From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751962AbZGUHVF (ORCPT ); Tue, 21 Jul 2009 03:21:05 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1751424AbZGUHVE (ORCPT ); Tue, 21 Jul 2009 03:21:04 -0400 Received: from cantor.suse.de ([195.135.220.2]:60361 "EHLO mx1.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751289AbZGUHVD (ORCPT ); Tue, 21 Jul 2009 03:21:03 -0400 Date: Tue, 21 Jul 2009 09:21:01 +0200 From: Nick Piggin To: Heiko Carstens Cc: Nigel Cunningham , Gerald Schaefer , "Rafael J. Wysocki" , Andrew Morton , linux-kernel@vger.kernel.org, Martin Schwidefsky , KOSAKI Motohiro , KAMEZAWA Hiroyuki , Yasunori Goto , linux-mm@kvack.org Subject: Re: [PATCH] hibernate / memory hotplug: always use for_each_populated_zone() Message-ID: <20090721072101.GC7816@wotan.suse.de> References: <1248103551.23961.0.camel@localhost.localdomain> <4A64E1D6.8090102@crca.org.au> <20090721071508.GB12734@osiris.boeblingen.de.ibm.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20090721071508.GB12734@osiris.boeblingen.de.ibm.com> User-Agent: Mutt/1.5.9i Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, Jul 21, 2009 at 09:15:08AM +0200, Heiko Carstens wrote: > On Tue, Jul 21, 2009 at 07:29:58AM +1000, Nigel Cunningham wrote: > > Hi. > > > > Gerald Schaefer wrote: > > > From: Gerald Schaefer > > > > > > Use for_each_populated_zone() instead of for_each_zone() in hibernation > > > code. This fixes a bug on s390, where we allow both config options > > > HIBERNATION and MEMORY_HOTPLUG, so that we also have a ZONE_MOVABLE > > > here. We only allow hibernation if no memory hotplug operation was > > > performed, so in fact both features can only be used exclusively, but > > > this way we don't need 2 differently configured (distribution) kernels. > > > > > > If we have an unpopulated ZONE_MOVABLE, we allow hibernation but run > > > into a BUG_ON() in memory_bm_test/set/clear_bit() because hibernation > > > code iterates through all zones, not only the populated zones, in > > > several places. For example, swsusp_free() does for_each_zone() and > > > then checks for pfn_valid(), which is true even if the zone is not > > > populated, resulting in a BUG_ON() later because the pfn cannot be > > > found in the memory bitmap. > > > > I agree with your logic and patch, but doesn't this also imply that the > > s390 implementation pfn_valid should be changed to return false for > > those pages? > > For CONFIG_SPARSEMEM, which s390 uses, there is no architecture specific > pfn_valid() implementation. > Also it looks like the semantics of pfn_valid() aren't clear. > At least for sparsemem it means nothing but "the memmap for the section > this page belongs to exists". So it just means the struct page for the > pfn exists. > We still have pfn_present() for CONFIG_SPARSEMEM. But that just means > "some pages in the section this pfn belongs to are present." > So it looks like checking for pfn_valid() and afterwards checking > for PG_Reserved (?) might give what one would expect. > Looks all a bit confusing to me. > Or maybe it's just me who is confused? :) It would be nice to remove PG_reserved (most architectures also set it I think for kernel text and IIRC bootmem), it could then be used as a PG_arch_2 bit, and we could ask architectures to impement pfn_is_ram (or whatever's going to be most useful).