28763b8bdbddd9caba1478cc9e8aa205a02cf397
[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/module.h>
16 #include <linux/spinlock.h>
17 #include <linux/fs.h>
18 #include <linux/mm.h>
19 #include <linux/swap.h>
20 #include <linux/slab.h>
21 #include <linux/pagemap.h>
22 #include <linux/writeback.h>
23 #include <linux/init.h>
24 #include <linux/backing-dev.h>
25 #include <linux/task_io_accounting_ops.h>
26 #include <linux/blkdev.h>
27 #include <linux/mpage.h>
28 #include <linux/rmap.h>
29 #include <linux/percpu.h>
30 #include <linux/notifier.h>
31 #include <linux/smp.h>
32 #include <linux/sysctl.h>
33 #include <linux/cpu.h>
34 #include <linux/syscalls.h>
35 #include <linux/buffer_head.h>
36 #include <linux/pagevec.h>
37 #include <trace/events/writeback.h>
38
39 /*
40  * After a CPU has dirtied this many pages, balance_dirty_pages_ratelimited
41  * will look to see if it needs to force writeback or throttling.
42  */
43 static long ratelimit_pages = 32;
44
45 /*
46  * When balance_dirty_pages decides that the caller needs to perform some
47  * non-background writeback, this is how many pages it will attempt to write.
48  * It should be somewhat larger than dirtied pages to ensure that reasonably
49  * large amounts of I/O are submitted.
50  */
51 static inline long sync_writeback_pages(unsigned long dirtied)
52 {
53         if (dirtied < ratelimit_pages)
54                 dirtied = ratelimit_pages;
55
56         return dirtied + dirtied / 2;
57 }
58
59 /* The following parameters are exported via /proc/sys/vm */
60
61 /*
62  * Start background writeback (via writeback threads) at this percentage
63  */
64 int dirty_background_ratio = 10;
65
66 /*
67  * dirty_background_bytes starts at 0 (disabled) so that it is a function of
68  * dirty_background_ratio * the amount of dirtyable memory
69  */
70 unsigned long dirty_background_bytes;
71
72 /*
73  * free highmem will not be subtracted from the total free memory
74  * for calculating free ratios if vm_highmem_is_dirtyable is true
75  */
76 int vm_highmem_is_dirtyable;
77
78 /*
79  * The generator of dirty data starts writeback at this percentage
80  */
81 int vm_dirty_ratio = 20;
82
83 /*
84  * vm_dirty_bytes starts at 0 (disabled) so that it is a function of
85  * vm_dirty_ratio * the amount of dirtyable memory
86  */
87 unsigned long vm_dirty_bytes;
88
89 /*
90  * The interval between `kupdate'-style writebacks
91  */
92 unsigned int dirty_writeback_interval = 5 * 100; /* centiseconds */
93
94 /*
95  * The longest time for which data is allowed to remain dirty
96  */
97 unsigned int dirty_expire_interval = 30 * 100; /* centiseconds */
98
99 /*
100  * Flag that makes the machine dump writes/reads and block dirtyings.
101  */
102 int block_dump;
103
104 /*
105  * Flag that puts the machine in "laptop mode". Doubles as a timeout in jiffies:
106  * a full sync is triggered after this time elapses without any disk activity.
107  */
108 int laptop_mode;
109
110 EXPORT_SYMBOL(laptop_mode);
111
112 /* End of sysctl-exported parameters */
113
114
115 /*
116  * Scale the writeback cache size proportional to the relative writeout speeds.
117  *
118  * We do this by keeping a floating proportion between BDIs, based on page
119  * writeback completions [end_page_writeback()]. Those devices that write out
120  * pages fastest will get the larger share, while the slower will get a smaller
121  * share.
122  *
123  * We use page writeout completions because we are interested in getting rid of
124  * dirty pages. Having them written out is the primary goal.
125  *
126  * We introduce a concept of time, a period over which we measure these events,
127  * because demand can/will vary over time. The length of this period itself is
128  * measured in page writeback completions.
129  *
130  */
131 static struct prop_descriptor vm_completions;
132 static struct prop_descriptor vm_dirties;
133
134 /*
135  * couple the period to the dirty_ratio:
136  *
137  *   period/2 ~ roundup_pow_of_two(dirty limit)
138  */
139 static int calc_period_shift(void)
140 {
141         unsigned long dirty_total;
142
143         if (vm_dirty_bytes)
144                 dirty_total = vm_dirty_bytes / PAGE_SIZE;
145         else
146                 dirty_total = (vm_dirty_ratio * determine_dirtyable_memory()) /
147                                 100;
148         return 2 + ilog2(dirty_total - 1);
149 }
150
151 /*
152  * update the period when the dirty threshold changes.
153  */
154 static void update_completion_period(void)
155 {
156         int shift = calc_period_shift();
157         prop_change_shift(&vm_completions, shift);
158         prop_change_shift(&vm_dirties, shift);
159 }
160
161 int dirty_background_ratio_handler(struct ctl_table *table, int write,
162                 void __user *buffer, size_t *lenp,
163                 loff_t *ppos)
164 {
165         int ret;
166
167         ret = proc_dointvec_minmax(table, write, buffer, lenp, ppos);
168         if (ret == 0 && write)
169                 dirty_background_bytes = 0;
170         return ret;
171 }
172
173 int dirty_background_bytes_handler(struct ctl_table *table, int write,
174                 void __user *buffer, size_t *lenp,
175                 loff_t *ppos)
176 {
177         int ret;
178
179         ret = proc_doulongvec_minmax(table, write, buffer, lenp, ppos);
180         if (ret == 0 && write)
181                 dirty_background_ratio = 0;
182         return ret;
183 }
184
185 int dirty_ratio_handler(struct ctl_table *table, int write,
186                 void __user *buffer, size_t *lenp,
187                 loff_t *ppos)
188 {
189         int old_ratio = vm_dirty_ratio;
190         int ret;
191
192         ret = proc_dointvec_minmax(table, write, buffer, lenp, ppos);
193         if (ret == 0 && write && vm_dirty_ratio != old_ratio) {
194                 update_completion_period();
195                 vm_dirty_bytes = 0;
196         }
197         return ret;
198 }
199
200
201 int dirty_bytes_handler(struct ctl_table *table, int write,
202                 void __user *buffer, size_t *lenp,
203                 loff_t *ppos)
204 {
205         unsigned long old_bytes = vm_dirty_bytes;
206         int ret;
207
208         ret = proc_doulongvec_minmax(table, write, buffer, lenp, ppos);
209         if (ret == 0 && write && vm_dirty_bytes != old_bytes) {
210                 update_completion_period();
211                 vm_dirty_ratio = 0;
212         }
213         return ret;
214 }
215
216 /*
217  * Increment the BDI's writeout completion count and the global writeout
218  * completion count. Called from test_clear_page_writeback().
