Merge branch 'writeback-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git...
[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  * bdi_min_ratio keeps the sum of the minimum dirty shares of all
255  * registered backing devices, which, for obvious reasons, can not
256  * exceed 100%.
257  */
258 static unsigned int bdi_min_ratio;
259
260 int bdi_set_min_ratio(struct backing_dev_info *bdi, unsigned int min_ratio)
261 {
262         int ret = 0;
263
264         spin_lock_bh(&bdi_lock);
265         if (min_ratio > bdi->max_ratio) {
266                 ret = -EINVAL;
267         } else {
268                 min_ratio -= bdi->min_ratio;
269                 if (bdi_min_ratio + min_ratio < 100) {
270                         bdi_min_ratio += min_ratio;
271                         bdi->min_ratio += min_ratio;
272                 } else {
273                         ret = -EINVAL;
274                 }
275         }
276         spin_unlock_bh(&bdi_lock);
277
278         return ret;
279 }
280
281 int bdi_set_max_ratio(struct backing_dev_info *bdi, unsigned max_ratio)
282 {
283         int ret = 0;
284
285         if (max_ratio > 100)
286                 return -EINVAL;
287
288         spin_lock_bh(&bdi_lock);
289         if (bdi->min_ratio > max_ratio) {
290                 ret = -EINVAL;
291         } else {
292                 bdi->max_ratio = max_ratio;
293                 bdi->max_prop_frac = (PROP_FRAC_BASE * max_ratio) / 100;
294         }
295         spin_unlock_bh(&bdi_lock);
296
297         return ret;
298 }
299 EXPORT_SYMBOL(bdi_set_max_ratio);
300
301 /*
302  * Work out the current dirty-memory clamping and background writeout
303  * thresholds.
304  *
305  * The main aim here is to lower them aggressively if there is a lot of mapped
306  * memory around.  To avoid stressing page reclaim with lots of unreclaimable
307  * pages.  It is better to clamp down on writers than to start swapping, and
308  * performing lots of scanning.
309  *
310  * We only allow 1/2 of the currently-unmapped memory to be dirtied.
311  *
312  * We don't permit the clamping level to fall below 5% - that is getting rather
313  * excessive.
314  *
315  * We make sure that the background writeout level is below the adjusted
316  * clamping level.
317  */
318
319 static unsigned long highmem_dirtyable_memory(unsigned long total)
320 {
321 #ifdef CONFIG_HIGHMEM
322         int node;
323         unsigned long x = 0;
324
325         for_each_node_state(node, N_HIGH_MEMORY) {
326                 struct zone *z =
327                         &NODE_DATA(node)->node_zones[ZONE_HIGHMEM];
328
329                 x += zone_page_state(z, NR_FREE_PAGES) +
330                      zone_reclaimable_pages(z);
331         }
332         /*
333          * Make sure that the number of highmem pages is never larger
334          * than the number of the total dirtyable memory. This can only
335          * occur in very strange VM situations but we want to make sure
336          * that this does not occur.
337          */
338         return min(x, total);
339 #else
340         return 0;
341 #endif
342 }
343
344 /**
345  * determine_dirtyable_memory - amount of memory that may be used
346  *
347  * Returns the numebr of pages that can currently be freed and used
348  * by the kernel for direct mappings.
349  */
350 unsigned long determine_dirtyable_memory(void)
351 {
352         unsigned long x;
353
354         x = global_page_state(NR_FREE_PAGES) + global_reclaimable_pages();
355
356         if (!vm_highmem_is_dirtyable)
357                 x -= highmem_dirtyable_memory(x);
358
359         return x + 1;   /* Ensure that we never return 0 */
360 }
361
362 static unsigned long dirty_freerun_ceiling(unsigned long thresh,
363                                            unsigned long bg_thresh)
364 {
365         return (thresh + bg_thresh) / 2;
366 }
367
368 static unsigned long hard_dirty_limit(unsigned long thresh)
369 {
370         return max(thresh, global_dirty_limit);
371 }
372
373 /*
374  * global_dirty_limits - background-writeback and dirty-throttling thresholds
375  *
376  * Calculate the dirty thresholds based on sysctl parameters
377  * - vm.dirty_background_ratio  or  vm.dirty_background_bytes
378  * - vm.dirty_ratio             or  vm.dirty_bytes
379  * The dirty limits will be lifted by 1/4 for PF_LESS_THROTTLE (ie. nfsd) and
380  * real-time tasks.
381  */
382 void global_dirty_limits(unsigned long *pbackground, unsigned long *pdirty)
383 {
384         unsigned long background;
385         unsigned long dirty;
386         unsigned long uninitialized_var(available_memory);
387         struct task_struct *tsk;
388
389         if (!vm_dirty_bytes || !dirty_background_bytes)
390                 available_memory = determine_dirtyable_memory();
391
392         if (vm_dirty_bytes)
393                 dirty = DIV_ROUND_UP(vm_dirty_bytes, PAGE_SIZE);
394         else
395                 dirty = (vm_dirty_ratio * available_memory) / 100;
396
397         if (dirty_background_bytes)
398                 background = DIV_ROUND_UP(dirty_background_bytes, PAGE_SIZE);
399         else
400                 background = (dirty_background_ratio * available_memory) / 100;
401
402         if (background >= dirty)
403                 background = dirty / 2;
404         tsk = current;
405         if (tsk->flags & PF_LESS_THROTTLE || rt_task(tsk)) {
406                 background += background / 4;
407                 dirty += dirty / 4;
408         }
409         *pbackground = background;
410         *pdirty = dirty;
411         trace_global_dirty_state(background, dirty);
412 }
413
414 /**
415  * bdi_dirty_limit - @bdi's share of dirty throttling threshold
416  * @bdi: the backing_dev_info to query
417  * @dirty: global dirty limit in pages
418  *
419  * Returns @bdi's dirty limit in pages. The term "dirty" in the context of
420  * dirty balancing includes all PG_dirty, PG_writeback and NFS unstable pages.
421  * And the "limit" in the name is not seriously taken as hard limit in
422  * balance_dirty_pages().
423  *
424  * It allocates high/low dirty limits to fast/slow devices, in order to prevent
425  * - starving fast devices
426  * - piling up dirty pages (that will take long time to sync) on slow devices
427  *
428  * The bdi's share of dirty limit will be adapting to its throughput and
429  * bounded by the bdi->min_ratio and/or bdi->max_ratio parameters, if set.
430  */
431 unsigned long bdi_dirty_limit(struct backing_dev_info *bdi, unsigned long dirty)
432 {
433         u64 bdi_dirty;
434         long numerator, denominator;
435
436         /*
437          * Calculate this BDI's share of the dirty ratio.
438          */
439         bdi_writeout_fraction(bdi, &numerator, &denominator);
440
441         bdi_dirty = (dirty * (100 - bdi_min_ratio)) / 100;
442         bdi_dirty *= numerator;
443         do_div(bdi_dirty, denominator);
444
445         bdi_dirty += (dirty * bdi->min_ratio) / 100;
446         if (bdi_dirty > (dirty * bdi->max_ratio) / 100)
447                 bdi_dirty = dirty * bdi->max_ratio / 100;
448
449         return bdi_dirty;
450 }
451
452 /*
453  * Dirty position control.
454  *
455  * (o) global/bdi setpoints
456  *
457  * We want the dirty pages be balanced around the global/bdi setpoints.
458  * When the number of dirty pages is higher/lower than the setpoint, the
459  * dirty position control ratio (and hence task dirty ratelimit) will be
460  * decreased/increased to bring the dirty pages back to the setpoint.
461  *
462  *     pos_ratio = 1 << RATELIMIT_CALC_SHIFT
463  *
464  *     if (dirty < setpoint) scale up   pos_ratio
465  *     if (dirty > setpoint) scale down pos_ratio
466  *
467  *     if (bdi_dirty < bdi_setpoint) scale up   pos_ratio
468  *     if (bdi_dirty > bdi_setpoint) scale down pos_ratio
469  *
470  *     task_ratelimit = dirty_ratelimit * pos_ratio >> RATELIMIT_CALC_SHIFT
471  *
472  * (o) global control line
473  *
474  *     ^ pos_ratio
475  *     |
476  *     |            |<===== global dirty control scope ======>|
477  * 2.0 .............*
478  *     |            .*
479  *     |            . *
480  *     |            .   *
481  *     |            .     *
482  *     |            .        *
483  *     |            .            *
484  * 1.0 ................................*
485  *     |            .                  .     *
486  *     |            .                  .          *
487  *     |            .                  .              *
488  *     |            .                  .                 *
489  *     |            .                  .                    *
490  *   0 +------------.------------------.----------------------*------------->
491  *           freerun^          setpoint^                 limit^   dirty pages
492  *
493  * (o) bdi control line
494  *
495  *     ^ pos_ratio
496  *     |
497  *     |            *
498  *     |              *
499  *     |                *
500  *     |                  *
501  *     |                    * |<=========== span ============>|
502  * 1.0 .......................*
503  *     |                      . *
504  *     |                      .   *
505  *     |                      .     *
506  *     |                      .       *
507  *     |                      .         *
508  *     |                      .           *
509  *     |                      .             *
510  *     |                      .               *
511  *     |                      .                 *
512  *     |                      .                   *
513  *     |                      .                     *
514  * 1/4 ...............................................* * * * * * * * * * * *
515  *     |                      .                         .
