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b=H0y4XfEsOVNCGqoUDscQt9w/W+I3LSbHnpHe1Q3eP70hx3DeqaSoxp9haRkO53gZG uOrt9UfMoiDrgf4vKFOMF4mHsKfjkKJ3UvprKlt6GGMVDg90xBqkTmyq8yIqaxAUst xEqQA5jNnla1N70yq3pjuYoblpBZiJ++mOvFORPK6FvDw4p0XCycxRAeXIs7dyi3Ig 5u713g83UW60jiTZsVNxFhSqA4bDVLADn5SaDjdE8QNdfYQ8iLx6Ky7Tu0eyjkcNWI y9MYoX1aqsiDkCBF0C+eO70343GPc46VtYnBTC85SuJFvJ/+yyuwYmX2QhiiwXWvji IbXw+p4MqfAfg== Message-ID: <8791028d-00a6-45a4-a46e-681d77d95dcd@kernel.org> Date: Mon, 18 May 2026 11:42:43 +0200 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH] mm/gup: fix GUP-fast fallback for NULL-mapping order-0 folios To: Balbir Singh , John Hubbard , Andrew Morton Cc: Jason Gunthorpe , Peter Xu , Mike Rapoport , LKML , linux-mm@kvack.org, Sourab Gupta , Zi Yan References: <20260409014647.397515-1-jhubbard@nvidia.com> <4d6c1af0-dee5-4f1b-b74c-2ebc23de7baf@kernel.org> <08afbec2-bbe7-4e8a-8d99-8a5eaecaeee7@nvidia.com> From: "David Hildenbrand (Arm)" Content-Language: en-US Autocrypt: addr=david@kernel.org; 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 B3JfpUqcWwE7vUaYrHG1nw54pLUoPG6sAA7Mehl3nd4pZUALHwARAQABzS5EYXZpZCBIaWxk ZW5icmFuZCAoQ3VycmVudCkgPGRhdmlkQGtlcm5lbC5vcmc+wsGQBBMBCAA6AhsDBQkmWAik AgsJBBUKCQgCFgICHgUCF4AWIQQb2cqtc1xMOkYN/MpN3hD3AP+DWgUCaYJt/AIZAQAKCRBN 3hD3AP+DWriiD/9BLGEKG+N8L2AXhikJg6YmXom9ytRwPqDgpHpVg2xdhopoWdMRXjzOrIKD g4LSnFaKneQD0hZhoArEeamG5tyo32xoRsPwkbpIzL0OKSZ8G6mVbFGpjmyDLQCAxteXCLXz ZI0VbsuJKelYnKcXWOIndOrNRvE5eoOfTt2XfBnAapxMYY2IsV+qaUXlO63GgfIOg8RBaj7x 3NxkI3rV0SHhI4GU9K6jCvGghxeS1QX6L/XI9mfAYaIwGy5B68kF26piAVYv/QZDEVIpo3t7 /fjSpxKT8plJH6rhhR0epy8dWRHk3qT5tk2P85twasdloWtkMZ7FsCJRKWscm1BLpsDn6EQ4 jeMHECiY9kGKKi8dQpv3FRyo2QApZ49NNDbwcR0ZndK0XFo15iH708H5Qja/8TuXCwnPWAcJ DQoNIDFyaxe26Rx3ZwUkRALa3iPcVjE0//TrQ4KnFf+lMBSrS33xDDBfevW9+Dk6IISmDH1R HFq2jpkN+FX/PE8eVhV68B2DsAPZ5rUwyCKUXPTJ/irrCCmAAb5Jpv11S7hUSpqtM/6oVESC 3z/7CzrVtRODzLtNgV4r5EI+wAv/3PgJLlMwgJM90Fb3CB2IgbxhjvmB1WNdvXACVydx55V7 LPPKodSTF29rlnQAf9HLgCphuuSrrPn5VQDaYZl4N/7zc2wcWM7BTQRVy5+RARAA59fefSDR 9nMGCb9LbMX+TFAoIQo/wgP5XPyzLYakO+94GrgfZjfhdaxPXMsl2+o8jhp/hlIzG56taNdt VZtPp3ih1AgbR8rHgXw1xwOpuAd5lE1qNd54ndHuADO9a9A0vPimIes78Hi1/yy+ZEEvRkHk /kDa6F3AtTc1m4rbbOk2fiKzzsE9YXweFjQvl9p+AMw6qd/iC4lUk9g0+FQXNdRs+o4o6Qvy iOQJfGQ4UcBuOy1IrkJrd8qq5jet1fcM2j4QvsW8CLDWZS1L7kZ5gT5EycMKxUWb8LuRjxzZ 3QY1aQH2kkzn6acigU3HLtgFyV1gBNV44ehjgvJpRY2cC8VhanTx0dZ9mj1YKIky5N+C0f21 zvntBqcxV0+3p8MrxRRcgEtDZNav+xAoT3G0W4SahAaUTWXpsZoOecwtxi74CyneQNPTDjNg azHmvpdBVEfj7k3p4dmJp5i0U66Onmf6mMFpArvBRSMOKU9DlAzMi4IvhiNWjKVaIE2Se9BY FdKVAJaZq85P2y20ZBd08ILnKcj7XKZkLU5FkoA0udEBvQ0f9QLNyyy3DZMCQWcwRuj1m73D sq8DEFBdZ5eEkj1dCyx+t/ga6x2rHyc8Sl86oK1tvAkwBNsfKou3v+jP/l14a7DGBvrmlYjO 59o3t6inu6H7pt7OL6u6BQj7DoMAEQEAAcLBfAQYAQgAJgIbDBYhBBvZyq1zXEw6Rg38yk3e EPcA/4NaBQJonNqrBQkmWAihAAoJEE3eEPcA/4NaKtMQALAJ8PzprBEXbXcEXwDKQu+P/vts IfUb1UNMfMV76BicGa5NCZnJNQASDP/+bFg6O3gx5NbhHHPeaWz/VxlOmYHokHodOvtL0WCC 