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