tcp: enforce tcp_min_snd_mss in tcp_mtu_probing()
[pandora-kernel.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>
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 = div64_s64(((s64)setpoint - (s64)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 = div64_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          * @written may have decreased due to account_page_redirty().
665          * Avoid underflowing @bw calculation.
666          */
667         bw = written - min(written, bdi->written_stamp);
668         bw *= HZ;
669         if (unlikely(elapsed > period)) {
670                 do_div(bw, elapsed);
671                 avg = bw;
672                 goto out;
673         }
674         bw += (u64)bdi->write_bandwidth * (period - elapsed);
675         bw >>= ilog2(period);
676
677         /*
678          * one more level of smoothing, for filtering out sudden spikes
679          */
680         if (avg > old && old >= (unsigned long)bw)
681                 avg -= (avg - old) >> 3;
682
683         if (avg < old && old <= (unsigned long)bw)
684                 avg += (old - avg) >> 3;
685
686 out:
687         bdi->write_bandwidth = bw;
688         bdi->avg_write_bandwidth = avg;
689 }
690
691 /*
692  * The global dirtyable memory and dirty threshold could be suddenly knocked
693  * down by a large amount (eg. on the startup of KVM in a swapless system).
694  * This may throw the system into deep dirty exceeded state and throttle
695  * heavy/light dirtiers alike. To retain good responsiveness, maintain
696  * global_dirty_limit for tracking slowly down to the knocked down dirty
697  * threshold.
698  */
699 static void update_dirty_limit(unsigned long thresh, unsigned long dirty)
700 {
701         unsigned long limit = global_dirty_limit;
702
703         /*
704          * Follow up in one step.
705          */
706         if (limit < thresh) {
707                 limit = thresh;
708                 goto update;
709         }
710
711         /*
712          * Follow down slowly. Use the higher one as the target, because thresh
713          * may drop below dirty. This is exactly the reason to introduce
714          * global_dirty_limit which is guaranteed to lie above the dirty pages.
715          */
716         thresh = max(thresh, dirty);
717         if (limit > thresh) {
718                 limit -= (limit - thresh) >> 5;
719                 goto update;
720         }
721         return;
722 update:
723         global_dirty_limit = limit;
724 }
725
726 static void global_update_bandwidth(unsigned long thresh,
727                                     unsigned long dirty,
728                                     unsigned long now)
729 {
730         static DEFINE_SPINLOCK(dirty_lock);
731         static unsigned long update_time = INITIAL_JIFFIES;
732
733         /*
734          * check locklessly first to optimize away locking for the most time
735          */
736         if (time_before(now, update_time + BANDWIDTH_INTERVAL))
737                 return;
738
739         spin_lock(&dirty_lock);
740         if (time_after_eq(now, update_time + BANDWIDTH_INTERVAL)) {
741                 update_dirty_limit(thresh, dirty);
742                 update_time = now;
743         }
744         spin_unlock(&dirty_lock);
745 }
746
747 /*
748  * Maintain bdi->dirty_ratelimit, the base dirty throttle rate.
749  *
750  * Normal bdi tasks will be curbed at or below it in long term.
751  * Obviously it should be around (write_bw / N) when there are N dd tasks.
752  */
753 static void bdi_update_dirty_ratelimit(struct backing_dev_info *bdi,
754                                        unsigned long thresh,
755                                        unsigned long bg_thresh,
756                                        unsigned long dirty,
757                                        unsigned long bdi_thresh,
758                                        unsigned long bdi_dirty,
759                                        unsigned long dirtied,
760                                        unsigned long elapsed)
761 {
762         unsigned long freerun = dirty_freerun_ceiling(thresh, bg_thresh);
763         unsigned long limit = hard_dirty_limit(thresh);
764         unsigned long setpoint = (freerun + limit) / 2;
765         unsigned long write_bw = bdi->avg_write_bandwidth;
766         unsigned long dirty_ratelimit = bdi->dirty_ratelimit;
767         unsigned long dirty_rate;
768         unsigned long task_ratelimit;
769         unsigned long balanced_dirty_ratelimit;
770         unsigned long pos_ratio;
771         unsigned long step;
772         unsigned long x;
773
774         /*
775          * The dirty rate will match the writeout rate in long term, except
776          * when dirty pages are truncated by userspace or re-dirtied by FS.
777          */
778         dirty_rate = (dirtied - bdi->dirtied_stamp) * HZ / elapsed;
779
780         pos_ratio = bdi_position_ratio(bdi, thresh, bg_thresh, dirty,
781                                        bdi_thresh, bdi_dirty);
782         /*
783          * task_ratelimit reflects each dd's dirty rate for the past 200ms.
784          */
785         task_ratelimit = (u64)dirty_ratelimit *
786                                         pos_ratio >> RATELIMIT_CALC_SHIFT;
787         task_ratelimit++; /* it helps rampup dirty_ratelimit from tiny values */
788
789         /*
790          * A linear estimation of the "balanced" throttle rate. The theory is,
791          * if there are N dd tasks, each throttled at task_ratelimit, the bdi's
792          * dirty_rate will be measured to be (N * task_ratelimit). So the below
793          * formula will yield the balanced rate limit (write_bw / N).
794          *
795          * Note that the expanded form is not a pure rate feedback:
796          *      rate_(i+1) = rate_(i) * (write_bw / dirty_rate)              (1)
797          * but also takes pos_ratio into account:
798          *      rate_(i+1) = rate_(i) * (write_bw / dirty_rate) * pos_ratio  (2)
799          *
800          * (1) is not realistic because pos_ratio also takes part in balancing
801          * the dirty rate.  Consider the state
802          *      pos_ratio = 0.5                                              (3)
803          *      rate = 2 * (write_bw / N)                                    (4)
804          * If (1) is used, it will stuck in that state! Because each dd will
805          * be throttled at
806          *      task_ratelimit = pos_ratio * rate = (write_bw / N)           (5)
807          * yielding
808          *      dirty_rate = N * task_ratelimit = write_bw                   (6)
809          * put (6) into (1) we get
810          *      rate_(i+1) = rate_(i)                                        (7)
811          *
812          * So we end up using (2) to always keep
813          *      rate_(i+1) ~= (write_bw / N)                                 (8)
814          * regardless of the value of pos_ratio. As long as (8) is satisfied,
815          * pos_ratio is able to drive itself to 1.0, which is not only where
816          * the dirty count meet the setpoint, but also where the slope of
817          * pos_ratio is most flat and hence task_ratelimit is least fluctuated.
818          */
819         balanced_dirty_ratelimit = div_u64((u64)task_ratelimit * write_bw,
820                                            dirty_rate | 1);
821
822         /*
823          * We could safely do this and return immediately:
824          *
825          *      bdi->dirty_ratelimit = balanced_dirty_ratelimit;
826          *
827          * However to get a more stable dirty_ratelimit, the below elaborated
828          * code makes use of task_ratelimit to filter out sigular points and
829          * limit the step size.
