Merge branch 'for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/mason/btrfs...
[linux-3.10.git] / fs / fs-writeback.c
1 /*
2  * fs/fs-writeback.c
3  *
4  * Copyright (C) 2002, Linus Torvalds.
5  *
6  * Contains all the functions related to writing back and waiting
7  * upon dirty inodes against superblocks, and writing back dirty
8  * pages against inodes.  ie: data writeback.  Writeout of the
9  * inode itself is not handled here.
10  *
11  * 10Apr2002    Andrew Morton
12  *              Split out of fs/inode.c
13  *              Additions for address_space-based writeback
14  */
15
16 #include <linux/kernel.h>
17 #include <linux/module.h>
18 #include <linux/spinlock.h>
19 #include <linux/slab.h>
20 #include <linux/sched.h>
21 #include <linux/fs.h>
22 #include <linux/mm.h>
23 #include <linux/kthread.h>
24 #include <linux/freezer.h>
25 #include <linux/writeback.h>
26 #include <linux/blkdev.h>
27 #include <linux/backing-dev.h>
28 #include <linux/buffer_head.h>
29 #include <linux/tracepoint.h>
30 #include "internal.h"
31
32 /*
33  * Passed into wb_writeback(), essentially a subset of writeback_control
34  */
35 struct wb_writeback_work {
36         long nr_pages;
37         struct super_block *sb;
38         enum writeback_sync_modes sync_mode;
39         unsigned int for_kupdate:1;
40         unsigned int range_cyclic:1;
41         unsigned int for_background:1;
42
43         struct list_head list;          /* pending work list */
44         struct completion *done;        /* set if the caller waits */
45 };
46
47 /*
48  * Include the creation of the trace points after defining the
49  * wb_writeback_work structure so that the definition remains local to this
50  * file.
51  */
52 #define CREATE_TRACE_POINTS
53 #include <trace/events/writeback.h>
54
55 /*
56  * We don't actually have pdflush, but this one is exported though /proc...
57  */
58 int nr_pdflush_threads;
59
60 /**
61  * writeback_in_progress - determine whether there is writeback in progress
62  * @bdi: the device's backing_dev_info structure.
63  *
64  * Determine whether there is writeback waiting to be handled against a
65  * backing device.
66  */
67 int writeback_in_progress(struct backing_dev_info *bdi)
68 {
69         return test_bit(BDI_writeback_running, &bdi->state);
70 }
71
72 static inline struct backing_dev_info *inode_to_bdi(struct inode *inode)
73 {
74         struct super_block *sb = inode->i_sb;
75
76         if (strcmp(sb->s_type->name, "bdev") == 0)
77                 return inode->i_mapping->backing_dev_info;
78
79         return sb->s_bdi;
80 }
81
82 static inline struct inode *wb_inode(struct list_head *head)
83 {
84         return list_entry(head, struct inode, i_wb_list);
85 }
86
87 static void bdi_queue_work(struct backing_dev_info *bdi,
88                 struct wb_writeback_work *work)
89 {
90         trace_writeback_queue(bdi, work);
91
92         spin_lock_bh(&bdi->wb_lock);
93         list_add_tail(&work->list, &bdi->work_list);
94         if (bdi->wb.task) {
95                 wake_up_process(bdi->wb.task);
96         } else {
97                 /*
98                  * The bdi thread isn't there, wake up the forker thread which
99                  * will create and run it.
100                  */
101                 trace_writeback_nothread(bdi, work);
102                 wake_up_process(default_backing_dev_info.wb.task);
103         }
104         spin_unlock_bh(&bdi->wb_lock);
105 }
106
107 static void
108 __bdi_start_writeback(struct backing_dev_info *bdi, long nr_pages,
109                 bool range_cyclic, bool for_background)
110 {
111         struct wb_writeback_work *work;
112
113         /*
114          * This is WB_SYNC_NONE writeback, so if allocation fails just
115          * wakeup the thread for old dirty data writeback
116          */
117         work = kzalloc(sizeof(*work), GFP_ATOMIC);
118         if (!work) {
119                 if (bdi->wb.task) {
120                         trace_writeback_nowork(bdi);
121                         wake_up_process(bdi->wb.task);
122                 }
123                 return;
124         }
125
126         work->sync_mode = WB_SYNC_NONE;
127         work->nr_pages  = nr_pages;
128         work->range_cyclic = range_cyclic;
129         work->for_background = for_background;
130
131         bdi_queue_work(bdi, work);
132 }
133
134 /**
135  * bdi_start_writeback - start writeback
136  * @bdi: the backing device to write from
137  * @nr_pages: the number of pages to write
138  *
139  * Description:
140  *   This does WB_SYNC_NONE opportunistic writeback. The IO is only
141  *   started when this function returns, we make no guarentees on
142  *   completion. Caller need not hold sb s_umount semaphore.
143  *
144  */
145 void bdi_start_writeback(struct backing_dev_info *bdi, long nr_pages)
146 {
147         __bdi_start_writeback(bdi, nr_pages, true, false);
148 }
149
150 /**
151  * bdi_start_background_writeback - start background writeback
152  * @bdi: the backing device to write from
153  *
154  * Description:
155  *   This does WB_SYNC_NONE background writeback. The IO is only
156  *   started when this function returns, we make no guarentees on
157  *   completion. Caller need not hold sb s_umount semaphore.
158  */
159 void bdi_start_background_writeback(struct backing_dev_info *bdi)
160 {
161         __bdi_start_writeback(bdi, LONG_MAX, true, true);
162 }
163
164 /*
165  * Redirty an inode: set its when-it-was dirtied timestamp and move it to the
166  * furthest end of its superblock's dirty-inode list.
