The Design and Implementation of the FreeBSD Operating System, Second Edition
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FreeBSD/Linux Kernel Cross Reference
sys/fs/fs-writeback.c

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

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