Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755609Ab1CXCLx (ORCPT ); Wed, 23 Mar 2011 22:11:53 -0400 Received: from fgwmail6.fujitsu.co.jp ([192.51.44.36]:45538 "EHLO fgwmail6.fujitsu.co.jp" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752277Ab1CXCLw convert rfc822-to-8bit (ORCPT ); Wed, 23 Mar 2011 22:11:52 -0400 X-SecurityPolicyCheck-FJ: OK by FujitsuOutboundMailChecker v1.3.1 From: KOSAKI Motohiro To: Minchan Kim Subject: Re: [PATCH 1/5] vmscan: remove all_unreclaimable check from direct reclaim path completely Cc: kosaki.motohiro@jp.fujitsu.com, linux-kernel@vger.kernel.org, Andrew Morton , David Rientjes , Linus Torvalds , Rik van Riel , Oleg Nesterov , linux-mm , Andrey Vagin , Hugh Dickins , KAMEZAWA Hiroyuki , Nick Piggin , Johannes Weiner In-Reply-To: References: <20110323174545.1AE2.A69D9226@jp.fujitsu.com> Message-Id: <20110324111200.1AF4.A69D9226@jp.fujitsu.com> MIME-Version: 1.0 Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: 8BIT X-Mailer: Becky! ver. 2.56.05 [ja] Date: Thu, 24 Mar 2011 11:11:46 +0900 (JST) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 6059 Lines: 177 > On Wed, Mar 23, 2011 at 5:44 PM, KOSAKI Motohiro > wrote: > >> > Boo. > >> > You seems forgot why you introduced current all_unreclaimable() function. > >> > While hibernation, we can't trust all_unreclaimable. > >> > >> Hmm. AFAIR, the why we add all_unreclaimable is when the hibernation is going on, > >> kswapd is freezed so it can't mark the zone->all_unreclaimable. > >> So I think hibernation can't be a problem. > >> Am I miss something? > > > > Ahh, I missed. thans correct me. Okay, I recognized both mine and your works. > > Can you please explain why do you like your one than mine? > > Just _simple_ :) > I don't want to change many lines although we can do it simple and very clear. > > > > > btw, Your one is very similar andrey's initial patch. If your one is > > better, I'd like to ack with andrey instead. > > When Andrey sent a patch, I though this as zone_reclaimable() is right > place to check it than out of zone_reclaimable. Why I didn't ack is > that Andrey can't explain root cause but you did so you persuade me. > > I don't mind if Andrey move the check in zone_reclaimable and resend > or I resend with concrete description. > > Anyway, most important thing is good description to show the root cause. > It is applied to your patch, too. > You should have written down root cause in description. honestly, I really dislike to use mixing zone->pages_scanned and zone->all_unreclaimable. because I think it's no simple. I don't think it's good taste nor easy to review. Even though you who VM expert didn't understand this issue at once, it's smell of too mess code. therefore, I prefore to take either 1) just remove the function or 2) just only check zone->all_unreclaimable and oom_killer_disabled instead zone->pages_scanned. And, I agree I need to rewrite the description. How's this? ================================================== >From 216bcf3fb0476b453080debf8999c74c635ed72f Mon Sep 17 00:00:00 2001 From: KOSAKI Motohiro Date: Sun, 8 May 2011 17:39:44 +0900 Subject: [PATCH] vmscan: remove all_unreclaimable check from direct reclaim path completely all_unreclaimable check in direct reclaim has been introduced at 2.6.19 by following commit. 2006 Sep 25; commit 408d8544; oom: use unreclaimable info And it went through strange history. firstly, following commit broke the logic unintentionally. 2008 Apr 29; commit a41f24ea; page allocator: smarter retry of costly-order allocations Two years later, I've found obvious meaningless code fragment and restored original intention by following commit. 2010 Jun 04; commit bb21c7ce; vmscan: fix do_try_to_free_pages() return value when priority==0 But, the logic didn't works when 32bit highmem system goes hibernation and Minchan slightly changed the algorithm and fixed it . 2010 Sep 22: commit d1908362: vmscan: check all_unreclaimable in direct reclaim path But, recently, Andrey Vagin found the new corner case. Look, struct zone { .. int all_unreclaimable; .. unsigned long pages_scanned; .. } zone->all_unreclaimable and zone->pages_scanned are neigher atomic variables nor protected by lock. Therefore zones can become a state of zone->page_scanned=0 and zone->all_unreclaimable=1. In this case, current all_unreclaimable() return false even though zone->all_unreclaimabe=1. Is this ignorable minor issue? No. Unfortunatelly, x86 has very small dma zone and it become zone->all_unreclamble=1 easily. and if it become all_unreclaimable=1, it never restore all_unreclaimable=0. Why? if all_unreclaimable=1, vmscan only try DEF_PRIORITY reclaim and a-few-lru-pages>>DEF_PRIORITY always makes 0. that mean no page scan at all! Eventually, oom-killer never works on such systems. Let's remove this problematic logic completely. Reported-by: Andrey Vagin Cc: Nick Piggin Cc: Minchan Kim Cc: Johannes Weiner Cc: Rik van Riel Cc: KAMEZAWA Hiroyuki Signed-off-by: KOSAKI Motohiro --- mm/vmscan.c | 36 +----------------------------------- 1 files changed, 1 insertions(+), 35 deletions(-) diff --git a/mm/vmscan.c b/mm/vmscan.c index 060e4c1..254aada 100644 --- a/mm/vmscan.c +++ b/mm/vmscan.c @@ -1989,33 +1989,6 @@ static bool zone_reclaimable(struct zone *zone) } /* - * As hibernation is going on, kswapd is freezed so that it can't mark - * the zone into all_unreclaimable. It can't handle OOM during hibernation. - * So let's check zone's unreclaimable in direct reclaim as well as kswapd. - */ -static bool all_unreclaimable(struct zonelist *zonelist, - struct scan_control *sc) -{ - struct zoneref *z; - struct zone *zone; - bool all_unreclaimable = true; - - for_each_zone_zonelist_nodemask(zone, z, zonelist, - gfp_zone(sc->gfp_mask), sc->nodemask) { - if (!populated_zone(zone)) - continue; - if (!cpuset_zone_allowed_hardwall(zone, GFP_KERNEL)) - continue; - if (zone_reclaimable(zone)) { - all_unreclaimable = false; - break; - } - } - - return all_unreclaimable; -} - -/* * This is the main entry point to direct page reclaim. * * If a full scan of the inactive list fails to free enough memory then we @@ -2105,14 +2078,7 @@ out: delayacct_freepages_end(); put_mems_allowed(); - if (sc->nr_reclaimed) - return sc->nr_reclaimed; - - /* top priority shrink_zones still had more to do? don't OOM, then */ - if (scanning_global_lru(sc) && !all_unreclaimable(zonelist, sc)) - return 1; - - return 0; + return sc->nr_reclaimed; } unsigned long try_to_free_pages(struct zonelist *zonelist, int order, -- 1.6.5.2 -- 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/