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[2003:cb:c71b:5d00:18d7:1475:24bc:2417]) by smtp.gmail.com with ESMTPSA id l6-20020a05600c4f0600b0040b45282f88sm2000544wmq.36.2023.12.07.05.35.44 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Thu, 07 Dec 2023 05:35:45 -0800 (PST) Message-ID: <5e9ca410-3273-493b-bb8a-8496ab0879c0@redhat.com> Date: Thu, 7 Dec 2023 14:35:43 +0100 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v6 3/5] mm/gup: Introduce memfd_pin_user_pages() for pinning memfd pages (v6) To: Jason Gunthorpe Cc: "Kasireddy, Vivek" , "dri-devel@lists.freedesktop.org" , "linux-mm@kvack.org" , Christoph Hellwig , Daniel Vetter , Mike Kravetz , Hugh Dickins , Peter Xu , Gerd Hoffmann , "Kim, Dongwon" , "Chang, Junxiao" References: <20231205053509.2342169-1-vivek.kasireddy@intel.com> <20231205053509.2342169-4-vivek.kasireddy@intel.com> <5ffe2ea3-83da-4b5f-adc8-af9cd9a57cd2@redhat.com> <20231207130532.GH2692119@nvidia.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: <20231207130532.GH2692119@nvidia.com> X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Language: en-US Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-Rspamd-Queue-Id: 4E7BC1A001B X-Rspam-User: X-Rspamd-Server: rspam05 X-Stat-Signature: hy9nxk8schxp5z6zhyft98tsjr3gbxga X-HE-Tag: 1701956149-251018 X-HE-Meta: U2FsdGVkX19PoRaRQk7Jq4xS2igBeO9gUUDm+6LtCnOiegkmVsekOw9/K07hU6inxQj7nYOTRFGxX+WvyAYHKJcbET7+K0xmRUyhaokhSpPdjB14PlOIJx1vshwsbaShFhMPR0uUCuLuPOnBCS63qk5LFv0DPLnko+U4c3+tSLaXUxbRs9QxNwg2dLDETB9ZoIj/ZMXdtt+soxn33E7apKIjQ5TE8Hty6ok+0HCqs7VTn4QbGDpXMgccWlsD5MF+2as3EGlajcIliyRplMvGRmTnftAAiaul61bdR3Z3CkF+bDQIS7D3MJtMVL8vVTiOUyb5z3K59P19TaUakQBNinIYvHYaQCxHdeLtjuGrADZtv5Ve7dcruVYojHKoSHQntHMHfZJYMqLXFb59xq0ufEmsxhUfl9L5swEobYrzD5vR22L/FGATmiSp16n8WxnEKQKdRFEe08drzXDU7Cdl6wFI4oaiO6b9ktCvCimWQFK26LD9y/0ToRIelcy61yNUcVwzrwJMC8VTKocok9d1aDwBFibRF6gSbrDjgeC5QHGjbLrt5L5b+kD7txxn93kAEJSaQRbEFP+cIMN17sipBHVnco+Zx8K+PVO/sodKAxPGm3Dmycwo8pCvr6OgGGxt9yfFi4cBh9XUi3nLp+V7QGrbPHhQYypXgnjefsbcS6QS9n4b9vOruOpr+uxq9Zkn+v+OYbg3H0EM3e+x08eMu4sRdgVU5z7RIoe98+Bfk3NtqBEkQpjqsCaPs8GtJ4ZM04q+oDSuKEKPkh9LAWmagCJpSFFXkFnDyoIYRJJHvcjWa2DsIf4Vzo9V73mp4Jmb3qGlFyD8+MqMceVYt67NBMUzBU0tqBX7vLyZlcrcoZC41lFs4/kZw7kz5TuF8OIfogeMPa88a3iLHQWwwkO8u3CjZUzFUAh3o/0NzdJxlECjts39FCdcivCFkWN909MYl6CIhZ2Rgt89Av5auUT MiQj7xTs 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 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: List-Subscribe: List-Unsubscribe: On 07.12.23 14:05, Jason Gunthorpe wrote: > On Thu, Dec 07, 2023 at 10:44:14AM +0100, David Hildenbrand wrote: > >>>> If you always want to return folios, then better name it >>>> "memfd_pin_user_folios" (or just "memfd_pin_folios") and pass in a range >>>> (instead of a nr_pages parameter), and somehow indicate to the caller >>>> how many folio were in that range, and if that range was fully covered. >>> I think it makes sense to return folios from this interface; and considering my >>> use-case, I'd like have this API return an error if it cannot pin (or allocate) >>> the exact number of folios the caller requested. >> >> Okay, then better use folios. >> >> Assuming a caller puts in "start = X" and gets some large folio back. How is >> the caller supposed to know at which offset to look into that folio (IOW< >> which subpage)? For "pages" it was obvious (you get the actual subpages), >> but as soon as we return a large folio, some information is missing for the >> caller. >> >> How can the caller figure that out? > > This can only work if the memfd is required to only have full folios > at aligned locations. Under that restriction computing the first folio > offset is easy enough: > > folio offset = (start % folio size) > > But is that true for the memfds here? I assume folios are always naturally aligned, like: [ 2m ][ 2m ][1m][1m][ 2m ] ^f0 ^f1 ^f2 ^f3 ^f4 If you query the range "3m -> 7m", you get back f1,f2,f3,f4 and have to start in the middle of the first folio with offset 1m. From there, it is indeed simply continuing with the full folio size -- until the last folio, where you want to only process 1m. folio offset = (1m % 2m) would be correct in that case. -- Cheers, David / dhildenb