Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756209Ab1EMFjH (ORCPT ); Fri, 13 May 2011 01:39:07 -0400 Received: from mail-qw0-f46.google.com ([209.85.216.46]:42017 "EHLO mail-qw0-f46.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755919Ab1EMFjF convert rfc822-to-8bit (ORCPT ); Fri, 13 May 2011 01:39:05 -0400 DomainKey-Signature: a=rsa-sha1; c=nofws; d=gmail.com; s=gamma; h=mime-version:in-reply-to:references:date:message-id:subject:from:to :cc:content-type:content-transfer-encoding; b=E/rW+4CCVmxwXcYPHCXEjNy2VxpwWqT87jVz389TLgN6CAj/IC1SoJ/ehn6C45+waz TJIfka1YDAKP1gUnqkA7/YimilAOT3nYpmpyogn14NPcY9UjaABn0lc/t+tXtWpdIuLO FGgs4XJfyeSkSmCft54ehLG7MHJZ/w2591mz8= MIME-Version: 1.0 In-Reply-To: References: <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> <1305237882.2575.100.camel@mulgrave.site> <20110512221506.GM16531@cmpxchg.org> Date: Fri, 13 May 2011 14:39:03 +0900 Message-ID: Subject: Re: [PATCH 3/3] mm: slub: Default slub_max_order to 0 From: Minchan Kim To: Johannes Weiner Cc: James Bottomley , 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 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8BIT Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2965 Lines: 76 On Fri, May 13, 2011 at 7:58 AM, Minchan Kim wrote: > On Fri, May 13, 2011 at 7:15 AM, Johannes Weiner wrote: >> On Thu, May 12, 2011 at 05:04:41PM -0500, James Bottomley wrote: >>> On Thu, 2011-05-12 at 15:04 -0500, James Bottomley wrote: >>> > 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. >>> >>> Just on a "if you don't know what's wrong poke about and see" basis, I >>> sliced out all the complex logic in sleeping_prematurely() and, as far >>> as I can tell, it cures the problem behaviour.  I've loaded up the >>> system, and taken the tar load generator through three runs without >>> producing a spinning kswapd (this is PREEMPT).  I'll try with a >>> non-PREEMPT kernel shortly. >>> >>> What this seems to say is that there's a problem with the complex logic >>> in sleeping_prematurely().  I'm pretty sure hacking up >>> sleeping_prematurely() just to dump all the calculations is the wrong >>> thing to do, but perhaps someone can see what the right thing is ... >> >> I think I see the problem: the boolean logic of sleeping_prematurely() >> is odd.  If it returns true, kswapd will keep running.  So if >> pgdat_balanced() returns true, kswapd should go to sleep. >> >> This? > > Yes. Good catch. In addition, I see some strange thing. The comment in pgdat_balanced says "Only zones that meet watermarks and are in a zone allowed by the callers classzone_idx are added to balanced_pages" It's true in case of balance_pgdat but it's not true in sleeping_prematurely. This? barrios@barrios-desktop:~/linux-mmotm$ git diff mm/vmscan.c diff --git a/mm/vmscan.c b/mm/vmscan.c index 292582c..d9078cf 100644 --- a/mm/vmscan.c +++ b/mm/vmscan.c @@ -2322,7 +2322,8 @@ static bool sleeping_prematurely(pg_data_t *pgdat, int order, long remaining, classzone_idx, 0)) all_zones_ok = false; else - balanced += zone->present_pages; + if (i <= classzone_idx) + balanced += zone->present_pages; } /* @@ -2331,7 +2332,7 @@ static bool sleeping_prematurely(pg_data_t *pgdat, int order, long remaining, * must be balanced */ if (order) - return pgdat_balanced(pgdat, balanced, classzone_idx); + return !pgdat_balanced(pgdat, balanced, classzone_idx); else return !all_zones_ok; } -- Kind regards, Minchan Kim -- 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/