Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S932749Ab1ELUbl (ORCPT ); Thu, 12 May 2011 16:31:41 -0400 Received: from bedivere.hansenpartnership.com ([66.63.167.143]:58777 "EHLO bedivere.hansenpartnership.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S932580Ab1ELUbj (ORCPT ); Thu, 12 May 2011 16:31:39 -0400 Subject: Re: [PATCH 3/3] mm: slub: Default slub_max_order to 0 From: James Bottomley To: Johannes Weiner Cc: Pekka Enberg , Christoph Lameter , Mel Gorman , Andrew Morton , Colin King , Raghavendra D Prabhu , Jan Kara , Chris Mason , Rik van Riel , linux-fsdevel , linux-mm , linux-kernel , linux-ext4 In-Reply-To: <20110512202917.GK16531@cmpxchg.org> References: <1305127773-10570-1-git-send-email-mgorman@suse.de> <1305127773-10570-4-git-send-email-mgorman@suse.de> <1305213359.2575.46.camel@mulgrave.site> <1305214993.2575.50.camel@mulgrave.site> <1305215742.27848.40.camel@jaguar> <1305225467.2575.66.camel@mulgrave.site> <1305229447.2575.71.camel@mulgrave.site> <1305230652.2575.72.camel@mulgrave.site> <20110512202917.GK16531@cmpxchg.org> Content-Type: text/plain; charset="UTF-8" Date: Thu, 12 May 2011 15:31:35 -0500 Message-ID: <1305232295.2575.82.camel@mulgrave.site> Mime-Version: 1.0 X-Mailer: Evolution 2.32.1 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2331 Lines: 54 On Thu, 2011-05-12 at 22:29 +0200, Johannes Weiner wrote: > On Thu, May 12, 2011 at 03:04:12PM -0500, James Bottomley wrote: > > On Thu, 2011-05-12 at 14:44 -0500, James Bottomley wrote: > > > On Thu, 2011-05-12 at 13:37 -0500, James Bottomley wrote: > > > > On Thu, 2011-05-12 at 18:55 +0300, Pekka Enberg wrote: > > > > > On Thu, 2011-05-12 at 10:43 -0500, James Bottomley wrote: > > > > > > However, since you admit even you see problems, let's concentrate on > > > > > > fixing them rather than recriminations? > > > > > > > > > > Yes, please. So does dropping max_order to 1 help? > > > > > PAGE_ALLOC_COSTLY_ORDER is set to 3 in 2.6.39-rc7. > > > > > > > > Just booting with max_slab_order=1 (and none of the other patches > > > > applied) I can still get the machine to go into kswapd at 99%, so it > > > > doesn't seem to make much of a difference. > > > > > > > > Do you want me to try with the other two patches and max_slab_order=1? > > > > > > OK, so patches 1 + 2 plus setting slub_max_order=1 still manages to > > > trigger the problem (kswapd spinning at 99%). This is still with > > > PREEMPT; it's possible that non-PREEMPT might be better, so I'll try > > > patches 1+2+3 with PREEMPT just to see if the perturbation is caused by > > > it. > > > > Confirmed, I'm afraid ... I can trigger the problem with all three > > patches under PREEMPT. It's not a hang this time, it's just kswapd > > taking 100% system time on 1 CPU and it won't calm down after I unload > > the system. > > That is kind of expected, though. If one CPU is busy with a streaming > IO load generating new pages, kswapd is busy reclaiming the old ones > so that the generator does not have to do the reclaim itself. > > By unload, do you mean stopping the generator? Correct. > And if so, how quickly > after you stop the generator does kswapd go back to sleep? It doesn't. At least not on its own; the CPU stays pegged. If I start other work (like a kernel compile), then sometimes it does go back to nothing. I'm speculating that this is the hang case for non-PREEMPT. James -- 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/