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[2003:cb:c714:d00:a1ab:bff4:268f:d7c5]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-42f86a20471sm11602735e9.17.2024.10.04.03.04.17 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Fri, 04 Oct 2024 03:04:18 -0700 (PDT) Message-ID: <210cb725-fdc5-4878-9e6b-4357d34afb9f@redhat.com> Date: Fri, 4 Oct 2024 12:04:17 +0200 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH V2] mm/gup: folio_split_user_page_pin To: Steven Sistare , Jason Gunthorpe Cc: linux-mm@kvack.org, Andrew Morton , Matthew Wilcox References: <1727190332-385657-1-git-send-email-steven.sistare@oracle.com> <982f3e26-c998-4e72-b374-3f31bf0ca9f5@redhat.com> <20240927155848.GD4568@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: 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-Rspam-User: X-Rspamd-Queue-Id: 8ACF218001D X-Rspamd-Server: rspam01 X-Stat-Signature: ote16uuoqzftkr8zksb59x1qxwuernng X-HE-Tag: 1728036262-566188 X-HE-Meta: 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 c3FGpd6r EwNyZGcAoTFCR/ZKNnS7j58ecONedMgGhI9eDolEzTEMzcESYkyNdAj0W77Pggw0MYUstlpFQ2iuCLVUNjybD3frxDAtYqv0ewQbjT2NLeJxJHrzUW35L8qgh2s5jbSPmSNMBCazGXrHP9gz0i5+XK/xiD1T8XurBVcrpNQ6chyz/+fa6f9c0ccAJXYnIsMyG2RYOHebZ1IPZoNh/srIviKG/6RLkRUvvgl4wESCmC7xAvdvYvlLtXKdnJiikqKegQteNifzxDm0OLS8k7fE+S6mQNSaoDbSecuLs8qOl0x2K+e4SGe7ZMqFZ0RMC2jat3Dy/lcSv7+PAtw5M7mEbMpHZcZijmsjVfU8dFN1xCTyq0NrNNYSC8j6SqRlIvbpQUlMfQqOHYRiERYSE/XEfLBbZk9yTpGu91vJa7mkVOmmkTa+ffckCz9JpXoBrXt2hd5uj 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 01.10.24 19:17, Steven Sistare wrote: > On 9/27/2024 11:58 AM, Jason Gunthorpe wrote: >> On Fri, Sep 27, 2024 at 05:44:52PM +0200, David Hildenbrand wrote: >>> /** >>> * folio_try_add_pins() - add pins to an already-pinned folio >>> * @folio: the folio to add more pins to >>> * >>> * Try to add more pins to an already-pinned folio. The semantics >>> * of the pin (e.g., FOLL_WRITE) follow any existing pin and cannot >>> * be changed. >>> * >>> * This function is helpful when having obtained a pin on a large folio >>> * using memfd_pin_folios(), but wanting to logically unpin parts >>> * (e.g., individual pages) of the folio later, for example, using >>> * unpin_user_page_range_dirty_lock(). >>> * >>> * This is not the right interface to initially pin a folio. >>> */ >>> int folio_try_add_pins(struct folio *folio, unsigned int pins) >>> { >>> VM_WARN_ON_ONCE(!folio_maybe_dma_pinned(folio)); >>> >>> return try_grab_folio(folio, pins, FOLL_PIN); >>> } >> >> That looks pretty good to me too > > Looks good and passes my tests, I will add this version in V3 of the patch series. > > Are you sure you want "try" in the name folio_try_add_pins? Usually try means > that any failure is transient and a future call may succeed And now I took another look at the codebase and we already do have folio_add_pin() that adds a single pin, but continues on overflows (not sure I like that, but at least it can be caught and debugged). So yes, we could simply turn folio_add_pin() into a wrapper around a folio_add_pins() that adds multiple pins. Looking at folio_add_pin() vs. try_grab_folio() I am not sure if the open-coding the logic in folio_add_pin() got the NR_FOLL_PIN_ACQUIRED accounting correct. -- Cheers, David / dhildenb