516  *     |                      .                           .
517  *     |                      .                             .
518  *   0 +----------------------.-------------------------------.------------->
519  *                bdi_setpoint^                    x_intercept^
520  *
521  * The bdi control line won't drop below pos_ratio=1/4, so that bdi_dirty can
522  * be smoothly throttled down to normal if it starts high in situations like
523  * - start writing to a slow SD card and a fast disk at the same time. The SD
524  *   card's bdi_dirty may rush to many times higher than bdi_setpoint.
525  * - the bdi dirty thresh drops quickly due to change of JBOD workload
526  */
527 static unsigned long bdi_position_ratio(struct backing_dev_info *bdi,
528                                         unsigned long thresh,
529                                         unsigned long bg_thresh,
530                                         unsigned long dirty,
531                                         unsigned long bdi_thresh,
532                                         unsigned long bdi_dirty)
533 {
534         unsigned long write_bw = bdi->avg_write_bandwidth;
535         unsigned long freerun = dirty_freerun_ceiling(thresh, bg_thresh);
536         unsigned long limit = hard_dirty_limit(thresh);
537         unsigned long x_intercept;
538         unsigned long setpoint;         /* dirty pages' target balance point */
539         unsigned long bdi_setpoint;
540         unsigned long span;
541         long long pos_ratio;            /* for scaling up/down the rate limit */
542         long x;
543
544         if (unlikely(dirty >= limit))
545                 return 0;
546
547         /*
548          * global setpoint
549          *
550          *                           setpoint - dirty 3
551          *        f(dirty) := 1.0 + (----------------)
552          *                           limit - setpoint
553          *
554          * it's a 3rd order polynomial that subjects to
555          *
556          * (1) f(freerun)  = 2.0 => rampup dirty_ratelimit reasonably fast
557          * (2) f(setpoint) = 1.0 => the balance point
558          * (3) f(limit)    = 0   => the hard limit
559          * (4) df/dx      <= 0   => negative feedback control
560          * (5) the closer to setpoint, the smaller |df/dx| (and the reverse)
561          *     => fast response on large errors; small oscillation near setpoint
562          */
563         setpoint = (freerun + limit) / 2;
564         x = div_s64((setpoint - dirty) << RATELIMIT_CALC_SHIFT,
565                     limit - setpoint + 1);
566         pos_ratio = x;
567         pos_ratio = pos_ratio * x >> RATELIMIT_CALC_SHIFT;
568         pos_ratio = pos_ratio * x >> RATELIMIT_CALC_SHIFT;
569         pos_ratio += 1 << RATELIMIT_CALC_SHIFT;
570
571         /*
572          * We have computed basic pos_ratio above based on global situation. If
573          * the bdi is over/under its share of dirty pages, we want to scale
574          * pos_ratio further down/up. That is done by the following mechanism.
575          */
576
577         /*
578          * bdi setpoint
579          *
580          *        f(bdi_dirty) := 1.0 + k * (bdi_dirty - bdi_setpoint)
581          *
582          *                        x_intercept - bdi_dirty
583          *                     := --------------------------
584          *                        x_intercept - bdi_setpoint
585          *
586          * The main bdi control line is a linear function that subjects to
587          *
588          * (1) f(bdi_setpoint) = 1.0
589          * (2) k = - 1 / (8 * write_bw)  (in single bdi case)
590          *     or equally: x_intercept = bdi_setpoint + 8 * write_bw
591          *
592          * For single bdi case, the dirty pages are observed to fluctuate
593          * regularly within range
594          *        [bdi_setpoint - write_bw/2, bdi_setpoint + write_bw/2]
595          * for various filesystems, where (2) can yield in a reasonable 12.5%
596          * fluctuation range for pos_ratio.
597          *
598          * For JBOD case, bdi_thresh (not bdi_dirty!) could fluctuate up to its
599          * own size, so move the slope over accordingly and choose a slope that
600          * yields 100% pos_ratio fluctuation on suddenly doubled bdi_thresh.
601          */
602         if (unlikely(bdi_thresh > thresh))
603                 bdi_thresh = thresh;
604         bdi_thresh = max(bdi_thresh, (limit - dirty) / 8);
605         /*
606          * scale global setpoint to bdi's:
607          *      bdi_setpoint = setpoint * bdi_thresh / thresh
608          */
609         x = div_u64((u64)bdi_thresh << 16, thresh + 1);
610         bdi_setpoint = setpoint * (u64)x >> 16;
611         /*
612          * Use span=(8*write_bw) in single bdi case as indicated by
613          * (thresh - bdi_thresh ~= 0) and transit to bdi_thresh in JBOD case.
614          *
615          *        bdi_thresh                    thresh - bdi_thresh
616          * span = ---------- * (8 * write_bw) + ------------------- * bdi_thresh
617          *          thresh                            thresh
618          */
619         span = (thresh - bdi_thresh + 8 * write_bw) * (u64)x >> 16;
620         x_intercept = bdi_setpoint + span;
621
622         if (bdi_dirty < x_intercept - span / 4) {
623                 pos_ratio = div_u64(pos_ratio * (x_intercept - bdi_dirty),
624                                     x_intercept - bdi_setpoint + 1);
625         } else
626                 pos_ratio /= 4;
627
628         /*
629          * bdi reserve area, safeguard against dirty pool underrun and disk idle
630          * It may push the desired control point of global dirty pages higher
631          * than setpoint.
632          */
633         x_intercept = bdi_thresh / 2;
634         if (bdi_dirty < x_intercept) {
635                 if (bdi_dirty > x_intercept / 8)
636                         pos_ratio = div_u64(pos_ratio * x_intercept, bdi_dirty);
637                 else
638                         pos_ratio *= 8;
639         }
640
641         return pos_ratio;
642 }
643
644 static void bdi_update_write_bandwidth(struct backing_dev_info *bdi,
645                                        unsigned long elapsed,
646                                        unsigned long written)
647 {
648         const unsigned long period = roundup_pow_of_two(3 * HZ);
649         unsigned long avg = bdi->avg_write_bandwidth;
650         unsigned long old = bdi->write_bandwidth;
651         u64 bw;
652
653         /*
654          * bw = written * HZ / elapsed
655          *
656          *                   bw * elapsed + write_bandwidth * (period - elapsed)
657          * write_bandwidth = ---------------------------------------------------
658          *                                          period
659          */
660         bw = written - bdi->written_stamp;
661         bw *= HZ;
662         if (unlikely(elapsed > period)) {
663                 do_div(bw, elapsed);
664                 avg = bw;
665                 goto out;
666         }
667         bw += (u64)bdi->write_bandwidth * (period - elapsed);
668         bw >>= ilog2(period);
669
670         /*
671          * one more level of smoothing, for filtering out sudden spikes
672          */
673         if (avg > old && old >= (unsigned long)bw)
674                 avg -= (avg - old) >> 3;
675
676         if (avg < old && old <= (unsigned long)bw)
677                 avg += (old - avg) >> 3;
678
679 out:
680         bdi->write_bandwidth = bw;
681         bdi->avg_write_bandwidth = avg;
682 }
683
684 /*
685  * The global dirtyable memory and dirty threshold could be suddenly knocked
686  * down by a large amount (eg. on the startup of KVM in a swapless system).
687  * This may throw the system into deep dirty exceeded state and throttle
688  * heavy/light dirtiers alike. To retain good responsiveness, maintain
689  * global_dirty_limit for tracking slowly down to the knocked down dirty
690  * threshold.
691  */
692 static void update_dirty_limit(unsigned long thresh, unsigned long dirty)
693 {
694         unsigned long limit = global_dirty_limit;
695
696         /*
697          * Follow up in one step.
698          */
699         if (limit < thresh) {
700                 limit = thresh;
701                 goto update;
702         }
703
704         /*
705          * Follow down slowly. Use the higher one as the target, because thresh
706          * may drop below dirty. This is exactly the reason to introduce
707          * global_dirty_limit which is guaranteed to lie above the dirty pages.
