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Tsirkin" Cc: David Rientjes , linux-kernel@vger.kernel.org, linux-mm@kvack.org, virtualization@lists.linux-foundation.org, Jason Wang , Stephen Rothwell , Tyler Sanderson , Wei Wang , Alexander Duyck , Nadav Amit , Michal Hocko , Andrew Morton References: <20200310113854.11515-1-david@redhat.com> <890da35b-1ac2-9c2e-b42d-96d24d3e0f4c@redhat.com> <20200311070952-mutt-send-email-mst@kernel.org> 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, 11 Mar 2020 12:21:07 +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: <20200311070952-mutt-send-email-mst@kernel.org> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit X-Scanned-By: MIMEDefang 2.79 on 10.5.11.14 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 11.03.20 12:12, Michael S. Tsirkin wrote: > On Tue, Mar 10, 2020 at 08:13:19PM +0100, David Hildenbrand wrote: >> On 10.03.20 20:05, David Rientjes wrote: >>> On Tue, 10 Mar 2020, David Hildenbrand wrote: >>> >>>> Commit 71994620bb25 ("virtio_balloon: replace oom notifier with shrinker") >>>> changed the behavior when deflation happens automatically. Instead of >>>> deflating when called by the OOM handler, the shrinker is used. >>>> >>>> However, the balloon is not simply some other slab cache that should be >>>> shrunk when under memory pressure. The shrinker does not have a concept of >>>> priorities yet, so this behavior cannot be configured. Eventually once >>>> that is in place, we might want to switch back after doing proper >>>> testing. >>>> >>>> There was a report that this results in undesired side effects when >>>> inflating the balloon to shrink the page cache. [1] >>>> "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." >>>> >>>> The name "deflate on OOM" makes it pretty clear when deflation should >>>> happen - after other approaches to reclaim memory failed, not while >>>> reclaiming. This allows to minimize the footprint of a guest - memory >>>> will only be taken out of the balloon when really needed. >>>> >>>> Keep using the shrinker for VIRTIO_BALLOON_F_FREE_PAGE_HINT, because >>>> this has no such side effects. Always register the shrinker with >>>> VIRTIO_BALLOON_F_FREE_PAGE_HINT now. We are always allowed to reuse free >>>> pages that are still to be processed by the guest. The hypervisor takes >>>> care of identifying and resolving possible races between processing a >>>> hinting request and the guest reusing a page. >>>> >>>> In contrast to pre commit 71994620bb25 ("virtio_balloon: replace oom >>>> notifier with shrinker"), don't add a moodule parameter to configure the >>>> number of pages to deflate on OOM. Can be re-added if really needed. >>>> Also, pay attention that leak_balloon() returns the number of 4k pages - >>>> convert it properly in virtio_balloon_oom_notify(). >>>> >>>> Testing done by Tyler for future reference: >>>> Test setup: VM with 16 CPU, 64GB RAM. Running Debian 10. We have a 42 >>>> GB file full of random bytes that we continually cat to /dev/null. >>>> This fills the page cache as the file is read. Meanwhile we trigger >>>> the balloon to inflate, with a target size of 53 GB. This setup causes >>>> the balloon inflation to pressure the page cache as the page cache is >>>> also trying to grow. Afterwards we shrink the balloon back to zero (so >>>> total deflate = total inflate). >>>> >>>> Without patch (kernel 4.19.0-5): >>>> Inflation never reaches the target until we stop the "cat file > >>>> /dev/null" process. Total inflation time was 542 seconds. The longest >>>> period that made no net forward progress was 315 seconds (see attached >>>> graph). >>>> Result of "grep balloon /proc/vmstat" after the test: >>>> balloon_inflate 154828377 >>>> balloon_deflate 154828377 >>>> >>>> With patch (kernel 5.6.0-rc4+): >>>> Total inflation duration was 63 seconds. No deflate-queue activity >>>> occurs when pressuring the page-cache. >>>> Result of "grep balloon /proc/vmstat" after the test: >>>> balloon_inflate 12968539 >>>> balloon_deflate 12968539 >>>> >>>> Conclusion: This patch fixes the issue. In the test it reduced >>>> inflate/deflate activity by 12x, and reduced inflation time by 8.6x. >>>> But more importantly, if we hadn't killed the "grep balloon >>>> /proc/vmstat" process then, without the patch, the inflation process >>>> would never reach the target. >>>> >>>> [1] https://www.spinics.net/lists/linux-virtualization/msg40863.html >>>> >>>> Reported-by: Tyler Sanderson >>>> Tested-by: Tyler Sanderson >>>> Fixes: 71994620bb25 ("virtio_balloon: replace oom notifier with shrinker") >>>> Cc: Michael S. Tsirkin >>>> Cc: Wei Wang >>>> Cc: Alexander Duyck >>>> Cc: David Rientjes >>>> Cc: Nadav Amit >>>> Cc: Michal Hocko >>>> Cc: Andrew Morton >>>> Signed-off-by: David Hildenbrand >>> >>> Acked-by: David Rientjes >>> >> >> Thanks! > > David could you repost with corrected commit log > so Andrew can merge? To make sure it's not missed, > it's probably a good idea to have a cover letter > mentioning mm in the subject. Yes, on my list, busy with some other stuff. Will make sure Andrew will see this mail :) -- Thanks, David / dhildenb