vfs: trivial __d_lookup_rcu() cleanups
[linux-2.6.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/pagemap.h>
24 #include <linux/kthread.h>
25 #include <linux/freezer.h>
26 #include <linux/writeback.h>
27 #include <linux/blkdev.h>
28 #include <linux/backing-dev.h>
29 #include <linux/tracepoint.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         enum wb_reason reason;          /* why was writeback initiated? */
50
51         struct list_head list;          /* pending work list */
52         struct completion *done;        /* set if the caller waits */
53 };
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 /*
88  * Include the creation of the trace points after defining the
89  * wb_writeback_work structure and inline functions so that the definition
90  * remains local to this file.
91  */
92 #define CREATE_TRACE_POINTS
93 #include <trace/events/writeback.h>
94
95 /* Wakeup flusher thread or forker thread to fork it. Requires bdi->wb_lock. */
96 static void bdi_wakeup_flusher(struct backing_dev_info *bdi)
97 {
98         if (bdi->wb.task) {
99                 wake_up_process(bdi->wb.task);
100         } else {
101                 /*
102                  * The bdi thread isn't there, wake up the forker thread which
103                  * will create and run it.
104                  */
105                 wake_up_process(default_backing_dev_info.wb.task);
106         }
107 }
108
109 static void bdi_queue_work(struct backing_dev_info *bdi,
110                            struct wb_writeback_work *work)
111 {
112         trace_writeback_queue(bdi, work);
113
114         spin_lock_bh(&bdi->wb_lock);
115         list_add_tail(&work->list, &bdi->work_list);
116         if (!bdi->wb.task)
117                 trace_writeback_nothread(bdi, work);
118         bdi_wakeup_flusher(bdi);
119         spin_unlock_bh(&bdi->wb_lock);
120 }
121
122 static void
123 __bdi_start_writeback(struct backing_dev_info *bdi, long nr_pages,
124                       bool range_cyclic, enum wb_reason reason)
125 {
126         struct wb_writeback_work *work;
127
128         /*
129          * This is WB_SYNC_NONE writeback, so if allocation fails just
130          * wakeup the thread for old dirty data writeback
131          */
132         work = kzalloc(sizeof(*work), GFP_ATOMIC);
133         if (!work) {
134                 if (bdi->wb.task) {
135                         trace_writeback_nowork(bdi);
136                         wake_up_process(bdi->wb.task);
137                 }
138                 return;
139         }
140
141         work->sync_mode = WB_SYNC_NONE;
142         work->nr_pages  = nr_pages;
143         work->range_cyclic = range_cyclic;
144         work->reason    = reason;
145
146         bdi_queue_work(bdi, work);
147 }
148
149 /**
150  * bdi_start_writeback - start writeback
151  * @bdi: the backing device to write from
152  * @nr_pages: the number of pages to write
153  * @reason: reason why some writeback work was initiated
154  *
155  * Description:
156  *   This does WB_SYNC_NONE opportunistic writeback. The IO is only
157  *   started when this function returns, we make no guarantees on
158  *   completion. Caller need not hold sb s_umount semaphore.
159  *
160  */
161 void bdi_start_writeback(struct backing_dev_info *bdi, long nr_pages,
162                         enum wb_reason reason)
163 {
164         __bdi_start_writeback(bdi, nr_pages, true, reason);
165 }
166
167 /**
168  * bdi_start_background_writeback - start background writeback
169  * @bdi: the backing device to write from
170  *
171  * Description:
172  *   This makes sure WB_SYNC_NONE background writeback happens. When
173  *   this function returns, it is only guaranteed that for given BDI
174  *   some IO is happening if we are over background dirty threshold.
175  *   Caller need not hold sb s_umount semaphore.
176  */
177 void bdi_start_background_writeback(struct backing_dev_info *bdi)
178 {
179         /*
180          * We just wake up the flusher thread. It will perform background
181          * writeback as soon as there is no other work to do.
182          */
183         trace_writeback_wake_background(bdi);
184         spin_lock_bh(&bdi->wb_lock);
185         bdi_wakeup_flusher(bdi);
186         spin_unlock_bh(&bdi->wb_lock);
187 }
188
189 /*
190  * Remove the inode from the writeback list it is on.
191  */
192 void inode_wb_list_del(struct inode *inode)
193 {
194         struct backing_dev_info *bdi = inode_to_bdi(inode);
195
196         spin_lock(&bdi->wb.list_lock);
197         list_del_init(&inode->i_wb_list);
198         spin_unlock(&bdi->wb.list_lock);
199 }
200
201 /*
202  * Redirty an inode: set its when-it-was dirtied timestamp and move it to the
203  * furthest end of its superblock's dirty-inode list.
204  *
205  * Before stamping the inode's ->dirtied_when, we check to see whether it is
206  * already the most-recently-dirtied inode on the b_dirty list.  If that is
207  * the case then the inode must have been redirtied while it was being written
208  * out and we don't reset its dirtied_when.
209  */
210 static void redirty_tail(struct inode *inode, struct bdi_writeback *wb)
211 {
212         assert_spin_locked(&wb->list_lock);
213         if (!list_empty(&wb->b_dirty)) {
214                 struct inode *tail;
215
216                 tail = wb_inode(wb->b_dirty.next);
217                 if (time_before(inode->dirtied_when, tail->dirtied_when))
218                         inode->dirtied_when = jiffies;
219         }
220         list_move(&inode->i_wb_list, &wb->b_dirty);
221 }
222
223 /*
224  * requeue inode for re-scanning after bdi->b_io list is exhausted.
225  */
226 static void requeue_io(struct inode *inode, struct bdi_writeback *wb)
227 {
228         assert_spin_locked(&wb->list_lock);
229         list_move(&inode->i_wb_list, &wb->b_more_io);
230 }
231
232 static void inode_sync_complete(struct inode *inode)
233 {
234         /*
235          * Prevent speculative execution through
236          * spin_unlock(&wb->list_lock);
237          */
238
239         smp_mb();
240         wake_up_bit(&inode->i_state, __I_SYNC);
241 }
242
243 static bool inode_dirtied_after(struct inode *inode, unsigned long t)
244 {
245         bool ret = time_after(inode->dirtied_when, t);
246 #ifndef CONFIG_64BIT
247         /*
248          * For inodes being constantly redirtied, dirtied_when can get stuck.
