initial_commit

1 files changed, 1373 insertions, 0 deletions

diff --git a/fs/fs-writeback.c b/fs/fs-writeback.c
new file mode 100644
index 00000000..539d0d25
--- /dev/null
+++ b/fs/fs-writeback.c
@@ -0,0 +1,1373 @@
+/*
+ * fs/fs-writeback.c
+ *
+ * Copyright (C) 2002, Linus Torvalds.
+ *
+ * Contains all the functions related to writing back and waiting
+ * upon dirty inodes against superblocks, and writing back dirty
+ * pages against inodes.  ie: data writeback.  Writeout of the
+ * inode itself is not handled here.
+ *
+ * 10Apr2002	Andrew Morton
+ *		Split out of fs/inode.c
+ *		Additions for address_space-based writeback
+ */
+
+#include <linux/kernel.h>
+#include <linux/module.h>
+#include <linux/spinlock.h>
+#include <linux/slab.h>
+#include <linux/sched.h>
+#include <linux/fs.h>
+#include <linux/mm.h>
+#include <linux/kthread.h>
+#include <linux/freezer.h>
+#include <linux/writeback.h>
+#include <linux/blkdev.h>
+#include <linux/backing-dev.h>
+#include <linux/buffer_head.h>
+#include <linux/tracepoint.h>
+#include "internal.h"
+
+/*
+ * Passed into wb_writeback(), essentially a subset of writeback_control
+ */
+struct wb_writeback_work {
+	long nr_pages;
+	struct super_block *sb;
+	enum writeback_sync_modes sync_mode;
+	unsigned int tagged_writepages:1;
+	unsigned int for_kupdate:1;
+	unsigned int range_cyclic:1;
+	unsigned int for_background:1;
+
+	struct list_head list;		/* pending work list */
+	struct completion *done;	/* set if the caller waits */
+};
+
+/*
+ * Include the creation of the trace points after defining the
+ * wb_writeback_work structure so that the definition remains local to this
+ * file.
+ */
+#define CREATE_TRACE_POINTS
+#include <trace/events/writeback.h>
+
+/*
+ * We don't actually have pdflush, but this one is exported though /proc...
+ */
+int nr_pdflush_threads;
+
+/**
+ * writeback_in_progress - determine whether there is writeback in progress
+ * @bdi: the device's backing_dev_info structure.
+ *
+ * Determine whether there is writeback waiting to be handled against a
+ * backing device.
+ */
+int writeback_in_progress(struct backing_dev_info *bdi)
+{
+	return test_bit(BDI_writeback_running, &bdi->state);
+}
+
+static inline struct backing_dev_info *inode_to_bdi(struct inode *inode)
+{
+	struct super_block *sb = inode->i_sb;
+
+	if (strcmp(sb->s_type->name, "bdev") == 0)
+		return inode->i_mapping->backing_dev_info;
+
+	return sb->s_bdi;
+}
+
+static inline struct inode *wb_inode(struct list_head *head)
+{
+	return list_entry(head, struct inode, i_wb_list);
+}
+
+/* Wakeup flusher thread or forker thread to fork it. Requires bdi->wb_lock. */
+static void bdi_wakeup_flusher(struct backing_dev_info *bdi)
+{
+	if (bdi->wb.task) {
+		wake_up_process(bdi->wb.task);
+	} else {
+		/*
+		 * The bdi thread isn't there, wake up the forker thread which
+		 * will create and run it.
+		 */
+		wake_up_process(default_backing_dev_info.wb.task);
+	}
+}
+
+static void bdi_queue_work(struct backing_dev_info *bdi,
+			   struct wb_writeback_work *work)
+{
+	trace_writeback_queue(bdi, work);
+
+	spin_lock_bh(&bdi->wb_lock);
+	list_add_tail(&work->list, &bdi->work_list);
+	if (!bdi->wb.task)
+		trace_writeback_nothread(bdi, work);
+	bdi_wakeup_flusher(bdi);
+	spin_unlock_bh(&bdi->wb_lock);
+}
+
+static void
+__bdi_start_writeback(struct backing_dev_info *bdi, long nr_pages,
+		      bool range_cyclic)
+{
+	struct wb_writeback_work *work;
+
+	/*
+	 * This is WB_SYNC_NONE writeback, so if allocation fails just
+	 * wakeup the thread for old dirty data writeback
+	 */
+	work = kzalloc(sizeof(*work), GFP_ATOMIC);
+	if (!work) {
+		if (bdi->wb.task) {
+			trace_writeback_nowork(bdi);
+			wake_up_process(bdi->wb.task);
+		}
+		return;
+	}
+
+	work->sync_mode	= WB_SYNC_NONE;
+	work->nr_pages	= nr_pages;
+	work->range_cyclic = range_cyclic;
+
+	bdi_queue_work(bdi, work);
+}
+
+/**
+ * bdi_start_writeback - start writeback
+ * @bdi: the backing device to write from
+ * @nr_pages: the number of pages to write
+ *
+ * Description:
+ *   This does WB_SYNC_NONE opportunistic writeback. The IO is only
+ *   started when this function returns, we make no guarantees on
+ *   completion. Caller need not hold sb s_umount semaphore.
+ *
+ */
+void bdi_start_writeback(struct backing_dev_info *bdi, long nr_pages)
+{
+	__bdi_start_writeback(bdi, nr_pages, true);
+}
+
+/**
+ * bdi_start_background_writeback - start background writeback
+ * @bdi: the backing device to write from
+ *
+ * Description:
+ *   This makes sure WB_SYNC_NONE background writeback happens. When
+ *   this function returns, it is only guaranteed that for given BDI
+ *   some IO is happening if we are over background dirty threshold.
+ *   Caller need not hold sb s_umount semaphore.
+ */
+void bdi_start_background_writeback(struct backing_dev_info *bdi)
+{
+	/*
+	 * We just wake up the flusher thread. It will perform background
+	 * writeback as soon as there is no other work to do.
