From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752895AbdGXJA7 (ORCPT ); Mon, 24 Jul 2017 05:00:59 -0400 Received: from mx2.suse.de ([195.135.220.15]:33541 "EHLO mx1.suse.de" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1752496AbdGXJAs (ORCPT ); Mon, 24 Jul 2017 05:00:48 -0400 Date: Mon, 24 Jul 2017 11:00:43 +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: <20170724090042.GF25221@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> <20170719081311.GC26779@dhcp22.suse.cz> <596F4A0E.4010507@intel.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <596F4A0E.4010507@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 Wed 19-07-17 20:01:18, Wei Wang wrote: > On 07/19/2017 04:13 PM, Michal Hocko wrote: [... > >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. > > Not necessarily - the guest struct page is not seen by the hypervisor. The > hypervisor only gets those guest pfns which are hinted as unused. From the > hypervisor (host) point of view, a guest physical address corresponds to a > virtual address of a host process. So, once the hypervisor knows a guest > physical page is unsued, it knows that the corresponding virtual memory of > the process doesn't need to be transferred in the 1st round. I am sorry, but I do not understand. Why cannot _guest_ simply check the struct page ref count and send them to the hypervisor? Is there any documentation which describes the workflow or code which would use your new API? -- Michal Hocko SUSE Labs