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Mon, 24 Feb 2020 18:59:24 +0000 (UTC) Received: from [10.36.116.78] (ovpn-116-78.ams2.redhat.com [10.36.116.78]) by smtp.corp.redhat.com (Postfix) with ESMTP id 34D481001B2C; Mon, 24 Feb 2020 18:59:11 +0000 (UTC) Subject: Re: [PATCH v2 00/13] migrate/ram: Fix resizing RAM blocks while migrating From: David Hildenbrand To: Peter Xu References: <20200221164204.105570-1-david@redhat.com> <20200221180440.GE37727@xz-x1> <20200224174515.GJ37727@xz-x1> <39ced494-023b-e020-e986-218919063af5@redhat.com> Autocrypt: addr=david@redhat.com; prefer-encrypt=mutual; keydata= mQINBFXLn5EBEAC+zYvAFJxCBY9Tr1xZgcESmxVNI/0ffzE/ZQOiHJl6mGkmA1R7/uUpiCjJ dBrn+lhhOYjjNefFQou6478faXE6o2AhmebqT4KiQoUQFV4R7y1KMEKoSyy8hQaK1umALTdL QZLQMzNE74ap+GDK0wnacPQFpcG1AE9RMq3aeErY5tujekBS32jfC/7AnH7I0v1v1TbbK3Gp XNeiN4QroO+5qaSr0ID2sz5jtBLRb15RMre27E1ImpaIv2Jw8NJgW0k/D1RyKCwaTsgRdwuK Kx/Y91XuSBdz0uOyU/S8kM1+ag0wvsGlpBVxRR/xw/E8M7TEwuCZQArqqTCmkG6HGcXFT0V9 PXFNNgV5jXMQRwU0O/ztJIQqsE5LsUomE//bLwzj9IVsaQpKDqW6TAPjcdBDPLHvriq7kGjt WhVhdl0qEYB8lkBEU7V2Yb+SYhmhpDrti9Fq1EsmhiHSkxJcGREoMK/63r9WLZYI3+4W2rAc UucZa4OT27U5ZISjNg3Ev0rxU5UH2/pT4wJCfxwocmqaRr6UYmrtZmND89X0KigoFD/XSeVv jwBRNjPAubK9/k5NoRrYqztM9W6sJqrH8+UWZ1Idd/DdmogJh0gNC0+N42Za9yBRURfIdKSb B3JfpUqcWwE7vUaYrHG1nw54pLUoPG6sAA7Mehl3nd4pZUALHwARAQABtCREYXZpZCBIaWxk ZW5icmFuZCA8ZGF2aWRAcmVkaGF0LmNvbT6JAlgEEwEIAEICGwMFCQlmAYAGCwkIBwMCBhUI AgkKCwQWAgMBAh4BAheAFiEEG9nKrXNcTDpGDfzKTd4Q9wD/g1oFAl3pImkCGQEACgkQTd4Q 9wD/g1o+VA//SFvIHUAvul05u6wKv/pIR6aICPdpF9EIgEU448g+7FfDgQwcEny1pbEzAmiw zAXIQ9H0NZh96lcq+yDLtONnXk/bEYWHHUA014A1wqcYNRY8RvY1+eVHb0uu0KYQoXkzvu+s Dncuguk470XPnscL27hs8PgOP6QjG4jt75K2LfZ0eAqTOUCZTJxA8A7E9+XTYuU0hs7QVrWJ jQdFxQbRMrYz7uP8KmTK9/Cnvqehgl4EzyRaZppshruKMeyheBgvgJd5On1wWq4ZUV5PFM4x II3QbD3EJfWbaJMR55jI9dMFa+vK7MFz3rhWOkEx/QR959lfdRSTXdxs8V3zDvChcmRVGN8U Vo93d1YNtWnA9w6oCW1dnDZ4kgQZZSBIjp6iHcA08apzh7DPi08jL7M9UQByeYGr8KuR4i6e RZI6xhlZerUScVzn35ONwOC91VdYiQgjemiVLq1WDDZ3B7DIzUZ4RQTOaIWdtXBWb8zWakt/ ztGhsx0e39Gvt3391O1PgcA7ilhvqrBPemJrlb9xSPPRbaNAW39P8ws/UJnzSJqnHMVxbRZC Am4add/SM+OCP0w3xYss1jy9T+XdZa0lhUvJfLy7tNcjVG/sxkBXOaSC24MFPuwnoC9WvCVQ ZBxouph3kqc4Dt5X1EeXVLeba+466P1fe1rC8MbcwDkoUo65Ag0EVcufkQEQAOfX3n0g0fZz Bgm/S2zF/kxQKCEKP8ID+Vz8sy2GpDvveBq4H2Y34XWsT1zLJdvqPI4af4ZSMxuerWjXbVWb T6d4odQIG0fKx4F8NccDqbgHeZRNajXeeJ3R7gAzvWvQNLz4piHrO/B4tf8svmRBL0ZB5P5A 2uhdwLU3NZuK22zpNn4is87BPWF8HhY0L5fafgDMOqnf4guJVJPYNPhUFzXUbPqOKOkL8ojk CXxkOFHAbjstSK5Ca3fKquY3rdX3DNo+EL7FvAiw1mUtS+5GeYE+RMnDCsVFm/C7kY8c2d0G NWkB9pJM5+mnIoFNxy7YBcldYATVeOHoY4LyaUWNnAvFYWp08dHWfZo9WCiJMuTfgtH9tc75 7QanMVdPt6fDK8UUXIBLQ2TWr/sQKE9xtFuEmoQGlE1l6bGaDnnMLcYu+Asp3kDT0w4zYGsx 5r6XQVRH4+5N6eHZiaeYtFOujp5n+pjBaQK7wUUjDilPQ5QMzIuCL4YjVoylWiBNknvQWBXS lQCWmavOT9sttGQXdPCC5ynI+1ymZC1ORZKANLnRAb0NH/UCzcsstw2TAkFnMEbo9Zu9w7Kv AxBQXWeXhJI9XQssfrf4Gusdqx8nPEpfOqCtbbwJMATbHyqLt7/oz/5deGuwxgb65pWIzufa