[PATCH 8/8] vfs: Avoid unnecessary WB_SYNC_NONE writeback during sys_sync and reorder sync passes
From: Jan Kara <jack@suse.cz>
Date: 2012-01-05 23:46:57
Subsystem:
filesystems (vfs and infrastructure), the rest · Maintainers:
Alexander Viro, Christian Brauner, Linus Torvalds
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> --- fs/sync.c | 19 +++++++++---------- 1 files changed, 9 insertions(+), 10 deletions(-)
diff --git a/fs/sync.c b/fs/sync.c
index d8b9dd1..5a2f1ba 100644
--- a/fs/sync.c
+++ b/fs/sync.c@@ -74,12 +74,6 @@ 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); -} - static void sync_fs_one_sb(struct super_block *sb, void *arg) { if (!(sb->s_flags & MS_RDONLY) && sb->s_op->sync_fs)
@@ -137,17 +131,22 @@ 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);
--
1.7.1