249          * It _appears_ to be in the future, but is actually in distant past.
250          * This test is necessary to prevent such wrapped-around relative times
251          * from permanently stopping the whole bdi writeback.
252          */
253         ret = ret && time_before_eq(inode->dirtied_when, jiffies);
254 #endif
255         return ret;
256 }
257
258 /*
259  * Move expired dirty inodes from @delaying_queue to @dispatch_queue.
260  */
261 static int move_expired_inodes(struct list_head *delaying_queue,
262                                struct list_head *dispatch_queue,
263                                struct wb_writeback_work *work)
264 {
265         LIST_HEAD(tmp);
266         struct list_head *pos, *node;
267         struct super_block *sb = NULL;
268         struct inode *inode;
269         int do_sb_sort = 0;
270         int moved = 0;
271
272         while (!list_empty(delaying_queue)) {
273                 inode = wb_inode(delaying_queue->prev);
274                 if (work->older_than_this &&
275                     inode_dirtied_after(inode, *work->older_than_this))
276                         break;
277                 if (sb && sb != inode->i_sb)
278                         do_sb_sort = 1;
279                 sb = inode->i_sb;
280                 list_move(&inode->i_wb_list, &tmp);
281                 moved++;
282         }
283
284         /* just one sb in list, splice to dispatch_queue and we're done */
285         if (!do_sb_sort) {
286                 list_splice(&tmp, dispatch_queue);
287                 goto out;
288         }
289
290         /* Move inodes from one superblock together */
291         while (!list_empty(&tmp)) {
292                 sb = wb_inode(tmp.prev)->i_sb;
293                 list_for_each_prev_safe(pos, node, &tmp) {
294                         inode = wb_inode(pos);
295                         if (inode->i_sb == sb)
296                                 list_move(&inode->i_wb_list, dispatch_queue);
297                 }
298         }
299 out:
300         return moved;
301 }
302
303 /*
304  * Queue all expired dirty inodes for io, eldest first.
305  * Before
306  *         newly dirtied     b_dirty    b_io    b_more_io
307  *         =============>    gf         edc     BA
308  * After
309  *         newly dirtied     b_dirty    b_io    b_more_io
310  *         =============>    g          fBAedc
311  *                                           |
312  *                                           +--> dequeue for IO
313  */
314 static void queue_io(struct bdi_writeback *wb, struct wb_writeback_work *work)
315 {
316         int moved;
317         assert_spin_locked(&wb->list_lock);
318         list_splice_init(&wb->b_more_io, &wb->b_io);
319         moved = move_expired_inodes(&wb->b_dirty, &wb->b_io, work);
320         trace_writeback_queue_io(wb, work, moved);
321 }
322
323 static int write_inode(struct inode *inode, struct writeback_control *wbc)
324 {
325         if (inode->i_sb->s_op->write_inode && !is_bad_inode(inode))
326                 return inode->i_sb->s_op->write_inode(inode, wbc);
327         return 0;
328 }
329
330 /*
331  * Wait for writeback on an inode to complete.
332  */
333 static void inode_wait_for_writeback(struct inode *inode,
334                                      struct bdi_writeback *wb)
335 {
336         DEFINE_WAIT_BIT(wq, &inode->i_state, __I_SYNC);
337         wait_queue_head_t *wqh;
338
339         wqh = bit_waitqueue(&inode->i_state, __I_SYNC);
340         while (inode->i_state & I_SYNC) {
341                 spin_unlock(&inode->i_lock);
342                 spin_unlock(&wb->list_lock);
343                 __wait_on_bit(wqh, &wq, inode_wait, TASK_UNINTERRUPTIBLE);
344                 spin_lock(&wb->list_lock);
345                 spin_lock(&inode->i_lock);
346         }
347 }
348
349 /*
350  * Write out an inode's dirty pages.  Called under wb->list_lock and
351  * inode->i_lock.  Either the caller has an active reference on the inode or
352  * the inode has I_WILL_FREE set.
353  *
354  * If `wait' is set, wait on the writeout.
355  *
356  * The whole writeout design is quite complex and fragile.  We want to avoid
357  * starvation of particular inodes when others are being redirtied, prevent
358  * livelocks, etc.
359  */
360 static int
361 writeback_single_inode(struct inode *inode, struct bdi_writeback *wb,
362                        struct writeback_control *wbc)
363 {
364         struct address_space *mapping = inode->i_mapping;
365         long nr_to_write = wbc->nr_to_write;
366         unsigned dirty;
367         int ret;
368
369         assert_spin_locked(&wb->list_lock);
370         assert_spin_locked(&inode->i_lock);
371
372         if (!atomic_read(&inode->i_count))
373                 WARN_ON(!(inode->i_state & (I_WILL_FREE|I_FREEING)));
374         else
375                 WARN_ON(inode->i_state & I_WILL_FREE);
376
377         if (inode->i_state & I_SYNC) {
378                 /*
379                  * If this inode is locked for writeback and we are not doing
380                  * writeback-for-data-integrity, move it to b_more_io so that
381                  * writeback can proceed with the other inodes on s_io.
382                  *
383                  * We'll have another go at writing back this inode when we
384                  * completed a full scan of b_io.
385                  */
386                 if (wbc->sync_mode != WB_SYNC_ALL) {
387                         requeue_io(inode, wb);
388                         trace_writeback_single_inode_requeue(inode, wbc,
389                                                              nr_to_write);
390                         return 0;
391                 }
392
393                 /*
394                  * It's a data-integrity sync.  We must wait.
395                  */
396                 inode_wait_for_writeback(inode, wb);
397         }
398
399         BUG_ON(inode->i_state & I_SYNC);
400
401         /* Set I_SYNC, reset I_DIRTY_PAGES */
402         inode->i_state |= I_SYNC;
403         inode->i_state &= ~I_DIRTY_PAGES;
404         spin_unlock(&inode->i_lock);
405         spin_unlock(&wb->list_lock);
406
407         ret = do_writepages(mapping, wbc);
408
409         /*
410          * Make sure to wait on the data before writing out the metadata.
