From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail137.messagelabs.com (mail137.messagelabs.com [216.82.249.19]) by kanga.kvack.org (Postfix) with ESMTP id 894176B002C for ; Tue, 11 Oct 2011 16:54:51 -0400 (EDT) Received: by pzk4 with SMTP id 4so1295pzk.6 for ; Tue, 11 Oct 2011 13:54:49 -0700 (PDT) Date: Tue, 11 Oct 2011 13:54:45 -0700 From: Andrew Morton Subject: Re: [PATCH -v2 -mm] add extra free kbytes tunable Message-Id: <20111011135445.f580749b.akpm@linux-foundation.org> In-Reply-To: <65795E11DBF1E645A09CEC7EAEE94B9CB516CBFE@USINDEVS02.corp.hds.com> 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> Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: owner-linux-mm@kvack.org List-ID: To: Satoru Moriya Cc: David Rientjes , Rik van Riel , 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 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. 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. > Also, if we increase the free-page reserves a.k.a min_free_kbytes, > the possibility of direct reclaim on other workloads increases. > I think it's a bad side effect. extra_free_kbytes has the same side-effect. -- 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