167  *
168  * Before stamping the inode's ->dirtied_when, we check to see whether it is
169  * already the most-recently-dirtied inode on the b_dirty list.  If that is
170  * the case then the inode must have been redirtied while it was being written
171  * out and we don't reset its dirtied_when.
172  */
173 static void redirty_tail(struct inode *inode)
174 {
175         struct bdi_writeback *wb = &inode_to_bdi(inode)->wb;
176
177         if (!list_empty(&wb->b_dirty)) {
178                 struct inode *tail;
179
180                 tail = wb_inode(wb->b_dirty.next);
181                 if (time_before(inode->dirtied_when, tail->dirtied_when))
182                         inode->dirtied_when = jiffies;
183         }
184         list_move(&inode->i_wb_list, &wb->b_dirty);
185 }
186
187 /*
188  * requeue inode for re-scanning after bdi->b_io list is exhausted.
189  */
190 static void requeue_io(struct inode *inode)
191 {
192         struct bdi_writeback *wb = &inode_to_bdi(inode)->wb;
193
194         list_move(&inode->i_wb_list, &wb->b_more_io);
195 }
196
197 static void inode_sync_complete(struct inode *inode)
198 {
199         /*
200          * Prevent speculative execution through spin_unlock(&inode_lock);
201          */
202         smp_mb();
203         wake_up_bit(&inode->i_state, __I_SYNC);
204 }
205
206 static bool inode_dirtied_after(struct inode *inode, unsigned long t)
207 {
208         bool ret = time_after(inode->dirtied_when, t);
209 #ifndef CONFIG_64BIT
210         /*
211          * For inodes being constantly redirtied, dirtied_when can get stuck.
212          * It _appears_ to be in the future, but is actually in distant past.
213          * This test is necessary to prevent such wrapped-around relative times
214          * from permanently stopping the whole bdi writeback.
215          */
216         ret = ret && time_before_eq(inode->dirtied_when, jiffies);
217 #endif
218         return ret;
219 }
220
221 /*
222  * Move expired dirty inodes from @delaying_queue to @dispatch_queue.
223  */
224 static void move_expired_inodes(struct list_head *delaying_queue,
225                                struct list_head *dispatch_queue,
226                                 unsigned long *older_than_this)
227 {
228         LIST_HEAD(tmp);
229         struct list_head *pos, *node;
230         struct super_block *sb = NULL;
231         struct inode *inode;
232         int do_sb_sort = 0;
233
234         while (!list_empty(delaying_queue)) {
235                 inode = wb_inode(delaying_queue->prev);
236                 if (older_than_this &&
237                     inode_dirtied_after(inode, *older_than_this))
238                         break;
239                 if (sb && sb != inode->i_sb)
240                         do_sb_sort = 1;
241                 sb = inode->i_sb;
242                 list_move(&inode->i_wb_list, &tmp);
243         }
244
245         /* just one sb in list, splice to dispatch_queue and we're done */
246         if (!do_sb_sort) {
247                 list_splice(&tmp, dispatch_queue);
248                 return;
249         }
250
251         /* Move inodes from one superblock together */
252         while (!list_empty(&tmp)) {
253                 sb = wb_inode(tmp.prev)->i_sb;
254                 list_for_each_prev_safe(pos, node, &tmp) {
255                         inode = wb_inode(pos);
256                         if (inode->i_sb == sb)
257                                 list_move(&inode->i_wb_list, dispatch_queue);
258                 }
259         }
260 }
261
262 /*
263  * Queue all expired dirty inodes for io, eldest first.
264  * Before
265  *         newly dirtied     b_dirty    b_io    b_more_io
266  *         =============>    gf         edc     BA
267  * After
268  *         newly dirtied     b_dirty    b_io    b_more_io
269  *         =============>    g          fBAedc
270  *                                           |
271  *                                           +--> dequeue for IO
272  */
273 static void queue_io(struct bdi_writeback *wb, unsigned long *older_than_this)
274 {
275         list_splice_init(&wb->b_more_io, &wb->b_io);
276         move_expired_inodes(&wb->b_dirty, &wb->b_io, older_than_this);
277 }
278
279 static int write_inode(struct inode *inode, struct writeback_control *wbc)
280 {
281         if (inode->i_sb->s_op->write_inode && !is_bad_inode(inode))
282                 return inode->i_sb->s_op->write_inode(inode, wbc);
283         return 0;
284 }
285
286 /*
287  * Wait for writeback on an inode to complete.
288  */
289 static void inode_wait_for_writeback(struct inode *inode)
290 {
291         DEFINE_WAIT_BIT(wq, &inode->i_state, __I_SYNC);
292         wait_queue_head_t *wqh;
293
294         wqh = bit_waitqueue(&inode->i_state, __I_SYNC);
295          while (inode->i_state & I_SYNC) {
296                 spin_unlock(&inode_lock);
297                 __wait_on_bit(wqh, &wq, inode_wait, TASK_UNINTERRUPTIBLE);
298                 spin_lock(&inode_lock);
299         }
300 }
301
302 /*
303  * Write out an inode's dirty pages.  Called under inode_lock.  Either the
304  * caller has ref on the inode (either via __iget or via syscall against an fd)
305  * or the inode has I_WILL_FREE set (via generic_forget_inode)
306  *
307  * If `wait' is set, wait on the writeout.
308  *
309  * The whole writeout design is quite complex and fragile.  We want to avoid
310  * starvation of particular inodes when others are being redirtied, prevent
311  * livelocks, etc.
312  *
313  * Called under inode_lock.
