Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S932137AbVLaK5k (ORCPT ); Sat, 31 Dec 2005 05:57:40 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S932134AbVLaK5k (ORCPT ); Sat, 31 Dec 2005 05:57:40 -0500 Received: from amsfep16-int.chello.nl ([213.46.243.25]:12321 "EHLO amsfep16-int.chello.nl") by vger.kernel.org with ESMTP id S932140AbVLaK5j (ORCPT ); Sat, 31 Dec 2005 05:57:39 -0500 Subject: Re: [PATCH 6/9] clockpro-clockpro.patch From: Peter Zijlstra To: Rik van Riel Cc: Marcelo Tosatti , linux-mm@kvack.org, linux-kernel@vger.kernel.org, Andrew Morton , Christoph Lameter , Wu Fengguang , Nick Piggin , Marijn Meijles In-Reply-To: References: <20051230223952.765.21096.sendpatchset@twins.localnet> <20051230224312.765.58575.sendpatchset@twins.localnet> <20051231002417.GA4913@dmt.cnet> <20051231032702.GA9136@dmt.cnet> Content-Type: text/plain Date: Sat, 31 Dec 2005 11:57:13 +0100 Message-Id: <1136026633.17853.52.camel@twins> Mime-Version: 1.0 X-Mailer: Evolution 2.4.1 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1353 Lines: 32 On Sat, 2005-12-31 at 00:24 -0500, Rik van Riel wrote: > > > > Why do you use only two clock hands and not three (HandHot, HandCold and > > > > HandTest) as in the original paper? > > > > > > Because the non-resident pages cannot be in the clock. > > > This is both because of space overhead, and because the > > > non-resident list cannot be per zone. > > > > I see - that is a fundamental change from the original CLOCK-Pro > > algorithm, right? > > > > Do you have a clear idea about the consequences of not having > > non-resident pages in the clock? > > The consequence is that we could falsely consider a non-resident > page to be active, or not to be active. However, this can only > happen if we let the scan rate in each of the memory zones get > way too much out of whack (which is bad regardless). Yes, the uncertainty of position causes a time uncertainty wrt. terminating the test period (heisenberg anyone?). So individual pages can be terminated either too soon or too late, however statistics make it come out even in the end. -- Peter Zijlstra - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/