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b=hFNsG5v7l1bYLH8AHxJxTQurUxLaGlnnjZizxaZlF/UEhI5QdtOB5BAiCbSRo/Mfj not+fjdMpz3CVNigeJdaM2uQryJnkDJD8NFLC5ihwXF2pEi5Me6go11Pbv7z/I+wvE 1bFE2d6Exx9+k4kqXSGQ7JtpX9M5soPFZb2lmqp9+qiOyzctZynL536Fdv2faUIEiR vBec35/Y2WYYh0VEMnUpdwAWtn+O+Xe7LXH/O34Bb6onANgav5zs/AequvluT/4sCc fGSYgVAqyNPCFgONkao4zDVJlU1s36Wsz6NU9lN6o1cZ84v+38L9Fa4dEcg8MkRalV 5hsIWsZ7EmhnQ== Message-ID: <5d91760e-79e6-4bb7-9c41-52d8ab17ee82@kernel.org> Date: Wed, 12 Aug 2026 13:41:13 +0200 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [RFC PATCH v3 0/8] batch lookups in follow_page_mask() 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> 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: <20260811025157.1632867-1-riel@surriel.com> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit X-Stat-Signature: gq77565abidfhhhogchr5mhueyz6mrxz X-Rspamd-Queue-Id: 3F24220004 X-Rspamd-Server: rspam03 X-Rspam-User: X-HE-Tag: 1786534878-146801 X-HE-Meta: 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 5HnbP26Q vzsSyll3zD5QRqhQ9lAMHpy7f6hwkQa6opCBqk4MHQWt6GySkz8IhJQJD5aYnyhUv3POyCyeJcM2mjT+UVHFfXuIrg6uSP4gicdu5zJ32B/8IzV0N6espQjMMVfslF0ZoqSLIQdRDcbzpV5sJWlEBkO/eq9uNfnSJF76KVNW9hZcUw6LSUbfmNxedheQHqTq0+4+0qHSUv1kSU/luJO8eIr/MoEoLXMZ0m+fYpVOYBkFtdGjXME65ZjEuPn1I26se6wbWaQ409SyjGHKddBkGp4zrZhXycPLuuGs2Shs6dFpsWh7AR+ebTMfnFQ== 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_mask() walks the page tables one page at a time, even when the > caller asked for a whole run of contiguous pages. Every page of a large folio > re-enters the pmd/pud/pte walk and re-takes the page table lock. > > This series changes follow_page_mask() to return a page count and a fill an > array of pages, instead of a single struct page, so a walker can hand back > more than one page per call. > > Patches 1 to 4 are preparation, no functional change: > > 1: move __get_user_pages()'s open-coded pages[] fill and cache flush into a > gup_fill_pages() helper, which the rest of the series reuses. > 2: convert the follow_page_mask()/follow_p4d_mask()/follow_pud_mask()/ > follow_pmd_mask()/follow_page_pte() call chain to return a long instead of > a struct page pointer or ERR_PTR(). Every path still handles one page. > 3: split the "commit to a resolved page" tail of follow_page_pte() into > follow_page_pte_commit(). > 4: split the "work out which page this PTE maps" half of follow_page_pte() > into follow_one_pte(), leaving one unlock and one exit. > > Patch 5 has the huge page paths store the page and leave the array fill to > follow_pud_mask()/follow_pmd_mask() after they unlock, so the cache flushes > happen outside the pud/pmd critical section. > > Patch 6 has follow_huge_pud()/follow_huge_pmd() report the huge page's real > subpage count instead of a separate *page_mask output, and retires *page_mask > and __get_user_pages()'s try_grab_folio() call and subpage loop. > > Patch 7 walks every PTE in a page table in one follow_page_pte() call instead > of one per page. > > Patch 8 adds follow_pte_batch() so a contiguous same-folio run is committed > with one refcount grab. This is the only patch whose benefit depends on folio > size; patch 7 alone covers plain base pages. > > Patches 7 and 8 carry their own benchmark tables, both measured against the > base of the series, so the split between the two mechanisms is visible: the > single-call walk is worth 2.3x on base pages and 2.2x on 64 kB mTHP, and > refcount batching adds a further 5.9x on the mTHP case. > > v3: > - split up the series into 8 much smaller patches (David & Lorenzo) > - shorten changelogs where they were too long (Lorenzo) > - fix FOLL_WRITE folio dirtying by gathering dirty bits from all PTEs I'll try getting to this soon. As I raised previously, the whole follow_page_* terminology is just stale, and likely we should just not add new functions that use this terminology. I.e., follow_page_pte_commit() -- Cheers, David