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Linux/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/export.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/pagemap.h>
 24 #include <linux/kthread.h>
 25 #include <linux/writeback.h>
 26 #include <linux/blkdev.h>
 27 #include <linux/backing-dev.h>
 28 #include <linux/tracepoint.h>
 29 #include <linux/device.h>
 30 #include "internal.h"
 31 
 32 /*
 33  * 4MB minimal write chunk size
 34  */
 35 #define MIN_WRITEBACK_PAGES     (4096UL >> (PAGE_CACHE_SHIFT - 10))
 36 
 37 /*
 38  * Passed into wb_writeback(), essentially a subset of writeback_control
 39  */
 40 struct wb_writeback_work {
 41         long nr_pages;
 42         struct super_block *sb;
 43         unsigned long *older_than_this;
 44         enum writeback_sync_modes sync_mode;
 45         unsigned int tagged_writepages:1;
 46         unsigned int for_kupdate:1;
 47         unsigned int range_cyclic:1;
 48         unsigned int for_background:1;
 49         unsigned int for_sync:1;        /* sync(2) WB_SYNC_ALL writeback */
 50         enum wb_reason reason;          /* why was writeback initiated? */
 51 
 52         struct list_head list;          /* pending work list */
 53         struct completion *done;        /* set if the caller waits */
 54 };
 55 
 56 /**
 57  * writeback_in_progress - determine whether there is writeback in progress
 58  * @bdi: the device's backing_dev_info structure.
 59  *
 60  * Determine whether there is writeback waiting to be handled against a
 61  * backing device.
 62  */
 63 int writeback_in_progress(struct backing_dev_info *bdi)
 64 {
 65         return test_bit(BDI_writeback_running, &bdi->state);
 66 }
 67 EXPORT_SYMBOL(writeback_in_progress);
 68 
 69 static inline struct backing_dev_info *inode_to_bdi(struct inode *inode)
 70 {
 71         struct super_block *sb = inode->i_sb;
 72 
 73         if (sb_is_blkdev_sb(sb))
 74                 return inode->i_mapping->backing_dev_info;
 75 
 76         return sb->s_bdi;
 77 }
 78 
 79 static inline struct inode *wb_inode(struct list_head *head)
 80 {
 81         return list_entry(head, struct inode, i_wb_list);
 82 }
 83 
 84 /*
 85  * Include the creation of the trace points after defining the
 86  * wb_writeback_work structure and inline functions so that the definition
 87  * remains local to this file.
 88  */
 89 #define CREATE_TRACE_POINTS
 90 #include <trace/events/writeback.h>
 91 
 92 EXPORT_TRACEPOINT_SYMBOL_GPL(wbc_writepage);
 93 
 94 static void bdi_wakeup_thread(struct backing_dev_info *bdi)
 95 {
 96         spin_lock_bh(&bdi->wb_lock);
 97         if (test_bit(BDI_registered, &bdi->state))
 98                 mod_delayed_work(bdi_wq, &bdi->wb.dwork, 0);
 99         spin_unlock_bh(&bdi->wb_lock);
100 }
101 
102 static void bdi_queue_work(struct backing_dev_info *bdi,
103                            struct wb_writeback_work *work)
104 {
105         trace_writeback_queue(bdi, work);
106 
107         spin_lock_bh(&bdi->wb_lock);
108         if (!test_bit(BDI_registered, &bdi->state)) {
109                 if (work->done)
110                         complete(work->done);
111                 goto out_unlock;
112         }
113         list_add_tail(&work->list, &bdi->work_list);
114         mod_delayed_work(bdi_wq, &bdi->wb.dwork, 0);
115 out_unlock:
116         spin_unlock_bh(&bdi->wb_lock);
117 }
118 
119 static void
120 __bdi_start_writeback(struct backing_dev_info *bdi, long nr_pages,
121                       bool range_cyclic, enum wb_reason reason)
122 {
123         struct wb_writeback_work *work;
124 
125         /*
126          * This is WB_SYNC_NONE writeback, so if allocation fails just
127          * wakeup the thread for old dirty data writeback
128          */
129         work = kzalloc(sizeof(*work), GFP_ATOMIC);
130         if (!work) {
131                 trace_writeback_nowork(bdi);
132                 bdi_wakeup_thread(bdi);
133                 return;
134         }
135 
136         work->sync_mode = WB_SYNC_NONE;
137         work->nr_pages  = nr_pages;
138         work->range_cyclic = range_cyclic;
139         work->reason    = reason;
140 
141         bdi_queue_work(bdi, work);
142 }
143 
144 /**
145  * bdi_start_writeback - start writeback
146  * @bdi: the backing device to write from
147  * @nr_pages: the number of pages to write
148  * @reason: reason why some writeback work was initiated
149  *
150  * Description:
151  *   This does WB_SYNC_NONE opportunistic writeback. The IO is only
152  *   started when this function returns, we make no guarantees on
153  *   completion. Caller need not hold sb s_umount semaphore.
154  *
155  */
156 void bdi_start_writeback(struct backing_dev_info *bdi, long nr_pages,
157                         enum wb_reason reason)
158 {
159         __bdi_start_writeback(bdi, nr_pages, true, reason);
160 }
161 
162 /**
163  * bdi_start_background_writeback - start background writeback
164  * @bdi: the backing device to write from
165  *
166  * Description:
167  *   This makes sure WB_SYNC_NONE background writeback happens. When
168  *   this function returns, it is only guaranteed that for given BDI
169  *   some IO is happening if we are over background dirty threshold.
170  *   Caller need not hold sb s_umount semaphore.
171  */
172 void bdi_start_background_writeback(struct backing_dev_info *bdi)
173 {
174         /*
175          * We just wake up the flusher thread. It will perform background
176          * writeback as soon as there is no other work to do.
177          */
178         trace_writeback_wake_background(bdi);
179         bdi_wakeup_thread(bdi);
180 }
181 
182 /*
183  * Remove the inode from the writeback list it is on.
184  */
185 void inode_wb_list_del(struct inode *inode)
186 {
187         struct backing_dev_info *bdi = inode_to_bdi(inode);
188 
189         spin_lock(&bdi->wb.list_lock);
190         list_del_init(&inode->i_wb_list);
191         spin_unlock(&bdi->wb.list_lock);
192 }
193 
194 /*
195  * Redirty an inode: set its when-it-was dirtied timestamp and move it to the
196  * furthest end of its superblock's dirty-inode list.
197  *
198  * Before stamping the inode's ->dirtied_when, we check to see whether it is
199  * already the most-recently-dirtied inode on the b_dirty list.  If that is
200  * the case then the inode must have been redirtied while it was being written
201  * out and we don't reset its dirtied_when.
