From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1030865AbXDTQXY (ORCPT ); Fri, 20 Apr 2007 12:23:24 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1030924AbXDTQXY (ORCPT ); Fri, 20 Apr 2007 12:23:24 -0400 Received: from netops-testserver-4-out.sgi.com ([192.48.171.29]:33080 "EHLO relay.sgi.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1030865AbXDTQXX (ORCPT ); Fri, 20 Apr 2007 12:23:23 -0400 Date: Fri, 20 Apr 2007 09:23:23 -0700 (PDT) From: Christoph Lameter X-X-Sender: clameter@schroedinger.engr.sgi.com To: Mel Gorman cc: linux-kernel@vger.kernel.org, Peter Zijlstra , Nick Piggin , Paul Jackson , Dave Chinner , Andi Kleen Subject: Re: [RFC 0/8] Variable Order Page Cache In-Reply-To: <20070420141406.GB16878@skynet.ie> Message-ID: References: <20070419163504.11948.58487.sendpatchset@schroedinger.engr.sgi.com> <20070420141406.GB16878@skynet.ie> MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org On Fri, 20 Apr 2007, Mel Gorman wrote: > I believe there is an assumption in parts of reclaim that LRU pages are > order-0. An interesting bug or two is likely to rear its head there. Correct. We need to deal with reclaim etc. > > Note that this is proof-of-concept. Lots of functionality is missing and > > various issues have not been dealt with. Use of higher order pages may cause > > memory fragmentation. Mel Gorman's anti-fragmentation work is probably > > essential if we want to do this. We likely need actual defragmentation > > support. > > > > Ok, anti-fragmentation will help up to a point but it's awkward with ramfs > because those pages are not reclaimable or migratable no matter what the > order. Normal filesystems would fare much better fragmentation-wise. > > The problem is that the mapping gfp_mask is normally GFP_HIGH_MOVABLE but it's > GFP_HIGHUSER for ramfs. This patchset will increase the number of non-movable > high-order allocations quite considerably and it will tend to fragment memory > worse than we do currently. I can think of ways it can be dealt with > (even marking them RECLAIMABLE would help) so I'm not massively worried > now but I'll keep it in mind as things develop. Well I think we will have xfs support soon. Then we can deal with more issues and be more complete. What I wanted from this post was a consensus on how to proceed. There are many subsystems involved and I do not want to go off the deep end.