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Mon, 24 Feb 2020 18:45:01 +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 9141F5C54A; Mon, 24 Feb 2020 18:44:47 +0000 (UTC) Subject: Re: [PATCH v2 00/13] migrate/ram: Fix resizing RAM blocks while migrating To: Peter Xu References: <20200221164204.105570-1-david@redhat.com> <20200221180440.GE37727@xz-x1> <20200224174515.GJ37727@xz-x1> From: David Hildenbrand 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: <39ced494-023b-e020-e986-218919063af5@redhat.com> Date: Mon, 24 Feb 2020 19:44:46 +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: <20200224174515.GJ37727@xz-x1> Content-Language: en-US X-Scanned-By: MIMEDefang 2.79 on 10.5.11.16 X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: quoted-printable X-detected-operating-system: by eggs.gnu.org: GNU/Linux 2.2.x-3.x [generic] [fuzzy] X-Received-From: 207.211.31.81 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 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 t= he >>>> 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 can= celed >>>> -- Test case for "migraton/ram: Handle RAM block resizes during precop= y" >>> >>>> - Resize (grow+shrink) on the migration target during postcopy migrati= on >>>> (when syncing RAM blocks), while not yet running on the target >>>> -- Test case for "migration/ram: Discard new RAM when growing RAM bloc= ks >>>> 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. >=20 > 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. >=20 > - 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 >=20 > - 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 >=20 > - 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 >=20 > So it's really a question/matter of whether we still even need to > consider that transition period for resizing event for postcopy. > Maybe we don't even need to. It's synchronous and not a race. So it does matter very much :) --=20 Thanks, David / dhildenb