdi is over/under its share of dirty pages, we want to scale
572          * pos_ratio further down/up. That is done by the following mechanism.
573          */
574
575         /*
576          * bdi setpoint
577          *
578          *        f(bdi_dirty) := 1.0 + k * (bdi_dirty - bdi_setpoint)
579          *
580          *                        x_intercept - bdi_dirty
581          *                     := --------------------------
582          *                        x_intercept - bdi_setpoint
583          *
584          * The main bdi control line is a linear function that subjects to
585          *
586          * (1) f(bdi_setpoint) = 1.0
587          * (2) k = - 1 / (8 * write_bw)  (in single bdi case)
588          *     or equally: x_intercept = bdi_setpoint + 8 * write_bw
589          *
590          * For single bdi case, the dirty pages are observed to fluctuate
591          * regularly within range
592          *        [bdi_setpoint - write_bw/2, bdi_setpoint + write_bw/2]
593          * for various filesystems, where (2) can yield in a reasonable 12.5%
594          * fluctuation range for pos_ratio.
595          *
596          * For JBOD case, bdi_thresh (not bdi_dirty!) could fluctuate up to its
597          * own size, so move the slope over accordingly and choose a slope that
598          * yields 100% pos_ratio fluctuation on suddenly doubled bdi_thresh.
599          */
600         if (unlikely(bdi_thresh > thresh))
601                 bdi_thresh = thresh;
602         bdi_thresh = max(bdi_thresh, (limit - dirty) / 8);
603         /*
604          * scale global setpoint to bdi's:
605          *      bdi_setpoint = setpoint * bdi_thresh / thresh
606          */
607         x = div_u64((u64)bdi_thresh << 16, thresh + 1);
608         bdi_setpoint = setpoint * (u64)x >> 16;
609         /*
610          * Use span=(8*write_bw) in single bdi case as indicated by
611          * (thresh - bdi_thresh ~= 0) and transit to bdi_thresh in JBOD case.
612          *
613          *        bdi_thresh                    thresh - bdi_thresh
614          * span = ---------- * (8 * write_bw) + ------------------- * bdi_thresh
615          *          thresh                            thresh
616          */
617         span = (thresh - bdi_thresh + 8 * write_bw) * (u64)x >> 16;
618         x_intercept = bdi_setpoint + span;
619
620         if (bdi_dirty < x_intercept - span / 4) {
621                 pos_ratio = div_u64(pos_ratio * (x_intercept - bdi_dirty),
622                                     x_intercept - bdi_setpoint + 1);
623         } else
624                 pos_ratio /= 4;
625
626         /*
627          * bdi reserve area, safeguard against dirty pool underrun and disk idle
628          * It may push the desired control point of global dirty pages higher
629          * than setpoint.
630          */
631         x_intercept = bdi_thresh / 2;
632         if (bdi_dirty < x_intercept) {
633                 if (bdi_dirty > x_intercept / 8)
634                         pos_ratio = div_u64(pos_ratio * x_intercept, bdi_dirty);
635                 else
636                         pos_ratio *= 8;
637         }
638
639         return pos_ratio;
640 }
641
642 static void bdi_update_write_bandwidth(struct backing_dev_info *bdi,
643                                        unsigned long elapsed,
644                                        unsigned long written)
645 {
646         const unsigned long period = roundup_pow_of_two(3 * HZ);
647         unsigned long avg = bdi->avg_write_bandwidth;
648         unsigned long old = bdi->write_bandwidth;
649         u64 bw;
650
651         /*
652          * bw = written * HZ / elapsed
653          *
654          *                   bw * elapsed + write_bandwidth * (period - elapsed)
655          * write_bandwidth = ---------------------------------------------------
656          *                                          period
657          */
658         bw = written - bdi->written_stamp;
659         bw *= HZ;
660         if (unlikely(elapsed > period)) {
661                 do_div(bw, elapsed);
662                 avg = bw;
663                 goto out;
664         }
665         bw += (u64)bdi->write_bandwidth * (period - elapsed);
666         bw >>= ilog2(period);
667
668         /*
669          * one more level of smoothing, for filtering out sudden spikes
670          */
671         if (avg > old && old >= (unsigned long)bw)
672                 avg -= (avg - old) >> 3;
673
674         if (avg < old && old <= (unsigned long)bw)
675                 avg += (old - avg) >> 3;
676
677 out:
678         bdi->write_bandwidth = bw;
679         bdi->avg_write_bandwidth = avg;
680 }
681
682 /*
683  * The global dirtyable memory and dirty threshold could be suddenly knocked
684  * down by a large amount (eg. on the startup of KVM in a swapless system).
685  * This may throw the system into deep dirty exceeded state and throttle
686  * heavy/light dirtiers alike. To retain good responsiveness, maintain
687  * global_dirty_limit for tracking slowly down to the knocked down dirty
688  * threshold.
689  */
690 static void update_dirty_limit(unsigned long thresh, unsigned long dirty)
691 {
692         unsigned long limit = global_dirty_limit;
693
694         /*
695          * Follow up in one step.
696          */
697         if (limit < thresh) {
698                 limit = thresh;
699                 goto update;
700         }
701
702         /*
703          * Follow down slowly. Use the higher one as the target, because thresh
704          * may drop below dirty. This is exactly the reason to introduce
705          * global_dirty_limit which is guaranteed to lie above the dirty pages.
706          */
707         thresh = max(thresh, dirty);
708         if (limit > thresh) {
709                 limit -= (limit - thresh) >> 5;
710                 goto update;
711         }
712         return;
713 update:
714         global_dirty_limit = limit;
715 }
716
717 static void global_update_bandwidth(unsigned long thresh,
718                                     unsigned long dirty,
719                                     unsigned long now)
720 {
721         static DEFINE_SPINLOCK(dirty_lock);
722         static unsigned long update_time;
723
724         /*
725          * check locklessly first to optimize away locking for the most time
726          */
727         if (time_before(now, update_time + BANDWIDTH_INTERVAL))
728                 return;
729
730         spin_lock(&dirty_lock);
731         if (time_after_eq(now, update_time + BANDWIDTH_INTERVAL)) {
732                 update_dirty_limit(thresh, dirty);
733                 update_time = now;
734         }
735         spin_unlock(&dirty_lock);
736 }
737
738 /*
739  * Maintain bdi->dirty_ratelimit, the base dirty throttle rate.
740  *
741  * Normal bdi tasks will be curbed at or below it in long term.
742  * Obviously it should be around (write_bw / N) when there are N dd tasks.
743  */
744 static void bdi_update_dirty_ratelimit(struct backing_dev_info *bdi,
745                                        unsigned long thresh,
746                                        unsigned long bg_thresh,
747                                        unsigned long dirty,
748                                        unsigned long bdi_thresh,
749                                        unsigned long bdi_dirty,
750                                        unsigned long dirtied,
751                                        unsigned long elapsed)
752 {
753         unsigned long freerun = dirty_freerun_ceiling(thresh, bg_thresh);
754         unsigned long limit = hard_dirty_limit(thresh);
755         unsigned long setpoint = (freerun + limit) / 2;
756         unsigned long write_bw = bdi->avg_write_bandwidth;
757         unsigned long dirty_ratelimit = bdi->dirty_ratelimit;
758         unsigned long dirty_rate;
759         unsigned long task_ratelimit;
760         unsigned long balanced_dirty_ratelimit;
761         unsigned long pos_ratio;
762         unsigned long step;
763         unsigned long x;
764
765         /*
766          * The dirty rate will match the writeout rate in long term, except
767          * when dirty pages are truncated by userspace or re-dirtied by FS.
