From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S937584Ab0CPJGP (ORCPT ); Tue, 16 Mar 2010 05:06:15 -0400 Received: from mx1.redhat.com ([209.132.183.28]:59082 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S934606Ab0CPJGL (ORCPT ); Tue, 16 Mar 2010 05:06:11 -0400 Message-ID: <4B9F49F1.70202@redhat.com> Date: Tue, 16 Mar 2010 11:05:53 +0200 From: Avi Kivity User-Agent: Mozilla/5.0 (X11; U; Linux x86_64; en-US; rv:1.9.1.8) Gecko/20100301 Fedora/3.0.3-1.fc12 Thunderbird/3.0.3 MIME-Version: 1.0 To: Anthony Liguori CC: balbir@linux.vnet.ibm.com, KVM development list , Rik van Riel , KAMEZAWA Hiroyuki , "linux-mm@kvack.org" , "linux-kernel@vger.kernel.org" Subject: Re: [PATCH][RF C/T/D] Unmapped page cache control - via boot parameter References: <20100315072214.GA18054@balbir.in.ibm.com> <4B9DE635.8030208@redhat.com> <20100315080726.GB18054@balbir.in.ibm.com> <4B9DEF81.6020802@redhat.com> <20100315091720.GC18054@balbir.in.ibm.com> <4B9DFD9C.8030608@redhat.com> <4B9E810E.9010706@codemonkey.ws> In-Reply-To: <4B9E810E.9010706@codemonkey.ws> Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 03/15/2010 08:48 PM, Anthony Liguori wrote: > On 03/15/2010 04:27 AM, Avi Kivity wrote: >> >> That's only beneficial if the cache is shared. Otherwise, you could >> use the balloon to evict cache when memory is tight. >> >> Shared cache is mostly a desktop thing where users run similar >> workloads. For servers, it's much less likely. So a modified-guest >> doesn't help a lot here. > > Not really. In many cloud environments, there's a set of common > images that are instantiated on each node. Usually this is because > you're running a horizontally scalable application or because you're > supporting an ephemeral storage model. But will these servers actually benefit from shared cache? So the images are shared, they boot up, what then? - apache really won't like serving static files from the host pagecache - dynamic content (java, cgi) will be mostly in anonymous memory, not pagecache - ditto for application servers - what else are people doing? > In fact, with ephemeral storage, you typically want to use > cache=writeback since you aren't providing data guarantees across > shutdown/failure. Interesting point. We'd need a cache=volatile for this use case to avoid the fdatasync()s we do now. Also useful for -snapshot. In fact I have a patch for this somewhere I can dig out. -- error compiling committee.c: too many arguments to function