411          * This is important for filesystems that modify metadata on data
412          * I/O completion.
413          */
414         if (wbc->sync_mode == WB_SYNC_ALL) {
415                 int err = filemap_fdatawait(mapping);
416                 if (ret == 0)
417                         ret = err;
418         }
419
420         /*
421          * Some filesystems may redirty the inode during the writeback
422          * due to delalloc, clear dirty metadata flags right before
423          * write_inode()
424          */
425         spin_lock(&inode->i_lock);
426         dirty = inode->i_state & I_DIRTY;
427         inode->i_state &= ~(I_DIRTY_SYNC | I_DIRTY_DATASYNC);
428         spin_unlock(&inode->i_lock);
429         /* Don't write the inode if only I_DIRTY_PAGES was set */
430         if (dirty & (I_DIRTY_SYNC | I_DIRTY_DATASYNC)) {
431                 int err = write_inode(inode, wbc);
432                 if (ret == 0)
433                         ret = err;
434         }
435
436         spin_lock(&wb->list_lock);
437         spin_lock(&inode->i_lock);
438         inode->i_state &= ~I_SYNC;
439         if (!(inode->i_state & I_FREEING)) {
440                 /*
441                  * Sync livelock prevention. Each inode is tagged and synced in
442                  * one shot. If still dirty, it will be redirty_tail()'ed below.
443                  * Update the dirty time to prevent enqueue and sync it again.
444                  */
445                 if ((inode->i_state & I_DIRTY) &&
446                     (wbc->sync_mode == WB_SYNC_ALL || wbc->tagged_writepages))
447                         inode->dirtied_when = jiffies;
448
449                 if (mapping_tagged(mapping, PAGECACHE_TAG_DIRTY)) {
450                         /*
451                          * We didn't write back all the pages.  nfs_writepages()
452                          * sometimes bales out without doing anything.
453                          */
454                         inode->i_state |= I_DIRTY_PAGES;
455                         if (wbc->nr_to_write <= 0) {
456                                 /*
457                                  * slice used up: queue for next turn
458                                  */
459                                 requeue_io(inode, wb);
460                         } else {
461                                 /*
462                                  * Writeback blocked by something other than
463                                  * congestion. Delay the inode for some time to
464                                  * avoid spinning on the CPU (100% iowait)
465                                  * retrying writeback of the dirty page/inode
466                                  * that cannot be performed immediately.
467                                  */
468                                 redirty_tail(inode, wb);
469                         }
470                 } else if (inode->i_state & I_DIRTY) {
471                         /*
472                          * Filesystems can dirty the inode during writeback
473                          * operations, such as delayed allocation during
474                          * submission or metadata updates after data IO
475                          * completion.
476                          */
477                         redirty_tail(inode, wb);
478                 } else {
479                         /*
480                          * The inode is clean.  At this point we either have
481                          * a reference to the inode or it's on it's way out.
482                          * No need to add it back to the LRU.
483                          */
484                         list_del_init(&inode->i_wb_list);
485                 }
486         }
487         inode_sync_complete(inode);
488         trace_writeback_single_inode(inode, wbc, nr_to_write);
489         return ret;
490 }
491
492 static long writeback_chunk_size(struct backing_dev_info *bdi,
493                                  struct wb_writeback_work *work)
494 {
495         long pages;
496
497         /*
498          * WB_SYNC_ALL mode does livelock avoidance by syncing dirty
499          * inodes/pages in one big loop. Setting wbc.nr_to_write=LONG_MAX
500          * here avoids calling into writeback_inodes_wb() more than once.
501          *
502          * The intended call sequence for WB_SYNC_ALL writeback is:
503          *
504          *      wb_writeback()
505          *          writeback_sb_inodes()       <== called only once
506          *              write_cache_pages()     <== called once for each inode
507          *                   (quickly) tag currently dirty pages
508          *                   (maybe slowly) sync all tagged pages
509          */
510         if (work->sync_mode == WB_SYNC_ALL || work->tagged_writepages)
511                 pages = LONG_MAX;
512         else {
513                 pages = min(bdi->avg_write_bandwidth / 2,
514                             global_dirty_limit / DIRTY_SCOPE);
515                 pages = min(pages, work->nr_pages);
516                 pages = round_down(pages + MIN_WRITEBACK_PAGES,
517                                    MIN_WRITEBACK_PAGES);
518         }
519
520         return pages;
521 }
522
523 /*
524  * Write a portion of b_io inodes which belong to @sb.
525  *
526  * If @only_this_sb is true, then find and write all such
527  * inodes. Otherwise write only ones which go sequentially
528  * in reverse order.
529  *
530  * Return the number of pages and/or inodes written.
531  */
532 static long writeback_sb_inodes(struct super_block *sb,
533                                 struct bdi_writeback *wb,
534                                 struct wb_writeback_work *work)
535 {
536         struct writeback_control wbc = {
537                 .sync_mode              = work->sync_mode,
538                 .tagged_writepages      = work->tagged_writepages,
539                 .for_kupdate            = work->for_kupdate,
540                 .for_background         = work->for_background,
541                 .range_cyclic           = work->range_cyclic,
542                 .range_start            = 0,
543                 .range_end              = LLONG_MAX,
544         };
545         unsigned long start_time = jiffies;
546         long write_chunk;
547         long wrote = 0;  /* count both pages and inodes */
548
549         while (!list_empty(&wb->b_io)) {
550                 struct inode *inode = wb_inode(wb->b_io.prev);
551
552                 if (inode->i_sb != sb) {
553                         if (work->sb) {
554                                 /*
555                                  * We only want to write back data for this
556                                  * superblock, move all inodes not belonging
557                                  * to it back onto the dirty list.
558                                  */
559                                 redirty_tail(inode, wb);
560                                 continue;
561                         }
562
563                         /*
564                          * The inode belongs to a different superblock.
565                          * Bounce back to the caller to unpin this and
566                          * pin the next superblock.
567                          */
568                         break;
569                 }
570
571                 /*
572                  * Don't bother with new inodes or inodes beeing freed, first
573                  * kind does not need peridic writeout yet, and for the latter
574                  * kind writeout is handled by the freer.