830          *
831          * The below code essentially only uses the relative value of
832          *
833          *      task_ratelimit - dirty_ratelimit
834          *      = (pos_ratio - 1) * dirty_ratelimit
835          *
836          * which reflects the direction and size of dirty position error.
837          */
838
839         /*
840          * dirty_ratelimit will follow balanced_dirty_ratelimit iff
841          * task_ratelimit is on the same side of dirty_ratelimit, too.
842          * For example, when
843          * - dirty_ratelimit > balanced_dirty_ratelimit
844          * - dirty_ratelimit > task_ratelimit (dirty pages are above setpoint)
845          * lowering dirty_ratelimit will help meet both the position and rate
846          * control targets. Otherwise, don't update dirty_ratelimit if it will
847          * only help meet the rate target. After all, what the users ultimately
848          * feel and care are stable dirty rate and small position error.
849          *
850          * |task_ratelimit - dirty_ratelimit| is used to limit the step size
851          * and filter out the sigular points of balanced_dirty_ratelimit. Which
852          * keeps jumping around randomly and can even leap far away at times
853          * due to the small 200ms estimation period of dirty_rate (we want to
854          * keep that period small to reduce time lags).
855          */
856         step = 0;
857         if (dirty < setpoint) {
858                 x = min(bdi->balanced_dirty_ratelimit,
859                          min(balanced_dirty_ratelimit, task_ratelimit));
860                 if (dirty_ratelimit < x)
861                         step = x - dirty_ratelimit;
862         } else {
863                 x = max(bdi->balanced_dirty_ratelimit,
864                          max(balanced_dirty_ratelimit, task_ratelimit));
865                 if (dirty_ratelimit > x)
866                         step = dirty_ratelimit - x;
867         }
868
869         /*
870          * Don't pursue 100% rate matching. It's impossible since the balanced
871          * rate itself is constantly fluctuating. So decrease the track speed
872          * when it gets close to the target. Helps eliminate pointless tremors.
873          */
874         step >>= dirty_ratelimit / (2 * step + 1);
875         /*
876          * Limit the tracking speed to avoid overshooting.
877          */
878         step = (step + 7) / 8;
879
880         if (dirty_ratelimit < balanced_dirty_ratelimit)
881                 dirty_ratelimit += step;
882         else
883                 dirty_ratelimit -= step;
884
885         bdi->dirty_ratelimit = max(dirty_ratelimit, 1UL);
886         bdi->balanced_dirty_ratelimit = balanced_dirty_ratelimit;
887
888         trace_bdi_dirty_ratelimit(bdi, dirty_rate, task_ratelimit);
889 }
890
891 void __bdi_update_bandwidth(struct backing_dev_info *bdi,
892                             unsigned long thresh,
893                             unsigned long bg_thresh,
894                             unsigned long dirty,
895                             unsigned long bdi_thresh,
896                             unsigned long bdi_dirty,
897                             unsigned long start_time)
898 {
899         unsigned long now = jiffies;
900         unsigned long elapsed = now - bdi->bw_time_stamp;
901         unsigned long dirtied;
902         unsigned long written;
903
904         /*
905          * rate-limit, only update once every 200ms.
906          */
907         if (elapsed < BANDWIDTH_INTERVAL)
908                 return;
909
910         dirtied = percpu_counter_read(&bdi->bdi_stat[BDI_DIRTIED]);
911         written = percpu_counter_read(&bdi->bdi_stat[BDI_WRITTEN]);
912
913         /*
914          * Skip quiet periods when disk bandwidth is under-utilized.
915          * (at least 1s idle time between two flusher runs)
916          */
917         if (elapsed > HZ && time_before(bdi->bw_time_stamp, start_time))
918                 goto snapshot;
919
920         if (thresh) {
921                 global_update_bandwidth(thresh, dirty, now);
922                 bdi_update_dirty_ratelimit(bdi, thresh, bg_thresh, dirty,
923                                            bdi_thresh, bdi_dirty,
924                                            dirtied, elapsed);
925         }
926         bdi_update_write_bandwidth(bdi, elapsed, written);
927
928 snapshot:
929         bdi->dirtied_stamp = dirtied;
930         bdi->written_stamp = written;
931         bdi->bw_time_stamp = now;
932 }
933
934 static void bdi_update_bandwidth(struct backing_dev_info *bdi,
935                                  unsigned long thresh,
936                                  unsigned long bg_thresh,
937                                  unsigned long dirty,
938                                  unsigned long bdi_thresh,
939                                  unsigned long bdi_dirty,
940                                  unsigned long start_time)
941 {
942         if (time_is_after_eq_jiffies(bdi->bw_time_stamp + BANDWIDTH_INTERVAL))
943                 return;
944         spin_lock(&bdi->wb.list_lock);
945         __bdi_update_bandwidth(bdi, thresh, bg_thresh, dirty,
946                                bdi_thresh, bdi_dirty, start_time);
947         spin_unlock(&bdi->wb.list_lock);
948 }
949
950 /*
951  * After a task dirtied this many pages, balance_dirty_pages_ratelimited_nr()
952  * will look to see if it needs to start dirty throttling.
953  *
954  * If dirty_poll_interval is too low, big NUMA machines will call the expensive
955  * global_page_state() too often. So scale it near-sqrt to the safety margin
956  * (the number of pages we may dirty without exceeding the dirty limits).
957  */
958 static unsigned long dirty_poll_interval(unsigned long dirty,
959                                          unsigned long thresh)
960 {
961         if (thresh > dirty)
962                 return 1UL << (ilog2(thresh - dirty) >> 1);
963
964         return 1;
965 }
966
967 static unsigned long bdi_max_pause(struct backing_dev_info *bdi,
968                                    unsigned long bdi_dirty)
969 {
970         unsigned long bw = bdi->avg_write_bandwidth;
971         unsigned long hi = ilog2(bw);
972         unsigned long lo = ilog2(bdi->dirty_ratelimit);
973         unsigned long t;
974
975         /* target for 20ms max pause on 1-dd case */
976         t = HZ / 50;
977
978         /*
979          * Scale up pause time for concurrent dirtiers in order to reduce CPU
980          * overheads.
981          *
982          * (N * 20ms) on 2^N concurrent tasks.
983          */
984         if (hi > lo)
985                 t += (hi - lo) * (20 * HZ) / 1024;
986
987         /*
988          * Limit pause time for small memory systems. If sleeping for too long
989          * time, a small pool of dirty/writeback pages may go empty and disk go
990          * idle.
991          *
992          * 8 serves as the safety ratio.
993          */
994         t = min(t, bdi_dirty * HZ / (8 * bw + 1));
995
996         /*
997          * The pause time will be settled within range (max_pause/4, max_pause).
998          * Apply a minimal value of 4 to get a non-zero max_pause/4.
999          */
1000         return clamp_val(t, 4, MAX_PAUSE);
1001 }
1002
1003 /*
1004  * balance_dirty_pages() must be called by processes which are generating dirty
1005  * data.  It looks at the number of dirty pages in the machine and will force
1006  * the caller to wait once crossing the (background_thresh + dirty_thresh) / 2.