768          */
769         dirty_rate = (dirtied - bdi->dirtied_stamp) * HZ / elapsed;
770
771         pos_ratio = bdi_position_ratio(bdi, thresh, bg_thresh, dirty,
772                                        bdi_thresh, bdi_dirty);
773         /*
774          * task_ratelimit reflects each dd's dirty rate for the past 200ms.
775          */
776         task_ratelimit = (u64)dirty_ratelimit *
777                                         pos_ratio >> RATELIMIT_CALC_SHIFT;
778         task_ratelimit++; /* it helps rampup dirty_ratelimit from tiny values */
779
780         /*
781          * A linear estimation of the "balanced" throttle rate. The theory is,
782          * if there are N dd tasks, each throttled at task_ratelimit, the bdi's
783          * dirty_rate will be measured to be (N * task_ratelimit). So the below
784          * formula will yield the balanced rate limit (write_bw / N).
785          *
786          * Note that the expanded form is not a pure rate feedback:
787          *      rate_(i+1) = rate_(i) * (write_bw / dirty_rate)              (1)
788          * but also takes pos_ratio into account:
789          *      rate_(i+1) = rate_(i) * (write_bw / dirty_rate) * pos_ratio  (2)
790          *
791          * (1) is not realistic because pos_ratio also takes part in balancing
792          * the dirty rate.  Consider the state
793          *      pos_ratio = 0.5                                              (3)
794          *      rate = 2 * (write_bw / N)                                    (4)
795          * If (1) is used, it will stuck in that state! Because each dd will
796          * be throttled at
797          *      task_ratelimit = pos_ratio * rate = (write_bw / N)           (5)
798          * yielding
799          *      dirty_rate = N * task_ratelimit = write_bw                   (6)
800          * put (6) into (1) we get
801          *      rate_(i+1) = rate_(i)                                        (7)
802          *
803          * So we end up using (2) to always keep
804          *      rate_(i+1) ~= (write_bw / N)                                 (8)
805          * regardless of the value of pos_ratio. As long as (8) is satisfied,
806          * pos_ratio is able to drive itself to 1.0, which is not only where
807          * the dirty count meet the setpoint, but also where the slope of
808          * pos_ratio is most flat and hence task_ratelimit is least fluctuated.
809          */
810         balanced_dirty_ratelimit = div_u64((u64)task_ratelimit * write_bw,
811                                            dirty_rate | 1);
812
813         /*
814          * We could safely do this and return immediately:
815          *
816          *      bdi->dirty_ratelimit = balanced_dirty_ratelimit;
817          *
818          * However to get a more stable dirty_ratelimit, the below elaborated
819          * code makes use of task_ratelimit to filter out sigular points and
820          * limit the step size.
821          *
822          * The below code essentially only uses the relative value of
823          *
824          *      task_ratelimit - dirty_ratelimit
825          *      = (pos_ratio - 1) * dirty_ratelimit
826          *
827          * which reflects the direction and size of dirty position error.
828          */
829
830         /*
831          * dirty_ratelimit will follow balanced_dirty_ratelimit iff
832          * task_ratelimit is on the same side of dirty_ratelimit, too.
833          * For example, when
834          * - dirty_ratelimit > balanced_dirty_ratelimit
835          * - dirty_ratelimit > task_ratelimit (dirty pages are above setpoint)
836          * lowering dirty_ratelimit will help meet both the position and rate
837          * control targets. Otherwise, don't update dirty_ratelimit if it will
838          * only help meet the rate target. After all, what the users ultimately
839          * feel and care are stable dirty rate and small position error.
840          *
841          * |task_ratelimit - dirty_ratelimit| is used to limit the step size
842          * and filter out the sigular points of balanced_dirty_ratelimit. Which
843          * keeps jumping around randomly and can even leap far away at times
844          * due to the small 200ms estimation period of dirty_rate (we want to
845          * keep that period small to reduce time lags).
846          */
847         step = 0;
848         if (dirty < setpoint) {
849                 x = min(bdi->balanced_dirty_ratelimit,
850                          min(balanced_dirty_ratelimit, task_ratelimit));
851                 if (dirty_ratelimit < x)
852                         step = x - dirty_ratelimit;
853         } else {
854                 x = max(bdi->balanced_dirty_ratelimit,
855                          max(balanced_dirty_ratelimit, task_ratelimit));
856                 if (dirty_ratelimit > x)
857                         step = dirty_ratelimit - x;
858         }
859
860         /*
861          * Don't pursue 100% rate matching. It's impossible since the balanced
862          * rate itself is constantly fluctuating. So decrease the track speed
863          * when it gets close to the target. Helps eliminate pointless tremors.
864          */
865         step >>= dirty_ratelimit / (2 * step + 1);
866         /*
867          * Limit the tracking speed to avoid overshooting.
868          */
869         step = (step + 7) / 8;
870
871         if (dirty_ratelimit < balanced_dirty_ratelimit)
872                 dirty_ratelimit += step;
873         else
874                 dirty_ratelimit -= step;
875
876         bdi->dirty_ratelimit = max(dirty_ratelimit, 1UL);
877         bdi->balanced_dirty_ratelimit = balanced_dirty_ratelimit;
878
879         trace_bdi_dirty_ratelimit(bdi, dirty_rate, task_ratelimit);
880 }
881
882 void __bdi_update_bandwidth(struct backing_dev_info *bdi,
883                             unsigned long thresh,
884                             unsigned long bg_thresh,
885                             unsigned long dirty,
886                             unsigned long bdi_thresh,
887                             unsigned long bdi_dirty,
888                             unsigned long start_time)
889 {
890         unsigned long now = jiffies;
891         unsigned long elapsed = now - bdi->bw_time_stamp;
892         unsigned long dirtied;
893         unsigned long written;
894
895         /*
896          * rate-limit, only update once every 200ms.
897          */
898         if (elapsed < BANDWIDTH_INTERVAL)
899                 return;
900
901         dirtied = percpu_counter_read(&bdi->bdi_stat[BDI_DIRTIED]);
902         written = percpu_counter_read(&bdi->bdi_stat[BDI_WRITTEN]);
903
904         /*
905          * Skip quiet periods when disk bandwidth is under-utilized.
906          * (at least 1s idle time between two flusher runs)
907          */
908         if (elapsed > HZ && time_before(bdi->bw_time_stamp, start_time))
909                 goto snapshot;
910
911         if (thresh) {
912                 global_update_bandwidth(thresh, dirty, now);
913                 bdi_update_dirty_ratelimit(bdi, thresh, bg_thresh, dirty,
914                                            bdi_thresh, bdi_dirty,
915                                            dirtied, elapsed);
916         }
917         bdi_update_write_bandwidth(bdi, elapsed, written);
918
919 snapshot:
920         bdi->dirtied_stamp = dirtied;
921         bdi->written_stamp = written;
922         bdi->bw_time_stamp = now;
923 }
924
925 static void bdi_update_bandwidth(struct backing_dev_info *bdi,
926                                  unsigned long thresh,
927                                  unsigned long bg_thresh,
928                                  unsigned long dirty,
929                                  unsigned long bdi_thresh,
930                                  unsigned long bdi_dirty,
931                                  unsigned long start_time)
932 {
933         if (time_is_after_eq_jiffies(bdi->bw_time_stamp + BANDWIDTH_INTERVAL))
934                 return;
935         spin_lock(&bdi->wb.list_lock);
936         __bdi_update_bandwidth(bdi, thresh, bg_thresh, dirty,
937                                bdi_thresh, bdi_dirty, start_time);
938         spin_unlock(&bdi->wb.list_lock);
939 }
940
941 /*
942  * After a task dirtied this many pages, balance_dirty_pages_ratelimited_nr()
943  * will look to see if it needs to start dirty throttling.
