From mboxrd@z Thu Jan 1 00:00:00 1970 From: Anthony Liguori Subject: Re: [Qemu-devel] [RFC PATCH 1/1] ceph/rbd block driver for qemu-kvm Date: Tue, 25 May 2010 08:55:25 -0500 Message-ID: <4BFBD6CD.3000503@codemonkey.ws> References: <20100519192222.GD61706@ncolin.muc.de> <4BF5A9D2.5080609@codemonkey.ws> <4BF91937.2070801@redhat.com> <4BFBAE46.5050801@redhat.com> <4BFBB3C1.9020905@redhat.com> <4BFBCFAC.9070807@codemonkey.ws> <4BFBD13C.60605@redhat.com> <4BFBD20E.5060207@codemonkey.ws> <4BFBD2D5.2000201@redhat.com> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Cc: Kevin Wolf , Blue Swirl , ceph-devel@vger.kernel.org, Christian Brunner , kvm@vger.kernel.org, qemu-devel@nongnu.org To: Avi Kivity Return-path: Received: from mail-vw0-f46.google.com ([209.85.212.46]:49344 "EHLO mail-vw0-f46.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1758505Ab0EYNza (ORCPT ); Tue, 25 May 2010 09:55:30 -0400 In-Reply-To: <4BFBD2D5.2000201@redhat.com> Sender: kvm-owner@vger.kernel.org List-ID: On 05/25/2010 08:38 AM, Avi Kivity wrote: > On 05/25/2010 04:35 PM, Anthony Liguori wrote: >> On 05/25/2010 08:31 AM, Avi Kivity wrote: >>>> A protocol based mechanism has the advantage of being more robust >>>> in the face of poorly written block backends so if it's possible to >>>> make it perform as well as a plugin, it's a preferable approach. >>> >>> May be hard due to difficulty of exposing guest memory. >> >> If someone did a series to add plugins, I would expect a very strong >> argument as to why a shared memory mechanism was not possible or at >> least plausible. >> >> I'm not sure I understand why shared memory is such a bad thing wrt >> KVM. Can you elaborate? Is it simply a matter of fork()? > > fork() doesn't work in the with of memory hotplug. What else is there? > Is it that fork() doesn't work or is it that fork() is very expensive? Regards, Anthony Liguori