From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1750737AbWAOOBm (ORCPT ); Sun, 15 Jan 2006 09:01:42 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1750796AbWAOOBm (ORCPT ); Sun, 15 Jan 2006 09:01:42 -0500 Received: from holly.csn.ul.ie ([136.201.105.4]:36569 "EHLO holly.csn.ul.ie") by vger.kernel.org with ESMTP id S1750737AbWAOOBl (ORCPT ); Sun, 15 Jan 2006 09:01:41 -0500 Date: Sun, 15 Jan 2006 14:00:21 +0000 (GMT) From: Mel Gorman X-X-Sender: mel@skynet To: =?ISO-8859-15?Q?Mika_Penttil=E4?= Cc: akpm@osdl.org, lhms-devel@lists.sourceforge.net, linux-mm@kvack.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH] BUG: gfp_zone() not mapping zone modifiers correctly and bad ordering of fallback lists In-Reply-To: <43C7EDCF.3050402@kolumbus.fi> Message-ID: References: <20060113155026.GA4811@skynet.ie> <43C7EDCF.3050402@kolumbus.fi> MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=ISO-8859-1 Content-Transfer-Encoding: 8BIT Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org On Fri, 13 Jan 2006, Mika Penttilä wrote: > Mel Gorman wrote: > > > Hi Andrew, > > > > This patch is divided into two parts and addresses a bug in how zone > > fallback lists are calculated and how __GFP_* zone modifiers are mapped to > > their equivilant ZONE_* type. It applies to 2.6.15-mm3 and has been tested > > on x86 and ppc64. It has been reported by Yasunori Goto that it boots on > > ia64. Details as follows; > > > > build_zonelists() attempts to be smart, and uses highest_zone() so that it > > doesn't attempt to call build_zonelists_node() for empty zones. However, > > build_zonelists_node() is smart enough to do the right thing by itself and > > build_zonelists() already has the zone index that highest_zone() is meant > > to provide. So, remove the unnecessary function highest_zone(). > > > > The helper function gfp_zone() assumes that the bits used in the zone > > modifier > > of a GFP flag maps directory on to their ZONE_* equivalent and just applies > > a > > mask. However, the bits do not map directly and the wrong fallback lists can > > be used. If unluckly, the system can go OOM when plenty of suitable memory > > is available. This patch redefines the __GFP_ zone modifier flags to allow > > a simple mapping to their equivilant ZONE_ type. > > > > > What's the exact failure case? Afaik, we loop though all the GFP_ZONETYPES, > building the appropriate zone lists at 0 - GFP_ZONETYPES-1 indexes. So the > direct GFP -> ZONE mapping should do the right thing. > It goes wrong if one tries to add a different zone. What is currently there happens to work, but there seemed to be confusion of when __GFP_ bits were being used or when ZONE_ indices were used. -- Mel Gorman Part-time Phd Student Linux Technology Center University of Limerick IBM Dublin Software Lab