1007  * If we're over `background_thresh' then the writeback threads are woken to
1008  * perform some writeout.
1009  */
1010 static void balance_dirty_pages(struct address_space *mapping,
1011                                 unsigned long pages_dirtied)
1012 {
1013         unsigned long nr_reclaimable;   /* = file_dirty + unstable_nfs */
1014         unsigned long bdi_reclaimable;
1015         unsigned long nr_dirty;  /* = file_dirty + writeback + unstable_nfs */
1016         unsigned long bdi_dirty;
1017         unsigned long freerun;
1018         unsigned long background_thresh;
1019         unsigned long dirty_thresh;
1020         unsigned long bdi_thresh;
1021         long pause = 0;
1022         long uninitialized_var(max_pause);
1023         bool dirty_exceeded = false;
1024         unsigned long task_ratelimit;
1025         unsigned long uninitialized_var(dirty_ratelimit);
1026         unsigned long pos_ratio;
1027         struct backing_dev_info *bdi = mapping->backing_dev_info;
1028         unsigned long start_time = jiffies;
1029
1030         for (;;) {
1031                 /*
1032                  * Unstable writes are a feature of certain networked
1033                  * filesystems (i.e. NFS) in which data may have been
1034                  * written to the server's write cache, but has not yet
1035                  * been flushed to permanent storage.
1036                  */
1037                 nr_reclaimable = global_page_state(NR_FILE_DIRTY) +
1038                                         global_page_state(NR_UNSTABLE_NFS);
1039                 nr_dirty = nr_reclaimable + global_page_state(NR_WRITEBACK);
1040
1041                 global_dirty_limits(&background_thresh, &dirty_thresh);
1042
1043                 /*
1044                  * Throttle it only when the background writeback cannot
1045                  * catch-up. This avoids (excessively) small writeouts
1046                  * when the bdi limits are ramping up.
1047                  */
1048                 freerun = dirty_freerun_ceiling(dirty_thresh,
1049                                                 background_thresh);
1050                 if (nr_dirty <= freerun)
1051                         break;
1052
1053                 if (unlikely(!writeback_in_progress(bdi)))
1054                         bdi_start_background_writeback(bdi);
1055
1056                 /*
1057                  * bdi_thresh is not treated as some limiting factor as
1058                  * dirty_thresh, due to reasons
1059                  * - in JBOD setup, bdi_thresh can fluctuate a lot
1060                  * - in a system with HDD and USB key, the USB key may somehow
1061                  *   go into state (bdi_dirty >> bdi_thresh) either because
1062                  *   bdi_dirty starts high, or because bdi_thresh drops low.
1063                  *   In this case we don't want to hard throttle the USB key
1064                  *   dirtiers for 100 seconds until bdi_dirty drops under
1065                  *   bdi_thresh. Instead the auxiliary bdi control line in
1066                  *   bdi_position_ratio() will let the dirtier task progress
1067                  *   at some rate <= (write_bw / 2) for bringing down bdi_dirty.
1068                  */
1069                 bdi_thresh = bdi_dirty_limit(bdi, dirty_thresh);
1070
1071                 /*
1072                  * In order to avoid the stacked BDI deadlock we need
1073                  * to ensure we accurately count the 'dirty' pages when
1074                  * the threshold is low.
1075                  *
1076                  * Otherwise it would be possible to get thresh+n pages
1077                  * reported dirty, even though there are thresh-m pages
1078                  * actually dirty; with m+n sitting in the percpu
1079                  * deltas.
1080                  */
1081                 if (bdi_thresh < 2 * bdi_stat_error(bdi)) {
1082                         bdi_reclaimable = bdi_stat_sum(bdi, BDI_RECLAIMABLE);
1083                         bdi_dirty = bdi_reclaimable +
1084                                     bdi_stat_sum(bdi, BDI_WRITEBACK);
1085                 } else {
1086                         bdi_reclaimable = bdi_stat(bdi, BDI_RECLAIMABLE);
1087                         bdi_dirty = bdi_reclaimable +
1088                                     bdi_stat(bdi, BDI_WRITEBACK);
1089                 }
1090
1091                 dirty_exceeded = (bdi_dirty > bdi_thresh) ||
1092                                   (nr_dirty > dirty_thresh);
1093                 if (dirty_exceeded && !bdi->dirty_exceeded)
1094                         bdi->dirty_exceeded = 1;
1095
1096                 bdi_update_bandwidth(bdi, dirty_thresh, background_thresh,
1097                                      nr_dirty, bdi_thresh, bdi_dirty,
1098                                      start_time);
1099
1100                 max_pause = bdi_max_pause(bdi, bdi_dirty);
1101
1102                 dirty_ratelimit = bdi->dirty_ratelimit;
1103                 pos_ratio = bdi_position_ratio(bdi, dirty_thresh,
1104                                                background_thresh, nr_dirty,
1105                                                bdi_thresh, bdi_dirty);
1106                 task_ratelimit = ((u64)dirty_ratelimit * pos_ratio) >>
1107                                                         RATELIMIT_CALC_SHIFT;
1108                 if (unlikely(task_ratelimit == 0)) {
1109                         pause = max_pause;
1110                         goto pause;
1111                 }
1112                 pause = HZ * pages_dirtied / task_ratelimit;
1113                 if (unlikely(pause <= 0)) {
1114                         trace_balance_dirty_pages(bdi,
1115                                                   dirty_thresh,
1116                                                   background_thresh,
1117                                                   nr_dirty,
1118                                                   bdi_thresh,
1119                                                   bdi_dirty,
1120                                                   dirty_ratelimit,
1121                                                   task_ratelimit,
1122                                                   pages_dirtied,
1123                                                   pause,
1124                                                   start_time);
1125                         pause = 1; /* avoid resetting nr_dirtied_pause below */
1126                         break;
1127                 }
1128                 pause = min(pause, max_pause);
1129
1130 pause:
1131                 trace_balance_dirty_pages(bdi,
1132                                           dirty_thresh,
1133                                           background_thresh,
1134                                           nr_dirty,
1135                                           bdi_thresh,
1136                                           bdi_dirty,
1137                                           dirty_ratelimit,
1138                                           task_ratelimit,
1139                                           pages_dirtied,
1140                                           pause,
1141                                           start_time);
1142                 __set_current_state(TASK_KILLABLE);
1143                 io_schedule_timeout(pause);
1144
1145                 /*
1146                  * This is typically equal to (nr_dirty < dirty_thresh) and can
1147                  * also keep "1000+ dd on a slow USB stick" under control.
1148                  */
1149                 if (task_ratelimit)
1150                         break;
1151
1152                 /*
1153                  * In the case of an unresponding NFS server and the NFS dirty
1154                  * pages exceeds dirty_thresh, give the other good bdi's a pipe
1155                  * to go through, so that tasks on them still remain responsive.