219  */
220 static inline void __bdi_writeout_inc(struct backing_dev_info *bdi)
221 {
222         __prop_inc_percpu_max(&vm_completions, &bdi->completions,
223                               bdi->max_prop_frac);
224 }
225
226 void bdi_writeout_inc(struct backing_dev_info *bdi)
227 {
228         unsigned long flags;
229
230         local_irq_save(flags);
231         __bdi_writeout_inc(bdi);
232         local_irq_restore(flags);
233 }
234 EXPORT_SYMBOL_GPL(bdi_writeout_inc);
235
236 void task_dirty_inc(struct task_struct *tsk)
237 {
238         prop_inc_single(&vm_dirties, &tsk->dirties);
239 }
240
241 /*
242  * Obtain an accurate fraction of the BDI's portion.
243  */
244 static void bdi_writeout_fraction(struct backing_dev_info *bdi,
245                 long *numerator, long *denominator)
246 {
247         if (bdi_cap_writeback_dirty(bdi)) {
248                 prop_fraction_percpu(&vm_completions, &bdi->completions,
249                                 numerator, denominator);
250         } else {
251                 *numerator = 0;
252                 *denominator = 1;
253         }
254 }
255
256 static inline void task_dirties_fraction(struct task_struct *tsk,
257                 long *numerator, long *denominator)
258 {
259         prop_fraction_single(&vm_dirties, &tsk->dirties,
260                                 numerator, denominator);
261 }
262
263 /*
264  * task_dirty_limit - scale down dirty throttling threshold for one task
265  *
266  * task specific dirty limit:
267  *
268  *   dirty -= (dirty/8) * p_{t}
269  *
270  * To protect light/slow dirtying tasks from heavier/fast ones, we start
271  * throttling individual tasks before reaching the bdi dirty limit.
272  * Relatively low thresholds will be allocated to heavy dirtiers. So when
273  * dirty pages grow large, heavy dirtiers will be throttled first, which will
274  * effectively curb the growth of dirty pages. Light dirtiers with high enough
275  * dirty threshold may never get throttled.
276  */
277 static unsigned long task_dirty_limit(struct task_struct *tsk,
278                                        unsigned long bdi_dirty)
279 {
280         long numerator, denominator;
281         unsigned long dirty = bdi_dirty;
282         u64 inv = dirty >> 3;
283
284         task_dirties_fraction(tsk, &numerator, &denominator);
285         inv *= numerator;
286         do_div(inv, denominator);
287
288         dirty -= inv;
289
290         return max(dirty, bdi_dirty/2);
291 }
292
293 /*
294  *
295  */
296 static unsigned int bdi_min_ratio;
297
298 int bdi_set_min_ratio(struct backing_dev_info *bdi, unsigned int min_ratio)
299 {
300         int ret = 0;
301
302         spin_lock_bh(&bdi_lock);
303         if (min_ratio > bdi->max_ratio) {
304                 ret = -EINVAL;
305         } else {
306                 min_ratio -= bdi->min_ratio;
307                 if (bdi_min_ratio + min_ratio < 100) {
308                         bdi_min_ratio += min_ratio;
309                         bdi->min_ratio += min_ratio;
310                 } else {
311                         ret = -EINVAL;
312                 }
313         }
314         spin_unlock_bh(&bdi_lock);
315
316         return ret;
317 }
318
319 int bdi_set_max_ratio(struct backing_dev_info *bdi, unsigned max_ratio)
320 {
321         int ret = 0;
322
323         if (max_ratio > 100)
324                 return -EINVAL;
325
326         spin_lock_bh(&bdi_lock);
327         if (bdi->min_ratio > max_ratio) {
328                 ret = -EINVAL;
329         } else {
330                 bdi->max_ratio = max_ratio;
331                 bdi->max_prop_frac = (PROP_FRAC_BASE * max_ratio) / 100;
332         }
333         spin_unlock_bh(&bdi_lock);
334
335         return ret;
336 }
337 EXPORT_SYMBOL(bdi_set_max_ratio);
338
339 /*
340  * Work out the current dirty-memory clamping and background writeout
341  * thresholds.
342  *
343  * The main aim here is to lower them aggressively if there is a lot of mapped
344  * memory around.  To avoid stressing page reclaim with lots of unreclaimable
345  * pages.  It is better to clamp down on writers than to start swapping, and
346  * performing lots of scanning.
347  *
348  * We only allow 1/2 of the currently-unmapped memory to be dirtied.
349  *
350  * We don't permit the clamping level to fall below 5% - that is getting rather
351  * excessive.
352  *
353  * We make sure that the background writeout level is below the adjusted
354  * clamping level.
355  */
356
357 static unsigned long highmem_dirtyable_memory(unsigned long total)
358 {
359 #ifdef CONFIG_HIGHMEM
360         int node;
361         unsigned long x = 0;
362
363         for_each_node_state(node, N_HIGH_MEMORY) {
364                 struct zone *z =
365                         &NODE_DATA(node)->node_zones[ZONE_HIGHMEM];
366
367                 x += zone_page_state(z, NR_FREE_PAGES) +
368                      zone_reclaimable_pages(z);
369         }
370         /*
371          * Make sure that the number of highmem pages is never larger
372          * than the number of the total dirtyable memory. This can only
373          * occur in very strange VM situations but we want to make sure
374          * that this does not occur.
375          */
376         return min(x, total);
377 #else
378         return 0;
379 #endif
380 }
381
382 /**
383  * determine_dirtyable_memory - amount of memory that may be used
384  *
385  * Returns the numebr of pages that can currently be freed and used
386  * by the kernel for direct mappings.
387  */
388 unsigned long determine_dirtyable_memory(void)
389 {
390         unsigned long x;
391
392         x = global_page_state(NR_FREE_PAGES) + global_reclaimable_pages();
393
394         if (!vm_highmem_is_dirtyable)
395                 x -= highmem_dirtyable_memory(x);
396
397         return x + 1;   /* Ensure that we never return 0 */
398 }
399
400 /*
401  * global_dirty_limits - background-writeback and dirty-throttling thresholds
402  *
403  * Calculate the dirty thresholds based on sysctl parameters
404  * - vm.dirty_background_ratio  or  vm.dirty_background_bytes
405  * - vm.dirty_ratio             or  vm.dirty_bytes
406  * The dirty limits will be lifted by 1/4 for PF_LESS_THROTTLE (ie. nfsd) and
407  * real-time tasks.