708          */
709         thresh = max(thresh, dirty);
710         if (limit > thresh) {
711                 limit -= (limit - thresh) >> 5;
712                 goto update;
713         }
714         return;
715 update:
716         global_dirty_limit = limit;
717 }
718
719 static void global_update_bandwidth(unsigned long thresh,
720                                     unsigned long dirty,
721                                     unsigned long now)
722 {
723         static DEFINE_SPINLOCK(dirty_lock);
724         static unsigned long update_time;
725
726         /*
727          * check locklessly first to optimize away locking for the most time
728          */
729         if (time_before(now, update_time + BANDWIDTH_INTERVAL))
730                 return;
731
732         spin_lock(&dirty_lock);
733         if (time_after_eq(now, update_time + BANDWIDTH_INTERVAL)) {
734                 update_dirty_limit(thresh, dirty);
735                 update_time = now;
736         }
737         spin_unlock(&dirty_lock);
738 }
739
740 /*
741  * Maintain bdi->dirty_ratelimit, the base dirty throttle rate.
742  *
743  * Normal bdi tasks will be curbed at or below it in long term.
744  * Obviously it should be around (write_bw / N) when there are N dd tasks.
745  */
746 static void bdi_update_dirty_ratelimit(struct backing_dev_info *bdi,
747                                        unsigned long thresh,
748                                        unsigned long bg_thresh,
749                                        unsigned long dirty,
750                                        unsigned long bdi_thresh,
751                                        unsigned long bdi_dirty,
752                                        unsigned long dirtied,
753                                        unsigned long elapsed)
754 {
755         unsigned long freerun = dirty_freerun_ceiling(thresh, bg_thresh);
756         unsigned long limit = hard_dirty_limit(thresh);
757         unsigned long setpoint = (freerun + limit) / 2;
758         unsigned long write_bw = bdi->avg_write_bandwidth;
759         unsigned long dirty_ratelimit = bdi->dirty_ratelimit;
760         unsigned long dirty_rate;
761         unsigned long task_ratelimit;
762         unsigned long balanced_dirty_ratelimit;
763         unsigned long pos_ratio;
764         unsigned long step;
765         unsigned long x;
766
767         /*
768          * The dirty rate will match the writeout rate in long term, except
769          * when dirty pages are truncated by userspace or re-dirtied by FS.
770          */
771         dirty_rate = (dirtied - bdi->dirtied_stamp) * HZ / elapsed;
772
773         pos_ratio = bdi_position_ratio(bdi, thresh, bg_thresh, dirty,
774                                        bdi_thresh, bdi_dirty);
775         /*
776          * task_ratelimit reflects each dd's dirty rate for the past 200ms.
777          */
778         task_ratelimit = (u64)dirty_ratelimit *
779                                         pos_ratio >> RATELIMIT_CALC_SHIFT;
780         task_ratelimit++; /* it helps rampup dirty_ratelimit from tiny values */
781
782         /*
783          * A linear estimation of the "balanced" throttle rate. The theory is,
784          * if there are N dd tasks, each throttled at task_ratelimit, the bdi's
785          * dirty_rate will be measured to be (N * task_ratelimit). So the below
786          * formula will yield the balanced rate limit (write_bw / N).
787          *
788          * Note that the expanded form is not a pure rate feedback:
789          *      rate_(i+1) = rate_(i) * (write_bw / dirty_rate)              (1)
790          * but also takes pos_ratio into account:
791          *      rate_(i+1) = rate_(i) * (write_bw / dirty_rate) * pos_ratio  (2)
792          *
793          * (1) is not realistic because pos_ratio also takes part in balancing
794          * the dirty rate.  Consider the state
795          *      pos_ratio = 0.5                                              (3)
796          *      rate = 2 * (write_bw / N)                                    (4)
797          * If (1) is used, it will stuck in that state! Because each dd will
798          * be throttled at
799          *      task_ratelimit = pos_ratio * rate = (write_bw / N)           (5)
800          * yielding
801          *      dirty_rate = N * task_ratelimit = write_bw                   (6)
802          * put (6) into (1) we get
803          *      rate_(i+1) = rate_(i)                                        (7)
804          *
805          * So we end up using (2) to always keep
806          *      rate_(i+1) ~= (write_bw / N)                                 (8)
807          * regardless of the value of pos_ratio. As long as (8) is satisfied,
808          * pos_ratio is able to drive itself to 1.0, which is not only where
809          * the dirty count meet the setpoint, but also where the slope of
810          * pos_ratio is most flat and hence task_ratelimit is least fluctuated.
811          */
812         balanced_dirty_ratelimit = div_u64((u64)task_ratelimit * write_bw,
813                                            dirty_rate | 1);
814
815         /*
816          * We could safely do this and return immediately:
817          *
818          *      bdi->dirty_ratelimit = balanced_dirty_ratelimit;
819          *
820          * However to get a more stable dirty_ratelimit, the below elaborated
821          * code makes use of task_ratelimit to filter out sigular points and
822          * limit the step size.
823          *
824          * The below code essentially only uses the relative value of
825          *
826          *      task_ratelimit - dirty_ratelimit
827          *      = (pos_ratio - 1) * dirty_ratelimit
828          *
829          * which reflects the direction and size of dirty position error.
830          */
831
832         /*
833          * dirty_ratelimit will follow balanced_dirty_ratelimit iff
834          * task_ratelimit is on the same side of dirty_ratelimit, too.
835          * For example, when
836          * - dirty_ratelimit > balanced_dirty_ratelimit
837          * - dirty_ratelimit > task_ratelimit (dirty pages are above setpoint)
838          * lowering dirty_ratelimit will help meet both the position and rate
839          * control targets. Otherwise, don't update dirty_ratelimit if it will
840          * only help meet the rate target. After all, what the users ultimately
841          * feel and care are stable dirty rate and small position error.
842          *
843          * |task_ratelimit - dirty_ratelimit| is used to limit the step size
844          * and filter out the sigular points of balanced_dirty_ratelimit. Which
845          * keeps jumping around randomly and can even leap far away at times
846          * due to the small 200ms estimation period of dirty_rate (we want to
847          * keep that period small to reduce time lags).
848          */
849         step = 0;
850         if (dirty < setpoint) {
851                 x = min(bdi->balanced_dirty_ratelimit,
852                          min(balanced_dirty_ratelimit, task_ratelimit));
853                 if (dirty_ratelimit < x)
854                         step = x - dirty_ratelimit;
855         } else {
856                 x = max(bdi->balanced_dirty_ratelimit,
857                          max(balanced_dirty_ratelimit, task_ratelimit));
858                 if (dirty_ratelimit > x)
859                         step = dirty_ratelimit - x;
860         }
861
862         /*
863          * Don't pursue 100% rate matching. It's impossible since the balanced
864          * rate itself is constantly fluctuating. So decrease the track speed
865          * when it gets close to the target. Helps eliminate pointless tremors.
866          */
867         step >>= dirty_ratelimit / (2 * step + 1);
868         /*
869          * Limit the tracking speed to avoid overshooting.
870          */
871         step = (step + 7) / 8;
872
873         if (dirty_ratelimit < balanced_dirty_ratelimit)
874                 dirty_ratelimit += step;
875         else
876                 dirty_ratelimit -= step;
877
878         bdi->dirty_ratelimit = max(dirty_ratelimit, 1UL);
879         bdi->balanced_dirty_ratelimit = balanced_dirty_ratelimit;
880
881         trace_bdi_dirty_ratelimit(bdi, dirty_rate, task_ratelimit);
882 }
883
884 void __bdi_update_bandwidth(struct backing_dev_info *bdi,
885                             unsigned long thresh,
886                             unsigned long bg_thresh,
887                             unsigned long dirty,
888                             unsigned long bdi_thresh,
889                             unsigned long bdi_dirty,
890                             unsigned long start_time)
891 {
892         unsigned long now = jiffies;
893         unsigned long elapsed = now - bdi->bw_time_stamp;
894         unsigned long dirtied;
895         unsigned long written;
896
897         /*
898          * rate-limit, only update once every 200ms.
899          */
900         if (elapsed < BANDWIDTH_INTERVAL)
901                 return;
902
903         dirtied = percpu_counter_read(&bdi->bdi_stat[BDI_DIRTIED]);
904         written = percpu_counter_read(&bdi->bdi_stat[BDI_WRITTEN]);
905
906         /*
907          * Skip quiet periods when disk bandwidth is under-utilized.