+	 */
+	trace_writeback_wake_background(bdi);
+	spin_lock_bh(&bdi->wb_lock);
+	bdi_wakeup_flusher(bdi);
+	spin_unlock_bh(&bdi->wb_lock);
+}
+
+/*
+ * Remove the inode from the writeback list it is on.
+ */
+void inode_wb_list_del(struct inode *inode)
+{
+	spin_lock(&inode_wb_list_lock);
+	list_del_init(&inode->i_wb_list);
+	spin_unlock(&inode_wb_list_lock);
+}
+
+
+/*
+ * Redirty an inode: set its when-it-was dirtied timestamp and move it to the
+ * furthest end of its superblock's dirty-inode list.
+ *
+ * Before stamping the inode's ->dirtied_when, we check to see whether it is
+ * already the most-recently-dirtied inode on the b_dirty list.  If that is
+ * the case then the inode must have been redirtied while it was being written
+ * out and we don't reset its dirtied_when.
+ */
+static void redirty_tail(struct inode *inode)
+{
+	struct bdi_writeback *wb = &inode_to_bdi(inode)->wb;
+
+	assert_spin_locked(&inode_wb_list_lock);
+	if (!list_empty(&wb->b_dirty)) {
+		struct inode *tail;
+
+		tail = wb_inode(wb->b_dirty.next);
+		if (time_before(inode->dirtied_when, tail->dirtied_when))
+			inode->dirtied_when = jiffies;
+	}
+	list_move(&inode->i_wb_list, &wb->b_dirty);
+}
+
+/*
+ * requeue inode for re-scanning after bdi->b_io list is exhausted.
+ */
+static void requeue_io(struct inode *inode)
+{
+	struct bdi_writeback *wb = &inode_to_bdi(inode)->wb;
+
+	assert_spin_locked(&inode_wb_list_lock);
+	list_move(&inode->i_wb_list, &wb->b_more_io);
+}
+
+static void inode_sync_complete(struct inode *inode)
+{
+	/*
+	 * Prevent speculative execution through
+	 * spin_unlock(&inode_wb_list_lock);
+	 */
+
+	smp_mb();
+	wake_up_bit(&inode->i_state, __I_SYNC);
+}
+
+static bool inode_dirtied_after(struct inode *inode, unsigned long t)
+{
+	bool ret = time_after(inode->dirtied_when, t);
+#ifndef CONFIG_64BIT
+	/*
+	 * For inodes being constantly redirtied, dirtied_when can get stuck.
+	 * It _appears_ to be in the future, but is actually in distant past.
+	 * This test is necessary to prevent such wrapped-around relative times
+	 * from permanently stopping the whole bdi writeback.
+	 */
+	ret = ret && time_before_eq(inode->dirtied_when, jiffies);
+#endif
+	return ret;
+}
+
+/*
+ * Move expired dirty inodes from @delaying_queue to @dispatch_queue.
+ */
+static void move_expired_inodes(struct list_head *delaying_queue,
+			       struct list_head *dispatch_queue,
+				unsigned long *older_than_this)
+{
+	LIST_HEAD(tmp);
+	struct list_head *pos, *node;
+	struct super_block *sb = NULL;
+	struct inode *inode;
+	int do_sb_sort = 0;
+
+	while (!list_empty(delaying_queue)) {
+		inode = wb_inode(delaying_queue->prev);
+		if (older_than_this &&
+		    inode_dirtied_after(inode, *older_than_this))
+			break;
+		if (sb && sb != inode->i_sb)
+			do_sb_sort = 1;
+		sb = inode->i_sb;
+		list_move(&inode->i_wb_list, &tmp);
+	}
+
+	/* just one sb in list, splice to dispatch_queue and we're done */
+	if (!do_sb_sort) {
+		list_splice(&tmp, dispatch_queue);
+		return;
+	}
+
+	/* Move inodes from one superblock together */
+	while (!list_empty(&tmp)) {
+		sb = wb_inode(tmp.prev)->i_sb;
+		list_for_each_prev_safe(pos, node, &tmp) {
+			inode = wb_inode(pos);
+			if (inode->i_sb == sb)
+				list_move(&inode->i_wb_list, dispatch_queue);
+		}
+	}
+}
+
+/*
+ * Queue all expired dirty inodes for io, eldest first.
+ * Before
+ *         newly dirtied     b_dirty    b_io    b_more_io
+ *         =============>    gf         edc     BA
+ * After
+ *         newly dirtied     b_dirty    b_io    b_more_io
+ *         =============>    g          fBAedc
+ *                                           |
+ *                                           +--> dequeue for IO
+ */
+static void queue_io(struct bdi_writeback *wb, unsigned long *older_than_this)
+{
+	assert_spin_locked(&inode_wb_list_lock);
+	list_splice_init(&wb->b_more_io, &wb->b_io);
+	move_expired_inodes(&wb->b_dirty, &wb->b_io, older_than_this);
+}
+
+static int write_inode(struct inode *inode, struct writeback_control *wbc)
+{
+	if (inode->i_sb->s_op->write_inode && !is_bad_inode(inode))
+		return inode->i_sb->s_op->write_inode(inode, wbc);
+	return 0;
+}
+
+/*
+ * Wait for writeback on an inode to complete.
+ */
+static void inode_wait_for_writeback(struct inode *inode)
+{
+	DEFINE_WAIT_BIT(wq, &inode->i_state, __I_SYNC);
+	wait_queue_head_t *wqh;
+
+	wqh = bit_waitqueue(&inode->i_state, __I_SYNC);
+	while (inode->i_state & I_SYNC) {
+		spin_unlock(&inode->i_lock);
+		spin_unlock(&inode_wb_list_lock);
+		__wait_on_bit(wqh, &wq, inode_wait, TASK_UNINTERRUPTIBLE);
+		spin_lock(&inode_wb_list_lock);
+		spin_lock(&inode->i_lock);
+	}
+}
+
+/*
+ * Write out an inode's dirty pages.  Called under inode_wb_list_lock and
+ * inode->i_lock.  Either the caller has an active reference on the inode or
+ * the inode has I_WILL_FREE set.