408  */
409 void global_dirty_limits(unsigned long *pbackground, unsigned long *pdirty)
410 {
411         unsigned long background;
412         unsigned long dirty;
413         unsigned long available_memory = determine_dirtyable_memory();
414         struct task_struct *tsk;
415
416         if (vm_dirty_bytes)
417                 dirty = DIV_ROUND_UP(vm_dirty_bytes, PAGE_SIZE);
418         else
419                 dirty = (vm_dirty_ratio * available_memory) / 100;
420
421         if (dirty_background_bytes)
422                 background = DIV_ROUND_UP(dirty_background_bytes, PAGE_SIZE);
423         else
424                 background = (dirty_background_ratio * available_memory) / 100;
425
426         if (background >= dirty)
427                 background = dirty / 2;
428         tsk = current;
429         if (tsk->flags & PF_LESS_THROTTLE || rt_task(tsk)) {
430                 background += background / 4;
431                 dirty += dirty / 4;
432         }
433         *pbackground = background;
434         *pdirty = dirty;
435 }
436
437 /*
438  * bdi_dirty_limit - @bdi's share of dirty throttling threshold
439  *
440  * Allocate high/low dirty limits to fast/slow devices, in order to prevent
441  * - starving fast devices
442  * - piling up dirty pages (that will take long time to sync) on slow devices
443  *
444  * The bdi's share of dirty limit will be adapting to its throughput and
445  * bounded by the bdi->min_ratio and/or bdi->max_ratio parameters, if set.
446  */
447 unsigned long bdi_dirty_limit(struct backing_dev_info *bdi, unsigned long dirty)
448 {
449         u64 bdi_dirty;
450         long numerator, denominator;
451
452         /*
453          * Calculate this BDI's share of the dirty ratio.
454          */
455         bdi_writeout_fraction(bdi, &numerator, &denominator);
456
457         bdi_dirty = (dirty * (100 - bdi_min_ratio)) / 100;
458         bdi_dirty *= numerator;
459         do_div(bdi_dirty, denominator);
460
461         bdi_dirty += (dirty * bdi->min_ratio) / 100;
462         if (bdi_dirty > (dirty * bdi->max_ratio) / 100)
463                 bdi_dirty = dirty * bdi->max_ratio / 100;
464
465         return bdi_dirty;
466 }
467
468 /*
469  * balance_dirty_pages() must be called by processes which are generating dirty
470  * data.  It looks at the number of dirty pages in the machine and will force
471  * the caller to perform writeback if the system is over `vm_dirty_ratio'.
472  * If we're over `background_thresh' then the writeback threads are woken to
473  * perform some writeout.
474  */
475 static void balance_dirty_pages(struct address_space *mapping,
476                                 unsigned long write_chunk)
477 {
478         long nr_reclaimable, bdi_nr_reclaimable;
479         long nr_writeback, bdi_nr_writeback;
480         unsigned long background_thresh;
481         unsigned long dirty_thresh;
482         unsigned long bdi_thresh;
483         unsigned long pages_written = 0;
484         unsigned long pause = 1;
485         bool dirty_exceeded = false;
486         struct backing_dev_info *bdi = mapping->backing_dev_info;
487
488         for (;;) {
489                 struct writeback_control wbc = {
490                         .sync_mode      = WB_SYNC_NONE,
491                         .older_than_this = NULL,
492                         .nr_to_write    = write_chunk,
493                         .range_cyclic   = 1,
494                 };
495
496                 nr_reclaimable = global_page_state(NR_FILE_DIRTY) +
497                                         global_page_state(NR_UNSTABLE_NFS);
498                 nr_writeback = global_page_state(NR_WRITEBACK);
499
500                 global_dirty_limits(&background_thresh, &dirty_thresh);
501
502                 /*
503                  * Throttle it only when the background writeback cannot
504                  * catch-up. This avoids (excessively) small writeouts
505                  * when the bdi limits are ramping up.
506                  */
507                 if (nr_reclaimable + nr_writeback <=
508                                 (background_thresh + dirty_thresh) / 2)
509                         break;
510
511                 bdi_thresh = bdi_dirty_limit(bdi, dirty_thresh);
512                 bdi_thresh = task_dirty_limit(current, bdi_thresh);
513
514                 /*
515                  * In order to avoid the stacked BDI deadlock we need
516                  * to ensure we accurately count the 'dirty' pages when
517                  * the threshold is low.
518                  *
519                  * Otherwise it would be possible to get thresh+n pages
520                  * reported dirty, even though there are thresh-m pages
521                  * actually dirty; with m+n sitting in the percpu
522                  * deltas.
523                  */
524                 if (bdi_thresh < 2*bdi_stat_error(bdi)) {
525                         bdi_nr_reclaimable = bdi_stat_sum(bdi, BDI_RECLAIMABLE);
526                         bdi_nr_writeback = bdi_stat_sum(bdi, BDI_WRITEBACK);
527                 } else {
528                         bdi_nr_reclaimable = bdi_stat(bdi, BDI_RECLAIMABLE);
529                         bdi_nr_writeback = bdi_stat(bdi, BDI_WRITEBACK);
530                 }
531
532                 /*
533                  * The bdi thresh is somehow "soft" limit derived from the
534                  * global "hard" limit. The former helps to prevent heavy IO
535                  * bdi or process from holding back light ones; The latter is
536                  * the last resort safeguard.
537                  */
538                 dirty_exceeded =
539                         (bdi_nr_reclaimable + bdi_nr_writeback > bdi_thresh)
540                         || (nr_reclaimable + nr_writeback > dirty_thresh);
541
542                 if (!dirty_exceeded)
543                         break;
544
545                 if (!bdi->dirty_exceeded)
546                         bdi->dirty_exceeded = 1;
547
548                 /* Note: nr_reclaimable denotes nr_dirty + nr_unstable.
549                  * Unstable writes are a feature of certain networked
550                  * filesystems (i.e. NFS) in which data may have been
551                  * written to the server's write cache, but has not yet
552                  * been flushed to permanent storage.
553                  * Only move pages to writeback if this bdi is over its
554                  * threshold otherwise wait until the disk writes catch
555                  * up.