1156                  *
1157                  * In theory 1 page is enough to keep the comsumer-producer
1158                  * pipe going: the flusher cleans 1 page => the task dirties 1
1159                  * more page. However bdi_dirty has accounting errors.  So use
1160                  * the larger and more IO friendly bdi_stat_error.
1161                  */
1162                 if (bdi_dirty <= bdi_stat_error(bdi))
1163                         break;
1164
1165                 if (fatal_signal_pending(current))
1166                         break;
1167         }
1168
1169         if (!dirty_exceeded && bdi->dirty_exceeded)
1170                 bdi->dirty_exceeded = 0;
1171
1172         current->nr_dirtied = 0;
1173         if (pause == 0) { /* in freerun area */
1174                 current->nr_dirtied_pause =
1175                                 dirty_poll_interval(nr_dirty, dirty_thresh);
1176         } else if (pause <= max_pause / 4 &&
1177                    pages_dirtied >= current->nr_dirtied_pause) {
1178                 current->nr_dirtied_pause = clamp_val(
1179                                         dirty_ratelimit * (max_pause / 2) / HZ,
1180                                         pages_dirtied + pages_dirtied / 8,
1181                                         pages_dirtied * 4);
1182         } else if (pause >= max_pause) {
1183                 current->nr_dirtied_pause = 1 | clamp_val(
1184                                         dirty_ratelimit * (max_pause / 2) / HZ,
1185                                         pages_dirtied / 4,
1186                                         pages_dirtied - pages_dirtied / 8);
1187         }
1188
1189         if (writeback_in_progress(bdi))
1190                 return;
1191
1192         /*
1193          * In laptop mode, we wait until hitting the higher threshold before
1194          * starting background writeout, and then write out all the way down
1195          * to the lower threshold.  So slow writers cause minimal disk activity.
1196          *
1197          * In normal mode, we start background writeout at the lower
1198          * background_thresh, to keep the amount of dirty memory low.
1199          */
1200         if (laptop_mode)
1201                 return;
1202
1203         if (nr_reclaimable > background_thresh)
1204                 bdi_start_background_writeback(bdi);
1205 }
1206
1207 static DEFINE_PER_CPU(int, bdp_ratelimits);
1208
1209 /**
1210  * balance_dirty_pages_ratelimited_nr - balance dirty memory state
1211  * @mapping: address_space which was dirtied
1212  * @nr_pages_dirtied: number of pages which the caller has just dirtied
1213  *
1214  * Processes which are dirtying memory should call in here once for each page
1215  * which was newly dirtied.  The function will periodically check the system's
1216  * dirty state and will initiate writeback if needed.
1217  *
1218  * On really big machines, get_writeback_state is expensive, so try to avoid
1219  * calling it too often (ratelimiting).  But once we're over the dirty memory
1220  * limit we decrease the ratelimiting by a lot, to prevent individual processes
1221  * from overshooting the limit by (ratelimit_pages) each.
1222  */
1223 void balance_dirty_pages_ratelimited_nr(struct address_space *mapping,
1224                                         unsigned long nr_pages_dirtied)
1225 {
1226         struct backing_dev_info *bdi = mapping->backing_dev_info;
1227         int ratelimit;
1228         int *p;
1229
1230         if (!bdi_cap_account_dirty(bdi))
1231                 return;
1232
1233         ratelimit = current->nr_dirtied_pause;
1234         if (bdi->dirty_exceeded)
1235                 ratelimit = min(ratelimit, 32 >> (PAGE_SHIFT - 10));
1236
1237         current->nr_dirtied += nr_pages_dirtied;
1238
1239         preempt_disable();
1240         /*
1241          * This prevents one CPU to accumulate too many dirtied pages without
1242          * calling into balance_dirty_pages(), which can happen when there are
1243          * 1000+ tasks, all of them start dirtying pages at exactly the same
1244          * time, hence all honoured too large initial task->nr_dirtied_pause.
1245          */
1246         p =  &__get_cpu_var(bdp_ratelimits);
1247         if (unlikely(current->nr_dirtied >= ratelimit))
1248                 *p = 0;
1249         else {
1250                 *p += nr_pages_dirtied;
1251                 if (unlikely(*p >= ratelimit_pages)) {
1252                         *p = 0;
1253                         ratelimit = 0;
1254                 }
1255         }
1256         preempt_enable();
1257
1258         if (unlikely(current->nr_dirtied >= ratelimit))
1259                 balance_dirty_pages(mapping, current->nr_dirtied);
1260 }
1261 EXPORT_SYMBOL(balance_dirty_pages_ratelimited_nr);
1262
1263 void throttle_vm_writeout(gfp_t gfp_mask)
1264 {
1265         unsigned long background_thresh;
1266         unsigned long dirty_thresh;
1267
1268         for ( ; ; ) {
1269                 global_dirty_limits(&background_thresh, &dirty_thresh);
1270
1271                 /*
1272                  * Boost the allowable dirty threshold a bit for page
1273                  * allocators so they don't get DoS'ed by heavy writers
1274                  */
1275                 dirty_thresh += dirty_thresh / 10;      /* wheeee... */
1276
1277                 if (global_page_state(NR_UNSTABLE_NFS) +
1278                         global_page_state(NR_WRITEBACK) <= dirty_thresh)
1279                                 break;
1280                 congestion_wait(BLK_RW_ASYNC, HZ/10);
1281
1282                 /*
1283                  * The caller might hold locks which can prevent IO completion
1284                  * or progress in the filesystem.  So we cannot just sit here
1285                  * waiting for IO to complete.
1286                  */
1287                 if ((gfp_mask & (__GFP_FS|__GFP_IO)) != (__GFP_FS|__GFP_IO))
1288                         break;
1289         }
1290 }
1291
1292 /*
1293  * sysctl handler for /proc/sys/vm/dirty_writeback_centisecs
1294  */
1295 int dirty_writeback_centisecs_handler(ctl_table *table, int write,
1296         void __user *buffer, size_t *length, loff_t *ppos)
1297 {
1298         proc_dointvec(table, write, buffer, length, ppos);
1299         bdi_arm_supers_timer();
1300         return 0;
1301 }
1302
1303 #ifdef CONFIG_BLOCK
1304 void laptop_mode_timer_fn(unsigned long data)
1305 {
1306         struct request_queue *q = (struct request_queue *)data;
1307         int nr_pages = global_page_state(NR_FILE_DIRTY) +
1308                 global_page_state(NR_UNSTABLE_NFS);
1309
1310         /*
1311          * We want to write everything out, not just down to the dirty
1312          * threshold
1313          */
1314         if (bdi_has_dirty_io(&q->backing_dev_info))
1315                 bdi_start_writeback(&q->backing_dev_info, nr_pages,
1316                                         WB_REASON_LAPTOP_TIMER);
1317 }
1318
1319 /*
1320  * We've spun up the disk and we're in laptop mode: schedule writeback
1321  * of all dirty data a few seconds from now.  If the flush is already scheduled
1322  * then push it back - the user is still using the disk.