+ *
+ * If `wait' is set, wait on the writeout.
+ *
+ * The whole writeout design is quite complex and fragile.  We want to avoid
+ * starvation of particular inodes when others are being redirtied, prevent
+ * livelocks, etc.
+ */
+static int
+writeback_single_inode(struct inode *inode, struct writeback_control *wbc)
+{
+	struct address_space *mapping = inode->i_mapping;
+	unsigned dirty;
+	int ret;
+
+	assert_spin_locked(&inode_wb_list_lock);
+	assert_spin_locked(&inode->i_lock);
+
+	if (!atomic_read(&inode->i_count))
+		WARN_ON(!(inode->i_state & (I_WILL_FREE|I_FREEING)));
+	else
+		WARN_ON(inode->i_state & I_WILL_FREE);
+
+	if (inode->i_state & I_SYNC) {
+		/*
+		 * If this inode is locked for writeback and we are not doing
+		 * writeback-for-data-integrity, move it to b_more_io so that
+		 * writeback can proceed with the other inodes on s_io.
+		 *
+		 * We'll have another go at writing back this inode when we
+		 * completed a full scan of b_io.
+		 */
+		if (wbc->sync_mode != WB_SYNC_ALL) {
+			requeue_io(inode);
+			return 0;
+		}
+
+		/*
+		 * It's a data-integrity sync.  We must wait.
+		 */
+		inode_wait_for_writeback(inode);
+	}
+
+	BUG_ON(inode->i_state & I_SYNC);
+
+	/* Set I_SYNC, reset I_DIRTY_PAGES */
+	inode->i_state |= I_SYNC;
+	inode->i_state &= ~I_DIRTY_PAGES;
+	spin_unlock(&inode->i_lock);
+	spin_unlock(&inode_wb_list_lock);
+
+	ret = do_writepages(mapping, wbc);
+
+	/*
+	 * Make sure to wait on the data before writing out the metadata.
+	 * This is important for filesystems that modify metadata on data
+	 * I/O completion.
+	 */
+	if (wbc->sync_mode == WB_SYNC_ALL) {
+		int err = filemap_fdatawait(mapping);
+		if (ret == 0)
+			ret = err;
+	}
+
+	/*
+	 * Some filesystems may redirty the inode during the writeback
+	 * due to delalloc, clear dirty metadata flags right before
+	 * write_inode()
+	 */
+	spin_lock(&inode->i_lock);
+	dirty = inode->i_state & I_DIRTY;
+	inode->i_state &= ~(I_DIRTY_SYNC | I_DIRTY_DATASYNC);
+	spin_unlock(&inode->i_lock);
+	/* Don't write the inode if only I_DIRTY_PAGES was set */
+	if (dirty & (I_DIRTY_SYNC | I_DIRTY_DATASYNC)) {
+		int err = write_inode(inode, wbc);
+		if (ret == 0)
+			ret = err;
+	}
+
+	spin_lock(&inode_wb_list_lock);
+	spin_lock(&inode->i_lock);
+	inode->i_state &= ~I_SYNC;
+	if (!(inode->i_state & I_FREEING)) {
+		/*
+		 * Sync livelock prevention. Each inode is tagged and synced in
+		 * one shot. If still dirty, it will be redirty_tail()'ed below.
+		 * Update the dirty time to prevent enqueue and sync it again.
+		 */
+		if ((inode->i_state & I_DIRTY) &&
+		    (wbc->sync_mode == WB_SYNC_ALL || wbc->tagged_writepages))
+			inode->dirtied_when = jiffies;
+
+		if (mapping_tagged(mapping, PAGECACHE_TAG_DIRTY)) {
+			/*
+			 * We didn't write back all the pages.  nfs_writepages()
+			 * sometimes bales out without doing anything.
+			 */
+			inode->i_state |= I_DIRTY_PAGES;
+			if (wbc->nr_to_write <= 0) {
+				/*
+				 * slice used up: queue for next turn
+				 */
+				requeue_io(inode);
+			} else {
+				/*
+				 * Writeback blocked by something other than
+				 * congestion. Delay the inode for some time to
+				 * avoid spinning on the CPU (100% iowait)
+				 * retrying writeback of the dirty page/inode
+				 * that cannot be performed immediately.
+				 */
+				redirty_tail(inode);
+			}
+		} else if (inode->i_state & I_DIRTY) {
+			/*
+			 * Filesystems can dirty the inode during writeback
+			 * operations, such as delayed allocation during
+			 * submission or metadata updates after data IO
+			 * completion.
+			 */
+			redirty_tail(inode);
+		} else {
+			/*
+			 * The inode is clean.  At this point we either have
+			 * a reference to the inode or it's on it's way out.
+			 * No need to add it back to the LRU.
+			 */
+			list_del_init(&inode->i_wb_list);
+		}
+	}
+	inode_sync_complete(inode);
+	return ret;
+}
+
+/*
+ * For background writeback the caller does not have the sb pinned
+ * before calling writeback. So make sure that we do pin it, so it doesn't
+ * go away while we are writing inodes from it.
+ */
+static bool pin_sb_for_writeback(struct super_block *sb)
+{
+	spin_lock(&sb_lock);
+	if (list_empty(&sb->s_instances)) {
+		spin_unlock(&sb_lock);
+		return false;
+	}
+
+	sb->s_count++;
+	spin_unlock(&sb_lock);
+
+	if (down_read_trylock(&sb->s_umount)) {
+		if (sb->s_root)
+			return true;
+		up_read(&sb->s_umount);
+	}
+
+	put_super(sb);
+	return false;
+}
+
+/*
+ * Write a portion of b_io inodes which belong to @sb.
+ *
+ * If @only_this_sb is true, then find and write all such
+ * inodes. Otherwise write only ones which go sequentially
+ * in reverse order.
+ *
+ * Return 1, if the caller writeback routine should be
+ * interrupted. Otherwise return 0.