908          * (at least 1s idle time between two flusher runs)
909          */
910         if (elapsed > HZ && time_before(bdi->bw_time_stamp, start_time))
911                 goto snapshot;
912
913         if (thresh) {
914                 global_update_bandwidth(thresh, dirty, now);
915                 bdi_update_dirty_ratelimit(bdi, thresh, bg_thresh, dirty,
916                                            bdi_thresh, bdi_dirty,
917                                            dirtied, elapsed);
918         }
919         bdi_update_write_bandwidth(bdi, elapsed, written);
920
921 snapshot:
922         bdi->dirtied_stamp = dirtied;
923         bdi->written_stamp = written;
924         bdi->bw_time_stamp = now;
925 }
926
927 static void bdi_update_bandwidth(struct backing_dev_info *bdi,
928                                  unsigned long thresh,
929                                  unsigned long bg_thresh,
930                                  unsigned long dirty,
931                                  unsigned long bdi_thresh,
932                                  unsigned long bdi_dirty,
933                                  unsigned long start_time)
934 {
935         if (time_is_after_eq_jiffies(bdi->bw_time_stamp + BANDWIDTH_INTERVAL))
936                 return;
937         spin_lock(&bdi->wb.list_lock);
938         __bdi_update_bandwidth(bdi, thresh, bg_thresh, dirty,
939                                bdi_thresh, bdi_dirty, start_time);
940         spin_unlock(&bdi->wb.list_lock);
941 }
942
943 /*
944  * After a task dirtied this many pages, balance_dirty_pages_ratelimited_nr()
945  * will look to see if it needs to start dirty throttling.
946  *
947  * If dirty_poll_interval is too low, big NUMA machines will call the expensive
948  * global_page_state() too often. So scale it near-sqrt to the safety margin
949  * (the number of pages we may dirty without exceeding the dirty limits).
950  */
951 static unsigned long dirty_poll_interval(unsigned long dirty,
952                                          unsigned long thresh)
953 {
954         if (thresh > dirty)
955                 return 1UL << (ilog2(thresh - dirty) >> 1);
956
957         return 1;
958 }
959
960 static unsigned long bdi_max_pause(struct backing_dev_info *bdi,
961                                    unsigned long bdi_dirty)
962 {
963         unsigned long bw = bdi->avg_write_bandwidth;
964         unsigned long hi = ilog2(bw);
965         unsigned long lo = ilog2(bdi->dirty_ratelimit);
966         unsigned long t;
967
968         /* target for 20ms max pause on 1-dd case */
969         t = HZ / 50;
970
971         /*
972          * Scale up pause time for concurrent dirtiers in order to reduce CPU
973          * overheads.
974          *
975          * (N * 20ms) on 2^N concurrent tasks.
976          */
977         if (hi > lo)
978                 t += (hi - lo) * (20 * HZ) / 1024;
979
980         /*
981          * Limit pause time for small memory systems. If sleeping for too long
982          * time, a small pool of dirty/writeback pages may go empty and disk go
983          * idle.
984          *
985          * 8 serves as the safety ratio.
986          */
987         if (bdi_dirty)
988                 t = min(t, bdi_dirty * HZ / (8 * bw + 1));
989
990         /*
991          * The pause time will be settled within range (max_pause/4, max_pause).
992          * Apply a minimal value of 4 to get a non-zero max_pause/4.
993          */
994         return clamp_val(t, 4, MAX_PAUSE);
995 }
996
997 /*
998  * balance_dirty_pages() must be called by processes which are generating dirty
999  * data.  It looks at the number of dirty pages in the machine and will force
1000  * the caller to wait once crossing the (background_thresh + dirty_thresh) / 2.
1001  * If we're over `background_thresh' then the writeback threads are woken to
1002  * perform some writeout.
1003  */
1004 static void balance_dirty_pages(struct address_space *mapping,
1005                                 unsigned long pages_dirtied)
1006 {
1007         unsigned long nr_reclaimable;   /* = file_dirty + unstable_nfs */
1008         unsigned long bdi_reclaimable;
1009         unsigned long nr_dirty;  /* = file_dirty + writeback + unstable_nfs */
1010         unsigned long bdi_dirty;
1011         unsigned long freerun;
1012         unsigned long background_thresh;
1013         unsigned long dirty_thresh;
1014         unsigned long bdi_thresh;
1015         long pause = 0;
1016         long uninitialized_var(max_pause);
1017         bool dirty_exceeded = false;
1018         unsigned long task_ratelimit;
1019         unsigned long uninitialized_var(dirty_ratelimit);
1020         unsigned long pos_ratio;
1021         struct backing_dev_info *bdi = mapping->backing_dev_info;
1022         unsigned long start_time = jiffies;
1023
1024         for (;;) {
1025                 /*
1026                  * Unstable writes are a feature of certain networked
1027                  * filesystems (i.e. NFS) in which data may have been
1028                  * written to the server's write cache, but has not yet
1029                  * been flushed to permanent storage.
1030                  */
1031                 nr_reclaimable = global_page_state(NR_FILE_DIRTY) +
1032                                         global_page_state(NR_UNSTABLE_NFS);
1033                 nr_dirty = nr_reclaimable + global_page_state(NR_WRITEBACK);
1034
1035                 global_dirty_limits(&background_thresh, &dirty_thresh);
1036
1037                 /*
1038                  * Throttle it only when the background writeback cannot
1039                  * catch-up. This avoids (excessively) small writeouts
1040                  * when the bdi limits are ramping up.
1041                  */
1042                 freerun = dirty_freerun_ceiling(dirty_thresh,
1043                                                 background_thresh);
1044                 if (nr_dirty <= freerun)
1045                         break;
1046
1047                 if (unlikely(!writeback_in_progress(bdi)))
1048                         bdi_start_background_writeback(bdi);
1049
1050                 /*
1051                  * bdi_thresh is not treated as some limiting factor as
1052                  * dirty_thresh, due to reasons
1053                  * - in JBOD setup, bdi_thresh can fluctuate a lot
1054                  * - in a system with HDD and USB key, the USB key may somehow
1055                  *   go into state (bdi_dirty >> bdi_thresh) either because
1056                  *   bdi_dirty starts high, or because bdi_thresh drops low.
1057                  *   In this case we don't want to hard throttle the USB key
1058                  *   dirtiers for 100 seconds until bdi_dirty drops under
1059                  *   bdi_thresh. Instead the auxiliary bdi control line in
1060                  *   bdi_position_ratio() will let the dirtier task progress
1061                  *   at some rate <= (write_bw / 2) for bringing down bdi_dirty.
1062                  */
1063                 bdi_thresh = bdi_dirty_limit(bdi, dirty_thresh);
1064
1065                 /*
1066                  * In order to avoid the stacked BDI deadlock we need
1067                  * to ensure we accurately count the 'dirty' pages when
1068                  * the threshold is low.
1069                  *
1070                  * Otherwise it would be possible to get thresh+n pages
1071                  * reported dirty, even though there are thresh-m pages
1072                  * actually dirty; with m+n sitting in the percpu
1073                  * deltas.
1074                  */
1075                 if (bdi_thresh < 2 * bdi_stat_error(bdi)) {
1076                         bdi_reclaimable = bdi_stat_sum(bdi, BDI_RECLAIMABLE);
1077                         bdi_dirty = bdi_reclaimable +
1078                                     bdi_stat_sum(bdi, BDI_WRITEBACK);
1079                 } else {
1080                         bdi_reclaimable = bdi_stat(bdi, BDI_RECLAIMABLE);
1081                         bdi_dirty = bdi_reclaimable +
1082                                     bdi_stat(bdi, BDI_WRITEBACK);
1083                 }
1084
1085                 dirty_exceeded = (bdi_dirty > bdi_thresh) ||
1086                                   (nr_dirty > dirty_thresh);
1087                 if (dirty_exceeded && !bdi->dirty_exceeded)
1088                         bdi->dirty_exceeded = 1;
1089
1090                 bdi_update_bandwidth(bdi, dirty_thresh, background_thresh,
1091                                      nr_dirty, bdi_thresh, bdi_dirty,
1092                                      start_time);
1093
1094                 max_pause = bdi_max_pause(bdi, bdi_dirty);
1095
1096                 dirty_ratelimit = bdi->dirty_ratelimit;
1097                 pos_ratio = bdi_position_ratio(bdi, dirty_thresh,
1098                                                background_thresh, nr_dirty,
1099                                                bdi_thresh, bdi_dirty);
1100                 if (unlikely(pos_ratio == 0)) {
1101                         pause = max_pause;
1102                         goto pause;
1103                 }
1104                 task_ratelimit = (u64)dirty_ratelimit *
1105                                         pos_ratio >> RATELIMIT_CALC_SHIFT;
1106                 pause = (HZ * pages_dirtied) / (task_ratelimit | 1);
1107                 if (unlikely(pause <= 0)) {
1108                         trace_balance_dirty_pages(bdi,
1109                                                   dirty_thresh,
1110                                                   background_thresh,
1111                                                   nr_dirty,
1112                                                   bdi_thresh,
1113                                                   bdi_dirty,
1114                                                   dirty_ratelimit,
1115                                                   task_ratelimit,
1116                                                   pages_dirtied,
1117                                                   pause,
1118                                                   start_time);
1119                         pause = 1; /* avoid resetting nr_dirtied_pause below */
1120                         break;
1121                 }
1122                 pause = min(pause, max_pause);
1123
1124 pause:
1125                 trace_balance_dirty_pages(bdi,
1126                                           dirty_thresh,
1127                                           background_thresh,
1128                                           nr_dirty,
1129                                           bdi_thresh,
1130                                           bdi_dirty,
1131                                           dirty_ratelimit,
1132                                           task_ratelimit,
1133                                           pages_dirtied,
1134                                           pause,
1135                                           start_time);
1136                 __set_current_state(TASK_UNINTERRUPTIBLE);
1137                 io_schedule_timeout(pause);
1138
1139                 dirty_thresh = hard_dirty_limit(dirty_thresh);
1140                 /*
1141                  * max-pause area. If dirty exceeded but still within this
1142                  * area, no need to sleep for more than 200ms: (a) 8 pages per
1143                  * 200ms is typically more than enough to curb heavy dirtiers;
1144                  * (b) the pause time limit makes the dirtiers more responsive.
