[lkml]   [2012]   [Jul]   [3]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
Messages in this thread
Patch in this message
Subject[PATCH 8/8] vfs: Avoid unnecessary WB_SYNC_NONE writeback during sys_sync and reorder sync passes
wakeup_flusher_threads(0) will queue work doing complete writeback for each
flusher thread. Thus there is not much point in submitting another work doing
full inode WB_SYNC_NONE writeback by writeback_inodes_sb().

After this change it does not make sense to call nonblocking ->sync_fs and
block device flush before calling sync_inodes_sb() because
wakeup_flusher_threads() is completely asynchronous and thus these functions
would be called in parallel with inode writeback running which will effectively
void any work they do. So we move sync_inodes_sb() call before these two

Signed-off-by: Jan Kara <>
fs/sync.c | 19 +++++++++----------
1 files changed, 9 insertions(+), 10 deletions(-)

diff --git a/fs/sync.c b/fs/sync.c
index 6d177d1..eb8722d 100644
--- a/fs/sync.c
+++ b/fs/sync.c
@@ -73,12 +73,6 @@ static void sync_inodes_one_sb(struct super_block *sb, void *arg)

-static void writeback_inodes_one_sb(struct super_block *sb, void *arg)
- if (!(sb->s_flags & MS_RDONLY))
- writeback_inodes_sb(sb);
static void sync_fs_one_sb(struct super_block *sb, void *arg)
if (!(sb->s_flags & MS_RDONLY) && sb->s_op->sync_fs)
@@ -96,17 +90,22 @@ static void fdatawait_one_bdev(struct block_device *bdev, void *arg)

- * sync everything. Start out by waking pdflush, because that writes back
- * all queues in parallel.
+ * Sync everything. We start by waking flusher threads so that most of
+ * writeback runs on all devices in parallel. Then we sync all inodes reliably
+ * which effectively also waits for all flusher threads to finish doing
+ * writeback. At this point all data is on disk so metadata should be stable
+ * and we tell filesystems to sync their metadata via ->sync_fs() calls.
+ * Finally, we writeout all block devices because some filesystems (e.g. ext2)
+ * just write metadata (such as inodes or bitmaps) to block device page cache
+ * and do not sync it on their own in ->sync_fs().
int nowait = 0, wait = 1;

wakeup_flusher_threads(0, WB_REASON_SYNC);
- iterate_supers(writeback_inodes_one_sb, NULL);
- iterate_supers(sync_fs_one_sb, &nowait);
iterate_supers(sync_inodes_one_sb, NULL);
+ iterate_supers(sync_fs_one_sb, &nowait);
iterate_supers(sync_fs_one_sb, &wait);
iterate_bdevs(fdatawrite_one_bdev, NULL);
iterate_bdevs(fdatawait_one_bdev, NULL);

 \ /
  Last update: 2012-07-03 17:21    [W:0.076 / U:0.136 seconds]
©2003-2018 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site