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[2003:cb:c708:e100:4f41:ff29:a59f:8c7a]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-436e2ddc5f5sm91661065e9.18.2025.01.10.09.01.17 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Fri, 10 Jan 2025 09:01:19 -0800 (PST) Message-ID: <5608af05-0b7a-4e11-b381-8b57b701e316@redhat.com> Date: Fri, 10 Jan 2025 18:01:16 +0100 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [RFC PATCH 0/2] mm: filemap: add filemap_grab_folios To: Nikita Kalyazin , 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> 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: <20250110154659.95464-1-kalyazin@amazon.com> X-Mimecast-Spam-Score: 0 X-Mimecast-MFC-PROC-ID: 2qiUXg_XGRD8Iau_xk160BtxDECmabPhjxIckETcX8U_1736528482 X-Mimecast-Originator: redhat.com Content-Language: en-US Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-Rspamd-Server: rspam10 X-Rspamd-Queue-Id: 93E64C0024 X-Stat-Signature: 6uw5pi1j8qtz5jqj8uoy333ixcxzjxcf X-Rspam-User: X-HE-Tag: 1736528485-410971 X-HE-Meta: U2FsdGVkX1+y+e6HcZ5N35sCFtihW41Pp+5go9Mwt3p6oxyklxj2PicpL0YkTz5HTtrZi4arByFDcV1ooEwyqm7mqjHscZoIJFD7Ao5iUCMPGaF6VlosZ8Yy9AJf7YP8zxMPq4mpnVZ67tYyvnywt55YcxPqF/L38qcxRv8Jw1QNJKRGZ4Cn+3gSGJGpQ2x0Is7M9dumWUP4nCW38jBrUwGCkkPFI8KaBwySeRj6SJ8tNo5IwubH6i4doNZ3K0kyF4tBREIR8PCqlbjl1MBb+157kOetlEx2ZKN8BAmF3Y9z88slwcPRTCLTMcxDfMWLN3XqIJb8KLo6RC5/XdwlJnyq9W19qRVaScAUs9UIf3iDt8DXS0Ucoe5Iy1IBpchBSBy/pX2oQj3txl82ndI9WoeiPvx1TsYum482mgnglJhtV8M8JQaHeCVL9+NX5nKZrzHWsM8y8U/8ah0WFbD5vZkhCya8GtAV6Wy4ZAobGz9JkyVXfi5xjajzcub28hw6nB/z2FLWeAz0auHd2sabWvdpN6aT9ZHmmie5iaAAgAAdxmDck0TSpdIWDR+MNSLdFX0zzq1ac1RVlMozvaNGQMMDPbpGisUV7uAA/wG+EZ72X2k4HhDw+QaCzZf9eL0RUTeh2IJ/h5tGAlh6jmO9i2LLpr8y0npxN66/LxBKX7kSZH+I55Bumc57PwEnBB9wOp3EOsrofD9Rp0yDrGX2AtcOLCrQQky4u7BgdxDSjUu9Q1mIolKMCtsBz1uWtgwoSTkvjQczYAkxM3MGPQpAaGzRAeBvATUOvHXFlfIAofXMoeHMnoSOUbt/pzUSCAtuRqlkQQtF1rDoD+bQG71FlMTKp9dMcuWdEBrjdPCbZGN0h9BNF9Hfy8W0UGuW6rHJtbCusN+iAwvxo+q9K9gbppSMhb3Hot+WXZ+hfKM+HoN2x2K9MhJhDbze04t0GUp7T20PIEICKzH3uTeCQYk gcoxBaUF O7JEceO8/3HShpCL+yXAfeRG5cPwx/qNZ2L4Ur8PFUy/bsScMec1FuXajELUudaYb2/LMSTYxE7xAT45OZGV/zC7olZ0lhdPcIAy2TyX0W0WU9m9PVkSJzynA6R6zI7JcKC3fb4dIJonFpltdOiZa8Yb1G++RVSSH358xT/viYCuo1pPU2XcH+gkmgPeQ9Kp/+1uForYoDQ7bZriBT0EYYjIoHI+nOemEjZoWZHJuy7Ng4wFjH2kgxOCG/XxfFzbCUtbIaGqAEiB6bFftrjLb8UlY2/m9IfuD+KU2BnK2ppK427/kCP6UvFPvRPTCLT2jcf4y2uawawfAZaRZvogzUGahNfsM/1XMIzAcLjvvhMU4lE2TExiNEgLyQO5DWI1nqfRI3BOE7JaA3YaLMOLctknLArOL4tdZKT4duN2DMSqN7LJO6wrGez9KgKcE3VIASmB0 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000002, 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 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, > 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? > > 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? We do have memfd_pin_folios() that can deal with that and provides a slightly similar interface (struct folio **folios). For reference, the interface is: long memfd_pin_folios(struct file *memfd, loff_t start, loff_t end, struct folio **folios, unsigned int max_folios, pgoff_t *offset) Maybe what you propose could even be used to further improve memfd_pin_folios() internally? However, it must do this FOLL_PIN thingy, so it must process each and every folio it processed. -- Cheers, David / dhildenb