From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from psmtp.com (na3sys010amx184.postini.com [74.125.245.184]) by kanga.kvack.org (Postfix) with SMTP id C0CF26B0087 for ; Tue, 30 Oct 2012 15:06:55 -0400 (EDT) Message-ID: <509025ED.8050207@redhat.com> Date: Tue, 30 Oct 2012 15:09:33 -0400 From: Rik van Riel MIME-Version: 1.0 Subject: Re: [PATCH RFC] mm,vmscan: only evict file pages when we have plenty References: <20121030144204.0aa14d92@dull> <20121030115451.f4c097f0.akpm@linux-foundation.org> In-Reply-To: <20121030115451.f4c097f0.akpm@linux-foundation.org> Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Sender: owner-linux-mm@kvack.org List-ID: To: Andrew Morton Cc: linux-mm@kvack.org, linux-kernel@vger.kernel.org, klamm@yandex-team.ru, mgorman@suse.de, hannes@cmpxchg.org On 10/30/2012 02:54 PM, Andrew Morton wrote: > On Tue, 30 Oct 2012 14:42:04 -0400 > Rik van Riel wrote: > >> If we have more inactive file pages than active file pages, we >> skip scanning the active file pages alltogether, with the idea >> that we do not want to evict the working set when there is >> plenty of streaming IO in the cache. > > Yes, I've never liked that. The "(active > inactive)" thing is a magic > number. And suddenly causing a complete cessation of vm scanning at a > particular magic threshold seems rather crude, compared to some complex > graduated thing which will also always do the wrong thing, only more > obscurely ;) > > Ho hum, in the absence of observed problems, I guess we don't muck with > it. The thing is, when we "suddenly switch behaviour" back to scanning all the lists, that does not have to suddenly lead to pages from the other lists being actually evicted. Instead, it will lead to referenced inactive_anon pages being moved back to the active_anon list, and any pages from the end of the active_file list being moved to the inactive_file list. There is a threshold, and Johannes has patches to set the threshold in a much more intelligent way, but the change in behaviour should not be sudden due to the inactive lists providing a rather large buffer. When the VM is bouncing around the threshold, it should look like a reduction in the rate at which the other lists are scanned. -- 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/ . Don't email: email@kvack.org