From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail202.messagelabs.com (mail202.messagelabs.com [216.82.254.227]) by kanga.kvack.org (Postfix) with SMTP id A90DF6B004F for ; Tue, 21 Jul 2009 03:40:42 -0400 (EDT) Received: from m6.gw.fujitsu.co.jp ([10.0.50.76]) by fgwmail7.fujitsu.co.jp (Fujitsu Gateway) with ESMTP id n6L7eiAW019866 for (envelope-from kamezawa.hiroyu@jp.fujitsu.com); Tue, 21 Jul 2009 16:40:44 +0900 Received: from smail (m6 [127.0.0.1]) by outgoing.m6.gw.fujitsu.co.jp (Postfix) with ESMTP id 0D5C845DE56 for ; Tue, 21 Jul 2009 16:40:44 +0900 (JST) Received: from s6.gw.fujitsu.co.jp (s6.gw.fujitsu.co.jp [10.0.50.96]) by m6.gw.fujitsu.co.jp (Postfix) with ESMTP id B7E7345DE4F for ; Tue, 21 Jul 2009 16:40:42 +0900 (JST) Received: from s6.gw.fujitsu.co.jp (localhost.localdomain [127.0.0.1]) by s6.gw.fujitsu.co.jp (Postfix) with ESMTP id 4B74A1DB8037 for ; Tue, 21 Jul 2009 16:40:42 +0900 (JST) Received: from m106.s.css.fujitsu.com (m106.s.css.fujitsu.com [10.249.87.106]) by s6.gw.fujitsu.co.jp (Postfix) with ESMTP id 9F495E0800C for ; Tue, 21 Jul 2009 16:40:41 +0900 (JST) Date: Tue, 21 Jul 2009 16:38:46 +0900 From: KAMEZAWA Hiroyuki Subject: Re: [PATCH] hibernate / memory hotplug: always use for_each_populated_zone() Message-Id: <20090721163846.2a8001c1.kamezawa.hiroyu@jp.fujitsu.com> In-Reply-To: <20090721071508.GB12734@osiris.boeblingen.de.ibm.com> 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-Transfer-Encoding: 7bit Sender: owner-linux-mm@kvack.org To: Heiko Carstens Cc: Nigel Cunningham , Gerald Schaefer , "Rafael J. Wysocki" , Andrew Morton , linux-kernel@vger.kernel.org, Martin Schwidefsky , KOSAKI Motohiro , Yasunori Goto , Nick Piggin , linux-mm@kvack.org List-ID: On Tue, 21 Jul 2009 09:15:08 +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. Historically, pfn_valid() just means "there is a memmap." no other meanings in any configs/archs. > We still have pfn_present() for CONFIG_SPARSEMEM. But that just means > "some pages in the section this pfn belongs to are present." It just exists for sparsemem internal purpose IIUC. > So it looks like checking for pfn_valid() and afterwards checking > for PG_Reserved (?) might give what one would expect. I think so, too. If memory is offline, PG_reserved is always set. In general, it's expected that "page is contiguous in MAX_ORDER range" and no memory holes in MAX_ORDER. In most case, PG_reserved is checked for skipping not-existing memory. > Looks all a bit confusing to me. > Or maybe it's just me who is confused? :) > IIRC, there are no generic interface to know whether there is a physical page. pfn_valid() is only for memmap and people have used if (pfn_valid(pfn) && !PageReserved(page)) check. But, hmm, If hibernation have to save PG_reserved memory, general solution is use copy_user_page() and handle fault. Alternative is making use of walk_memory_resource() as memory hotplug does. It checks resource information registered. Thanks, -Kame -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: email@kvack.org