lib/radix-tree.c: fix overflow in radix_tree_range_tag_if_tagged()
[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  * runtime 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                 int dirty_ratio;
420
421                 dirty_ratio = vm_dirty_ratio;
422                 if (dirty_ratio < 5)
423                         dirty_ratio = 5;
424                 dirty = (dirty_ratio * available_memory) / 100;
425         }
426
427         if (dirty_background_bytes)
428                 background = DIV_ROUND_UP(dirty_background_bytes, PAGE_SIZE);
429         else
430                 background = (dirty_background_ratio * available_memory) / 100;
431
432         if (background >= dirty)
433                 background = dirty / 2;
434         tsk = current;
435         if (tsk->flags & PF_LESS_THROTTLE || rt_task(tsk)) {
436                 background += background / 4;
437                 dirty += dirty / 4;
438         }
439         *pbackground = background;
440         *pdirty = dirty;
441 }
442
443 /*
444  * bdi_dirty_limit - @bdi's share of dirty throttling threshold
445  *
446  * Allocate high/low dirty limits to fast/slow devices, in order to prevent
447  * - starving fast devices
448  * - piling up dirty pages (that will take long time to sync) on slow devices
449  *
450  * The bdi's share of dirty limit will be adapting to its throughput and
451  * bounded by the bdi->min_ratio and/or bdi->max_ratio parameters, if set.
452  */
453 unsigned long bdi_dirty_limit(struct backing_dev_info *bdi, unsigned long dirty)
454 {
455         u64 bdi_dirty;
456         long numerator, denominator;
457
458         /*
459          * Calculate this BDI's share of the dirty ratio.
460          */
461         bdi_writeout_fraction(bdi, &numerator, &denominator);
462
463         bdi_dirty = (dirty * (100 - bdi_min_ratio)) / 100;
464         bdi_dirty *= numerator;
465         do_div(bdi_dirty, denominator);
466
467         bdi_dirty += (dirty * bdi->min_ratio) / 100;
468         if (bdi_dirty > (dirty * bdi->max_ratio) / 100)
469                 bdi_dirty = dirty * bdi->max_ratio / 100;
470
471         return bdi_dirty;
472 }
473
474 /*
475  * balance_dirty_pages() must be called by processes which are generating dirty
476  * data.  It looks at the number of dirty pages in the machine and will force
477  * the caller to perform writeback if the system is over `vm_dirty_ratio'.
478  * If we're over `background_thresh' then the writeback threads are woken to
479  * perform some writeout.
480  */
481 static void balance_dirty_pages(struct address_space *mapping,
482                                 unsigned long write_chunk)
483 {
484         long nr_reclaimable, bdi_nr_reclaimable;
485         long nr_writeback, bdi_nr_writeback;
486         unsigned long background_thresh;
487         unsigned long dirty_thresh;
488         unsigned long bdi_thresh;
489         unsigned long pages_written = 0;
490         unsigned long pause = 1;
491         bool dirty_exceeded = false;
492         struct backing_dev_info *bdi = mapping->backing_dev_info;
493
494         for (;;) {
495                 struct writeback_control wbc = {
496                         .sync_mode      = WB_SYNC_NONE,
497                         .older_than_this = NULL,
498                         .nr_to_write    = write_chunk,
499                         .range_cyclic   = 1,
500                 };
501
502                 nr_reclaimable = global_page_state(NR_FILE_DIRTY) +
503                                         global_page_state(NR_UNSTABLE_NFS);
504                 nr_writeback = global_page_state(NR_WRITEBACK);
505
506                 global_dirty_limits(&background_thresh, &dirty_thresh);
507
508                 /*
509                  * Throttle it only when the background writeback cannot
510                  * catch-up. This avoids (excessively) small writeouts
511                  * when the bdi limits are ramping up.
512                  */
513                 if (nr_reclaimable + nr_writeback <
514                                 (background_thresh + dirty_thresh) / 2)
515                         break;
516
517                 bdi_thresh = bdi_dirty_limit(bdi, dirty_thresh);
518                 bdi_thresh = task_dirty_limit(current, bdi_thresh);
519
520                 /*
521                  * In order to avoid the stacked BDI deadlock we need
522                  * to ensure we accurately count the 'dirty' pages when
523                  * the threshold is low.
524                  *
525                  * Otherwise it would be possible to get thresh+n pages
526                  * reported dirty, even though there are thresh-m pages
527                  * actually dirty; with m+n sitting in the percpu
528                  * deltas.
