Commit 4ea425b6 authored by Jan Kara's avatar Jan Kara Committed by Al Viro
Browse files

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: default avatarJan Kara <jack@suse.cz>
Signed-off-by: default avatarAl Viro <viro@zeniv.linux.org.uk>
parent d0e91b13

fs/sync.c

+9 −10
Original line number Diff line number Diff line
@@ -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);

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