mm: exclude reserved pages from dirtyable memory
[linux-2.6.git] / mm / page-writeback.c
1 /*
2  * mm/page-writeback.c
3  *
4  * Copyright (C) 2002, Linus Torvalds.
5  * Copyright (C) 2007 Red Hat, Inc., Peter Zijlstra <pzijlstr@redhat.com>
6  *
7  * Contains functions related to writing back dirty pages at the
8  * address_space level.
9  *
10  * 10Apr2002    Andrew Morton
11  *              Initial version
12  */
13
14 #include <linux/kernel.h>
15 #include <linux/export.h>
16 #include <linux/spinlock.h>
17 #include <linux/fs.h>
18 #include <linux/mm.h>
19 #include <linux/swap.h>
20 #include <linux/slab.h>
21 #include <linux/pagemap.h>
22 #include <linux/writeback.h>
23 #include <linux/init.h>
24 #include <linux/backing-dev.h>
25 #include <linux/task_io_accounting_ops.h>
26 #include <linux/blkdev.h>
27 #include <linux/mpage.h>
28 #include <linux/rmap.h>
29 #include <linux/percpu.h>
30 #include <linux/notifier.h>
31 #include <linux/smp.h>
32 #include <linux/sysctl.h>
33 #include <linux/cpu.h>
34 #include <linux/syscalls.h>
35 #include <linux/buffer_head.h> /* __set_page_dirty_buffers */
36 #include <linux/pagevec.h>
37 #include <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
132 /*
133  * Work out the current dirty-memory clamping and background writeout
134  * thresholds.
135  *
136  * The main aim here is to lower them aggressively if there is a lot of mapped
137  * memory around.  To avoid stressing page reclaim with lots of unreclaimable
138  * pages.  It is better to clamp down on writers than to start swapping, and
139  * performing lots of scanning.
140  *
141  * We only allow 1/2 of the currently-unmapped memory to be dirtied.
142  *
143  * We don't permit the clamping level to fall below 5% - that is getting rather
144  * excessive.
145  *
146  * We make sure that the background writeout level is below the adjusted
147  * clamping level.
148  */
149 static unsigned long highmem_dirtyable_memory(unsigned long total)
150 {
151 #ifdef CONFIG_HIGHMEM
152         int node;
153         unsigned long x = 0;
154
155         for_each_node_state(node, N_HIGH_MEMORY) {
156                 struct zone *z =
157                         &NODE_DATA(node)->node_zones[ZONE_HIGHMEM];
158
159                 x += zone_page_state(z, NR_FREE_PAGES) +
160                      zone_reclaimable_pages(z) - z->dirty_balance_reserve;
161         }
162         /*
163          * Make sure that the number of highmem pages is never larger
164          * than the number of the total dirtyable memory. This can only
165          * occur in very strange VM situations but we want to make sure
166          * that this does not occur.
167          */
168         return min(x, total);
169 #else
170         return 0;
171 #endif
172 }
173
174 /**
175  * determine_dirtyable_memory - amount of memory that may be used
176  *
177  * Returns the numebr of pages that can currently be freed and used
178  * by the kernel for direct mappings.
179  */
180 static unsigned long determine_dirtyable_memory(void)
181 {
182         unsigned long x;
183
184         x = global_page_state(NR_FREE_PAGES) + global_reclaimable_pages() -
185             dirty_balance_reserve;
186
187         if (!vm_highmem_is_dirtyable)
188                 x -= highmem_dirtyable_memory(x);
189
190         return x + 1;   /* Ensure that we never return 0 */
191 }
192
193 /*
194  * couple the period to the dirty_ratio:
195  *
196  *   period/2 ~ roundup_pow_of_two(dirty limit)
197  */
198 static int calc_period_shift(void)
199 {
200         unsigned long dirty_total;
201
202         if (vm_dirty_bytes)
203                 dirty_total = vm_dirty_bytes / PAGE_SIZE;
204         else
205                 dirty_total = (vm_dirty_ratio * determine_dirtyable_memory()) /
206                                 100;
207         return 2 + ilog2(dirty_total - 1);
208 }
209
210 /*
211  * update the period when the dirty threshold changes.
212  */
213 static void update_completion_period(void)
214 {
215         int shift = calc_period_shift();
216         prop_change_shift(&vm_completions, shift);
217
218         writeback_set_ratelimit();
219 }
220
221 int dirty_background_ratio_handler(struct ctl_table *table, int write,
222                 void __user *buffer, size_t *lenp,
223                 loff_t *ppos)
224 {
225         int ret;
226
227         ret = proc_dointvec_minmax(table, write, buffer, lenp, ppos);
228         if (ret == 0 && write)
229                 dirty_background_bytes = 0;
230         return ret;
231 }
232
233 int dirty_background_bytes_handler(struct ctl_table *table, int write,
234                 void __user *buffer, size_t *lenp,
235                 loff_t *ppos)
236 {
237         int ret;
238
239         ret = proc_doulongvec_minmax(table, write, buffer, lenp, ppos);
240         if (ret == 0 && write)
241                 dirty_background_ratio = 0;
242         return ret;
243 }
244
245 int dirty_ratio_handler(struct ctl_table *table, int write,
246                 void __user *buffer, size_t *lenp,
247                 loff_t *ppos)
248 {
249         int old_ratio = vm_dirty_ratio;
250         int ret;
251
252         ret = proc_dointvec_minmax(table, write, buffer, lenp, ppos);
253         if (ret == 0 && write && vm_dirty_ratio != old_ratio) {
254                 update_completion_period();
255                 vm_dirty_bytes = 0;
256         }
257         return ret;
258 }
259
260 int dirty_bytes_handler(struct ctl_table *table, int write,
261                 void __user *buffer, size_t *lenp,
262                 loff_t *ppos)
263 {
264         unsigned long old_bytes = vm_dirty_bytes;
265         int ret;
266
267         ret = proc_doulongvec_minmax(table, write, buffer, lenp, ppos);
268         if (ret == 0 && write && vm_dirty_bytes != old_bytes) {
269                 update_completion_period();
270                 vm_dirty_ratio = 0;
271         }
272         return ret;
273 }
274
275 /*
276  * Increment the BDI's writeout completion count and the global writeout
277  * completion count. Called from test_clear_page_writeback().
278  */
279 static inline void __bdi_writeout_inc(struct backing_dev_info *bdi)
280 {
281         __inc_bdi_stat(bdi, BDI_WRITTEN);
282         __prop_inc_percpu_max(&vm_completions, &bdi->completions,
283                               bdi->max_prop_frac);
284 }
285
286 void bdi_writeout_inc(struct backing_dev_info *bdi)
287 {
288         unsigned long flags;
289
290         local_irq_save(flags);
291         __bdi_writeout_inc(bdi);
292         local_irq_restore(flags);
293 }
294 EXPORT_SYMBOL_GPL(bdi_writeout_inc);
295
296 /*
297  * Obtain an accurate fraction of the BDI's portion.
298  */
299 static void bdi_writeout_fraction(struct backing_dev_info *bdi,
300                 long *numerator, long *denominator)
301 {
302         prop_fraction_percpu(&vm_completions, &bdi->completions,
303                                 numerator, denominator);
304 }
305
306 /*
307  * bdi_min_ratio keeps the sum of the minimum dirty shares of all
308  * registered backing devices, which, for obvious reasons, can not
309  * exceed 100%.
310  */
311 static unsigned int bdi_min_ratio;
312
313 int bdi_set_min_ratio(struct backing_dev_info *bdi, unsigned int min_ratio)
314 {
315         int ret = 0;
316
317         spin_lock_bh(&bdi_lock);
318         if (min_ratio > bdi->max_ratio) {
319                 ret = -EINVAL;
320         } else {
321                 min_ratio -= bdi->min_ratio;
322                 if (bdi_min_ratio + min_ratio < 100) {
323                         bdi_min_ratio += min_ratio;
324                         bdi->min_ratio += min_ratio;
325                 } else {
326                         ret = -EINVAL;
327                 }
328         }
329         spin_unlock_bh(&bdi_lock);
330
331         return ret;
332 }
333
334 int bdi_set_max_ratio(struct backing_dev_info *bdi, unsigned max_ratio)
335 {
336         int ret = 0;
337
338         if (max_ratio > 100)
339                 return -EINVAL;
340
341         spin_lock_bh(&bdi_lock);
342         if (bdi->min_ratio > max_ratio) {
343                 ret = -EINVAL;
344         } else {
345                 bdi->max_ratio = max_ratio;
346                 bdi->max_prop_frac = (PROP_FRAC_BASE * max_ratio) / 100;
347         }
348         spin_unlock_bh(&bdi_lock);
349
350         return ret;
351 }
352 EXPORT_SYMBOL(bdi_set_max_ratio);
353
354 static unsigned long dirty_freerun_ceiling(unsigned long thresh,
355                                            unsigned long bg_thresh)
356 {
357         return (thresh + bg_thresh) / 2;
358 }
359
360 static unsigned long hard_dirty_limit(unsigned long thresh)
361 {
362         return max(thresh, global_dirty_limit);
363 }
364
365 /*
366  * global_dirty_limits - background-writeback and dirty-throttling thresholds
367  *
368  * Calculate the dirty thresholds based on sysctl parameters
369  * - vm.dirty_background_ratio  or  vm.dirty_background_bytes
370  * - vm.dirty_ratio             or  vm.dirty_bytes
371  * The dirty limits will be lifted by 1/4 for PF_LESS_THROTTLE (ie. nfsd) and
372  * real-time tasks.
