Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1759001Ab0D3Sg5 (ORCPT ); Fri, 30 Apr 2010 14:36:57 -0400 Received: from mx1.redhat.com ([209.132.183.28]:30982 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S933111Ab0D3RVv (ORCPT ); Fri, 30 Apr 2010 13:21:51 -0400 Message-ID: <4BDA8324.7090409@redhat.com> Date: Fri, 30 Apr 2010 10:13:40 +0300 From: Avi Kivity User-Agent: Mozilla/5.0 (X11; U; Linux x86_64; en-US; rv:1.9.1.9) Gecko/20100330 Fedora/3.0.4-1.fc12 Thunderbird/3.0.4 MIME-Version: 1.0 To: Dave Hansen CC: Pavel Machek , Dan Magenheimer , linux-kernel@vger.kernel.org, linux-mm@kvack.org, jeremy@goop.org, hugh.dickins@tiscali.co.uk, ngupta@vflare.org, JBeulich@novell.com, chris.mason@oracle.com, kurt.hackel@oracle.com, dave.mccracken@oracle.com, npiggin@suse.de, akpm@linux-foundation.org, riel@redhat.com Subject: Re: Frontswap [PATCH 0/4] (was Transcendent Memory): overview References: <4BD16D09.2030803@redhat.com> <4BD1A74A.2050003@redhat.com> <4830bd20-77b7-46c8-994b-8b4fa9a79d27@default> <4BD1B427.9010905@redhat.com> <4BD1B626.7020702@redhat.com> <5fa93086-b0d7-4603-bdeb-1d6bfca0cd08@default> <4BD3377E.6010303@redhat.com> <1c02a94a-a6aa-4cbb-a2e6-9d4647760e91@default4BD43033.7090706@redhat.com> <20100428055538.GA1730@ucw.cz> <1272591924.23895.807.camel@nimitz> In-Reply-To: <1272591924.23895.807.camel@nimitz> 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 Content-Length: 1192 Lines: 27 On 04/30/2010 04:45 AM, Dave Hansen wrote: > > A large portion of CMM2's gain came from the fact that you could take > memory away from guests without _them_ doing any work. If the system is > experiencing a load spike, you increase load even more by making the > guests swap. If you can just take some of their memory away, you can > smooth that spike out. CMM2 and frontswap do that. The guests > explicitly give up page contents that the hypervisor does not have to > first consult with the guest before discarding. > Frontswap does not do this. Once a page has been frontswapped, the host is committed to retaining it until the guest releases it. It's really not very different from a synchronous swap device. I think cleancache allows the hypervisor to drop pages without the guest's immediate knowledge, but I'm not sure. -- I have a truly marvellous patch that fixes the bug which this signature is too narrow to contain. -- 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/