575                  */
576                 spin_lock(&inode->i_lock);
577                 if (inode->i_state & (I_NEW | I_FREEING | I_WILL_FREE)) {
578                         spin_unlock(&inode->i_lock);
579                         redirty_tail(inode, wb);
580                         continue;
581                 }
582                 __iget(inode);
583                 write_chunk = writeback_chunk_size(wb->bdi, work);
584                 wbc.nr_to_write = write_chunk;
585                 wbc.pages_skipped = 0;
586
587                 writeback_single_inode(inode, wb, &wbc);
588
589                 work->nr_pages -= write_chunk - wbc.nr_to_write;
590                 wrote += write_chunk - wbc.nr_to_write;
591                 if (!(inode->i_state & I_DIRTY))
592                         wrote++;
593                 if (wbc.pages_skipped) {
594                         /*
595                          * writeback is not making progress due to locked
596                          * buffers.  Skip this inode for now.
597                          */
598                         redirty_tail(inode, wb);
599                 }
600                 spin_unlock(&inode->i_lock);
601                 spin_unlock(&wb->list_lock);
602                 iput(inode);
603                 cond_resched();
604                 spin_lock(&wb->list_lock);
605                 /*
606                  * bail out to wb_writeback() often enough to check
607                  * background threshold and other termination conditions.
608                  */
609                 if (wrote) {
610                         if (time_is_before_jiffies(start_time + HZ / 10UL))
611                                 break;
612                         if (work->nr_pages <= 0)
613                                 break;
614                 }
615         }
616         return wrote;
617 }
618
619 static long __writeback_inodes_wb(struct bdi_writeback *wb,
620                                   struct wb_writeback_work *work)
621 {
622         unsigned long start_time = jiffies;
623         long wrote = 0;
624
625         while (!list_empty(&wb->b_io)) {
626                 struct inode *inode = wb_inode(wb->b_io.prev);
627                 struct super_block *sb = inode->i_sb;
628
629                 if (!grab_super_passive(sb)) {
630                         /*
631                          * grab_super_passive() may fail consistently due to
632                          * s_umount being grabbed by someone else. Don't use
633                          * requeue_io() to avoid busy retrying the inode/sb.
634                          */
635                         redirty_tail(inode, wb);
636                         continue;
637                 }
638                 wrote += writeback_sb_inodes(sb, wb, work);
639                 drop_super(sb);
640
641                 /* refer to the same tests at the end of writeback_sb_inodes */
642                 if (wrote) {
643                         if (time_is_before_jiffies(start_time + HZ / 10UL))
644                                 break;
645                         if (work->nr_pages <= 0)
646                                 break;
647                 }
648         }
649         /* Leave any unwritten inodes on b_io */
650         return wrote;
651 }
652
653 long writeback_inodes_wb(struct bdi_writeback *wb, long nr_pages,
654                                 enum wb_reason reason)
655 {
656         struct wb_writeback_work work = {
657                 .nr_pages       = nr_pages,
658                 .sync_mode      = WB_SYNC_NONE,
659                 .range_cyclic   = 1,
660                 .reason         = reason,
661         };
662
663         spin_lock(&wb->list_lock);
664         if (list_empty(&wb->b_io))
665                 queue_io(wb, &work);
666         __writeback_inodes_wb(wb, &work);
667         spin_unlock(&wb->list_lock);
668
669         return nr_pages - work.nr_pages;
670 }
671
672 static bool over_bground_thresh(struct backing_dev_info *bdi)
673 {
674         unsigned long background_thresh, dirty_thresh;
675
676         global_dirty_limits(&background_thresh, &dirty_thresh);
677
678         if (global_page_state(NR_FILE_DIRTY) +
679             global_page_state(NR_UNSTABLE_NFS) > background_thresh)
680                 return true;
681
682         if (bdi_stat(bdi, BDI_RECLAIMABLE) >
683                                 bdi_dirty_limit(bdi, background_thresh))
684                 return true;
685
686         return false;
687 }
688
689 /*
690  * Called under wb->list_lock. If there are multiple wb per bdi,
691  * only the flusher working on the first wb should do it.
692  */
693 static void wb_update_bandwidth(struct bdi_writeback *wb,
694                                 unsigned long start_time)
695 {
696         __bdi_update_bandwidth(wb->bdi, 0, 0, 0, 0, 0, start_time);
697 }
698
699 /*
700  * Explicit flushing or periodic writeback of "old" data.
701  *
702  * Define "old": the first time one of an inode's pages is dirtied, we mark the
703  * dirtying-time in the inode's address_space.  So this periodic writeback code
704  * just walks the superblock inode list, writing back any inodes which are
705  * older than a specific point in time.
706  *
707  * Try to run once per dirty_writeback_interval.  But if a writeback event
708  * takes longer than a dirty_writeback_interval interval, then leave a
709  * one-second gap.
710  *
711  * older_than_this takes precedence over nr_to_write.  So we'll only write back
712  * all dirty pages if they are all attached to "old" mappings.
713  */
714 static long wb_writeback(struct bdi_writeback *wb,
715                          struct wb_writeback_work *work)
716 {
717         unsigned long wb_start = jiffies;
718         long nr_pages = work->nr_pages;
719         unsigned long oldest_jif;
720         struct inode *inode;
721         long progress;
722
723         oldest_jif = jiffies;
724         work->older_than_this = &oldest_jif;
725
726         spin_lock(&wb->list_lock);
727         for (;;) {
728                 /*
729                  * Stop writeback when nr_pages has been consumed
730                  */
731                 if (work->nr_pages <= 0)
732                         break;
733
734                 /*
735                  * Background writeout and kupdate-style writeback may
736                  * run forever. Stop them if there is other work to do
737                  * so that e.g. sync can proceed. They'll be restarted
738                  * after the other works are all done.
739                  */
740                 if ((work->for_background || work->for_kupdate) &&
741                     !list_empty(&wb->bdi->work_list))
742                         break;
743
744                 /*
745                  * For background writeout, stop when we are below the
746                  * background dirty threshold
747                  */
748                 if (work->for_background && !over_bground_thresh(wb->bdi))
749                         break;
750
751                 /*
752                  * Kupdate and background works are special and we want to
753                  * include all inodes that need writing. Livelock avoidance is
754                  * handled by these works yielding to any other work so we are
755                  * safe.