373  */
374 void global_dirty_limits(unsigned long *pbackground, unsigned long *pdirty)
375 {
376         unsigned long background;
377         unsigned long dirty;
378         unsigned long uninitialized_var(available_memory);
379         struct task_struct *tsk;
380
381         if (!vm_dirty_bytes || !dirty_background_bytes)
382                 available_memory = determine_dirtyable_memory();
383
384         if (vm_dirty_bytes)
385                 dirty = DIV_ROUND_UP(vm_dirty_bytes, PAGE_SIZE);
386         else
387                 dirty = (vm_dirty_ratio * available_memory) / 100;
388
389         if (dirty_background_bytes)
390                 background = DIV_ROUND_UP(dirty_background_bytes, PAGE_SIZE);
391         else
392                 background = (dirty_background_ratio * available_memory) / 100;
393
394         if (background >= dirty)
395                 background = dirty / 2;
396         tsk = current;
397         if (tsk->flags & PF_LESS_THROTTLE || rt_task(tsk)) {
398                 background += background / 4;
399                 dirty += dirty / 4;
400         }
401         *pbackground = background;
402         *pdirty = dirty;
403         trace_global_dirty_state(background, dirty);
404 }
405
406 /**
407  * bdi_dirty_limit - @bdi's share of dirty throttling threshold
408  * @bdi: the backing_dev_info to query
409  * @dirty: global dirty limit in pages
410  *
411  * Returns @bdi's dirty limit in pages. The term "dirty" in the context of
412  * dirty balancing includes all PG_dirty, PG_writeback and NFS unstable pages.
413  *
414  * Note that balance_dirty_pages() will only seriously take it as a hard limit
415  * when sleeping max_pause per page is not enough to keep the dirty pages under
416  * control. For example, when the device is completely stalled due to some error
417  * conditions, or when there are 1000 dd tasks writing to a slow 10MB/s USB key.
418  * In the other normal situations, it acts more gently by throttling the tasks
419  * more (rather than completely block them) when the bdi dirty pages go high.
420  *
421  * It allocates high/low dirty limits to fast/slow devices, in order to prevent
422  * - starving fast devices
423  * - piling up dirty pages (that will take long time to sync) on slow devices
424  *
425  * The bdi's share of dirty limit will be adapting to its throughput and
426  * bounded by the bdi->min_ratio and/or bdi->max_ratio parameters, if set.
427  */
428 unsigned long bdi_dirty_limit(struct backing_dev_info *bdi, unsigned long dirty)
429 {
430         u64 bdi_dirty;
431         long numerator, denominator;
432
433         /*
434          * Calculate this BDI's share of the dirty ratio.
435          */
436         bdi_writeout_fraction(bdi, &numerator, &denominator);
437
438         bdi_dirty = (dirty * (100 - bdi_min_ratio)) / 100;
439         bdi_dirty *= numerator;
440         do_div(bdi_dirty, denominator);
441
442         bdi_dirty += (dirty * bdi->min_ratio) / 100;
443         if (bdi_dirty > (dirty * bdi->max_ratio) / 100)
444                 bdi_dirty = dirty * bdi->max_ratio / 100;
445
446         return bdi_dirty;
447 }
448
449 /*
450  * Dirty position control.
451  *
452  * (o) global/bdi setpoints
453  *
454  * We want the dirty pages be balanced around the global/bdi setpoints.
455  * When the number of dirty pages is higher/lower than the setpoint, the
456  * dirty position control ratio (and hence task dirty ratelimit) will be
457  * decreased/increased to bring the dirty pages back to the setpoint.
458  *
459  *     pos_ratio = 1 << RATELIMIT_CALC_SHIFT
460  *
461  *     if (dirty < setpoint) scale up   pos_ratio
462  *     if (dirty > setpoint) scale down pos_ratio
463  *
464  *     if (bdi_dirty < bdi_setpoint) scale up   pos_ratio
465  *     if (bdi_dirty > bdi_setpoint) scale down pos_ratio
466  *
467  *     task_ratelimit = dirty_ratelimit * pos_ratio >> RATELIMIT_CALC_SHIFT
468  *
469  * (o) global control line
470  *
471  *     ^ pos_ratio
472  *     |
473  *     |            |<===== global dirty control scope ======>|
474  * 2.0 .............*
475  *     |            .*
476  *     |            . *
477  *     |            .   *
478  *     |            .     *
479  *     |            .        *
480  *     |            .            *
481  * 1.0 ................................*
482  *     |            .                  .     *
483  *     |            .                  .          *
484  *     |            .                  .              *
485  *     |            .                  .                 *
486  *     |            .                  .                    *
487  *   0 +------------.------------------.----------------------*------------->
488  *           freerun^          setpoint^                 limit^   dirty pages
489  *
490  * (o) bdi control line
491  *
492  *     ^ pos_ratio
493  *     |
494  *     |            *
495  *     |              *
496  *     |                *
497  *     |                  *
498  *     |                    * |<=========== span ============>|
499  * 1.0 .......................*
500  *     |                      . *
501  *     |                      .   *
502  *     |                      .     *
503  *     |                      .       *
504  *     |                      .         *
505  *     |                      .           *
506  *     |                      .             *
507  *     |                      .               *
508  *     |                      .                 *
509  *     |                      .                   *
510  *     |                      .                     *
511  * 1/4 ...............................................* * * * * * * * * * * *
512  *     |                      .                         .
513  *     |                      .                           .
514  *     |                      .                             .
515  *   0 +----------------------.-------------------------------.------------->
516  *                bdi_setpoint^                    x_intercept^
517  *
518  * The bdi control line won't drop below pos_ratio=1/4, so that bdi_dirty can
519  * be smoothly throttled down to normal if it starts high in situations like
520  * - start writing to a slow SD card and a fast disk at the same time. The SD
521  *   card's bdi_dirty may rush to many times higher than bdi_setpoint.
522  * - the bdi dirty thresh drops quickly due to change of JBOD workload
523  */
524 static unsigned long bdi_position_ratio(struct backing_dev_info *bdi,
525                                         unsigned long thresh,
526                                         unsigned long bg_thresh,
527                                         unsigned long dirty,
528                                         unsigned long bdi_thresh,
529                                         unsigned long bdi_dirty)
530 {
531         unsigned long write_bw = bdi->avg_write_bandwidth;
532         unsigned long freerun = dirty_freerun_ceiling(thresh, bg_thresh);
533         unsigned long limit = hard_dirty_limit(thresh);
534         unsigned long x_intercept;
535         unsigned long setpoint;         /* dirty pages' target balance point */
536         unsigned long bdi_setpoint;
537         unsigned long span;
538         long long pos_ratio;            /* for scaling up/down the rate limit */
539         long x;
540
541         if (unlikely(dirty >= limit))
542                 return 0;
543
544         /*
545          * global setpoint
546          *
547          *                           setpoint - dirty 3
548          *        f(dirty) := 1.0 + (----------------)
549          *                           limit - setpoint
550          *
551          * it's a 3rd order polynomial that subjects to
552          *
553          * (1) f(freerun)  = 2.0 => rampup dirty_ratelimit reasonably fast
554          * (2) f(setpoint) = 1.0 => the balance point
555          * (3) f(limit)    = 0   => the hard limit
556          * (4) df/dx      <= 0   => negative feedback control
557          * (5) the closer to setpoint, the smaller |df/dx| (and the reverse)
558          *     => fast response on large errors; small oscillation near setpoint
559          */
560         setpoint = (freerun + limit) / 2;
561         x = div_s64((setpoint - dirty) << RATELIMIT_CALC_SHIFT,
562                     limit - setpoint + 1);
563         pos_ratio = x;
564         pos_ratio = pos_ratio * x >> RATELIMIT_CALC_SHIFT;
565         pos_ratio = pos_ratio * x >> RATELIMIT_CALC_SHIFT;
566         pos_ratio += 1 << RATELIMIT_CALC_SHIFT;
567
568         /*
569          * We have computed basic pos_ratio above based on global situation. If
570          * the bdi is over/under its share of dirty pages, we want to scale
571          * pos_ratio further down/up. That is done by the following mechanism.
572          */
573
574         /*
575          * bdi setpoint
576          *
577          *        f(bdi_dirty) := 1.0 + k * (bdi_dirty - bdi_setpoint)
578          *
579          *                        x_intercept - bdi_dirty
580          *                     := --------------------------
581          *                        x_intercept - bdi_setpoint
582          *
583          * The main bdi control line is a linear function that subjects to
584          *
585          * (1) f(bdi_setpoint) = 1.0
586          * (2) k = - 1 / (8 * write_bw)  (in single bdi case)
587          *     or equally: x_intercept = bdi_setpoint + 8 * write_bw
588          *
589          * For single bdi case, the dirty pages are observed to fluctuate
590          * regularly within range
591          *        [bdi_setpoint - write_bw/2, bdi_setpoint + write_bw/2]
592          * for various filesystems, where (2) can yield in a reasonable 12.5%
593          * fluctuation range for pos_ratio.
594          *
595          * For JBOD case, bdi_thresh (not bdi_dirty!) could fluctuate up to its
596          * own size, so move the slope over accordingly and choose a slope that
597          * yields 100% pos_ratio fluctuation on suddenly doubled bdi_thresh.
598          */
599         if (unlikely(bdi_thresh > thresh))
600                 bdi_thresh = thresh;
601         /*
602          * It's very possible that bdi_thresh is close to 0 not because the
603          * device is slow, but that it has remained inactive for long time.
