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David Alan Gilbert" , Markus Armbruster , Peter Xu References: <20201126151734.743849-1-andrey.gruzdev@virtuozzo.com> <20201201070820.GO105758@angien.pipo.sk> <20201201105300.GQ105758@angien.pipo.sk> From: Andrey Gruzdev Message-ID: Date: Tue, 1 Dec 2020 14:24:12 +0300 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101 Thunderbird/78.5.0 In-Reply-To: <20201201105300.GQ105758@angien.pipo.sk> Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-US Content-Transfer-Encoding: 7bit X-Originating-IP: [95.165.26.68] X-ClientProxiedBy: AM4PR0701CA0029.eurprd07.prod.outlook.com (2603:10a6:200:42::39) To VI1PR0802MB2510.eurprd08.prod.outlook.com (2603:10a6:800:ad::14) MIME-Version: 1.0 X-MS-Exchange-MessageSentRepresentingType: 1 Received: from [192.168.1.64] (95.165.26.68) by AM4PR0701CA0029.eurprd07.prod.outlook.com (2603:10a6:200:42::39) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id 15.20.3632.6 via Frontend Transport; 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envelope-from=andrey.gruzdev@virtuozzo.com; helo=EUR02-HE1-obe.outbound.protection.outlook.com X-Spam_score_int: -27 X-Spam_score: -2.8 X-Spam_bar: -- X-Spam_report: (-2.8 / 5.0 requ) BAYES_00=-1.9, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, MSGID_FROM_MTA_HEADER=0.001, NICE_REPLY_A=-0.001, RCVD_IN_DNSWL_LOW=-0.7, RCVD_IN_MSPIKE_H2=-0.001, SPF_HELO_PASS=-0.001, SPF_PASS=-0.001 autolearn=ham autolearn_force=no X-Spam_action: no action X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.23 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" On 01.12.2020 13:53, Peter Krempa wrote: > On Tue, Dec 01, 2020 at 11:42:18 +0300, Andrey Gruzdev wrote: >> On 01.12.2020 10:08, Peter Krempa wrote: >>> On Thu, Nov 26, 2020 at 18:17:28 +0300, Andrey Gruzdev via wrote: >>>> This patch series is a kind of 'rethinking' of Denis Plotnikov's ideas he's > > [...] > >>> Note that in cases when qemu can't guarantee that the >>> background_snapshot feature will work it should not advertise it. We >>> need a way to check whether it's possible to use it, so we can replace >>> the existing --live flag with it rather than adding a new one and >>> shifting the problem of checking whether the feature works to the user. >>> >> >> Hi, >> >> May be you are using hugetlbfs as memory backend? > > Not exactly hugepages, but I had: > > > > > > which resulted into the following commandline to instantiate memory: > > -object memory-backend-file,id=pc.ram,mem-path=/var/lib/libvirt/qemu/ram/6-upstream-bj/pc.ram,share=yes,size=33554432000,host-nodes=0,policy=bind \ > > When I've removed it I got: > > -object memory-backend-ram,id=pc.ram,size=33554432000,host-nodes=0,policy=bind \ > > And the migration didn't fail in my quick test. I'll have a more > detailed look later, thanks for the pointer. > Yep, seems that current userfaultfd supports hugetlbfs and shared memory for missing pages but not for wr-protected.. >> I totally agree that we need somehow check that kernel and VM memory backend >> support the feature before one can enable the capability. >> Need to think about that.. > > Definitely. Also note that memory backed by memory-backend-file will be > more and more common, for cases such as virtiofs DAX sharing and > similar. > I see.. That needs support from kernel side, so far 'background-snapshots' are incompatible with memory-backend-file sharing. -- Andrey Gruzdev, Principal Engineer Virtuozzo GmbH +7-903-247-6397 virtuzzo.com