314  */
315 static int
316 writeback_single_inode(struct inode *inode, struct writeback_control *wbc)
317 {
318         struct address_space *mapping = inode->i_mapping;
319         unsigned dirty;
320         int ret;
321
322         if (!atomic_read(&inode->i_count))
323                 WARN_ON(!(inode->i_state & (I_WILL_FREE|I_FREEING)));
324         else
325                 WARN_ON(inode->i_state & I_WILL_FREE);
326
327         if (inode->i_state & I_SYNC) {
328                 /*
329                  * If this inode is locked for writeback and we are not doing
330                  * writeback-for-data-integrity, move it to b_more_io so that
331                  * writeback can proceed with the other inodes on s_io.
332                  *
333                  * We'll have another go at writing back this inode when we
334                  * completed a full scan of b_io.
335                  */
336                 if (wbc->sync_mode != WB_SYNC_ALL) {
337                         requeue_io(inode);
338                         return 0;
339                 }
340
341                 /*
342                  * It's a data-integrity sync.  We must wait.
343                  */
344                 inode_wait_for_writeback(inode);
345         }
346
347         BUG_ON(inode->i_state & I_SYNC);
348
349         /* Set I_SYNC, reset I_DIRTY_PAGES */
350         inode->i_state |= I_SYNC;
351         inode->i_state &= ~I_DIRTY_PAGES;
352         spin_unlock(&inode_lock);
353
354         ret = do_writepages(mapping, wbc);
355
356         /*
357          * Make sure to wait on the data before writing out the metadata.
358          * This is important for filesystems that modify metadata on data
359          * I/O completion.
360          */
361         if (wbc->sync_mode == WB_SYNC_ALL) {
362                 int err = filemap_fdatawait(mapping);
363                 if (ret == 0)
364                         ret = err;
365         }
366
367         /*
368          * Some filesystems may redirty the inode during the writeback
369          * due to delalloc, clear dirty metadata flags right before
370          * write_inode()
371          */
372         spin_lock(&inode_lock);
373         dirty = inode->i_state & I_DIRTY;
374         inode->i_state &= ~(I_DIRTY_SYNC | I_DIRTY_DATASYNC);
375         spin_unlock(&inode_lock);
376         /* Don't write the inode if only I_DIRTY_PAGES was set */
377         if (dirty & (I_DIRTY_SYNC | I_DIRTY_DATASYNC)) {
378                 int err = write_inode(inode, wbc);
379                 if (ret == 0)
380                         ret = err;
381         }
382
383         spin_lock(&inode_lock);
384         inode->i_state &= ~I_SYNC;
385         if (!(inode->i_state & I_FREEING)) {
386                 if (mapping_tagged(mapping, PAGECACHE_TAG_DIRTY)) {
387                         /*
388                          * We didn't write back all the pages.  nfs_writepages()
389                          * sometimes bales out without doing anything.
390                          */
391                         inode->i_state |= I_DIRTY_PAGES;
392                         if (wbc->nr_to_write <= 0) {
393                                 /*
394                                  * slice used up: queue for next turn
395                                  */
396                                 requeue_io(inode);
397                         } else {
398                                 /*
399                                  * Writeback blocked by something other than
400                                  * congestion. Delay the inode for some time to
401                                  * avoid spinning on the CPU (100% iowait)
402                                  * retrying writeback of the dirty page/inode
403                                  * that cannot be performed immediately.
404                                  */
405                                 redirty_tail(inode);
406                         }
407                 } else if (inode->i_state & I_DIRTY) {
408                         /*
409                          * Filesystems can dirty the inode during writeback
410                          * operations, such as delayed allocation during
411                          * submission or metadata updates after data IO
412                          * completion.
413                          */
414                         redirty_tail(inode);
415                 } else {
416                         /*
417                          * The inode is clean.  At this point we either have
418                          * a reference to the inode or it's on it's way out.
419                          * No need to add it back to the LRU.
420                          */
421                         list_del_init(&inode->i_wb_list);
422                 }
423         }
424         inode_sync_complete(inode);
425         return ret;
426 }
427
428 /*
429  * For background writeback the caller does not have the sb pinned
430  * before calling writeback. So make sure that we do pin it, so it doesn't
431  * go away while we are writing inodes from it.
432  */
433 static bool pin_sb_for_writeback(struct super_block *sb)
434 {
435         spin_lock(&sb_lock);
436         if (list_empty(&sb->s_instances)) {
437                 spin_unlock(&sb_lock);
438                 return false;
439         }
440
441         sb->s_count++;
442         spin_unlock(&sb_lock);
443
444         if (down_read_trylock(&sb->s_umount)) {
445                 if (sb->s_root)
446                         return true;
447                 up_read(&sb->s_umount);
448         }
449
450         put_super(sb);
451         return false;
452 }
453
454 /*
455  * Write a portion of b_io inodes which belong to @sb.
456  *
457  * If @only_this_sb is true, then find and write all such
458  * inodes. Otherwise write only ones which go sequentially
459  * in reverse order.
460  *
461  * Return 1, if the caller writeback routine should be
462  * interrupted. Otherwise return 0.
463  */
464 static int writeback_sb_inodes(struct super_block *sb, struct bdi_writeback *wb,
465                 struct writeback_control *wbc, bool only_this_sb)
466 {
467         while (!list_empty(&wb->b_io)) {
468                 long pages_skipped;
469                 struct inode *inode = wb_inode(wb->b_io.prev);
470
471                 if (inode->i_sb != sb) {
472                         if (only_this_sb) {
473                                 /*
474                                  * We only want to write back data for this
475                                  * superblock, move all inodes not belonging
476                                  * to it back onto the dirty list.
