Re: [PATCH 10/27] xfs: improve sync behaviour in the fact of aggressive dirtying
From: Dave Chinner <david@fromorbit.com>
Date: 2011-06-30 02:52:42
On Wed, Jun 29, 2011 at 10:01:19AM -0400, Christoph Hellwig wrote:
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 lifelock protection in the core
writeback code, and another issue is the lock-less xfs_ioend_wait call,
which doesn't prevent new ioend from beeing 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 ------------------------------
Reported-by: Wu Fengguang <redacted>
Signed-off-by: Christoph Hellwig <hch@lst.de>Reviewed-by: Dave Chinner <redacted> -- Dave Chinner david@fromorbit.com _______________________________________________ xfs mailing list xfs@oss.sgi.com http://oss.sgi.com/mailman/listinfo/xfs