From mboxrd@z Thu Jan 1 00:00:00 1970 From: Bob Bell Subject: Re: [PATCH 0/3] Intro: Better handling coarse-grained timestamps Date: Tue, 15 Jan 2008 20:55:27 -0500 Message-ID: <20080116015526.GC26010@newbie.thebellsplace.net> References: <20080115162658.GA18911@newbie.thebellsplace.net> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii; format=flowed To: linux-nfs@vger.kernel.org Return-path: Received: from srv03.macroped.com ([74.52.9.226]:53660 "EHLO srv03.macroped.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750762AbYAPBzb (ORCPT ); Tue, 15 Jan 2008 20:55:31 -0500 Received: from newbie (c-75-67-251-249.hsd1.nh.comcast.net [75.67.251.249]) (authenticated bits=0) by srv03.macroped.com (8.13.8/8.13.8) with ESMTP id m0G1vLig009254 for ; Tue, 15 Jan 2008 20:57:22 -0500 In-Reply-To: <20080115162658.GA18911-y89O8yXFYpDSsb2jM9SCN5/hYUUxywnI@public.gmane.org> Sender: linux-nfs-owner@vger.kernel.org List-ID: On Tue, Jan 15, 2008 at 11:27:01AM -0500, Bob Bell wrote: >Secondly, a modification to the kernel has been made to disable the >caching of negative dentries when the NFS_MOUNT_NONEGDE flag is set. >Note that this does nothing to address outdated information being >returned by readdir(). However, it does allow a file to be open()ed or >lstat()ed if the filename is known. Because this has a potential >performance impact, it is left as an option for the user to select. Someone pointed me to this page on NFSv4.1 directory delegations: http://wiki.linux-nfs.org/wiki/index.php/NFSv4.1_Directory_Delegations I found the following quotes intriguing: "Even though the directories along the path are cached, [without directory delegations] negative dentry caching is not allowed because it potentially violates close-to-open consistency semantics." "Close-to-open consistency currently requires that even in a case where previous LOOKUPs or OPENs for a given file have recently and repeatedly failed, subsequent LOOKUPs and OPENs must nevertheless be sent to the server (i.e., negative caching provides no benefit in those cases)." I admittedly know little about what is being discussed here. However, is it possible that the Linux NFS client should *NEVER* cache negative entries? (well, maybe with the exception of "nocto") I'm interested if anyone has thoughts on the matter, though I know don't enough to argue either side, so here's a really easy chance to win an argument. :) -- Bob Bell