529                  */
530                 if (bdi_thresh < 2*bdi_stat_error(bdi)) {
531                         bdi_nr_reclaimable = bdi_stat_sum(bdi, BDI_RECLAIMABLE);
532                         bdi_nr_writeback = bdi_stat_sum(bdi, BDI_WRITEBACK);
533                 } else {
534                         bdi_nr_reclaimable = bdi_stat(bdi, BDI_RECLAIMABLE);
535                         bdi_nr_writeback = bdi_stat(bdi, BDI_WRITEBACK);
536                 }
537
538                 /*
539                  * The bdi thresh is somehow "soft" limit derived from the
540                  * global "hard" limit. The former helps to prevent heavy IO
541                  * bdi or process from holding back light ones; The latter is
542                  * the last resort safeguard.
543                  */
544                 dirty_exceeded =
545                         (bdi_nr_reclaimable + bdi_nr_writeback >= bdi_thresh)
546                         || (nr_reclaimable + nr_writeback >= dirty_thresh);
547
548                 if (!dirty_exceeded)
549                         break;
550
551                 if (!bdi->dirty_exceeded)
552                         bdi->dirty_exceeded = 1;
553
554                 /* Note: nr_reclaimable denotes nr_dirty + nr_unstable.
555                  * Unstable writes are a feature of certain networked
556                  * filesystems (i.e. NFS) in which data may have been
557                  * written to the server's write cache, but has not yet
558                  * been flushed to permanent storage.
559                  * Only move pages to writeback if this bdi is over its
560                  * threshold otherwise wait until the disk writes catch
561                  * up.
562                  */
563                 trace_wbc_balance_dirty_start(&wbc, bdi);
564                 if (bdi_nr_reclaimable > bdi_thresh) {
565                         writeback_inodes_wb(&bdi->wb, &wbc);
566                         pages_written += write_chunk - wbc.nr_to_write;
567                         trace_wbc_balance_dirty_written(&wbc, bdi);
568                         if (pages_written >= write_chunk)
569                                 break;          /* We've done our duty */
570                 }
571                 trace_wbc_balance_dirty_wait(&wbc, bdi);
572                 __set_current_state(TASK_INTERRUPTIBLE);
573                 io_schedule_timeout(pause);
574
575                 /*
576                  * Increase the delay for each loop, up to our previous
577                  * default of taking a 100ms nap.
578                  */
579                 pause <<= 1;
580                 if (pause > HZ / 10)
581                         pause = HZ / 10;
582         }
583
584         if (!dirty_exceeded && bdi->dirty_exceeded)
585                 bdi->dirty_exceeded = 0;
586
587         if (writeback_in_progress(bdi))
588                 return;
589
590         /*
591          * In laptop mode, we wait until hitting the higher threshold before
592          * starting background writeout, and then write out all the way down
593          * to the lower threshold.  So slow writers cause minimal disk activity.
594          *
595          * In normal mode, we start background writeout at the lower
596          * background_thresh, to keep the amount of dirty memory low.
597          */
598         if ((laptop_mode && pages_written) ||
599             (!laptop_mode && (nr_reclaimable > background_thresh)))
600                 bdi_start_background_writeback(bdi);
601 }
602
603 void set_page_dirty_balance(struct page *page, int page_mkwrite)
604 {
605         if (set_page_dirty(page) || page_mkwrite) {
606                 struct address_space *mapping = page_mapping(page);
607
608                 if (mapping)
609                         balance_dirty_pages_ratelimited(mapping);
610         }
611 }
612
613 static DEFINE_PER_CPU(unsigned long, bdp_ratelimits) = 0;
614
615 /**
616  * balance_dirty_pages_ratelimited_nr - balance dirty memory state
617  * @mapping: address_space which was dirtied
618  * @nr_pages_dirtied: number of pages which the caller has just dirtied
619  *
620  * Processes which are dirtying memory should call in here once for each page
621  * which was newly dirtied.  The function will periodically check the system's
622  * dirty state and will initiate writeback if needed.
623  *
624  * On really big machines, get_writeback_state is expensive, so try to avoid
625  * calling it too often (ratelimiting).  But once we're over the dirty memory
626  * limit we decrease the ratelimiting by a lot, to prevent individual processes
627  * from overshooting the limit by (ratelimit_pages) each.
628  */
629 void balance_dirty_pages_ratelimited_nr(struct address_space *mapping,
630                                         unsigned long nr_pages_dirtied)
631 {
632         unsigned long ratelimit;
633         unsigned long *p;
634
635         ratelimit = ratelimit_pages;
636         if (mapping->backing_dev_info->dirty_exceeded)
637                 ratelimit = 8;
638
639         /*
640          * Check the rate limiting. Also, we do not want to throttle real-time
641          * tasks in balance_dirty_pages(). Period.
