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authorJan Kara <jack@suse.cz>2012-07-03 16:45:34 +0200
committerAl Viro <viro@zeniv.linux.org.uk>2012-07-22 23:59:01 +0400
commit4ea425b63a3dfeb7707fc7cc7161c11a51e871ed (patch)
treef82060e43047424014436f88e808c3f1bba068f3
parentd0e91b13eb34d449922124c34f8a05e498daa089 (diff)
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 functions. Signed-off-by: Jan Kara <jack@suse.cz> Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
-rw-r--r--fs/sync.c19
1 files changed, 9 insertions, 10 deletions
diff --git a/fs/sync.c b/fs/sync.c
index 131ddae87a1d..eb8722dc556f 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)
sync_inodes_sb(sb);
}
-static void writeback_inodes_one_sb(struct super_block *sb, void *arg)
-{
- if (!(sb->s_flags & MS_RDONLY))
- writeback_inodes_sb(sb, WB_REASON_SYNC);
-}
-
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().
*/
SYSCALL_DEFINE0(sync)
{
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);