756                  */
757                 if (work->for_kupdate) {
758                         oldest_jif = jiffies -
759                                 msecs_to_jiffies(dirty_expire_interval * 10);
760                 } else if (work->for_background)
761                         oldest_jif = jiffies;
762
763                 trace_writeback_start(wb->bdi, work);
764                 if (list_empty(&wb->b_io))
765                         queue_io(wb, work);
766                 if (work->sb)
767                         progress = writeback_sb_inodes(work->sb, wb, work);
768                 else
769                         progress = __writeback_inodes_wb(wb, work);
770                 trace_writeback_written(wb->bdi, work);
771
772                 wb_update_bandwidth(wb, wb_start);
773
774                 /*
775                  * Did we write something? Try for more
776                  *
777                  * Dirty inodes are moved to b_io for writeback in batches.
778                  * The completion of the current batch does not necessarily
779                  * mean the overall work is done. So we keep looping as long
780                  * as made some progress on cleaning pages or inodes.
781                  */
782                 if (progress)
783                         continue;
784                 /*
785                  * No more inodes for IO, bail
786                  */
787                 if (list_empty(&wb->b_more_io))
788                         break;
789                 /*
790                  * Nothing written. Wait for some inode to
791                  * become available for writeback. Otherwise
792                  * we'll just busyloop.
793                  */
794                 if (!list_empty(&wb->b_more_io))  {
795                         trace_writeback_wait(wb->bdi, work);
796                         inode = wb_inode(wb->b_more_io.prev);
797                         spin_lock(&inode->i_lock);
798                         inode_wait_for_writeback(inode, wb);
799                         spin_unlock(&inode->i_lock);
800                 }
801         }
802         spin_unlock(&wb->list_lock);
803
804         return nr_pages - work->nr_pages;
805 }
806
807 /*
808  * Return the next wb_writeback_work struct that hasn't been processed yet.
809  */
810 static struct wb_writeback_work *
811 get_next_work_item(struct backing_dev_info *bdi)
812 {
813         struct wb_writeback_work *work = NULL;
814
815         spin_lock_bh(&bdi->wb_lock);
816         if (!list_empty(&bdi->work_list)) {
817                 work = list_entry(bdi->work_list.next,
818                                   struct wb_writeback_work, list);
819                 list_del_init(&work->list);
820         }
821         spin_unlock_bh(&bdi->wb_lock);
822         return work;
823 }
824
825 /*
826  * Add in the number of potentially dirty inodes, because each inode
827  * write can dirty pagecache in the underlying blockdev.
828  */
829 static unsigned long get_nr_dirty_pages(void)
830 {
831         return global_page_state(NR_FILE_DIRTY) +
832                 global_page_state(NR_UNSTABLE_NFS) +
833                 get_nr_dirty_inodes();
834 }
835
836 static long wb_check_background_flush(struct bdi_writeback *wb)
837 {
838         if (over_bground_thresh(wb->bdi)) {
839
840                 struct wb_writeback_work work = {
841                         .nr_pages       = LONG_MAX,
842                         .sync_mode      = WB_SYNC_NONE,
843                         .for_background = 1,
844                         .range_cyclic   = 1,
845                         .reason         = WB_REASON_BACKGROUND,
846                 };
847
848                 return wb_writeback(wb, &work);
849         }
850
851         return 0;
852 }
853
854 static long wb_check_old_data_flush(struct bdi_writeback *wb)
855 {
856         unsigned long expired;
857         long nr_pages;
858
859         /*
860          * When set to zero, disable periodic writeback
861          */
862         if (!dirty_writeback_interval)
863                 return 0;
864
865         expired = wb->last_old_flush +
866                         msecs_to_jiffies(dirty_writeback_interval * 10);
867         if (time_before(jiffies, expired))
868                 return 0;
869
870         wb->last_old_flush = jiffies;
871         nr_pages = get_nr_dirty_pages();
872
873         if (nr_pages) {
874                 struct wb_writeback_work work = {
875                         .nr_pages       = nr_pages,
876                         .sync_mode      = WB_SYNC_NONE,
877                         .for_kupdate    = 1,
878                         .range_cyclic   = 1,
879                         .reason         = WB_REASON_PERIODIC,
880                 };
881
882                 return wb_writeback(wb, &work);
883         }
884
885         return 0;
886 }
887
888 /*
889  * Retrieve work items and do the writeback they describe
890  */
891 long wb_do_writeback(struct bdi_writeback *wb, int force_wait)
892 {
893         struct backing_dev_info *bdi = wb->bdi;
894         struct wb_writeback_work *work;
895         long wrote = 0;
896
897         set_bit(BDI_writeback_running, &wb->bdi->state);
898         while ((work = get_next_work_item(bdi)) != NULL) {
899                 /*
900                  * Override sync mode, in case we must wait for completion
901                  * because this thread is exiting now.
902                  */
903                 if (force_wait)
904                         work->sync_mode = WB_SYNC_ALL;
905
906                 trace_writeback_exec(bdi, work);
907
908                 wrote += wb_writeback(wb, work);
909
910                 /*
911                  * Notify the caller of completion if this is a synchronous
912                  * work item, otherwise just free it.
913                  */
914                 if (work->done)
915                         complete(work->done);
916                 else
917                         kfree(work);
918         }
919
920         /*
921          * Check for periodic writeback, kupdated() style
922          */
923         wrote += wb_check_old_data_flush(wb);
924         wrote += wb_check_background_flush(wb);
925         clear_bit(BDI_writeback_running, &wb->bdi->state);
926
927         return wrote;
928 }
929
930 /*
931  * Handle writeback of dirty data for the device backed by this bdi. Also
932  * wakes up periodically and does kupdated style flushing.
933  */
934 int bdi_writeback_thread(void *data)
935 {
936         struct bdi_writeback *wb = data;
937         struct backing_dev_info *bdi = wb->bdi;
938         long pages_written;
939
940         current->flags |= PF_SWAPWRITE;
941         set_freezable();
942         wb->last_active = jiffies;
943
944         /*
945          * Our parent may run at a different priority, just set us to normal
946          */
947         set_user_nice(current, 0);
948
949         trace_writeback_thread_start(bdi);
950
951         while (!kthread_freezable_should_stop(NULL)) {
952                 /*
953                  * Remove own delayed wake-up timer, since we are already awake
954                  * and we'll take care of the preriodic write-back.
