From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:47978) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1gXkDO-0005KN-0h for qemu-devel@nongnu.org; Fri, 14 Dec 2018 04:57:02 -0500 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1gXkDL-0006ht-Kj for qemu-devel@nongnu.org; Fri, 14 Dec 2018 04:57:01 -0500 Received: from mx1.redhat.com ([209.132.183.28]:48542) by eggs.gnu.org with esmtps (TLS1.0:DHE_RSA_AES_256_CBC_SHA1:32) (Exim 4.71) (envelope-from ) id 1gXkDL-0006h6-Dz for qemu-devel@nongnu.org; Fri, 14 Dec 2018 04:56:59 -0500 Date: Fri, 14 Dec 2018 09:56:47 +0000 From: "Dr. David Alan Gilbert" Message-ID: <20181214095646.GB2454@work-vm> References: <1544516693-5395-1-git-send-email-wei.w.wang@intel.com> <1544516693-5395-8-git-send-email-wei.w.wang@intel.com> <20181213154548.GP2313@work-vm> <5C135017.3070203@intel.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <5C135017.3070203@intel.com> Subject: Re: [Qemu-devel] [PATCH v11 7/7] virtio-balloon: VIRTIO_BALLOON_F_FREE_PAGE_HINT List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Wei Wang Cc: qemu-devel@nongnu.org, mst@redhat.com, quintela@redhat.com, peterx@redhat.com, pbonzini@redhat.com, liliang.opensource@gmail.com, nilal@redhat.com, riel@redhat.com * Wei Wang (wei.w.wang@intel.com) wrote: > On 12/13/2018 11:45 PM, Dr. David Alan Gilbert wrote: > > * Wei Wang (wei.w.wang@intel.com) wrote: > > > The new feature enables the virtio-balloon device to receive hints of > > > guest free pages from the free page vq. > > > > > > A notifier is registered to the migration precopy notifier chain. The > > > notifier calls free_page_start after the migration thread syncs the dirty > > > bitmap, so that the free page optimization starts to clear bits of free > > > pages from the bitmap. It calls the free_page_stop before the migration > > > thread syncs the bitmap, which is the end of the current round of ram > > > save. The free_page_stop is also called to stop the optimization in the > > > case when there is an error occurred in the process of ram saving. > > > > > > Note: balloon will report pages which were free at the time of this call. > > > As the reporting happens asynchronously, dirty bit logging must be > > > enabled before this free_page_start call is made. Guest reporting must be > > > disabled before the migration dirty bitmap is synchronized. > > > > > > Signed-off-by: Wei Wang > > > CC: Michael S. Tsirkin > > > CC: Dr. David Alan Gilbert > > > CC: Juan Quintela > > > CC: Peter Xu > > I think I'm OK for this from the migration side, I'd appreciate > > someone checking the virtio and aio bits. > > > > I'm not too sure how it gets switched on and off - i.e. if we get a nice > > new qemu on a new kernel, what happens when I try and migrate to the > > same qemu on an older kernel without these hints? > > > > This feature doesn't rely on the host kernel. Those hints are reported from > the guest kernel. > So migration across different hosts wouldn't affect the use of this feature. > Please correct me if I didn't get your point. Ah OK, yes; now what about migrating from new->old qemu with a new guest but old machine type? Dave > Best, > Wei -- Dr. David Alan Gilbert / dgilbert@redhat.com / Manchester, UK