> I'm facing the issue about the performance degradation, and once I glanced > that changing the value in /proc/sys > /vm/vfs_cache_pressure will do a favour.
> Can anyone explain to me whether and why it is useful? Hi, When this is set to a lower value the kernel will try to keep the inode/dentry cache longer in memory. Since the swift replicator is scanning the filesystem continuously it will eat up a lot of iops if those are not in memory. To see if a lot of cache misses are happening, for xfs, you can look at xs_dir_lookup and xs_ig_missed. ( look at http://xfs.org/index.php/Runtime_Stats ) We greatly benefited from setting this to a low value but we have quite a lot of files on a node ( 30 million) Note that setting this to zero will result in the OOM killer killing the machine sooner or later. (especially if files are moved around due to a cluster change ;) Cheers, Robert van Leeuwen _______________________________________________ Mailing list: https://launchpad.net/~openstack Post to : openstack@lists.launchpad.net Unsubscribe : https://launchpad.net/~openstack More help : https://help.launchpad.net/ListHelp
