From mboxrd@z Thu Jan 1 00:00:00 1970 From: Avi Kivity Subject: Re: [PATCH][RF C/T/D] Unmapped page cache control - via boot parameter Date: Wed, 17 Mar 2010 11:10:53 +0200 Message-ID: <4BA09C9D.1030608@redhat.com> 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> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit 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 To: Christoph Hellwig Return-path: In-Reply-To: <20100317084911.GA9098@lst.de> Sender: owner-linux-mm@kvack.org List-Id: kvm.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 -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: email@kvack.org