From: Trond Myklebust Subject: Re: [PATCH] improve the performance of large sequential write NFS workloads Date: Wed, 23 Dec 2009 20:12:54 +0100 Message-ID: <1261595574.6775.2.camel@localhost> References: <1261015420.1947.54.camel@serenity> <1261037877.27920.36.camel@laptop> <20091219122033.GA11360@localhost> <1261232747.1947.194.camel@serenity> <20091222015907.GA6223@localhost> <1261578107.2606.11.camel@localhost> <20091223180551.GD3159@quack.suse.cz> Mime-Version: 1.0 Content-Type: text/plain; charset="UTF-8" Cc: Wu Fengguang , Steve Rago , Peter Zijlstra , "linux-nfs@vger.kernel.org" , "linux-kernel@vger.kernel.org" , "jens.axboe" , Peter Staubach , Arjan van de Ven , Ingo Molnar , linux-fsdevel@vger.kernel.org To: Jan Kara Return-path: Received: from mx2.netapp.com ([216.240.18.37]:31523 "EHLO mx2.netapp.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752153AbZLWTN6 convert rfc822-to-8bit (ORCPT ); Wed, 23 Dec 2009 14:13:58 -0500 In-Reply-To: <20091223180551.GD3159-+0h/O2h83AeN3ZZ/Hiejyg@public.gmane.org> Sender: linux-nfs-owner@vger.kernel.org List-ID: On Wed, 2009-12-23 at 19:05 +0100, Jan Kara wrote: > On Wed 23-12-09 15:21:47, Trond Myklebust wrote: > > @@ -474,6 +482,18 @@ writeback_single_inode(struct inode *inode, struct writeback_control *wbc) > > } > > > > spin_lock(&inode_lock); > > + /* > > + * Special state for cleaning NFS unstable pages > > + */ > > + if (inode->i_state & I_UNSTABLE_PAGES) { > > + int err; > > + inode->i_state &= ~I_UNSTABLE_PAGES; > > + spin_unlock(&inode_lock); > > + err = commit_unstable_pages(inode, wait); > > + if (ret == 0) > > + ret = err; > > + spin_lock(&inode_lock); > > + } > I don't quite understand this chunk: We've called writeback_single_inode > because it had some dirty pages. Thus it has I_DIRTY_DATASYNC set and a few > lines above your chunk, we've called nfs_write_inode which sent commit to > the server. Now here you sometimes send the commit again? What's the > purpose? We no longer set I_DIRTY_DATASYNC. We only set I_DIRTY_PAGES (and later I_UNSTABLE_PAGES). The point is that we now do the commit only _after_ we've sent all the dirty pages, and waited for writeback to complete, whereas previously we did it in the wrong order. Cheers Trond