From 33b8f7c2479dfcbc5c27174e44b5f659d9f33c70 Mon Sep 17 00:00:00 2001 From: Christoph Hellwig Date: Fri, 8 Jul 2011 14:34:39 +0200 Subject: [PATCH] xfs: improve sync behaviour in the face of aggressive dirtying The following script from Wu Fengguang shows very bad behaviour in XFS when aggressively dirtying data during a sync on XFS, with sync times up to almost 10 times as long as ext4. A large part of the issue is that XFS writes data out itself two times in the ->sync_fs method, overriding the livelock protection in the core writeback code, and another issue is the lock-less xfs_ioend_wait call, which doesn't prevent new ioend from being queue up while waiting for the count to reach zero. This patch removes the XFS-internal sync calls and relies on the VFS to do it's work just like all other filesystems do. Note that the i_iocount wait which is rather suboptimal is simply removed here. We already do it in ->write_inode, which keeps the current supoptimal behaviour. We'll eventually need to remove that as well, but that's material for a separate commit. ------------------------------ snip ------------------------------ #!/bin/sh umount /dev/sda7 mkfs.xfs -f /dev/sda7 # mkfs.ext4 /dev/sda7 # mkfs.btrfs /dev/sda7 mount /dev/sda7 /fs echo $((50<<20)) > /proc/sys/vm/dirty_bytes pid= for i in `seq 10` do dd if=/dev/zero of=/fs/zero-$i bs=1M count=1000 & pid="$pid $!" done sleep 1 tic=$(date +'%s') sync tac=$(date +'%s') echo echo sync time: $((tac-tic)) egrep '(Dirty|Writeback|NFS_Unstable)' /proc/meminfo pidof dd > /dev/null && { kill -9 $pid; echo sync NOT livelocked; } ------------------------------ snip ------------------------------ Signed-off-by: Christoph Hellwig Reported-by: Wu Fengguang Reviewed-by: Alex Elder Reviewed-by: Dave Chinner --- fs/xfs/linux-2.6/xfs_sync.c | 8 +++----- 1 file changed, 3 insertions(+), 5 deletions(-) diff --git a/fs/xfs/linux-2.6/xfs_sync.c b/fs/xfs/linux-2.6/xfs_sync.c index 8ecad5ff9f9..f54e8ee1ed6 100644 --- a/fs/xfs/linux-2.6/xfs_sync.c +++ b/fs/xfs/linux-2.6/xfs_sync.c @@ -359,14 +359,12 @@ xfs_quiesce_data( { int error, error2 = 0; - /* push non-blocking */ - xfs_sync_data(mp, 0); xfs_qm_sync(mp, SYNC_TRYLOCK); - - /* push and block till complete */ - xfs_sync_data(mp, SYNC_WAIT); xfs_qm_sync(mp, SYNC_WAIT); + /* force out the newly dirtied log buffers */ + xfs_log_force(mp, XFS_LOG_SYNC); + /* write superblock and hoover up shutdown errors */ error = xfs_sync_fsdata(mp); -- 2.46.0