202  */
203 static void redirty_tail(struct inode *inode, struct bdi_writeback *wb)
204 {
205         assert_spin_locked(&wb->list_lock);
206         if (!list_empty(&wb->b_dirty)) {
207                 struct inode *tail;
208 
209                 tail = wb_inode(wb->b_dirty.next);
210                 if (time_before(inode->dirtied_when, tail->dirtied_when))
211                         inode->dirtied_when = jiffies;
212         }
213         list_move(&inode->i_wb_list, &wb->b_dirty);
214 }
215 
216 /*
217  * requeue inode for re-scanning after bdi->b_io list is exhausted.
218  */
219 static void requeue_io(struct inode *inode, struct bdi_writeback *wb)
220 {
221         assert_spin_locked(&wb->list_lock);
222         list_move(&inode->i_wb_list, &wb->b_more_io);
223 }
224 
225 static void inode_sync_complete(struct inode *inode)
226 {
227         inode->i_state &= ~I_SYNC;
228         /* If inode is clean an unused, put it into LRU now... */
229         inode_add_lru(inode);
230         /* Waiters must see I_SYNC cleared before being woken up */
231         smp_mb();
232         wake_up_bit(&inode->i_state, __I_SYNC);
233 }
234 
235 static bool inode_dirtied_after(struct inode *inode, unsigned long t)
236 {
237         bool ret = time_after(inode->dirtied_when, t);
238 #ifndef CONFIG_64BIT
239         /*
240          * For inodes being constantly redirtied, dirtied_when can get stuck.
241          * It _appears_ to be in the future, but is actually in distant past.
242          * This test is necessary to prevent such wrapped-around relative times
243          * from permanently stopping the whole bdi writeback.
244          */
245         ret = ret && time_before_eq(inode->dirtied_when, jiffies);
246 #endif
247         return ret;
248 }
249 
250 /*
251  * Move expired (dirtied before work->older_than_this) dirty inodes from
252  * @delaying_queue to @dispatch_queue.
253  */
254 static int move_expired_inodes(struct list_head *delaying_queue,
255                                struct list_head *dispatch_queue,
256                                struct wb_writeback_work *work)
257 {
258         LIST_HEAD(tmp);
259         struct list_head *pos, *node;
260         struct super_block *sb = NULL;
261         struct inode *inode;
262         int do_sb_sort = 0;
263         int moved = 0;
264 
265         while (!list_empty(delaying_queue)) {
266                 inode = wb_inode(delaying_queue->prev);
267                 if (work->older_than_this &&
268                     inode_dirtied_after(inode, *work->older_than_this))
269                         break;
270                 list_move(&inode->i_wb_list, &tmp);
271                 moved++;
272                 if (sb_is_blkdev_sb(inode->i_sb))
273                         continue;
274                 if (sb && sb != inode->i_sb)
275                         do_sb_sort = 1;
276                 sb = inode->i_sb;
277         }
278 
279         /* just one sb in list, splice to dispatch_queue and we're done */
280         if (!do_sb_sort) {
281                 list_splice(&tmp, dispatch_queue);
282                 goto out;
283         }
284 
285         /* Move inodes from one superblock together */
286         while (!list_empty(&tmp)) {
287                 sb = wb_inode(tmp.prev)->i_sb;
288                 list_for_each_prev_safe(pos, node, &tmp) {
289                         inode = wb_inode(pos);
290                         if (inode->i_sb == sb)
291                                 list_move(&inode->i_wb_list, dispatch_queue);
292                 }
293         }
294 out:
295         return moved;
296 }
297 
298 /*
299  * Queue all expired dirty inodes for io, eldest first.
300  * Before
301  *         newly dirtied     b_dirty    b_io    b_more_io
302  *         =============>    gf         edc     BA
303  * After
304  *         newly dirtied     b_dirty    b_io    b_more_io
305  *         =============>    g          fBAedc
306  *                                           |
307  *                                           +--> dequeue for IO
308  */
309 static void queue_io(struct bdi_writeback *wb, struct wb_writeback_work *work)
310 {
311         int moved;
312         assert_spin_locked(&wb->list_lock);
313         list_splice_init(&wb->b_more_io, &wb->b_io);
314         moved = move_expired_inodes(&wb->b_dirty, &wb->b_io, work);
315         trace_writeback_queue_io(wb, work, moved);
316 }
317 
318 static int write_inode(struct inode *inode, struct writeback_control *wbc)
319 {
320         int ret;
321 
322         if (inode->i_sb->s_op->write_inode && !is_bad_inode(inode)) {
323                 trace_writeback_write_inode_start(inode, wbc);
324                 ret = inode->i_sb->s_op->write_inode(inode, wbc);
325                 trace_writeback_write_inode(inode, wbc);
326                 return ret;
327         }
328         return 0;
329 }
330 
331 /*
332  * Wait for writeback on an inode to complete. Called with i_lock held.
333  * Caller must make sure inode cannot go away when we drop i_lock.
334  */
335 static void __inode_wait_for_writeback(struct inode *inode)
336         __releases(inode->i_lock)
337         __acquires(inode->i_lock)
338 {
339         DEFINE_WAIT_BIT(wq, &inode->i_state, __I_SYNC);
340         wait_queue_head_t *wqh;
341 
342         wqh = bit_waitqueue(&inode->i_state, __I_SYNC);
343         while (inode->i_state & I_SYNC) {
344                 spin_unlock(&inode->i_lock);
345                 __wait_on_bit(wqh, &wq, bit_wait,
346                               TASK_UNINTERRUPTIBLE);
347                 spin_lock(&inode->i_lock);
348         }
349 }
350 
351 /*
352  * Wait for writeback on an inode to complete. Caller must have inode pinned.
353  */
354 void inode_wait_for_writeback(struct inode *inode)
355 {
356         spin_lock(&inode->i_lock);
357         __inode_wait_for_writeback(inode);
358         spin_unlock(&inode->i_lock);
359 }
360 
361 /*
362  * Sleep until I_SYNC is cleared. This function must be called with i_lock
363  * held and drops it. It is aimed for callers not holding any inode reference
364  * so once i_lock is dropped, inode can go away.
365  */
366 static void inode_sleep_on_writeback(struct inode *inode)
367         __releases(inode->i_lock)
368 {
369         DEFINE_WAIT(wait);
370         wait_queue_head_t *wqh = bit_waitqueue(&inode->i_state, __I_SYNC);
371         int sleep;
372 
373         prepare_to_wait(wqh, &wait, TASK_UNINTERRUPTIBLE);
374         sleep = inode->i_state & I_SYNC;
375         spin_unlock(&inode->i_lock);
376         if (sleep)
377                 schedule();
378         finish_wait(wqh, &wait);
379 }
380 
381 /*
382  * Find proper writeback list for the inode depending on its current state and
383  * possibly also change of its state while we were doing writeback.  Here we
384  * handle things such as livelock prevention or fairness of writeback among
385  * inodes. This function can be called only by flusher thread - noone else
386  * processes all inodes in writeback lists and requeueing inodes behind flusher
387  * thread's back can have unexpected consequences.