556                  */
557                 trace_wbc_balance_dirty_start(&wbc, bdi);
558                 if (bdi_nr_reclaimable > bdi_thresh) {
559                         writeback_inodes_wb(&bdi->wb, &wbc);
560                         pages_written += write_chunk - wbc.nr_to_write;
561                         trace_wbc_balance_dirty_written(&wbc, bdi);
562                         if (pages_written >= write_chunk)
563                                 break;          /* We've done our duty */
564                 }
565                 trace_wbc_balance_dirty_wait(&wbc, bdi);
566                 __set_current_state(TASK_UNINTERRUPTIBLE);
567                 io_schedule_timeout(pause);
568
569                 /*
570                  * Increase the delay for each loop, up to our previous
571                  * default of taking a 100ms nap.
572                  */
573                 pause <<= 1;
574                 if (pause > HZ / 10)
575                         pause = HZ / 10;
576         }
577
578         if (!dirty_exceeded && bdi->dirty_exceeded)
579                 bdi->dirty_exceeded = 0;
580
581         if (writeback_in_progress(bdi))
582                 return;
583
584         /*
585          * In laptop mode, we wait until hitting the higher threshold before
586          * starting background writeout, and then write out all the way down
587          * to the lower threshold.  So slow writers cause minimal disk activity.
588          *
589          * In normal mode, we start background writeout at the lower
590          * background_thresh, to keep the amount of dirty memory low.
591          */
592         if ((laptop_mode && pages_written) ||
593             (!laptop_mode && (nr_reclaimable > background_thresh)))
594                 bdi_start_background_writeback(bdi);
595 }
596
597 void set_page_dirty_balance(struct page *page, int page_mkwrite)
598 {
599         if (set_page_dirty(page) || page_mkwrite) {
600                 struct address_space *mapping = page_mapping(page);
601
602                 if (mapping)
603                         balance_dirty_pages_ratelimited(mapping);
604         }
605 }
606
607 static DEFINE_PER_CPU(unsigned long, bdp_ratelimits) = 0;
608
609 /**
610  * balance_dirty_pages_ratelimited_nr - balance dirty memory state
611  * @mapping: address_space which was dirtied
612  * @nr_pages_dirtied: number of pages which the caller has just dirtied
613  *
614  * Processes which are dirtying memory should call in here once for each page
615  * which was newly dirtied.  The function will periodically check the system's
616  * dirty state and will initiate writeback if needed.
617  *
618  * On really big machines, get_writeback_state is expensive, so try to avoid
619  * calling it too often (ratelimiting).  But once we're over the dirty memory
620  * limit we decrease the ratelimiting by a lot, to prevent individual processes
621  * from overshooting the limit by (ratelimit_pages) each.
622  */
623 void balance_dirty_pages_ratelimited_nr(struct address_space *mapping,
624                                         unsigned long nr_pages_dirtied)
625 {
626         unsigned long ratelimit;
627         unsigned long *p;
628
629         ratelimit = ratelimit_pages;
630         if (mapping->backing_dev_info->dirty_exceeded)
631                 ratelimit = 8;
632
633         /*
634          * Check the rate limiting. Also, we do not want to throttle real-time
635          * tasks in balance_dirty_pages(). Period.
636          */
637         preempt_disable();
638         p =  &__get_cpu_var(bdp_ratelimits);
639         *p += nr_pages_dirtied;
640         if (unlikely(*p >= ratelimit)) {
641                 ratelimit = sync_writeback_pages(*p);
642                 *p = 0;
643                 preempt_enable();
644                 balance_dirty_pages(mapping, ratelimit);
645                 return;
646         }
647         preempt_enable();
648 }
649 EXPORT_SYMBOL(balance_dirty_pages_ratelimited_nr);
650
651 void throttle_vm_writeout(gfp_t gfp_mask)
652 {
653         unsigned long background_thresh;
654         unsigned long dirty_thresh;
655
656         for ( ; ; ) {
657                 global_dirty_limits(&background_thresh, &dirty_thresh);
658
659                 /*
660                  * Boost the allowable dirty threshold a bit for page
661                  * allocators so they don't get DoS'ed by heavy writers
662                  */
663                 dirty_thresh += dirty_thresh / 10;      /* wheeee... */
664
665                 if (global_page_state(NR_UNSTABLE_NFS) +
666                         global_page_state(NR_WRITEBACK) <= dirty_thresh)
667                                 break;
668                 congestion_wait(BLK_RW_ASYNC, HZ/10);
669
670                 /*
671                  * The caller might hold locks which can prevent IO completion
672                  * or progress in the filesystem.  So we cannot just sit here
673                  * waiting for IO to complete.
674                  */
675                 if ((gfp_mask & (__GFP_FS|__GFP_IO)) != (__GFP_FS|__GFP_IO))
676                         break;
677         }
678 }
679
680 /*
681  * sysctl handler for /proc/sys/vm/dirty_writeback_centisecs
682  */
683 int dirty_writeback_centisecs_handler(ctl_table *table, int write,
684         void __user *buffer, size_t *length, loff_t *ppos)
685 {
686         proc_dointvec(table, write, buffer, length, ppos);
687         bdi_arm_supers_timer();
688         return 0;
689 }
690
691 #ifdef CONFIG_BLOCK
692 void laptop_mode_timer_fn(unsigned long data)
693 {
694         struct request_queue *q = (struct request_queue *)data;
695         int nr_pages = global_page_state(NR_FILE_DIRTY) +
696                 global_page_state(NR_UNSTABLE_NFS);
697
698         /*
699          * We want to write everything out, not just down to the dirty
700          * threshold
701          */
702         if (bdi_has_dirty_io(&q->backing_dev_info))
703                 bdi_start_writeback(&q->backing_dev_info, nr_pages);
704 }
705
706 /*
707  * We've spun up the disk and we're in laptop mode: schedule writeback
708  * of all dirty data a few seconds from now.  If the flush is already scheduled
709  * then push it back - the user is still using the disk.
710  */
711 void laptop_io_completion(struct backing_dev_info *info)
712 {
713         mod_timer(&info->laptop_mode_wb_timer, jiffies + laptop_mode);
714 }
715
716 /*
717  * We're in laptop mode and we've just synced. The sync's writes will have
718  * caused another writeback to be scheduled by laptop_io_completion.
719  * Nothing needs to be written back anymore, so we unschedule the writeback.
