From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753315Ab1JLNJc (ORCPT ); Wed, 12 Oct 2011 09:09:32 -0400 Received: from mx1.redhat.com ([209.132.183.28]:17603 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753023Ab1JLNJ3 (ORCPT ); Wed, 12 Oct 2011 09:09:29 -0400 Message-ID: <4E95917D.3080507@redhat.com> Date: Wed, 12 Oct 2011 09:09:17 -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> In-Reply-To: <20111011135445.f580749b.akpm@linux-foundation.org> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 10/11/2011 04:54 PM, Andrew Morton wrote: > On Tue, 11 Oct 2011 16:23:22 -0400 > Satoru Moriya wrote: > >> On 10/11/2011 03:55 PM, Andrew Morton wrote: >>> On Tue, 11 Oct 2011 15:32:11 -0400 >>> Satoru Moriya wrote: >>> >>>> On 10/10/2011 06:37 PM, Andrew Morton wrote: >>>>> On Fri, 7 Oct 2011 20:08:19 -0700 (PDT) David Rientjes >>>>> wrote: >>>>> >>>>>> On Thu, 1 Sep 2011, Rik van Riel wrote: >>>> >>>> Actually page allocator decreases min watermark to 3/4 * min >>>> watermark for rt-task. But in our case some applications create a lot >>>> of processes and if all of them are rt-task, the amount of watermark >>>> bonus(1/4 * min watermark) is not enough. >>>> >>>> If we can tune the amount of bonus, it may be fine. But that is >>>> almost all same as extra free kbytes. >>> >>> This situation is detectable at runtime. If realtime tasks are being >>> stalled in the page allocator then start to increase the free-page >>> reserves. A little control system. >> >> Detecting at runtime is too late for some latency critical systems. >> At that system, we must avoid a stall before it happens. > > It's pretty darn obvious that the kernel can easily see the situation > developing before it happens. By comparing a few integers. 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. > 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 :( -- All rights reversed From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail6.bemta8.messagelabs.com (mail6.bemta8.messagelabs.com [216.82.243.55]) by kanga.kvack.org (Postfix) with ESMTP id EBED06B016D for ; Wed, 12 Oct 2011 09:09:28 -0400 (EDT) Message-ID: <4E95917D.3080507@redhat.com> Date: Wed, 12 Oct 2011 09:09:17 -0400 From: Rik van Riel MIME-Version: 1.0 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> In-Reply-To: <20111011135445.f580749b.akpm@linux-foundation.org> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit Sender: owner-linux-mm@kvack.org List-ID: 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" On 10/11/2011 04:54 PM, Andrew Morton wrote: > On Tue, 11 Oct 2011 16:23:22 -0400 > Satoru Moriya wrote: > >> On 10/11/2011 03:55 PM, Andrew Morton wrote: >>> On Tue, 11 Oct 2011 15:32:11 -0400 >>> Satoru Moriya wrote: >>> >>>> On 10/10/2011 06:37 PM, Andrew Morton wrote: >>>>> On Fri, 7 Oct 2011 20:08:19 -0700 (PDT) David Rientjes >>>>> wrote: >>>>> >>>>>> On Thu, 1 Sep 2011, Rik van Riel wrote: >>>> >>>> Actually page allocator decreases min watermark to 3/4 * min >>>> watermark for rt-task. But in our case some applications create a lot >>>> of processes and if all of them are rt-task, the amount of watermark >>>> bonus(1/4 * min watermark) is not enough. >>>> >>>> If we can tune the amount of bonus, it may be fine. But that is >>>> almost all same as extra free kbytes. >>> >>> This situation is detectable at runtime. If realtime tasks are being >>> stalled in the page allocator then start to increase the free-page >>> reserves. A little control system. >> >> Detecting at runtime is too late for some latency critical systems. >> At that system, we must avoid a stall before it happens. > > It's pretty darn obvious that the kernel can easily see the situation > developing before it happens. By comparing a few integers. 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. > 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 :( -- All rights reversed -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Fight unfair telecom internet charges in Canada: sign http://stopthemeter.ca/ Don't email: email@kvack.org