388  */
389 static void requeue_inode(struct inode *inode, struct bdi_writeback *wb,
390                           struct writeback_control *wbc)
391 {
392         if (inode->i_state & I_FREEING)
393                 return;
394 
395         /*
396          * Sync livelock prevention. Each inode is tagged and synced in one
397          * shot. If still dirty, it will be redirty_tail()'ed below.  Update
398          * the dirty time to prevent enqueue and sync it again.
399          */
400         if ((inode->i_state & I_DIRTY) &&
401             (wbc->sync_mode == WB_SYNC_ALL || wbc->tagged_writepages))
402                 inode->dirtied_when = jiffies;
403 
404         if (wbc->pages_skipped) {
405                 /*
406                  * writeback is not making progress due to locked
407                  * buffers. Skip this inode for now.
408                  */
409                 redirty_tail(inode, wb);
410                 return;
411         }
412 
413         if (mapping_tagged(inode->i_mapping, PAGECACHE_TAG_DIRTY)) {
414                 /*
415                  * We didn't write back all the pages.  nfs_writepages()
416                  * sometimes bales out without doing anything.
417                  */
418                 if (wbc->nr_to_write <= 0) {
419                         /* Slice used up. Queue for next turn. */
420                         requeue_io(inode, wb);
421                 } else {
422                         /*
423                          * Writeback blocked by something other than
424                          * congestion. Delay the inode for some time to
425                          * avoid spinning on the CPU (100% iowait)
426                          * retrying writeback of the dirty page/inode
427                          * that cannot be performed immediately.
428                          */
429                         redirty_tail(inode, wb);
430                 }
431         } else if (inode->i_state & I_DIRTY) {
432                 /*
433                  * Filesystems can dirty the inode during writeback operations,
434                  * such as delayed allocation during submission or metadata
435                  * updates after data IO completion.
436                  */
437                 redirty_tail(inode, wb);
438         } else {
439                 /* The inode is clean. Remove from writeback lists. */
440                 list_del_init(&inode->i_wb_list);
441         }
442 }
443 
444 /*
445  * Write out an inode and its dirty pages. Do not update the writeback list
446  * linkage. That is left to the caller. The caller is also responsible for
447  * setting I_SYNC flag and calling inode_sync_complete() to clear it.
448  */
449 static int
450 __writeback_single_inode(struct inode *inode, struct writeback_control *wbc)
451 {
452         struct address_space *mapping = inode->i_mapping;
453         long nr_to_write = wbc->nr_to_write;
454         unsigned dirty;
455         int ret;
456 
457         WARN_ON(!(inode->i_state & I_SYNC));
458 
459         trace_writeback_single_inode_start(inode, wbc, nr_to_write);
460 
461         ret = do_writepages(mapping, wbc);
462 
463         /*
464          * Make sure to wait on the data before writing out the metadata.
465          * This is important for filesystems that modify metadata on data
466          * I/O completion. We don't do it for sync(2) writeback because it has a
467          * separate, external IO completion path and ->sync_fs for guaranteeing
468          * inode metadata is written back correctly.
469          */
470         if (wbc->sync_mode == WB_SYNC_ALL && !wbc->for_sync) {
471                 int err = filemap_fdatawait(mapping);
472                 if (ret == 0)
473                         ret = err;
474         }
475 
476         /*
477          * Some filesystems may redirty the inode during the writeback
478          * due to delalloc, clear dirty metadata flags right before
479          * write_inode()
480          */
481         spin_lock(&inode->i_lock);
482 
483         dirty = inode->i_state & I_DIRTY;
484         inode->i_state &= ~I_DIRTY;
485 
486         /*
487          * Paired with smp_mb() in __mark_inode_dirty().  This allows
488          * __mark_inode_dirty() to test i_state without grabbing i_lock -
489          * either they see the I_DIRTY bits cleared or we see the dirtied
490          * inode.
491          *
492          * I_DIRTY_PAGES is always cleared together above even if @mapping
493          * still has dirty pages.  The flag is reinstated after smp_mb() if
494          * necessary.  This guarantees that either __mark_inode_dirty()
495          * sees clear I_DIRTY_PAGES or we see PAGECACHE_TAG_DIRTY.
496          */
497         smp_mb();
498 
499         if (mapping_tagged(mapping, PAGECACHE_TAG_DIRTY))
500                 inode->i_state |= I_DIRTY_PAGES;
501 
502         spin_unlock(&inode->i_lock);
503 
504         /* Don't write the inode if only I_DIRTY_PAGES was set */
505         if (dirty & (I_DIRTY_SYNC | I_DIRTY_DATASYNC)) {
506                 int err = write_inode(inode, wbc);
507                 if (ret == 0)
508                         ret = err;
509         }
510         trace_writeback_single_inode(inode, wbc, nr_to_write);
511         return ret;
512 }
513 
514 /*
515  * Write out an inode's dirty pages. Either the caller has an active reference
516  * on the inode or the inode has I_WILL_FREE set.
517  *
518  * This function is designed to be called for writing back one inode which
519  * we go e.g. from filesystem. Flusher thread uses __writeback_single_inode()
520  * and does more profound writeback list handling in writeback_sb_inodes().
521  */
522 static int
523 writeback_single_inode(struct inode *inode, struct bdi_writeback *wb,
524                        struct writeback_control *wbc)
525 {
526         int ret = 0;
527 
528         spin_lock(&inode->i_lock);
529         if (!atomic_read(&inode->i_count))
530                 WARN_ON(!(inode->i_state & (I_WILL_FREE|I_FREEING)));
531         else
532                 WARN_ON(inode->i_state & I_WILL_FREE);
533 
534         if (inode->i_state & I_SYNC) {
535                 if (wbc->sync_mode != WB_SYNC_ALL)
536                         goto out;
537                 /*
538                  * It's a data-integrity sync. We must wait. Since callers hold
539                  * inode reference or inode has I_WILL_FREE set, it cannot go
540                  * away under us.
541                  */
542                 __inode_wait_for_writeback(inode);
543         }
544         WARN_ON(inode->i_state & I_SYNC);
545         /*
546          * Skip inode if it is clean and we have no outstanding writeback in
547          * WB_SYNC_ALL mode. We don't want to mess with writeback lists in this
548          * function since flusher thread may be doing for example sync in
549          * parallel and if we move the inode, it could get skipped. So here we
550          * make sure inode is on some writeback list and leave it there unless
551          * we have completely cleaned the inode.
552          */
553         if (!(inode->i_state & I_DIRTY) &&
554             (wbc->sync_mode != WB_SYNC_ALL ||
555              !mapping_tagged(inode->i_mapping, PAGECACHE_TAG_WRITEBACK)))
556                 goto out;
557         inode->i_state |= I_SYNC;
558         spin_unlock(&inode->i_lock);
559 
560         ret = __writeback_single_inode(inode, wbc);
561 
562         spin_lock(&wb->list_lock);
563         spin_lock(&inode->i_lock);
564         /*
565          * If inode is clean, remove it from writeback lists. Otherwise don't
566          * touch it. See comment above for explanation.