8A5PEP8tOk6029Z+J+xUcMrJClNVFpzVvOpb1lCbhjwAV465Hy+NUSbbUiRxdzNQtLtgZzOV Zw7jxUCs4UUZLQTCuBpFgb15bBxYZ/BL9MbzxPxvfUQIPbnzQMcqtpUs21CMK2PdfCh5c4gS sDci6D5/ZIBw94UQWmGpM/O1ilGXde2ZzzGYl64glmccD8e87OnEgKnH3FbnJnT4iJchtSvx yJNi1+t0+qDti4m88+/9IuPqCKb6Stl+s2dnLtJNrjXBGJtsQG/sRpqsJz5x1/2nPJSRMsx9 5YfqbdrJSOFXDzZ8/r82HgQEtUvlSXNaXCa95ez0UkOG7+bDm2b3s0XahBQeLVCH0mw3RAQg r7xDAYKIrAwfHHmMTnBQDPJwVqxJjVNr7yBic4yfzVWGCGNE4DnOW0vcIeoyhy9vnIa3w1uZ 3iyY2Nsd7JxfKu1PRhCGwXzRw5TlfEsoRI7V9A8isUCoqE2Dzh3FvYHVeX4Us+bRL/oqareJ CIFqgYMyvHj7Q06kTKmauOe4Nf0l0qEkIuIzfoLJ3qr5UyXc2hLtWyT9Ir+lYlX9efqh7mOY qIws/H2t In-Reply-To: <08afbec2-bbe7-4e8a-8d99-8a5eaecaeee7@nvidia.com> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit X-Rspamd-Server: rspam09 X-Rspamd-Queue-Id: E06A41C0007 X-Rspam-User: X-Stat-Signature: bqofeqqq1w56a5rkai8dskpq775jgud5 X-HE-Tag: 1779097370-278496 X-HE-Meta: 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 kuZXz0UN ZkKviHVCeWQnPUyBUexXCrXtFf9pHu2CIwgPBMPMUVgMvszMJDvHsfsdJE10A9Lb1tBpkWNJ/7gA2o51XVjAXUEyR1QCQAkV73R9d2mEAujApGCCQ7DbV35uRi1EDXT/i21Y1n8pV7NAvylfw4Chjf2teItnCoPxDA5Kkn2nxA5+H5vSSdmP0OaA2IyaoM0PsQuNu8vSVR82RePaoGJP/Ll+qR+P1SJ8+IJiOKjrXLIssqT3FfpyOq22lGtaHSeurl7St Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On 5/15/26 02:09, Balbir Singh wrote: > On 4/9/26 17:52, David Hildenbrand (Arm) wrote: >> On 4/9/26 03:46, John Hubbard wrote: >>> Since commit f002882ca369 ("mm: merge folio_is_secretmem() and >>> folio_fast_pin_allowed() into gup_fast_folio_allowed()"), >>> gup_fast_folio_allowed() falls back to the slow path for any order-0 >>> folio with a NULL mapping when CONFIG_SECRETMEM=y. This causes a >>> performance regression for drivers that allocate pages with alloc_page() >>> and insert them into VMAs via vm_insert_page(). These pages legitimately >>> have a NULL folio->mapping, but they cannot be secretmem pages. >>> >>> Secretmem pages are always added to the secretmem inode's page cache via >>> filemap_add_folio(), which sets folio->mapping to the inode's i_mapping. >>> A folio with a NULL mapping can never be a secretmem folio. The >>> NULL-mapping check was intended to handle truncated file-backed pages (a >>> reject_file_backed concern), not secretmem detection. >>> >>> When only check_secretmem is true (and reject_file_backed is false), a >>> NULL mapping is sufficient to prove the folio is not secretmem, so the >>> fast path can proceed. >> >> Hm, what if secretmem folio just got truncated? I hate to rely on some >> handling in the caller to detect truncation differently during GUP-fast, >> but this function returning "true". >> > > Can secretmem folios be truncated? I assume you are referring to > ftruncate(), I am looking at the setattr implementation of secretmem > and it does not seem like it can be truncated. I thought FALLOC_FL_PUNCH_HOLE would work. But indeed, that does not seem to be wired up. -- Cheers, David