From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753820Ab0CQJLT (ORCPT ); Wed, 17 Mar 2010 05:11:19 -0400 Received: from mx1.redhat.com ([209.132.183.28]:48881 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753358Ab0CQJLR (ORCPT ); Wed, 17 Mar 2010 05:11:17 -0400 Message-ID: <4BA09C9D.1030608@redhat.com> Date: Wed, 17 Mar 2010 11:10:53 +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: Christoph Hellwig CC: Chris Webb , balbir@linux.vnet.ibm.com, KVM development list , Rik van Riel , KAMEZAWA Hiroyuki , "linux-mm@kvack.org" , "linux-kernel@vger.kernel.org" , Kevin Wolf 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> <20100315202353.GJ3840@arachsys.com> <4B9F4CBD.3020805@redhat.com> <20100316102637.GA23584@lst.de> <4B9F5F2F.8020501@redhat.com> <20100316104422.GA24258@lst.de> <4B9F66AC.5080400@redhat.com> <20100317084911.GA9098@lst.de> In-Reply-To: <20100317084911.GA9098@lst.de> 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 03/17/2010 10:49 AM, Christoph Hellwig wrote: > On Tue, Mar 16, 2010 at 01:08:28PM +0200, Avi Kivity wrote: > >> If the batch size is larger than the virtio queue size, or if there are >> no flushes at all, then yes the huge write cache gives more opportunity >> for reordering. But we're already talking hundreds of requests here. >> > Yes. And rememember those don't have to come from the same host. Also > remember that we rather limit execssive reodering of O_DIRECT requests > in the I/O scheduler because they are "synchronous" type I/O while > we don't do that for pagecache writeback. > Maybe we should relax that for kvm. Perhaps some of the problem comes from the fact that we call io_submit() once per request. > And we don't have unlimited virtio queue size, in fact it's quite > limited. > That can be extended easily if it fixes the problem. -- error compiling committee.c: too many arguments to function