567          */
568         if (!(inode->i_state & I_DIRTY))
569                 list_del_init(&inode->i_wb_list);
570         spin_unlock(&wb->list_lock);
571         inode_sync_complete(inode);
572 out:
573         spin_unlock(&inode->i_lock);
574         return ret;
575 }
576 
577 static long writeback_chunk_size(struct backing_dev_info *bdi,
578                                  struct wb_writeback_work *work)
579 {
580         long pages;
581 
582         /*
583          * WB_SYNC_ALL mode does livelock avoidance by syncing dirty
584          * inodes/pages in one big loop. Setting wbc.nr_to_write=LONG_MAX
585          * here avoids calling into writeback_inodes_wb() more than once.
586          *
587          * The intended call sequence for WB_SYNC_ALL writeback is:
588          *
589          *      wb_writeback()
590          *          writeback_sb_inodes()       <== called only once
591          *              write_cache_pages()     <== called once for each inode
592          *                   (quickly) tag currently dirty pages
593          *                   (maybe slowly) sync all tagged pages
594          */
595         if (work->sync_mode == WB_SYNC_ALL || work->tagged_writepages)
596                 pages = LONG_MAX;
597         else {
598                 pages = min(bdi->avg_write_bandwidth / 2,
599                             global_dirty_limit / DIRTY_SCOPE);
600                 pages = min(pages, work->nr_pages);
601                 pages = round_down(pages + MIN_WRITEBACK_PAGES,
602                                    MIN_WRITEBACK_PAGES);
603         }
604 
605         return pages;
606 }
607 
608 /*
609  * Write a portion of b_io inodes which belong to @sb.
610  *
611  * Return the number of pages and/or inodes written.
612  */
613 static long writeback_sb_inodes(struct super_block *sb,
614                                 struct bdi_writeback *wb,
615                                 struct wb_writeback_work *work)
616 {
617         struct writeback_control wbc = {
618                 .sync_mode              = work->sync_mode,
619                 .tagged_writepages      = work->tagged_writepages,
620                 .for_kupdate            = work->for_kupdate,
621                 .for_background         = work->for_background,
622                 .for_sync               = work->for_sync,
623                 .range_cyclic           = work->range_cyclic,
624                 .range_start            = 0,
625                 .range_end              = LLONG_MAX,
626         };
627         unsigned long start_time = jiffies;
628         long write_chunk;
629         long wrote = 0;  /* count both pages and inodes */
630 
631         while (!list_empty(&wb->b_io)) {
632                 struct inode *inode = wb_inode(wb->b_io.prev);
633 
634                 if (inode->i_sb != sb) {
635                         if (work->sb) {
636                                 /*
637                                  * We only want to write back data for this
638                                  * superblock, move all inodes not belonging
639                                  * to it back onto the dirty list.
640                                  */
641                                 redirty_tail(inode, wb);
642                                 continue;
643                         }
644 
645                         /*
646                          * The inode belongs to a different superblock.
647                          * Bounce back to the caller to unpin this and
648                          * pin the next superblock.
649                          */
650                         break;
651                 }
652 
653                 /*
654                  * Don't bother with new inodes or inodes being freed, first
655                  * kind does not need periodic writeout yet, and for the latter
656                  * kind writeout is handled by the freer.
657                  */
658                 spin_lock(&inode->i_lock);
659                 if (inode->i_state & (I_NEW | I_FREEING | I_WILL_FREE)) {
660                         spin_unlock(&inode->i_lock);
661                         redirty_tail(inode, wb);
662                         continue;
663                 }
664                 if ((inode->i_state & I_SYNC) && wbc.sync_mode != WB_SYNC_ALL) {
665                         /*
666                          * If this inode is locked for writeback and we are not
667                          * doing writeback-for-data-integrity, move it to
668                          * b_more_io so that writeback can proceed with the
669                          * other inodes on s_io.
670                          *
671                          * We'll have another go at writing back this inode
672                          * when we completed a full scan of b_io.
673                          */
674                         spin_unlock(&inode->i_lock);
675                         requeue_io(inode, wb);
676                         trace_writeback_sb_inodes_requeue(inode);
677                         continue;
678                 }
679                 spin_unlock(&wb->list_lock);
680 
681                 /*
682                  * We already requeued the inode if it had I_SYNC set and we
683                  * are doing WB_SYNC_NONE writeback. So this catches only the
684                  * WB_SYNC_ALL case.
685                  */
686                 if (inode->i_state & I_SYNC) {
687                         /* Wait for I_SYNC. This function drops i_lock... */
688                         inode_sleep_on_writeback(inode);
689                         /* Inode may be gone, start again */
690                         spin_lock(&wb->list_lock);
691                         continue;
692                 }
693                 inode->i_state |= I_SYNC;
694                 spin_unlock(&inode->i_lock);
695 
696                 write_chunk = writeback_chunk_size(wb->bdi, work);
697                 wbc.nr_to_write = write_chunk;
698                 wbc.pages_skipped = 0;
699 
700                 /*
701                  * We use I_SYNC to pin the inode in memory. While it is set
702                  * evict_inode() will wait so the inode cannot be freed.
703                  */
704                 __writeback_single_inode(inode, &wbc);
705 
706                 work->nr_pages -= write_chunk - wbc.nr_to_write;
707                 wrote += write_chunk - wbc.nr_to_write;
708                 spin_lock(&wb->list_lock);
709                 spin_lock(&inode->i_lock);
710                 if (!(inode->i_state & I_DIRTY))
711                         wrote++;
712                 requeue_inode(inode, wb, &wbc);
713                 inode_sync_complete(inode);
714                 spin_unlock(&inode->i_lock);
715                 cond_resched_lock(&wb->list_lock);
716                 /*
717                  * bail out to wb_writeback() often enough to check
718                  * background threshold and other termination conditions.
719                  */
720                 if (wrote) {
721                         if (time_is_before_jiffies(start_time + HZ / 10UL))
722                                 break;
723                         if (work->nr_pages <= 0)
724                                 break;
725                 }
726         }
727         return wrote;
728 }
729 
730 static long __writeback_inodes_wb(struct bdi_writeback *wb,
731                                   struct wb_writeback_work *work)
732 {
733         unsigned long start_time = jiffies;
734         long wrote = 0;
735 
736         while (!list_empty(&wb->b_io)) {
737                 struct inode *inode = wb_inode(wb->b_io.prev);
738                 struct super_block *sb = inode->i_sb;
739 
740                 if (!grab_super_passive(sb)) {
741                         /*
742                          * grab_super_passive() may fail consistently due to
743                          * s_umount being grabbed by someone else. Don't use
744                          * requeue_io() to avoid busy retrying the inode/sb.