477                                  */
478                                 redirty_tail(inode);
479                                 continue;
480                         }
481
482                         /*
483                          * The inode belongs to a different superblock.
484                          * Bounce back to the caller to unpin this and
485                          * pin the next superblock.
486                          */
487                         return 0;
488                 }
489
490                 /*
491                  * Don't bother with new inodes or inodes beeing freed, first
492                  * kind does not need peridic writeout yet, and for the latter
493                  * kind writeout is handled by the freer.
494                  */
495                 if (inode->i_state & (I_NEW | I_FREEING | I_WILL_FREE)) {
496                         requeue_io(inode);
497                         continue;
498                 }
499
500                 /*
501                  * Was this inode dirtied after sync_sb_inodes was called?
502                  * This keeps sync from extra jobs and livelock.
503                  */
504                 if (inode_dirtied_after(inode, wbc->wb_start))
505                         return 1;
506
507                 __iget(inode);
508                 pages_skipped = wbc->pages_skipped;
509                 writeback_single_inode(inode, wbc);
510                 if (wbc->pages_skipped != pages_skipped) {
511                         /*
512                          * writeback is not making progress due to locked
513                          * buffers.  Skip this inode for now.
514                          */
515                         redirty_tail(inode);
516                 }
517                 spin_unlock(&inode_lock);
518                 iput(inode);
519                 cond_resched();
520                 spin_lock(&inode_lock);
521                 if (wbc->nr_to_write <= 0) {
522                         wbc->more_io = 1;
523                         return 1;
524                 }
525                 if (!list_empty(&wb->b_more_io))
526                         wbc->more_io = 1;
527         }
528         /* b_io is empty */
529         return 1;
530 }
531
532 void writeback_inodes_wb(struct bdi_writeback *wb,
533                 struct writeback_control *wbc)
534 {
535         int ret = 0;
536
537         if (!wbc->wb_start)
538                 wbc->wb_start = jiffies; /* livelock avoidance */
539         spin_lock(&inode_lock);
540         if (!wbc->for_kupdate || list_empty(&wb->b_io))
541                 queue_io(wb, wbc->older_than_this);
542
543         while (!list_empty(&wb->b_io)) {
544                 struct inode *inode = wb_inode(wb->b_io.prev);
545                 struct super_block *sb = inode->i_sb;
546
547                 if (!pin_sb_for_writeback(sb)) {
548                         requeue_io(inode);
549                         continue;
550                 }
551                 ret = writeback_sb_inodes(sb, wb, wbc, false);
552                 drop_super(sb);
553
554                 if (ret)
555                         break;
556         }
557         spin_unlock(&inode_lock);
558         /* Leave any unwritten inodes on b_io */
559 }
560
561 static void __writeback_inodes_sb(struct super_block *sb,
562                 struct bdi_writeback *wb, struct writeback_control *wbc)
563 {
564         WARN_ON(!rwsem_is_locked(&sb->s_umount));
565
566         spin_lock(&inode_lock);
567         if (!wbc->for_kupdate || list_empty(&wb->b_io))
568                 queue_io(wb, wbc->older_than_this);
569         writeback_sb_inodes(sb, wb, wbc, true);
570         spin_unlock(&inode_lock);
571 }
572
573 /*
574  * The maximum number of pages to writeout in a single bdi flush/kupdate
575  * operation.  We do this so we don't hold I_SYNC against an inode for
576  * enormous amounts of time, which would block a userspace task which has
577  * been forced to throttle against that inode.  Also, the code reevaluates
578  * the dirty each time it has written this many pages.
579  */
580 #define MAX_WRITEBACK_PAGES     1024
581
582 static inline bool over_bground_thresh(void)
583 {
584         unsigned long background_thresh, dirty_thresh;
585
586         global_dirty_limits(&background_thresh, &dirty_thresh);
587
588         return (global_page_state(NR_FILE_DIRTY) +
589                 global_page_state(NR_UNSTABLE_NFS) > background_thresh);
590 }
591
592 /*
593  * Explicit flushing or periodic writeback of "old" data.
594  *
595  * Define "old": the first time one of an inode's pages is dirtied, we mark the
596  * dirtying-time in the inode's address_space.  So this periodic writeback code
597  * just walks the superblock inode list, writing back any inodes which are
598  * older than a specific point in time.
599  *
600  * Try to run once per dirty_writeback_interval.  But if a writeback event
601  * takes longer than a dirty_writeback_interval interval, then leave a
602  * one-second gap.
603  *
604  * older_than_this takes precedence over nr_to_write.  So we'll only write back
605  * all dirty pages if they are all attached to "old" mappings.
