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Tsirkin" , Tyler Sanderson Cc: "Wang, Wei W" , "virtualization@lists.linux-foundation.org" , David Rientjes , "linux-mm@kvack.org" , Michal Hocko References: <91270a68-ff48-88b0-219c-69801f0c252f@redhat.com> <75d4594f-0864-5172-a0f8-f97affedb366@redhat.com> <286AC319A985734F985F78AFA26841F73E3F8A02@shsmsx102.ccr.corp.intel.com> <20200203080520-mutt-send-email-mst@kernel.org> <5ac131de8e3b7fc1fafd05a61feb5f6889aeb917.camel@linux.intel.com> 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: Date: Mon, 3 Feb 2020 17:34:20 +0100 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.3.1 MIME-Version: 1.0 In-Reply-To: <5ac131de8e3b7fc1fafd05a61feb5f6889aeb917.camel@linux.intel.com> Content-Language: en-US X-Scanned-By: MIMEDefang 2.79 on 10.5.11.12 X-MC-Unique: zxD6shzvNXqZ3DMfEPygnQ-1 X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: quoted-printable X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On 03.02.20 17:18, Alexander Duyck wrote: > On Mon, 2020-02-03 at 08:11 -0500, Michael S. Tsirkin wrote: >> On Thu, Jan 30, 2020 at 11:59:46AM -0800, Tyler Sanderson wrote: >>> >>> On Thu, Jan 30, 2020 at 7:31 AM Wang, Wei W wrot= e: >>> >>> On Thursday, January 30, 2020 11:03 PM, David Hildenbrand wrote: >>> > On 29.01.20 20:11, Tyler Sanderson wrote: >>> > > >>> > > >>> > > On Wed, Jan 29, 2020 at 2:31 AM David Hildenbrand >> > > > wrote: >>> > > >>> > > On 29.01.20 01:22, Tyler Sanderson via Virtualization wrote= : >>> > > > A primary advantage of virtio balloon over other memory r= eclaim >>> > > > mechanisms is that it can pressure the guest's page cache= into >>> > > shrinking. >>> > > > >>> > > > However, since the balloon driver changed to using the sh= rinker >>> API >>> > > > >>> > > >>> > >> > e99a28e355255a#diff-fd202acf694d9eba19c8c64da3e480c9> this >>> > > > use case has become a bit more tricky. I'm wondering what= the >>> > intended >>> > > > device implementation is. >>> > > > >>> > > > When inflating the balloon against page cache (i.e. no fr= ee >>> memory >>> > > > remains) vmscan.c will both shrink page cache, but also i= nvoke >>> the >>> > > > shrinkers -- including the balloon's shrinker. So the bal= loon >>> driver >>> > > > allocates memory which requires reclaim, vmscan gets this= memory >>> > by >>> > > > shrinking the balloon, and then the driver adds the memor= y back >>> to >>> > the >>> > > > balloon. Basically a busy no-op. >>> >>> Per my understanding, the balloon allocation won=E2=80=99t invoke s= hrinker as >>> __GFP_DIRECT_RECLAIM isn't set, no? >>> >>> I could be wrong about the mechanism, but the device sees lots of activ= ity on >>> the deflate queue. The balloon is being shrunk. And this only starts on= ce all >>> free memory is depleted and we're inflating into page cache. >> >> So given this looks like a regression, maybe we should revert the >> patch in question 71994620bb25 ("virtio_balloon: replace oom notifier wi= th shrinker") >> Besides, with VIRTIO_BALLOON_F_FREE_PAGE_HINT >> shrinker also ignores VIRTIO_BALLOON_F_MUST_TELL_HOST which isn't nice >> at all. >> >> So it looks like all this rework introduced more issues than it >> addressed ... >> >> I also CC Alex Duyck for an opinion on this. >> Alex, what do you use to put pressure on page cache? >=20 > I would say reverting probably makes sense. I'm not sure there is much > value to having a shrinker running deflation when you are actively trying > to increase the balloon. It would make more sense to wait until you are > actually about to start hitting oom. I think the shrinker makes sense for free page hinting feature (everything on free_page_list). So instead of only reverting, I think we should split it up and always register the shrinker for VIRTIO_BALLOON_F_FREE_PAGE_HINT and the OOM notifier (as before) for VIRTIO_BALLOON_F_MUST_TELL_HOST. (Of course, adapting what is being done in the shrinker and in the OOM notifier) --=20 Thanks, David / dhildenb