720  */
721 void laptop_sync_completion(void)
722 {
723         struct backing_dev_info *bdi;
724
725         rcu_read_lock();
726
727         list_for_each_entry_rcu(bdi, &bdi_list, bdi_list)
728                 del_timer(&bdi->laptop_mode_wb_timer);
729
730         rcu_read_unlock();
731 }
732 #endif
733
734 /*
735  * If ratelimit_pages is too high then we can get into dirty-data overload
736  * if a large number of processes all perform writes at the same time.
737  * If it is too low then SMP machines will call the (expensive)
738  * get_writeback_state too often.
739  *
740  * Here we set ratelimit_pages to a level which ensures that when all CPUs are
741  * dirtying in parallel, we cannot go more than 3% (1/32) over the dirty memory
742  * thresholds before writeback cuts in.
743  *
744  * But the limit should not be set too high.  Because it also controls the
745  * amount of memory which the balance_dirty_pages() caller has to write back.
746  * If this is too large then the caller will block on the IO queue all the
747  * time.  So limit it to four megabytes - the balance_dirty_pages() caller
748  * will write six megabyte chunks, max.
749  */
750
751 void writeback_set_ratelimit(void)
752 {
753         ratelimit_pages = vm_total_pages / (num_online_cpus() * 32);
754         if (ratelimit_pages < 16)
755                 ratelimit_pages = 16;
756         if (ratelimit_pages * PAGE_CACHE_SIZE > 4096 * 1024)
757                 ratelimit_pages = (4096 * 1024) / PAGE_CACHE_SIZE;
758 }
759
760 static int __cpuinit
761 ratelimit_handler(struct notifier_block *self, unsigned long u, void *v)
762 {
763         writeback_set_ratelimit();
764         return NOTIFY_DONE;
765 }
766
767 static struct notifier_block __cpuinitdata ratelimit_nb = {
768         .notifier_call  = ratelimit_handler,
769         .next           = NULL,
770 };
771
772 /*
773  * Called early on to tune the page writeback dirty limits.
774  *
775  * We used to scale dirty pages according to how total memory
776  * related to pages that could be allocated for buffers (by
777  * comparing nr_free_buffer_pages() to vm_total_pages.
778  *
779  * However, that was when we used "dirty_ratio" to scale with
780  * all memory, and we don't do that any more. "dirty_ratio"
781  * is now applied to total non-HIGHPAGE memory (by subtracting
782  * totalhigh_pages from vm_total_pages), and as such we can't
783  * get into the old insane situation any more where we had
784  * large amounts of dirty pages compared to a small amount of
785  * non-HIGHMEM memory.
786  *
787  * But we might still want to scale the dirty_ratio by how
788  * much memory the box has..
789  */
790 void __init page_writeback_init(void)
791 {
792         int shift;
793
794         writeback_set_ratelimit();
795         register_cpu_notifier(&ratelimit_nb);
796
797         shift = calc_period_shift();
798         prop_descriptor_init(&vm_completions, shift);
799         prop_descriptor_init(&vm_dirties, shift);
800 }
801
802 /**
803  * tag_pages_for_writeback - tag pages to be written by write_cache_pages
804  * @mapping: address space structure to write
805  * @start: starting page index
806  * @end: ending page index (inclusive)
807  *
808  * This function scans the page range from @start to @end (inclusive) and tags
809  * all pages that have DIRTY tag set with a special TOWRITE tag. The idea is
810  * that write_cache_pages (or whoever calls this function) will then use
811  * TOWRITE tag to identify pages eligible for writeback.  This mechanism is
812  * used to avoid livelocking of writeback by a process steadily creating new
813  * dirty pages in the file (thus it is important for this function to be quick
814  * so that it can tag pages faster than a dirtying process can create them).
815  */
816 /*
817  * We tag pages in batches of WRITEBACK_TAG_BATCH to reduce tree_lock latency.
818  */
819 void tag_pages_for_writeback(struct address_space *mapping,
820                              pgoff_t start, pgoff_t end)
821 {
822 #define WRITEBACK_TAG_BATCH 4096
823         unsigned long tagged;
824
825         do {
826                 spin_lock_irq(&mapping->tree_lock);
827                 tagged = radix_tree_range_tag_if_tagged(&mapping->page_tree,
828                                 &start, end, WRITEBACK_TAG_BATCH,
829                                 PAGECACHE_TAG_DIRTY, PAGECACHE_TAG_TOWRITE);
830                 spin_unlock_irq(&mapping->tree_lock);
831                 WARN_ON_ONCE(tagged > WRITEBACK_TAG_BATCH);
832                 cond_resched();
833                 /* We check 'start' to handle wrapping when end == ~0UL */
834         } while (tagged >= WRITEBACK_TAG_BATCH && start);
835 }
836 EXPORT_SYMBOL(tag_pages_for_writeback);
837
838 /**
839  * write_cache_pages - walk the list of dirty pages of the given address space and write all of them.
840  * @mapping: address space structure to write
841  * @wbc: subtract the number of written pages from *@wbc->nr_to_write
842  * @writepage: function called for each page
843  * @data: data passed to writepage function
844  *
845  * If a page is already under I/O, write_cache_pages() skips it, even
846  * if it's dirty.  This is desirable behaviour for memory-cleaning writeback,
847  * but it is INCORRECT for data-integrity system calls such as fsync().  fsync()
848  * and msync() need to guarantee that all the data which was dirty at the time
849  * the call was made get new I/O started against them.  If wbc->sync_mode is
850  * WB_SYNC_ALL then we were called for data integrity and we must wait for
851  * existing IO to complete.
852  *
853  * To avoid livelocks (when other process dirties new pages), we first tag
854  * pages which should be written back with TOWRITE tag and only then start
855  * writing them. For data-integrity sync we have to be careful so that we do
856  * not miss some pages (e.g., because some other process has cleared TOWRITE
857  * tag we set). The rule we follow is that TOWRITE tag can be cleared only
858  * by the process clearing the DIRTY tag (and submitting the page for IO).
