From mboxrd@z Thu Jan 1 00:00:00 1970 Date: Wed, 19 Sep 2007 15:17:45 -0700 From: Andrew Morton Subject: Re: [PATCH] mm: use pagevec to rotate reclaimable page Message-Id: <20070919151745.1e12a671.akpm@linux-foundation.org> In-Reply-To: <6.0.0.20.2.20070918193944.038e2ea0@172.19.0.2> References: <6.0.0.20.2.20070907113025.024dfbb8@172.19.0.2> <20070913193711.ecc825f7.akpm@linux-foundation.org> <6.0.0.20.2.20070918193944.038e2ea0@172.19.0.2> Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: owner-linux-mm@kvack.org Return-Path: To: Hisashi Hifumi Cc: linux-kernel@vger.kernel.org, linux-mm@kvack.org List-ID: On Tue, 18 Sep 2007 19:41:14 +0900 Hisashi Hifumi wrote: > > > >So I do think that for safety and sanity's sake, we should be taking a ref > >on the pages when they are in a pagevec. That's going to hurt your nice > >performance numbers :( > > > > I did ping test again to observe performance deterioration caused by taking > a ref. > > -2.6.23-rc6-with-modifiedpatch > --- testmachine ping statistics --- > 3000 packets transmitted, 3000 received, 0% packet loss, time 53386ms > rtt min/avg/max/mdev = 0.074/0.110/4.716/0.147 ms, pipe 2, ipg/ewma > 17.801/0.129 ms > > The result for my original patch is as follows. > > -2.6.23-rc5-with-originalpatch > --- testmachine ping statistics --- > 3000 packets transmitted, 3000 received, 0% packet loss, time 51924ms > rtt min/avg/max/mdev = 0.072/0.108/3.884/0.114 ms, pipe 2, ipg/ewma > 17.314/0.091 ms > > > The influence to response was small. well.. that's not really the test which will show up any regressions. The extra get_page/put_page will affect things like kernel CPU utilisation on fast writeout on a single CPU. Say, run a huge write against a fast storage system on a single pentium 4 CPU and see how much the system CPU time is increased. The kernel's internal cpu accounting probably won't be accurate enough to get believeable numbers from a test like this - better to use the subtractive approach: see http://www.zipworld.com.au/~akpm/linux/#zc -- 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