From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753012AbdLKNYu (ORCPT ); Mon, 11 Dec 2017 08:24:50 -0500 Received: from mx1.redhat.com ([209.132.183.28]:37994 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752723AbdLKNYr (ORCPT ); Mon, 11 Dec 2017 08:24:47 -0500 Date: Mon, 11 Dec 2017 15:24:38 +0200 From: "Michael S. Tsirkin" To: Wei Wang Cc: virtio-dev@lists.oasis-open.org, linux-kernel@vger.kernel.org, qemu-devel@nongnu.org, virtualization@lists.linux-foundation.org, kvm@vger.kernel.org, linux-mm@kvack.org, mhocko@kernel.org, akpm@linux-foundation.org, mawilcox@microsoft.com, david@redhat.com, penguin-kernel@I-love.SAKURA.ne.jp, cornelia.huck@de.ibm.com, mgorman@techsingularity.net, aarcange@redhat.com, amit.shah@redhat.com, pbonzini@redhat.com, willy@infradead.org, liliang.opensource@gmail.com, yang.zhang.wz@gmail.com, quan.xu@aliyun.com, nilal@redhat.com, riel@redhat.com Subject: Re: [PATCH v18 10/10] virtio-balloon: don't report free pages when page poisoning is enabled Message-ID: <20171211152258-mutt-send-email-mst@kernel.org> References: <1511963726-34070-1-git-send-email-wei.w.wang@intel.com> <1511963726-34070-11-git-send-email-wei.w.wang@intel.com> <20171201173951-mutt-send-email-mst@kernel.org> <5A2E27F5.2010703@intel.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <5A2E27F5.2010703@intel.com> X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.5.110.30]); Mon, 11 Dec 2017 13:24:47 +0000 (UTC) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, Dec 11, 2017 at 02:38:45PM +0800, Wei Wang wrote: > On 12/01/2017 11:49 PM, Michael S. Tsirkin wrote: > > On Wed, Nov 29, 2017 at 09:55:26PM +0800, Wei Wang wrote: > > > The guest free pages should not be discarded by the live migration thread > > > when page poisoning is enabled with PAGE_POISONING_NO_SANITY=n, because > > > skipping the transfer of such poisoned free pages will trigger false > > > positive when new pages are allocated and checked on the destination. > > > This patch skips the reporting of free pages in the above case. > > > > > > Reported-by: Michael S. Tsirkin > > > Signed-off-by: Wei Wang > > > Cc: Michal Hocko > > > --- > > > drivers/virtio/virtio_balloon.c | 4 +++- > > > 1 file changed, 3 insertions(+), 1 deletion(-) > > > > > > diff --git a/drivers/virtio/virtio_balloon.c b/drivers/virtio/virtio_balloon.c > > > index 035bd3a..6ac4cff 100644 > > > --- a/drivers/virtio/virtio_balloon.c > > > +++ b/drivers/virtio/virtio_balloon.c > > > @@ -652,7 +652,9 @@ static void report_free_page(struct work_struct *work) > > > /* Start by sending the obtained cmd id to the host with an outbuf */ > > > send_one_desc(vb, vb->free_page_vq, virt_to_phys(&vb->start_cmd_id), > > > sizeof(uint32_t), false, true, false); > > > - walk_free_mem_block(vb, 0, &virtio_balloon_send_free_pages); > > > + if (!(page_poisoning_enabled() && > > > + !IS_ENABLED(CONFIG_PAGE_POISONING_NO_SANITY))) > > > + walk_free_mem_block(vb, 0, &virtio_balloon_send_free_pages); > > > /* > > > * End by sending the stop id to the host with an outbuf. Use the > > > * non-batching mode here to trigger a kick after adding the stop id. > > PAGE_POISONING_ZERO is actually OK. > > > > But I really would prefer it that we still send pages to host, > > otherwise debugging becomes much harder. > > > > And it does not have to be completely useless, even though > > you can not discard them as they would be zero-filled then. > > > > How about a config field telling host what should be there in the free > > pages? This way even though host can not discard them, host can send > > them out without reading them, still a win. > > > > > > Since this poison value comes with the free page reporting feature, how > about sending the poison value via the free_page_vq, along with the cmd id > in the outbuf? That is, use the following interface: > > struct virtio_balloon_free_page_vq_hdr { > bool page_poisoning; > __virtio32 poison_value; > __virtio32 cmd_id; > } Can we put the value in config space instead? > We need "bool page_poisoning" because "poison_value=0" doesn't tell whether > page poising is in use by the guest. Can we use a feature bit for this? > PAGE_POISONING_ZERO sets > "page_poisoning=true, poisoning_value=0", and the host will send the > 0-filled pages to the destination (if not sending 0-filled pages, the > destination host would offer non-zero pages to the guest) Why would it? Linux zeroes all pages on alloc. > The host can discard free pages only when "page_poisoning=false". > > Best, > Wei