1145                  */
1146                 if (nr_dirty < dirty_thresh)
1147                         break;
1148         }
1149
1150         if (!dirty_exceeded && bdi->dirty_exceeded)
1151                 bdi->dirty_exceeded = 0;
1152
1153         current->nr_dirtied = 0;
1154         if (pause == 0) { /* in freerun area */
1155                 current->nr_dirtied_pause =
1156                                 dirty_poll_interval(nr_dirty, dirty_thresh);
1157         } else if (pause <= max_pause / 4 &&
1158                    pages_dirtied >= current->nr_dirtied_pause) {
1159                 current->nr_dirtied_pause = clamp_val(
1160                                         dirty_ratelimit * (max_pause / 2) / HZ,
1161                                         pages_dirtied + pages_dirtied / 8,
1162                                         pages_dirtied * 4);
1163         } else if (pause >= max_pause) {
1164                 current->nr_dirtied_pause = 1 | clamp_val(
1165                                         dirty_ratelimit * (max_pause / 2) / HZ,
1166                                         pages_dirtied / 4,
1167                                         pages_dirtied - pages_dirtied / 8);
1168         }
1169
1170         if (writeback_in_progress(bdi))
1171                 return;
1172
1173         /*
1174          * In laptop mode, we wait until hitting the higher threshold before
1175          * starting background writeout, and then write out all the way down
1176          * to the lower threshold.  So slow writers cause minimal disk activity.
1177          *
1178          * In normal mode, we start background writeout at the lower
1179          * background_thresh, to keep the amount of dirty memory low.
1180          */
1181         if (laptop_mode)
1182                 return;
1183
1184         if (nr_reclaimable > background_thresh)
1185                 bdi_start_background_writeback(bdi);
1186 }
1187
1188 void set_page_dirty_balance(struct page *page, int page_mkwrite)
1189 {
1190         if (set_page_dirty(page) || page_mkwrite) {
1191                 struct address_space *mapping = page_mapping(page);
1192
1193                 if (mapping)
1194                         balance_dirty_pages_ratelimited(mapping);
1195         }
1196 }
1197
1198 static DEFINE_PER_CPU(int, bdp_ratelimits);
1199
1200 /**
1201  * balance_dirty_pages_ratelimited_nr - balance dirty memory state
1202  * @mapping: address_space which was dirtied
1203  * @nr_pages_dirtied: number of pages which the caller has just dirtied
1204  *
1205  * Processes which are dirtying memory should call in here once for each page
1206  * which was newly dirtied.  The function will periodically check the system's
1207  * dirty state and will initiate writeback if needed.
1208  *
1209  * On really big machines, get_writeback_state is expensive, so try to avoid
1210  * calling it too often (ratelimiting).  But once we're over the dirty memory
1211  * limit we decrease the ratelimiting by a lot, to prevent individual processes
1212  * from overshooting the limit by (ratelimit_pages) each.
1213  */
1214 void balance_dirty_pages_ratelimited_nr(struct address_space *mapping,
1215                                         unsigned long nr_pages_dirtied)
1216 {
1217         struct backing_dev_info *bdi = mapping->backing_dev_info;
1218         int ratelimit;
1219         int *p;
1220
1221         if (!bdi_cap_account_dirty(bdi))
1222                 return;
1223
1224         ratelimit = current->nr_dirtied_pause;
1225         if (bdi->dirty_exceeded)
1226                 ratelimit = min(ratelimit, 32 >> (PAGE_SHIFT - 10));
1227
1228         current->nr_dirtied += nr_pages_dirtied;
1229
1230         preempt_disable();
1231         /*
1232          * This prevents one CPU to accumulate too many dirtied pages without
1233          * calling into balance_dirty_pages(), which can happen when there are
1234          * 1000+ tasks, all of them start dirtying pages at exactly the same
1235          * time, hence all honoured too large initial task->nr_dirtied_pause.
1236          */
1237         p =  &__get_cpu_var(bdp_ratelimits);
1238         if (unlikely(current->nr_dirtied >= ratelimit))
1239                 *p = 0;
1240         else {
1241                 *p += nr_pages_dirtied;
1242                 if (unlikely(*p >= ratelimit_pages)) {
1243                         *p = 0;
1244                         ratelimit = 0;
1245                 }
1246         }
1247         preempt_enable();
1248
1249         if (unlikely(current->nr_dirtied >= ratelimit))
1250                 balance_dirty_pages(mapping, current->nr_dirtied);
1251 }
1252 EXPORT_SYMBOL(balance_dirty_pages_ratelimited_nr);
1253
1254 void throttle_vm_writeout(gfp_t gfp_mask)
1255 {
1256         unsigned long background_thresh;
1257         unsigned long dirty_thresh;
1258
1259         for ( ; ; ) {
1260                 global_dirty_limits(&background_thresh, &dirty_thresh);
1261
1262                 /*
1263                  * Boost the allowable dirty threshold a bit for page
1264                  * allocators so they don't get DoS'ed by heavy writers
1265                  */
1266                 dirty_thresh += dirty_thresh / 10;      /* wheeee... */
1267
1268                 if (global_page_state(NR_UNSTABLE_NFS) +
1269                         global_page_state(NR_WRITEBACK) <= dirty_thresh)
1270                                 break;
1271                 congestion_wait(BLK_RW_ASYNC, HZ/10);
1272
1273                 /*
1274                  * The caller might hold locks which can prevent IO completion
1275                  * or progress in the filesystem.  So we cannot just sit here
1276                  * waiting for IO to complete.
1277                  */
1278                 if ((gfp_mask & (__GFP_FS|__GFP_IO)) != (__GFP_FS|__GFP_IO))
1279                         break;
1280         }
1281 }
1282
1283 /*
1284  * sysctl handler for /proc/sys/vm/dirty_writeback_centisecs
1285  */
1286 int dirty_writeback_centisecs_handler(ctl_table *table, int write,
1287         void __user *buffer, size_t *length, loff_t *ppos)
1288 {
1289         proc_dointvec(table, write, buffer, length, ppos);
1290         bdi_arm_supers_timer();
1291         return 0;
1292 }
1293
1294 #ifdef CONFIG_BLOCK
1295 void laptop_mode_timer_fn(unsigned long data)
1296 {
1297         struct request_queue *q = (struct request_queue *)data;
1298         int nr_pages = global_page_state(NR_FILE_DIRTY) +
1299                 global_page_state(NR_UNSTABLE_NFS);
1300
1301         /*
1302          * We want to write everything out, not just down to the dirty
1303          * threshold
1304          */
1305         if (bdi_has_dirty_io(&q->backing_dev_info))
1306                 bdi_start_writeback(&q->backing_dev_info, nr_pages,
1307                                         WB_REASON_LAPTOP_TIMER);
1308 }
1309
1310 /*
1311  * We've spun up the disk and we're in laptop mode: schedule writeback
1312  * of all dirty data a few seconds from now.  If the flush is already scheduled
1313  * then push it back - the user is still using the disk.
1314  */
1315 void laptop_io_completion(struct backing_dev_info *info)
1316 {
1317         mod_timer(&info->laptop_mode_wb_timer, jiffies + laptop_mode);
1318 }
1319
1320 /*
1321  * We're in laptop mode and we've just synced. The sync's writes will have
1322  * caused another writeback to be scheduled by laptop_io_completion.
1323  * Nothing needs to be written back anymore, so we unschedule the writeback.
1324  */
1325 void laptop_sync_completion(void)
1326 {
1327         struct backing_dev_info *bdi;
1328
1329         rcu_read_lock();
1330
1331         list_for_each_entry_rcu(bdi, &bdi_list, bdi_list)
1332                 del_timer(&bdi->laptop_mode_wb_timer);
1333
1334         rcu_read_unlock();
1335 }
1336 #endif
1337
1338 /*
1339  * If ratelimit_pages is too high then we can get into dirty-data overload
1340  * if a large number of processes all perform writes at the same time.