745                          */
746                         redirty_tail(inode, wb);
747                         continue;
748                 }
749                 wrote += writeback_sb_inodes(sb, wb, work);
750                 drop_super(sb);
751 
752                 /* refer to the same tests at the end of writeback_sb_inodes */
753                 if (wrote) {
754                         if (time_is_before_jiffies(start_time + HZ / 10UL))
755                                 break;
756                         if (work->nr_pages <= 0)
757                                 break;
758                 }
759         }
760         /* Leave any unwritten inodes on b_io */
761         return wrote;
762 }
763 
764 static long writeback_inodes_wb(struct bdi_writeback *wb, long nr_pages,
765                                 enum wb_reason reason)
766 {
767         struct wb_writeback_work work = {
768                 .nr_pages       = nr_pages,
769                 .sync_mode      = WB_SYNC_NONE,
770                 .range_cyclic   = 1,
771                 .reason         = reason,
772         };
773 
774         spin_lock(&wb->list_lock);
775         if (list_empty(&wb->b_io))
776                 queue_io(wb, &work);
777         __writeback_inodes_wb(wb, &work);
778         spin_unlock(&wb->list_lock);
779 
780         return nr_pages - work.nr_pages;
781 }
782 
783 static bool over_bground_thresh(struct backing_dev_info *bdi)
784 {
785         unsigned long background_thresh, dirty_thresh;
786 
787         global_dirty_limits(&background_thresh, &dirty_thresh);
788 
789         if (global_page_state(NR_FILE_DIRTY) +
790             global_page_state(NR_UNSTABLE_NFS) > background_thresh)
791                 return true;
792 
793         if (bdi_stat(bdi, BDI_RECLAIMABLE) >
794                                 bdi_dirty_limit(bdi, background_thresh))
795                 return true;
796 
797         return false;
798 }
799 
800 /*
801  * Called under wb->list_lock. If there are multiple wb per bdi,
802  * only the flusher working on the first wb should do it.
803  */
804 static void wb_update_bandwidth(struct bdi_writeback *wb,
805                                 unsigned long start_time)
806 {
807         __bdi_update_bandwidth(wb->bdi, 0, 0, 0, 0, 0, start_time);
808 }
809 
810 /*
811  * Explicit flushing or periodic writeback of "old" data.
812  *
813  * Define "old": the first time one of an inode's pages is dirtied, we mark the
814  * dirtying-time in the inode's address_space.  So this periodic writeback code
815  * just walks the superblock inode list, writing back any inodes which are
816  * older than a specific point in time.
817  *
818  * Try to run once per dirty_writeback_interval.  But if a writeback event
819  * takes longer than a dirty_writeback_interval interval, then leave a
820  * one-second gap.
821  *
822  * older_than_this takes precedence over nr_to_write.  So we'll only write back
823  * all dirty pages if they are all attached to "old" mappings.
824  */
825 static long wb_writeback(struct bdi_writeback *wb,
826                          struct wb_writeback_work *work)
827 {
828         unsigned long wb_start = jiffies;
829         long nr_pages = work->nr_pages;
830         unsigned long oldest_jif;
831         struct inode *inode;
832         long progress;
833 
834         oldest_jif = jiffies;
835         work->older_than_this = &oldest_jif;
836 
837         spin_lock(&wb->list_lock);
838         for (;;) {
839                 /*
840                  * Stop writeback when nr_pages has been consumed
841                  */
842                 if (work->nr_pages <= 0)
843                         break;
844 
845                 /*
846                  * Background writeout and kupdate-style writeback may
847                  * run forever. Stop them if there is other work to do
848                  * so that e.g. sync can proceed. They'll be restarted
849                  * after the other works are all done.
850                  */
851                 if ((work->for_background || work->for_kupdate) &&
852                     !list_empty(&wb->bdi->work_list))
853                         break;
854 
855                 /*
856                  * For background writeout, stop when we are below the
857                  * background dirty threshold
858                  */
859                 if (work->for_background && !over_bground_thresh(wb->bdi))
860                         break;
861 
862                 /*
863                  * Kupdate and background works are special and we want to
864                  * include all inodes that need writing. Livelock avoidance is
865                  * handled by these works yielding to any other work so we are
866                  * safe.
867                  */
868                 if (work->for_kupdate) {
869                         oldest_jif = jiffies -
870                                 msecs_to_jiffies(dirty_expire_interval * 10);
871                 } else if (work->for_background)
872                         oldest_jif = jiffies;
873 
874                 trace_writeback_start(wb->bdi, work);
875                 if (list_empty(&wb->b_io))
876                         queue_io(wb, work);
877                 if (work->sb)
878                         progress = writeback_sb_inodes(work->sb, wb, work);
879                 else
880                         progress = __writeback_inodes_wb(wb, work);
881                 trace_writeback_written(wb->bdi, work);
882 
883                 wb_update_bandwidth(wb, wb_start);
884 
885                 /*
886                  * Did we write something? Try for more
887                  *
888                  * Dirty inodes are moved to b_io for writeback in batches.
889                  * The completion of the current batch does not necessarily
890                  * mean the overall work is done. So we keep looping as long
891                  * as made some progress on cleaning pages or inodes.
892                  */
893                 if (progress)
894                         continue;
895                 /*
896                  * No more inodes for IO, bail
897                  */
898                 if (list_empty(&wb->b_more_io))
899                         break;
900                 /*
901                  * Nothing written. Wait for some inode to
902                  * become available for writeback. Otherwise
903                  * we'll just busyloop.
904                  */
905                 if (!list_empty(&wb->b_more_io))  {
906                         trace_writeback_wait(wb->bdi, work);
907                         inode = wb_inode(wb->b_more_io.prev);
908                         spin_lock(&inode->i_lock);
909                         spin_unlock(&wb->list_lock);
910                         /* This function drops i_lock... */
911                         inode_sleep_on_writeback(inode);
912                         spin_lock(&wb->list_lock);
913                 }
914         }
915         spin_unlock(&wb->list_lock);
916 
917         return nr_pages - work->nr_pages;
918 }
919 
920 /*
921  * Return the next wb_writeback_work struct that hasn't been processed yet.
922  */
923 static struct wb_writeback_work *
924 get_next_work_item(struct backing_dev_info *bdi)
925 {
926         struct wb_writeback_work *work = NULL;
927 
928         spin_lock_bh(&bdi->wb_lock);
929         if (!list_empty(&bdi->work_list)) {
930                 work = list_entry(bdi->work_list.next,
931                                   struct wb_writeback_work, list);
932                 list_del_init(&work->list);
933         }
934         spin_unlock_bh(&bdi->wb_lock);
935         return work;
936 }
937 
938 /*
939  * Add in the number of potentially dirty inodes, because each inode
940  * write can dirty pagecache in the underlying blockdev.