944  *
945  * If dirty_poll_interval is too low, big NUMA machines will call the expensive
946  * global_page_state() too often. So scale it near-sqrt to the safety margin
947  * (the number of pages we may dirty without exceeding the dirty limits).
948  */
949 static unsigned long dirty_poll_interval(unsigned long dirty,
950                                          unsigned long thresh)
951 {
952         if (thresh > dirty)
953                 return 1UL << (ilog2(thresh - dirty) >> 1);
954
955         return 1;
956 }
957
958 static unsigned long bdi_max_pause(struct backing_dev_info *bdi,
959                                    unsigned long bdi_dirty)
960 {
961         unsigned long bw = bdi->avg_write_bandwidth;
962         unsigned long hi = ilog2(bw);
963         unsigned long lo = ilog2(bdi->dirty_ratelimit);
964         unsigned long t;
965
966         /* target for 20ms max pause on 1-dd case */
967         t = HZ / 50;
968
969         /*
970          * Scale up pause time for concurrent dirtiers in order to reduce CPU
971          * overheads.
972          *
973          * (N * 20ms) on 2^N concurrent tasks.
974          */
975         if (hi > lo)
976                 t += (hi - lo) * (20 * HZ) / 1024;
977
978         /*
979          * Limit pause time for small memory systems. If sleeping for too long
980          * time, a small pool of dirty/writeback pages may go empty and disk go
981          * idle.
982          *
983          * 8 serves as the safety ratio.
984          */
985         if (bdi_dirty)
986                 t = min(t, bdi_dirty * HZ / (8 * bw + 1));
987
988         /*
989          * The pause time will be settled within range (max_pause/4, max_pause).
990          * Apply a minimal value of 4 to get a non-zero max_pause/4.
991          */
992         return clamp_val(t, 4, MAX_PAUSE);
993 }
994
995 /*
996  * balance_dirty_pages() must be called by processes which are generating dirty
997  * data.  It looks at the number of dirty pages in the machine and will force
998  * the caller to wait once crossing the (background_thresh + dirty_thresh) / 2.
999  * If we're over `background_thresh' then the writeback threads are woken to
1000  * perform some writeout.
1001  */
1002 static void balance_dirty_pages(struct address_space *mapping,
1003                                 unsigned long pages_dirtied)
1004 {
1005         unsigned long nr_reclaimable;   /* = file_dirty + unstable_nfs */
1006         unsigned long bdi_reclaimable;
1007         unsigned long nr_dirty;  /* = file_dirty + writeback + unstable_nfs */
1008         unsigned long bdi_dirty;
1009         unsigned long freerun;
1010         unsigned long background_thresh;
1011         unsigned long dirty_thresh;
1012         unsigned long bdi_thresh;
1013         long pause = 0;
1014         long uninitialized_var(max_pause);
1015         bool dirty_exceeded = false;
1016         unsigned long task_ratelimit;
1017         unsigned long uninitialized_var(dirty_ratelimit);
1018         unsigned long pos_ratio;
1019         struct backing_dev_info *bdi = mapping->backing_dev_info;
1020         unsigned long start_time = jiffies;
1021
1022         for (;;) {
1023                 /*
1024                  * Unstable writes are a feature of certain networked
1025                  * filesystems (i.e. NFS) in which data may have been
1026                  * written to the server's write cache, but has not yet
1027                  * been flushed to permanent storage.
1028                  */
1029                 nr_reclaimable = global_page_state(NR_FILE_DIRTY) +
1030                                         global_page_state(NR_UNSTABLE_NFS);
1031                 nr_dirty = nr_reclaimable + global_page_state(NR_WRITEBACK);
1032
1033                 global_dirty_limits(&background_thresh, &dirty_thresh);
1034
1035                 /*
1036                  * Throttle it only when the background writeback cannot
1037                  * catch-up. This avoids (excessively) small writeouts
1038                  * when the bdi limits are ramping up.
1039                  */
1040                 freerun = dirty_freerun_ceiling(dirty_thresh,
1041                                                 background_thresh);
1042                 if (nr_dirty <= freerun)
1043                         break;
1044
1045                 if (unlikely(!writeback_in_progress(bdi)))
1046                         bdi_start_background_writeback(bdi);
1047
1048                 /*
1049                  * bdi_thresh is not treated as some limiting factor as
1050                  * dirty_thresh, due to reasons
1051                  * - in JBOD setup, bdi_thresh can fluctuate a lot
1052                  * - in a system with HDD and USB key, the USB key may somehow
1053                  *   go into state (bdi_dirty >> bdi_thresh) either because
1054                  *   bdi_dirty starts high, or because bdi_thresh drops low.
1055                  *   In this case we don't want to hard throttle the USB key
1056                  *   dirtiers for 100 seconds until bdi_dirty drops under
1057                  *   bdi_thresh. Instead the auxiliary bdi control line in
1058                  *   bdi_position_ratio() will let the dirtier task progress
1059                  *   at some rate <= (write_bw / 2) for bringing down bdi_dirty.
1060                  */
1061                 bdi_thresh = bdi_dirty_limit(bdi, dirty_thresh);
1062
1063                 /*
1064                  * In order to avoid the stacked BDI deadlock we need
1065                  * to ensure we accurately count the 'dirty' pages when
1066                  * the threshold is low.
1067                  *
1068                  * Otherwise it would be possible to get thresh+n pages
1069                  * reported dirty, even though there are thresh-m pages
1070                  * actually dirty; with m+n sitting in the percpu
1071                  * deltas.