642          */
643         preempt_disable();
644         p =  &__get_cpu_var(bdp_ratelimits);
645         *p += nr_pages_dirtied;
646         if (unlikely(*p >= ratelimit)) {
647                 ratelimit = sync_writeback_pages(*p);
648                 *p = 0;
649                 preempt_enable();
650                 balance_dirty_pages(mapping, ratelimit);
651                 return;
652         }
653         preempt_enable();
654 }
655 EXPORT_SYMBOL(balance_dirty_pages_ratelimited_nr);
656
657 void throttle_vm_writeout(gfp_t gfp_mask)
658 {
659         unsigned long background_thresh;
660         unsigned long dirty_thresh;
661
662         for ( ; ; ) {
663                 global_dirty_limits(&background_thresh, &dirty_thresh);
664
665                 /*
666                  * Boost the allowable dirty threshold a bit for page
667                  * allocators so they don't get DoS'ed by heavy writers
668                  */
669                 dirty_thresh += dirty_thresh / 10;      /* wheeee... */
670
671                 if (global_page_state(NR_UNSTABLE_NFS) +
672                         global_page_state(NR_WRITEBACK) <= dirty_thresh)
673                                 break;
674                 congestion_wait(BLK_RW_ASYNC, HZ/10);
675
676                 /*
677                  * The caller might hold locks which can prevent IO completion
678                  * or progress in the filesystem.  So we cannot just sit here
679                  * waiting for IO to complete.
680                  */
681                 if ((gfp_mask & (__GFP_FS|__GFP_IO)) != (__GFP_FS|__GFP_IO))
682                         break;
683         }
684 }
685
686 /*
687  * sysctl handler for /proc/sys/vm/dirty_writeback_centisecs
688  */
689 int dirty_writeback_centisecs_handler(ctl_table *table, int write,
690         void __user *buffer, size_t *length, loff_t *ppos)
691 {
692         proc_dointvec(table, write, buffer, length, ppos);
693         bdi_arm_supers_timer();
694         return 0;
695 }
696
697 #ifdef CONFIG_BLOCK
698 void laptop_mode_timer_fn(unsigned long data)
699 {
700         struct request_queue *q = (struct request_queue *)data;
701         int nr_pages = global_page_state(NR_FILE_DIRTY) +
702                 global_page_state(NR_UNSTABLE_NFS);
703
704         /*
705          * We want to write everything out, not just down to the dirty
706          * threshold
707          */
708         if (bdi_has_dirty_io(&q->backing_dev_info))
709                 bdi_start_writeback(&q->backing_dev_info, nr_pages);
710 }
711
712 /*
713  * We've spun up the disk and we're in laptop mode: schedule writeback
714  * of all dirty data a few seconds from now.  If the flush is already scheduled
715  * then push it back - the user is still using the disk.
716  */
717 void laptop_io_completion(struct backing_dev_info *info)
718 {
719         mod_timer(&info->laptop_mode_wb_timer, jiffies + laptop_mode);
720 }
721
722 /*
723  * We're in laptop mode and we've just synced. The sync's writes will have
724  * caused another writeback to be scheduled by laptop_io_completion.
725  * Nothing needs to be written back anymore, so we unschedule the writeback.
726  */
727 void laptop_sync_completion(void)
728 {
729         struct backing_dev_info *bdi;
730
731         rcu_read_lock();
732
733         list_for_each_entry_rcu(bdi, &bdi_list, bdi_list)
734                 del_timer(&bdi->laptop_mode_wb_timer);
735
736         rcu_read_unlock();
737 }
738 #endif
739
740 /*
741  * If ratelimit_pages is too high then we can get into dirty-data overload
742  * if a large number of processes all perform writes at the same time.
743  * If it is too low then SMP machines will call the (expensive)
744  * get_writeback_state too often.
745  *
746  * Here we set ratelimit_pages to a level which ensures that when all CPUs are
747  * dirtying in parallel, we cannot go more than 3% (1/32) over the dirty memory
748  * thresholds before writeback cuts in.
749  *
750  * But the limit should not be set too high.  Because it also controls the
751  * amount of memory which the balance_dirty_pages() caller has to write back.
752  * If this is too large then the caller will block on the IO queue all the
753  * time.  So limit it to four megabytes - the balance_dirty_pages() caller
754  * will write six megabyte chunks, max.
755  */
756
757 void writeback_set_ratelimit(void)
758 {
759         ratelimit_pages = vm_total_pages / (num_online_cpus() * 32);
760         if (ratelimit_pages < 16)
761                 ratelimit_pages = 16;
762         if (ratelimit_pages * PAGE_CACHE_SIZE > 4096 * 1024)
763                 ratelimit_pages = (4096 * 1024) / PAGE_CACHE_SIZE;
764 }
765
766 static int __cpuinit
767 ratelimit_handler(struct notifier_block *self, unsigned long u, void *v)
768 {
769         writeback_set_ratelimit();
770         return NOTIFY_DONE;
771 }
772
773 static struct notifier_block __cpuinitdata ratelimit_nb = {
774         .notifier_call  = ratelimit_handler,
775         .next           = NULL,
776 };
777
778 /*
779  * Called early on to tune the page writeback dirty limits.
