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b=B1/yfabyBjcixN4UA0vcVlXQ0twNP3kOpUIfZrRJ5Fu2xVyX3ggAcZfXZeCmhYKxl naEE2DNROhkFbIb/vR3yZKYZ/W16PeVLE4tTZ9DdGiTW3YpFbsR7KZipVdPgDgNecq QSGD2TN/HT+6CrE8Y0Kc/vx7WxFRUvAU9VzDReOchwM/BNC7M3JEGS/JwQ2KaJ7DrI z9Dee90kEEgtpIAeqxYMWt8AK6iUNzezWHkbgETqVUvZoDSa6jcY74aG1DSMuyhnxF BjNcg9JXXNIbYxVCflZeR67OdQg3/1g6UqFg6KjrD8AbNK4S9ZzuIey/F5H1vB2SCL a7lhdpe4PNYqw== Message-ID: <8a9d5a6f-a7c6-468f-8b50-a7aa2b4dea2c@kernel.org> Date: Wed, 12 Aug 2026 13:50:17 +0200 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [RFC PATCH v3 3/8] mm/gup: split follow_page_pte_commit() out of follow_page_pte() To: Rik van Riel , linux-kernel@vger.kernel.org Cc: kernel-team@meta.com, Andrew Morton , Jason Gunthorpe , John Hubbard , Peter Xu , linux-mm@kvack.org References: <20260811025157.1632867-1-riel@surriel.com> <20260811025157.1632867-4-riel@surriel.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: <20260811025157.1632867-4-riel@surriel.com> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit X-Stat-Signature: xmtiow5r83buktwbnr3dqwsajwd469pf X-Rspamd-Queue-Id: 65AAE14000B X-Rspam-User: X-Rspamd-Server: rspam12 X-HE-Tag: 1786535422-155359 X-HE-Meta: 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 z9NfGmRX PqEz+pzNefwOu7DRQrHvzBH9VNdy3ICXYCJl8f3xeVXCUxMUV2nWdE41ZJusVtb1SXZuUpV7nivxG1sG5P2DY0E8VY/BrKZeBWUKk9DtNm3PsrOaqiluOVi0wwHwlZODzuIGoQQSt/dz36PcBQRSgDn7hWdi8Qy0TcPxSF3is78q7UlVlpuyGNJnR+spxUBQ6u8nX5BWBW5Fyzqdsn+suKjiwAQcmZavwA+oop13OUCL4WpEjXvoDT0ypsOo0onAYL31rFdm5FChTFp2lNRo2USBgZ+nzAUP5UqZH4M+r2q4595Crn3AisNsQpOPVP2iVtMH0t0XIUa9+MLmgOEXw6xt3o9Zr2OFRdHtKi8SHt7EBbMC6+VheWEY1YQ53GNRda9sv Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On 8/11/26 04:51, Rik van Riel wrote: > follow_page_pte() does two things once it has resolved a present PTE > to a page: run the per-PTE safety checks (write-fault, unshare), then > commit to that page: grab a ref, fault it in if pinning, mark it > dirty/accessed, and hand it back to the caller. > > Split the second part into its own follow_page_pte_commit(), unchanged > except for taking its inputs as parameters instead of local variables, > so the checks and the commit can be applied at different granularities. > > No functional changes intended. > > Suggested-by: David Hildenbrand > Assisted-by: Claude:claude-opus-4-8 > Signed-off-by: Rik van Riel > --- > mm/gup.c | 78 +++++++++++++++++++++++++++++++++++--------------------- > 1 file changed, 49 insertions(+), 29 deletions(-) > > diff --git a/mm/gup.c b/mm/gup.c > index e4e6d0993424..b755ceaac0f5 100644 > --- a/mm/gup.c > +++ b/mm/gup.c > @@ -822,6 +822,52 @@ static inline bool can_follow_write_pte(pte_t pte, struct page *page, > return !userfaultfd_pte_wp(vma, pte); > } > > +/* > + * The caller has already run every per-PTE safety check (present, > + * write-fault, gup_must_unshare()) on the PTE, so this only does the > + * per-folio work: the refcount grab, the FOLL_PIN accessibility fault-in, > + * dirty/accessed marking, and the array fill with the cache flush. > + */ If a function needs 4 lines of internal doc to understand what it does, then maybe it's not the right function name or abstraction. :) I don't particularly enjoy the "commit" terminology, it looses the detail of the most important thing this function is supposed to to: grab a folio reference. We're passing in the pte only to do a single pte_dirty(). If the helper is actually what we want, likely we just just pass in the pte_dirty() directly and remove all pte leftovers from the helper. I'd assume that we'd want a function where we can similarly punch in a PMD/PUD and have it do the same thing as well, instead of special-casing ptes. Let me think about this some more, I might have to play with the code myself to understand how this should all be cleaned up. -- Cheers, David