604          * Honour such devices a reasonable good (hopefully IO efficient)
605          * threshold, so that the occasional writes won't be blocked and active
606          * writes can rampup the threshold quickly.
607          */
608         bdi_thresh = max(bdi_thresh, (limit - dirty) / 8);
609         /*
610          * scale global setpoint to bdi's:
611          *      bdi_setpoint = setpoint * bdi_thresh / thresh
612          */
613         x = div_u64((u64)bdi_thresh << 16, thresh + 1);
614         bdi_setpoint = setpoint * (u64)x >> 16;
615         /*
616          * Use span=(8*write_bw) in single bdi case as indicated by
617          * (thresh - bdi_thresh ~= 0) and transit to bdi_thresh in JBOD case.
618          *
619          *        bdi_thresh                    thresh - bdi_thresh
620          * span = ---------- * (8 * write_bw) + ------------------- * bdi_thresh
621          *          thresh                            thresh
622          */
623         span = (thresh - bdi_thresh + 8 * write_bw) * (u64)x >> 16;
624         x_intercept = bdi_setpoint + span;
625
626         if (bdi_dirty < x_intercept - span / 4) {
627                 pos_ratio = div_u64(pos_ratio * (x_intercept - bdi_dirty),
628                                     x_intercept - bdi_setpoint + 1);
629         } else
630                 pos_ratio /= 4;
631
632         /*
633          * bdi reserve area, safeguard against dirty pool underrun and disk idle
634          * It may push the desired control point of global dirty pages higher
635          * than setpoint.
636          */
637         x_intercept = bdi_thresh / 2;
638         if (bdi_dirty < x_intercept) {
639                 if (bdi_dirty > x_intercept / 8)
640                         pos_ratio = div_u64(pos_ratio * x_intercept, bdi_dirty);
641                 else
642                         pos_ratio *= 8;
643         }
644
645         return pos_ratio;
646 }
647
648 static void bdi_update_write_bandwidth(struct backing_dev_info *bdi,
649                                        unsigned long elapsed,
650                                        unsigned long written)
651 {
652         const unsigned long period = roundup_pow_of_two(3 * HZ);
653         unsigned long avg = bdi->avg_write_bandwidth;
654         unsigned long old = bdi->write_bandwidth;
655         u64 bw;
656
657         /*
658          * bw = written * HZ / elapsed
659          *
660          *                   bw * elapsed + write_bandwidth * (period - elapsed)
661          * write_bandwidth = ---------------------------------------------------
662          *                                          period
663          */
664         bw = written - bdi->written_stamp;
665         bw *= HZ;
666         if (unlikely(elapsed > period)) {
667                 do_div(bw, elapsed);
668                 avg = bw;
669                 goto out;
670         }
671         bw += (u64)bdi->write_bandwidth * (period - elapsed);
672         bw >>= ilog2(period);
673
674         /*
675          * one more level of smoothing, for filtering out sudden spikes
676          */
677         if (avg > old && old >= (unsigned long)bw)
678                 avg -= (avg - old) >> 3;
679
680         if (avg < old && old <= (unsigned long)bw)
681                 avg += (old - avg) >> 3;
682
683 out:
684         bdi->write_bandwidth = bw;
685         bdi->avg_write_bandwidth = avg;
686 }
687
688 /*
689  * The global dirtyable memory and dirty threshold could be suddenly knocked
690  * down by a large amount (eg. on the startup of KVM in a swapless system).
691  * This may throw the system into deep dirty exceeded state and throttle
692  * heavy/light dirtiers alike. To retain good responsiveness, maintain
693  * global_dirty_limit for tracking slowly down to the knocked down dirty
694  * threshold.
695  */
696 static void update_dirty_limit(unsigned long thresh, unsigned long dirty)
697 {
698         unsigned long limit = global_dirty_limit;
699
700         /*
701          * Follow up in one step.
702          */
703         if (limit < thresh) {
704                 limit = thresh;
705                 goto update;
706         }
707
708         /*
709          * Follow down slowly. Use the higher one as the target, because thresh
710          * may drop below dirty. This is exactly the reason to introduce
711          * global_dirty_limit which is guaranteed to lie above the dirty pages.
712          */
713         thresh = max(thresh, dirty);
714         if (limit > thresh) {
715                 limit -= (limit - thresh) >> 5;
716                 goto update;
717         }
718         return;
719 update:
720         global_dirty_limit = limit;
721 }
722
723 static void global_update_bandwidth(unsigned long thresh,
724                                     unsigned long dirty,
725                                     unsigned long now)
726 {
727         static DEFINE_SPINLOCK(dirty_lock);
728         static unsigned long update_time;
729
730         /*
731          * check locklessly first to optimize away locking for the most time
732          */
733         if (time_before(now, update_time + BANDWIDTH_INTERVAL))
734                 return;
735
736         spin_lock(&dirty_lock);
737         if (time_after_eq(now, update_time + BANDWIDTH_INTERVAL)) {
738                 update_dirty_limit(thresh, dirty);
739                 update_time = now;
740         }
741         spin_unlock(&dirty_lock);
742 }
743
744 /*
745  * Maintain bdi->dirty_ratelimit, the base dirty throttle rate.
746  *
747  * Normal bdi tasks will be curbed at or below it in long term.
748  * Obviously it should be around (write_bw / N) when there are N dd tasks.
749  */
750 static void bdi_update_dirty_ratelimit(struct backing_dev_info *bdi,
751                                        unsigned long thresh,
752                                        unsigned long bg_thresh,
753                                        unsigned long dirty,
754                                        unsigned long bdi_thresh,
755                                        unsigned long bdi_dirty,
756                                        unsigned long dirtied,
757                                        unsigned long elapsed)
758 {
759         unsigned long freerun = dirty_freerun_ceiling(thresh, bg_thresh);
760         unsigned long limit = hard_dirty_limit(thresh);
761         unsigned long setpoint = (freerun + limit) / 2;
762         unsigned long write_bw = bdi->avg_write_bandwidth;
763         unsigned long dirty_ratelimit = bdi->dirty_ratelimit;
764         unsigned long dirty_rate;
765         unsigned long task_ratelimit;
766         unsigned long balanced_dirty_ratelimit;
767         unsigned long pos_ratio;
768         unsigned long step;
769         unsigned long x;
770
771         /*
772          * The dirty rate will match the writeout rate in long term, except
773          * when dirty pages are truncated by userspace or re-dirtied by FS.
774          */
775         dirty_rate = (dirtied - bdi->dirtied_stamp) * HZ / elapsed;
776
777         pos_ratio = bdi_position_ratio(bdi, thresh, bg_thresh, dirty,
778                                        bdi_thresh, bdi_dirty);
779         /*
780          * task_ratelimit reflects each dd's dirty rate for the past 200ms.
781          */
782         task_ratelimit = (u64)dirty_ratelimit *
783                                         pos_ratio >> RATELIMIT_CALC_SHIFT;
784         task_ratelimit++; /* it helps rampup dirty_ratelimit from tiny values */
785
786         /*
787          * A linear estimation of the "balanced" throttle rate. The theory is,
788          * if there are N dd tasks, each throttled at task_ratelimit, the bdi's
789          * dirty_rate will be measured to be (N * task_ratelimit). So the below
790          * formula will yield the balanced rate limit (write_bw / N).
791          *
792          * Note that the expanded form is not a pure rate feedback:
793          *      rate_(i+1) = rate_(i) * (write_bw / dirty_rate)              (1)
794          * but also takes pos_ratio into account:
795          *      rate_(i+1) = rate_(i) * (write_bw / dirty_rate) * pos_ratio  (2)
796          *
797          * (1) is not realistic because pos_ratio also takes part in balancing
798          * the dirty rate.  Consider the state
799          *      pos_ratio = 0.5                                              (3)
800          *      rate = 2 * (write_bw / N)                                    (4)
801          * If (1) is used, it will stuck in that state! Because each dd will
802          * be throttled at
803          *      task_ratelimit = pos_ratio * rate = (write_bw / N)           (5)
804          * yielding
805          *      dirty_rate = N * task_ratelimit = write_bw                   (6)
806          * put (6) into (1) we get
807          *      rate_(i+1) = rate_(i)                                        (7)
808          *
809          * So we end up using (2) to always keep
810          *      rate_(i+1) ~= (write_bw / N)                                 (8)
811          * regardless of the value of pos_ratio. As long as (8) is satisfied,
812          * pos_ratio is able to drive itself to 1.0, which is not only where
813          * the dirty count meet the setpoint, but also where the slope of
814          * pos_ratio is most flat and hence task_ratelimit is least fluctuated.
815          */
816         balanced_dirty_ratelimit = div_u64((u64)task_ratelimit * write_bw,
817                                            dirty_rate | 1);
818
819         /*
820          * We could safely do this and return immediately:
821          *
822          *      bdi->dirty_ratelimit = balanced_dirty_ratelimit;
823          *
824          * However to get a more stable dirty_ratelimit, the below elaborated
825          * code makes use of task_ratelimit to filter out sigular points and
826          * limit the step size.
827          *
828          * The below code essentially only uses the relative value of
829          *
830          *      task_ratelimit - dirty_ratelimit
831          *      = (pos_ratio - 1) * dirty_ratelimit
832          *
833          * which reflects the direction and size of dirty position error.
834          */
835
836         /*
837          * dirty_ratelimit will follow balanced_dirty_ratelimit iff
838          * task_ratelimit is on the same side of dirty_ratelimit, too.