1323  */
1324 void laptop_io_completion(struct backing_dev_info *info)
1325 {
1326         mod_timer(&info->laptop_mode_wb_timer, jiffies + laptop_mode);
1327 }
1328
1329 /*
1330  * We're in laptop mode and we've just synced. The sync's writes will have
1331  * caused another writeback to be scheduled by laptop_io_completion.
1332  * Nothing needs to be written back anymore, so we unschedule the writeback.
1333  */
1334 void laptop_sync_completion(void)
1335 {
1336         struct backing_dev_info *bdi;
1337
1338         rcu_read_lock();
1339
1340         list_for_each_entry_rcu(bdi, &bdi_list, bdi_list)
1341                 del_timer(&bdi->laptop_mode_wb_timer);
1342
1343         rcu_read_unlock();
1344 }
1345 #endif
1346
1347 /*
1348  * If ratelimit_pages is too high then we can get into dirty-data overload
1349  * if a large number of processes all perform writes at the same time.
1350  * If it is too low then SMP machines will call the (expensive)
1351  * get_writeback_state too often.
1352  *
1353  * Here we set ratelimit_pages to a level which ensures that when all CPUs are
1354  * dirtying in parallel, we cannot go more than 3% (1/32) over the dirty memory
1355  * thresholds.
1356  */
1357
1358 void writeback_set_ratelimit(void)
1359 {
1360         unsigned long background_thresh;
1361         unsigned long dirty_thresh;
1362         global_dirty_limits(&background_thresh, &dirty_thresh);
1363         ratelimit_pages = dirty_thresh / (num_online_cpus() * 32);
1364         if (ratelimit_pages < 16)
1365                 ratelimit_pages = 16;
1366 }
1367
1368 static int __cpuinit
1369 ratelimit_handler(struct notifier_block *self, unsigned long u, void *v)
1370 {
1371         writeback_set_ratelimit();
1372         return NOTIFY_DONE;
1373 }
1374
1375 static struct notifier_block __cpuinitdata ratelimit_nb = {
1376         .notifier_call  = ratelimit_handler,
1377         .next           = NULL,
1378 };
1379
1380 /*
1381  * Called early on to tune the page writeback dirty limits.
1382  *
1383  * We used to scale dirty pages according to how total memory
1384  * related to pages that could be allocated for buffers (by
1385  * comparing nr_free_buffer_pages() to vm_total_pages.
1386  *
1387  * However, that was when we used "dirty_ratio" to scale with
1388  * all memory, and we don't do that any more. "dirty_ratio"
1389  * is now applied to total non-HIGHPAGE memory (by subtracting
1390  * totalhigh_pages from vm_total_pages), and as such we can't
1391  * get into the old insane situation any more where we had
1392  * large amounts of dirty pages compared to a small amount of
1393  * non-HIGHMEM memory.
1394  *
1395  * But we might still want to scale the dirty_ratio by how
1396  * much memory the box has..
1397  */
1398 void __init page_writeback_init(void)
1399 {
1400         int shift;
1401
1402         writeback_set_ratelimit();
1403         register_cpu_notifier(&ratelimit_nb);
1404
1405         shift = calc_period_shift();
1406         prop_descriptor_init(&vm_completions, shift);
1407 }
1408
1409 /**
1410  * tag_pages_for_writeback - tag pages to be written by write_cache_pages
1411  * @mapping: address space structure to write
1412  * @start: starting page index
1413  * @end: ending page index (inclusive)
1414  *
1415  * This function scans the page range from @start to @end (inclusive) and tags
1416  * all pages that have DIRTY tag set with a special TOWRITE tag. The idea is
1417  * that write_cache_pages (or whoever calls this function) will then use
1418  * TOWRITE tag to identify pages eligible for writeback.  This mechanism is
1419  * used to avoid livelocking of writeback by a process steadily creating new
1420  * dirty pages in the file (thus it is important for this function to be quick
1421  * so that it can tag pages faster than a dirtying process can create them).
1422  */
1423 /*
1424  * We tag pages in batches of WRITEBACK_TAG_BATCH to reduce tree_lock latency.
1425  */
1426 void tag_pages_for_writeback(struct address_space *mapping,
1427                              pgoff_t start, pgoff_t end)
1428 {
1429 #define WRITEBACK_TAG_BATCH 4096
1430         unsigned long tagged;
1431
1432         do {
1433                 spin_lock_irq(&mapping->tree_lock);
1434                 tagged = radix_tree_range_tag_if_tagged(&mapping->page_tree,
1435                                 &start, end, WRITEBACK_TAG_BATCH,
1436                                 PAGECACHE_TAG_DIRTY, PAGECACHE_TAG_TOWRITE);
1437                 spin_unlock_irq(&mapping->tree_lock);
1438                 WARN_ON_ONCE(tagged > WRITEBACK_TAG_BATCH);
1439                 cond_resched();
1440                 /* We check 'start' to handle wrapping when end == ~0UL */
1441         } while (tagged >= WRITEBACK_TAG_BATCH && start);
1442 }
1443 EXPORT_SYMBOL(tag_pages_for_writeback);
1444
1445 /**
1446  * write_cache_pages - walk the list of dirty pages of the given address space and write all of them.
1447  * @mapping: address space structure to write
1448  * @wbc: subtract the number of written pages from *@wbc->nr_to_write
1449  * @writepage: function called for each page
1450  * @data: data passed to writepage function
1451  *
1452  * If a page is already under I/O, write_cache_pages() skips it, even
1453  * if it's dirty.  This is desirable behaviour for memory-cleaning writeback,
1454  * but it is INCORRECT for data-integrity system calls such as fsync().  fsync()
1455  * and msync() need to guarantee that all the data which was dirty at the time
1456  * the call was made get new I/O started against them.  If wbc->sync_mode is
1457  * WB_SYNC_ALL then we were called for data integrity and we must wait for
1458  * existing IO to complete.
1459  *
1460  * To avoid livelocks (when other process dirties new pages), we first tag
1461  * pages which should be written back with TOWRITE tag and only then start
1462  * writing them. For data-integrity sync we have to be careful so that we do
1463  * not miss some pages (e.g., because some other process has cleared TOWRITE
1464  * tag we set). The rule we follow is that TOWRITE tag can be cleared only
1465  * by the process clearing the DIRTY tag (and submitting the page for IO).
