From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:48428) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1elcUL-0006cV-8o for qemu-devel@nongnu.org; Tue, 13 Feb 2018 10:27:22 -0500 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1elcUK-0002yF-B1 for qemu-devel@nongnu.org; Tue, 13 Feb 2018 10:27:21 -0500 Date: Tue, 13 Feb 2018 15:27:11 +0000 From: "Dr. David Alan Gilbert" Message-ID: <20180213152711.GI2378@work-vm> References: <20180111130427.GG8326@redhat.com> <20180213105024.GC5083@localhost.localdomain> <20180213143001.GA2354@rkaganb.sw.ru> <20180213143615.GN573@redhat.com> <20180213144521.GI5083@localhost.localdomain> <20180213144838.GO573@redhat.com> <20180213145913.GE2378@work-vm> <6845a694-aa22-90e8-7a9b-ce0283be450c@virtuozzo.com> <20180213150503.GF2378@work-vm> <20180213151352.GF2307@rkaganb.sw.ru> MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1 Content-Disposition: inline In-Reply-To: <20180213151352.GF2307@rkaganb.sw.ru> 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: Roman Kagan , "Denis V. Lunev" , Daniel =?iso-8859-1?Q?P=2E_Berrang=E9?= , Kevin Wolf , Richard Palethorpe , Qemu-block , quintela@redhat.com, qemu-devel@nongnu.org, armbru@redhat.com, Max Reitz , rpalethorpe@suse.com, Denis Plotnikov , aarcange@redhat.com * Roman Kagan (rkagan@virtuozzo.com) wrote: > On Tue, Feb 13, 2018 at 03:05:03PM +0000, Dr. David Alan Gilbert wrote: > > * Denis V. Lunev (den@virtuozzo.com) wrote: > > > On 02/13/2018 05:59 PM, Dr. David Alan Gilbert wrote: > > > > * Daniel P. Berrang=E9 (berrange@redhat.com) wrote: > > > >> That doesn't seem practical unless you can instantaneously write= out > > > >> the entire guest RAM to disk without blocking, or can somehow sn= apshot > > > >> the RAM so you can write out a consistent view of the original R= AM, > > > >> while the guest continues to dirty RAM pages. > > > > People have suggested doing something like that with userfault wr= ite > > > > mode; but the same would also be doable just by write protecting = the > > > > whole of RAM and then following the faults. > > >=20 > > > nope, userfault fd does not help :( We have tried, the functionalit= y is not > > > enough. Better to have small extension to KVM to protect all memory > > > and notify QEMU with accessed address. > >=20 > > Can you explain why? I thought the write-protect mode of userfaultfd = was > > supposed to be able to do that; cc'ing in Andrea >=20 > IIRC it would if it worked; it just didn't when we tried. Hmm that doesn't seem to be the ideal reason to create new KVM functionality, especially since there were a bunch of people wanting the userfaultfd-write mode for other uses. Dave > Roman. -- Dr. David Alan Gilbert / dgilbert@redhat.com / Manchester, UK