From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-pg0-f72.google.com (mail-pg0-f72.google.com [74.125.83.72]) by kanga.kvack.org (Postfix) with ESMTP id AB5926B0033 for ; Tue, 12 Dec 2017 07:19:30 -0500 (EST) Received: by mail-pg0-f72.google.com with SMTP id 200so15571453pge.12 for ; Tue, 12 Dec 2017 04:19:30 -0800 (PST) Received: from mga12.intel.com (mga12.intel.com. [192.55.52.136]) by mx.google.com with ESMTPS id 5si11538044plx.384.2017.12.12.04.19.29 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Tue, 12 Dec 2017 04:19:29 -0800 (PST) Message-ID: <5A2FC9CB.7030508@intel.com> Date: Tue, 12 Dec 2017 20:21:31 +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> <5A2E27F5.2010703@intel.com> <20171211152258-mutt-send-email-mst@kernel.org> In-Reply-To: <20171211152258-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 12/11/2017 09:24 PM, Michael S. Tsirkin wrote: > 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. > Thanks, that is the case. I think we don't need a feature bit then. Please have a check the v19 patches. 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