+ */
+static int writeback_sb_inodes(struct super_block *sb, struct bdi_writeback *wb,
+		struct writeback_control *wbc, bool only_this_sb)
+{
+	while (!list_empty(&wb->b_io)) {
+		long pages_skipped;
+		struct inode *inode = wb_inode(wb->b_io.prev);
+
+		if (inode->i_sb != sb) {
+			if (only_this_sb) {
+				/*
+				 * We only want to write back data for this
+				 * superblock, move all inodes not belonging
+				 * to it back onto the dirty list.
+				 */
+				redirty_tail(inode);
+				continue;
+			}
+
+			/*
+			 * The inode belongs to a different superblock.
+			 * Bounce back to the caller to unpin this and
+			 * pin the next superblock.
+			 */
+			return 0;
+		}
+
+		/*
+		 * Don't bother with new inodes or inodes beeing freed, first
+		 * kind does not need peridic writeout yet, and for the latter
+		 * kind writeout is handled by the freer.
+		 */
+		spin_lock(&inode->i_lock);
+		if (inode->i_state & (I_NEW | I_FREEING | I_WILL_FREE)) {
+			spin_unlock(&inode->i_lock);
+			requeue_io(inode);
+			continue;
+		}
+
+		/*
+		 * Was this inode dirtied after sync_sb_inodes was called?
+		 * This keeps sync from extra jobs and livelock.
+		 */
+		if (inode_dirtied_after(inode, wbc->wb_start)) {
+			spin_unlock(&inode->i_lock);
+			return 1;
+		}
+
+		__iget(inode);
+
+		pages_skipped = wbc->pages_skipped;
+		writeback_single_inode(inode, wbc);
+		if (wbc->pages_skipped != pages_skipped) {
+			/*
+			 * writeback is not making progress due to locked
+			 * buffers.  Skip this inode for now.
+			 */
+			redirty_tail(inode);
+		}
+		spin_unlock(&inode->i_lock);
+		spin_unlock(&inode_wb_list_lock);
+		iput(inode);
+		cond_resched();
+		spin_lock(&inode_wb_list_lock);
+		if (wbc->nr_to_write <= 0) {
+			wbc->more_io = 1;
+			return 1;
+		}
+		if (!list_empty(&wb->b_more_io))
+			wbc->more_io = 1;
+	}
+	/* b_io is empty */
+	return 1;
+}
+
+void writeback_inodes_wb(struct bdi_writeback *wb,
+		struct writeback_control *wbc)
+{
+	int ret = 0;
+
+	if (!wbc->wb_start)
+		wbc->wb_start = jiffies; /* livelock avoidance */
+	spin_lock(&inode_wb_list_lock);
+	if (!wbc->for_kupdate || list_empty(&wb->b_io))
+		queue_io(wb, wbc->older_than_this);
+
+	while (!list_empty(&wb->b_io)) {
+		struct inode *inode = wb_inode(wb->b_io.prev);
+		struct super_block *sb = inode->i_sb;
+
+		if (!pin_sb_for_writeback(sb)) {
+			requeue_io(inode);
+			continue;
+		}
+		ret = writeback_sb_inodes(sb, wb, wbc, false);
+		drop_super(sb);
+
+		if (ret)
+			break;
+	}
+	spin_unlock(&inode_wb_list_lock);
+	/* Leave any unwritten inodes on b_io */
+}
+
+static void __writeback_inodes_sb(struct super_block *sb,
+		struct bdi_writeback *wb, struct writeback_control *wbc)
+{
+	WARN_ON(!rwsem_is_locked(&sb->s_umount));
+
+	spin_lock(&inode_wb_list_lock);
+	if (!wbc->for_kupdate || list_empty(&wb->b_io))
+		queue_io(wb, wbc->older_than_this);
+	writeback_sb_inodes(sb, wb, wbc, true);
+	spin_unlock(&inode_wb_list_lock);
+}
+
+/*
+ * The maximum number of pages to writeout in a single bdi flush/kupdate
+ * operation.  We do this so we don't hold I_SYNC against an inode for
+ * enormous amounts of time, which would block a userspace task which has
+ * been forced to throttle against that inode.  Also, the code reevaluates
+ * the dirty each time it has written this many pages.
+ */
+#define MAX_WRITEBACK_PAGES     1024
+
+static inline bool over_bground_thresh(void)
+{
+	unsigned long background_thresh, dirty_thresh;
+
+	global_dirty_limits(&background_thresh, &dirty_thresh);
+
+	return (global_page_state(NR_FILE_DIRTY) +
+		global_page_state(NR_UNSTABLE_NFS) > background_thresh);
+}
+
+/*
+ * Explicit flushing or periodic writeback of "old" data.
+ *
+ * Define "old": the first time one of an inode's pages is dirtied, we mark the
+ * dirtying-time in the inode's address_space.  So this periodic writeback code
+ * just walks the superblock inode list, writing back any inodes which are
+ * older than a specific point in time.
+ *
+ * Try to run once per dirty_writeback_interval.  But if a writeback event
+ * takes longer than a dirty_writeback_interval interval, then leave a
+ * one-second gap.
+ *
+ * older_than_this takes precedence over nr_to_write.  So we'll only write back
+ * all dirty pages if they are all attached to "old" mappings.
+ */
+static long wb_writeback(struct bdi_writeback *wb,
+			 struct wb_writeback_work *work)
+{
+	struct writeback_control wbc = {
+		.sync_mode		= work->sync_mode,
+		.tagged_writepages	= work->tagged_writepages,
+		.older_than_this	= NULL,
+		.for_kupdate		= work->for_kupdate,
+		.for_background		= work->for_background,
+		.range_cyclic		= work->range_cyclic,
+	};
+	unsigned long oldest_jif;
+	long wrote = 0;
+	long write_chunk = MAX_WRITEBACK_PAGES;
+	struct inode *inode;
+
+	if (wbc.for_kupdate) {
+		wbc.older_than_this = &oldest_jif;
+		oldest_jif = jiffies -
+				msecs_to_jiffies(dirty_expire_interval * 10);
+	}
+	if (!wbc.range_cyclic) {
+		wbc.range_start = 0;
+		wbc.range_end = LLONG_MAX;
+	}
+
+	/*
+	 * WB_SYNC_ALL mode does livelock avoidance by syncing dirty
+	 * inodes/pages in one big loop. Setting wbc.nr_to_write=LONG_MAX
+	 * here avoids calling into writeback_inodes_wb() more than once.
