From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from psmtp.com (na3sys010amx198.postini.com [74.125.245.198]) by kanga.kvack.org (Postfix) with SMTP id E78566B0069 for ; Thu, 14 Jun 2012 12:11:09 -0400 (EDT) Received: by yhr47 with SMTP id 47so2068018yhr.14 for ; Thu, 14 Jun 2012 09:11:09 -0700 (PDT) MIME-Version: 1.0 In-Reply-To: <20120614145716.GA2097@barrios> References: <1339661592-3915-1-git-send-email-kosaki.motohiro@gmail.com> <20120614145716.GA2097@barrios> From: KOSAKI Motohiro Date: Thu, 14 Jun 2012 12:10:47 -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: Minchan Kim Cc: linux-kernel@vger.kernel.org, linux-mm@kvack.org, akpm@linux-foundation.org, Nick Piggin , Michal Hocko , Johannes Weiner , Mel Gorman , KAMEZAWA Hiroyuki , Minchan Kim On Thu, Jun 14, 2012 at 10:57 AM, Minchan Kim wrote: > Hi KOSAKI, > > Sorry for late response. > Let me ask a question about description. > > On Thu, Jun 14, 2012 at 04:13:12AM -0400, 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. > > I have tried imagined scenario you mentioned above with code level but > unfortunately I got failed. > If kswapd can't meet high watermark on order-0, it doesn't sleep if I don= 't miss something. pgdat_balanced() doesn't recognized zone. Therefore kswapd may sleep if node has multiple zones. Hm ok, I realized my descriptions was slightly misleading. priority 0 is not needed. bakance_pddat() calls pgdat_balanced() every priority. Most easy case is, movable zone has a lot of free pages and normal zone has no reclaimable page. btw, current pgdat_balanced() logic seems not correct. kswapd should sleep only if every zones have much free pages than high water mark _and_ 25% of present pages in node are free. > So if kswapd sleeps, it means we already have enough order-0 free pages. > Hmm, could you describe scenario you found in detail with code level? > > Anyway, as I look at your patch, I can't find any problem. > I just want to understand scenario you mentioned completely in my head. > Maybe It can help making description clear. > -- 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