N7eop7uh+6bezi+rugUI+w6DABEBAAGJAiUEGAECAA8FAlXLn5ECGwwFCQlmAYAACgkQTd4Q 9wD/g1qA6w/+M+ggFv+JdVsz5+ZIc6MSyGUozASX+bmIuPeIecc9UsFRatc91LuJCKMkD9Uv GOcWSeFpLrSGRQ1Z7EMzFVU//qVs6uzhsNk0RYMyS0B6oloW3FpyQ+zOVylFWQCzoyyf227y GW8HnXunJSC+4PtlL2AY4yZjAVAPLK2l6mhgClVXTQ/S7cBoTQKP+jvVJOoYkpnFxWE9pn4t H5QIFk7Ip8TKr5k3fXVWk4lnUi9MTF/5L/mWqdyIO1s7cjharQCstfWCzWrVeVctpVoDfJWp 4LwTuQ5yEM2KcPeElLg5fR7WB2zH97oI6/Ko2DlovmfQqXh9xWozQt0iGy5tWzh6I0JrlcxJ ileZWLccC4XKD1037Hy2FLAjzfoWgwBLA6ULu0exOOdIa58H4PsXtkFPrUF980EEibUp0zFz GotRVekFAceUaRvAj7dh76cToeZkfsjAvBVb4COXuhgX6N4pofgNkW2AtgYu1nUsPAo+NftU CxrhjHtLn4QEBpkbErnXQyMjHpIatlYGutVMS91XTQXYydCh5crMPs7hYVsvnmGHIaB9ZMfB njnuI31KBiLUks+paRkHQlFcgS2N3gkRBzH7xSZ+t7Re3jvXdXEzKBbQ+dC3lpJB0wPnyMcX FOTT3aZT7IgePkt5iC/BKBk3hqKteTnJFeVIT7EC+a6YUFg= Organization: Red Hat GmbH Message-ID: <0ffb449a-84a3-3555-e0c1-0bc842977bb2@redhat.com> Date: Mon, 24 Feb 2020 19:59:10 +0100 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.5.0 MIME-Version: 1.0 In-Reply-To: <39ced494-023b-e020-e986-218919063af5@redhat.com> Content-Language: en-US X-Scanned-By: MIMEDefang 2.84 on 10.5.11.22 X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 7bit X-detected-operating-system: by eggs.gnu.org: GNU/Linux 2.2.x-3.x [generic] [fuzzy] X-Received-From: 207.211.31.120 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: , Cc: Andrea Arcangeli , Stefano Stabellini , Eduardo Habkost , Juan Quintela , Stefan Hajnoczi , "Michael S. Tsirkin" , Richard Henderson , qemu-devel@nongnu.org, "Dr . David Alan Gilbert" , Paul Durrant , Alex Williamson , Shannon Zhao , Igor Mammedov , Anthony Perard , Paolo Bonzini , =?UTF-8?Q?Alex_Benn=c3=a9e?= , Richard Henderson Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" On 24.02.20 19:44, David Hildenbrand wrote: > On 24.02.20 18:45, Peter Xu wrote: >> On Mon, Feb 24, 2020 at 10:09:19AM +0100, David Hildenbrand wrote: >>> On 21.02.20 19:04, Peter Xu wrote: >>>> On Fri, Feb 21, 2020 at 05:41:51PM +0100, David Hildenbrand wrote: >>>>> I was now able to actually test resizing while migrating. I am using the >>>>> prototype of virtio-mem to test (which also makes use of resizable >>>>> allocations). Things I was able to reproduce: >>>> >>>> The test cases cover quite a lot. Thanks for doing that. >>>> >>>>> - Resize while still running on the migration source. Migration is canceled >>>>> -- Test case for "migraton/ram: Handle RAM block resizes during precopy" >>>> >>>>> - Resize (grow+shrink) on the migration target during postcopy migration >>>>> (when syncing RAM blocks), while not yet running on the target >>>>> -- Test case for "migration/ram: Discard new RAM when growing RAM blocks >>>>> and the VM is stopped", and overall RAM size synchronization. Seems to >>>>> work just fine. >>>> >>>> This won't be able to trigger without