606  */
607 static long wb_writeback(struct bdi_writeback *wb,
608                          struct wb_writeback_work *work)
609 {
610         struct writeback_control wbc = {
611                 .sync_mode              = work->sync_mode,
612                 .older_than_this        = NULL,
613                 .for_kupdate            = work->for_kupdate,
614                 .for_background         = work->for_background,
615                 .range_cyclic           = work->range_cyclic,
616         };
617         unsigned long oldest_jif;
618         long wrote = 0;
619         struct inode *inode;
620
621         if (wbc.for_kupdate) {
622                 wbc.older_than_this = &oldest_jif;
623                 oldest_jif = jiffies -
624                                 msecs_to_jiffies(dirty_expire_interval * 10);
625         }
626         if (!wbc.range_cyclic) {
627                 wbc.range_start = 0;
628                 wbc.range_end = LLONG_MAX;
629         }
630
631         wbc.wb_start = jiffies; /* livelock avoidance */
632         for (;;) {
633                 /*
634                  * Stop writeback when nr_pages has been consumed
635                  */
636                 if (work->nr_pages <= 0)
637                         break;
638
639                 /*
640                  * For background writeout, stop when we are below the
641                  * background dirty threshold
642                  */
643                 if (work->for_background && !over_bground_thresh())
644                         break;
645
646                 wbc.more_io = 0;
647                 wbc.nr_to_write = MAX_WRITEBACK_PAGES;
648                 wbc.pages_skipped = 0;
649
650                 trace_wbc_writeback_start(&wbc, wb->bdi);
651                 if (work->sb)
652                         __writeback_inodes_sb(work->sb, wb, &wbc);
653                 else
654                         writeback_inodes_wb(wb, &wbc);
655                 trace_wbc_writeback_written(&wbc, wb->bdi);
656
657                 work->nr_pages -= MAX_WRITEBACK_PAGES - wbc.nr_to_write;
658                 wrote += MAX_WRITEBACK_PAGES - wbc.nr_to_write;
659
660                 /*
661                  * If we consumed everything, see if we have more
662                  */
663                 if (wbc.nr_to_write <= 0)
664                         continue;
665                 /*
666                  * Didn't write everything and we don't have more IO, bail
667                  */
668                 if (!wbc.more_io)
669                         break;
670                 /*
671                  * Did we write something? Try for more
672                  */
673                 if (wbc.nr_to_write < MAX_WRITEBACK_PAGES)
674                         continue;
675                 /*
676                  * Nothing written. Wait for some inode to
677                  * become available for writeback. Otherwise
678                  * we'll just busyloop.
679                  */
680                 spin_lock(&inode_lock);
681                 if (!list_empty(&wb->b_more_io))  {
682                         inode = wb_inode(wb->b_more_io.prev);
683                         trace_wbc_writeback_wait(&wbc, wb->bdi);
684                         inode_wait_for_writeback(inode);
685                 }
686                 spin_unlock(&inode_lock);
687         }
688
689         return wrote;
690 }
691
692 /*
693  * Return the next wb_writeback_work struct that hasn't been processed yet.
694  */
695 static struct wb_writeback_work *
696 get_next_work_item(struct backing_dev_info *bdi)
697 {
698         struct wb_writeback_work *work = NULL;
699
700         spin_lock_bh(&bdi->wb_lock);
701         if (!list_empty(&bdi->work_list)) {
702                 work = list_entry(bdi->work_list.next,
703                                   struct wb_writeback_work, list);
704                 list_del_init(&work->list);
705         }
706         spin_unlock_bh(&bdi->wb_lock);
707         return work;
708 }
709
710 /*
711  * Add in the number of potentially dirty inodes, because each inode
712  * write can dirty pagecache in the underlying blockdev.
713  */
714 static unsigned long get_nr_dirty_pages(void)
715 {
716         return global_page_state(NR_FILE_DIRTY) +
717                 global_page_state(NR_UNSTABLE_NFS) +
718                 get_nr_dirty_inodes();
719 }
720
721 static long wb_check_old_data_flush(struct bdi_writeback *wb)
722 {
723         unsigned long expired;
724         long nr_pages;
725
726         /*
727          * When set to zero, disable periodic writeback
728          */
729         if (!dirty_writeback_interval)
730                 return 0;
731
732         expired = wb->last_old_flush +
733                         msecs_to_jiffies(dirty_writeback_interval * 10);
734         if (time_before(jiffies, expired))
735                 return 0;
736
737         wb->last_old_flush = jiffies;
738         nr_pages = get_nr_dirty_pages();
739
740         if (nr_pages) {
741                 struct wb_writeback_work work = {
742                         .nr_pages       = nr_pages,
743                         .sync_mode      = WB_SYNC_NONE,
744                         .for_kupdate    = 1,
745                         .range_cyclic   = 1,
746                 };
747
748                 return wb_writeback(wb, &work);
749         }
750
751         return 0;
752 }
753
754 /*
755  * Retrieve work items and do the writeback they describe
756  */
757 long wb_do_writeback(struct bdi_writeback *wb, int force_wait)
758 {
759         struct backing_dev_info *bdi = wb->bdi;
760         struct wb_writeback_work *work;
761         long wrote = 0;
762
763         set_bit(BDI_writeback_running, &wb->bdi->state);
764         while ((work = get_next_work_item(bdi)) != NULL) {
765                 /*
766                  * Override sync mode, in case we must wait for completion
767                  * because this thread is exiting now.
768                  */
769                 if (force_wait)
770                         work->sync_mode = WB_SYNC_ALL;
771
772                 trace_writeback_exec(bdi, work);
773
774                 wrote += wb_writeback(wb, work);
775
776                 /*
777                  * Notify the caller of completion if this is a synchronous
778                  * work item, otherwise just free it.
779                  */
780                 if (work->done)
781                         complete(work->done);
782                 else
783                         kfree(work);
784         }
785
786         /*
787          * Check for periodic writeback, kupdated() style
788          */
789         wrote += wb_check_old_data_flush(wb);
790         clear_bit(BDI_writeback_running, &wb->bdi->state);
791
792         return wrote;
793 }
794
795 /*
796  * Handle writeback of dirty data for the device backed by this bdi. Also
797  * wakes up periodically and does kupdated style flushing.
798  */
799 int bdi_writeback_thread(void *data)
800 {
801         struct bdi_writeback *wb = data;
802         struct backing_dev_info *bdi = wb->bdi;
803         long pages_written;
804
805         current->flags |= PF_SWAPWRITE;
806         set_freezable();
807         wb->last_active = jiffies;
808
809         /*
810          * Our parent may run at a different priority, just set us to normal
811          */
812         set_user_nice(current, 0);
813
814         trace_writeback_thread_start(bdi);
815
816         while (!kthread_should_stop()) {
817                 /*
818                  * Remove own delayed wake-up timer, since we are already awake
819                  * and we'll take care of the preriodic write-back.