1072                  */
1073                 if (bdi_thresh < 2 * bdi_stat_error(bdi)) {
1074                         bdi_reclaimable = bdi_stat_sum(bdi, BDI_RECLAIMABLE);
1075                         bdi_dirty = bdi_reclaimable +
1076                                     bdi_stat_sum(bdi, BDI_WRITEBACK);
1077                 } else {
1078                         bdi_reclaimable = bdi_stat(bdi, BDI_RECLAIMABLE);
1079                         bdi_dirty = bdi_reclaimable +
1080                                     bdi_stat(bdi, BDI_WRITEBACK);
1081                 }
1082
1083                 dirty_exceeded = (bdi_dirty > bdi_thresh) ||
1084                                   (nr_dirty > dirty_thresh);
1085                 if (dirty_exceeded && !bdi->dirty_exceeded)
1086                         bdi->dirty_exceeded = 1;
1087
1088                 bdi_update_bandwidth(bdi, dirty_thresh, background_thresh,
1089                                      nr_dirty, bdi_thresh, bdi_dirty,
1090                                      start_time);
1091
1092                 max_pause = bdi_max_pause(bdi, bdi_dirty);
1093
1094                 dirty_ratelimit = bdi->dirty_ratelimit;
1095                 pos_ratio = bdi_position_ratio(bdi, dirty_thresh,
1096                                                background_thresh, nr_dirty,
1097                                                bdi_thresh, bdi_dirty);
1098                 if (unlikely(pos_ratio == 0)) {
1099                         pause = max_pause;
1100                         goto pause;
1101                 }
1102                 task_ratelimit = (u64)dirty_ratelimit *
1103                                         pos_ratio >> RATELIMIT_CALC_SHIFT;
1104                 pause = (HZ * pages_dirtied) / (task_ratelimit | 1);
1105                 if (unlikely(pause <= 0)) {
1106                         trace_balance_dirty_pages(bdi,
1107                                                   dirty_thresh,
1108                                                   background_thresh,
1109                                                   nr_dirty,
1110                                                   bdi_thresh,
1111                                                   bdi_dirty,
1112                                                   dirty_ratelimit,
1113                                                   task_ratelimit,
1114                                                   pages_dirtied,
1115                                                   pause,
1116                                                   start_time);
1117                         pause = 1; /* avoid resetting nr_dirtied_pause below */
1118                         break;
1119                 }
1120                 pause = min(pause, max_pause);
1121
1122 pause:
1123                 trace_balance_dirty_pages(bdi,
1124                                           dirty_thresh,
1125                                           background_thresh,
1126                                           nr_dirty,
1127                                           bdi_thresh,
1128                                           bdi_dirty,
1129                                           dirty_ratelimit,
1130                                           task_ratelimit,
1131                                           pages_dirtied,
1132                                           pause,
1133                                           start_time);
1134                 __set_current_state(TASK_UNINTERRUPTIBLE);
1135                 io_schedule_timeout(pause);
1136
1137                 dirty_thresh = hard_dirty_limit(dirty_thresh);
1138                 /*
1139                  * max-pause area. If dirty exceeded but still within this
1140                  * area, no need to sleep for more than 200ms: (a) 8 pages per
1141                  * 200ms is typically more than enough to curb heavy dirtiers;
1142                  * (b) the pause time limit makes the dirtiers more responsive.
1143                  */
1144                 if (nr_dirty < dirty_thresh)
1145                         break;
1146         }
1147
1148         if (!dirty_exceeded && bdi->dirty_exceeded)
1149                 bdi->dirty_exceeded = 0;
1150
1151         current->nr_dirtied = 0;
1152         if (pause == 0) { /* in freerun area */
1153                 current->nr_dirtied_pause =
1154                                 dirty_poll_interval(nr_dirty, dirty_thresh);
1155         } else if (pause <= max_pause / 4 &&
1156                    pages_dirtied >= current->nr_dirtied_pause) {
1157                 current->nr_dirtied_pause = clamp_val(
1158                                         dirty_ratelimit * (max_pause / 2) / HZ,
1159                                         pages_dirtied + pages_dirtied / 8,
1160                                         pages_dirtied * 4);
1161         } else if (pause >= max_pause) {
1162                 current->nr_dirtied_pause = 1 | clamp_val(
1163                                         dirty_ratelimit * (max_pause / 2) / HZ,
1164                                         pages_dirtied / 4,
1165                                         pages_dirtied - pages_dirtied / 8);
1166         }
1167
1168         if (writeback_in_progress(bdi))
1169                 return;
1170
1171         /*
1172          * In laptop mode, we wait until hitting the higher threshold before
1173          * starting background writeout, and then write out all the way down
1174          * to the lower threshold.  So slow writers cause minimal disk activity.
1175          *
1176          * In normal mode, we start background writeout at the lower
1177          * background_thresh, to keep the amount of dirty memory low.
1178          */
1179         if (laptop_mode)
1180                 return;
1181
1182         if (nr_reclaimable > background_thresh)
1183                 bdi_start_background_writeback(bdi);
1184 }
1185
1186 void set_page_dirty_balance(struct page *page, int page_mkwrite)
1187 {
1188         if (set_page_dirty(page) || page_mkwrite) {
1189                 struct address_space *mapping = page_mapping(page);
1190
1191                 if (mapping)
1192                         balance_dirty_pages_ratelimited(mapping);
1193         }
1194 }
1195
1196 static DEFINE_PER_CPU(int, bdp_ratelimits);
1197
1198 /**
1199  * balance_dirty_pages_ratelimited_nr - balance dirty memory state
1200  * @mapping: address_space which was dirtied
1201  * @nr_pages_dirtied: number of pages which the caller has just dirtied
1202  *
1203  * Processes which are dirtying memory should call in here once for each page
1204  * which was newly dirtied.  The function will periodically check the system's
1205  * dirty state and will initiate writeback if needed.
1206  *
1207  * On really big machines, get_writeback_state is expensive, so try to avoid
1208  * calling it too often (ratelimiting).  But once we're over the dirty memory
1209  * limit we decrease the ratelimiting by a lot, to prevent individual processes
1210  * from overshooting the limit by (ratelimit_pages) each.
1211  */
1212 void balance_dirty_pages_ratelimited_nr(struct address_space *mapping,
1213                                         unsigned long nr_pages_dirtied)
1214 {
1215         struct backing_dev_info *bdi = mapping->backing_dev_info;
1216         int ratelimit;
1217         int *p;
1218
1219         if (!bdi_cap_account_dirty(bdi))
1220                 return;
1221
1222         ratelimit = current->nr_dirtied_pause;
1223         if (bdi->dirty_exceeded)
1224                 ratelimit = min(ratelimit, 32 >> (PAGE_SHIFT - 10));
1225
1226         current->nr_dirtied += nr_pages_dirtied;
1227
1228         preempt_disable();
1229         /*
1230          * This prevents one CPU to accumulate too many dirtied pages without
1231          * calling into balance_dirty_pages(), which can happen when there are
1232          * 1000+ tasks, all of them start dirtying pages at exactly the same
1233          * time, hence all honoured too large initial task->nr_dirtied_pause.
1234          */
1235         p =  &__get_cpu_var(bdp_ratelimits);
1236         if (unlikely(current->nr_dirtied >= ratelimit))
1237                 *p = 0;
1238         else {
1239                 *p += nr_pages_dirtied;
1240                 if (unlikely(*p >= ratelimit_pages)) {
1241                         *p = 0;
1242                         ratelimit = 0;
1243                 }
1244         }
1245         preempt_enable();
1246
1247         if (unlikely(current->nr_dirtied >= ratelimit))
1248                 balance_dirty_pages(mapping, current->nr_dirtied);
1249 }
1250 EXPORT_SYMBOL(balance_dirty_pages_ratelimited_nr);
1251
1252 void throttle_vm_writeout(gfp_t gfp_mask)
1253 {
1254         unsigned long background_thresh;
1255         unsigned long dirty_thresh;
1256
1257         for ( ; ; ) {
1258                 global_dirty_limits(&background_thresh, &dirty_thresh);
1259
1260                 /*
1261                  * Boost the allowable dirty threshold a bit for page
1262                  * allocators so they don't get DoS'ed by heavy writers
1263                  */
1264                 dirty_thresh += dirty_thresh / 10;      /* wheeee... */
1265
1266                 if (global_page_state(NR_UNSTABLE_NFS) +
1267                         global_page_state(NR_WRITEBACK) <= dirty_thresh)
1268                                 break;
1269                 congestion_wait(BLK_RW_ASYNC, HZ/10);
1270
1271                 /*
1272                  * The caller might hold locks which can prevent IO completion
1273                  * or progress in the filesystem.  So we cannot just sit here
1274                  * waiting for IO to complete.