941  */
942 static unsigned long get_nr_dirty_pages(void)
943 {
944         return global_page_state(NR_FILE_DIRTY) +
945                 global_page_state(NR_UNSTABLE_NFS) +
946                 get_nr_dirty_inodes();
947 }
948 
949 static long wb_check_background_flush(struct bdi_writeback *wb)
950 {
951         if (over_bground_thresh(wb->bdi)) {
952 
953                 struct wb_writeback_work work = {
954                         .nr_pages       = LONG_MAX,
955                         .sync_mode      = WB_SYNC_NONE,
956                         .for_background = 1,
957                         .range_cyclic   = 1,
958                         .reason         = WB_REASON_BACKGROUND,
959                 };
960 
961                 return wb_writeback(wb, &work);
962         }
963 
964         return 0;
965 }
966 
967 static long wb_check_old_data_flush(struct bdi_writeback *wb)
968 {
969         unsigned long expired;
970         long nr_pages;
971 
972         /*
973          * When set to zero, disable periodic writeback
974          */
975         if (!dirty_writeback_interval)
976                 return 0;
977 
978         expired = wb->last_old_flush +
979                         msecs_to_jiffies(dirty_writeback_interval * 10);
980         if (time_before(jiffies, expired))
981                 return 0;
982 
983         wb->last_old_flush = jiffies;
984         nr_pages = get_nr_dirty_pages();
985 
986         if (nr_pages) {
987                 struct wb_writeback_work work = {
988                         .nr_pages       = nr_pages,
989                         .sync_mode      = WB_SYNC_NONE,
990                         .for_kupdate    = 1,
991                         .range_cyclic   = 1,
992                         .reason         = WB_REASON_PERIODIC,
993                 };
994 
995                 return wb_writeback(wb, &work);
996         }
997 
998         return 0;
999 }
1000 
1001 /*
1002  * Retrieve work items and do the writeback they describe
1003  */
1004 static long wb_do_writeback(struct bdi_writeback *wb)
1005 {
1006         struct backing_dev_info *bdi = wb->bdi;
1007         struct wb_writeback_work *work;
1008         long wrote = 0;
1009 
1010         set_bit(BDI_writeback_running, &wb->bdi->state);
1011         while ((work = get_next_work_item(bdi)) != NULL) {
1012 
1013                 trace_writeback_exec(bdi, work);
1014 
1015                 wrote += wb_writeback(wb, work);
1016 
1017                 /*
1018                  * Notify the caller of completion if this is a synchronous
1019                  * work item, otherwise just free it.
1020                  */
1021                 if (work->done)
1022                         complete(work->done);
1023                 else
1024                         kfree(work);
1025         }
1026 
1027         /*
1028          * Check for periodic writeback, kupdated() style
1029          */
1030         wrote += wb_check_old_data_flush(wb);
1031         wrote += wb_check_background_flush(wb);
1032         clear_bit(BDI_writeback_running, &wb->bdi->state);
1033 
1034         return wrote;
1035 }
1036 
1037 /*
1038  * Handle writeback of dirty data for the device backed by this bdi. Also
1039  * reschedules periodically and does kupdated style flushing.
1040  */
1041 void bdi_writeback_workfn(struct work_struct *work)
1042 {
1043         struct bdi_writeback *wb = container_of(to_delayed_work(work),
1044                                                 struct bdi_writeback, dwork);
1045         struct backing_dev_info *bdi = wb->bdi;
1046         long pages_written;
1047 
1048         set_worker_desc("flush-%s", dev_name(bdi->dev));
1049         current->flags |= PF_SWAPWRITE;
1050 
1051         if (likely(!current_is_workqueue_rescuer() ||
1052                    !test_bit(BDI_registered, &bdi->state))) {
1053                 /*
1054                  * The normal path.  Keep writing back @bdi until its
1055                  * work_list is empty.  Note that this path is also taken
1056                  * if @bdi is shutting down even when we're running off the
1057                  * rescuer as work_list needs to be drained.
1058                  */
1059                 do {
1060                         pages_written = wb_do_writeback(wb);
1061                         trace_writeback_pages_written(pages_written);
1062                 } while (!list_empty(&bdi->work_list));
1063         } else {
1064                 /*
1065                  * bdi_wq can't get enough workers and we're running off
1066                  * the emergency worker.  Don't hog it.  Hopefully, 1024 is
1067                  * enough for efficient IO.
1068                  */
1069                 pages_written = writeback_inodes_wb(&bdi->wb, 1024,
1070                                                     WB_REASON_FORKER_THREAD);
1071                 trace_writeback_pages_written(pages_written);
1072         }
1073 
1074         if (!list_empty(&bdi->work_list))
1075                 mod_delayed_work(bdi_wq, &wb->dwork, 0);
1076         else if (wb_has_dirty_io(wb) && dirty_writeback_interval)
1077                 bdi_wakeup_thread_delayed(bdi);
1078 
1079         current->flags &= ~PF_SWAPWRITE;
1080 }
1081 
1082 /*
1083  * Start writeback of `nr_pages' pages.  If `nr_pages' is zero, write back
1084  * the whole world.
1085  */
1086 void wakeup_flusher_threads(long nr_pages, enum wb_reason reason)
1087 {
1088         struct backing_dev_info *bdi;
1089 
1090         if (!nr_pages)
1091                 nr_pages = get_nr_dirty_pages();
1092 
1093         rcu_read_lock();
1094         list_for_each_entry_rcu(bdi, &bdi_list, bdi_list) {
1095                 if (!bdi_has_dirty_io(bdi))
1096                         continue;
1097                 __bdi_start_writeback(bdi, nr_pages, false, reason);
1098         }
1099         rcu_read_unlock();
1100 }
1101 
1102 static noinline void block_dump___mark_inode_dirty(struct inode *inode)
1103 {
1104         if (inode->i_ino || strcmp(inode->i_sb->s_id, "bdev")) {
1105                 struct dentry *dentry;
1106                 const char *name = "?";
1107 
1108                 dentry = d_find_alias(inode);
1109                 if (dentry) {
1110                         spin_lock(&dentry->d_lock);
1111                         name = (const char *) dentry->d_name.name;
1112                 }
1113                 printk(KERN_DEBUG
1114                        "%s(%d): dirtied inode %lu (%s) on %s\n",
1115                        current->comm, task_pid_nr(current), inode->i_ino,
1116                        name, inode->i_sb->s_id);
1117                 if (dentry) {
1118                         spin_unlock(&dentry->d_lock);
1119                         dput(dentry);
1120                 }
1121         }
1122 }
1123 
1124 /**
1125  *      __mark_inode_dirty -    internal function
1126  *      @inode: inode to mark
1127  *      @flags: what kind of dirty (i.e. I_DIRTY_SYNC)
1128  *      Mark an inode as dirty. Callers should use mark_inode_dirty or
1129  *      mark_inode_dirty_sync.
1130  *
1131  * Put the inode on the super block's dirty list.