820                  */
821                 del_timer(&wb->wakeup_timer);
822
823                 pages_written = wb_do_writeback(wb, 0);
824
825                 trace_writeback_pages_written(pages_written);
826
827                 if (pages_written)
828                         wb->last_active = jiffies;
829
830                 set_current_state(TASK_INTERRUPTIBLE);
831                 if (!list_empty(&bdi->work_list) || kthread_should_stop()) {
832                         __set_current_state(TASK_RUNNING);
833                         continue;
834                 }
835
836                 if (wb_has_dirty_io(wb) && dirty_writeback_interval)
837                         schedule_timeout(msecs_to_jiffies(dirty_writeback_interval * 10));
838                 else {
839                         /*
840                          * We have nothing to do, so can go sleep without any
841                          * timeout and save power. When a work is queued or
842                          * something is made dirty - we will be woken up.
843                          */
844                         schedule();
845                 }
846
847                 try_to_freeze();
848         }
849
850         /* Flush any work that raced with us exiting */
851         if (!list_empty(&bdi->work_list))
852                 wb_do_writeback(wb, 1);
853
854         trace_writeback_thread_stop(bdi);
855         return 0;
856 }
857
858
859 /*
860  * Start writeback of `nr_pages' pages.  If `nr_pages' is zero, write back
861  * the whole world.
862  */
863 void wakeup_flusher_threads(long nr_pages)
864 {
865         struct backing_dev_info *bdi;
866
867         if (!nr_pages) {
868                 nr_pages = global_page_state(NR_FILE_DIRTY) +
869                                 global_page_state(NR_UNSTABLE_NFS);
870         }
871
872         rcu_read_lock();
873         list_for_each_entry_rcu(bdi, &bdi_list, bdi_list) {
874                 if (!bdi_has_dirty_io(bdi))
875                         continue;
876                 __bdi_start_writeback(bdi, nr_pages, false, false);
877         }
878         rcu_read_unlock();
879 }
880
881 static noinline void block_dump___mark_inode_dirty(struct inode *inode)
882 {
883         if (inode->i_ino || strcmp(inode->i_sb->s_id, "bdev")) {
884                 struct dentry *dentry;
885                 const char *name = "?";
886
887                 dentry = d_find_alias(inode);
888                 if (dentry) {
889                         spin_lock(&dentry->d_lock);
890                         name = (const char *) dentry->d_name.name;
891                 }
892                 printk(KERN_DEBUG
893                        "%s(%d): dirtied inode %lu (%s) on %s\n",
894                        current->comm, task_pid_nr(current), inode->i_ino,
895                        name, inode->i_sb->s_id);
896                 if (dentry) {
897                         spin_unlock(&dentry->d_lock);
898                         dput(dentry);
899                 }
900         }
901 }
902
903 /**
904  *      __mark_inode_dirty -    internal function
905  *      @inode: inode to mark
906  *      @flags: what kind of dirty (i.e. I_DIRTY_SYNC)
907  *      Mark an inode as dirty. Callers should use mark_inode_dirty or
908  *      mark_inode_dirty_sync.
909  *
910  * Put the inode on the super block's dirty list.
911  *
912  * CAREFUL! We mark it dirty unconditionally, but move it onto the
913  * dirty list only if it is hashed or if it refers to a blockdev.
914  * If it was not hashed, it will never be added to the dirty list
915  * even if it is later hashed, as it will have been marked dirty already.
916  *
917  * In short, make sure you hash any inodes _before_ you start marking
918  * them dirty.
919  *
920  * This function *must* be atomic for the I_DIRTY_PAGES case -
921  * set_page_dirty() is called under spinlock in several places.
922  *
923  * Note that for blockdevs, inode->dirtied_when represents the dirtying time of
924  * the block-special inode (/dev/hda1) itself.  And the ->dirtied_when field of
925  * the kernel-internal blockdev inode represents the dirtying time of the
926  * blockdev's pages.  This is why for I_DIRTY_PAGES we always use
927  * page->mapping->host, so the page-dirtying time is recorded in the internal
928  * blockdev inode.
929  */
930 void __mark_inode_dirty(struct inode *inode, int flags)
931 {
932         struct super_block *sb = inode->i_sb;
933         struct backing_dev_info *bdi = NULL;
934         bool wakeup_bdi = false;
935
936         /*
937          * Don't do this for I_DIRTY_PAGES - that doesn't actually
938          * dirty the inode itself
939          */
940         if (flags & (I_DIRTY_SYNC | I_DIRTY_DATASYNC)) {
941                 if (sb->s_op->dirty_inode)
942                         sb->s_op->dirty_inode(inode);
943         }
944
945         /*
946          * make sure that changes are seen by all cpus before we test i_state
947          * -- mikulas
948          */
949         smp_mb();
950
951         /* avoid the locking if we can */
952         if ((inode->i_state & flags) == flags)
953                 return;
954
955         if (unlikely(block_dump))
956                 block_dump___mark_inode_dirty(inode);
957
958         spin_lock(&inode_lock);
959         if ((inode->i_state & flags) != flags) {
960                 const int was_dirty = inode->i_state & I_DIRTY;
961
962                 inode->i_state |= flags;
963
964                 /*
965                  * If the inode is being synced, just update its dirty state.
966                  * The unlocker will place the inode on the appropriate
967                  * superblock list, based upon its state.