1341  * If it is too low then SMP machines will call the (expensive)
1342  * get_writeback_state too often.
1343  *
1344  * Here we set ratelimit_pages to a level which ensures that when all CPUs are
1345  * dirtying in parallel, we cannot go more than 3% (1/32) over the dirty memory
1346  * thresholds.
1347  */
1348
1349 void writeback_set_ratelimit(void)
1350 {
1351         unsigned long background_thresh;
1352         unsigned long dirty_thresh;
1353         global_dirty_limits(&background_thresh, &dirty_thresh);
1354         ratelimit_pages = dirty_thresh / (num_online_cpus() * 32);
1355         if (ratelimit_pages < 16)
1356                 ratelimit_pages = 16;
1357 }
1358
1359 static int __cpuinit
1360 ratelimit_handler(struct notifier_block *self, unsigned long u, void *v)
1361 {
1362         writeback_set_ratelimit();
1363         return NOTIFY_DONE;
1364 }
1365
1366 static struct notifier_block __cpuinitdata ratelimit_nb = {
1367         .notifier_call  = ratelimit_handler,
1368         .next           = NULL,
1369 };
1370
1371 /*
1372  * Called early on to tune the page writeback dirty limits.
1373  *
1374  * We used to scale dirty pages according to how total memory
1375  * related to pages that could be allocated for buffers (by
1376  * comparing nr_free_buffer_pages() to vm_total_pages.
1377  *
1378  * However, that was when we used "dirty_ratio" to scale with
1379  * all memory, and we don't do that any more. "dirty_ratio"
1380  * is now applied to total non-HIGHPAGE memory (by subtracting
1381  * totalhigh_pages from vm_total_pages), and as such we can't
1382  * get into the old insane situation any more where we had
1383  * large amounts of dirty pages compared to a small amount of
1384  * non-HIGHMEM memory.
1385  *
1386  * But we might still want to scale the dirty_ratio by how
1387  * much memory the box has..
1388  */
1389 void __init page_writeback_init(void)
1390 {
1391         int shift;
1392
1393         writeback_set_ratelimit();
1394         register_cpu_notifier(&ratelimit_nb);
1395
1396         shift = calc_period_shift();
1397         prop_descriptor_init(&vm_completions, shift);
1398         prop_descriptor_init(&vm_dirties, shift);
1399 }
1400
1401 /**
1402  * tag_pages_for_writeback - tag pages to be written by write_cache_pages
1403  * @mapping: address space structure to write
1404  * @start: starting page index
1405  * @end: ending page index (inclusive)
1406  *
1407  * This function scans the page range from @start to @end (inclusive) and tags
1408  * all pages that have DIRTY tag set with a special TOWRITE tag. The idea is
1409  * that write_cache_pages (or whoever calls this function) will then use
1410  * TOWRITE tag to identify pages eligible for writeback.  This mechanism is
1411  * used to avoid livelocking of writeback by a process steadily creating new
1412  * dirty pages in the file (thus it is important for this function to be quick
1413  * so that it can tag pages faster than a dirtying process can create them).
1414  */
1415 /*
1416  * We tag pages in batches of WRITEBACK_TAG_BATCH to reduce tree_lock latency.
1417  */
1418 void tag_pages_for_writeback(struct address_space *mapping,
1419                              pgoff_t start, pgoff_t end)
1420 {
1421 #define WRITEBACK_TAG_BATCH 4096
1422         unsigned long tagged;
1423
1424         do {
1425                 spin_lock_irq(&mapping->tree_lock);
1426                 tagged = radix_tree_range_tag_if_tagged(&mapping->page_tree,
1427                                 &start, end, WRITEBACK_TAG_BATCH,
1428                                 PAGECACHE_TAG_DIRTY, PAGECACHE_TAG_TOWRITE);
1429                 spin_unlock_irq(&mapping->tree_lock);
1430                 WARN_ON_ONCE(tagged > WRITEBACK_TAG_BATCH);
1431                 cond_resched();
1432                 /* We check 'start' to handle wrapping when end == ~0UL */
1433         } while (tagged >= WRITEBACK_TAG_BATCH && start);
1434 }
1435 EXPORT_SYMBOL(tag_pages_for_writeback);
1436
1437 /**
1438  * write_cache_pages - walk the list of dirty pages of the given address space and write all of them.
1439  * @mapping: address space structure to write
1440  * @wbc: subtract the number of written pages from *@wbc->nr_to_write
1441  * @writepage: function called for each page
1442  * @data: data passed to writepage function
1443  *
1444  * If a page is already under I/O, write_cache_pages() skips it, even
1445  * if it's dirty.  This is desirable behaviour for memory-cleaning writeback,
1446  * but it is INCORRECT for data-integrity system calls such as fsync().  fsync()
1447  * and msync() need to guarantee that all the data which was dirty at the time
1448  * the call was made get new I/O started against them.  If wbc->sync_mode is
1449  * WB_SYNC_ALL then we were called for data integrity and we must wait for
1450  * existing IO to complete.
1451  *
1452  * To avoid livelocks (when other process dirties new pages), we first tag
1453  * pages which should be written back with TOWRITE tag and only then start
1454  * writing them. For data-integrity sync we have to be careful so that we do
1455  * not miss some pages (e.g., because some other process has cleared TOWRITE
1456  * tag we set). The rule we follow is that TOWRITE tag can be cleared only
1457  * by the process clearing the DIRTY tag (and submitting the page for IO).
1458  */
1459 int write_cache_pages(struct address_space *mapping,
1460                       struct writeback_control *wbc, writepage_t writepage,
1461                       void *data)
1462 {
1463         int ret = 0;
1464         int done = 0;
1465         struct pagevec pvec;
1466         int nr_pages;
1467         pgoff_t uninitialized_var(writeback_index);
1468         pgoff_t index;
1469         pgoff_t end;            /* Inclusive */
1470         pgoff_t done_index;
1471         int cycled;
1472         int range_whole = 0;
1473         int tag;
1474
1475         pagevec_init(&pvec, 0);
1476         if (wbc->range_cyclic) {
1477                 writeback_index = mapping->writeback_index; /* prev offset */
1478                 index = writeback_index;
1479                 if (index == 0)
1480                         cycled = 1;
1481                 else
1482                         cycled = 0;
1483                 end = -1;
1484         } else {
1485                 index = wbc->range_start >> PAGE_CACHE_SHIFT;
1486                 end = wbc->range_end >> PAGE_CACHE_SHIFT;
1487                 if (wbc->range_start == 0 && wbc->range_end == LLONG_MAX)
1488                         range_whole = 1;
1489                 cycled = 1; /* ignore range_cyclic tests */
1490         }
1491         if (wbc->sync_mode == WB_SYNC_ALL || wbc->tagged_writepages)
1492                 tag = PAGECACHE_TAG_TOWRITE;
1493         else
1494                 tag = PAGECACHE_TAG_DIRTY;
1495 retry:
1496         if (wbc->sync_mode == WB_SYNC_ALL || wbc->tagged_writepages)
1497                 tag_pages_for_writeback(mapping, index, end);
1498         done_index = index;
1499         while (!done && (index <= end)) {
1500                 int i;
1501
1502                 nr_pages = pagevec_lookup_tag(&pvec, mapping, &index, tag,
1503                               min(end - index, (pgoff_t)PAGEVEC_SIZE-1) + 1);
1504                 if (nr_pages == 0)
1505                         break;
1506
1507                 for (i = 0; i < nr_pages; i++) {
1508                         struct page *page = pvec.pages[i];
1509
1510                         /*
1511                          * At this point, the page may be truncated or
1512                          * invalidated (changing page->mapping to NULL), or
1513                          * even swizzled back from swapper_space to tmpfs file
1514                          * mapping. However, page->index will not change
1515                          * because we have a reference on the page.
1516                          */
1517                         if (page->index > end) {
1518                                 /*
1519                                  * can't be range_cyclic (1st pass) because
1520                                  * end == -1 in that case.
1521                                  */
1522                                 done = 1;
1523                                 break;
1524                         }
1525
1526                         done_index = page->index;
1527
1528                         lock_page(page);
1529
1530                         /*
1531                          * Page truncated or invalidated. We can freely skip it
1532                          * then, even for data integrity operations: the page
1533                          * has disappeared concurrently, so there could be no
1534                          * real expectation of this data interity operation
1535                          * even if there is now a new, dirty page at the same
1536                          * pagecache address.