1275                  */
1276                 if ((gfp_mask & (__GFP_FS|__GFP_IO)) != (__GFP_FS|__GFP_IO))
1277                         break;
1278         }
1279 }
1280
1281 /*
1282  * sysctl handler for /proc/sys/vm/dirty_writeback_centisecs
1283  */
1284 int dirty_writeback_centisecs_handler(ctl_table *table, int write,
1285         void __user *buffer, size_t *length, loff_t *ppos)
1286 {
1287         proc_dointvec(table, write, buffer, length, ppos);
1288         bdi_arm_supers_timer();
1289         return 0;
1290 }
1291
1292 #ifdef CONFIG_BLOCK
1293 void laptop_mode_timer_fn(unsigned long data)
1294 {
1295         struct request_queue *q = (struct request_queue *)data;
1296         int nr_pages = global_page_state(NR_FILE_DIRTY) +
1297                 global_page_state(NR_UNSTABLE_NFS);
1298
1299         /*
1300          * We want to write everything out, not just down to the dirty
1301          * threshold
1302          */
1303         if (bdi_has_dirty_io(&q->backing_dev_info))
1304                 bdi_start_writeback(&q->backing_dev_info, nr_pages,
1305                                         WB_REASON_LAPTOP_TIMER);
1306 }
1307
1308 /*
1309  * We've spun up the disk and we're in laptop mode: schedule writeback
1310  * of all dirty data a few seconds from now.  If the flush is already scheduled
1311  * then push it back - the user is still using the disk.
1312  */
1313 void laptop_io_completion(struct backing_dev_info *info)
1314 {
1315         mod_timer(&info->laptop_mode_wb_timer, jiffies + laptop_mode);
1316 }
1317
1318 /*
1319  * We're in laptop mode and we've just synced. The sync's writes will have
1320  * caused another writeback to be scheduled by laptop_io_completion.
1321  * Nothing needs to be written back anymore, so we unschedule the writeback.
1322  */
1323 void laptop_sync_completion(void)
1324 {
1325         struct backing_dev_info *bdi;
1326
1327         rcu_read_lock();
1328
1329         list_for_each_entry_rcu(bdi, &bdi_list, bdi_list)
1330                 del_timer(&bdi->laptop_mode_wb_timer);
1331
1332         rcu_read_unlock();
1333 }
1334 #endif
1335
1336 /*
1337  * If ratelimit_pages is too high then we can get into dirty-data overload
1338  * if a large number of processes all perform writes at the same time.
1339  * If it is too low then SMP machines will call the (expensive)
1340  * get_writeback_state too often.
1341  *
1342  * Here we set ratelimit_pages to a level which ensures that when all CPUs are
1343  * dirtying in parallel, we cannot go more than 3% (1/32) over the dirty memory
1344  * thresholds.
1345  */
1346
1347 void writeback_set_ratelimit(void)
1348 {
1349         unsigned long background_thresh;
1350         unsigned long dirty_thresh;
1351         global_dirty_limits(&background_thresh, &dirty_thresh);
1352         ratelimit_pages = dirty_thresh / (num_online_cpus() * 32);
1353         if (ratelimit_pages < 16)
1354                 ratelimit_pages = 16;
1355 }
1356
1357 static int __cpuinit
1358 ratelimit_handler(struct notifier_block *self, unsigned long u, void *v)
1359 {
1360         writeback_set_ratelimit();
1361         return NOTIFY_DONE;
1362 }
1363
1364 static struct notifier_block __cpuinitdata ratelimit_nb = {
1365         .notifier_call  = ratelimit_handler,
1366         .next           = NULL,
1367 };
1368
1369 /*
1370  * Called early on to tune the page writeback dirty limits.
1371  *
1372  * We used to scale dirty pages according to how total memory
1373  * related to pages that could be allocated for buffers (by
1374  * comparing nr_free_buffer_pages() to vm_total_pages.
1375  *
1376  * However, that was when we used "dirty_ratio" to scale with
1377  * all memory, and we don't do that any more. "dirty_ratio"
1378  * is now applied to total non-HIGHPAGE memory (by subtracting
1379  * totalhigh_pages from vm_total_pages), and as such we can't
1380  * get into the old insane situation any more where we had
1381  * large amounts of dirty pages compared to a small amount of
1382  * non-HIGHMEM memory.
1383  *
1384  * But we might still want to scale the dirty_ratio by how
1385  * much memory the box has..
1386  */
1387 void __init page_writeback_init(void)
1388 {
1389         int shift;
1390
1391         writeback_set_ratelimit();
1392         register_cpu_notifier(&ratelimit_nb);
1393
1394         shift = calc_period_shift();
1395         prop_descriptor_init(&vm_completions, shift);
1396         prop_descriptor_init(&vm_dirties, shift);
1397 }
1398
1399 /**
1400  * tag_pages_for_writeback - tag pages to be written by write_cache_pages
1401  * @mapping: address space structure to write
1402  * @start: starting page index
1403  * @end: ending page index (inclusive)
1404  *
1405  * This function scans the page range from @start to @end (inclusive) and tags
1406  * all pages that have DIRTY tag set with a special TOWRITE tag. The idea is
1407  * that write_cache_pages (or whoever calls this function) will then use
1408  * TOWRITE tag to identify pages eligible for writeback.  This mechanism is
1409  * used to avoid livelocking of writeback by a process steadily creating new
1410  * dirty pages in the file (thus it is important for this function to be quick
1411  * so that it can tag pages faster than a dirtying process can create them).
1412  */
1413 /*
1414  * We tag pages in batches of WRITEBACK_TAG_BATCH to reduce tree_lock latency.
1415  */
1416 void tag_pages_for_writeback(struct address_space *mapping,
1417                              pgoff_t start, pgoff_t end)
1418 {
1419 #define WRITEBACK_TAG_BATCH 4096
1420         unsigned long tagged;
1421
1422         do {
1423                 spin_lock_irq(&mapping->tree_lock);
1424                 tagged = radix_tree_range_tag_if_tagged(&mapping->page_tree,
1425                                 &start, end, WRITEBACK_TAG_BATCH,
1426                                 PAGECACHE_TAG_DIRTY, PAGECACHE_TAG_TOWRITE);
1427                 spin_unlock_irq(&mapping->tree_lock);
1428                 WARN_ON_ONCE(tagged > WRITEBACK_TAG_BATCH);
1429                 cond_resched();
1430                 /* We check 'start' to handle wrapping when end == ~0UL */
1431         } while (tagged >= WRITEBACK_TAG_BATCH && start);
1432 }
1433 EXPORT_SYMBOL(tag_pages_for_writeback);
1434
1435 /**
1436  * write_cache_pages - walk the list of dirty pages of the given address space and write all of them.
