From: Trond Myklebust Subject: Re: [PATCH 2/3] NFS: Add NFS_MOUNT_NONEGDE flag to avoid caching negative dentries Date: Wed, 16 Jan 2008 18:21:09 -0500 Message-ID: <1200525669.7695.21.camel@heimdal.trondhjem.org> References: <20080115163013.GC18911@newbie.thebellsplace.net> <1200415972.7702.7.camel@heimdal.trondhjem.org> <20080116012209.GB26010@newbie.thebellsplace.net> <1200451350.28088.43.camel@heimdal.trondhjem.org> <478DFD5A.1040501@RedHat.com> <01AE8AF878612047A442668306EAEB05018178E7@SACEXMV01.hq.netapp.com> <1200516219.6932.22.camel@heimdal.trondhjem.org> <478E7345.8080003@cypress.com> <1200520574.15282.24.camel@heimdal.trondhjem.org> <30593E98-7C5B-4841-94E2-40E7CD7D4857@oracle.com> Mime-Version: 1.0 Content-Type: text/plain Cc: NFS list To: Chuck Lever Return-path: Received: from pat.uio.no ([129.240.10.15]:59637 "EHLO pat.uio.no" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1756216AbYAPXVP (ORCPT ); Wed, 16 Jan 2008 18:21:15 -0500 In-Reply-To: <30593E98-7C5B-4841-94E2-40E7CD7D4857@oracle.com> Sender: linux-nfs-owner@vger.kernel.org List-ID: On Wed, 2008-01-16 at 17:09 -0500, Chuck Lever wrote: > On Jan 16, 2008, at 4:56 PM, Trond Myklebust wrote: > > On Wed, 2008-01-16 at 13:12 -0800, Risto Bell wrote: > >> Already decided not to go the distance, with separate controls of > >> time-to-live of positive and negative lookup cache entries (or is it > >> not considered good form to overload negttl=0 as means to disable)? > > > > We don't have a time-to-live scheme for dentries. > > Adding a TTL heuristic to dentry revalidation might help our > directory mtime problem. :-) I have a serious problem seeing how it might 'solve' anything at all. If you're worried about correctness, then ttl is a completely useless scheme: you can defeat it just as easily as you can defeat the mtime resolution. The only difference is that you will eventually catch onto the mistake, but you may have been operating on the wrong file for quite some time before the ttl expires. IOW: The only useful ttl values are ttl=infinity and ttl=0. Trond