859  */
860 int write_cache_pages(struct address_space *mapping,
861                       struct writeback_control *wbc, writepage_t writepage,
862                       void *data)
863 {
864         int ret = 0;
865         int done = 0;
866         struct pagevec pvec;
867         int nr_pages;
868         pgoff_t uninitialized_var(writeback_index);
869         pgoff_t index;
870         pgoff_t end;            /* Inclusive */
871         pgoff_t done_index;
872         int cycled;
873         int range_whole = 0;
874         int tag;
875
876         pagevec_init(&pvec, 0);
877         if (wbc->range_cyclic) {
878                 writeback_index = mapping->writeback_index; /* prev offset */
879                 index = writeback_index;
880                 if (index == 0)
881                         cycled = 1;
882                 else
883                         cycled = 0;
884                 end = -1;
885         } else {
886                 index = wbc->range_start >> PAGE_CACHE_SHIFT;
887                 end = wbc->range_end >> PAGE_CACHE_SHIFT;
888                 if (wbc->range_start == 0 && wbc->range_end == LLONG_MAX)
889                         range_whole = 1;
890                 cycled = 1; /* ignore range_cyclic tests */
891         }
892         if (wbc->sync_mode == WB_SYNC_ALL)
893                 tag = PAGECACHE_TAG_TOWRITE;
894         else
895                 tag = PAGECACHE_TAG_DIRTY;
896 retry:
897         if (wbc->sync_mode == WB_SYNC_ALL)
898                 tag_pages_for_writeback(mapping, index, end);
899         done_index = index;
900         while (!done && (index <= end)) {
901                 int i;
902
903                 nr_pages = pagevec_lookup_tag(&pvec, mapping, &index, tag,
904                               min(end - index, (pgoff_t)PAGEVEC_SIZE-1) + 1);
905                 if (nr_pages == 0)
906                         break;
907
908                 for (i = 0; i < nr_pages; i++) {
909                         struct page *page = pvec.pages[i];
910
911                         /*
912                          * At this point, the page may be truncated or
913                          * invalidated (changing page->mapping to NULL), or
914                          * even swizzled back from swapper_space to tmpfs file
915                          * mapping. However, page->index will not change
916                          * because we have a reference on the page.
917                          */
918                         if (page->index > end) {
919                                 /*
920                                  * can't be range_cyclic (1st pass) because
921                                  * end == -1 in that case.
922                                  */
923                                 done = 1;
924                                 break;
925                         }
926
927                         done_index = page->index + 1;
928
929                         lock_page(page);
930
931                         /*
932                          * Page truncated or invalidated. We can freely skip it
933                          * then, even for data integrity operations: the page
934                          * has disappeared concurrently, so there could be no
935                          * real expectation of this data interity operation
936                          * even if there is now a new, dirty page at the same
937                          * pagecache address.
938                          */
939                         if (unlikely(page->mapping != mapping)) {
940 continue_unlock:
941                                 unlock_page(page);
942                                 continue;
943                         }
944
945                         if (!PageDirty(page)) {
946                                 /* someone wrote it for us */
947                                 goto continue_unlock;
948                         }
949
950                         if (PageWriteback(page)) {
951                                 if (wbc->sync_mode != WB_SYNC_NONE)
952                                         wait_on_page_writeback(page);
953                                 else
954                                         goto continue_unlock;
955                         }
956
957                         BUG_ON(PageWriteback(page));
958                         if (!clear_page_dirty_for_io(page))
959                                 goto continue_unlock;
960
961                         trace_wbc_writepage(wbc, mapping->backing_dev_info);
962                         ret = (*writepage)(page, wbc, data);
963                         if (unlikely(ret)) {
964                                 if (ret == AOP_WRITEPAGE_ACTIVATE) {
965                                         unlock_page(page);
966                                         ret = 0;
967                                 } else {
968                                         /*
969                                          * done_index is set past this page,
970                                          * so media errors will not choke
971                                          * background writeout for the entire
972                                          * file. This has consequences for
973                                          * range_cyclic semantics (ie. it may
974                                          * not be suitable for data integrity
975                                          * writeout).
976                                          */
977                                         done = 1;
978                                         break;
979                                 }
980                         }
981
982                         /*
983                          * We stop writing back only if we are not doing
984                          * integrity sync. In case of integrity sync we have to
985                          * keep going until we have written all the pages
986                          * we tagged for writeback prior to entering this loop.
987                          */
988                         if (--wbc->nr_to_write <= 0 &&
989                             wbc->sync_mode == WB_SYNC_NONE) {
990                                 done = 1;
991                                 break;
992                         }
993                 }
994                 pagevec_release(&pvec);
995                 cond_resched();
996         }
997         if (!cycled && !done) {
998                 /*
999                  * range_cyclic:
1000                  * We hit the last page and there is more work to be done: wrap
1001                  * back to the start of the file
1002                  */
1003                 cycled = 1;
1004                 index = 0;
1005                 end = writeback_index - 1;
1006                 goto retry;
1007         }
1008         if (wbc->range_cyclic || (range_whole && wbc->nr_to_write > 0))
1009                 mapping->writeback_index = done_index;
1010
1011         return ret;
1012 }
1013 EXPORT_SYMBOL(write_cache_pages);
1014
1015 /*
1016  * Function used by generic_writepages to call the real writepage
1017  * function and set the mapping flags on error
1018  */
1019 static int __writepage(struct page *page, struct writeback_control *wbc,
1020                        void *data)
1021 {
1022         struct address_space *mapping = data;
1023         int ret = mapping->a_ops->writepage(page, wbc);
1024         mapping_set_error(mapping, ret);
1025         return ret;
1026 }
1027
1028 /**
1029  * generic_writepages - walk the list of dirty pages of the given address space and writepage() all of them.
1030  * @mapping: address space structure to write
1031  * @wbc: subtract the number of written pages from *@wbc->nr_to_write
1032  *
1033  * This is a library function, which implements the writepages()
1034  * address_space_operation.
1035  */
1036 int generic_writepages(struct address_space *mapping,
1037                        struct writeback_control *wbc)
1038 {
1039         /* deal with chardevs and other special file */
1040         if (!mapping->a_ops->writepage)
1041                 return 0;
1042
1043         return write_cache_pages(mapping, wbc, __writepage, mapping);
1044 }
1045
1046 EXPORT_SYMBOL(generic_writepages);
1047
1048 int do_writepages(struct address_space *mapping, struct writeback_control *wbc)
1049 {
1050         int ret;
1051
1052         if (wbc->nr_to_write <= 0)
1053                 return 0;
1054         if (mapping->a_ops->writepages)
1055                 ret = mapping->a_ops->writepages(mapping, wbc);
1056         else
1057                 ret = generic_writepages(mapping, wbc);
1058         return ret;
1059 }
1060
1061 /**
1062  * write_one_page - write out a single page and optionally wait on I/O
1063  * @page: the page to write
1064  * @wait: if true, wait on writeout
1065  *
1066  * The page must be locked by the caller and will be unlocked upon return.
