From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1757458Ab0CLMPW (ORCPT ); Fri, 12 Mar 2010 07:15:22 -0500 Received: from mtagate6.uk.ibm.com ([194.196.100.166]:33061 "EHLO mtagate6.uk.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753879Ab0CLMPV (ORCPT ); Fri, 12 Mar 2010 07:15:21 -0500 Message-ID: <4B9A3049.7010602@linux.vnet.ibm.com> Date: Fri, 12 Mar 2010 13:15:05 +0100 From: Christian Ehrhardt User-Agent: Thunderbird 2.0.0.23 (X11/20090817) MIME-Version: 1.0 To: Mel Gorman CC: Andrew Morton , linux-mm@kvack.org, Nick Piggin , Chris Mason , Jens Axboe , linux-kernel@vger.kernel.org Subject: Re: [RFC PATCH 0/3] Avoid the use of congestion_wait under zone pressure References: <1268048904-19397-1-git-send-email-mel@csn.ul.ie> <20100311154124.e1e23900.akpm@linux-foundation.org> <4B99E19E.6070301@linux.vnet.ibm.com> <20100312020526.d424f2a8.akpm@linux-foundation.org> <20100312104712.GB18274@csn.ul.ie> In-Reply-To: <20100312104712.GB18274@csn.ul.ie> Content-Type: text/plain; charset=ISO-8859-15; format=flowed Content-Transfer-Encoding: 8bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Mel Gorman wrote: > On Fri, Mar 12, 2010 at 02:05:26AM -0500, Andrew Morton wrote: >> On Fri, 12 Mar 2010 07:39:26 +0100 Christian Ehrhardt wrote: >> >>> >>> Andrew Morton wrote: >>>> On Mon, 8 Mar 2010 11:48:20 +0000 >>>> Mel Gorman wrote: [...] >> If not, we broke it again. >> > > We were broken with respect to this in the first place. That > cond_reched() is badly placed and waiting on congestion when congestion > might not be involved is also a bit odd. > > It's possible that Christian's specific problem would also be addressed > by the following patch. Christian, willing to test? Will is here, but no chance before monday/tuesday to get a free machine slot - I'll post results as soon as I get them. > It still feels a bit unnatural though that the page allocator waits on > congestion when what it really cares about is watermarks. Even if this > patch works for Christian, I think it still has merit so will kick it a > few more times. In whatever way I can look at it watermark_wait should be supperior to congestion_wait. Because as Mel points out waiting for watermarks is what is semantically correct there. If there eventually some day comes a solution without any of those waits I'm fine too - e.g. by closing whatever races we have and fixing that one context can never run into this in direct_reclaim: 1. free pages with try_to_free 2. not getting one in the subsequent get_page call But as long as we have a wait - watermark waiting > congestion waiting (IMHO). > ==== CUT HERE ==== > page-allocator: Attempt page allocation immediately after direct reclaim [...] -- Grüsse / regards, Christian Ehrhardt IBM Linux Technology Center, System z Linux Performance