1437  * @mapping: address space structure to write
1438  * @wbc: subtract the number of written pages from *@wbc->nr_to_write
1439  * @writepage: function called for each page
1440  * @data: data passed to writepage function
1441  *
1442  * If a page is already under I/O, write_cache_pages() skips it, even
1443  * if it's dirty.  This is desirable behaviour for memory-cleaning writeback,
1444  * but it is INCORRECT for data-integrity system calls such as fsync().  fsync()
1445  * and msync() need to guarantee that all the data which was dirty at the time
1446  * the call was made get new I/O started against them.  If wbc->sync_mode is
1447  * WB_SYNC_ALL then we were called for data integrity and we must wait for
1448  * existing IO to complete.
1449  *
1450  * To avoid livelocks (when other process dirties new pages), we first tag
1451  * pages which should be written back with TOWRITE tag and only then start
1452  * writing them. For data-integrity sync we have to be careful so that we do
1453  * not miss some pages (e.g., because some other process has cleared TOWRITE
1454  * tag we set). The rule we follow is that TOWRITE tag can be cleared only
1455  * by the process clearing the DIRTY tag (and submitting the page for IO).
1456  */
1457 int write_cache_pages(struct address_space *mapping,
1458                       struct writeback_control *wbc, writepage_t writepage,
1459                       void *data)
1460 {
1461         int ret = 0;
1462         int done = 0;
1463         struct pagevec pvec;
1464         int nr_pages;
1465         pgoff_t uninitialized_var(writeback_index);
1466         pgoff_t index;
1467         pgoff_t end;            /* Inclusive */
1468         pgoff_t done_index;
1469         int cycled;
1470         int range_whole = 0;
1471         int tag;
1472
1473         pagevec_init(&pvec, 0);
1474         if (wbc->range_cyclic) {
1475                 writeback_index = mapping->writeback_index; /* prev offset */
1476                 index = writeback_index;
1477                 if (index == 0)
1478                         cycled = 1;
1479                 else
1480                         cycled = 0;
1481                 end = -1;
1482         } else {
1483                 index = wbc->range_start >> PAGE_CACHE_SHIFT;
1484                 end = wbc->range_end >> PAGE_CACHE_SHIFT;
1485                 if (wbc->range_start == 0 && wbc->range_end == LLONG_MAX)
1486                         range_whole = 1;
1487                 cycled = 1; /* ignore range_cyclic tests */
1488         }
1489         if (wbc->sync_mode == WB_SYNC_ALL || wbc->tagged_writepages)
1490                 tag = PAGECACHE_TAG_TOWRITE;
1491         else
1492                 tag = PAGECACHE_TAG_DIRTY;
1493 retry:
1494         if (wbc->sync_mode == WB_SYNC_ALL || wbc->tagged_writepages)
1495                 tag_pages_for_writeback(mapping, index, end);
1496         done_index = index;
1497         while (!done && (index <= end)) {
1498                 int i;
1499
1500                 nr_pages = pagevec_lookup_tag(&pvec, mapping, &index, tag,
1501                               min(end - index, (pgoff_t)PAGEVEC_SIZE-1) + 1);
1502                 if (nr_pages == 0)
1503                         break;
1504
1505                 for (i = 0; i < nr_pages; i++) {
1506                         struct page *page = pvec.pages[i];
1507
1508                         /*
1509                          * At this point, the page may be truncated or
1510                          * invalidated (changing page->mapping to NULL), or
1511                          * even swizzled back from swapper_space to tmpfs file
1512                          * mapping. However, page->index will not change
1513                          * because we have a reference on the page.
1514                          */
1515                         if (page->index > end) {
1516                                 /*
1517                                  * can't be range_cyclic (1st pass) because
1518                                  * end == -1 in that case.
1519                                  */
1520                                 done = 1;
1521                                 break;
1522                         }
1523
1524                         done_index = page->index;
1525
1526                         lock_page(page);
1527
1528                         /*
1529                          * Page truncated or invalidated. We can freely skip it
1530                          * then, even for data integrity operations: the page
1531                          * has disappeared concurrently, so there could be no
1532                          * real expectation of this data interity operation
1533                          * even if there is now a new, dirty page at the same
1534                          * pagecache address.
1535                          */
1536                         if (unlikely(page->mapping != mapping)) {
1537 continue_unlock:
1538                                 unlock_page(page);
1539                                 continue;
1540                         }
1541
1542                         if (!PageDirty(page)) {
1543                                 /* someone wrote it for us */
1544                                 goto continue_unlock;
1545                         }
1546
1547                         if (PageWriteback(page)) {
1548                                 if (wbc->sync_mode != WB_SYNC_NONE)
1549                                         wait_on_page_writeback(page);
1550                                 else
1551                                         goto continue_unlock;
1552                         }
1553
1554                         BUG_ON(PageWriteback(page));
1555                         if (!clear_page_dirty_for_io(page))
1556                                 goto continue_unlock;
1557
1558                         trace_wbc_writepage(wbc, mapping->backing_dev_info);
1559                         ret = (*writepage)(page, wbc, data);
1560                         if (unlikely(ret)) {
1561                                 if (ret == AOP_WRITEPAGE_ACTIVATE) {
1562                                         unlock_page(page);
1563                                         ret = 0;
1564                                 } else {
1565                                         /*
1566                                          * done_index is set past this page,
1567                                          * so media errors will not choke
1568                                          * background writeout for the entire
1569                                          * file. This has consequences for
1570                                          * range_cyclic semantics (ie. it may
1571                                          * not be suitable for data integrity
1572                                          * writeout).
1573                                          */
1574                                         done_index = page->index + 1;
1575                                         done = 1;
1576                                         break;
1577                                 }
1578                         }
1579
1580                         /*
1581                          * We stop writing back only if we are not doing
1582                          * integrity sync. In case of integrity sync we have to
1583                          * keep going until we have written all the pages
1584                          * we tagged for writeback prior to entering this loop.
1585                          */
1586                         if (--wbc->nr_to_write <= 0 &&
1587                             wbc->sync_mode == WB_SYNC_NONE) {
1588                                 done = 1;
1589                                 break;
1590                         }
1591                 }
1592                 pagevec_release(&pvec);
1593                 cond_resched();
1594         }
1595         if (!cycled && !done) {
1596                 /*
1597                  * range_cyclic:
1598                  * We hit the last page and there is more work to be done: wrap
1599                  * back to the start of the file
1600                  */
1601                 cycled = 1;
1602                 index = 0;
1603                 end = writeback_index - 1;
1604                 goto retry;
1605         }
1606         if (wbc->range_cyclic || (range_whole && wbc->nr_to_write > 0))
1607                 mapping->writeback_index = done_index;
1608
1609         return ret;
1610 }
1611 EXPORT_SYMBOL(write_cache_pages);
1612
1613 /*
1614  * Function used by generic_writepages to call the real writepage
1615  * function and set the mapping flags on error
1616  */
1617 static int __writepage(struct page *page, struct writeback_control *wbc,
1618                        void *data)
1619 {
1620         struct address_space *mapping = data;
1621         int ret = mapping->a_ops->writepage(page, wbc);
1622         mapping_set_error(mapping, ret);
1623         return ret;
1624 }
1625
1626 /**
1627  * generic_writepages - walk the list of dirty pages of the given address space and writepage() all of them.
1628  * @mapping: address space structure to write
1629  * @wbc: subtract the number of written pages from *@wbc->nr_to_write
1630  *
1631  * This is a library function, which implements the writepages()
1632  * address_space_operation.
