Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756598Ab1CGV7Q (ORCPT ); Mon, 7 Mar 2011 16:59:16 -0500 Received: from smtp1.linux-foundation.org ([140.211.169.13]:49399 "EHLO smtp1.linux-foundation.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1756476Ab1CGV7O (ORCPT ); Mon, 7 Mar 2011 16:59:14 -0500 Date: Mon, 7 Mar 2011 13:58:31 -0800 From: Andrew Morton To: Minchan Kim Cc: Andrew Vagin , Andrey Vagin , Mel Gorman , KOSAKI Motohiro , linux-mm@kvack.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH] mm: check zone->all_unreclaimable in all_unreclaimable() Message-Id: <20110307135831.9e0d7eaa.akpm@linux-foundation.org> In-Reply-To: <20110305170759.GC1918@barrios-desktop> References: <1299325456-2687-1-git-send-email-avagin@openvz.org> <20110305152056.GA1918@barrios-desktop> <4D72580D.4000208@gmail.com> <20110305155316.GB1918@barrios-desktop> <4D7267B6.6020406@gmail.com> <20110305170759.GC1918@barrios-desktop> X-Mailer: Sylpheed 3.0.2 (GTK+ 2.20.1; x86_64-pc-linux-gnu) Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 4002 Lines: 100 On Sun, 6 Mar 2011 02:07:59 +0900 Minchan Kim wrote: > On Sat, Mar 05, 2011 at 07:41:26PM +0300, Andrew Vagin wrote: > > On 03/05/2011 06:53 PM, Minchan Kim wrote: > > >On Sat, Mar 05, 2011 at 06:34:37PM +0300, Andrew Vagin wrote: > > >>On 03/05/2011 06:20 PM, Minchan Kim wrote: > > >>>On Sat, Mar 05, 2011 at 02:44:16PM +0300, Andrey Vagin wrote: > > >>>>Check zone->all_unreclaimable in all_unreclaimable(), otherwise the > > >>>>kernel may hang up, because shrink_zones() will do nothing, but > > >>>>all_unreclaimable() will say, that zone has reclaimable pages. > > >>>> > > >>>>do_try_to_free_pages() > > >>>> shrink_zones() > > >>>> for_each_zone > > >>>> if (zone->all_unreclaimable) > > >>>> continue > > >>>> if !all_unreclaimable(zonelist, sc) > > >>>> return 1 > > >>>> > > >>>>__alloc_pages_slowpath() > > >>>>retry: > > >>>> did_some_progress = do_try_to_free_pages(page) > > >>>> ... > > >>>> if (!page&& did_some_progress) > > >>>> retry; > > >>>> > > >>>>Signed-off-by: Andrey Vagin > > >>>>--- > > >>>> mm/vmscan.c | 2 ++ > > >>>> 1 files changed, 2 insertions(+), 0 deletions(-) > > >>>> > > >>>>diff --git a/mm/vmscan.c b/mm/vmscan.c > > >>>>index 6771ea7..1c056f7 100644 > > >>>>--- a/mm/vmscan.c > > >>>>+++ b/mm/vmscan.c > > >>>>@@ -2002,6 +2002,8 @@ static bool all_unreclaimable(struct zonelist *zonelist, > > >>>> > > >>>> for_each_zone_zonelist_nodemask(zone, z, zonelist, > > >>>> gfp_zone(sc->gfp_mask), sc->nodemask) { > > >>>>+ if (zone->all_unreclaimable) > > >>>>+ continue; > > >>>> if (!populated_zone(zone)) > > >>>> continue; > > >>>> if (!cpuset_zone_allowed_hardwall(zone, GFP_KERNEL)) > > >>>zone_reclaimable checks it. Isn't it enough? > > >>I sent one more patch [PATCH] mm: skip zombie in OOM-killer. > > >>This two patches are enough. > > >Sorry if I confused you. > > >I mean zone->all_unreclaimable become true if !zone_reclaimable in balance_pgdat. > > >zone_reclaimable compares recent pages_scanned with the number of zone lru pages. > > >So too many page scanning in small lru pages makes the zone to unreclaimable zone. > > > > > >In all_unreclaimable, we calls zone_reclaimable to detect it. > > >It's the same thing with your patch. > > balance_pgdat set zone->all_unreclaimable, but the problem is that > > it is cleaned late. > > Yes. It can be delayed by pcp so (zone->all_unreclaimable = true) is > a false alram since zone have a free page and it can be returned > to free list by drain_all_pages in next turn. > > > > > The problem is that zone->all_unreclaimable = True, but > > zone_reclaimable() returns True too. > > Why is it a problem? > If zone->all_unreclaimable gives a false alram, we does need to check > it again by zone_reclaimable call. > > If we believe a false alarm and give up the reclaim, maybe we have to make > unnecessary oom kill. > > > > > zone->all_unreclaimable will be cleaned in free_*_pages, but this > > may be late. It is enough allocate one page from page cache, that > > zone_reclaimable() returns True and zone->all_unreclaimable becomes > > True. > > >>>Does the hang up really happen or see it by code review? > > >>Yes. You can reproduce it for help the attached python program. It's > > >>not very clever:) > > >>It make the following actions in loop: > > >>1. fork > > >>2. mmap > > >>3. touch memory > > >>4. read memory > > >>5. munmmap > > >It seems the test program makes fork bombs and memory hogging. > > >If you applied this patch, the problem is gone? > > Yes. > > Hmm.. Although it solves the problem, I think it's not a good idea that > depends on false alram and give up the retry. Any alternative proposals? We should get the livelock fixed if possible.. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/