From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:35779) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1elbq4-0003k0-NI for qemu-devel@nongnu.org; Tue, 13 Feb 2018 09:45:45 -0500 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1elbq3-0007dq-Qn for qemu-devel@nongnu.org; Tue, 13 Feb 2018 09:45:44 -0500 Date: Tue, 13 Feb 2018 15:45:21 +0100 From: Kevin Wolf Message-ID: <20180213144521.GI5083@localhost.localdomain> References: <20180107122336.29333-1-richiejp@f-m.fm> <5cf19623-72ac-fb8b-2054-a60d42419ec6@redhat.com> <20180111130427.GG8326@redhat.com> <20180213105024.GC5083@localhost.localdomain> <20180213143001.GA2354@rkaganb.sw.ru> <20180213143615.GN573@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1 Content-Disposition: inline In-Reply-To: <20180213143615.GN573@redhat.com> Content-Transfer-Encoding: quoted-printable Subject: Re: [Qemu-devel] [Qemu-block] [PATCH 1/2] Add save-snapshot, load-snapshot and delete-snapshot to QAPI List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Daniel =?iso-8859-1?Q?P=2E_Berrang=E9?= Cc: Roman Kagan , Richard Palethorpe , Qemu-block , quintela@redhat.com, qemu-devel@nongnu.org, armbru@redhat.com, Max Reitz , rpalethorpe@suse.com, dgilbert@redhat.com, Denis Plotnikov , Denis Lunev Am 13.02.2018 um 15:36 hat Daniel P. Berrang=E9 geschrieben: > On Tue, Feb 13, 2018 at 05:30:02PM +0300, Roman Kagan wrote: > > On Tue, Feb 13, 2018 at 11:50:24AM +0100, Kevin Wolf wrote: > > > Am 11.01.2018 um 14:04 hat Daniel P. Berrange geschrieben: > > > > Then you could just use the regular migrate QMP commands for load= ing > > > > and saving snapshots. > > >=20 > > > Yes, you could. I think for a proper implementation you would want = to do > > > better, though. Live migration provides just a stream, but that's n= ot > > > really well suited for snapshots. When a RAM page is dirtied, you j= ust > > > want to overwrite the old version of it in a snapshot [...] > >=20 > > This means the point in time where the guest state is snapshotted is = not > > when the command is issued, but any unpredictable amount of time late= r. > >=20 > > I'm not sure this is what a user expects. > > > > A better approach for the save part appears to be to stop the vcpus, > > dump the device state, resume the vcpus, and save the memory contents= in > > the background, prioritizing the old copies of the pages that change. > > No multiple copies of the same page would have to be saved so the str= eam > > format would be fine. For the load part the usual inmigrate should > > work. >=20 > No, that's policy decision that doesn't matter from QMP pov. If the mgm= t > app wants the snapshot to be wrt to the initial time, it can simply > invoke the "stop" QMP command before doing the live migration and > "cont" afterwards. That would be non-live. I think Roman means a live snapshot that saves the state at the beginning of the operation. Basically the difference between blockdev-backup (state at the beginning) and blockdev-mirror (state at the end), except for a whole VM. Kevin