From: Michal Novotny Subject: Re: [PATCH] extend e2fsprogs functionality to add EXT2_FLAG_DIRECT option Date: Tue, 12 Jan 2010 17:43:21 +0100 Message-ID: <4B4CA6A9.3030401@redhat.com> References: <4B46FCB2.1090308@redhat.com> <4B4B84E2.1050508@redhat.com> <4B4C54DC.4040006@redhat.com> <4B4C6429.6090803@redhat.com> <4B4C67F5.1020009@redhat.com> <20100112122319.GA20596@infradead.org> <4B4C6B70.1050205@redhat.com> <20100112124600.GA7151@infradead.org> <4B4C7297.5030905@redhat.com> <20100112163828.GA14633@infradead.org> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Cc: Ric Wheeler , linux-ext4@vger.kernel.org, linux-kernel@vger.kernel.org To: Christoph Hellwig Return-path: Received: from mx1.redhat.com ([209.132.183.28]:27343 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751937Ab0ALQnv (ORCPT ); Tue, 12 Jan 2010 11:43:51 -0500 In-Reply-To: <20100112163828.GA14633@infradead.org> Sender: linux-ext4-owner@vger.kernel.org List-ID: On 01/12/2010 05:38 PM, Christoph Hellwig wrote: > Ok, I looked at the issue. The problem is that the Xen backend drivers > are (as expected) utterly braindead and submit bios directly from the > virtualization backed without using proper abstractions and thus > bypassing all the cache coherency features in the fileystems (the block > device nodes are just another mini-filesystem in that respect). So > when you first have buffered access in the host pages may stay in cache > and get overwritten directly on disk by a Xen guest, and once the guest > is down the host may still use the now stale cached data. > > I would recommend to migrate your cutomers to KVM which uses the proper > abtractions and thus doesn't have this problem. There's a reason after > all why all the Xen dom0 mess never got merged to mainline. > So, do you think the problem is in the Xen backend drivers and to make it working right in Xen the driver fix is needed?