839          * For example, when
840          * - dirty_ratelimit > balanced_dirty_ratelimit
841          * - dirty_ratelimit > task_ratelimit (dirty pages are above setpoint)
842          * lowering dirty_ratelimit will help meet both the position and rate
843          * control targets. Otherwise, don't update dirty_ratelimit if it will
844          * only help meet the rate target. After all, what the users ultimately
845          * feel and care are stable dirty rate and small position error.
846          *
847          * |task_ratelimit - dirty_ratelimit| is used to limit the step size
848          * and filter out the sigular points of balanced_dirty_ratelimit. Which
849          * keeps jumping around randomly and can even leap far away at times
850          * due to the small 200ms estimation period of dirty_rate (we want to
851          * keep that period small to reduce time lags).
852          */
853         step = 0;
854         if (dirty < setpoint) {
855                 x = min(bdi->balanced_dirty_ratelimit,
856                          min(balanced_dirty_ratelimit, task_ratelimit));
857                 if (dirty_ratelimit < x)
858                         step = x - dirty_ratelimit;
859         } else {
860                 x = max(bdi->balanced_dirty_ratelimit,
861                          max(balanced_dirty_ratelimit, task_ratelimit));
862                 if (dirty_ratelimit > x)
863                         step = dirty_ratelimit - x;
864         }
865
866         /*
867          * Don't pursue 100% rate matching. It's impossible since the balanced
868          * rate itself is constantly fluctuating. So decrease the track speed
869          * when it gets close to the target. Helps eliminate pointless tremors.
870          */
871         step >>= dirty_ratelimit / (2 * step + 1);
872         /*
873          * Limit the tracking speed to avoid overshooting.
874          */
875         step = (step + 7) / 8;
876
877         if (dirty_ratelimit < balanced_dirty_ratelimit)
878                 dirty_ratelimit += step;
879         else
880                 dirty_ratelimit -= step;
881
882         bdi->dirty_ratelimit = max(dirty_ratelimit, 1UL);
883         bdi->balanced_dirty_ratelimit = balanced_dirty_ratelimit;
884
885         trace_bdi_dirty_ratelimit(bdi, dirty_rate, task_ratelimit);
886 }
887
888 void __bdi_update_bandwidth(struct backing_dev_info *bdi,
889                             unsigned long thresh,
890                             unsigned long bg_thresh,
891                             unsigned long dirty,
892                             unsigned long bdi_thresh,
893                             unsigned long bdi_dirty,
894                             unsigned long start_time)
895 {
896         unsigned long now = jiffies;
897         unsigned long elapsed = now - bdi->bw_time_stamp;
898         unsigned long dirtied;
899         unsigned long written;
900
901         /*
902          * rate-limit, only update once every 200ms.
903          */
904         if (elapsed < BANDWIDTH_INTERVAL)
905                 return;
906
907         dirtied = percpu_counter_read(&bdi->bdi_stat[BDI_DIRTIED]);
908         written = percpu_counter_read(&bdi->bdi_stat[BDI_WRITTEN]);
909
910         /*
911          * Skip quiet periods when disk bandwidth is under-utilized.
912          * (at least 1s idle time between two flusher runs)
913          */
914         if (elapsed > HZ && time_before(bdi->bw_time_stamp, start_time))
915                 goto snapshot;
916
917         if (thresh) {
918                 global_update_bandwidth(thresh, dirty, now);
919                 bdi_update_dirty_ratelimit(bdi, thresh, bg_thresh, dirty,
920                                            bdi_thresh, bdi_dirty,
921                                            dirtied, elapsed);
922         }
923         bdi_update_write_bandwidth(bdi, elapsed, written);
924
925 snapshot:
926         bdi->dirtied_stamp = dirtied;
927         bdi->written_stamp = written;
928         bdi->bw_time_stamp = now;
929 }
930
931 static void bdi_update_bandwidth(struct backing_dev_info *bdi,
932                                  unsigned long thresh,
933                                  unsigned long bg_thresh,
934                                  unsigned long dirty,
935                                  unsigned long bdi_thresh,
936                                  unsigned long bdi_dirty,
937                                  unsigned long start_time)
938 {
939         if (time_is_after_eq_jiffies(bdi->bw_time_stamp + BANDWIDTH_INTERVAL))
940                 return;
941         spin_lock(&bdi->wb.list_lock);
942         __bdi_update_bandwidth(bdi, thresh, bg_thresh, dirty,
943                                bdi_thresh, bdi_dirty, start_time);
944         spin_unlock(&bdi->wb.list_lock);
945 }
946
947 /*
948  * After a task dirtied this many pages, balance_dirty_pages_ratelimited_nr()
949  * will look to see if it needs to start dirty throttling.
950  *
951  * If dirty_poll_interval is too low, big NUMA machines will call the expensive
952  * global_page_state() too often. So scale it near-sqrt to the safety margin
953  * (the number of pages we may dirty without exceeding the dirty limits).
954  */
955 static unsigned long dirty_poll_interval(unsigned long dirty,
956                                          unsigned long thresh)
957 {
958         if (thresh > dirty)
959                 return 1UL << (ilog2(thresh - dirty) >> 1);
960
961         return 1;
962 }
963
964 static unsigned long bdi_max_pause(struct backing_dev_info *bdi,
965                                    unsigned long bdi_dirty)
966 {
967         unsigned long bw = bdi->avg_write_bandwidth;
968         unsigned long hi = ilog2(bw);
969         unsigned long lo = ilog2(bdi->dirty_ratelimit);
970         unsigned long t;
971
972         /* target for 20ms max pause on 1-dd case */
973         t = HZ / 50;
974
975         /*
976          * Scale up pause time for concurrent dirtiers in order to reduce CPU
977          * overheads.
978          *
979          * (N * 20ms) on 2^N concurrent tasks.
980          */
981         if (hi > lo)
982                 t += (hi - lo) * (20 * HZ) / 1024;
983
984         /*
985          * Limit pause time for small memory systems. If sleeping for too long
986          * time, a small pool of dirty/writeback pages may go empty and disk go
987          * idle.
988          *
989          * 8 serves as the safety ratio.
990          */
991         t = min(t, bdi_dirty * HZ / (8 * bw + 1));
992
993         /*
994          * The pause time will be settled within range (max_pause/4, max_pause).
995          * Apply a minimal value of 4 to get a non-zero max_pause/4.
996          */
997         return clamp_val(t, 4, MAX_PAUSE);
998 }
999
1000 /*
1001  * balance_dirty_pages() must be called by processes which are generating dirty
1002  * data.  It looks at the number of dirty pages in the machine and will force
1003  * the caller to wait once crossing the (background_thresh + dirty_thresh) / 2.
1004  * If we're over `background_thresh' then the writeback threads are woken to
1005  * perform some writeout.
1006  */
1007 static void balance_dirty_pages(struct address_space *mapping,
1008                                 unsigned long pages_dirtied)
1009 {
1010         unsigned long nr_reclaimable;   /* = file_dirty + unstable_nfs */
1011         unsigned long bdi_reclaimable;
1012         unsigned long nr_dirty;  /* = file_dirty + writeback + unstable_nfs */
1013         unsigned long bdi_dirty;
1014         unsigned long freerun;
1015         unsigned long background_thresh;
1016         unsigned long dirty_thresh;
1017         unsigned long bdi_thresh;
1018         long pause = 0;
1019         long uninitialized_var(max_pause);
1020         bool dirty_exceeded = false;
1021         unsigned long task_ratelimit;
1022         unsigned long uninitialized_var(dirty_ratelimit);
1023         unsigned long pos_ratio;
1024         struct backing_dev_info *bdi = mapping->backing_dev_info;
1025         unsigned long start_time = jiffies;
1026
1027         for (;;) {
1028                 /*
1029                  * Unstable writes are a feature of certain networked
1030                  * filesystems (i.e. NFS) in which data may have been
1031                  * written to the server's write cache, but has not yet
1032                  * been flushed to permanent storage.
1033                  */
1034                 nr_reclaimable = global_page_state(NR_FILE_DIRTY) +
1035                                         global_page_state(NR_UNSTABLE_NFS);
1036                 nr_dirty = nr_reclaimable + global_page_state(NR_WRITEBACK);
1037
1038                 global_dirty_limits(&background_thresh, &dirty_thresh);
1039
1040                 /*
1041                  * Throttle it only when the background writeback cannot
1042                  * catch-up. This avoids (excessively) small writeouts
1043                  * when the bdi limits are ramping up.
1044                  */
1045                 freerun = dirty_freerun_ceiling(dirty_thresh,
1046                                                 background_thresh);
1047                 if (nr_dirty <= freerun)
1048                         break;
1049
1050                 if (unlikely(!writeback_in_progress(bdi)))
1051                         bdi_start_background_writeback(bdi);
1052
1053                 /*
1054                  * bdi_thresh is not treated as some limiting factor as
1055                  * dirty_thresh, due to reasons
1056                  * - in JBOD setup, bdi_thresh can fluctuate a lot
1057                  * - in a system with HDD and USB key, the USB key may somehow
1058                  *   go into state (bdi_dirty >> bdi_thresh) either because
1059                  *   bdi_dirty starts high, or because bdi_thresh drops low.
1060                  *   In this case we don't want to hard throttle the USB key
1061                  *   dirtiers for 100 seconds until bdi_dirty drops under
1062                  *   bdi_thresh. Instead the auxiliary bdi control line in
1063                  *   bdi_position_ratio() will let the dirtier task progress
1064                  *   at some rate <= (write_bw / 2) for bringing down bdi_dirty.