1537                          */
1538                         if (unlikely(page->mapping != mapping)) {
1539 continue_unlock:
1540                                 unlock_page(page);
1541                                 continue;
1542                         }
1543
1544                         if (!PageDirty(page)) {
1545                                 /* someone wrote it for us */
1546                                 goto continue_unlock;
1547                         }
1548
1549                         if (PageWriteback(page)) {
1550                                 if (wbc->sync_mode != WB_SYNC_NONE)
1551                                         wait_on_page_writeback(page);
1552                                 else
1553                                         goto continue_unlock;
1554                         }
1555
1556                         BUG_ON(PageWriteback(page));
1557                         if (!clear_page_dirty_for_io(page))
1558                                 goto continue_unlock;
1559
1560                         trace_wbc_writepage(wbc, mapping->backing_dev_info);
1561                         ret = (*writepage)(page, wbc, data);
1562                         if (unlikely(ret)) {
1563                                 if (ret == AOP_WRITEPAGE_ACTIVATE) {
1564                                         unlock_page(page);
1565                                         ret = 0;
1566                                 } else {
1567                                         /*
1568                                          * done_index is set past this page,
1569                                          * so media errors will not choke
1570                                          * background writeout for the entire
1571                                          * file. This has consequences for
1572                                          * range_cyclic semantics (ie. it may
1573                                          * not be suitable for data integrity
1574                                          * writeout).
1575                                          */
1576                                         done_index = page->index + 1;
1577                                         done = 1;
1578                                         break;
1579                                 }
1580                         }
1581
1582                         /*
1583                          * We stop writing back only if we are not doing
1584                          * integrity sync. In case of integrity sync we have to
1585                          * keep going until we have written all the pages
1586                          * we tagged for writeback prior to entering this loop.
1587                          */
1588                         if (--wbc->nr_to_write <= 0 &&
1589                             wbc->sync_mode == WB_SYNC_NONE) {
1590                                 done = 1;
1591                                 break;
1592                         }
1593                 }
1594                 pagevec_release(&pvec);
1595                 cond_resched();
1596         }
1597         if (!cycled && !done) {
1598                 /*
1599                  * range_cyclic:
1600                  * We hit the last page and there is more work to be done: wrap
1601                  * back to the start of the file
1602                  */
1603                 cycled = 1;
1604                 index = 0;
1605                 end = writeback_index - 1;
1606                 goto retry;
1607         }
1608         if (wbc->range_cyclic || (range_whole && wbc->nr_to_write > 0))
1609                 mapping->writeback_index = done_index;
1610
1611         return ret;
1612 }
1613 EXPORT_SYMBOL(write_cache_pages);
1614
1615 /*
1616  * Function used by generic_writepages to call the real writepage
1617  * function and set the mapping flags on error
1618  */
1619 static int __writepage(struct page *page, struct writeback_control *wbc,
1620                        void *data)
1621 {
1622         struct address_space *mapping = data;
1623         int ret = mapping->a_ops->writepage(page, wbc);
1624         mapping_set_error(mapping, ret);
1625         return ret;
1626 }
1627
1628 /**
1629  * generic_writepages - walk the list of dirty pages of the given address space and writepage() all of them.
1630  * @mapping: address space structure to write
1631  * @wbc: subtract the number of written pages from *@wbc->nr_to_write
1632  *
1633  * This is a library function, which implements the writepages()
1634  * address_space_operation.
1635  */
1636 int generic_writepages(struct address_space *mapping,
1637                        struct writeback_control *wbc)
1638 {
1639         struct blk_plug plug;
1640         int ret;
1641
1642         /* deal with chardevs and other special file */
1643         if (!mapping->a_ops->writepage)
1644                 return 0;
1645
1646         blk_start_plug(&plug);
1647         ret = write_cache_pages(mapping, wbc, __writepage, mapping);
1648         blk_finish_plug(&plug);
1649         return ret;
1650 }
1651
1652 EXPORT_SYMBOL(generic_writepages);
1653
1654 int do_writepages(struct address_space *mapping, struct writeback_control *wbc)
1655 {
1656         int ret;
1657
1658         if (wbc->nr_to_write <= 0)
1659                 return 0;
1660         if (mapping->a_ops->writepages)
1661                 ret = mapping->a_ops->writepages(mapping, wbc);
1662         else
1663                 ret = generic_writepages(mapping, wbc);
1664         return ret;
1665 }
1666
1667 /**
1668  * write_one_page - write out a single page and optionally wait on I/O
1669  * @page: the page to write
1670  * @wait: if true, wait on writeout
1671  *
1672  * The page must be locked by the caller and will be unlocked upon return.
1673  *
1674  * write_one_page() returns a negative error code if I/O failed.
1675  */
1676 int write_one_page(struct page *page, int wait)
1677 {
1678         struct address_space *mapping = page->mapping;
1679         int ret = 0;
1680         struct writeback_control wbc = {
1681                 .sync_mode = WB_SYNC_ALL,
1682                 .nr_to_write = 1,
1683         };
1684
1685         BUG_ON(!PageLocked(page));
1686
1687         if (wait)
1688                 wait_on_page_writeback(page);
1689
1690         if (clear_page_dirty_for_io(page)) {
1691                 page_cache_get(page);
1692                 ret = mapping->a_ops->writepage(page, &wbc);
1693                 if (ret == 0 && wait) {
1694                         wait_on_page_writeback(page);
1695                         if (PageError(page))
1696                                 ret = -EIO;
1697                 }
1698                 page_cache_release(page);
1699         } else {
1700                 unlock_page(page);
1701         }
1702         return ret;
1703 }
1704 EXPORT_SYMBOL(write_one_page);
1705
1706 /*
1707  * For address_spaces which do not use buffers nor write back.
1708  */
1709 int __set_page_dirty_no_writeback(struct page *page)
1710 {
1711         if (!PageDirty(page))
1712                 return !TestSetPageDirty(page);
1713         return 0;
1714 }
1715
1716 /*
1717  * Helper function for set_page_dirty family.
1718  * NOTE: This relies on being atomic wrt interrupts.
1719  */
1720 void account_page_dirtied(struct page *page, struct address_space *mapping)
1721 {
1722         if (mapping_cap_account_dirty(mapping)) {
1723                 __inc_zone_page_state(page, NR_FILE_DIRTY);
1724                 __inc_zone_page_state(page, NR_DIRTIED);
1725                 __inc_bdi_stat(mapping->backing_dev_info, BDI_RECLAIMABLE);
1726                 __inc_bdi_stat(mapping->backing_dev_info, BDI_DIRTIED);
1727                 task_dirty_inc(current);
1728                 task_io_account_write(PAGE_CACHE_SIZE);
1729         }
1730 }
1731 EXPORT_SYMBOL(account_page_dirtied);
1732
1733 /*
1734  * Helper function for set_page_writeback family.
1735  * NOTE: Unlike account_page_dirtied this does not rely on being atomic
1736  * wrt interrupts.
1737  */
1738 void account_page_writeback(struct page *page)
1739 {
1740         inc_zone_page_state(page, NR_WRITEBACK);
1741 }
1742 EXPORT_SYMBOL(account_page_writeback);
1743
1744 /*
1745  * For address_spaces which do not use buffers.  Just tag the page as dirty in
1746  * its radix tree.
1747  *
1748  * This is also used when a single buffer is being dirtied: we want to set the
1749  * page dirty in that case, but not all the buffers.  This is a "bottom-up"
1750  * dirtying, whereas __set_page_dirty_buffers() is a "top-down" dirtying.
1751  *
1752  * Most callers have locked the page, which pins the address_space in memory.
1753  * But zap_pte_range() does not lock the page, however in that case the
1754  * mapping is pinned by the vma's ->vm_file reference.
1755  *
1756  * We take care to handle the case where the page was truncated from the
1757  * mapping by re-checking page_mapping() inside tree_lock.
1758  */
1759 int __set_page_dirty_nobuffers(struct page *page)
1760 {
1761         if (!TestSetPageDirty(page)) {
1762                 struct address_space *mapping = page_mapping(page);
1763                 struct address_space *mapping2;
1764
1765                 if (!mapping)
1766                         return 1;
1767
1768                 spin_lock_irq(&mapping->tree_lock);
1769                 mapping2 = page_mapping(page);
1770                 if (mapping2) { /* Race with truncate? */
1771                         BUG_ON(mapping2 != mapping);
1772                         WARN_ON_ONCE(!PagePrivate(page) && !PageUptodate(page));
1773                         account_page_dirtied(page, mapping);
1774                         radix_tree_tag_set(&mapping->page_tree,
1775                                 page_index(page), PAGECACHE_TAG_DIRTY);
1776                 }
1777                 spin_unlock_irq(&mapping->tree_lock);
1778                 if (mapping->host) {
1779                         /* !PageAnon && !swapper_space */
1780                         __mark_inode_dirty(mapping->host, I_DIRTY_PAGES);
1781                 }
1782                 return 1;
1783         }
1784         return 0;
1785 }
1786 EXPORT_SYMBOL(__set_page_dirty_nobuffers);
1787
1788 /*
1789  * When a writepage implementation decides that it doesn't want to write this
1790  * page for some reason, it should redirty the locked page via
1791  * redirty_page_for_writepage() and it should then unlock the page and return 0
1792  */
1793 int redirty_page_for_writepage(struct writeback_control *wbc, struct page *page)
1794 {
1795         wbc->pages_skipped++;
1796         return __set_page_dirty_nobuffers(page);
1797 }
1798 EXPORT_SYMBOL(redirty_page_for_writepage);
1799
1800 /*
1801  * Dirty a page.