+	 *
+	 * The intended call sequence for WB_SYNC_ALL writeback is:
+	 *
+	 *      wb_writeback()
+	 *          __writeback_inodes_sb()     <== called only once
+	 *              write_cache_pages()     <== called once for each inode
+	 *                   (quickly) tag currently dirty pages
+	 *                   (maybe slowly) sync all tagged pages
+	 */
+	if (wbc.sync_mode == WB_SYNC_ALL || wbc.tagged_writepages)
+		write_chunk = LONG_MAX;
+
+	wbc.wb_start = jiffies; /* livelock avoidance */
+	for (;;) {
+		/*
+		 * Stop writeback when nr_pages has been consumed
+		 */
+		if (work->nr_pages <= 0)
+			break;
+
+		/*
+		 * Background writeout and kupdate-style writeback may
+		 * run forever. Stop them if there is other work to do
+		 * so that e.g. sync can proceed. They'll be restarted
+		 * after the other works are all done.
+		 */
+		if ((work->for_background || work->for_kupdate) &&
+		    !list_empty(&wb->bdi->work_list))
+			break;
+
+		/*
+		 * For background writeout, stop when we are below the
+		 * background dirty threshold
+		 */
+		if (work->for_background && !over_bground_thresh())
+			break;
+
+		wbc.more_io = 0;
+		wbc.nr_to_write = write_chunk;
+		wbc.pages_skipped = 0;
+
+		trace_wbc_writeback_start(&wbc, wb->bdi);
+		if (work->sb)
+			__writeback_inodes_sb(work->sb, wb, &wbc);
+		else
+			writeback_inodes_wb(wb, &wbc);
+		trace_wbc_writeback_written(&wbc, wb->bdi);
+
+		work->nr_pages -= write_chunk - wbc.nr_to_write;
+		wrote += write_chunk - wbc.nr_to_write;
+
+		/*
+		 * If we consumed everything, see if we have more
+		 */
+		if (wbc.nr_to_write <= 0)
+			continue;
+		/*
+		 * Didn't write everything and we don't have more IO, bail
+		 */
+		if (!wbc.more_io)
+			break;
+		/*
+		 * Did we write something? Try for more
+		 */
+		if (wbc.nr_to_write < write_chunk)
+			continue;
+		/*
+		 * Nothing written. Wait for some inode to
+		 * become available for writeback. Otherwise
+		 * we'll just busyloop.
+		 */
+		spin_lock(&inode_wb_list_lock);
+		if (!list_empty(&wb->b_more_io))  {
+			inode = wb_inode(wb->b_more_io.prev);
+			trace_wbc_writeback_wait(&wbc, wb->bdi);
+			spin_lock(&inode->i_lock);
+			inode_wait_for_writeback(inode);
+			spin_unlock(&inode->i_lock);
+		}
+		spin_unlock(&inode_wb_list_lock);
+	}
+
+	return wrote;
+}
+
+/*
+ * Return the next wb_writeback_work struct that hasn't been processed yet.
+ */
+static struct wb_writeback_work *
+get_next_work_item(struct backing_dev_info *bdi)
+{
+	struct wb_writeback_work *work = NULL;
+
+	spin_lock_bh(&bdi->wb_lock);
+	if (!list_empty(&bdi->work_list)) {
+		work = list_entry(bdi->work_list.next,
+				  struct wb_writeback_work, list);
+		list_del_init(&work->list);
+	}
+	spin_unlock_bh(&bdi->wb_lock);
+	return work;
+}
+
+/*
+ * Add in the number of potentially dirty inodes, because each inode
+ * write can dirty pagecache in the underlying blockdev.
+ */
+static unsigned long get_nr_dirty_pages(void)
+{
+	return global_page_state(NR_FILE_DIRTY) +
+		global_page_state(NR_UNSTABLE_NFS) +
+		get_nr_dirty_inodes();
+}
+
+static long wb_check_background_flush(struct bdi_writeback *wb)
+{
+	if (over_bground_thresh()) {
+
+		struct wb_writeback_work work = {
+			.nr_pages	= LONG_MAX,
+			.sync_mode	= WB_SYNC_NONE,
+			.for_background	= 1,
+			.range_cyclic	= 1,
+		};
+
+		return wb_writeback(wb, &work);
+	}
+
+	return 0;
+}
+
+static long wb_check_old_data_flush(struct bdi_writeback *wb)
+{
+	unsigned long expired;
+	long nr_pages;
+
+	/*
+	 * When set to zero, disable periodic writeback
+	 */
+	if (!dirty_writeback_interval)
+		return 0;
+
+	expired = wb->last_old_flush +
+			msecs_to_jiffies(dirty_writeback_interval * 10);
+	if (time_before(jiffies, expired))
+		return 0;
+
+	wb->last_old_flush = jiffies;
+	nr_pages = get_nr_dirty_pages();
+
+	if (nr_pages) {
+		struct wb_writeback_work work = {
+			.nr_pages	= nr_pages,
+			.sync_mode	= WB_SYNC_NONE,
+			.for_kupdate	= 1,
+			.range_cyclic	= 1,
+		};
+
+		return wb_writeback(wb, &work);
+	}
+
+	return 0;
+}
+
+/*
+ * Retrieve work items and do the writeback they describe
+ */
+long wb_do_writeback(struct bdi_writeback *wb, int force_wait)
+{
+	struct backing_dev_info *bdi = wb->bdi;
+	struct wb_writeback_work *work;
+	long wrote = 0;
+
+	set_bit(BDI_writeback_running, &wb->bdi->state);
+	while ((work = get_next_work_item(bdi)) != NULL) {
+		/*
+		 * Override sync mode, in case we must wait for completion
+		 * because this thread is exiting now.