1466  */
1467 int write_cache_pages(struct address_space *mapping,
1468                       struct writeback_control *wbc, writepage_t writepage,
1469                       void *data)
1470 {
1471         int ret = 0;
1472         int done = 0;
1473         struct pagevec pvec;
1474         int nr_pages;
1475         pgoff_t uninitialized_var(writeback_index);
1476         pgoff_t index;
1477         pgoff_t end;            /* Inclusive */
1478         pgoff_t done_index;
1479         int cycled;
1480         int range_whole = 0;
1481         int tag;
1482
1483         pagevec_init(&pvec, 0);
1484         if (wbc->range_cyclic) {
1485                 writeback_index = mapping->writeback_index; /* prev offset */
1486                 index = writeback_index;
1487                 if (index == 0)
1488                         cycled = 1;
1489                 else
1490                         cycled = 0;
1491                 end = -1;
1492         } else {
1493                 index = wbc->range_start >> PAGE_CACHE_SHIFT;
1494                 end = wbc->range_end >> PAGE_CACHE_SHIFT;
1495                 if (wbc->range_start == 0 && wbc->range_end == LLONG_MAX)
1496                         range_whole = 1;
1497                 cycled = 1; /* ignore range_cyclic tests */
1498         }
1499         if (wbc->sync_mode == WB_SYNC_ALL || wbc->tagged_writepages)
1500                 tag = PAGECACHE_TAG_TOWRITE;
1501         else
1502                 tag = PAGECACHE_TAG_DIRTY;
1503 retry:
1504         if (wbc->sync_mode == WB_SYNC_ALL || wbc->tagged_writepages)
1505                 tag_pages_for_writeback(mapping, index, end);
1506         done_index = index;
1507         while (!done && (index <= end)) {
1508                 int i;
1509
1510                 nr_pages = pagevec_lookup_tag(&pvec, mapping, &index, tag,
1511                               min(end - index, (pgoff_t)PAGEVEC_SIZE-1) + 1);
1512                 if (nr_pages == 0)
1513                         break;
1514
1515                 for (i = 0; i < nr_pages; i++) {
1516                         struct page *page = pvec.pages[i];
1517
1518                         /*
1519                          * At this point, the page may be truncated or
1520                          * invalidated (changing page->mapping to NULL), or
1521                          * even swizzled back from swapper_space to tmpfs file
1522                          * mapping. However, page->index will not change
1523                          * because we have a reference on the page.
1524                          */
1525                         if (page->index > end) {
1526                                 /*
1527                                  * can't be range_cyclic (1st pass) because
1528                                  * end == -1 in that case.
1529                                  */
1530                                 done = 1;
1531                                 break;
1532                         }
1533
1534                         done_index = page->index;
1535
1536                         lock_page(page);
1537
1538                         /*
1539                          * Page truncated or invalidated. We can freely skip it
1540                          * then, even for data integrity operations: the page
1541                          * has disappeared concurrently, so there could be no
1542                          * real expectation of this data interity operation
1543                          * even if there is now a new, dirty page at the same
1544                          * pagecache address.
1545                          */
1546                         if (unlikely(page->mapping != mapping)) {
1547 continue_unlock:
1548                                 unlock_page(page);
1549                                 continue;
1550                         }
1551
1552                         if (!PageDirty(page)) {
1553                                 /* someone wrote it for us */
1554                                 goto continue_unlock;
1555                         }
1556
1557                         if (PageWriteback(page)) {
1558                                 if (wbc->sync_mode != WB_SYNC_NONE)
1559                                         wait_on_page_writeback(page);
1560                                 else
1561                                         goto continue_unlock;
1562                         }
1563
1564                         BUG_ON(PageWriteback(page));
1565                         if (!clear_page_dirty_for_io(page))
1566                                 goto continue_unlock;
1567
1568                         trace_wbc_writepage(wbc, mapping->backing_dev_info);
1569                         ret = (*writepage)(page, wbc, data);
1570                         if (unlikely(ret)) {
1571                                 if (ret == AOP_WRITEPAGE_ACTIVATE) {
1572                                         unlock_page(page);
1573                                         ret = 0;
1574                                 } else {
1575                                         /*
1576                                          * done_index is set past this page,
1577                                          * so media errors will not choke
1578                                          * background writeout for the entire
1579                                          * file. This has consequences for
1580                                          * range_cyclic semantics (ie. it may
1581                                          * not be suitable for data integrity
1582                                          * writeout).
1583                                          */
1584                                         done_index = page->index + 1;
1585                                         done = 1;
1586                                         break;
1587                                 }
1588                         }
1589
1590                         /*
1591                          * We stop writing back only if we are not doing
1592                          * integrity sync. In case of integrity sync we have to
1593                          * keep going until we have written all the pages
1594                          * we tagged for writeback prior to entering this loop.
1595                          */
1596                         if (--wbc->nr_to_write <= 0 &&
1597                             wbc->sync_mode == WB_SYNC_NONE) {
1598                                 done = 1;
1599                                 break;
1600                         }
1601                 }
1602                 pagevec_release(&pvec);
1603                 cond_resched();
1604         }
1605         if (!cycled && !done) {
1606                 /*
1607                  * range_cyclic:
1608                  * We hit the last page and there is more work to be done: wrap
1609                  * back to the start of the file
1610                  */
1611                 cycled = 1;
1612                 index = 0;
1613                 end = writeback_index - 1;
1614                 goto retry;
1615         }
1616         if (wbc->range_cyclic || (range_whole && wbc->nr_to_write > 0))
1617                 mapping->writeback_index = done_index;
1618
1619         return ret;
1620 }
1621 EXPORT_SYMBOL(write_cache_pages);
1622
1623 /*
1624  * Function used by generic_writepages to call the real writepage
1625  * function and set the mapping flags on error
1626  */
1627 static int __writepage(struct page *page, struct writeback_control *wbc,
1628                        void *data)
1629 {
1630         struct address_space *mapping = data;
1631         int ret = mapping->a_ops->writepage(page, wbc);
1632         mapping_set_error(mapping, ret);
1633         return ret;
1634 }
1635
1636 /**
1637  * generic_writepages - walk the list of dirty pages of the given address space and writepage() all of them.
1638  * @mapping: address space structure to write
1639  * @wbc: subtract the number of written pages from *@wbc->nr_to_write
1640  *
1641  * This is a library function, which implements the writepages()
1642  * address_space_operation.
1643  */
1644 int generic_writepages(struct address_space *mapping,
1645                        struct writeback_control *wbc)
1646 {
1647         struct blk_plug plug;
1648         int ret;
1649
1650         /* deal with chardevs and other special file */
1651         if (!mapping->a_ops->writepage)
1652                 return 0;
1653
1654         blk_start_plug(&plug);
1655         ret = write_cache_pages(mapping, wbc, __writepage, mapping);
1656         blk_finish_plug(&plug);
1657         return ret;
1658 }
1659
1660 EXPORT_SYMBOL(generic_writepages);
1661
1662 int do_writepages(struct address_space *mapping, struct writeback_control *wbc)
1663 {
1664         int ret;
1665
1666         if (wbc->nr_to_write <= 0)
1667                 return 0;
1668         if (mapping->a_ops->writepages)
1669                 ret = mapping->a_ops->writepages(mapping, wbc);
1670         else
1671                 ret = generic_writepages(mapping, wbc);
1672         return ret;
1673 }
1674
1675 /**
1676  * write_one_page - write out a single page and optionally wait on I/O
1677  * @page: the page to write
1678  * @wait: if true, wait on writeout
1679  *
1680  * The page must be locked by the caller and will be unlocked upon return.
