Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756383Ab2FNPrM (ORCPT ); Thu, 14 Jun 2012 11:47:12 -0400 Received: from mail-gg0-f174.google.com ([209.85.161.174]:36870 "EHLO mail-gg0-f174.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1756000Ab2FNPrL convert rfc822-to-8bit (ORCPT ); Thu, 14 Jun 2012 11:47:11 -0400 MIME-Version: 1.0 In-Reply-To: <20120614152537.GR27397@tiehlicka.suse.cz> References: <1339661592-3915-1-git-send-email-kosaki.motohiro@gmail.com> <20120614152537.GR27397@tiehlicka.suse.cz> From: KOSAKI Motohiro Date: Thu, 14 Jun 2012 11:46:47 -0400 Message-ID: Subject: Re: [resend][PATCH] mm, vmscan: fix do_try_to_free_pages() livelock To: Michal Hocko Cc: linux-kernel@vger.kernel.org, linux-mm@kvack.org, akpm@linux-foundation.org, Nick Piggin , Johannes Weiner , Mel Gorman , KAMEZAWA Hiroyuki , Minchan Kim Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 8BIT Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 3199 Lines: 72 On Thu, Jun 14, 2012 at 11:25 AM, Michal Hocko wrote: > On Thu 14-06-12 04:13:12, kosaki.motohiro@gmail.com wrote: >> From: KOSAKI Motohiro >> >> Currently, do_try_to_free_pages() can enter livelock. Because of, >> now vmscan has two conflicted policies. >> >> 1) kswapd sleep when it couldn't reclaim any page when reaching >> ? ?priority 0. This is because to avoid kswapd() infinite >> ? ?loop. That said, kswapd assume direct reclaim makes enough >> ? ?free pages to use either regular page reclaim or oom-killer. >> ? ?This logic makes kswapd -> direct-reclaim dependency. >> 2) direct reclaim continue to reclaim without oom-killer until >> ? ?kswapd turn on zone->all_unreclaimble. This is because >> ? ?to avoid too early oom-kill. >> ? ?This logic makes direct-reclaim -> kswapd dependency. >> >> In worst case, direct-reclaim may continue to page reclaim forever >> when kswapd sleeps forever. >> >> We can't turn on zone->all_unreclaimable from direct reclaim path >> because direct reclaim path don't take any lock and this way is racy. >> >> Thus this patch removes zone->all_unreclaimable field completely and >> recalculates zone reclaimable state every time. >> >> Note: we can't take the idea that direct-reclaim see zone->pages_scanned >> directly and kswapd continue to use zone->all_unreclaimable. Because, it >> is racy. commit 929bea7c71 (vmscan: all_unreclaimable() use >> zone->all_unreclaimable as a name) describes the detail. >> >> Reported-by: Aaditya Kumar >> Reported-by: Ying Han >> Cc: Nick Piggin >> Acked-by: Rik van Riel >> Cc: Michal Hocko >> Cc: Johannes Weiner >> Cc: Mel Gorman >> Cc: KAMEZAWA Hiroyuki >> Cc: Minchan Kim >> Signed-off-by: KOSAKI Motohiro > > Looks good, just one comment bellow: > > Reviewed-by: Michal Hocko > > [...] >> diff --git a/mm/vmscan.c b/mm/vmscan.c >> index eeb3bc9..033671c 100644 >> --- a/mm/vmscan.c >> +++ b/mm/vmscan.c > [...] >> @@ -1936,8 +1936,8 @@ static bool shrink_zones(struct zonelist *zonelist, struct scan_control *sc) >> ? ? ? ? ? ? ? if (global_reclaim(sc)) { >> ? ? ? ? ? ? ? ? ? ? ? if (!cpuset_zone_allowed_hardwall(zone, GFP_KERNEL)) >> ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? continue; >> - ? ? ? ? ? ? ? ? ? ? if (zone->all_unreclaimable && >> - ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? sc->priority != DEF_PRIORITY) >> + ? ? ? ? ? ? ? ? ? ? if (!zone_reclaimable(zone) && >> + ? ? ? ? ? ? ? ? ? ? ? ? sc->priority != DEF_PRIORITY) > > Not exactly a hot path but still would be nice to test the priority > first as the test is cheaper (maybe compiler is clever enough to reorder > this, as both expressions are independent and without any side-effects > but...). ok, will fix. -- 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/