virtio-mem, right? >>> >>> AFAIK all cases can also be triggered without virtio-mem (not just that >>> easily :) ). This case would be "RAM block is bigger on source than on >>> destination.". >>> >>>> >>>> And I'm also curious on how to test this even with virtio-mem. Is >>>> that a QMP command to extend/shrink virtio-mem? >>> >>> Currently, there is a single qom property that can be modifed via >>> QMP/HMP - "requested-size". With resizable resizable memory backends, >>> increasing the requested size will also implicitly grow the RAM block. >>> Shrinking the requested size will currently result in shrinking the RAM >>> block on the next reboot. >>> >>> So, to trigger growing of a RAM block (assuming requested-size was >>> smaller before, e.g., 1000M) >>> >>> echo "qom-set vm1 requested-size 6000M" | sudo nc -U $MON >>> >>> To trigger shrinking (assuming requested-size was bigger before) >>> >>> echo "qom-set vm1 requested-size 100M" | sudo nc -U $MON >>> echo 'system_reset' | sudo nc -U $MON >>> >>> >>> Placing these at the right spots during a migration allows to test this >>> very reliably. >> >> I see, thanks for the context. The question was majorly about when >> you say "during postcopy migration (when syncing RAM blocks), while >> not yet running on the target" - it's not easy to do so imho, because: > > This case is very easy to trigger, even with acpi. Simply have a ram > block on the source be bigger than one on the target. The sync code > (migration/ram.c:qemu_ram_resize()) will perform the resize during > precopy. Postcopy misses to discard the additional memory. > > Maybe my description was confusing. But this really just triggers when > > - Postcopy is advised and discards memory on all ram blocks > - Precopy grows the RAM block when syncing the RAM block sizes with the > source > > Postcopy misses to discard the new RAM. > >> >> - it's a very short transition period between precopy and postcopy, >> so I was curious about how you made sure that the grow/shrink >> happened exactly during that period >> >> - during the period, IIUC it was still in the main thread, which >> means logically QEMU should not be able to respond to any QMP/HMP >> command at all... So even if you send a command, I think it'll >> only be executed later after the transition completes >> >> - this I'm not sure, but ... even for virtio-mem, the resizing can >> only happen after guest ack it, right? During the precopy to >> postcopy transition period, the VM is stopped, AFAICT, so >> logically we can't trigger resizing during the transition Regarding that question: Resizes will happen without guest interaction (e.g., during a reboot, or when increasing the requested size). In the future, there are theoretical plans to have resizes that can be triggered by guest interaction/request to some extend as well. -- Thanks, David / dhildenb