From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1764233AbXGTOBU (ORCPT ); Fri, 20 Jul 2007 10:01:20 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1752976AbXGTOBE (ORCPT ); Fri, 20 Jul 2007 10:01:04 -0400 Received: from calculon.skynet.ie ([193.1.99.88]:49125 "EHLO calculon.skynet.ie" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750768AbXGTOBB (ORCPT ); Fri, 20 Jul 2007 10:01:01 -0400 Date: Fri, 20 Jul 2007 15:00:59 +0100 To: KAMEZAWA Hiroyuki Cc: Paul Mundt , torvalds@linux-foundation.org, akpm@linux-foundation.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH] mm: Fix memory hotplug oops from ZONE_MOVABLE changes. Message-ID: <20070720140058.GA3079@skynet.ie> References: <20070720060342.GA24765@linux-sh.org> <20070720112025.GA14495@skynet.ie> <20070720114246.GA27391@linux-sh.org> <20070720223909.d4c1e848.kamezawa.hiroyu@jp.fujitsu.com> MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-15 Content-Disposition: inline In-Reply-To: <20070720223909.d4c1e848.kamezawa.hiroyu@jp.fujitsu.com> User-Agent: Mutt/1.5.13 (2006-08-11) From: mel@skynet.ie (Mel Gorman) Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org On (20/07/07 22:39), KAMEZAWA Hiroyuki didst pronounce: > On Fri, 20 Jul 2007 20:42:46 +0900 > Paul Mundt wrote: > > > > I expect that the memory gets added to the same zone as historically but > > > when ZONE_MOVABLE is set, you'll see a situation where zones are overlapping > > > after memory hot-add. i.e. Before memory hot-add, you'd see > > > > > > DDDDMM > > > > > > for ZONE_DMA and ZONE_MOVABLE and after hotadd, you'd see something like > > > > > > DDDDMMDDDD > > > > > As similar case, I hear powerpc has followig memory layout > > (1)(1)(0)(0)(0)(1)(1)(1) # (0) is node 0, (1) is node 1. all zones are ZONE_DMA. > Not always, but it happens. We used to have two test machines available that exhibited this behaviour although they went missing at some point which is unfortunate. > So zone is overlapped without memory hotplug. Zones overlapping have some subtle differences to nodes but the place this is really noticeable is during memory init when a range of PFNs are initialised by memmap_init_zone(). If zones overlap there, they can initialise the struct page fields twice but that is not an issue with memory hot-add. The potential issue I am thinking of is users that manually walk the memmap but no functionality outside of debugging should be doing anything like that. > But I agree we have to take care of this kind of corner cases. > Indeed. I think we're ok, but it should be checked out anyway. -- Mel Gorman Part-time Phd Student Linux Technology Center University of Limerick IBM Dublin Software Lab