From mboxrd@z Thu Jan 1 00:00:00 1970 From: "Dr. David Alan Gilbert" Subject: Re: [RFC Design Doc]Speed up live migration by skipping free pages Date: Tue, 19 Apr 2016 20:12:02 +0100 Message-ID: <20160419191202.GI2255@work-vm> References: <20160324102354.GB2230@work-vm> <20160324165530-mutt-send-email-mst@redhat.com> <20160324175503-mutt-send-email-mst@redhat.com> <20160324181031-mutt-send-email-mst@redhat.com> <20160324174933.GA11662@work-vm> <20160418142704-mutt-send-email-mst@redhat.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Cc: "Li, Liang Z" , Wei Yang , "qemu-devel@nongnu.org" , "kvm@vger.kernel.org" , "linux-kernel@vger.kenel.org" , "pbonzini@redhat.com" , "rth@twiddle.net" , "ehabkost@redhat.com" , "amit.shah@redhat.com" , "quintela@redhat.com" , "mohan_parthasarathy@hpe.com" , "jitendra.kolhe@hpe.com" , "simhan@hpe.com" , "rkagan@virtuozzo.com" , "riel@redhat.com" To: "Michael S. Tsirkin" Return-path: Received: from mx1.redhat.com ([209.132.183.28]:34665 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S932098AbcDSTMJ (ORCPT ); Tue, 19 Apr 2016 15:12:09 -0400 Content-Disposition: inline In-Reply-To: <20160418142704-mutt-send-email-mst@redhat.com> Sender: kvm-owner@vger.kernel.org List-ID: * Michael S. Tsirkin (mst@redhat.com) wrote: > On Mon, Apr 18, 2016 at 11:08:31AM +0000, Li, Liang Z wrote: > > Hi Dave, > > > > I am now working on how to benefit post-copy by skipping the free pages, > > and I remember you have said we should let the destination know the info > > of free pages so as to avoid request the free pages from the source. > > > > We have two solutions: > > > > a. send the migration dirty page bitmap to destination before post > > copy start, so the destination can decide whether to request the pages or > > place zero pages by checking the migration dirty page bitmap. The advantage > > is that we can avoid sending the free pages. the disadvantage is that we have > > to send extra data to destination. > > > > b. Check the page request on the source side, if it's not a dirty page, send a zero > > page header to the destination. > > > > What's your opinion about them? > > > > Liang > > > > Both are ad-hoc solutions imho. > > c. put the bitmap in a ramblock, check it on destination before > requesting pages. > > This way it's migrated on-demand. I can see where you're coming from, but I don't like this idea, because sending data controlling the RAM migration process in RAM blocks controlled by the same data just sounds too recursive to ever debug. Dave > > -- > MST -- Dr. David Alan Gilbert / dgilbert@redhat.com / Manchester, UK