+		 */
+		if (force_wait)
+			work->sync_mode = WB_SYNC_ALL;
+
+		trace_writeback_exec(bdi, work);
+
+		wrote += wb_writeback(wb, work);
+
+		/*
+		 * Notify the caller of completion if this is a synchronous
+		 * work item, otherwise just free it.
+		 */
+		if (work->done)
+			complete(work->done);
+		else
+			kfree(work);
+	}
+
+	/*
+	 * Check for periodic writeback, kupdated() style
+	 */
+	wrote += wb_check_old_data_flush(wb);
+	wrote += wb_check_background_flush(wb);
+	clear_bit(BDI_writeback_running, &wb->bdi->state);
+
+	return wrote;
+}
+
+/*
+ * Handle writeback of dirty data for the device backed by this bdi. Also
+ * wakes up periodically and does kupdated style flushing.
+ */
+int bdi_writeback_thread(void *data)
+{
+	struct bdi_writeback *wb = data;
+	struct backing_dev_info *bdi = wb->bdi;
+	long pages_written;
+
+	current->flags |= PF_SWAPWRITE;
+	set_freezable();
+	wb->last_active = jiffies;
+
+	/*
+	 * Our parent may run at a different priority, just set us to normal
+	 */
+	set_user_nice(current, 0);
+
+	trace_writeback_thread_start(bdi);
+
+	while (!kthread_should_stop()) {
+		/*
+		 * Remove own delayed wake-up timer, since we are already awake
+		 * and we'll take care of the preriodic write-back.
+		 */
+		del_timer(&wb->wakeup_timer);
+
+		pages_written = wb_do_writeback(wb, 0);
+
+		trace_writeback_pages_written(pages_written);
+
+		if (pages_written)
+			wb->last_active = jiffies;
+
+		set_current_state(TASK_INTERRUPTIBLE);
+		if (!list_empty(&bdi->work_list) || kthread_should_stop()) {
+			__set_current_state(TASK_RUNNING);
+			continue;
+		}
+
+		if (wb_has_dirty_io(wb) && dirty_writeback_interval)
+			schedule_timeout(msecs_to_jiffies(dirty_writeback_interval * 10));
+		else {
+			/*
+			 * We have nothing to do, so can go sleep without any
+			 * timeout and save power. When a work is queued or
+			 * something is made dirty - we will be woken up.
+			 */
+			schedule();
+		}
+
+		try_to_freeze();
+	}
+
+	/* Flush any work that raced with us exiting */
+	if (!list_empty(&bdi->work_list))
+		wb_do_writeback(wb, 1);
+
+	trace_writeback_thread_stop(bdi);
+	return 0;
+}
+
+
+/*
+ * Start writeback of `nr_pages' pages.  If `nr_pages' is zero, write back
+ * the whole world.
+ */
+void wakeup_flusher_threads(long nr_pages)
+{
+	struct backing_dev_info *bdi;
+
+	if (!nr_pages) {
+		nr_pages = global_page_state(NR_FILE_DIRTY) +
+				global_page_state(NR_UNSTABLE_NFS);
+	}
+
+	rcu_read_lock();
+	list_for_each_entry_rcu(bdi, &bdi_list, bdi_list) {
+		if (!bdi_has_dirty_io(bdi))
+			continue;
+		__bdi_start_writeback(bdi, nr_pages, false);
+	}
+	rcu_read_unlock();
+}
+
+static noinline void block_dump___mark_inode_dirty(struct inode *inode)
+{
+	if (inode->i_ino || strcmp(inode->i_sb->s_id, "bdev")) {
+		struct dentry *dentry;
+		const char *name = "?";
+
+		dentry = d_find_alias(inode);
+		if (dentry) {
+			spin_lock(&dentry->d_lock);
+			name = (const char *) dentry->d_name.name;
+		}
+		printk(KERN_DEBUG
+		       "%s(%d): dirtied inode %lu (%s) on %s\n",
+		       current->comm, task_pid_nr(current), inode->i_ino,
+		       name, inode->i_sb->s_id);
+		if (dentry) {
+			spin_unlock(&dentry->d_lock);
+			dput(dentry);
+		}
+	}
+}
+
+/**
+ *	__mark_inode_dirty -	internal function
+ *	@inode: inode to mark
+ *	@flags: what kind of dirty (i.e. I_DIRTY_SYNC)
+ *	Mark an inode as dirty. Callers should use mark_inode_dirty or
+ *  	mark_inode_dirty_sync.
+ *
+ * Put the inode on the super block's dirty list.
+ *
+ * CAREFUL! We mark it dirty unconditionally, but move it onto the
+ * dirty list only if it is hashed or if it refers to a blockdev.
+ * If it was not hashed, it will never be added to the dirty list
+ * even if it is later hashed, as it will have been marked dirty already.
+ *
+ * In short, make sure you hash any inodes _before_ you start marking
+ * them dirty.
+ *
+ * Note that for blockdevs, inode->dirtied_when represents the dirtying time of
+ * the block-special inode (/dev/hda1) itself.  And the ->dirtied_when field of
+ * the kernel-internal blockdev inode represents the dirtying time of the
+ * blockdev's pages.  This is why for I_DIRTY_PAGES we always use
+ * page->mapping->host, so the page-dirtying time is recorded in the internal
+ * blockdev inode.
