From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from psmtp.com (na3sys010amx137.postini.com [74.125.245.137]) by kanga.kvack.org (Postfix) with SMTP id 6461B6B005C for ; Thu, 14 Jun 2012 11:47:11 -0400 (EDT) Received: by yenr5 with SMTP id r5so1294096yen.14 for ; Thu, 14 Jun 2012 08:47:10 -0700 (PDT) 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 Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: quoted-printable Sender: owner-linux-mm@kvack.org List-ID: 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 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 >> =A0 =A0priority 0. This is because to avoid kswapd() infinite >> =A0 =A0loop. That said, kswapd assume direct reclaim makes enough >> =A0 =A0free pages to use either regular page reclaim or oom-killer. >> =A0 =A0This logic makes kswapd -> direct-reclaim dependency. >> 2) direct reclaim continue to reclaim without oom-killer until >> =A0 =A0kswapd turn on zone->all_unreclaimble. This is because >> =A0 =A0to avoid too early oom-kill. >> =A0 =A0This 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) >> =A0 =A0 =A0 =A0 =A0 =A0 =A0 if (global_reclaim(sc)) { >> =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 if (!cpuset_zone_allowed_har= dwall(zone, GFP_KERNEL)) >> =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 continue; >> - =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 if (zone->all_unreclaimable && >> - =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 = =A0 sc->priority !=3D DEF_PRIORITY) >> + =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 if (!zone_reclaimable(zone) && >> + =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 sc->priority !=3D 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, 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