From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753123AbXCMFGE (ORCPT ); Tue, 13 Mar 2007 01:06:04 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1753120AbXCMFGE (ORCPT ); Tue, 13 Mar 2007 01:06:04 -0400 Received: from smtp.osdl.org ([65.172.181.24]:60790 "EHLO smtp.osdl.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753124AbXCMFGC (ORCPT ); Tue, 13 Mar 2007 01:06:02 -0400 Date: Mon, 12 Mar 2007 22:04:39 -0800 From: Andrew Morton To: Herbert Poetzl Cc: hansendc@us.ibm.com, containers@lists.osdl.org, linux-kernel@vger.kernel.org, menage@google.com, xemul@sw.ru Subject: Re: [RFC][PATCH 2/7] RSS controller core Message-Id: <20070312220439.677b4787.akpm@linux-foundation.org> In-Reply-To: <20070312224129.GC21258@MAIL.13thfloor.at> References: <45ED7DEC.7010403@sw.ru> <45ED80E1.7030406@sw.ru> <20070306140036.4e85bd2f.akpm@linux-foundation.org> <45F3F581.9030503@sw.ru> <20070311045111.62d3e9f9.akpm@linux-foundation.org> <20070312010039.GC21861@MAIL.13thfloor.at> <1173724979.11945.103.camel@localhost.localdomain> <20070312224129.GC21258@MAIL.13thfloor.at> X-Mailer: Sylpheed version 2.2.4 (GTK+ 2.8.19; i686-pc-linux-gnu) Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org > On Mon, 12 Mar 2007 23:41:29 +0100 Herbert Poetzl wrote: > On Mon, Mar 12, 2007 at 11:42:59AM -0700, Dave Hansen wrote: > > How about we drill down on these a bit more. > > > > On Mon, 2007-03-12 at 02:00 +0100, Herbert Poetzl wrote: > > > - shared mappings of 'shared' files (binaries > > > and libraries) to allow for reduced memory > > > footprint when N identical guests are running > > > > So, it sounds like this can be phrased as a requirement like: > > > > "Guests must be able to share pages." > > > > Can you give us an idea why this is so? > > sure, one reason for this is that guests tend to > be similar (or almost identical) which results > in quite a lot of 'shared' libraries and executables > which would otherwise get cached for each guest and > would also be mapped for each guest separately nooooooo. What you're saying there amounts to text replication. There is no proposal here to create duplicated copies of pagecache pages: the VM just doesn't support that (Nick has soe protopatches which do this as a possible NUMA optimisation). So these mmapped pages will contiue to be shared across all guests. The problem boils down to "which guest(s) get charged for each shared page". A simple and obvious and easy-to-implement answer is "the guest which paged it in". I think we should firstly explain why that is insufficient.