1132  *
1133  * CAREFUL! We mark it dirty unconditionally, but move it onto the
1134  * dirty list only if it is hashed or if it refers to a blockdev.
1135  * If it was not hashed, it will never be added to the dirty list
1136  * even if it is later hashed, as it will have been marked dirty already.
1137  *
1138  * In short, make sure you hash any inodes _before_ you start marking
1139  * them dirty.
1140  *
1141  * Note that for blockdevs, inode->dirtied_when represents the dirtying time of
1142  * the block-special inode (/dev/hda1) itself.  And the ->dirtied_when field of
1143  * the kernel-internal blockdev inode represents the dirtying time of the
1144  * blockdev's pages.  This is why for I_DIRTY_PAGES we always use
1145  * page->mapping->host, so the page-dirtying time is recorded in the internal
1146  * blockdev inode.
1147  */
1148 void __mark_inode_dirty(struct inode *inode, int flags)
1149 {
1150         struct super_block *sb = inode->i_sb;
1151         struct backing_dev_info *bdi = NULL;
1152 
1153         /*
1154          * Don't do this for I_DIRTY_PAGES - that doesn't actually
1155          * dirty the inode itself
1156          */
1157         if (flags & (I_DIRTY_SYNC | I_DIRTY_DATASYNC)) {
1158                 trace_writeback_dirty_inode_start(inode, flags);
1159 
1160                 if (sb->s_op->dirty_inode)
1161                         sb->s_op->dirty_inode(inode, flags);
1162 
1163                 trace_writeback_dirty_inode(inode, flags);
1164         }
1165 
1166         /*
1167          * Paired with smp_mb() in __writeback_single_inode() for the
1168          * following lockless i_state test.  See there for details.
1169          */
1170         smp_mb();
1171 
1172         if ((inode->i_state & flags) == flags)
1173                 return;
1174 
1175         if (unlikely(block_dump))
1176                 block_dump___mark_inode_dirty(inode);
1177 
1178         spin_lock(&inode->i_lock);
1179         if ((inode->i_state & flags) != flags) {
1180                 const int was_dirty = inode->i_state & I_DIRTY;
1181 
1182                 inode->i_state |= flags;
1183 
1184                 /*
1185                  * If the inode is being synced, just update its dirty state.
1186                  * The unlocker will place the inode on the appropriate
1187                  * superblock list, based upon its state.
1188                  */
1189                 if (inode->i_state & I_SYNC)
1190                         goto out_unlock_inode;
1191 
1192                 /*
1193                  * Only add valid (hashed) inodes to the superblock's
1194                  * dirty list.  Add blockdev inodes as well.
1195                  */
1196                 if (!S_ISBLK(inode->i_mode)) {
1197                         if (inode_unhashed(inode))
1198                                 goto out_unlock_inode;
1199                 }
1200                 if (inode->i_state & I_FREEING)
1201                         goto out_unlock_inode;
1202 
1203                 /*
1204                  * If the inode was already on b_dirty/b_io/b_more_io, don't
1205                  * reposition it (that would break b_dirty time-ordering).
1206                  */
1207                 if (!was_dirty) {
1208                         bool wakeup_bdi = false;
1209                         bdi = inode_to_bdi(inode);
1210 
1211                         spin_unlock(&inode->i_lock);
1212                         spin_lock(&bdi->wb.list_lock);
1213                         if (bdi_cap_writeback_dirty(bdi)) {
1214                                 WARN(!test_bit(BDI_registered, &bdi->state),
1215                                      "bdi-%s not registered\n", bdi->name);
1216 
1217                                 /*
1218                                  * If this is the first dirty inode for this
1219                                  * bdi, we have to wake-up the corresponding
1220                                  * bdi thread to make sure background
1221                                  * write-back happens later.
1222                                  */
1223                                 if (!wb_has_dirty_io(&bdi->wb))
1224                                         wakeup_bdi = true;
1225                         }
1226 
1227                         inode->dirtied_when = jiffies;
1228                         list_move(&inode->i_wb_list, &bdi->wb.b_dirty);
1229                         spin_unlock(&bdi->wb.list_lock);
1230 
1231                         if (wakeup_bdi)
1232                                 bdi_wakeup_thread_delayed(bdi);
1233                         return;
1234                 }
1235         }
1236 out_unlock_inode:
1237         spin_unlock(&inode->i_lock);
1238 
1239 }
1240 EXPORT_SYMBOL(__mark_inode_dirty);
1241 
1242 static void wait_sb_inodes(struct super_block *sb)
1243 {
1244         struct inode *inode, *old_inode = NULL;
1245 
1246         /*
1247          * We need to be protected against the filesystem going from
1248          * r/o to r/w or vice versa.
1249          */
1250         WARN_ON(!rwsem_is_locked(&sb->s_umount));
1251 
1252         spin_lock(&inode_sb_list_lock);
1253 
1254         /*
1255          * Data integrity sync. Must wait for all pages under writeback,
1256          * because there may have been pages dirtied before our sync
1257          * call, but which had writeout started before we write it out.
1258          * In which case, the inode may not be on the dirty list, but
1259          * we still have to wait for that writeout.
1260          */
1261         list_for_each_entry(inode, &sb->s_inodes, i_sb_list) {
1262                 struct address_space *mapping = inode->i_mapping;
1263 
1264                 spin_lock(&inode->i_lock);
1265                 if ((inode->i_state & (I_FREEING|I_WILL_FREE|I_NEW)) ||
1266                     (mapping->nrpages == 0)) {
1267                         spin_unlock(&inode->i_lock);
1268                         continue;
1269                 }
1270                 __iget(inode);
1271                 spin_unlock(&inode->i_lock);
1272                 spin_unlock(&inode_sb_list_lock);
1273 
1274                 /*
1275                  * We hold a reference to 'inode' so it couldn't have been
1276                  * removed from s_inodes list while we dropped the
1277                  * inode_sb_list_lock.  We cannot iput the inode now as we can
1278                  * be holding the last reference and we cannot iput it under
1279                  * inode_sb_list_lock. So we keep the reference and iput it
1280                  * later.
1281                  */
1282                 iput(old_inode);
1283                 old_inode = inode;
1284 
1285                 filemap_fdatawait(mapping);
1286 
1287                 cond_resched();
1288 
1289                 spin_lock(&inode_sb_list_lock);
1290         }
1291         spin_unlock(&inode_sb_list_lock);
1292         iput(old_inode);
1293 }
1294 
1295 /**
1296  * writeback_inodes_sb_nr -     writeback dirty inodes from given super_block
1297  * @sb: the superblock
1298  * @nr: the number of pages to write
1299  * @reason: reason why some writeback work initiated
1300  *
1301  * Start writeback on some inodes on this super_block. No guarantees are made
1302  * on how many (if any) will be written, and this function does not wait
1303  * for IO completion of submitted IO.
