From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([208.118.235.92]:34731) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1UIH4H-000112-Nf for qemu-devel@nongnu.org; Wed, 20 Mar 2013 07:20:34 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1UIH4E-0007Tt-Lp for qemu-devel@nongnu.org; Wed, 20 Mar 2013 07:20:29 -0400 Received: from mail.avalus.com ([2001:41c8:10:1dd::10]:51358) by eggs.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1UIH4E-0007TD-GN for qemu-devel@nongnu.org; Wed, 20 Mar 2013 07:20:26 -0400 Date: Wed, 20 Mar 2013 11:20:12 +0000 From: Alex Bligh Message-ID: In-Reply-To: <514998A3.9090903@redhat.com> References: <1363609123-20748-1-git-send-email-alex@alex.org.uk> <51471767.8030604@redhat.com> <7AC8953FE45335FB794B6DFE@Ximines.local> <51471F14.7030209@redhat.com> <6D0F4ACDA3B7FCF1A50F8B52@Ximines.local> <5147298C.8080900@redhat.com> <51473E82.1020806@redhat.com> <861AFE1A9C44444FD8BAEE16@Ximines.local> <5147512E.5050501@eu.citrix.com> <5147562E.1090203@redhat.com> <5148414C.7060303@redhat.com> <51484328.4030301@eu.citrix.com> <5148489C.70808@redhat.com> <51484A2B.10202@eu.citrix.com> <0E09404F0675BA19C550B743@nimrod.local> <51499157.2060202@eu.citrix.com> <514998A3.9090903@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii; format=flowed Content-Transfer-Encoding: 7bit Content-Disposition: inline Subject: Re: [Qemu-devel] [Xen-devel] [PATCHv3] QEMU(upstream): Disable xen's use of O_DIRECT by default as it results in crashes. Reply-To: Alex Bligh List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Paolo Bonzini , George Dunlap Cc: Ian Campbell , Stefano Stabellini , Alex Bligh , Ian Jackson , qemu-devel@nongnu.org, xen-devel , Anthony Liguori --On 20 March 2013 12:08:19 +0100 Paolo Bonzini wrote: > To make it safe, just use cache=none. There are downsides (for example > tmpfs does not support it), but perhaps you can use a global option or > environment variable to toggle the behavior. If you don't use cache=none, you it is unsafe because of the page cache issue. If you use cache=none, it uses O_DIRECT, and it is unsafe because of the kernel issue. My preference would be to leave this can of worms to the end user. I'd rather take the risk on the first (as I'd rather domU broke than dom0) but that's because I always use network drives. Some documentation would be useful. -- Alex Bligh