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b=IEjH+kweDnrDGMvGvPfuOOsJDJfRm7la8rOgwBQPs6ZW4p+I1DS7AWtD3F9EkMAAa hO8KIzaeggQQZ9rhJXPUopHBi+oH/FcU21xL88tsCOn2hTaef2b3wIhOGoxvcv4T2s hxu1FmnrQfImqYACRzwXZSdMlw2y3MZ41Vbx4U/8Bcw2Brp2ziuwZxxdbFSHxVPJJ5 /IlRtQwHMcBihXeJ1bgeDmAGLOIN+ZLnR79gxtMJK8YU7oDb0XxEU+J+Hw0ECEU412 oRiuW27VbE3Jgh+AD/cXh/EMdfTVI5yxRIRxYONSRqomWEaklTiPkntzTzoKdRpzkm fqRnREjbmQKnA== Message-ID: Date: Tue, 3 Nov 2026 09:35:35 +0100 X-Archived-By: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH 8/8] mm/gup: batch contiguous same-folio PTEs into one refcount grab To: Rik van Riel , linux-kernel@vger.kernel.org Cc: Andrew Morton , Jason Gunthorpe , John Hubbard , Peter Xu , Suren Baghdasaryan , Yuan-Hao Hsu , Christoph Hellwig , linux-mm@kvack.org References: <20261102193026.3860700-1-riel@surriel.com> <20261102193026.3860700-9-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: <20261102193026.3860700-9-riel@surriel.com> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit X-Rspamd-Server: rspam06 X-Stat-Signature: ir4cz9k1tm6mf11qbxmo55f86mhy96fy X-Spam-Status: No, score=-17.3 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_CR_TRAILER,INCLUDES_PATCH,MAILING_LIST_MULTI,SPF_HELO_PASS, SPF_PASS,USER_AGENT_SANE_1 autolearn=ham autolearn_force=no version=4.0.1 X-Rspamd-Queue-Id: 0147E40005 X-Rspam-User: X-HE-Tag: 1793694942-605170 X-HE-Meta: U2FsdGVkX1+jUkm+aPx7vohW2/orO3FAWYsZEijWMVK9D7jUFiwM7dn+rqRX9dReyo5PKY20AeuX5Vfer2v9oLm9HE06OQxbuWGpwaxspkNI74tKaaLOwDJmwheKfRyRolcIWJAUCiDdYRjbrBlzMWdoI8TrUjudPwTSuzgSi94VPfqK9nCggQlLD0FVFLlBmUrFn4E0Jgejal9tOxhvtculMTqWhHu8UD9lRlOUgPgFCQOn4BcYRELwSD9fEEKFJZ9ORNt5hf0kZrA2nc0L9oyRYuE5rtiRDfZNINOwLzkoUu8V9v1p7qNpk3cXtn1U51/wNCLgrLntcIu+lRJkYkPttKE0ODz+F3V9r3DBTiIbkQoqn3SPYIPMCS4ykxm/QcqaU0gQvA7ZHhpzz4yoZi7zOw4CHWqq/AKg15p3wmuuuqMbD1zcAEWZ6C68SeRsbZ4dypgZ7HXdvVD/dYGTCTDj44mN0kFzdCf4Z5s0VsMR70dTPmsti9EAr5V8ypKFryXgOsQ97wFTkOnzuFycXQSRk99X7jUeYTqVWeoJXE3op2UsIDkZcyefoTPxnCTFGfZ15vnTt+hVNQU4qGO/5uz4rmVQg2wrA87c3YqEZ7K+nnYE99MFS1y+mtO3bveqmmh8SoLxG6j9hib5VALVSAk4WuRa160iVIwszsNog2NWSahRWwbVxWNRc3dqliER5LaJyqYqgtnLDyyD7R7LTmgdI2jX4UCJDcX2qk3iJuaIgYmAv2cIqmmldNJhV3dD/ZuEKo8d4Gt4fh18iM4WRFnyp/iiM/a1UmaF8fD3eR212BABGvFPs5oSb4slFIiqQtiFiYo7GR38jSkDN40KiD2AYF5VExCkOIk/Ey6pm1jXS3kgljem68w5eYhDWw8021OEzZp5l+kzbO82jAQiBW6C4to8JrQQlW6YfFZf/eIJFYPNiXwnVngJzmAMVh9BFLg8BJ3dl4reloS6KQe MfJTS2LF YgSPJbCBUqctiK92Ax/7Q72fyENQbWp40An4zlfOlyi2InDu8MNv6YY4u8zJGYjUjqaYD0qYLcjt+uCQC2jlnhcHjZ60hGS335gWIH5z61jXqmozRTML3JpNntv1pbwMPEMMTXgd43YBpb8oOKvky4B+oQCCPZO6YpzQRMwLBTRC5wjnDL/PcRyV5Zpn6+2fwUfRT/lN7NrXIM5Aq+iXWiVMEQAX/CbvLD7lkd7YWhMpng/18o9hSOyfOcztTco2HlvW2WuAcen2qyv56pyy7j17X5+/VJ7j93d44YnS4BO9amOqbGGcK03TQdCruaWqmp8QNuB169uklblFoXS3oylO2QA== Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: X-Spam-Checker-Version: SpamAssassin 4.0.1 (2024-03-26) on aws-us-west-2-korg-listserv-alma10-1 On 11/2/26 20:30, Rik van Riel wrote: > follow_page_pte() now walks a whole page table in one call, but still > resolves and commits each PTE on its own, so a PTE-mapped large folio > (mTHP) pays one try_grab_folio() per subpage. > > Add gup_pte_batch_len() and give gup_grab_folio_pages() a run > length. Each run starts with a full per-PTE resolve, then > gup_pte_batch_len() finds how many more PTEs extend it with a pte_same() > scan rather than a re-derivation of each page, and the run is committed > with one refcount grab. Runs stop at folio boundaries, so plain base > pages are unaffected. > > Gather the dirty bits from all the PTEs in a batch, in order to mark > the folio dirty for FOLL_WRITE. > > Same benchmark as the previous change, with before again taken at the > base of the series: > > gup_test -L -m 256 -n 65536 -r 16 -t > before after > 64 kB mTHP 2946 us 231 us (12.8x) > 4 kB base (control) 2753 us 1198 us (2.3x) > 2 MB THP (control) 72 us 71 us > > The 4 kB column is the previous change's 2.3x, unchanged: base pages > share no folio, so there is nothing to batch. 64 kB mTHP goes from that > change's 2.2x to 12.8x, a further 5.9x from committing a run with one > refcount grab instead of one per subpage. > > With FOLL_TOUCH, folio_mark_accessed() runs once per run instead of > once per page: 512 calls before and 32 after over 2 MB of 64 kB > folios, leaving them referenced but inactive after the first call. > That matches the huge-page and fast paths, which mark once > per folio. (Measured by Yuan-Hao Hsu.) > > Suggested-by: David Hildenbrand > Signed-off-by: Rik van Riel > --- > mm/gup.c | 49 ++++++++++++++++++++++++++++++++++++++++++++++--- > 1 file changed, 46 insertions(+), 3 deletions(-) > > diff --git a/mm/gup.c b/mm/gup.c > index 67e20b326be6e..47f204e21a3a7 100644 > --- a/mm/gup.c > +++ b/mm/gup.c > @@ -937,6 +937,35 @@ static long gup_lookup_pte(struct vm_area_struct *vma, unsigned long address, > return 0; > } > > +/* > + * Return how many PTEs map consecutive pages of the same folio and can be > + * committed as one run. Always at least 1. > + * > + * The write-fault and unshare checks in gup_lookup_pte() are per PTE, but a > + * writable run needs no repeat: a writable anon page is exclusive. A read-only > + * run under FOLL_WRITE or FOLL_PIN does need the per-page check, so it stays > + * one page at a time. That's a clear indication that this needs more work. I'll try to get to it soon and see how it could be done in a cleaner way, likely it should be based on top of the gup-fast series where we will have helpers to check for required unsharing of multiple PTEs. -- Cheers, David