+ */
+void __mark_inode_dirty(struct inode *inode, int flags)
+{
+	struct super_block *sb = inode->i_sb;
+	struct backing_dev_info *bdi = NULL;
+
+	/*
+	 * Don't do this for I_DIRTY_PAGES - that doesn't actually
+	 * dirty the inode itself
+	 */
+	if (flags & (I_DIRTY_SYNC | I_DIRTY_DATASYNC)) {
+		if (sb->s_op->dirty_inode)
+			sb->s_op->dirty_inode(inode, flags);
+	}
+
+	/*
+	 * make sure that changes are seen by all cpus before we test i_state
+	 * -- mikulas
+	 */
+	smp_mb();
+
+	/* avoid the locking if we can */
+	if ((inode->i_state & flags) == flags)
+		return;
+
+	if (unlikely(block_dump > 1))
+		block_dump___mark_inode_dirty(inode);
+
+	spin_lock(&inode->i_lock);
+	if ((inode->i_state & flags) != flags) {
+		const int was_dirty = inode->i_state & I_DIRTY;
+
+		inode->i_state |= flags;
+
+		/*
+		 * If the inode is being synced, just update its dirty state.
+		 * The unlocker will place the inode on the appropriate
+		 * superblock list, based upon its state.
+		 */
+		if (inode->i_state & I_SYNC)
+			goto out_unlock_inode;
+
+		/*
+		 * Only add valid (hashed) inodes to the superblock's
+		 * dirty list.  Add blockdev inodes as well.
+		 */
+		if (!S_ISBLK(inode->i_mode)) {
+			if (inode_unhashed(inode))
+				goto out_unlock_inode;
+		}
+		if (inode->i_state & I_FREEING)
+			goto out_unlock_inode;
+
+		/*
+		 * If the inode was already on b_dirty/b_io/b_more_io, don't
+		 * reposition it (that would break b_dirty time-ordering).
+		 */
+		if (!was_dirty) {
+			bool wakeup_bdi = false;
+			bdi = inode_to_bdi(inode);
+			if (!bdi)
+				goto out_unlock_inode;
+
+			if (bdi_cap_writeback_dirty(bdi)) {
+				WARN(!test_bit(BDI_registered, &bdi->state),
+				     "bdi-%s not registered\n", bdi->name);
+
+				/*
+				 * If this is the first dirty inode for this
+				 * bdi, we have to wake-up the corresponding
+				 * bdi thread to make sure background
+				 * write-back happens later.
+				 */
+				if (!wb_has_dirty_io(&bdi->wb))
+					wakeup_bdi = true;
+			}
+
+			spin_unlock(&inode->i_lock);
+			spin_lock(&inode_wb_list_lock);
+			inode->dirtied_when = jiffies;
+			list_move(&inode->i_wb_list, &bdi->wb.b_dirty);
+			spin_unlock(&inode_wb_list_lock);
+
+			if (wakeup_bdi)
+				bdi_wakeup_thread_delayed(bdi);
+			return;
+		}
+	}
+out_unlock_inode:
+	spin_unlock(&inode->i_lock);
+
+}
+EXPORT_SYMBOL(__mark_inode_dirty);
+
+/*
+ * Write out a superblock's list of dirty inodes.  A wait will be performed
+ * upon no inodes, all inodes or the final one, depending upon sync_mode.
+ *
+ * If older_than_this is non-NULL, then only write out inodes which
+ * had their first dirtying at a time earlier than *older_than_this.
+ *
+ * If `bdi' is non-zero then we're being asked to writeback a specific queue.
+ * This function assumes that the blockdev superblock's inodes are backed by
+ * a variety of queues, so all inodes are searched.  For other superblocks,
+ * assume that all inodes are backed by the same queue.
+ *
+ * The inodes to be written are parked on bdi->b_io.  They are moved back onto
+ * bdi->b_dirty as they are selected for writing.  This way, none can be missed
+ * on the writer throttling path, and we get decent balancing between many
+ * throttled threads: we don't want them all piling up on inode_sync_wait.
+ */
+static void wait_sb_inodes(struct super_block *sb)
+{
+	struct inode *inode, *old_inode = NULL;
+
+	/*
+	 * We need to be protected against the filesystem going from
+	 * r/o to r/w or vice versa.
+	 */
+	WARN_ON(!rwsem_is_locked(&sb->s_umount));
+
+	spin_lock(&inode_sb_list_lock);
+
+	/*
+	 * Data integrity sync. Must wait for all pages under writeback,
+	 * because there may have been pages dirtied before our sync
+	 * call, but which had writeout started before we write it out.
+	 * In which case, the inode may not be on the dirty list, but
+	 * we still have to wait for that writeout.
+	 */
+	list_for_each_entry(inode, &sb->s_inodes, i_sb_list) {
+		struct address_space *mapping = inode->i_mapping;
+
+		spin_lock(&inode->i_lock);
+		if ((inode->i_state & (I_FREEING|I_WILL_FREE|I_NEW)) ||
+		    (mapping->nrpages == 0)) {
+			spin_unlock(&inode->i_lock);
+			continue;
+		}
+		__iget(inode);
+		spin_unlock(&inode->i_lock);
+		spin_unlock(&inode_sb_list_lock);
+
+		/*
+		 * We hold a reference to 'inode' so it couldn't have been
+		 * removed from s_inodes list while we dropped the
+		 * inode_sb_list_lock.  We cannot iput the inode now as we can
+		 * be holding the last reference and we cannot iput it under
+		 * inode_sb_list_lock. So we keep the reference and iput it
+		 * later.
+		 */
+		iput(old_inode);
+		old_inode = inode;
+
+		filemap_fdatawait(mapping);
+
+		cond_resched();
+
+		spin_lock(&inode_sb_list_lock);
+	}
+	spin_unlock(&inode_sb_list_lock);
+	iput(old_inode);
+}
+
+/**
+ * writeback_inodes_sb_nr -	writeback dirty inodes from given super_block
+ * @sb: the superblock
+ * @nr: the number of pages to write
+ *
+ * Start writeback on some inodes on this super_block. No guarantees are made
+ * on how many (if any) will be written, and this function does not wait
+ * for IO completion of submitted IO.