968                  */
969                 if (inode->i_state & I_SYNC)
970                         goto out;
971
972                 /*
973                  * Only add valid (hashed) inodes to the superblock's
974                  * dirty list.  Add blockdev inodes as well.
975                  */
976                 if (!S_ISBLK(inode->i_mode)) {
977                         if (inode_unhashed(inode))
978                                 goto out;
979                 }
980                 if (inode->i_state & I_FREEING)
981                         goto out;
982
983                 /*
984                  * If the inode was already on b_dirty/b_io/b_more_io, don't
985                  * reposition it (that would break b_dirty time-ordering).
986                  */
987                 if (!was_dirty) {
988                         bdi = inode_to_bdi(inode);
989
990                         if (bdi_cap_writeback_dirty(bdi)) {
991                                 WARN(!test_bit(BDI_registered, &bdi->state),
992                                      "bdi-%s not registered\n", bdi->name);
993
994                                 /*
995                                  * If this is the first dirty inode for this
996                                  * bdi, we have to wake-up the corresponding
997                                  * bdi thread to make sure background
998                                  * write-back happens later.
999                                  */
1000                                 if (!wb_has_dirty_io(&bdi->wb))
1001                                         wakeup_bdi = true;
1002                         }
1003
1004                         inode->dirtied_when = jiffies;
1005                         list_move(&inode->i_wb_list, &bdi->wb.b_dirty);
1006                 }
1007         }
1008 out:
1009         spin_unlock(&inode_lock);
1010
1011         if (wakeup_bdi)
1012                 bdi_wakeup_thread_delayed(bdi);
1013 }
1014 EXPORT_SYMBOL(__mark_inode_dirty);
1015
1016 /*
1017  * Write out a superblock's list of dirty inodes.  A wait will be performed
1018  * upon no inodes, all inodes or the final one, depending upon sync_mode.
1019  *
1020  * If older_than_this is non-NULL, then only write out inodes which
1021  * had their first dirtying at a time earlier than *older_than_this.
1022  *
1023  * If `bdi' is non-zero then we're being asked to writeback a specific queue.
1024  * This function assumes that the blockdev superblock's inodes are backed by
1025  * a variety of queues, so all inodes are searched.  For other superblocks,
1026  * assume that all inodes are backed by the same queue.
1027  *
1028  * The inodes to be written are parked on bdi->b_io.  They are moved back onto
1029  * bdi->b_dirty as they are selected for writing.  This way, none can be missed
1030  * on the writer throttling path, and we get decent balancing between many
1031  * throttled threads: we don't want them all piling up on inode_sync_wait.
1032  */
1033 static void wait_sb_inodes(struct super_block *sb)
1034 {
1035         struct inode *inode, *old_inode = NULL;
1036
1037         /*
1038          * We need to be protected against the filesystem going from
1039          * r/o to r/w or vice versa.
1040          */
1041         WARN_ON(!rwsem_is_locked(&sb->s_umount));
1042
1043         spin_lock(&inode_lock);
1044
1045         /*
1046          * Data integrity sync. Must wait for all pages under writeback,
1047          * because there may have been pages dirtied before our sync
1048          * call, but which had writeout started before we write it out.
1049          * In which case, the inode may not be on the dirty list, but
1050          * we still have to wait for that writeout.
1051          */
1052         list_for_each_entry(inode, &sb->s_inodes, i_sb_list) {
1053                 struct address_space *mapping;
1054
1055                 if (inode->i_state & (I_FREEING|I_WILL_FREE|I_NEW))
1056                         continue;
1057                 mapping = inode->i_mapping;
1058                 if (mapping->nrpages == 0)
1059                         continue;
1060                 __iget(inode);
1061                 spin_unlock(&inode_lock);
1062                 /*
1063                  * We hold a reference to 'inode' so it couldn't have
1064                  * been removed from s_inodes list while we dropped the
1065                  * inode_lock.  We cannot iput the inode now as we can
1066                  * be holding the last reference and we cannot iput it
1067                  * under inode_lock. So we keep the reference and iput
1068                  * it later.
1069                  */
1070                 iput(old_inode);
1071                 old_inode = inode;
1072
1073                 filemap_fdatawait(mapping);
1074
1075                 cond_resched();
1076
1077                 spin_lock(&inode_lock);
1078         }
1079         spin_unlock(&inode_lock);
1080         iput(old_inode);
1081 }
1082
1083 /**
1084  * writeback_inodes_sb_nr -     writeback dirty inodes from given super_block
1085  * @sb: the superblock
1086  * @nr: the number of pages to write
1087  *
1088  * Start writeback on some inodes on this super_block. No guarantees are made
1089  * on how many (if any) will be written, and this function does not wait
1090  * for IO completion of submitted IO.
1091  */
1092 void writeback_inodes_sb_nr(struct super_block *sb, unsigned long nr)
1093 {
1094         DECLARE_COMPLETION_ONSTACK(done);
1095         struct wb_writeback_work work = {
1096                 .sb             = sb,
1097                 .sync_mode      = WB_SYNC_NONE,
1098                 .done           = &done,
1099                 .nr_pages       = nr,
1100         };
1101
1102         WARN_ON(!rwsem_is_locked(&sb->s_umount));
1103         bdi_queue_work(sb->s_bdi, &work);
1104         wait_for_completion(&done);
1105 }
1106 EXPORT_SYMBOL(writeback_inodes_sb_nr);
1107
1108 /**
1109  * writeback_inodes_sb  -       writeback dirty inodes from given super_block
1110  * @sb: the superblock
1111  *
1112  * Start writeback on some inodes on this super_block. No guarantees are made
1113  * on how many (if any) will be written, and this function does not wait
1114  * for IO completion of submitted IO.
