Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756413Ab2FNQLM (ORCPT ); Thu, 14 Jun 2012 12:11:12 -0400 Received: from mail-yw0-f46.google.com ([209.85.213.46]:41015 "EHLO mail-yw0-f46.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1756313Ab2FNQLJ convert rfc822-to-8bit (ORCPT ); Thu, 14 Jun 2012 12:11:09 -0400 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 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 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: 2357 Lines: 54 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 >> ? ?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. > > 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 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/