955                  */
956                 del_timer(&wb->wakeup_timer);
957
958                 pages_written = wb_do_writeback(wb, 0);
959
960                 trace_writeback_pages_written(pages_written);
961
962                 if (pages_written)
963                         wb->last_active = jiffies;
964
965                 set_current_state(TASK_INTERRUPTIBLE);
966                 if (!list_empty(&bdi->work_list) || kthread_should_stop()) {
967                         __set_current_state(TASK_RUNNING);
968                         continue;
969                 }
970
971                 if (wb_has_dirty_io(wb) && dirty_writeback_interval)
972                         schedule_timeout(msecs_to_jiffies(dirty_writeback_interval * 10));
973                 else {
974                         /*
975                          * We have nothing to do, so can go sleep without any
976                          * timeout and save power. When a work is queued or
977                          * something is made dirty - we will be woken up.
978                          */
979                         schedule();
980                 }
981         }
982
983         /* Flush any work that raced with us exiting */
984         if (!list_empty(&bdi->work_list))
985                 wb_do_writeback(wb, 1);
986
987         trace_writeback_thread_stop(bdi);
988         return 0;
989 }
990
991
992 /*
993  * Start writeback of `nr_pages' pages.  If `nr_pages' is zero, write back
994  * the whole world.
995  */
996 void wakeup_flusher_threads(long nr_pages, enum wb_reason reason)
997 {
998         struct backing_dev_info *bdi;
999
1000         if (!nr_pages) {
1001                 nr_pages = global_page_state(NR_FILE_DIRTY) +
1002                                 global_page_state(NR_UNSTABLE_NFS);
1003         }
1004
1005         rcu_read_lock();
1006         list_for_each_entry_rcu(bdi, &bdi_list, bdi_list) {
1007                 if (!bdi_has_dirty_io(bdi))
1008                         continue;
1009                 __bdi_start_writeback(bdi, nr_pages, false, reason);
1010         }
1011         rcu_read_unlock();
1012 }
1013
1014 static noinline void block_dump___mark_inode_dirty(struct inode *inode)
1015 {
1016         if (inode->i_ino || strcmp(inode->i_sb->s_id, "bdev")) {
1017                 struct dentry *dentry;
1018                 const char *name = "?";
1019
1020                 dentry = d_find_alias(inode);
1021                 if (dentry) {
1022                         spin_lock(&dentry->d_lock);
1023                         name = (const char *) dentry->d_name.name;
1024                 }
1025                 printk(KERN_DEBUG
1026                        "%s(%d): dirtied inode %lu (%s) on %s\n",
1027                        current->comm, task_pid_nr(current), inode->i_ino,
1028                        name, inode->i_sb->s_id);
1029                 if (dentry) {
1030                         spin_unlock(&dentry->d_lock);
1031                         dput(dentry);
1032                 }
1033         }
1034 }
1035
1036 /**
1037  *      __mark_inode_dirty -    internal function
1038  *      @inode: inode to mark
1039  *      @flags: what kind of dirty (i.e. I_DIRTY_SYNC)
1040  *      Mark an inode as dirty. Callers should use mark_inode_dirty or
1041  *      mark_inode_dirty_sync.
1042  *
1043  * Put the inode on the super block's dirty list.
1044  *
1045  * CAREFUL! We mark it dirty unconditionally, but move it onto the
1046  * dirty list only if it is hashed or if it refers to a blockdev.
1047  * If it was not hashed, it will never be added to the dirty list
1048  * even if it is later hashed, as it will have been marked dirty already.
1049  *
1050  * In short, make sure you hash any inodes _before_ you start marking
1051  * them dirty.
1052  *
1053  * Note that for blockdevs, inode->dirtied_when represents the dirtying time of
1054  * the block-special inode (/dev/hda1) itself.  And the ->dirtied_when field of
1055  * the kernel-internal blockdev inode represents the dirtying time of the
1056  * blockdev's pages.  This is why for I_DIRTY_PAGES we always use
1057  * page->mapping->host, so the page-dirtying time is recorded in the internal
1058  * blockdev inode.
1059  */
1060 void __mark_inode_dirty(struct inode *inode, int flags)
1061 {
1062         struct super_block *sb = inode->i_sb;
1063         struct backing_dev_info *bdi = NULL;
1064
1065         /*
1066          * Don't do this for I_DIRTY_PAGES - that doesn't actually
1067          * dirty the inode itself
1068          */
1069         if (flags & (I_DIRTY_SYNC | I_DIRTY_DATASYNC)) {
1070                 if (sb->s_op->dirty_inode)
1071                         sb->s_op->dirty_inode(inode, flags);
1072         }
1073
1074         /*
1075          * make sure that changes are seen by all cpus before we test i_state
1076          * -- mikulas
1077          */
1078         smp_mb();
1079
1080         /* avoid the locking if we can */
1081         if ((inode->i_state & flags) == flags)
1082                 return;
1083
1084         if (unlikely(block_dump))
1085                 block_dump___mark_inode_dirty(inode);
1086
1087         spin_lock(&inode->i_lock);
1088         if ((inode->i_state & flags) != flags) {
1089                 const int was_dirty = inode->i_state & I_DIRTY;
1090
1091                 inode->i_state |= flags;
1092
1093                 /*
1094                  * If the inode is being synced, just update its dirty state.
1095                  * The unlocker will place the inode on the appropriate
1096                  * superblock list, based upon its state.
1097                  */
1098                 if (inode->i_state & I_SYNC)
1099                         goto out_unlock_inode;
1100
1101                 /*
1102                  * Only add valid (hashed) inodes to the superblock's
1103                  * dirty list.  Add blockdev inodes as well.