1304  */
1305 void writeback_inodes_sb_nr(struct super_block *sb,
1306                             unsigned long nr,
1307                             enum wb_reason reason)
1308 {
1309         DECLARE_COMPLETION_ONSTACK(done);
1310         struct wb_writeback_work work = {
1311                 .sb                     = sb,
1312                 .sync_mode              = WB_SYNC_NONE,
1313                 .tagged_writepages      = 1,
1314                 .done                   = &done,
1315                 .nr_pages               = nr,
1316                 .reason                 = reason,
1317         };
1318 
1319         if (sb->s_bdi == &noop_backing_dev_info)
1320                 return;
1321         WARN_ON(!rwsem_is_locked(&sb->s_umount));
1322         bdi_queue_work(sb->s_bdi, &work);
1323         wait_for_completion(&done);
1324 }
1325 EXPORT_SYMBOL(writeback_inodes_sb_nr);
1326 
1327 /**
1328  * writeback_inodes_sb  -       writeback dirty inodes from given super_block
1329  * @sb: the superblock
1330  * @reason: reason why some writeback work was initiated
1331  *
1332  * Start writeback on some inodes on this super_block. No guarantees are made
1333  * on how many (if any) will be written, and this function does not wait
1334  * for IO completion of submitted IO.
1335  */
1336 void writeback_inodes_sb(struct super_block *sb, enum wb_reason reason)
1337 {
1338         return writeback_inodes_sb_nr(sb, get_nr_dirty_pages(), reason);
1339 }
1340 EXPORT_SYMBOL(writeback_inodes_sb);
1341 
1342 /**
1343  * try_to_writeback_inodes_sb_nr - try to start writeback if none underway
1344  * @sb: the superblock
1345  * @nr: the number of pages to write
1346  * @reason: the reason of writeback
1347  *
1348  * Invoke writeback_inodes_sb_nr if no writeback is currently underway.
1349  * Returns 1 if writeback was started, 0 if not.
1350  */
1351 int try_to_writeback_inodes_sb_nr(struct super_block *sb,
1352                                   unsigned long nr,
1353                                   enum wb_reason reason)
1354 {
1355         if (writeback_in_progress(sb->s_bdi))
1356                 return 1;
1357 
1358         if (!down_read_trylock(&sb->s_umount))
1359                 return 0;
1360 
1361         writeback_inodes_sb_nr(sb, nr, reason);
1362         up_read(&sb->s_umount);
1363         return 1;
1364 }
1365 EXPORT_SYMBOL(try_to_writeback_inodes_sb_nr);
1366 
1367 /**
1368  * try_to_writeback_inodes_sb - try to start writeback if none underway
1369  * @sb: the superblock
1370  * @reason: reason why some writeback work was initiated
1371  *
1372  * Implement by try_to_writeback_inodes_sb_nr()
1373  * Returns 1 if writeback was started, 0 if not.
1374  */
1375 int try_to_writeback_inodes_sb(struct super_block *sb, enum wb_reason reason)
1376 {
1377         return try_to_writeback_inodes_sb_nr(sb, get_nr_dirty_pages(), reason);
1378 }
1379 EXPORT_SYMBOL(try_to_writeback_inodes_sb);
1380 
1381 /**
1382  * sync_inodes_sb       -       sync sb inode pages
1383  * @sb: the superblock
1384  *
1385  * This function writes and waits on any dirty inode belonging to this
1386  * super_block.
1387  */
1388 void sync_inodes_sb(struct super_block *sb)
1389 {
1390         DECLARE_COMPLETION_ONSTACK(done);
1391         struct wb_writeback_work work = {
1392                 .sb             = sb,
1393                 .sync_mode      = WB_SYNC_ALL,
1394                 .nr_pages       = LONG_MAX,
1395                 .range_cyclic   = 0,
1396                 .done           = &done,
1397                 .reason         = WB_REASON_SYNC,
1398                 .for_sync       = 1,
1399         };
1400 
1401         /* Nothing to do? */
1402         if (sb->s_bdi == &noop_backing_dev_info)
1403                 return;
1404         WARN_ON(!rwsem_is_locked(&sb->s_umount));
1405 
1406         bdi_queue_work(sb->s_bdi, &work);
1407         wait_for_completion(&done);
1408 
1409         wait_sb_inodes(sb);
1410 }
1411 EXPORT_SYMBOL(sync_inodes_sb);
1412 
1413 /**
1414  * write_inode_now      -       write an inode to disk
1415  * @inode: inode to write to disk
1416  * @sync: whether the write should be synchronous or not
1417  *
1418  * This function commits an inode to disk immediately if it is dirty. This is
1419  * primarily needed by knfsd.
1420  *
1421  * The caller must either have a ref on the inode or must have set I_WILL_FREE.
1422  */
1423 int write_inode_now(struct inode *inode, int sync)
1424 {
1425         struct bdi_writeback *wb = &inode_to_bdi(inode)->wb;
1426         struct writeback_control wbc = {
1427                 .nr_to_write = LONG_MAX,
1428                 .sync_mode = sync ? WB_SYNC_ALL : WB_SYNC_NONE,
1429                 .range_start = 0,
1430                 .range_end = LLONG_MAX,
1431         };
1432 
1433         if (!mapping_cap_writeback_dirty(inode->i_mapping))
1434                 wbc.nr_to_write = 0;
1435 
1436         might_sleep();
1437         return writeback_single_inode(inode, wb, &wbc);
1438 }
1439 EXPORT_SYMBOL(write_inode_now);
1440 
1441 /**
1442  * sync_inode - write an inode and its pages to disk.
1443  * @inode: the inode to sync
1444  * @wbc: controls the writeback mode
1445  *
1446  * sync_inode() will write an inode and its pages to disk.  It will also
1447  * correctly update the inode on its superblock's dirty inode lists and will
1448  * update inode->i_state.
1449  *
1450  * The caller must have a ref on the inode.
1451  */
1452 int sync_inode(struct inode *inode, struct writeback_control *wbc)
1453 {
1454         return writeback_single_inode(inode, &inode_to_bdi(inode)->wb, wbc);
1455 }
1456 EXPORT_SYMBOL(sync_inode);
1457 
1458 /**
1459  * sync_inode_metadata - write an inode to disk
1460  * @inode: the inode to sync
1461  * @wait: wait for I/O to complete.
1462  *
1463  * Write an inode to disk and adjust its dirty state after completion.
1464  *
1465  * Note: only writes the actual inode, no associated data or other metadata.
1466  */
1467 int sync_inode_metadata(struct inode *inode, int wait)
1468 {
1469         struct writeback_control wbc = {
1470                 .sync_mode = wait ? WB_SYNC_ALL : WB_SYNC_NONE,
1471                 .nr_to_write = 0, /* metadata-only */
1472         };
1473 
1474         return sync_inode(inode, &wbc);
1475 }
1476 EXPORT_SYMBOL(sync_inode_metadata);
1477 

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