780  *
781  * We used to scale dirty pages according to how total memory
782  * related to pages that could be allocated for buffers (by
783  * comparing nr_free_buffer_pages() to vm_total_pages.
784  *
785  * However, that was when we used "dirty_ratio" to scale with
786  * all memory, and we don't do that any more. "dirty_ratio"
787  * is now applied to total non-HIGHPAGE memory (by subtracting
788  * totalhigh_pages from vm_total_pages), and as such we can't
789  * get into the old insane situation any more where we had
790  * large amounts of dirty pages compared to a small amount of
791  * non-HIGHMEM memory.
792  *
793  * But we might still want to scale the dirty_ratio by how
794  * much memory the box has..
795  */
796 void __init page_writeback_init(void)
797 {
798         int shift;
799
800         writeback_set_ratelimit();
801         register_cpu_notifier(&ratelimit_nb);
802
803         shift = calc_period_shift();
804         prop_descriptor_init(&vm_completions, shift);
805         prop_descriptor_init(&vm_dirties, shift);
806 }
807
808 /**
809  * tag_pages_for_writeback - tag pages to be written by write_cache_pages
810  * @mapping: address space structure to write
811  * @start: starting page index
812  * @end: ending page index (inclusive)
813  *
814  * This function scans the page range from @start to @end (inclusive) and tags
815  * all pages that have DIRTY tag set with a special TOWRITE tag. The idea is
816  * that write_cache_pages (or whoever calls this function) will then use
817  * TOWRITE tag to identify pages eligible for writeback.  This mechanism is
818  * used to avoid livelocking of writeback by a process steadily creating new
819  * dirty pages in the file (thus it is important for this function to be quick
820  * so that it can tag pages faster than a dirtying process can create them).
821  */
822 /*
823  * We tag pages in batches of WRITEBACK_TAG_BATCH to reduce tree_lock latency.
824  */
825 void tag_pages_for_writeback(struct address_space *mapping,
826                              pgoff_t start, pgoff_t end)
827 {
828 #define WRITEBACK_TAG_BATCH 4096
829         unsigned long tagged;
830
831         do {
832                 spin_lock_irq(&mapping->tree_lock);
833                 tagged = radix_tree_range_tag_if_tagged(&mapping->page_tree,
834                                 &start, end, WRITEBACK_TAG_BATCH,
835                                 PAGECACHE_TAG_DIRTY, PAGECACHE_TAG_TOWRITE);
836                 spin_unlock_irq(&mapping->tree_lock);
837                 WARN_ON_ONCE(tagged > WRITEBACK_TAG_BATCH);
838                 cond_resched();
839                 /* We check 'start' to handle wrapping when end == ~0UL */
840         } while (tagged >= WRITEBACK_TAG_BATCH && start);
841 }
842 EXPORT_SYMBOL(tag_pages_for_writeback);
843
844 /**
845  * write_cache_pages - walk the list of dirty pages of the given address space and write all of them.
846  * @mapping: address space structure to write
847  * @wbc: subtract the number of written pages from *@wbc->nr_to_write
848  * @writepage: function called for each page
849  * @data: data passed to writepage function
850  *
851  * If a page is already under I/O, write_cache_pages() skips it, even
852  * if it's dirty.  This is desirable behaviour for memory-cleaning writeback,
853  * but it is INCORRECT for data-integrity system calls such as fsync().  fsync()
854  * and msync() need to guarantee that all the data which was dirty at the time
855  * the call was made get new I/O started against them.  If wbc->sync_mode is
856  * WB_SYNC_ALL then we were called for data integrity and we must wait for
857  * existing IO to complete.
858  *
859  * To avoid livelocks (when other process dirties new pages), we first tag
860  * pages which should be written back with TOWRITE tag and only then start
861  * writing them. For data-integrity sync we have to be careful so that we do
862  * not miss some pages (e.g., because some other process has cleared TOWRITE
863  * tag we set). The rule we follow is that TOWRITE tag can be cleared only
864  * by the process clearing the DIRTY tag (and submitting the page for IO).
