From: David Chinner Subject: Re: [patch 10/21] buffer heads: Support slab defrag Date: Tue, 20 May 2008 10:25:03 +1000 Message-ID: <20080520002503.GC173056135@sgi.com> References: <20080510030831.796641881@sgi.com> <20080510030916.935905242@sgi.com> <20080512002403.GP103491721@sgi.com> <20080515231045.GY155679365@sgi.com> <20080519054554.GY103491721@sgi.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Cc: David Chinner , akpm@linux-foundation.org, linux-kernel@vger.kernel.org, linux-fsdevel@vger.kernel.org, Mel Gorman , andi@firstfloor.org, Rik van Riel , Pekka Enberg , mpm@selenic.com To: Christoph Lameter Return-path: Received: from relay2.sgi.com ([192.48.171.30]:59955 "EHLO relay.sgi.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1752213AbYETAZj (ORCPT ); Mon, 19 May 2008 20:25:39 -0400 Content-Disposition: inline In-Reply-To: Sender: linux-fsdevel-owner@vger.kernel.org List-ID: On Mon, May 19, 2008 at 09:44:11AM -0700, Christoph Lameter wrote: > On Mon, 19 May 2008, David Chinner wrote: > > > Defragmentation is triggered as part of the usual memory reclaim > > process. Which implies we've run out of free memory, correct? > > Yes but we have already reclaimed some memory. > > > > How do you trigger such a special writeout? > > > > filemap_fdatawrite_range() perhaps? > > Could you provide me such a patch? I would not know how much to writeout. > If we had such a method then we could also use that for the swap case > where we also write out single pages? How hard is it? I don't have time right now to do this, but it's essentially: mapping = page->mapping; ...... - mapping->aops->writepage(); + filemap_fdatawrite_range(mapping, start, end); Where [start,end] span page->index and are is large enough to get a substantial sized I/O to disk (say at least SWAP_CLUSTER_MAX pages, preferrably larger for 4k page size machines). Cheers, Dave. -- Dave Chinner Principal Engineer SGI Australian Software Group