1065                  */
1066                 bdi_thresh = bdi_dirty_limit(bdi, dirty_thresh);
1067
1068                 /*
1069                  * In order to avoid the stacked BDI deadlock we need
1070                  * to ensure we accurately count the 'dirty' pages when
1071                  * the threshold is low.
1072                  *
1073                  * Otherwise it would be possible to get thresh+n pages
1074                  * reported dirty, even though there are thresh-m pages
1075                  * actually dirty; with m+n sitting in the percpu
1076                  * deltas.
1077                  */
1078                 if (bdi_thresh < 2 * bdi_stat_error(bdi)) {
1079                         bdi_reclaimable = bdi_stat_sum(bdi, BDI_RECLAIMABLE);
1080                         bdi_dirty = bdi_reclaimable +
1081                                     bdi_stat_sum(bdi, BDI_WRITEBACK);
1082                 } else {
1083                         bdi_reclaimable = bdi_stat(bdi, BDI_RECLAIMABLE);
1084                         bdi_dirty = bdi_reclaimable +
1085                                     bdi_stat(bdi, BDI_WRITEBACK);
1086                 }
1087
1088                 dirty_exceeded = (bdi_dirty > bdi_thresh) ||
1089                                   (nr_dirty > dirty_thresh);
1090                 if (dirty_exceeded && !bdi->dirty_exceeded)
1091                         bdi->dirty_exceeded = 1;
1092
1093                 bdi_update_bandwidth(bdi, dirty_thresh, background_thresh,
1094                                      nr_dirty, bdi_thresh, bdi_dirty,
1095                                      start_time);
1096
1097                 max_pause = bdi_max_pause(bdi, bdi_dirty);
1098
1099                 dirty_ratelimit = bdi->dirty_ratelimit;
1100                 pos_ratio = bdi_position_ratio(bdi, dirty_thresh,
1101                                                background_thresh, nr_dirty,
1102                                                bdi_thresh, bdi_dirty);
1103                 task_ratelimit = ((u64)dirty_ratelimit * pos_ratio) >>
1104                                                         RATELIMIT_CALC_SHIFT;
1105                 if (unlikely(task_ratelimit == 0)) {
1106                         pause = max_pause;
1107                         goto pause;
1108                 }
1109                 pause = HZ * pages_dirtied / task_ratelimit;
1110                 if (unlikely(pause <= 0)) {
1111                         trace_balance_dirty_pages(bdi,
1112                                                   dirty_thresh,
1113                                                   background_thresh,
1114                                                   nr_dirty,
1115                                                   bdi_thresh,
1116                                                   bdi_dirty,
1117                                                   dirty_ratelimit,
1118                                                   task_ratelimit,
1119                                                   pages_dirtied,
1120                                                   pause,
1121                                                   start_time);
1122                         pause = 1; /* avoid resetting nr_dirtied_pause below */
1123                         break;
1124                 }
1125                 pause = min(pause, max_pause);
1126
1127 pause:
1128                 trace_balance_dirty_pages(bdi,
1129                                           dirty_thresh,
1130                                           background_thresh,
1131                                           nr_dirty,
1132                                           bdi_thresh,
1133                                           bdi_dirty,
1134                                           dirty_ratelimit,
1135                                           task_ratelimit,
1136                                           pages_dirtied,
1137                                           pause,
1138                                           start_time);
1139                 __set_current_state(TASK_KILLABLE);
1140                 io_schedule_timeout(pause);
1141
1142                 /*
1143                  * This is typically equal to (nr_dirty < dirty_thresh) and can
1144                  * also keep "1000+ dd on a slow USB stick" under control.
1145                  */
1146                 if (task_ratelimit)
1147                         break;
1148
1149                 /*
1150                  * In the case of an unresponding NFS server and the NFS dirty
1151                  * pages exceeds dirty_thresh, give the other good bdi's a pipe
1152                  * to go through, so that tasks on them still remain responsive.
1153                  *
1154                  * In theory 1 page is enough to keep the comsumer-producer
1155                  * pipe going: the flusher cleans 1 page => the task dirties 1
1156                  * more page. However bdi_dirty has accounting errors.  So use
1157                  * the larger and more IO friendly bdi_stat_error.
1158                  */
1159                 if (bdi_dirty <= bdi_stat_error(bdi))
1160                         break;
1161
1162                 if (fatal_signal_pending(current))
1163                         break;
1164         }
1165
1166         if (!dirty_exceeded && bdi->dirty_exceeded)
1167                 bdi->dirty_exceeded = 0;
1168
1169         current->nr_dirtied = 0;
1170         if (pause == 0) { /* in freerun area */
1171                 current->nr_dirtied_pause =
1172                                 dirty_poll_interval(nr_dirty, dirty_thresh);
1173         } else if (pause <= max_pause / 4 &&
1174                    pages_dirtied >= current->nr_dirtied_pause) {
1175                 current->nr_dirtied_pause = clamp_val(
1176                                         dirty_ratelimit * (max_pause / 2) / HZ,
1177                                         pages_dirtied + pages_dirtied / 8,
1178                                         pages_dirtied * 4);
1179         } else if (pause >= max_pause) {
1180                 current->nr_dirtied_pause = 1 | clamp_val(
1181                                         dirty_ratelimit * (max_pause / 2) / HZ,
1182                                         pages_dirtied / 4,
1183                                         pages_dirtied - pages_dirtied / 8);
1184         }
1185
1186         if (writeback_in_progress(bdi))
1187                 return;
1188
1189         /*
1190          * In laptop mode, we wait until hitting the higher threshold before
1191          * starting background writeout, and then write out all the way down
1192          * to the lower threshold.  So slow writers cause minimal disk activity.
1193          *
1194          * In normal mode, we start background writeout at the lower
1195          * background_thresh, to keep the amount of dirty memory low.
1196          */
1197         if (laptop_mode)
1198                 return;
1199
1200         if (nr_reclaimable > background_thresh)
1201                 bdi_start_background_writeback(bdi);
1202 }
1203
1204 void set_page_dirty_balance(struct page *page, int page_mkwrite)
1205 {
1206         if (set_page_dirty(page) || page_mkwrite) {
1207                 struct address_space *mapping = page_mapping(page);
1208
1209                 if (mapping)
1210                         balance_dirty_pages_ratelimited(mapping);
1211         }
1212 }
1213
1214 static DEFINE_PER_CPU(int, bdp_ratelimits);
1215
1216 /**
1217  * balance_dirty_pages_ratelimited_nr - balance dirty memory state
1218  * @mapping: address_space which was dirtied
1219  * @nr_pages_dirtied: number of pages which the caller has just dirtied
1220  *
1221  * Processes which are dirtying memory should call in here once for each page
1222  * which was newly dirtied.  The function will periodically check the system's
1223  * dirty state and will initiate writeback if needed.
1224  *
1225  * On really big machines, get_writeback_state is expensive, so try to avoid
1226  * calling it too often (ratelimiting).  But once we're over the dirty memory
1227  * limit we decrease the ratelimiting by a lot, to prevent individual processes
1228  * from overshooting the limit by (ratelimit_pages) each.
1229  */
1230 void balance_dirty_pages_ratelimited_nr(struct address_space *mapping,
1231                                         unsigned long nr_pages_dirtied)
1232 {
1233         struct backing_dev_info *bdi = mapping->backing_dev_info;
1234         int ratelimit;
1235         int *p;
1236
1237         if (!bdi_cap_account_dirty(bdi))
1238                 return;
1239
1240         ratelimit = current->nr_dirtied_pause;
1241         if (bdi->dirty_exceeded)
1242                 ratelimit = min(ratelimit, 32 >> (PAGE_SHIFT - 10));
1243
1244         current->nr_dirtied += nr_pages_dirtied;
1245
1246         preempt_disable();
1247         /*
1248          * This prevents one CPU to accumulate too many dirtied pages without
1249          * calling into balance_dirty_pages(), which can happen when there are
1250          * 1000+ tasks, all of them start dirtying pages at exactly the same
1251          * time, hence all honoured too large initial task->nr_dirtied_pause.
1252          */
1253         p =  &__get_cpu_var(bdp_ratelimits);
1254         if (unlikely(current->nr_dirtied >= ratelimit))
1255                 *p = 0;
1256         else {
1257                 *p += nr_pages_dirtied;
1258                 if (unlikely(*p >= ratelimit_pages)) {
1259                         *p = 0;
1260                         ratelimit = 0;
1261                 }
1262         }
1263         preempt_enable();
1264
1265         if (unlikely(current->nr_dirtied >= ratelimit))
1266                 balance_dirty_pages(mapping, current->nr_dirtied);
1267 }
1268 EXPORT_SYMBOL(balance_dirty_pages_ratelimited_nr);
1269
1270 void throttle_vm_writeout(gfp_t gfp_mask)
1271 {
1272         unsigned long background_thresh;
1273         unsigned long dirty_thresh;
1274
1275         for ( ; ; ) {
1276                 global_dirty_limits(&background_thresh, &dirty_thresh);
1277
1278                 /*
1279                  * Boost the allowable dirty threshold a bit for page
1280                  * allocators so they don't get DoS'ed by heavy writers
1281                  */
1282                 dirty_thresh += dirty_thresh / 10;      /* wheeee... */
1283
1284                 if (global_page_state(NR_UNSTABLE_NFS) +
1285                         global_page_state(NR_WRITEBACK) <= dirty_thresh)
1286                                 break;
1287                 congestion_wait(BLK_RW_ASYNC, HZ/10);
1288
1289                 /*
1290                  * The caller might hold locks which can prevent IO completion
1291                  * or progress in the filesystem.  So we cannot just sit here
1292                  * waiting for IO to complete.
