From: Greg Banks Subject: Re: Read/Write NFS I/O performance degraded by FLUSH_STABLE page flushing Date: Sat, 30 May 2009 23:02:47 +1000 Message-ID: References: <5ECD2205-4DC9-41F1-AC5C-ADFA984745D3@oracle.com> <49FA0CE8.9090706@redhat.com> <1241126587.15476.62.camel@heimdal.trondhjem.org> <1243615595.7155.48.camel@heimdal.trondhjem.org> <1243618500.7155.56.camel@heimdal.trondhjem.org> <1243686363.5209.16.camel@heimdal.trondhjem.org> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1 Cc: Brian R Cowan , Chuck Lever , linux-nfs@vger.kernel.org, linux-nfs-owner@vger.kernel.org, Peter Staubach To: Trond Myklebust Return-path: Received: from qw-out-2122.google.com ([74.125.92.24]:5907 "EHLO qw-out-2122.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1756594AbZE3NCr (ORCPT ); Sat, 30 May 2009 09:02:47 -0400 In-Reply-To: <1243686363.5209.16.camel-rJ7iovZKK19ZJLDQqaL3InhyD016LWXt@public.gmane.org> Sender: linux-nfs-owner@vger.kernel.org List-ID: On Sat, May 30, 2009 at 10:26 PM, Trond Myklebust wrote: > On Sat, 2009-05-30 at 10:22 +1000, Greg Banks wrote: >> On Sat, May 30, 2009 at 3:35 AM, Trond Myklebust >> wrote: >> > On Fri, 2009-05-29 at 13:25 -0400, Brian R Cowan wrote: >> >> >> > > Firstly, the server only uses O_SYNC if you turn off write gathering > (a.k.a. the 'wdelay' option). The default behaviour for the Linux nfs > server is to always try write gathering and hence no O_SYNC. Well, write gathering is a total crock that AFAICS only helps single-file writes on NFSv2. For today's workloads all it does is provide a hotspot on the two global variables that track writes in an attempt to gather them. Back when I worked on a server product, no_wdelay was one of the standard options for new exports. > Secondly, even if it were the case, then this does not justify changing > the client behaviour. I totally agree, it was just an observation. In any case, as Christoph points out, the ext3 performance difference makes an unstable WRITE+COMMIT slower than a stable WRITE, and you already assumed that. -- Greg.