On Mon, Nov 28, 2011 at 03:27:30AM -0500, Christoph Hellwig wrote: > Do not remove dquots from the freelist when we grab a reference to them in > xfs_qm_dqlookup, but leave them on the freelist util scanning notices that > they have a reference. This speeds up the lookup fastpath, and greatly > simplifies the lock ordering constraints. Note that the same scheme is > used by the VFS inode and dentry caches. > > Signed-off-by: Christoph Hellwig <hch@xxxxxx> That cleans things up nicely, and should be significantly faster if the VFS cache examples are anything to go by.... Reviewed-by: Dave Chinner <dchinner@xxxxxxxxxx> As an aside: > + /* > + * move the dquot to the front of the hashchain > + */ > + list_move(&dqp->q_hashlist, &qh->qh_list); > + trace_xfs_dqlookup_done(dqp); > + *O_dqpp = dqp; > + return 0; Back when the inode cache used a hash, we found that this moving of the item to the front of the list actually slowed down lookups - the impact of dirtying cachelines (i.e. remote CPU cache invalidation) to move the item in the list was greater than the time saved during lookups. That was because that when there are no hash chain modifications taking place, then the frequently hit chains simply end up shared in all the cpu caches rather than being turfed out on every successful lookup on a different CPU.... Cheers, Dave. -- Dave Chinner david@xxxxxxxxxxxxx _______________________________________________ xfs mailing list xfs@xxxxxxxxxxx http://oss.sgi.com/mailman/listinfo/xfs