1104                  */
1105                 if (!S_ISBLK(inode->i_mode)) {
1106                         if (inode_unhashed(inode))
1107                                 goto out_unlock_inode;
1108                 }
1109                 if (inode->i_state & I_FREEING)
1110                         goto out_unlock_inode;
1111
1112                 /*
1113                  * If the inode was already on b_dirty/b_io/b_more_io, don't
1114                  * reposition it (that would break b_dirty time-ordering).
1115                  */
1116                 if (!was_dirty) {
1117                         bool wakeup_bdi = false;
1118                         bdi = inode_to_bdi(inode);
1119
1120                         if (bdi_cap_writeback_dirty(bdi)) {
1121                                 WARN(!test_bit(BDI_registered, &bdi->state),
1122                                      "bdi-%s not registered\n", bdi->name);
1123
1124                                 /*
1125                                  * If this is the first dirty inode for this
1126                                  * bdi, we have to wake-up the corresponding
1127                                  * bdi thread to make sure background
1128                                  * write-back happens later.
1129                                  */
1130                                 if (!wb_has_dirty_io(&bdi->wb))
1131                                         wakeup_bdi = true;
1132                         }
1133
1134                         spin_unlock(&inode->i_lock);
1135                         spin_lock(&bdi->wb.list_lock);
1136                         inode->dirtied_when = jiffies;
1137                         list_move(&inode->i_wb_list, &bdi->wb.b_dirty);
1138                         spin_unlock(&bdi->wb.list_lock);
1139
1140                         if (wakeup_bdi)
1141                                 bdi_wakeup_thread_delayed(bdi);
1142                         return;
1143                 }
1144         }
1145 out_unlock_inode:
1146         spin_unlock(&inode->i_lock);
1147
1148 }
1149 EXPORT_SYMBOL(__mark_inode_dirty);
1150
1151 /*
1152  * Write out a superblock's list of dirty inodes.  A wait will be performed
1153  * upon no inodes, all inodes or the final one, depending upon sync_mode.
1154  *
1155  * If older_than_this is non-NULL, then only write out inodes which
1156  * had their first dirtying at a time earlier than *older_than_this.
1157  *
1158  * If `bdi' is non-zero then we're being asked to writeback a specific queue.
1159  * This function assumes that the blockdev superblock's inodes are backed by
1160  * a variety of queues, so all inodes are searched.  For other superblocks,
1161  * assume that all inodes are backed by the same queue.
1162  *
1163  * The inodes to be written are parked on bdi->b_io.  They are moved back onto
1164  * bdi->b_dirty as they are selected for writing.  This way, none can be missed
1165  * on the writer throttling path, and we get decent balancing between many
1166  * throttled threads: we don't want them all piling up on inode_sync_wait.
1167  */
1168 static void wait_sb_inodes(struct super_block *sb)
1169 {
1170         struct inode *inode, *old_inode = NULL;
1171
1172         /*
1173          * We need to be protected against the filesystem going from
1174          * r/o to r/w or vice versa.
1175          */
1176         WARN_ON(!rwsem_is_locked(&sb->s_umount));
1177
1178         spin_lock(&inode_sb_list_lock);
1179
1180         /*
1181          * Data integrity sync. Must wait for all pages under writeback,
1182          * because there may have been pages dirtied before our sync
1183          * call, but which had writeout started before we write it out.
1184          * In which case, the inode may not be on the dirty list, but
1185          * we still have to wait for that writeout.
1186          */
1187         list_for_each_entry(inode, &sb->s_inodes, i_sb_list) {
1188                 struct address_space *mapping = inode->i_mapping;
1189
1190                 spin_lock(&inode->i_lock);
1191                 if ((inode->i_state & (I_FREEING|I_WILL_FREE|I_NEW)) ||
1192                     (mapping->nrpages == 0)) {
1193                         spin_unlock(&inode->i_lock);
1194                         continue;
1195                 }
1196                 __iget(inode);
1197                 spin_unlock(&inode->i_lock);
1198                 spin_unlock(&inode_sb_list_lock);
1199
1200                 /*
1201                  * We hold a reference to 'inode' so it couldn't have been
1202                  * removed from s_inodes list while we dropped the
1203                  * inode_sb_list_lock.  We cannot iput the inode now as we can
1204                  * be holding the last reference and we cannot iput it under
1205                  * inode_sb_list_lock. So we keep the reference and iput it
1206                  * later.
1207                  */
1208                 iput(old_inode);
1209                 old_inode = inode;
1210
1211                 filemap_fdatawait(mapping);
1212
1213                 cond_resched();
1214
1215                 spin_lock(&inode_sb_list_lock);
1216         }
1217         spin_unlock(&inode_sb_list_lock);
1218         iput(old_inode);
1219 }
1220
1221 /**
1222  * writeback_inodes_sb_nr -     writeback dirty inodes from given super_block
1223  * @sb: the superblock
1224  * @nr: the number of pages to write
1225  * @reason: reason why some writeback work initiated
1226  *
1227  * Start writeback on some inodes on this super_block. No guarantees are made
1228  * on how many (if any) will be written, and this function does not wait
1229  * for IO completion of submitted IO.
1230  */
1231 void writeback_inodes_sb_nr(struct super_block *sb,
1232                             unsigned long nr,
1233                             enum wb_reason reason)
1234 {
1235         DECLARE_COMPLETION_ONSTACK(done);
1236         struct wb_writeback_work work = {
1237                 .sb                     = sb,
1238                 .sync_mode              = WB_SYNC_NONE,
1239                 .tagged_writepages      = 1,
1240                 .done                   = &done,
1241                 .nr_pages               = nr,
1242                 .reason                 = reason,
1243         };
1244
1245         WARN_ON(!rwsem_is_locked(&sb->s_umount));
1246         bdi_queue_work(sb->s_bdi, &work);
1247         wait_for_completion(&done);
1248 }
1249 EXPORT_SYMBOL(writeback_inodes_sb_nr);
1250
1251 /**
1252  * writeback_inodes_sb  -       writeback dirty inodes from given super_block
1253  * @sb: the superblock
1254  * @reason: reason why some writeback work was initiated
1255  *
1256  * Start writeback on some inodes on this super_block. No guarantees are made
1257  * on how many (if any) will be written, and this function does not wait
1258  * for IO completion of submitted IO.