1293                  */
1294                 if ((gfp_mask & (__GFP_FS|__GFP_IO)) != (__GFP_FS|__GFP_IO))
1295                         break;
1296         }
1297 }
1298
1299 /*
1300  * sysctl handler for /proc/sys/vm/dirty_writeback_centisecs
1301  */
1302 int dirty_writeback_centisecs_handler(ctl_table *table, int write,
1303         void __user *buffer, size_t *length, loff_t *ppos)
1304 {
1305         proc_dointvec(table, write, buffer, length, ppos);
1306         bdi_arm_supers_timer();
1307         return 0;
1308 }
1309
1310 #ifdef CONFIG_BLOCK
1311 void laptop_mode_timer_fn(unsigned long data)
1312 {
1313         struct request_queue *q = (struct request_queue *)data;
1314         int nr_pages = global_page_state(NR_FILE_DIRTY) +
1315                 global_page_state(NR_UNSTABLE_NFS);
1316
1317         /*
1318          * We want to write everything out, not just down to the dirty
1319          * threshold
1320          */
1321         if (bdi_has_dirty_io(&q->backing_dev_info))
1322                 bdi_start_writeback(&q->backing_dev_info, nr_pages,
1323                                         WB_REASON_LAPTOP_TIMER);
1324 }
1325
1326 /*
1327  * We've spun up the disk and we're in laptop mode: schedule writeback
1328  * of all dirty data a few seconds from now.  If the flush is already scheduled
1329  * then push it back - the user is still using the disk.
1330  */
1331 void laptop_io_completion(struct backing_dev_info *info)
1332 {
1333         mod_timer(&info->laptop_mode_wb_timer, jiffies + laptop_mode);
1334 }
1335
1336 /*
1337  * We're in laptop mode and we've just synced. The sync's writes will have
1338  * caused another writeback to be scheduled by laptop_io_completion.
1339  * Nothing needs to be written back anymore, so we unschedule the writeback.
1340  */
1341 void laptop_sync_completion(void)
1342 {
1343         struct backing_dev_info *bdi;
1344
1345         rcu_read_lock();
1346
1347         list_for_each_entry_rcu(bdi, &bdi_list, bdi_list)
1348                 del_timer(&bdi->laptop_mode_wb_timer);
1349
1350         rcu_read_unlock();
1351 }
1352 #endif
1353
1354 /*
1355  * If ratelimit_pages is too high then we can get into dirty-data overload
1356  * if a large number of processes all perform writes at the same time.
1357  * If it is too low then SMP machines will call the (expensive)
1358  * get_writeback_state too often.
1359  *
1360  * Here we set ratelimit_pages to a level which ensures that when all CPUs are
1361  * dirtying in parallel, we cannot go more than 3% (1/32) over the dirty memory
1362  * thresholds.
1363  */
1364
1365 void writeback_set_ratelimit(void)
1366 {
1367         unsigned long background_thresh;
1368         unsigned long dirty_thresh;
1369         global_dirty_limits(&background_thresh, &dirty_thresh);
1370         ratelimit_pages = dirty_thresh / (num_online_cpus() * 32);
1371         if (ratelimit_pages < 16)
1372                 ratelimit_pages = 16;
1373 }
1374
1375 static int __cpuinit
1376 ratelimit_handler(struct notifier_block *self, unsigned long u, void *v)
1377 {
1378         writeback_set_ratelimit();
1379         return NOTIFY_DONE;
1380 }
1381
1382 static struct notifier_block __cpuinitdata ratelimit_nb = {
1383         .notifier_call  = ratelimit_handler,
1384         .next           = NULL,
1385 };
1386
1387 /*
1388  * Called early on to tune the page writeback dirty limits.
1389  *
1390  * We used to scale dirty pages according to how total memory
1391  * related to pages that could be allocated for buffers (by
1392  * comparing nr_free_buffer_pages() to vm_total_pages.
1393  *
1394  * However, that was when we used "dirty_ratio" to scale with
1395  * all memory, and we don't do that any more. "dirty_ratio"
1396  * is now applied to total non-HIGHPAGE memory (by subtracting
1397  * totalhigh_pages from vm_total_pages), and as such we can't
1398  * get into the old insane situation any more where we had
1399  * large amounts of dirty pages compared to a small amount of
1400  * non-HIGHMEM memory.
1401  *
1402  * But we might still want to scale the dirty_ratio by how
1403  * much memory the box has..
1404  */
1405 void __init page_writeback_init(void)
1406 {
1407         int shift;
1408
1409         writeback_set_ratelimit();
1410         register_cpu_notifier(&ratelimit_nb);
1411
1412         shift = calc_period_shift();
1413         prop_descriptor_init(&vm_completions, shift);
1414 }
1415
1416 /**
1417  * tag_pages_for_writeback - tag pages to be written by write_cache_pages
1418  * @mapping: address space structure to write
1419  * @start: starting page index
1420  * @end: ending page index (inclusive)
1421  *
1422  * This function scans the page range from @start to @end (inclusive) and tags
1423  * all pages that have DIRTY tag set with a special TOWRITE tag. The idea is
1424  * that write_cache_pages (or whoever calls this function) will then use
1425  * TOWRITE tag to identify pages eligible for writeback.  This mechanism is
1426  * used to avoid livelocking of writeback by a process steadily creating new
1427  * dirty pages in the file (thus it is important for this function to be quick
1428  * so that it can tag pages faster than a dirtying process can create them).
1429  */
1430 /*
1431  * We tag pages in batches of WRITEBACK_TAG_BATCH to reduce tree_lock latency.
1432  */
1433 void tag_pages_for_writeback(struct address_space *mapping,
1434                              pgoff_t start, pgoff_t end)
1435 {
1436 #define WRITEBACK_TAG_BATCH 4096
1437         unsigned long tagged;
1438
1439         do {
1440                 spin_lock_irq(&mapping->tree_lock);
1441                 tagged = radix_tree_range_tag_if_tagged(&mapping->page_tree,
1442                                 &start, end, WRITEBACK_TAG_BATCH,
1443                                 PAGECACHE_TAG_DIRTY, PAGECACHE_TAG_TOWRITE);
1444                 spin_unlock_irq(&mapping->tree_lock);
1445                 WARN_ON_ONCE(tagged > WRITEBACK_TAG_BATCH);
1446                 cond_resched();
1447                 /* We check 'start' to handle wrapping when end == ~0UL */
1448         } while (tagged >= WRITEBACK_TAG_BATCH && start);
1449 }
1450 EXPORT_SYMBOL(tag_pages_for_writeback);
1451
1452 /**
1453  * write_cache_pages - walk the list of dirty pages of the given address space and write all of them.
1454  * @mapping: address space structure to write
1455  * @wbc: subtract the number of written pages from *@wbc->nr_to_write
1456  * @writepage: function called for each page
1457  * @data: data passed to writepage function
1458  *
1459  * If a page is already under I/O, write_cache_pages() skips it, even
1460  * if it's dirty.  This is desirable behaviour for memory-cleaning writeback,
1461  * but it is INCORRECT for data-integrity system calls such as fsync().  fsync()
1462  * and msync() need to guarantee that all the data which was dirty at the time
1463  * the call was made get new I/O started against them.  If wbc->sync_mode is
1464  * WB_SYNC_ALL then we were called for data integrity and we must wait for
1465  * existing IO to complete.
1466  *
1467  * To avoid livelocks (when other process dirties new pages), we first tag
1468  * pages which should be written back with TOWRITE tag and only then start
1469  * writing them. For data-integrity sync we have to be careful so that we do
1470  * not miss some pages (e.g., because some other process has cleared TOWRITE
1471  * tag we set). The rule we follow is that TOWRITE tag can be cleared only
1472  * by the process clearing the DIRTY tag (and submitting the page for IO).
1473  */
1474 int write_cache_pages(struct address_space *mapping,
1475                       struct writeback_control *wbc, writepage_t writepage,
1476                       void *data)
1477 {
1478         int ret = 0;
1479         int done = 0;
1480         struct pagevec pvec;
1481         int nr_pages;
1482         pgoff_t uninitialized_var(writeback_index);
1483         pgoff_t index;
1484         pgoff_t end;            /* Inclusive */
1485         pgoff_t done_index;
1486         int cycled;
1487         int range_whole = 0;
1488         int tag;
1489
1490         pagevec_init(&pvec, 0);
1491         if (wbc->range_cyclic) {
1492                 writeback_index = mapping->writeback_index; /* prev offset */
1493                 index = writeback_index;
1494                 if (index == 0)
1495                         cycled = 1;
1496                 else
1497                         cycled = 0;
1498                 end = -1;
1499         } else {
1500                 index = wbc->range_start >> PAGE_CACHE_SHIFT;
1501                 end = wbc->range_end >> PAGE_CACHE_SHIFT;
1502                 if (wbc->range_start == 0 && wbc->range_end == LLONG_MAX)
1503                         range_whole = 1;
1504                 cycled = 1; /* ignore range_cyclic tests */
1505         }
1506         if (wbc->sync_mode == WB_SYNC_ALL || wbc->tagged_writepages)
1507                 tag = PAGECACHE_TAG_TOWRITE;
1508         else
1509                 tag = PAGECACHE_TAG_DIRTY;
1510 retry:
1511         if (wbc->sync_mode == WB_SYNC_ALL || wbc->tagged_writepages)
1512                 tag_pages_for_writeback(mapping, index, end);
1513         done_index = index;
1514         while (!done && (index <= end)) {
1515                 int i;
1516
1517                 nr_pages = pagevec_lookup_tag(&pvec, mapping, &index, tag,
1518                               min(end - index, (pgoff_t)PAGEVEC_SIZE-1) + 1);
1519                 if (nr_pages == 0)
1520                         break;
1521
1522                 for (i = 0; i < nr_pages; i++) {
1523                         struct page *page = pvec.pages[i];
1524
1525                         /*
1526                          * At this point, the page may be truncated or
1527                          * invalidated (changing page->mapping to NULL), or
1528                          * even swizzled back from swapper_space to tmpfs file
1529                          * mapping. However, page->index will not change
1530                          * because we have a reference on the page.