1802  *
1803  * For pages with a mapping this should be done under the page lock
1804  * for the benefit of asynchronous memory errors who prefer a consistent
1805  * dirty state. This rule can be broken in some special cases,
1806  * but should be better not to.
1807  *
1808  * If the mapping doesn't provide a set_page_dirty a_op, then
1809  * just fall through and assume that it wants buffer_heads.
1810  */
1811 int set_page_dirty(struct page *page)
1812 {
1813         struct address_space *mapping = page_mapping(page);
1814
1815         if (likely(mapping)) {
1816                 int (*spd)(struct page *) = mapping->a_ops->set_page_dirty;
1817                 /*
1818                  * readahead/lru_deactivate_page could remain
1819                  * PG_readahead/PG_reclaim due to race with end_page_writeback
1820                  * About readahead, if the page is written, the flags would be
1821                  * reset. So no problem.
1822                  * About lru_deactivate_page, if the page is redirty, the flag
1823                  * will be reset. So no problem. but if the page is used by readahead
1824                  * it will confuse readahead and make it restart the size rampup
1825                  * process. But it's a trivial problem.
1826                  */
1827                 ClearPageReclaim(page);
1828 #ifdef CONFIG_BLOCK
1829                 if (!spd)
1830                         spd = __set_page_dirty_buffers;
1831 #endif
1832                 return (*spd)(page);
1833         }
1834         if (!PageDirty(page)) {
1835                 if (!TestSetPageDirty(page))
1836                         return 1;
1837         }
1838         return 0;
1839 }
1840 EXPORT_SYMBOL(set_page_dirty);
1841
1842 /*
1843  * set_page_dirty() is racy if the caller has no reference against
1844  * page->mapping->host, and if the page is unlocked.  This is because another
1845  * CPU could truncate the page off the mapping and then free the mapping.
1846  *
1847  * Usually, the page _is_ locked, or the caller is a user-space process which
1848  * holds a reference on the inode by having an open file.
1849  *
1850  * In other cases, the page should be locked before running set_page_dirty().
1851  */
1852 int set_page_dirty_lock(struct page *page)
1853 {
1854         int ret;
1855
1856         lock_page(page);
1857         ret = set_page_dirty(page);
1858         unlock_page(page);
1859         return ret;
1860 }
1861 EXPORT_SYMBOL(set_page_dirty_lock);
1862
1863 /*
1864  * Clear a page's dirty flag, while caring for dirty memory accounting.
1865  * Returns true if the page was previously dirty.
1866  *
1867  * This is for preparing to put the page under writeout.  We leave the page
1868  * tagged as dirty in the radix tree so that a concurrent write-for-sync
1869  * can discover it via a PAGECACHE_TAG_DIRTY walk.  The ->writepage
1870  * implementation will run either set_page_writeback() or set_page_dirty(),
1871  * at which stage we bring the page's dirty flag and radix-tree dirty tag
1872  * back into sync.
1873  *
1874  * This incoherency between the page's dirty flag and radix-tree tag is
1875  * unfortunate, but it only exists while the page is locked.
1876  */
1877 int clear_page_dirty_for_io(struct page *page)
1878 {
1879         struct address_space *mapping = page_mapping(page);
1880
1881         BUG_ON(!PageLocked(page));
1882
1883         if (mapping && mapping_cap_account_dirty(mapping)) {
1884                 /*
1885                  * Yes, Virginia, this is indeed insane.
1886                  *
1887                  * We use this sequence to make sure that
1888                  *  (a) we account for dirty stats properly
1889                  *  (b) we tell the low-level filesystem to
1890                  *      mark the whole page dirty if it was
1891                  *      dirty in a pagetable. Only to then
1892                  *  (c) clean the page again and return 1 to
1893                  *      cause the writeback.
1894                  *
1895                  * This way we avoid all nasty races with the
1896                  * dirty bit in multiple places and clearing
1897                  * them concurrently from different threads.
1898                  *
1899                  * Note! Normally the "set_page_dirty(page)"
1900                  * has no effect on the actual dirty bit - since
1901                  * that will already usually be set. But we
1902                  * need the side effects, and it can help us
1903                  * avoid races.
1904                  *
1905                  * We basically use the page "master dirty bit"
1906                  * as a serialization point for all the different
1907                  * threads doing their things.
1908                  */
1909                 if (page_mkclean(page))
1910                         set_page_dirty(page);
1911                 /*
1912                  * We carefully synchronise fault handlers against
1913                  * installing a dirty pte and marking the page dirty
1914                  * at this point. We do this by having them hold the
1915                  * page lock at some point after installing their
1916                  * pte, but before marking the page dirty.
1917                  * Pages are always locked coming in here, so we get
1918                  * the desired exclusion. See mm/memory.c:do_wp_page()
1919                  * for more comments.
1920                  */
1921                 if (TestClearPageDirty(page)) {
1922                         dec_zone_page_state(page, NR_FILE_DIRTY);
1923                         dec_bdi_stat(mapping->backing_dev_info,
1924                                         BDI_RECLAIMABLE);
1925                         return 1;
1926                 }
1927                 return 0;
1928         }
1929         return TestClearPageDirty(page);
1930 }
1931 EXPORT_SYMBOL(clear_page_dirty_for_io);
1932
1933 int test_clear_page_writeback(struct page *page)
1934 {
1935         struct address_space *mapping = page_mapping(page);
1936         int ret;
1937
1938         if (mapping) {
1939                 struct backing_dev_info *bdi = mapping->backing_dev_info;
1940                 unsigned long flags;
1941
1942                 spin_lock_irqsave(&mapping->tree_lock, flags);
1943                 ret = TestClearPageWriteback(page);
1944                 if (ret) {
1945                         radix_tree_tag_clear(&mapping->page_tree,
1946                                                 page_index(page),
1947                                                 PAGECACHE_TAG_WRITEBACK);
1948                         if (bdi_cap_account_writeback(bdi)) {
1949                                 __dec_bdi_stat(bdi, BDI_WRITEBACK);
1950                                 __bdi_writeout_inc(bdi);
1951                         }
1952                 }
1953                 spin_unlock_irqrestore(&mapping->tree_lock, flags);
1954         } else {
1955                 ret = TestClearPageWriteback(page);
1956         }
1957         if (ret) {
1958                 dec_zone_page_state(page, NR_WRITEBACK);
1959                 inc_zone_page_state(page, NR_WRITTEN);
1960         }
1961         return ret;
1962 }
1963
1964 int test_set_page_writeback(struct page *page)
1965 {
1966         struct address_space *mapping = page_mapping(page);
1967         int ret;
1968
1969         if (mapping) {
1970                 struct backing_dev_info *bdi = mapping->backing_dev_info;
1971                 unsigned long flags;
1972
1973                 spin_lock_irqsave(&mapping->tree_lock, flags);
1974                 ret = TestSetPageWriteback(page);
1975                 if (!ret) {
1976                         radix_tree_tag_set(&mapping->page_tree,
1977                                                 page_index(page),
1978                                                 PAGECACHE_TAG_WRITEBACK);
1979                         if (bdi_cap_account_writeback(bdi))
1980                                 __inc_bdi_stat(bdi, BDI_WRITEBACK);
1981                 }
1982                 if (!PageDirty(page))
1983                         radix_tree_tag_clear(&mapping->page_tree,
1984                                                 page_index(page),
1985                                                 PAGECACHE_TAG_DIRTY);
1986                 radix_tree_tag_clear(&mapping->page_tree,
1987                                      page_index(page),
1988                                      PAGECACHE_TAG_TOWRITE);
1989                 spin_unlock_irqrestore(&mapping->tree_lock, flags);
1990         } else {
1991                 ret = TestSetPageWriteback(page);
1992         }
1993         if (!ret)
1994                 account_page_writeback(page);
1995         return ret;
1996
1997 }
1998 EXPORT_SYMBOL(test_set_page_writeback);
1999
2000 /*
2001  * Return true if any of the pages in the mapping are marked with the
2002  * passed tag.
2003  */
2004 int mapping_tagged(struct address_space *mapping, int tag)
2005 {
2006         return radix_tree_tagged(&mapping->page_tree, tag);
2007 }
2008 EXPORT_SYMBOL(mapping_tagged);