865  */
866 int write_cache_pages(struct address_space *mapping,
867                       struct writeback_control *wbc, writepage_t writepage,
868                       void *data)
869 {
870         int ret = 0;
871         int done = 0;
872         struct pagevec pvec;
873         int nr_pages;
874         pgoff_t uninitialized_var(writeback_index);
875         pgoff_t index;
876         pgoff_t end;            /* Inclusive */
877         pgoff_t done_index;
878         int cycled;
879         int range_whole = 0;
880         int tag;
881
882         pagevec_init(&pvec, 0);
883         if (wbc->range_cyclic) {
884                 writeback_index = mapping->writeback_index; /* prev offset */
885                 index = writeback_index;
886                 if (index == 0)
887                         cycled = 1;
888                 else
889                         cycled = 0;
890                 end = -1;
891         } else {
892                 index = wbc->range_start >> PAGE_CACHE_SHIFT;
893                 end = wbc->range_end >> PAGE_CACHE_SHIFT;
894                 if (wbc->range_start == 0 && wbc->range_end == LLONG_MAX)
895                         range_whole = 1;
896                 cycled = 1; /* ignore range_cyclic tests */
897         }
898         if (wbc->sync_mode == WB_SYNC_ALL)
899                 tag = PAGECACHE_TAG_TOWRITE;
900         else
901                 tag = PAGECACHE_TAG_DIRTY;
902 retry:
903         if (wbc->sync_mode == WB_SYNC_ALL)
904                 tag_pages_for_writeback(mapping, index, end);
905         done_index = index;
906         while (!done && (index <= end)) {
907                 int i;
908
909                 nr_pages = pagevec_lookup_tag(&pvec, mapping, &index, tag,
910                               min(end - index, (pgoff_t)PAGEVEC_SIZE-1) + 1);
911                 if (nr_pages == 0)
912                         break;
913
914                 for (i = 0; i < nr_pages; i++) {
915                         struct page *page = pvec.pages[i];
916
917                         /*
918                          * At this point, the page may be truncated or
919                          * invalidated (changing page->mapping to NULL), or
920                          * even swizzled back from swapper_space to tmpfs file
921                          * mapping. However, page->index will not change
922                          * because we have a reference on the page.
923                          */
924                         if (page->index > end) {
925                                 /*
926                                  * can't be range_cyclic (1st pass) because
927                                  * end == -1 in that case.
928                                  */
929                                 done = 1;
930                                 break;
931                         }
932
933                         done_index = page->index + 1;
934
935                         lock_page(page);
936
937                         /*
938                          * Page truncated or invalidated. We can freely skip it
939                          * then, even for data integrity operations: the page
940                          * has disappeared concurrently, so there could be no
941                          * real expectation of this data interity operation
942                          * even if there is now a new, dirty page at the same
943                          * pagecache address.
944                          */
945                         if (unlikely(page->mapping != mapping)) {
946 continue_unlock:
947                                 unlock_page(page);
948                                 continue;
949                         }
950
951                         if (!PageDirty(page)) {
952                                 /* someone wrote it for us */
953                                 goto continue_unlock;
954                         }
955
956                         if (PageWriteback(page)) {
957                                 if (wbc->sync_mode != WB_SYNC_NONE)
958                                         wait_on_page_writeback(page);
959                                 else
960                                         goto continue_unlock;
961                         }
962
963                         BUG_ON(PageWriteback(page));
964                         if (!clear_page_dirty_for_io(page))
965                                 goto continue_unlock;
966
967                         trace_wbc_writepage(wbc, mapping->backing_dev_info);
968                         ret = (*writepage)(page, wbc, data);
969                         if (unlikely(ret)) {
970                                 if (ret == AOP_WRITEPAGE_ACTIVATE) {
971                                         unlock_page(page);
972                                         ret = 0;
973                                 } else {
974                                         /*
975                                          * done_index is set past this page,
976                                          * so media errors will not choke
977                                          * background writeout for the entire
978                                          * file. This has consequences for
979                                          * range_cyclic semantics (ie. it may
980                                          * not be suitable for data integrity
981                                          * writeout).
982                                          */
983                                         done = 1;
984                                         break;
985                                 }
986                         }
987
988                         if (wbc->nr_to_write > 0) {
989                                 if (--wbc->nr_to_write == 0 &&
990                                     wbc->sync_mode == WB_SYNC_NONE) {
991                                         /*
992                                          * We stop writing back only if we are
993                                          * not doing integrity sync. In case of
994                                          * integrity sync we have to keep going
995                                          * because someone may be concurrently
996                                          * dirtying pages, and we might have
997                                          * synced a lot of newly appeared dirty
998                                          * pages, but have not synced all of the
999                                          * old dirty pages.