+ */
+void writeback_inodes_sb_nr(struct super_block *sb, unsigned long nr)
+{
+	DECLARE_COMPLETION_ONSTACK(done);
+	struct wb_writeback_work work = {
+		.sb			= sb,
+		.sync_mode		= WB_SYNC_NONE,
+		.tagged_writepages	= 1,
+		.done			= &done,
+		.nr_pages		= nr,
+	};
+
+	WARN_ON(!rwsem_is_locked(&sb->s_umount));
+	bdi_queue_work(sb->s_bdi, &work);
+	wait_for_completion(&done);
+}
+EXPORT_SYMBOL(writeback_inodes_sb_nr);
+
+/**
+ * writeback_inodes_sb	-	writeback dirty inodes from given super_block
+ * @sb: the superblock
+ *
+ * Start writeback on some inodes on this super_block. No guarantees are made
+ * on how many (if any) will be written, and this function does not wait
+ * for IO completion of submitted IO.
+ */
+void writeback_inodes_sb(struct super_block *sb)
+{
+	return writeback_inodes_sb_nr(sb, get_nr_dirty_pages());
+}
+EXPORT_SYMBOL(writeback_inodes_sb);
+
+/**
+ * writeback_inodes_sb_if_idle	-	start writeback if none underway
+ * @sb: the superblock
+ *
+ * Invoke writeback_inodes_sb if no writeback is currently underway.
+ * Returns 1 if writeback was started, 0 if not.
+ */
+int writeback_inodes_sb_if_idle(struct super_block *sb)
+{
+	if (!writeback_in_progress(sb->s_bdi)) {
+		down_read(&sb->s_umount);
+		writeback_inodes_sb(sb);
+		up_read(&sb->s_umount);
+		return 1;
+	} else
+		return 0;
+}
+EXPORT_SYMBOL(writeback_inodes_sb_if_idle);
+
+/**
+ * writeback_inodes_sb_if_idle	-	start writeback if none underway
+ * @sb: the superblock
+ * @nr: the number of pages to write
+ *
+ * Invoke writeback_inodes_sb if no writeback is currently underway.
+ * Returns 1 if writeback was started, 0 if not.
+ */
+int writeback_inodes_sb_nr_if_idle(struct super_block *sb,
+				   unsigned long nr)
+{
+	if (!writeback_in_progress(sb->s_bdi)) {
+		down_read(&sb->s_umount);
+		writeback_inodes_sb_nr(sb, nr);
+		up_read(&sb->s_umount);
+		return 1;
+	} else
+		return 0;
+}
+EXPORT_SYMBOL(writeback_inodes_sb_nr_if_idle);
+
+/**
+ * sync_inodes_sb	-	sync sb inode pages
+ * @sb: the superblock
+ *
+ * This function writes and waits on any dirty inode belonging to this
+ * super_block.
+ */
+void sync_inodes_sb(struct super_block *sb)
+{
+	DECLARE_COMPLETION_ONSTACK(done);
+	struct wb_writeback_work work = {
+		.sb		= sb,
+		.sync_mode	= WB_SYNC_ALL,
+		.nr_pages	= LONG_MAX,
+		.range_cyclic	= 0,
+		.done		= &done,
+	};
+
+	WARN_ON(!rwsem_is_locked(&sb->s_umount));
+
+	bdi_queue_work(sb->s_bdi, &work);
+	wait_for_completion(&done);
+
+	wait_sb_inodes(sb);
+}
+EXPORT_SYMBOL(sync_inodes_sb);
+
+/**
+ * write_inode_now	-	write an inode to disk
+ * @inode: inode to write to disk
+ * @sync: whether the write should be synchronous or not
+ *
+ * This function commits an inode to disk immediately if it is dirty. This is
+ * primarily needed by knfsd.
+ *
+ * The caller must either have a ref on the inode or must have set I_WILL_FREE.
+ */
+int write_inode_now(struct inode *inode, int sync)
+{
+	int ret;
+	struct writeback_control wbc = {
+		.nr_to_write = LONG_MAX,
+		.sync_mode = sync ? WB_SYNC_ALL : WB_SYNC_NONE,
+		.range_start = 0,
+		.range_end = LLONG_MAX,
+	};
+
+	if (!mapping_cap_writeback_dirty(inode->i_mapping))
+		wbc.nr_to_write = 0;
+
+	might_sleep();
+	spin_lock(&inode_wb_list_lock);
+	spin_lock(&inode->i_lock);
+	ret = writeback_single_inode(inode, &wbc);
+	spin_unlock(&inode->i_lock);
+	spin_unlock(&inode_wb_list_lock);
+	if (sync)
+		inode_sync_wait(inode);
+	return ret;
+}
+EXPORT_SYMBOL(write_inode_now);
+
+/**
+ * sync_inode - write an inode and its pages to disk.
+ * @inode: the inode to sync
+ * @wbc: controls the writeback mode
+ *
+ * sync_inode() will write an inode and its pages to disk.  It will also
+ * correctly update the inode on its superblock's dirty inode lists and will
+ * update inode->i_state.
+ *
+ * The caller must have a ref on the inode.
+ */
+int sync_inode(struct inode *inode, struct writeback_control *wbc)
+{
+	int ret;
+
+	spin_lock(&inode_wb_list_lock);
+	spin_lock(&inode->i_lock);
+	ret = writeback_single_inode(inode, wbc);
+	spin_unlock(&inode->i_lock);
+	spin_unlock(&inode_wb_list_lock);
+	return ret;
+}
+EXPORT_SYMBOL(sync_inode);
+
+/**
+ * sync_inode_metadata - write an inode to disk
+ * @inode: the inode to sync
+ * @wait: wait for I/O to complete.
+ *
+ * Write an inode to disk and adjust its dirty state after completion.
+ *
+ * Note: only writes the actual inode, no associated data or other metadata.
+ */
+int sync_inode_metadata(struct inode *inode, int wait)
+{
+	struct writeback_control wbc = {
+		.sync_mode = wait ? WB_SYNC_ALL : WB_SYNC_NONE,
+		.nr_to_write = 0, /* metadata-only */
+	};
+
+	return sync_inode(inode, &wbc);
+}
+EXPORT_SYMBOL(sync_inode_metadata);