1067  *
1068  * write_one_page() returns a negative error code if I/O failed.
1069  */
1070 int write_one_page(struct page *page, int wait)
1071 {
1072         struct address_space *mapping = page->mapping;
1073         int ret = 0;
1074         struct writeback_control wbc = {
1075                 .sync_mode = WB_SYNC_ALL,
1076                 .nr_to_write = 1,
1077         };
1078
1079         BUG_ON(!PageLocked(page));
1080
1081         if (wait)
1082                 wait_on_page_writeback(page);
1083
1084         if (clear_page_dirty_for_io(page)) {
1085                 page_cache_get(page);
1086                 ret = mapping->a_ops->writepage(page, &wbc);
1087                 if (ret == 0 && wait) {
1088                         wait_on_page_writeback(page);
1089                         if (PageError(page))
1090                                 ret = -EIO;
1091                 }
1092                 page_cache_release(page);
1093         } else {
1094                 unlock_page(page);
1095         }
1096         return ret;
1097 }
1098 EXPORT_SYMBOL(write_one_page);
1099
1100 /*
1101  * For address_spaces which do not use buffers nor write back.
1102  */
1103 int __set_page_dirty_no_writeback(struct page *page)
1104 {
1105         if (!PageDirty(page))
1106                 return !TestSetPageDirty(page);
1107         return 0;
1108 }
1109
1110 /*
1111  * Helper function for set_page_dirty family.
1112  * NOTE: This relies on being atomic wrt interrupts.
1113  */
1114 void account_page_dirtied(struct page *page, struct address_space *mapping)
1115 {
1116         if (mapping_cap_account_dirty(mapping)) {
1117                 __inc_zone_page_state(page, NR_FILE_DIRTY);
1118                 __inc_zone_page_state(page, NR_DIRTIED);
1119                 __inc_bdi_stat(mapping->backing_dev_info, BDI_RECLAIMABLE);
1120                 task_dirty_inc(current);
1121                 task_io_account_write(PAGE_CACHE_SIZE);
1122         }
1123 }
1124 EXPORT_SYMBOL(account_page_dirtied);
1125
1126 /*
1127  * Helper function for set_page_writeback family.
1128  * NOTE: Unlike account_page_dirtied this does not rely on being atomic
1129  * wrt interrupts.
1130  */
1131 void account_page_writeback(struct page *page)
1132 {
1133         inc_zone_page_state(page, NR_WRITEBACK);
1134         inc_zone_page_state(page, NR_WRITTEN);
1135 }
1136 EXPORT_SYMBOL(account_page_writeback);
1137
1138 /*
1139  * For address_spaces which do not use buffers.  Just tag the page as dirty in
1140  * its radix tree.
1141  *
1142  * This is also used when a single buffer is being dirtied: we want to set the
1143  * page dirty in that case, but not all the buffers.  This is a "bottom-up"
1144  * dirtying, whereas __set_page_dirty_buffers() is a "top-down" dirtying.
1145  *
1146  * Most callers have locked the page, which pins the address_space in memory.
1147  * But zap_pte_range() does not lock the page, however in that case the
1148  * mapping is pinned by the vma's ->vm_file reference.
1149  *
1150  * We take care to handle the case where the page was truncated from the
1151  * mapping by re-checking page_mapping() inside tree_lock.
1152  */
1153 int __set_page_dirty_nobuffers(struct page *page)
1154 {
1155         if (!TestSetPageDirty(page)) {
1156                 struct address_space *mapping = page_mapping(page);
1157                 struct address_space *mapping2;
1158
1159                 if (!mapping)
1160                         return 1;
1161
1162                 spin_lock_irq(&mapping->tree_lock);
1163                 mapping2 = page_mapping(page);
1164                 if (mapping2) { /* Race with truncate? */
1165                         BUG_ON(mapping2 != mapping);
1166                         WARN_ON_ONCE(!PagePrivate(page) && !PageUptodate(page));
1167                         account_page_dirtied(page, mapping);
1168                         radix_tree_tag_set(&mapping->page_tree,
1169                                 page_index(page), PAGECACHE_TAG_DIRTY);
1170                 }
1171                 spin_unlock_irq(&mapping->tree_lock);
1172                 if (mapping->host) {
1173                         /* !PageAnon && !swapper_space */
1174                         __mark_inode_dirty(mapping->host, I_DIRTY_PAGES);
1175                 }
1176                 return 1;
1177         }
1178         return 0;
1179 }
1180 EXPORT_SYMBOL(__set_page_dirty_nobuffers);
1181
1182 /*
1183  * When a writepage implementation decides that it doesn't want to write this
1184  * page for some reason, it should redirty the locked page via
1185  * redirty_page_for_writepage() and it should then unlock the page and return 0
1186  */
1187 int redirty_page_for_writepage(struct writeback_control *wbc, struct page *page)
1188 {
1189         wbc->pages_skipped++;
1190         return __set_page_dirty_nobuffers(page);
1191 }
1192 EXPORT_SYMBOL(redirty_page_for_writepage);
1193
1194 /*
1195  * Dirty a page.
1196  *
1197  * For pages with a mapping this should be done under the page lock
1198  * for the benefit of asynchronous memory errors who prefer a consistent
1199  * dirty state. This rule can be broken in some special cases,
1200  * but should be better not to.
1201  *
1202  * If the mapping doesn't provide a set_page_dirty a_op, then
1203  * just fall through and assume that it wants buffer_heads.
1204  */
1205 int set_page_dirty(struct page *page)
1206 {
1207         struct address_space *mapping = page_mapping(page);
1208
1209         if (likely(mapping)) {
1210                 int (*spd)(struct page *) = mapping->a_ops->set_page_dirty;
1211 #ifdef CONFIG_BLOCK
1212                 if (!spd)
1213                         spd = __set_page_dirty_buffers;
1214 #endif
1215                 return (*spd)(page);
1216         }
1217         if (!PageDirty(page)) {
1218                 if (!TestSetPageDirty(page))
1219                         return 1;
1220         }
1221         return 0;
1222 }
1223 EXPORT_SYMBOL(set_page_dirty);
1224
1225 /*
1226  * set_page_dirty() is racy if the caller has no reference against
1227  * page->mapping->host, and if the page is unlocked.  This is because another
1228  * CPU could truncate the page off the mapping and then free the mapping.
1229  *
1230  * Usually, the page _is_ locked, or the caller is a user-space process which
1231  * holds a reference on the inode by having an open file.
