From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753444Ab1JLT6u (ORCPT ); Wed, 12 Oct 2011 15:58:50 -0400 Received: from mx1.redhat.com ([209.132.183.28]:43461 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752039Ab1JLT6t (ORCPT ); Wed, 12 Oct 2011 15:58:49 -0400 Message-ID: <4E95F167.5050709@redhat.com> Date: Wed, 12 Oct 2011 15:58:31 -0400 From: Rik van Riel User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:6.0.2) Gecko/20110906 Thunderbird/6.0.2 MIME-Version: 1.0 To: Andrew Morton CC: Satoru Moriya , David Rientjes , Randy Dunlap , Satoru Moriya , "linux-kernel@vger.kernel.org" , "linux-mm@kvack.org" , "lwoodman@redhat.com" , Seiji Aguchi , "hughd@google.com" , "hannes@cmpxchg.org" Subject: Re: [PATCH -v2 -mm] add extra free kbytes tunable References: <20110901105208.3849a8ff@annuminas.surriel.com> <20110901100650.6d884589.rdunlap@xenotime.net> <20110901152650.7a63cb8b@annuminas.surriel.com> <20111010153723.6397924f.akpm@linux-foundation.org> <65795E11DBF1E645A09CEC7EAEE94B9CB516CBC4@USINDEVS02.corp.hds.com> <20111011125419.2702b5dc.akpm@linux-foundation.org> <65795E11DBF1E645A09CEC7EAEE94B9CB516CBFE@USINDEVS02.corp.hds.com> <20111011135445.f580749b.akpm@linux-foundation.org> <4E95917D.3080507@redhat.com> <20111012122018.690bdf28.akpm@linux-foundation.org> In-Reply-To: <20111012122018.690bdf28.akpm@linux-foundation.org> Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 10/12/2011 03:20 PM, Andrew Morton wrote: > On Wed, 12 Oct 2011 09:09:17 -0400 > Rik van Riel wrote: >> The problem is that we may be dealing with bursts, not steady >> states of allocations. Without knowing the size of a burst, >> we have no idea when we should wake up kswapd to get enough >> memory freed ahead of the application's allocations. > > That problem remains with this patch - it just takes a larger burst. > > Unless the admin somehow manages to configure the tunable large enough > to cover the largest burst, and there aren't other applications > allocating memory during that burst, and the time between bursts is > sufficient for kswapd to be able to sufficiently replenish free-page > reserves. All of which sounds rather unlikely. It depends on the system. For a setup which is packed to the brim with workloads, this patch is not likely to help. On the other hand, on a system that is packed to the brim with workloads, you are unlikely to get low latencies anyway. For situations where people really care about low latencies, I imagine having dedicated hardware for a workload is not at all unusual, and the patch works for that. >>> Look, please don't go bending over backwards like this to defend a bad >>> patch. It's a bad patch! It would be better not to have to merge it. >>> Let's do something better. >> >> I would love it if we could come up with something better, >> and have thought about it a lot. >> >> However, so far we do not seem to have an alternative yet :( > > Do we actually have a real-world application which is hurting from > this? Satoru-san?