1531                          */
1532                         if (page->index > end) {
1533                                 /*
1534                                  * can't be range_cyclic (1st pass) because
1535                                  * end == -1 in that case.
1536                                  */
1537                                 done = 1;
1538                                 break;
1539                         }
1540
1541                         done_index = page->index;
1542
1543                         lock_page(page);
1544
1545                         /*
1546                          * Page truncated or invalidated. We can freely skip it
1547                          * then, even for data integrity operations: the page
1548                          * has disappeared concurrently, so there could be no
1549                          * real expectation of this data interity operation
1550                          * even if there is now a new, dirty page at the same
1551                          * pagecache address.
1552                          */
1553                         if (unlikely(page->mapping != mapping)) {
1554 continue_unlock:
1555                                 unlock_page(page);
1556                                 continue;
1557                         }
1558
1559                         if (!PageDirty(page)) {
1560                                 /* someone wrote it for us */
1561                                 goto continue_unlock;
1562                         }
1563
1564                         if (PageWriteback(page)) {
1565                                 if (wbc->sync_mode != WB_SYNC_NONE)
1566                                         wait_on_page_writeback(page);
1567                                 else
1568                                         goto continue_unlock;
1569                         }
1570
1571                         BUG_ON(PageWriteback(page));
1572                         if (!clear_page_dirty_for_io(page))
1573                                 goto continue_unlock;
1574
1575                         trace_wbc_writepage(wbc, mapping->backing_dev_info);
1576                         ret = (*writepage)(page, wbc, data);
1577                         if (unlikely(ret)) {
1578                                 if (ret == AOP_WRITEPAGE_ACTIVATE) {
1579                                         unlock_page(page);
1580                                         ret = 0;
1581                                 } else {
1582                                         /*
1583                                          * done_index is set past this page,
1584                                          * so media errors will not choke
1585                                          * background writeout for the entire
1586                                          * file. This has consequences for
1587                                          * range_cyclic semantics (ie. it may
1588                                          * not be suitable for data integrity
1589                                          * writeout).
1590                                          */
1591                                         done_index = page->index + 1;
1592                                         done = 1;
1593                                         break;
1594                                 }
1595                         }
1596
1597                         /*
1598                          * We stop writing back only if we are not doing
1599                          * integrity sync. In case of integrity sync we have to
1600                          * keep going until we have written all the pages
1601                          * we tagged for writeback prior to entering this loop.
1602                          */
1603                         if (--wbc->nr_to_write <= 0 &&
1604                             wbc->sync_mode == WB_SYNC_NONE) {
1605                                 done = 1;
1606                                 break;
1607                         }
1608                 }
1609                 pagevec_release(&pvec);
1610                 cond_resched();
1611         }
1612         if (!cycled && !done) {
1613                 /*
1614                  * range_cyclic:
1615                  * We hit the last page and there is more work to be done: wrap
1616                  * back to the start of the file
1617                  */
1618                 cycled = 1;
1619                 index = 0;
1620                 end = writeback_index - 1;
1621                 goto retry;
1622         }
1623         if (wbc->range_cyclic || (range_whole && wbc->nr_to_write > 0))
1624                 mapping->writeback_index = done_index;
1625
1626         return ret;
1627 }
1628 EXPORT_SYMBOL(write_cache_pages);
1629
1630 /*
1631  * Function used by generic_writepages to call the real writepage
1632  * function and set the mapping flags on error
1633  */
1634 static int __writepage(struct page *page, struct writeback_control *wbc,
1635                        void *data)
1636 {
1637         struct address_space *mapping = data;
1638         int ret = mapping->a_ops->writepage(page, wbc);
1639         mapping_set_error(mapping, ret);
1640         return ret;
1641 }
1642
1643 /**
1644  * generic_writepages - walk the list of dirty pages of the given address space and writepage() all of them.
1645  * @mapping: address space structure to write
1646  * @wbc: subtract the number of written pages from *@wbc->nr_to_write
1647  *
1648  * This is a library function, which implements the writepages()
1649  * address_space_operation.
1650  */
1651 int generic_writepages(struct address_space *mapping,
1652                        struct writeback_control *wbc)
1653 {
1654         struct blk_plug plug;
1655         int ret;
1656
1657         /* deal with chardevs and other special file */
1658         if (!mapping->a_ops->writepage)
1659                 return 0;
1660
1661         blk_start_plug(&plug);
1662         ret = write_cache_pages(mapping, wbc, __writepage, mapping);
1663         blk_finish_plug(&plug);
1664         return ret;
1665 }
1666
1667 EXPORT_SYMBOL(generic_writepages);
1668
1669 int do_writepages(struct address_space *mapping, struct writeback_control *wbc)
1670 {
1671         int ret;
1672
1673         if (wbc->nr_to_write <= 0)
1674                 return 0;
1675         if (mapping->a_ops->writepages)
1676                 ret = mapping->a_ops->writepages(mapping, wbc);
1677         else
1678                 ret = generic_writepages(mapping, wbc);
1679         return ret;
1680 }
1681
1682 /**
1683  * write_one_page - write out a single page and optionally wait on I/O
1684  * @page: the page to write
1685  * @wait: if true, wait on writeout
1686  *
1687  * The page must be locked by the caller and will be unlocked upon return.
1688  *
1689  * write_one_page() returns a negative error code if I/O failed.
1690  */
1691 int write_one_page(struct page *page, int wait)
1692 {
1693         struct address_space *mapping = page->mapping;
1694         int ret = 0;
1695         struct writeback_control wbc = {
1696                 .sync_mode = WB_SYNC_ALL,
1697                 .nr_to_write = 1,
1698         };
1699
1700         BUG_ON(!PageLocked(page));
1701
1702         if (wait)
1703                 wait_on_page_writeback(page);
1704
1705         if (clear_page_dirty_for_io(page)) {
1706                 page_cache_get(page);
1707                 ret = mapping->a_ops->writepage(page, &wbc);
1708                 if (ret == 0 && wait) {
1709                         wait_on_page_writeback(page);
1710                         if (PageError(page))
1711                                 ret = -EIO;
1712                 }
1713                 page_cache_release(page);
1714         } else {
1715                 unlock_page(page);
1716         }
1717         return ret;
1718 }
1719 EXPORT_SYMBOL(write_one_page);
1720
1721 /*
1722  * For address_spaces which do not use buffers nor write back.
1723  */
1724 int __set_page_dirty_no_writeback(struct page *page)
1725 {
1726         if (!PageDirty(page))
1727                 return !TestSetPageDirty(page);
1728         return 0;
1729 }
1730
1731 /*
1732  * Helper function for set_page_dirty family.
1733  * NOTE: This relies on being atomic wrt interrupts.
1734  */
1735 void account_page_dirtied(struct page *page, struct address_space *mapping)
1736 {
1737         if (mapping_cap_account_dirty(mapping)) {
1738                 __inc_zone_page_state(page, NR_FILE_DIRTY);
1739                 __inc_zone_page_state(page, NR_DIRTIED);
1740                 __inc_bdi_stat(mapping->backing_dev_info, BDI_RECLAIMABLE);
1741                 __inc_bdi_stat(mapping->backing_dev_info, BDI_DIRTIED);
1742                 task_io_account_write(PAGE_CACHE_SIZE);
1743         }
1744 }
1745 EXPORT_SYMBOL(account_page_dirtied);
1746
1747 /*
1748  * Helper function for set_page_writeback family.
1749  * NOTE: Unlike account_page_dirtied this does not rely on being atomic
1750  * wrt interrupts.
1751  */
1752 void account_page_writeback(struct page *page)
1753 {
1754         inc_zone_page_state(page, NR_WRITEBACK);
1755 }
1756 EXPORT_SYMBOL(account_page_writeback);
1757
1758 /*
1759  * For address_spaces which do not use buffers.  Just tag the page as dirty in
1760  * its radix tree.
1761  *
1762  * This is also used when a single buffer is being dirtied: we want to set the
1763  * page dirty in that case, but not all the buffers.  This is a "bottom-up"
1764  * dirtying, whereas __set_page_dirty_buffers() is a "top-down" dirtying.
1765  *
1766  * Most callers have locked the page, which pins the address_space in memory.
1767  * But zap_pte_range() does not lock the page, however in that case the
1768  * mapping is pinned by the vma's ->vm_file reference.
1769  *
1770  * We take care to handle the case where the page was truncated from the
1771  * mapping by re-checking page_mapping() inside tree_lock.
