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Tsirkin" , Tyler Sanderson , "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> <539B606A-A0CA-4AA4-B99A-759C874A1EF8@vmware.com> <08D323B9-0B4A-47B2-9955-511B8FBA056B@vmware.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: Wed, 5 Feb 2020 09:19:58 +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: <08D323B9-0B4A-47B2-9955-511B8FBA056B@vmware.com> Content-Language: en-US X-Scanned-By: MIMEDefang 2.79 on 10.5.11.15 X-MC-Unique: Ht8HAqdANX-9Ti2ApN923Q-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 05.02.20 08:35, Nadav Amit wrote: >> On Feb 3, 2020, at 2:50 PM, Nadav Amit wrote: >> >>> On Feb 3, 2020, at 8:34 AM, David Hildenbrand wrote: >>> >>> 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 w= rote: >>>>>> >>>>>> 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 reclaim >>>>>>>>> mechanisms is that it can pressure the guest's page cache into >>>>>>>> shrinking. >>>>>>>>> However, since the balloon driver changed to using the shrinker >>>>>> 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 free >>>>>> memory >>>>>>>>> remains) vmscan.c will both shrink page cache, but also invoke >>>>>> the >>>>>>>>> shrinkers -- including the balloon's shrinker. So the balloon >>>>>> driver >>>>>>>>> allocates memory which requires reclaim, vmscan gets this memory >>>>>>> by >>>>>>>>> shrinking the balloon, and then the driver adds the memory back >>>>>> to >>>>>>> the >>>>>>>>> balloon. Basically a busy no-op. >>>>>> >>>>>> Per my understanding, the balloon allocation won=E2=80=99t invoke = shrinker as >>>>>> __GFP_DIRECT_RECLAIM isn't set, no? >>>>>> >>>>>> I could be wrong about the mechanism, but the device sees lots of ac= tivity on >>>>>> the deflate queue. The balloon is being shrunk. And this only starts= once 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= with shrinker") >>>>> Besides, with VIRTIO_BALLOON_F_FREE_PAGE_HINT >>>>> shrinker also ignores VIRTIO_BALLOON_F_MUST_TELL_HOST which isn't nic= e >>>>> 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? >>>> >>>> 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 try= ing >>>> to increase the balloon. It would make more sense to wait until you ar= e >>>> 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) >> >> David, >> >> Please keep me posted. I decided to adapt the same solution as the virti= o >> balloon for the VMware balloon. If the verdict is that this is damaging = and >> the OOM notifier should be used instead, I will submit patches to move t= o >> OOM notifier as well. >=20 > Adding some information for the record (if someone googles this thread): >=20 > In the VMware balloon driver, the shrinker is disabled by default since w= e > encountered a performance degradation in testing. I tried to avoid rapid > inflation/shrinker-deflation cycles by adding a timeout, but apparently i= t > did not help in avoiding the performance regression. Thanks for that info. To me that sounds like the shrinker is the wrong approach to "auto-deflation". It's not just "some slab cache". --=20 Thanks, David / dhildenb