From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751542Ab0EQAZN (ORCPT ); Sun, 16 May 2010 20:25:13 -0400 Received: from bld-mail12.adl6.internode.on.net ([150.101.137.97]:43167 "EHLO mail.internode.on.net" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1750793Ab0EQAZL (ORCPT ); Sun, 16 May 2010 20:25:11 -0400 Date: Mon, 17 May 2010 10:24:44 +1000 From: Dave Chinner To: Ed Tomlinson Cc: Andi Kleen , Christoph Lameter , linux-kernel@vger.kernel.org, xfs@oss.sgi.com, linux-fsdevel@vger.kernel.org, linux-mm@kvack.org, Pekka Enberg , npiggin@suse.de Subject: Re: Defrag in shrinkers Message-ID: <20100517002444.GJ8120@dastard> References: <1273821863-29524-1-git-send-email-david@fromorbit.com> <87y6fmmdak.fsf@basil.nowhere.org> <201005151308.18090.edt@aei.ca> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <201005151308.18090.edt@aei.ca> User-Agent: Mutt/1.5.20 (2009-06-14) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Sat, May 15, 2010 at 01:08:17PM -0400, Ed Tomlinson wrote: > On Friday 14 May 2010 16:36:03 Andi Kleen wrote: > > Christoph Lameter writes: > > > > > Would it also be possible to add some defragmentation logic when you > > > revise the shrinkers? Here is a prototype patch that would allow you to > > > determine the other objects sitting in the same page as a given object. > > > > > > With that I hope that you have enough information to determine if its > > > worth to evict the other objects as well to reclaim the slab page. > > > > I like the idea, it would be useful for the hwpoison code too, > > when it tries to clean a page. > > If this is done generally we probably want to retune the 'pressure' put on the slab. The > whole reason for the callbacks was to keep the 'pressure on the slab proportional to the > memory pressure (scan rate). I don't see that defrag based reclaim changes the concept of pressure at all. As long as reclaim follows the nr_to_scan guideline, then it doesn't matter if we do reclaim from the LRU or reclaim from a list provided by the slab cache.... FWIW, one thing that would be necessary, I think, is to avoid defrag until a certain level of fragmentation has occurred - we should do LRU-based reclaim as much as possible, and only trigger defrag-style reclaim once we hit a trigger (e.g. once the slab is 25% partial pages). Cheers, Dave. -- Dave Chinner david@fromorbit.com