1000                                          */
1001                                         done = 1;
1002                                         break;
1003                                 }
1004                         }
1005                 }
1006                 pagevec_release(&pvec);
1007                 cond_resched();
1008         }
1009         if (!cycled && !done) {
1010                 /*
1011                  * range_cyclic:
1012                  * We hit the last page and there is more work to be done: wrap
1013                  * back to the start of the file
1014                  */
1015                 cycled = 1;
1016                 index = 0;
1017                 end = writeback_index - 1;
1018                 goto retry;
1019         }
1020         if (wbc->range_cyclic || (range_whole && wbc->nr_to_write > 0))
1021                 mapping->writeback_index = done_index;
1022
1023         return ret;
1024 }
1025 EXPORT_SYMBOL(write_cache_pages);
1026
1027 /*
1028  * Function used by generic_writepages to call the real writepage
1029  * function and set the mapping flags on error
1030  */
1031 static int __writepage(struct page *page, struct writeback_control *wbc,
1032                        void *data)
1033 {
1034         struct address_space *mapping = data;
1035         int ret = mapping->a_ops->writepage(page, wbc);
1036         mapping_set_error(mapping, ret);
1037         return ret;
1038 }
1039
1040 /**
1041  * generic_writepages - walk the list of dirty pages of the given address space and writepage() all of them.
1042  * @mapping: address space structure to write
1043  * @wbc: subtract the number of written pages from *@wbc->nr_to_write
1044  *
1045  * This is a library function, which implements the writepages()
1046  * address_space_operation.
1047  */
1048 int generic_writepages(struct address_space *mapping,
1049                        struct writeback_control *wbc)
1050 {
1051         /* deal with chardevs and other special file */
1052         if (!mapping->a_ops->writepage)
1053                 return 0;
1054
1055         return write_cache_pages(mapping, wbc, __writepage, mapping);
1056 }
1057
1058 EXPORT_SYMBOL(generic_writepages);
1059
1060 int do_writepages(struct address_space *mapping, struct writeback_control *wbc)
1061 {
1062         int ret;
1063
1064         if (wbc->nr_to_write <= 0)
1065                 return 0;
1066         if (mapping->a_ops->writepages)
1067                 ret = mapping->a_ops->writepages(mapping, wbc);
1068         else
1069                 ret = generic_writepages(mapping, wbc);
1070         return ret;
1071 }
1072
1073 /**
1074  * write_one_page - write out a single page and optionally wait on I/O
1075  * @page: the page to write
1076  * @wait: if true, wait on writeout
1077  *
1078  * The page must be locked by the caller and will be unlocked upon return.
1079  *
1080  * write_one_page() returns a negative error code if I/O failed.
1081  */
1082 int write_one_page(struct page *page, int wait)
1083 {
1084         struct address_space *mapping = page->mapping;
1085         int ret = 0;
1086         struct writeback_control wbc = {
1087                 .sync_mode = WB_SYNC_ALL,
1088                 .nr_to_write = 1,
1089         };
1090
1091         BUG_ON(!PageLocked(page));
1092
1093         if (wait)
1094                 wait_on_page_writeback(page);
1095
1096         if (clear_page_dirty_for_io(page)) {
1097                 page_cache_get(page);
1098                 ret = mapping->a_ops->writepage(page, &wbc);
1099                 if (ret == 0 && wait) {
1100                         wait_on_page_writeback(page);
1101                         if (PageError(page))
1102                                 ret = -EIO;
1103                 }
1104                 page_cache_release(page);
1105         } else {
1106                 unlock_page(page);
1107         }
1108         return ret;
1109 }
1110 EXPORT_SYMBOL(write_one_page);
1111
1112 /*
1113  * For address_spaces which do not use buffers nor write back.
1114  */
1115 int __set_page_dirty_no_writeback(struct page *page)
1116 {
1117         if (!PageDirty(page))
1118                 SetPageDirty(page);
1119         return 0;
1120 }
1121
1122 /*
1123  * Helper function for set_page_dirty family.
1124  * NOTE: This relies on being atomic wrt interrupts.
1125  */
1126 void account_page_dirtied(struct page *page, struct address_space *mapping)
1127 {
1128         if (mapping_cap_account_dirty(mapping)) {
1129                 __inc_zone_page_state(page, NR_FILE_DIRTY);
1130                 __inc_bdi_stat(mapping->backing_dev_info, BDI_RECLAIMABLE);
1131                 task_dirty_inc(current);
1132                 task_io_account_write(PAGE_CACHE_SIZE);
1133         }
1134 }
1135
1136 /*
1137  * For address_spaces which do not use buffers.  Just tag the page as dirty in
1138  * its radix tree.
1139  *
1140  * This is also used when a single buffer is being dirtied: we want to set the
1141  * page dirty in that case, but not all the buffers.  This is a "bottom-up"
1142  * dirtying, whereas __set_page_dirty_buffers() is a "top-down" dirtying.
1143  *
1144  * Most callers have locked the page, which pins the address_space in memory.
1145  * But zap_pte_range() does not lock the page, however in that case the
1146  * mapping is pinned by the vma's ->vm_file reference.
1147  *
1148  * We take care to handle the case where the page was truncated from the
1149  * mapping by re-checking page_mapping() inside tree_lock.
