From mboxrd@z Thu Jan 1 00:00:00 1970 From: "Michael S. Tsirkin" Subject: Re: [RFC Design Doc]Speed up live migration by skipping free pages Date: Mon, 18 Apr 2016 18:38:17 +0300 Message-ID: <20160418183257-mutt-send-email-mst@redhat.com> References: <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: "Dr. David Alan Gilbert" , 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: "Li, Liang Z" Return-path: Received: from mx1.redhat.com ([209.132.183.28]:59591 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752093AbcDRPiZ (ORCPT ); Mon, 18 Apr 2016 11:38:25 -0400 Content-Disposition: inline In-Reply-To: Sender: kvm-owner@vger.kernel.org List-ID: On Mon, Apr 18, 2016 at 02:36:31PM +0000, Li, Liang Z 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. > > > Hi MST, > > I think you mean putting the free page bitmap in a ramblock. Right? > If some of the free pages become dirty after updating the free page bitmap, > and these pages are discarded by destination, how can we distinguish these > discarded pages with the free pages? > > Could you elaborate how it works? > > Thanks! > Liang Maybe I'm confused - IIUC it's postcopy so VM is running on destination, if page is dirty it was modified there so we don't need to get it from source. But really I agree with David here - at step 1 just ignore postcopy, don't special-case it, even if it becomes slower with your patch. Think about it later. > > > > -- > > MST > > -- > > To unsubscribe from this list: send the line "unsubscribe kvm" in the body of > > a message to majordomo@vger.kernel.org More majordomo info at > > http://vger.kernel.org/majordomo-info.html From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:49153) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1asBFv-00017X-BV for qemu-devel@nongnu.org; Mon, 18 Apr 2016 11:38:32 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1asBFq-0000TM-Ao for qemu-devel@nongnu.org; Mon, 18 Apr 2016 11:38:31 -0400 Received: from mx1.redhat.com ([209.132.183.28]:58559) by eggs.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1asBFq-0000TC-4N for qemu-devel@nongnu.org; Mon, 18 Apr 2016 11:38:26 -0400 Date: Mon, 18 Apr 2016 18:38:17 +0300 From: "Michael S. Tsirkin" Message-ID: <20160418183257-mutt-send-email-mst@redhat.com> References: <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 Content-Disposition: inline In-Reply-To: Subject: Re: [Qemu-devel] [RFC Design Doc]Speed up live migration by skipping free pages List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: "Li, Liang Z" Cc: "Dr. David Alan Gilbert" , 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" On Mon, Apr 18, 2016 at 02:36:31PM +0000, Li, Liang Z 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. > > > Hi MST, > > I think you mean putting the free page bitmap in a ramblock. Right? > If some of the free pages become dirty after updating the free page bitmap, > and these pages are discarded by destination, how can we distinguish these > discarded pages with the free pages? > > Could you elaborate how it works? > > Thanks! > Liang Maybe I'm confused - IIUC it's postcopy so VM is running on destination, if page is dirty it was modified there so we don't need to get it from source. But really I agree with David here - at step 1 just ignore postcopy, don't special-case it, even if it becomes slower with your patch. Think about it later. > > > > -- > > MST > > -- > > To unsubscribe from this list: send the line "unsubscribe kvm" in the body of > > a message to majordomo@vger.kernel.org More majordomo info at > > http://vger.kernel.org/majordomo-info.html