1681  *
1682  * write_one_page() returns a negative error code if I/O failed.
1683  */
1684 int write_one_page(struct page *page, int wait)
1685 {
1686         struct address_space *mapping = page->mapping;
1687         int ret = 0;
1688         struct writeback_control wbc = {
1689                 .sync_mode = WB_SYNC_ALL,
1690                 .nr_to_write = 1,
1691         };
1692
1693         BUG_ON(!PageLocked(page));
1694
1695         if (wait)
1696                 wait_on_page_writeback(page);
1697
1698         if (clear_page_dirty_for_io(page)) {
1699                 page_cache_get(page);
1700                 ret = mapping->a_ops->writepage(page, &wbc);
1701                 if (ret == 0 && wait) {
1702                         wait_on_page_writeback(page);
1703                         if (PageError(page))
1704                                 ret = -EIO;
1705                 }
1706                 page_cache_release(page);
1707         } else {
1708                 unlock_page(page);
1709         }
1710         return ret;
1711 }
1712 EXPORT_SYMBOL(write_one_page);
1713
1714 /*
1715  * For address_spaces which do not use buffers nor write back.
1716  */
1717 int __set_page_dirty_no_writeback(struct page *page)
1718 {
1719         if (!PageDirty(page))
1720                 return !TestSetPageDirty(page);
1721         return 0;
1722 }
1723
1724 /*
1725  * Helper function for set_page_dirty family.
1726  * NOTE: This relies on being atomic wrt interrupts.
1727  */
1728 void account_page_dirtied(struct page *page, struct address_space *mapping)
1729 {
1730         if (mapping_cap_account_dirty(mapping)) {
1731                 __inc_zone_page_state(page, NR_FILE_DIRTY);
1732                 __inc_zone_page_state(page, NR_DIRTIED);
1733                 __inc_bdi_stat(mapping->backing_dev_info, BDI_RECLAIMABLE);
1734                 __inc_bdi_stat(mapping->backing_dev_info, BDI_DIRTIED);
1735                 task_io_account_write(PAGE_CACHE_SIZE);
1736         }
1737 }
1738 EXPORT_SYMBOL(account_page_dirtied);
1739
1740 /*
1741  * Helper function for set_page_writeback family.
1742  * NOTE: Unlike account_page_dirtied this does not rely on being atomic
1743  * wrt interrupts.
1744  */
1745 void account_page_writeback(struct page *page)
1746 {
1747         inc_zone_page_state(page, NR_WRITEBACK);
1748 }
1749 EXPORT_SYMBOL(account_page_writeback);
1750
1751 /*
1752  * For address_spaces which do not use buffers.  Just tag the page as dirty in
1753  * its radix tree.
1754  *
1755  * This is also used when a single buffer is being dirtied: we want to set the
1756  * page dirty in that case, but not all the buffers.  This is a "bottom-up"
1757  * dirtying, whereas __set_page_dirty_buffers() is a "top-down" dirtying.
1758  *
1759  * The caller must ensure this doesn't race with truncation.  Most will simply
1760  * hold the page lock, but e.g. zap_pte_range() calls with the page mapped and
1761  * the pte lock held, which also locks out truncation.
1762  */
1763 int __set_page_dirty_nobuffers(struct page *page)
1764 {
1765         if (!TestSetPageDirty(page)) {
1766                 struct address_space *mapping = page_mapping(page);
1767                 unsigned long flags;
1768
1769                 if (!mapping)
1770                         return 1;
1771
1772                 spin_lock_irqsave(&mapping->tree_lock, flags);
1773                 BUG_ON(page_mapping(page) != mapping);
1774                 WARN_ON_ONCE(!PagePrivate(page) && !PageUptodate(page));
1775                 account_page_dirtied(page, mapping);
1776                 radix_tree_tag_set(&mapping->page_tree, page_index(page),
1777                                    PAGECACHE_TAG_DIRTY);
1778                 spin_unlock_irqrestore(&mapping->tree_lock, flags);
1779                 if (mapping->host) {
1780                         /* !PageAnon && !swapper_space */
1781                         __mark_inode_dirty(mapping->host, I_DIRTY_PAGES);
1782                 }
1783                 return 1;
1784         }
1785         return 0;
1786 }
1787 EXPORT_SYMBOL(__set_page_dirty_nobuffers);
1788
1789 /*
1790  * Call this whenever redirtying a page, to de-account the dirty counters
1791  * (NR_DIRTIED, BDI_DIRTIED, tsk->nr_dirtied), so that they match the written
1792  * counters (NR_WRITTEN, BDI_WRITTEN) in long term. The mismatches will lead to
1793  * systematic errors in balanced_dirty_ratelimit and the dirty pages position
1794  * control.
1795  */
1796 void account_page_redirty(struct page *page)
1797 {
1798         struct address_space *mapping = page->mapping;
1799         if (mapping && mapping_cap_account_dirty(mapping)) {
1800                 current->nr_dirtied--;
1801                 dec_zone_page_state(page, NR_DIRTIED);
1802                 dec_bdi_stat(mapping->backing_dev_info, BDI_DIRTIED);
1803         }
1804 }
1805 EXPORT_SYMBOL(account_page_redirty);
1806
1807 /*
1808  * When a writepage implementation decides that it doesn't want to write this
1809  * page for some reason, it should redirty the locked page via
1810  * redirty_page_for_writepage() and it should then unlock the page and return 0
1811  */
1812 int redirty_page_for_writepage(struct writeback_control *wbc, struct page *page)
1813 {
1814         wbc->pages_skipped++;
1815         account_page_redirty(page);
1816         return __set_page_dirty_nobuffers(page);
1817 }
1818 EXPORT_SYMBOL(redirty_page_for_writepage);
1819
1820 /*
1821  * Dirty a page.
1822  *
1823  * For pages with a mapping this should be done under the page lock
1824  * for the benefit of asynchronous memory errors who prefer a consistent
1825  * dirty state. This rule can be broken in some special cases,
1826  * but should be better not to.
1827  *
1828  * If the mapping doesn't provide a set_page_dirty a_op, then
1829  * just fall through and assume that it wants buffer_heads.
1830  */
1831 int set_page_dirty(struct page *page)
1832 {
1833         struct address_space *mapping = page_mapping(page);
1834
1835         if (likely(mapping)) {
1836                 int (*spd)(struct page *) = mapping->a_ops->set_page_dirty;
1837                 /*
1838                  * readahead/lru_deactivate_page could remain
1839                  * PG_readahead/PG_reclaim due to race with end_page_writeback
1840                  * About readahead, if the page is written, the flags would be
1841                  * reset. So no problem.
1842                  * About lru_deactivate_page, if the page is redirty, the flag
1843                  * will be reset. So no problem. but if the page is used by readahead
1844                  * it will confuse readahead and make it restart the size rampup
1845                  * process. But it's a trivial problem.