1772  */
1773 int __set_page_dirty_nobuffers(struct page *page)
1774 {
1775         if (!TestSetPageDirty(page)) {
1776                 struct address_space *mapping = page_mapping(page);
1777                 struct address_space *mapping2;
1778
1779                 if (!mapping)
1780                         return 1;
1781
1782                 spin_lock_irq(&mapping->tree_lock);
1783                 mapping2 = page_mapping(page);
1784                 if (mapping2) { /* Race with truncate? */
1785                         BUG_ON(mapping2 != mapping);
1786                         WARN_ON_ONCE(!PagePrivate(page) && !PageUptodate(page));
1787                         account_page_dirtied(page, mapping);
1788                         radix_tree_tag_set(&mapping->page_tree,
1789                                 page_index(page), PAGECACHE_TAG_DIRTY);
1790                 }
1791                 spin_unlock_irq(&mapping->tree_lock);
1792                 if (mapping->host) {
1793                         /* !PageAnon && !swapper_space */
1794                         __mark_inode_dirty(mapping->host, I_DIRTY_PAGES);
1795                 }
1796                 return 1;
1797         }
1798         return 0;
1799 }
1800 EXPORT_SYMBOL(__set_page_dirty_nobuffers);
1801
1802 /*
1803  * When a writepage implementation decides that it doesn't want to write this
1804  * page for some reason, it should redirty the locked page via
1805  * redirty_page_for_writepage() and it should then unlock the page and return 0
1806  */
1807 int redirty_page_for_writepage(struct writeback_control *wbc, struct page *page)
1808 {
1809         wbc->pages_skipped++;
1810         return __set_page_dirty_nobuffers(page);
1811 }
1812 EXPORT_SYMBOL(redirty_page_for_writepage);
1813
1814 /*
1815  * Dirty a page.
1816  *
1817  * For pages with a mapping this should be done under the page lock
1818  * for the benefit of asynchronous memory errors who prefer a consistent
1819  * dirty state. This rule can be broken in some special cases,
1820  * but should be better not to.
1821  *
1822  * If the mapping doesn't provide a set_page_dirty a_op, then
1823  * just fall through and assume that it wants buffer_heads.
1824  */
1825 int set_page_dirty(struct page *page)
1826 {
1827         struct address_space *mapping = page_mapping(page);
1828
1829         if (likely(mapping)) {
1830                 int (*spd)(struct page *) = mapping->a_ops->set_page_dirty;
1831                 /*
1832                  * readahead/lru_deactivate_page could remain
1833                  * PG_readahead/PG_reclaim due to race with end_page_writeback
1834                  * About readahead, if the page is written, the flags would be
1835                  * reset. So no problem.
1836                  * About lru_deactivate_page, if the page is redirty, the flag
1837                  * will be reset. So no problem. but if the page is used by readahead
1838                  * it will confuse readahead and make it restart the size rampup
1839                  * process. But it's a trivial problem.
1840                  */
1841                 ClearPageReclaim(page);
1842 #ifdef CONFIG_BLOCK
1843                 if (!spd)
1844                         spd = __set_page_dirty_buffers;
1845 #endif
1846                 return (*spd)(page);
1847         }
1848         if (!PageDirty(page)) {
1849                 if (!TestSetPageDirty(page))
1850                         return 1;
1851         }
1852         return 0;
1853 }
1854 EXPORT_SYMBOL(set_page_dirty);
1855
1856 /*
1857  * set_page_dirty() is racy if the caller has no reference against
1858  * page->mapping->host, and if the page is unlocked.  This is because another
1859  * CPU could truncate the page off the mapping and then free the mapping.
1860  *
1861  * Usually, the page _is_ locked, or the caller is a user-space process which
1862  * holds a reference on the inode by having an open file.
1863  *
1864  * In other cases, the page should be locked before running set_page_dirty().
1865  */
1866 int set_page_dirty_lock(struct page *page)
1867 {
1868         int ret;
1869
1870         lock_page(page);
1871         ret = set_page_dirty(page);
1872         unlock_page(page);
1873         return ret;
1874 }
1875 EXPORT_SYMBOL(set_page_dirty_lock);
1876
1877 /*
1878  * Clear a page's dirty flag, while caring for dirty memory accounting.
1879  * Returns true if the page was previously dirty.
1880  *
1881  * This is for preparing to put the page under writeout.  We leave the page
1882  * tagged as dirty in the radix tree so that a concurrent write-for-sync
1883  * can discover it via a PAGECACHE_TAG_DIRTY walk.  The ->writepage
1884  * implementation will run either set_page_writeback() or set_page_dirty(),
1885  * at which stage we bring the page's dirty flag and radix-tree dirty tag
1886  * back into sync.
1887  *
1888  * This incoherency between the page's dirty flag and radix-tree tag is
1889  * unfortunate, but it only exists while the page is locked.
1890  */
1891 int clear_page_dirty_for_io(struct page *page)
1892 {
1893         struct address_space *mapping = page_mapping(page);
1894
1895         BUG_ON(!PageLocked(page));
1896
1897         if (mapping && mapping_cap_account_dirty(mapping)) {
1898                 /*
1899                  * Yes, Virginia, this is indeed insane.
1900                  *
1901                  * We use this sequence to make sure that
1902                  *  (a) we account for dirty stats properly
1903                  *  (b) we tell the low-level filesystem to
1904                  *      mark the whole page dirty if it was
1905                  *      dirty in a pagetable. Only to then
1906                  *  (c) clean the page again and return 1 to
1907                  *      cause the writeback.
1908                  *
1909                  * This way we avoid all nasty races with the
1910                  * dirty bit in multiple places and clearing
1911                  * them concurrently from different threads.
1912                  *
1913                  * Note! Normally the "set_page_dirty(page)"
1914                  * has no effect on the actual dirty bit - since
1915                  * that will already usually be set. But we
1916                  * need the side effects, and it can help us
1917                  * avoid races.
1918                  *
1919                  * We basically use the page "master dirty bit"
1920                  * as a serialization point for all the different
1921                  * threads doing their things.
1922                  */
1923                 if (page_mkclean(page))
1924                         set_page_dirty(page);
1925                 /*
1926                  * We carefully synchronise fault handlers against
1927                  * installing a dirty pte and marking the page dirty
1928                  * at this point. We do this by having them hold the
1929                  * page lock at some point after installing their
1930                  * pte, but before marking the page dirty.
1931                  * Pages are always locked coming in here, so we get
1932                  * the desired exclusion. See mm/memory.c:do_wp_page()
1933                  * for more comments.
1934                  */
1935                 if (TestClearPageDirty(page)) {
1936                         dec_zone_page_state(page, NR_FILE_DIRTY);
1937                         dec_bdi_stat(mapping->backing_dev_info,
1938                                         BDI_RECLAIMABLE);
1939                         return 1;
1940                 }
1941                 return 0;
1942         }
1943         return TestClearPageDirty(page);
1944 }
1945 EXPORT_SYMBOL(clear_page_dirty_for_io);
1946
1947 int test_clear_page_writeback(struct page *page)
1948 {
1949         struct address_space *mapping = page_mapping(page);
1950         int ret;
1951
1952         if (mapping) {
1953                 struct backing_dev_info *bdi = mapping->backing_dev_info;
1954                 unsigned long flags;
1955
1956                 spin_lock_irqsave(&mapping->tree_lock, flags);
1957                 ret = TestClearPageWriteback(page);
1958                 if (ret) {
1959                         radix_tree_tag_clear(&mapping->page_tree,
1960                                                 page_index(page),
1961                                                 PAGECACHE_TAG_WRITEBACK);
1962                         if (bdi_cap_account_writeback(bdi)) {
1963                                 __dec_bdi_stat(bdi, BDI_WRITEBACK);
1964                                 __bdi_writeout_inc(bdi);
1965                         }
1966                 }
1967                 spin_unlock_irqrestore(&mapping->tree_lock, flags);
1968         } else {
1969                 ret = TestClearPageWriteback(page);
1970         }
1971         if (ret) {
1972                 dec_zone_page_state(page, NR_WRITEBACK);
1973                 inc_zone_page_state(page, NR_WRITTEN);
1974         }
1975         return ret;
1976 }
1977
1978 int test_set_page_writeback(struct page *page)
1979 {
1980         struct address_space *mapping = page_mapping(page);
1981         int ret;
1982
1983         if (mapping) {
1984                 struct backing_dev_info *bdi = mapping->backing_dev_info;
1985                 unsigned long flags;
1986
1987                 spin_lock_irqsave(&mapping->tree_lock, flags);
1988                 ret = TestSetPageWriteback(page);
1989                 if (!ret) {
1990                         radix_tree_tag_set(&mapping->page_tree,
1991                                                 page_index(page),
1992                                                 PAGECACHE_TAG_WRITEBACK);
1993                         if (bdi_cap_account_writeback(bdi))
1994                                 __inc_bdi_stat(bdi, BDI_WRITEBACK);
1995                 }
1996                 if (!PageDirty(page))
1997                         radix_tree_tag_clear(&mapping->page_tree,
1998                                                 page_index(page),
1999                                                 PAGECACHE_TAG_DIRTY);
2000                 radix_tree_tag_clear(&mapping->page_tree,
2001                                      page_index(page),
2002                                      PAGECACHE_TAG_TOWRITE);
2003                 spin_unlock_irqrestore(&mapping->tree_lock, flags);
2004         } else {
2005                 ret = TestSetPageWriteback(page);
2006         }
2007         if (!ret)
2008                 account_page_writeback(page);
2009         return ret;
2010
2011 }
2012 EXPORT_SYMBOL(test_set_page_writeback);
2013
2014 /*
2015  * Return true if any of the pages in the mapping are marked with the
2016  * passed tag.
2017  */
2018 int mapping_tagged(struct address_space *mapping, int tag)
2019 {
2020         return radix_tree_tagged(&mapping->page_tree, tag);
2021 }
2022 EXPORT_SYMBOL(mapping_tagged);