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([2a09:80c0:192:0:5dac:bf3d:c41:c3e7]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-436dcc8f8dfsm146389445e9.0.2025.01.13.04.20.23 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Mon, 13 Jan 2025 04:20:24 -0800 (PST) Message-ID: <5c62bdbb-7a4e-4178-8c03-e84491d8d150@redhat.com> Date: Mon, 13 Jan 2025 13:20:23 +0100 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [RFC PATCH 0/2] mm: filemap: add filemap_grab_folios To: kalyazin@amazon.com, willy@infradead.org, pbonzini@redhat.com, linux-fsdevel@vger.kernel.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org, kvm@vger.kernel.org Cc: michael.day@amd.com, jthoughton@google.com, michael.roth@amd.com, ackerleytng@google.com, graf@amazon.de, jgowans@amazon.com, roypat@amazon.co.uk, derekmn@amazon.com, nsaenz@amazon.es, xmarcalx@amazon.com References: <20250110154659.95464-1-kalyazin@amazon.com> <5608af05-0b7a-4e11-b381-8b57b701e316@redhat.com> From: David Hildenbrand Autocrypt: addr=david@redhat.com; keydata= xsFNBFXLn5EBEAC+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 B3JfpUqcWwE7vUaYrHG1nw54pLUoPG6sAA7Mehl3nd4pZUALHwARAQABzSREYXZpZCBIaWxk ZW5icmFuZCA8ZGF2aWRAcmVkaGF0LmNvbT7CwZgEEwEIAEICGwMGCwkIBwMCBhUIAgkKCwQW AgMBAh4BAheAAhkBFiEEG9nKrXNcTDpGDfzKTd4Q9wD/g1oFAl8Ox4kFCRKpKXgACgkQTd4Q 9wD/g1oHcA//a6Tj7SBNjFNM1iNhWUo1lxAja0lpSodSnB2g4FCZ4R61SBR4l/psBL73xktp rDHrx4aSpwkRP6Epu6mLvhlfjmkRG4OynJ5HG1gfv7RJJfnUdUM1z5kdS8JBrOhMJS2c/gPf wv1TGRq2XdMPnfY2o0CxRqpcLkx4vBODvJGl2mQyJF/gPepdDfcT8/PY9BJ7FL6Hrq1gnAo4 3Iv9qV0JiT2wmZciNyYQhmA1V6dyTRiQ4YAc31zOo2IM+xisPzeSHgw3ONY/XhYvfZ9r7W1l pNQdc2G+o4Di9NPFHQQhDw3YTRR1opJaTlRDzxYxzU6ZnUUBghxt9cwUWTpfCktkMZiPSDGd KgQBjnweV2jw9UOTxjb4LXqDjmSNkjDdQUOU69jGMUXgihvo4zhYcMX8F5gWdRtMR7DzW/YE BgVcyxNkMIXoY1aYj6npHYiNQesQlqjU6azjbH70/SXKM5tNRplgW8TNprMDuntdvV9wNkFs 9TyM02V5aWxFfI42+aivc4KEw69SE9KXwC7FSf5wXzuTot97N9Phj/Z3+jx443jo2NR34XgF 89cct7wJMjOF7bBefo0fPPZQuIma0Zym71cP61OP/i11ahNye6HGKfxGCOcs5wW9kRQEk8P9 M/k2wt3mt/fCQnuP/mWutNPt95w9wSsUyATLmtNrwccz63XOwU0EVcufkQEQAOfX3n0g0fZz 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+w6DABEBAAHCwXwEGAEIACYCGwwWIQQb2cqtc1xMOkYN/MpN3hD3 AP+DWgUCXw7HsgUJEqkpoQAKCRBN3hD3AP+DWrrpD/4qS3dyVRxDcDHIlmguXjC1Q5tZTwNB boaBTPHSy/Nksu0eY7x6HfQJ3xajVH32Ms6t1trDQmPx2iP5+7iDsb7OKAb5eOS8h+BEBDeq 3ecsQDv0fFJOA9ag5O3LLNk+3x3q7e0uo06XMaY7UHS341ozXUUI7wC7iKfoUTv03iO9El5f XpNMx/YrIMduZ2+nd9Di7o5+KIwlb2mAB9sTNHdMrXesX8eBL6T9b+MZJk+mZuPxKNVfEQMQ a5SxUEADIPQTPNvBewdeI80yeOCrN+Zzwy/Mrx9EPeu59Y5vSJOx/z6OUImD/GhX7Xvkt3kq Er5KTrJz3++B6SH9pum9PuoE/k+nntJkNMmQpR4MCBaV/J9gIOPGodDKnjdng+mXliF3Ptu6 3oxc2RCyGzTlxyMwuc2U5Q7KtUNTdDe8T0uE+9b8BLMVQDDfJjqY0VVqSUwImzTDLX9S4g/8 kC4HRcclk8hpyhY2jKGluZO0awwTIMgVEzmTyBphDg/Gx7dZU1Xf8HFuE+UZ5UDHDTnwgv7E th6RC9+WrhDNspZ9fJjKWRbveQgUFCpe1sa77LAw+XFrKmBHXp9ZVIe90RMe2tRL06BGiRZr jPrnvUsUUsjRoRNJjKKA/REq+sAnhkNPPZ/NNMjaZ5b8Tovi8C0tmxiCHaQYqj7G2rgnT0kt WNyWQQ== Organization: Red Hat In-Reply-To: X-Mimecast-Spam-Score: 0 X-Mimecast-MFC-PROC-ID: RHuRjk0CAaH-QnTkdPbFKZnzsAvRef9EAuPW5y-iLsI_1736770825 X-Mimecast-Originator: redhat.com Content-Language: en-US Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit X-Rspamd-Queue-Id: 69B7A80012 X-Rspam-User: X-Rspamd-Server: rspam07 X-Stat-Signature: e71ptzwuz7fq795ust1mjpwd3da38aun X-HE-Tag: 1736770828-294110 X-HE-Meta: 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 U/SFDYsv 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 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000444, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On 10.01.25 19:54, Nikita Kalyazin wrote: > On 10/01/2025 17:01, David Hildenbrand wrote: >> On 10.01.25 16:46, Nikita Kalyazin wrote: >>> Based on David's suggestion for speeding up guest_memfd memory >>> population [1] made at the guest_memfd upstream call on 5 Dec 2024 [2], >>> this adds `filemap_grab_folios` that grabs multiple folios at a time. >>> >> >> Hi, > > Hi :) > >> >>> Motivation >>> >>> When profiling guest_memfd population and comparing the results with >>> population of anonymous memory via UFFDIO_COPY, I observed that the >>> former was up to 20% slower, mainly due to adding newly allocated pages >>> to the pagecache.  As far as I can see, the two main contributors to it >>> are pagecache locking and tree traversals needed for every folio.  The >>> RFC attempts to partially mitigate those by adding multiple folios at a >>> time to the pagecache. >>> >>> Testing >>> >>> With the change applied, I was able to observe a 10.3% (708 to 635 ms) >>> speedup in a selftest that populated 3GiB guest_memfd and a 9.5% (990 to >>> 904 ms) speedup when restoring a 3GiB guest_memfd VM snapshot using a >>> custom Firecracker version, both on Intel Ice Lake. >> >> Does that mean that it's still 10% slower (based on the 20% above), or >> were the 20% from a different micro-benchmark? > > Yes, it is still slower: > - isolated/selftest: 2.3% > - Firecracker setup: 8.9% > > Not sure why the values are so different though. I'll try to find an > explanation. The 2.3% looks very promising. > >>> >>> Limitations >>> >>> While `filemap_grab_folios` handles THP/large folios internally and >>> deals with reclaim artifacts in the pagecache (shadows), for simplicity >>> reasons, the RFC does not support those as it demonstrates the >>> optimisation applied to guest_memfd, which only uses small folios and >>> does not support reclaim at the moment. >> >> It might be worth pointing out that, while support for larger folios is >> in the works, there will be scenarios where small folios are unavoidable >> in the future (mixture of shared and private memory). >> >> How hard would it be to just naturally support large folios as well? > > I don't think it's going to be impossible. It's just one more dimension > that needs to be handled. `__filemap_add_folio` logic is already rather > complex, and processing multiple folios while also splitting when > necessary correctly looks substantially convoluted to me. So my idea > was to discuss/validate the multi-folio approach first before rolling > the sleeves up. We should likely try making this as generic as possible, meaning we'll support roughly what filemap_grab_folio() would have supported (e.g., also large folios). Now I find filemap_get_folios_contig() [thas is already used in memfd code], and wonder if that could be reused/extended fairly easily. -- Cheers, David / dhildenb