1846                  */
1847                 ClearPageReclaim(page);
1848 #ifdef CONFIG_BLOCK
1849                 if (!spd)
1850                         spd = __set_page_dirty_buffers;
1851 #endif
1852                 return (*spd)(page);
1853         }
1854         if (!PageDirty(page)) {
1855                 if (!TestSetPageDirty(page))
1856                         return 1;
1857         }
1858         return 0;
1859 }
1860 EXPORT_SYMBOL(set_page_dirty);
1861
1862 /*
1863  * set_page_dirty() is racy if the caller has no reference against
1864  * page->mapping->host, and if the page is unlocked.  This is because another
1865  * CPU could truncate the page off the mapping and then free the mapping.
1866  *
1867  * Usually, the page _is_ locked, or the caller is a user-space process which
1868  * holds a reference on the inode by having an open file.
1869  *
1870  * In other cases, the page should be locked before running set_page_dirty().
1871  */
1872 int set_page_dirty_lock(struct page *page)
1873 {
1874         int ret;
1875
1876         lock_page(page);
1877         ret = set_page_dirty(page);
1878         unlock_page(page);
1879         return ret;
1880 }
1881 EXPORT_SYMBOL(set_page_dirty_lock);
1882
1883 /*
1884  * Clear a page's dirty flag, while caring for dirty memory accounting.
1885  * Returns true if the page was previously dirty.
1886  *
1887  * This is for preparing to put the page under writeout.  We leave the page
1888  * tagged as dirty in the radix tree so that a concurrent write-for-sync
1889  * can discover it via a PAGECACHE_TAG_DIRTY walk.  The ->writepage
1890  * implementation will run either set_page_writeback() or set_page_dirty(),
1891  * at which stage we bring the page's dirty flag and radix-tree dirty tag
1892  * back into sync.
1893  *
1894  * This incoherency between the page's dirty flag and radix-tree tag is
1895  * unfortunate, but it only exists while the page is locked.
1896  */
1897 int clear_page_dirty_for_io(struct page *page)
1898 {
1899         struct address_space *mapping = page_mapping(page);
1900
1901         BUG_ON(!PageLocked(page));
1902
1903         if (mapping && mapping_cap_account_dirty(mapping)) {
1904                 /*
1905                  * Yes, Virginia, this is indeed insane.
1906                  *
1907                  * We use this sequence to make sure that
1908                  *  (a) we account for dirty stats properly
1909                  *  (b) we tell the low-level filesystem to
1910                  *      mark the whole page dirty if it was
1911                  *      dirty in a pagetable. Only to then
1912                  *  (c) clean the page again and return 1 to
1913                  *      cause the writeback.
1914                  *
1915                  * This way we avoid all nasty races with the
1916                  * dirty bit in multiple places and clearing
1917                  * them concurrently from different threads.
1918                  *
1919                  * Note! Normally the "set_page_dirty(page)"
1920                  * has no effect on the actual dirty bit - since
1921                  * that will already usually be set. But we
1922                  * need the side effects, and it can help us
1923                  * avoid races.
1924                  *
1925                  * We basically use the page "master dirty bit"
1926                  * as a serialization point for all the different
1927                  * threads doing their things.
1928                  */
1929                 if (page_mkclean(page))
1930                         set_page_dirty(page);
1931                 /*
1932                  * We carefully synchronise fault handlers against
1933                  * installing a dirty pte and marking the page dirty
1934                  * at this point.  We do this by having them hold the
1935                  * page lock while dirtying the page, and pages are
1936                  * always locked coming in here, so we get the desired
1937                  * exclusion.
1938                  */
1939                 if (TestClearPageDirty(page)) {
1940                         dec_zone_page_state(page, NR_FILE_DIRTY);
1941                         dec_bdi_stat(mapping->backing_dev_info,
1942                                         BDI_RECLAIMABLE);
1943                         return 1;
1944                 }
1945                 return 0;
1946         }
1947         return TestClearPageDirty(page);
1948 }
1949 EXPORT_SYMBOL(clear_page_dirty_for_io);
1950
1951 int test_clear_page_writeback(struct page *page)
1952 {
1953         struct address_space *mapping = page_mapping(page);
1954         int ret;
1955
1956         if (mapping) {
1957                 struct backing_dev_info *bdi = mapping->backing_dev_info;
1958                 unsigned long flags;
1959
1960                 spin_lock_irqsave(&mapping->tree_lock, flags);
1961                 ret = TestClearPageWriteback(page);
1962                 if (ret) {
1963                         radix_tree_tag_clear(&mapping->page_tree,
1964                                                 page_index(page),
1965                                                 PAGECACHE_TAG_WRITEBACK);
1966                         if (bdi_cap_account_writeback(bdi)) {
1967                                 __dec_bdi_stat(bdi, BDI_WRITEBACK);
1968                                 __bdi_writeout_inc(bdi);
1969                         }
1970                 }
1971                 spin_unlock_irqrestore(&mapping->tree_lock, flags);
1972         } else {
1973                 ret = TestClearPageWriteback(page);
1974         }
1975         if (ret) {
1976                 dec_zone_page_state(page, NR_WRITEBACK);
1977                 inc_zone_page_state(page, NR_WRITTEN);
1978         }
1979         return ret;
1980 }
1981
1982 int test_set_page_writeback(struct page *page)
1983 {
1984         struct address_space *mapping = page_mapping(page);
1985         int ret;
1986
1987         if (mapping) {
1988                 struct backing_dev_info *bdi = mapping->backing_dev_info;
1989                 unsigned long flags;
1990
1991                 spin_lock_irqsave(&mapping->tree_lock, flags);
1992                 ret = TestSetPageWriteback(page);
1993                 if (!ret) {
1994                         radix_tree_tag_set(&mapping->page_tree,
1995                                                 page_index(page),
1996                                                 PAGECACHE_TAG_WRITEBACK);
1997                         if (bdi_cap_account_writeback(bdi))
1998                                 __inc_bdi_stat(bdi, BDI_WRITEBACK);
1999                 }
2000                 if (!PageDirty(page))
2001                         radix_tree_tag_clear(&mapping->page_tree,
2002                                                 page_index(page),
2003                                                 PAGECACHE_TAG_DIRTY);
2004                 radix_tree_tag_clear(&mapping->page_tree,
2005                                      page_index(page),
2006                                      PAGECACHE_TAG_TOWRITE);
2007                 spin_unlock_irqrestore(&mapping->tree_lock, flags);
2008         } else {
2009                 ret = TestSetPageWriteback(page);
2010         }
2011         if (!ret)
2012                 account_page_writeback(page);
2013         return ret;
2014
2015 }
2016 EXPORT_SYMBOL(test_set_page_writeback);
2017
2018 /*
2019  * Return true if any of the pages in the mapping are marked with the
2020  * passed tag.
2021  */
2022 int mapping_tagged(struct address_space *mapping, int tag)
2023 {
2024         return radix_tree_tagged(&mapping->page_tree, tag);
2025 }
2026 EXPORT_SYMBOL(mapping_tagged);