From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753643Ab0CQItx (ORCPT ); Wed, 17 Mar 2010 04:49:53 -0400 Received: from verein.lst.de ([213.95.11.210]:47955 "EHLO verein.lst.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752807Ab0CQItv (ORCPT ); Wed, 17 Mar 2010 04:49:51 -0400 Date: Wed, 17 Mar 2010 09:49:11 +0100 From: Christoph Hellwig To: Avi Kivity Cc: Christoph Hellwig , 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 Message-ID: <20100317084911.GA9098@lst.de> 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> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <4B9F66AC.5080400@redhat.com> User-Agent: Mutt/1.3.28i X-Spam-Score: 0 () Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 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. And we don't have unlimited virtio queue size, in fact it's quite limited.