From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-wi0-f179.google.com (mail-wi0-f179.google.com [209.85.212.179]) by kanga.kvack.org (Postfix) with ESMTP id A14CD82BEF for ; Sat, 8 Nov 2014 17:18:41 -0500 (EST) Received: by mail-wi0-f179.google.com with SMTP id h11so7450064wiw.0 for ; Sat, 08 Nov 2014 14:18:41 -0800 (PST) Received: from mx2.suse.de (cantor2.suse.de. [195.135.220.15]) by mx.google.com with ESMTPS id eu6si22328440wjb.48.2014.11.08.14.18.40 for (version=TLSv1 cipher=ECDHE-RSA-RC4-SHA bits=128/128); Sat, 08 Nov 2014 14:18:40 -0800 (PST) Message-ID: <545E96BD.5040103@suse.cz> Date: Sat, 08 Nov 2014 23:18:37 +0100 From: Vlastimil Babka MIME-Version: 1.0 Subject: Re: Early test: hangs in mm/compact.c w. Linus's 12d7aacab56e9ef185c References: <12996532.NCRhVKzS9J@xorhgos3.pefnos> <3583067.00bS4AInhm@xorhgos3.pefnos> <545BEA3B.40005@suse.cz> <3443150.6EQzxj6Rt9@xorhgos3.pefnos> In-Reply-To: <3443150.6EQzxj6Rt9@xorhgos3.pefnos> Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 7bit Sender: owner-linux-mm@kvack.org List-ID: To: "P. Christeas" Cc: linux-mm@kvack.org, Joonsoo Kim , lkml , David Rientjes , Norbert Preining , Markus Trippelsdorf , Pavel Machek On 11/08/2014 02:11 PM, P. Christeas wrote: > On Thursday 06 November 2014, Vlastimil Babka wrote: >>> On Wednesday 05 November 2014, Vlastimil Babka wrote: >>>> Can you please try the following patch? >>>> - compaction_defer_reset(zone, order, false); >> Oh and did I ask in this thread for /proc/zoneinfo yet? :) > > Using that same kernel[1], got again into a race, gathered a few more data. > > This time, I had 1x "urpmq" process [2] hung at 100% CPU , when "kwin" got > apparently blocked (100% CPU, too) trying to resize a GUI window. I suppose > the resizing operation would mean heavy memory alloc/free. > > The rest of the system was responsive, I could easily get a console, login, > gather the files.. Then, I have *killed* -9 the "urpmq" process, which solved > the race and my system is still alive! "kwin" is still running, returned to > regular CPU load. > > Attached is traces from SysRq+l (pressed a few times, wanted to "snapshot" the > stack) and /proc/zoneinfo + /proc/vmstat > > Bisection is not yet meaningful, IMHO, because I cannot be sure that "good" > points are really free from this issue. I'd estimate that each test would take > +3days, unless I really find a deterministic way to reproduce the issue . Hi, I think I finally found the cause by staring into the code... CCing people from all 4 separate threads I know about this issue. The problem with finding the cause was that the first report I got from Markus was about isolate_freepages_block() overhead, and later Norbert reported that reverting a patch for isolate_freepages* helped. But the problem seems to be that although the loop in isolate_migratepages exits because the scanners almost meet (they are within same pageblock), they don't truly meet, therefore compact_finished() decides to continue, but isolate_migratepages() exits immediately... boom! But indeed e14c720efdd7 made this situation possible, as free scaner pfn can now point to a middle of pageblock. So I hope the attached patch will fix the soft-lockup issues in compact_zone. Please apply on 3.18-rc3 or later without any other reverts, and test. It probably won't help Markus and his isolate_freepages_block() overhead though... Thanks, Vlastimil ------8<------