1115  */
1116 void writeback_inodes_sb(struct super_block *sb)
1117 {
1118         return writeback_inodes_sb_nr(sb, get_nr_dirty_pages());
1119 }
1120 EXPORT_SYMBOL(writeback_inodes_sb);
1121
1122 /**
1123  * writeback_inodes_sb_if_idle  -       start writeback if none underway
1124  * @sb: the superblock
1125  *
1126  * Invoke writeback_inodes_sb if no writeback is currently underway.
1127  * Returns 1 if writeback was started, 0 if not.
1128  */
1129 int writeback_inodes_sb_if_idle(struct super_block *sb)
1130 {
1131         if (!writeback_in_progress(sb->s_bdi)) {
1132                 down_read(&sb->s_umount);
1133                 writeback_inodes_sb(sb);
1134                 up_read(&sb->s_umount);
1135                 return 1;
1136         } else
1137                 return 0;
1138 }
1139 EXPORT_SYMBOL(writeback_inodes_sb_if_idle);
1140
1141 /**
1142  * writeback_inodes_sb_if_idle  -       start writeback if none underway
1143  * @sb: the superblock
1144  * @nr: the number of pages to write
1145  *
1146  * Invoke writeback_inodes_sb if no writeback is currently underway.
1147  * Returns 1 if writeback was started, 0 if not.
1148  */
1149 int writeback_inodes_sb_nr_if_idle(struct super_block *sb,
1150                                    unsigned long nr)
1151 {
1152         if (!writeback_in_progress(sb->s_bdi)) {
1153                 down_read(&sb->s_umount);
1154                 writeback_inodes_sb_nr(sb, nr);
1155                 up_read(&sb->s_umount);
1156                 return 1;
1157         } else
1158                 return 0;
1159 }
1160 EXPORT_SYMBOL(writeback_inodes_sb_nr_if_idle);
1161
1162 /**
1163  * sync_inodes_sb       -       sync sb inode pages
1164  * @sb: the superblock
1165  *
1166  * This function writes and waits on any dirty inode belonging to this
1167  * super_block. The number of pages synced is returned.
1168  */
1169 void sync_inodes_sb(struct super_block *sb)
1170 {
1171         DECLARE_COMPLETION_ONSTACK(done);
1172         struct wb_writeback_work work = {
1173                 .sb             = sb,
1174                 .sync_mode      = WB_SYNC_ALL,
1175                 .nr_pages       = LONG_MAX,
1176                 .range_cyclic   = 0,
1177                 .done           = &done,
1178         };
1179
1180         WARN_ON(!rwsem_is_locked(&sb->s_umount));
1181
1182         bdi_queue_work(sb->s_bdi, &work);
1183         wait_for_completion(&done);
1184
1185         wait_sb_inodes(sb);
1186 }
1187 EXPORT_SYMBOL(sync_inodes_sb);
1188
1189 /**
1190  * write_inode_now      -       write an inode to disk
1191  * @inode: inode to write to disk
1192  * @sync: whether the write should be synchronous or not
1193  *
1194  * This function commits an inode to disk immediately if it is dirty. This is
1195  * primarily needed by knfsd.
1196  *
1197  * The caller must either have a ref on the inode or must have set I_WILL_FREE.
1198  */
1199 int write_inode_now(struct inode *inode, int sync)
1200 {
1201         int ret;
1202         struct writeback_control wbc = {
1203                 .nr_to_write = LONG_MAX,
1204                 .sync_mode = sync ? WB_SYNC_ALL : WB_SYNC_NONE,
1205                 .range_start = 0,
1206                 .range_end = LLONG_MAX,
1207         };
1208
1209         if (!mapping_cap_writeback_dirty(inode->i_mapping))
1210                 wbc.nr_to_write = 0;
1211
1212         might_sleep();
1213         spin_lock(&inode_lock);
1214         ret = writeback_single_inode(inode, &wbc);
1215         spin_unlock(&inode_lock);
1216         if (sync)
1217                 inode_sync_wait(inode);
1218         return ret;
1219 }
1220 EXPORT_SYMBOL(write_inode_now);
1221
1222 /**
1223  * sync_inode - write an inode and its pages to disk.
1224  * @inode: the inode to sync
1225  * @wbc: controls the writeback mode
1226  *
1227  * sync_inode() will write an inode and its pages to disk.  It will also
1228  * correctly update the inode on its superblock's dirty inode lists and will
1229  * update inode->i_state.
1230  *
1231  * The caller must have a ref on the inode.
1232  */
1233 int sync_inode(struct inode *inode, struct writeback_control *wbc)
1234 {
1235         int ret;
1236
1237         spin_lock(&inode_lock);
1238         ret = writeback_single_inode(inode, wbc);
1239         spin_unlock(&inode_lock);
1240         return ret;
1241 }
1242 EXPORT_SYMBOL(sync_inode);
1243
1244 /**
1245  * sync_inode - write an inode to disk
1246  * @inode: the inode to sync
1247  * @wait: wait for I/O to complete.
1248  *
1249  * Write an inode to disk and adjust it's dirty state after completion.
1250  *
1251  * Note: only writes the actual inode, no associated data or other metadata.
1252  */
1253 int sync_inode_metadata(struct inode *inode, int wait)
1254 {
1255         struct writeback_control wbc = {
1256                 .sync_mode = wait ? WB_SYNC_ALL : WB_SYNC_NONE,
1257                 .nr_to_write = 0, /* metadata-only */
1258         };
1259
1260         return sync_inode(inode, &wbc);
1261 }
1262 EXPORT_SYMBOL(sync_inode_metadata);