1633  */
1634 int generic_writepages(struct address_space *mapping,
1635                        struct writeback_control *wbc)
1636 {
1637         struct blk_plug plug;
1638         int ret;
1639
1640         /* deal with chardevs and other special file */
1641         if (!mapping->a_ops->writepage)
1642                 return 0;
1643
1644         blk_start_plug(&plug);
1645         ret = write_cache_pages(mapping, wbc, __writepage, mapping);
1646         blk_finish_plug(&plug);
1647         return ret;
1648 }
1649
1650 EXPORT_SYMBOL(generic_writepages);
1651
1652 int do_writepages(struct address_space *mapping, struct writeback_control *wbc)
1653 {
1654         int ret;
1655
1656         if (wbc->nr_to_write <= 0)
1657                 return 0;
1658         if (mapping->a_ops->writepages)
1659                 ret = mapping->a_ops->writepages(mapping, wbc);
1660         else
1661                 ret = generic_writepages(mapping, wbc);
1662         return ret;
1663 }
1664
1665 /**
1666  * write_one_page - write out a single page and optionally wait on I/O
1667  * @page: the page to write
1668  * @wait: if true, wait on writeout
1669  *
1670  * The page must be locked by the caller and will be unlocked upon return.
1671  *
1672  * write_one_page() returns a negative error code if I/O failed.
1673  */
1674 int write_one_page(struct page *page, int wait)
1675 {
1676         struct address_space *mapping = page->mapping;
1677         int ret = 0;
1678         struct writeback_control wbc = {
1679                 .sync_mode = WB_SYNC_ALL,
1680                 .nr_to_write = 1,
1681         };
1682
1683         BUG_ON(!PageLocked(page));
1684
1685         if (wait)
1686                 wait_on_page_writeback(page);
1687
1688         if (clear_page_dirty_for_io(page)) {
1689                 page_cache_get(page);
1690                 ret = mapping->a_ops->writepage(page, &wbc);
1691                 if (ret == 0 && wait) {
1692                         wait_on_page_writeback(page);
1693                         if (PageError(page))
1694                                 ret = -EIO;
1695                 }
1696                 page_cache_release(page);
1697         } else {
1698                 unlock_page(page);
1699         }
1700         return ret;
1701 }
1702 EXPORT_SYMBOL(write_one_page);
1703
1704 /*
1705  * For address_spaces which do not use buffers nor write back.
1706  */
1707 int __set_page_dirty_no_writeback(struct page *page)
1708 {
1709         if (!PageDirty(page))
1710                 return !TestSetPageDirty(page);
1711         return 0;
1712 }
1713
1714 /*
1715  * Helper function for set_page_dirty family.
1716  * NOTE: This relies on being atomic wrt interrupts.
1717  */
1718 void account_page_dirtied(struct page *page, struct address_space *mapping)
1719 {
1720         if (mapping_cap_account_dirty(mapping)) {
1721                 __inc_zone_page_state(page, NR_FILE_DIRTY);
1722                 __inc_zone_page_state(page, NR_DIRTIED);
1723                 __inc_bdi_stat(mapping->backing_dev_info, BDI_RECLAIMABLE);
1724                 __inc_bdi_stat(mapping->backing_dev_info, BDI_DIRTIED);
1725                 task_dirty_inc(current);
1726                 task_io_account_write(PAGE_CACHE_SIZE);
1727         }
1728 }
1729 EXPORT_SYMBOL(account_page_dirtied);
1730
1731 /*
1732  * Helper function for set_page_writeback family.
1733  * NOTE: Unlike account_page_dirtied this does not rely on being atomic
1734  * wrt interrupts.
1735  */
1736 void account_page_writeback(struct page *page)
1737 {
1738         inc_zone_page_state(page, NR_WRITEBACK);
1739 }
1740 EXPORT_SYMBOL(account_page_writeback);
1741
1742 /*
1743  * For address_spaces which do not use buffers.  Just tag the page as dirty in
1744  * its radix tree.
1745  *
1746  * This is also used when a single buffer is being dirtied: we want to set the
1747  * page dirty in that case, but not all the buffers.  This is a "bottom-up"
1748  * dirtying, whereas __set_page_dirty_buffers() is a "top-down" dirtying.
1749  *
1750  * Most callers have locked the page, which pins the address_space in memory.
1751  * But zap_pte_range() does not lock the page, however in that case the
1752  * mapping is pinned by the vma's ->vm_file reference.
1753  *
1754  * We take care to handle the case where the page was truncated from the
1755  * mapping by re-checking page_mapping() inside tree_lock.
1756  */
1757 int __set_page_dirty_nobuffers(struct page *page)
1758 {
1759         if (!TestSetPageDirty(page)) {
1760                 struct address_space *mapping = page_mapping(page);
1761                 struct address_space *mapping2;
1762
1763                 if (!mapping)
1764                         return 1;
1765
1766                 spin_lock_irq(&mapping->tree_lock);
1767                 mapping2 = page_mapping(page);
1768                 if (mapping2) { /* Race with truncate? */
1769                         BUG_ON(mapping2 != mapping);
1770                         WARN_ON_ONCE(!PagePrivate(page) && !PageUptodate(page));
1771                         account_page_dirtied(page, mapping);
1772                         radix_tree_tag_set(&mapping->page_tree,
1773                                 page_index(page), PAGECACHE_TAG_DIRTY);
1774                 }
1775                 spin_unlock_irq(&mapping->tree_lock);
1776                 if (mapping->host) {
1777                         /* !PageAnon && !swapper_space */
1778                         __mark_inode_dirty(mapping->host, I_DIRTY_PAGES);
1779                 }
1780                 return 1;
1781         }
1782         return 0;
1783 }
1784 EXPORT_SYMBOL(__set_page_dirty_nobuffers);
1785
1786 /*
1787  * When a writepage implementation decides that it doesn't want to write this
1788  * page for some reason, it should redirty the locked page via
1789  * redirty_page_for_writepage() and it should then unlock the page and return 0
1790  */
1791 int redirty_page_for_writepage(struct writeback_control *wbc, struct page *page)
1792 {
1793         wbc->pages_skipped++;
1794         return __set_page_dirty_nobuffers(page);
1795 }
1796 EXPORT_SYMBOL(redirty_page_for_writepage);
1797
1798 /*
1799  * Dirty a page.
1800  *
1801  * For pages with a mapping this should be done under the page lock
1802  * for the benefit of asynchronous memory errors who prefer a consistent
1803  * dirty state. This rule can be broken in some special cases,
1804  * but should be better not to.
1805  *
1806  * If the mapping doesn't provide a set_page_dirty a_op, then
1807  * just fall through and assume that it wants buffer_heads.
1808  */
1809 int set_page_dirty(struct page *page)
1810 {
1811         struct address_space *mapping = page_mapping(page);
1812
1813         if (likely(mapping)) {
1814                 int (*spd)(struct page *) = mapping->a_ops->set_page_dirty;
1815                 /*
1816                  * readahead/lru_deactivate_page could remain
1817                  * PG_readahead/PG_reclaim due to race with end_page_writeback
1818                  * About readahead, if the page is written, the flags would be
1819                  * reset. So no problem.