1259  */
1260 void writeback_inodes_sb(struct super_block *sb, enum wb_reason reason)
1261 {
1262         return writeback_inodes_sb_nr(sb, get_nr_dirty_pages(), reason);
1263 }
1264 EXPORT_SYMBOL(writeback_inodes_sb);
1265
1266 /**
1267  * writeback_inodes_sb_if_idle  -       start writeback if none underway
1268  * @sb: the superblock
1269  * @reason: reason why some writeback work was initiated
1270  *
1271  * Invoke writeback_inodes_sb if no writeback is currently underway.
1272  * Returns 1 if writeback was started, 0 if not.
1273  */
1274 int writeback_inodes_sb_if_idle(struct super_block *sb, enum wb_reason reason)
1275 {
1276         if (!writeback_in_progress(sb->s_bdi)) {
1277                 down_read(&sb->s_umount);
1278                 writeback_inodes_sb(sb, reason);
1279                 up_read(&sb->s_umount);
1280                 return 1;
1281         } else
1282                 return 0;
1283 }
1284 EXPORT_SYMBOL(writeback_inodes_sb_if_idle);
1285
1286 /**
1287  * writeback_inodes_sb_if_idle  -       start writeback if none underway
1288  * @sb: the superblock
1289  * @nr: the number of pages to write
1290  * @reason: reason why some writeback work was initiated
1291  *
1292  * Invoke writeback_inodes_sb if no writeback is currently underway.
1293  * Returns 1 if writeback was started, 0 if not.
1294  */
1295 int writeback_inodes_sb_nr_if_idle(struct super_block *sb,
1296                                    unsigned long nr,
1297                                    enum wb_reason reason)
1298 {
1299         if (!writeback_in_progress(sb->s_bdi)) {
1300                 down_read(&sb->s_umount);
1301                 writeback_inodes_sb_nr(sb, nr, reason);
1302                 up_read(&sb->s_umount);
1303                 return 1;
1304         } else
1305                 return 0;
1306 }
1307 EXPORT_SYMBOL(writeback_inodes_sb_nr_if_idle);
1308
1309 /**
1310  * sync_inodes_sb       -       sync sb inode pages
1311  * @sb: the superblock
1312  *
1313  * This function writes and waits on any dirty inode belonging to this
1314  * super_block.
1315  */
1316 void sync_inodes_sb(struct super_block *sb)
1317 {
1318         DECLARE_COMPLETION_ONSTACK(done);
1319         struct wb_writeback_work work = {
1320                 .sb             = sb,
1321                 .sync_mode      = WB_SYNC_ALL,
1322                 .nr_pages       = LONG_MAX,
1323                 .range_cyclic   = 0,
1324                 .done           = &done,
1325                 .reason         = WB_REASON_SYNC,
1326         };
1327
1328         WARN_ON(!rwsem_is_locked(&sb->s_umount));
1329
1330         bdi_queue_work(sb->s_bdi, &work);
1331         wait_for_completion(&done);
1332
1333         wait_sb_inodes(sb);
1334 }
1335 EXPORT_SYMBOL(sync_inodes_sb);
1336
1337 /**
1338  * write_inode_now      -       write an inode to disk
1339  * @inode: inode to write to disk
1340  * @sync: whether the write should be synchronous or not
1341  *
1342  * This function commits an inode to disk immediately if it is dirty. This is
1343  * primarily needed by knfsd.
1344  *
1345  * The caller must either have a ref on the inode or must have set I_WILL_FREE.
1346  */
1347 int write_inode_now(struct inode *inode, int sync)
1348 {
1349         struct bdi_writeback *wb = &inode_to_bdi(inode)->wb;
1350         int ret;
1351         struct writeback_control wbc = {
1352                 .nr_to_write = LONG_MAX,
1353                 .sync_mode = sync ? WB_SYNC_ALL : WB_SYNC_NONE,
1354                 .range_start = 0,
1355                 .range_end = LLONG_MAX,
1356         };
1357
1358         if (!mapping_cap_writeback_dirty(inode->i_mapping))
1359                 wbc.nr_to_write = 0;
1360
1361         might_sleep();
1362         spin_lock(&wb->list_lock);
1363         spin_lock(&inode->i_lock);
1364         ret = writeback_single_inode(inode, wb, &wbc);
1365         spin_unlock(&inode->i_lock);
1366         spin_unlock(&wb->list_lock);
1367         if (sync)
1368                 inode_sync_wait(inode);
1369         return ret;
1370 }
1371 EXPORT_SYMBOL(write_inode_now);
1372
1373 /**
1374  * sync_inode - write an inode and its pages to disk.
1375  * @inode: the inode to sync
1376  * @wbc: controls the writeback mode
1377  *
1378  * sync_inode() will write an inode and its pages to disk.  It will also
1379  * correctly update the inode on its superblock's dirty inode lists and will
1380  * update inode->i_state.
1381  *
1382  * The caller must have a ref on the inode.
1383  */
1384 int sync_inode(struct inode *inode, struct writeback_control *wbc)
1385 {
1386         struct bdi_writeback *wb = &inode_to_bdi(inode)->wb;
1387         int ret;
1388
1389         spin_lock(&wb->list_lock);
1390         spin_lock(&inode->i_lock);
1391         ret = writeback_single_inode(inode, wb, wbc);
1392         spin_unlock(&inode->i_lock);
1393         spin_unlock(&wb->list_lock);
1394         return ret;
1395 }
1396 EXPORT_SYMBOL(sync_inode);
1397
1398 /**
1399  * sync_inode_metadata - write an inode to disk
1400  * @inode: the inode to sync
1401  * @wait: wait for I/O to complete.
1402  *
1403  * Write an inode to disk and adjust its dirty state after completion.
1404  *
1405  * Note: only writes the actual inode, no associated data or other metadata.
1406  */
1407 int sync_inode_metadata(struct inode *inode, int wait)
1408 {
1409         struct writeback_control wbc = {
1410                 .sync_mode = wait ? WB_SYNC_ALL : WB_SYNC_NONE,
1411                 .nr_to_write = 0, /* metadata-only */
1412         };
1413
1414         return sync_inode(inode, &wbc);
1415 }
1416 EXPORT_SYMBOL(sync_inode_metadata);