From mboxrd@z Thu Jan 1 00:00:00 1970 From: Avi Kivity Subject: Re: [PATCH +stable] block: don't attempt to merge overlapping requests Date: Wed, 19 May 2010 11:09:07 +0300 Message-ID: <4BF39CA3.9020305@redhat.com> References: <1274203124-14318-1-git-send-email-avi@redhat.com> Mime-Version: 1.0 Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit Cc: Kevin Wolf , qemu-devel@nongnu.org, kvm@vger.kernel.org, Christoph Hellwig To: Stefan Hajnoczi Return-path: Received: from mx1.redhat.com ([209.132.183.28]:63614 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752241Ab0ESIJP (ORCPT ); Wed, 19 May 2010 04:09:15 -0400 In-Reply-To: Sender: kvm-owner@vger.kernel.org List-ID: On 05/18/2010 10:22 PM, Stefan Hajnoczi wrote: > On Tue, May 18, 2010 at 6:18 PM, Avi Kivity wrote: > >> The block multiwrite code pretends to be able to merge overlapping requests, >> but doesn't do so in fact. This leads to I/O errors (for example on mkfs >> of a large virtio disk). >> > Are overlapping write requests correct guest behavior? I thought the > ordering semantics require a flush between overlapping writes to > ensure A is written before B. > > What cache= mode are you running? > writeback. -- Do not meddle in the internals of kernels, for they are subtle and quick to panic.