From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-pg0-f69.google.com (mail-pg0-f69.google.com [74.125.83.69]) by kanga.kvack.org (Postfix) with ESMTP id 5EADD6B0033 for ; Mon, 11 Dec 2017 01:36:46 -0500 (EST) Received: by mail-pg0-f69.google.com with SMTP id q186so12152387pga.23 for ; Sun, 10 Dec 2017 22:36:46 -0800 (PST) Received: from mga17.intel.com (mga17.intel.com. [192.55.52.151]) by mx.google.com with ESMTPS id d67si9449155pgc.607.2017.12.10.22.36.44 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Sun, 10 Dec 2017 22:36:44 -0800 (PST) Message-ID: <5A2E27F5.2010703@intel.com> Date: Mon, 11 Dec 2017 14:38:45 +0800 From: Wei Wang MIME-Version: 1.0 Subject: Re: [PATCH v18 10/10] virtio-balloon: don't report free pages when page poisoning is enabled 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> In-Reply-To: <20171201173951-mutt-send-email-mst@kernel.org> Content-Type: text/plain; charset=windows-1252; format=flowed Content-Transfer-Encoding: 7bit Sender: owner-linux-mm@kvack.org List-ID: To: "Michael S. Tsirkin" 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 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; } We need "bool page_poisoning" because "poison_value=0" doesn't tell whether page poising is in use by the guest. 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) The host can discard free pages only when "page_poisoning=false". Best, Wei -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: email@kvack.org