1232  *
1233  * In other cases, the page should be locked before running set_page_dirty().
1234  */
1235 int set_page_dirty_lock(struct page *page)
1236 {
1237         int ret;
1238
1239         lock_page_nosync(page);
1240         ret = set_page_dirty(page);
1241         unlock_page(page);
1242         return ret;
1243 }
1244 EXPORT_SYMBOL(set_page_dirty_lock);
1245
1246 /*
1247  * Clear a page's dirty flag, while caring for dirty memory accounting.
1248  * Returns true if the page was previously dirty.
1249  *
1250  * This is for preparing to put the page under writeout.  We leave the page
1251  * tagged as dirty in the radix tree so that a concurrent write-for-sync
1252  * can discover it via a PAGECACHE_TAG_DIRTY walk.  The ->writepage
1253  * implementation will run either set_page_writeback() or set_page_dirty(),
1254  * at which stage we bring the page's dirty flag and radix-tree dirty tag
1255  * back into sync.
1256  *
1257  * This incoherency between the page's dirty flag and radix-tree tag is
1258  * unfortunate, but it only exists while the page is locked.
1259  */
1260 int clear_page_dirty_for_io(struct page *page)
1261 {
1262         struct address_space *mapping = page_mapping(page);
1263
1264         BUG_ON(!PageLocked(page));
1265
1266         ClearPageReclaim(page);
1267         if (mapping && mapping_cap_account_dirty(mapping)) {
1268                 /*
1269                  * Yes, Virginia, this is indeed insane.
1270                  *
1271                  * We use this sequence to make sure that
1272                  *  (a) we account for dirty stats properly
1273                  *  (b) we tell the low-level filesystem to
1274                  *      mark the whole page dirty if it was
1275                  *      dirty in a pagetable. Only to then
1276                  *  (c) clean the page again and return 1 to
1277                  *      cause the writeback.
1278                  *
1279                  * This way we avoid all nasty races with the
1280                  * dirty bit in multiple places and clearing
1281                  * them concurrently from different threads.
1282                  *
1283                  * Note! Normally the "set_page_dirty(page)"
1284                  * has no effect on the actual dirty bit - since
1285                  * that will already usually be set. But we
1286                  * need the side effects, and it can help us
1287                  * avoid races.
1288                  *
1289                  * We basically use the page "master dirty bit"
1290                  * as a serialization point for all the different
1291                  * threads doing their things.
1292                  */
1293                 if (page_mkclean(page))
1294                         set_page_dirty(page);
1295                 /*
1296                  * We carefully synchronise fault handlers against
1297                  * installing a dirty pte and marking the page dirty
1298                  * at this point. We do this by having them hold the
1299                  * page lock at some point after installing their
1300                  * pte, but before marking the page dirty.
1301                  * Pages are always locked coming in here, so we get
1302                  * the desired exclusion. See mm/memory.c:do_wp_page()
1303                  * for more comments.
1304                  */
1305                 if (TestClearPageDirty(page)) {
1306                         dec_zone_page_state(page, NR_FILE_DIRTY);
1307                         dec_bdi_stat(mapping->backing_dev_info,
1308                                         BDI_RECLAIMABLE);
1309                         return 1;
1310                 }
1311                 return 0;
1312         }
1313         return TestClearPageDirty(page);
1314 }
1315 EXPORT_SYMBOL(clear_page_dirty_for_io);
1316
1317 int test_clear_page_writeback(struct page *page)
1318 {
1319         struct address_space *mapping = page_mapping(page);
1320         int ret;
1321
1322         if (mapping) {
1323                 struct backing_dev_info *bdi = mapping->backing_dev_info;
1324                 unsigned long flags;
1325
1326                 spin_lock_irqsave(&mapping->tree_lock, flags);
1327                 ret = TestClearPageWriteback(page);
1328                 if (ret) {
1329                         radix_tree_tag_clear(&mapping->page_tree,
1330                                                 page_index(page),
1331                                                 PAGECACHE_TAG_WRITEBACK);
1332                         if (bdi_cap_account_writeback(bdi)) {
1333                                 __dec_bdi_stat(bdi, BDI_WRITEBACK);
1334                                 __bdi_writeout_inc(bdi);
1335                         }
1336                 }
1337                 spin_unlock_irqrestore(&mapping->tree_lock, flags);
1338         } else {
1339                 ret = TestClearPageWriteback(page);
1340         }
1341         if (ret)
1342                 dec_zone_page_state(page, NR_WRITEBACK);
1343         return ret;
1344 }
1345
1346 int test_set_page_writeback(struct page *page)
1347 {
1348         struct address_space *mapping = page_mapping(page);
1349         int ret;
1350
1351         if (mapping) {
1352                 struct backing_dev_info *bdi = mapping->backing_dev_info;
1353                 unsigned long flags;
1354
1355                 spin_lock_irqsave(&mapping->tree_lock, flags);
1356                 ret = TestSetPageWriteback(page);
1357                 if (!ret) {
1358                         radix_tree_tag_set(&mapping->page_tree,
1359                                                 page_index(page),
1360                                                 PAGECACHE_TAG_WRITEBACK);
1361                         if (bdi_cap_account_writeback(bdi))
1362                                 __inc_bdi_stat(bdi, BDI_WRITEBACK);
1363                 }
1364                 if (!PageDirty(page))
1365                         radix_tree_tag_clear(&mapping->page_tree,
1366                                                 page_index(page),
1367                                                 PAGECACHE_TAG_DIRTY);
1368                 radix_tree_tag_clear(&mapping->page_tree,
1369                                      page_index(page),
1370                                      PAGECACHE_TAG_TOWRITE);
1371                 spin_unlock_irqrestore(&mapping->tree_lock, flags);
1372         } else {
1373                 ret = TestSetPageWriteback(page);
1374         }
1375         if (!ret)
1376                 account_page_writeback(page);
1377         return ret;
1378
1379 }
1380 EXPORT_SYMBOL(test_set_page_writeback);
1381
1382 /*
1383  * Return true if any of the pages in the mapping are marked with the
1384  * passed tag.
1385  */
1386 int mapping_tagged(struct address_space *mapping, int tag)
1387 {
1388         int ret;
1389         rcu_read_lock();
1390         ret = radix_tree_tagged(&mapping->page_tree, tag);
1391         rcu_read_unlock();
1392         return ret;
1393 }
1394 EXPORT_SYMBOL(mapping_tagged);