1150  */
1151 int __set_page_dirty_nobuffers(struct page *page)
1152 {
1153         if (!TestSetPageDirty(page)) {
1154                 struct address_space *mapping = page_mapping(page);
1155                 struct address_space *mapping2;
1156
1157                 if (!mapping)
1158                         return 1;
1159
1160                 spin_lock_irq(&mapping->tree_lock);
1161                 mapping2 = page_mapping(page);
1162                 if (mapping2) { /* Race with truncate? */
1163                         BUG_ON(mapping2 != mapping);
1164                         WARN_ON_ONCE(!PagePrivate(page) && !PageUptodate(page));
1165                         account_page_dirtied(page, mapping);
1166                         radix_tree_tag_set(&mapping->page_tree,
1167                                 page_index(page), PAGECACHE_TAG_DIRTY);
1168                 }
1169                 spin_unlock_irq(&mapping->tree_lock);
1170                 if (mapping->host) {
1171                         /* !PageAnon && !swapper_space */
1172                         __mark_inode_dirty(mapping->host, I_DIRTY_PAGES);
1173                 }
1174                 return 1;
1175         }
1176         return 0;
1177 }
1178 EXPORT_SYMBOL(__set_page_dirty_nobuffers);
1179
1180 /*
1181  * When a writepage implementation decides that it doesn't want to write this
1182  * page for some reason, it should redirty the locked page via
1183  * redirty_page_for_writepage() and it should then unlock the page and return 0
1184  */
1185 int redirty_page_for_writepage(struct writeback_control *wbc, struct page *page)
1186 {
1187         wbc->pages_skipped++;
1188         return __set_page_dirty_nobuffers(page);
1189 }
1190 EXPORT_SYMBOL(redirty_page_for_writepage);
1191
1192 /*
1193  * Dirty a page.
1194  *
1195  * For pages with a mapping this should be done under the page lock
1196  * for the benefit of asynchronous memory errors who prefer a consistent
1197  * dirty state. This rule can be broken in some special cases,
1198  * but should be better not to.
1199  *
1200  * If the mapping doesn't provide a set_page_dirty a_op, then
1201  * just fall through and assume that it wants buffer_heads.
1202  */
1203 int set_page_dirty(struct page *page)
1204 {
1205         struct address_space *mapping = page_mapping(page);
1206
1207         if (likely(mapping)) {
1208                 int (*spd)(struct page *) = mapping->a_ops->set_page_dirty;
1209 #ifdef CONFIG_BLOCK
1210                 if (!spd)
1211                         spd = __set_page_dirty_buffers;
1212 #endif
1213                 return (*spd)(page);
1214         }
1215         if (!PageDirty(page)) {
1216                 if (!TestSetPageDirty(page))
1217                         return 1;
1218         }
1219         return 0;
1220 }
1221 EXPORT_SYMBOL(set_page_dirty);
1222
1223 /*
1224  * set_page_dirty() is racy if the caller has no reference against
1225  * page->mapping->host, and if the page is unlocked.  This is because another
1226  * CPU could truncate the page off the mapping and then free the mapping.
1227  *
1228  * Usually, the page _is_ locked, or the caller is a user-space process which
1229  * holds a reference on the inode by having an open file.
1230  *
1231  * In other cases, the page should be locked before running set_page_dirty().
1232  */
1233 int set_page_dirty_lock(struct page *page)
1234 {
1235         int ret;
1236
1237         lock_page_nosync(page);
1238         ret = set_page_dirty(page);
1239         unlock_page(page);
1240         return ret;
1241 }
1242 EXPORT_SYMBOL(set_page_dirty_lock);
1243
1244 /*
1245  * Clear a page's dirty flag, while caring for dirty memory accounting.
1246  * Returns true if the page was previously dirty.
1247  *
1248  * This is for preparing to put the page under writeout.  We leave the page
1249  * tagged as dirty in the radix tree so that a concurrent write-for-sync
1250  * can discover it via a PAGECACHE_TAG_DIRTY walk.  The ->writepage
1251  * implementation will run either set_page_writeback() or set_page_dirty(),
1252  * at which stage we bring the page's dirty flag and radix-tree dirty tag
1253  * back into sync.
1254  *
1255  * This incoherency between the page's dirty flag and radix-tree tag is
1256  * unfortunate, but it only exists while the page is locked.
1257  */
1258 int clear_page_dirty_for_io(struct page *page)
1259 {
1260         struct address_space *mapping = page_mapping(page);
1261
1262         BUG_ON(!PageLocked(page));
1263
1264         ClearPageReclaim(page);
1265         if (mapping && mapping_cap_account_dirty(mapping)) {
1266                 /*
1267                  * Yes, Virginia, this is indeed insane.
1268                  *
1269                  * We use this sequence to make sure that
1270                  *  (a) we account for dirty stats properly
1271                  *  (b) we tell the low-level filesystem to
1272                  *      mark the whole page dirty if it was
1273                  *      dirty in a pagetable. Only to then
1274                  *  (c) clean the page again and return 1 to
1275                  *      cause the writeback.
