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