1820                  * About lru_deactivate_page, if the page is redirty, the flag
1821                  * will be reset. So no problem. but if the page is used by readahead
1822                  * it will confuse readahead and make it restart the size rampup
1823                  * process. But it's a trivial problem.
1824                  */
1825                 ClearPageReclaim(page);
1826 #ifdef CONFIG_BLOCK
1827                 if (!spd)
1828                         spd = __set_page_dirty_buffers;
1829 #endif
1830                 return (*spd)(page);
1831         }
1832         if (!PageDirty(page)) {
1833                 if (!TestSetPageDirty(page))
1834                         return 1;
1835         }
1836         return 0;
1837 }
1838 EXPORT_SYMBOL(set_page_dirty);
1839
1840 /*
1841  * set_page_dirty() is racy if the caller has no reference against
1842  * page->mapping->host, and if the page is unlocked.  This is because another
1843  * CPU could truncate the page off the mapping and then free the mapping.
1844  *
1845  * Usually, the page _is_ locked, or the caller is a user-space process which
1846  * holds a reference on the inode by having an open file.
1847  *
1848  * In other cases, the page should be locked before running set_page_dirty().
1849  */
1850 int set_page_dirty_lock(struct page *page)
1851 {
1852         int ret;
1853
1854         lock_page(page);
1855         ret = set_page_dirty(page);
1856         unlock_page(page);
1857         return ret;
1858 }
1859 EXPORT_SYMBOL(set_page_dirty_lock);
1860
1861 /*
1862  * Clear a page's dirty flag, while caring for dirty memory accounting.
1863  * Returns true if the page was previously dirty.
1864  *
1865  * This is for preparing to put the page under writeout.  We leave the page
1866  * tagged as dirty in the radix tree so that a concurrent write-for-sync
1867  * can discover it via a PAGECACHE_TAG_DIRTY walk.  The ->writepage
1868  * implementation will run either set_page_writeback() or set_page_dirty(),
1869  * at which stage we bring the page's dirty flag and radix-tree dirty tag
1870  * back into sync.
1871  *
1872  * This incoherency between the page's dirty flag and radix-tree tag is
1873  * unfortunate, but it only exists while the page is locked.
1874  */
1875 int clear_page_dirty_for_io(struct page *page)
1876 {
1877         struct address_space *mapping = page_mapping(page);
1878
1879         BUG_ON(!PageLocked(page));
1880
1881         if (mapping && mapping_cap_account_dirty(mapping)) {
1882                 /*
1883                  * Yes, Virginia, this is indeed insane.
1884                  *
1885                  * We use this sequence to make sure that
1886                  *  (a) we account for dirty stats properly
1887                  *  (b) we tell the low-level filesystem to
1888                  *      mark the whole page dirty if it was
1889                  *      dirty in a pagetable. Only to then
1890                  *  (c) clean the page again and return 1 to
1891                  *      cause the writeback.
1892                  *
1893                  * This way we avoid all nasty races with the
1894                  * dirty bit in multiple places and clearing
1895                  * them concurrently from different threads.
1896                  *
1897                  * Note! Normally the "set_page_dirty(page)"
1898                  * has no effect on the actual dirty bit - since
1899                  * that will already usually be set. But we
1900                  * need the side effects, and it can help us
1901                  * avoid races.
1902                  *
1903                  * We basically use the page "master dirty bit"
1904                  * as a serialization point for all the different
1905                  * threads doing their things.
1906                  */
1907                 if (page_mkclean(page))
1908                         set_page_dirty(page);
1909                 /*
1910                  * We carefully synchronise fault handlers against
1911                  * installing a dirty pte and marking the page dirty
1912                  * at this point. We do this by having them hold the
1913                  * page lock at some point after installing their
1914                  * pte, but before marking the page dirty.
1915                  * Pages are always locked coming in here, so we get
1916                  * the desired exclusion. See mm/memory.c:do_wp_page()
1917                  * for more comments.
1918                  */
1919                 if (TestClearPageDirty(page)) {
1920                         dec_zone_page_state(page, NR_FILE_DIRTY);
1921                         dec_bdi_stat(mapping->backing_dev_info,
1922                                         BDI_RECLAIMABLE);
1923                         return 1;
1924                 }
1925                 return 0;
1926         }
1927         return TestClearPageDirty(page);
1928 }
1929 EXPORT_SYMBOL(clear_page_dirty_for_io);
1930
1931 int test_clear_page_writeback(struct page *page)
1932 {
1933         struct address_space *mapping = page_mapping(page);
1934         int ret;
1935
1936         if (mapping) {
1937                 struct backing_dev_info *bdi = mapping->backing_dev_info;
1938                 unsigned long flags;
1939
1940                 spin_lock_irqsave(&mapping->tree_lock, flags);
1941                 ret = TestClearPageWriteback(page);
1942                 if (ret) {
1943                         radix_tree_tag_clear(&mapping->page_tree,
1944                                                 page_index(page),
1945                                                 PAGECACHE_TAG_WRITEBACK);
1946                         if (bdi_cap_account_writeback(bdi)) {
1947                                 __dec_bdi_stat(bdi, BDI_WRITEBACK);
1948                                 __bdi_writeout_inc(bdi);
1949                         }
1950                 }
1951                 spin_unlock_irqrestore(&mapping->tree_lock, flags);
1952         } else {
1953                 ret = TestClearPageWriteback(page);
1954         }
1955         if (ret) {
1956                 dec_zone_page_state(page, NR_WRITEBACK);
1957                 inc_zone_page_state(page, NR_WRITTEN);
1958         }
1959         return ret;
1960 }
1961
1962 int test_set_page_writeback(struct page *page)
1963 {
1964         struct address_space *mapping = page_mapping(page);
1965         int ret;
1966
1967         if (mapping) {
1968                 struct backing_dev_info *bdi = mapping->backing_dev_info;
1969                 unsigned long flags;
1970
1971                 spin_lock_irqsave(&mapping->tree_lock, flags);
1972                 ret = TestSetPageWriteback(page);
1973                 if (!ret) {
1974                         radix_tree_tag_set(&mapping->page_tree,
1975                                                 page_index(page),
1976                                                 PAGECACHE_TAG_WRITEBACK);
1977                         if (bdi_cap_account_writeback(bdi))
1978                                 __inc_bdi_stat(bdi, BDI_WRITEBACK);
1979                 }
1980                 if (!PageDirty(page))
1981                         radix_tree_tag_clear(&mapping->page_tree,
1982                                                 page_index(page),
1983                                                 PAGECACHE_TAG_DIRTY);
1984                 radix_tree_tag_clear(&mapping->page_tree,
1985                                      page_index(page),
1986                                      PAGECACHE_TAG_TOWRITE);
1987                 spin_unlock_irqrestore(&mapping->tree_lock, flags);
1988         } else {
1989                 ret = TestSetPageWriteback(page);
1990         }
1991         if (!ret)
1992                 account_page_writeback(page);
1993         return ret;
1994
1995 }
1996 EXPORT_SYMBOL(test_set_page_writeback);
1997
1998 /*
1999  * Return true if any of the pages in the mapping are marked with the
2000  * passed tag.
2001  */
2002 int mapping_tagged(struct address_space *mapping, int tag)
2003 {
2004         return radix_tree_tagged(&mapping->page_tree, tag);
2005 }
2006 EXPORT_SYMBOL(mapping_tagged);