1276                  *
1277                  * This way we avoid all nasty races with the
1278                  * dirty bit in multiple places and clearing
1279                  * them concurrently from different threads.
1280                  *
1281                  * Note! Normally the "set_page_dirty(page)"
1282                  * has no effect on the actual dirty bit - since
1283                  * that will already usually be set. But we
1284                  * need the side effects, and it can help us
1285                  * avoid races.
1286                  *
1287                  * We basically use the page "master dirty bit"
1288                  * as a serialization point for all the different
1289                  * threads doing their things.
1290                  */
1291                 if (page_mkclean(page))
1292                         set_page_dirty(page);
1293                 /*
1294                  * We carefully synchronise fault handlers against
1295                  * installing a dirty pte and marking the page dirty
1296                  * at this point. We do this by having them hold the
1297                  * page lock at some point after installing their
1298                  * pte, but before marking the page dirty.
1299                  * Pages are always locked coming in here, so we get
1300                  * the desired exclusion. See mm/memory.c:do_wp_page()
1301                  * for more comments.
1302                  */
1303                 if (TestClearPageDirty(page)) {
1304                         dec_zone_page_state(page, NR_FILE_DIRTY);
1305                         dec_bdi_stat(mapping->backing_dev_info,
1306                                         BDI_RECLAIMABLE);
1307                         return 1;
1308                 }
1309                 return 0;
1310         }
1311         return TestClearPageDirty(page);
1312 }
1313 EXPORT_SYMBOL(clear_page_dirty_for_io);
1314
1315 int test_clear_page_writeback(struct page *page)
1316 {
1317         struct address_space *mapping = page_mapping(page);
1318         int ret;
1319
1320         if (mapping) {
1321                 struct backing_dev_info *bdi = mapping->backing_dev_info;
1322                 unsigned long flags;
1323
1324                 spin_lock_irqsave(&mapping->tree_lock, flags);
1325                 ret = TestClearPageWriteback(page);
1326                 if (ret) {
1327                         radix_tree_tag_clear(&mapping->page_tree,
1328                                                 page_index(page),
1329                                                 PAGECACHE_TAG_WRITEBACK);
1330                         if (bdi_cap_account_writeback(bdi)) {
1331                                 __dec_bdi_stat(bdi, BDI_WRITEBACK);
1332                                 __bdi_writeout_inc(bdi);
1333                         }
1334                 }
1335                 spin_unlock_irqrestore(&mapping->tree_lock, flags);
1336         } else {
1337                 ret = TestClearPageWriteback(page);
1338         }
1339         if (ret)
1340                 dec_zone_page_state(page, NR_WRITEBACK);
1341         return ret;
1342 }
1343
1344 int test_set_page_writeback(struct page *page)
1345 {
1346         struct address_space *mapping = page_mapping(page);
1347         int ret;
1348
1349         if (mapping) {
1350                 struct backing_dev_info *bdi = mapping->backing_dev_info;
1351                 unsigned long flags;
1352
1353                 spin_lock_irqsave(&mapping->tree_lock, flags);
1354                 ret = TestSetPageWriteback(page);
1355                 if (!ret) {
1356                         radix_tree_tag_set(&mapping->page_tree,
1357                                                 page_index(page),
1358                                                 PAGECACHE_TAG_WRITEBACK);
1359                         if (bdi_cap_account_writeback(bdi))
1360                                 __inc_bdi_stat(bdi, BDI_WRITEBACK);
1361                 }
1362                 if (!PageDirty(page))
1363                         radix_tree_tag_clear(&mapping->page_tree,
1364                                                 page_index(page),
1365                                                 PAGECACHE_TAG_DIRTY);
1366                 radix_tree_tag_clear(&mapping->page_tree,
1367                                      page_index(page),
1368                                      PAGECACHE_TAG_TOWRITE);
1369                 spin_unlock_irqrestore(&mapping->tree_lock, flags);
1370         } else {
1371                 ret = TestSetPageWriteback(page);
1372         }
1373         if (!ret)
1374                 inc_zone_page_state(page, NR_WRITEBACK);
1375         return ret;
1376
1377 }
1378 EXPORT_SYMBOL(test_set_page_writeback);
1379
1380 /*
1381  * Return true if any of the pages in the mapping are marked with the
1382  * passed tag.
1383  */
1384 int mapping_tagged(struct address_space *mapping, int tag)
1385 {
1386         int ret;
1387         rcu_read_lock();
1388         ret = radix_tree_tagged(&mapping->page_tree, tag);
1389         rcu_read_unlock();
1390         return ret;
1391 }
1392 EXPORT_SYMBOL(mapping_tagged);