From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752932AbdGSINT (ORCPT ); Wed, 19 Jul 2017 04:13:19 -0400 Received: from mx2.suse.de ([195.135.220.15]:54870 "EHLO mx1.suse.de" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1751448AbdGSINQ (ORCPT ); Wed, 19 Jul 2017 04:13:16 -0400 Date: Wed, 19 Jul 2017 10:13:12 +0200 From: Michal Hocko To: Wei Wang Cc: "Michael S. Tsirkin" , linux-kernel@vger.kernel.org, qemu-devel@nongnu.org, virtualization@lists.linux-foundation.org, kvm@vger.kernel.org, linux-mm@kvack.org, david@redhat.com, cornelia.huck@de.ibm.com, akpm@linux-foundation.org, mgorman@techsingularity.net, aarcange@redhat.com, amit.shah@redhat.com, pbonzini@redhat.com, liliang.opensource@gmail.com, virtio-dev@lists.oasis-open.org, yang.zhang.wz@gmail.com, quan.xu@aliyun.com Subject: Re: [PATCH v12 6/8] mm: support reporting free page blocks Message-ID: <20170719081311.GC26779@dhcp22.suse.cz> References: <1499863221-16206-1-git-send-email-wei.w.wang@intel.com> <1499863221-16206-7-git-send-email-wei.w.wang@intel.com> <20170714123023.GA2624@dhcp22.suse.cz> <20170714181523-mutt-send-email-mst@kernel.org> <20170717152448.GN12888@dhcp22.suse.cz> <596D6E7E.4070700@intel.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <596D6E7E.4070700@intel.com> User-Agent: Mutt/1.5.23 (2014-03-12) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue 18-07-17 10:12:14, Wei Wang wrote: [...] > Probably I should have included the introduction of the usages in > the log. Hope it is not too later to explain here: Yes this should have been described in the cover. > Live migration needs to transfer the VM's memory from the source > machine to the destination round by round. For the 1st round, all the VM's > memory is transferred. From the 2nd round, only the pieces of memory > that were written by the guest (after the 1st round) are transferred. One > method that is popularly used by the hypervisor to track which part of > memory is written is to write-protect all the guest memory. > > This patch enables the optimization of the 1st round memory transfer - > the hypervisor can skip the transfer of guest unused pages in the 1st round. All you should need is the check for the page reference count, no? I assume you do some sort of pfn walk and so you should be able to get an access to the struct page. -- Michal Hocko SUSE Labs