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b=qTjlT+Z33eRpwuN3qRicMSrxRdg+ybY/sOd850b1NNr7iV9YylLG1TIu7htcvWEPe PHS2kK7t164uPMtgxaSJWoytBMROaoHFIA+zD1FuW6WI7vo56Y5V1f08v1GoTb7D1P zVkWh+YNPmGx4lj2Azna2IfuiHOEPOs0JKJQIdQGfBOTqMU9wypeTe3piIiPUz3lCo Oq3/Uv0hI5C6AoiMYKGLqQms82bvPDnkQ6Sk9sFVcq4gti7llUxibJrn3xn/uJqsKM 7z/6L+/LYV3TZz4Z9+7KKN6pvLtlYlu1BxruR81iDsTUsm/l5y6HJxiPLXNdgzCBGU Qw4tB6QbsjKBg== Message-ID: Date: Wed, 1 Apr 2026 09:30:14 +0200 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v2] mm/page_io: fix PSWPIN undercount for large folios in sio_read_complete() To: David CARLIER , Barry Song <21cnbao@gmail.com> Cc: Kairui Song , Chris Li , Andrew Morton , Kemeng Shi , Nhat Pham , Baoquan He , Youngjun Park , NeilBrown , linux-kernel@vger.kernel.org, linux-mm@kvack.org References: <20260330071229.14614-1-devnexen@gmail.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: Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit X-Rspamd-Queue-Id: 4414718000C X-Stat-Signature: gws3ra5px1jtw4nrf6wefnhpw5yrtd3e X-Rspam-User: X-Rspamd-Server: rspam02 X-HE-Tag: 1775028620-392736 X-HE-Meta: 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 vJThG5Er 9lg9WdFIaFNwabtyl1nZCrcGRNuKZNU9Q1tADddCg0tfzPzUHmwHFW0TCo1u/6mAv8CrIBHtD7kJi6lGAaARFWvE7jfxBT0CSMyH7uoy6fD9J/8bqTFPbpH/FYFa9A2dCQz9nyQUn8Ugmft4p7cWjeOYvxO0weSciI3721EnTXYqiNdI2U/CnB165q94uDo6XKwTiSHeIAGa65VtmIVuAwDl0QN8JGgEwyiP/2RfxF8PqO61j3leAaM2OWL3rsnfuBASDaWk7sw1ksA9aJS1PIaE/kq52ePsSQT/6Pgc5c1s6B6YICrhVwCsffTd77MBHgrPUrQMvPtoiWVXwBfq3DInVYJLut1p5n/+H Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On 4/1/26 09:10, David CARLIER wrote: > On Tue, 31 Mar 2026 at 23:33, Barry Song <21cnbao@gmail.com> wrote: >> >> On Mon, Mar 30, 2026 at 3:12 PM David Carlier wrote: >>> >>> sio_read_complete() uses sio->pages to account global PSWPIN vm events, >>> but sio->pages tracks the number of bvec entries (folios), not base >>> pages. For large folios this undercounts compared to the per-memcg path >>> which correctly uses folio_nr_pages(), and compared to the bdev read >>> paths which also use folio_nr_pages(). >>> >>> Use sio->len >> PAGE_SHIFT instead, which gives the correct base page >>> count since sio->len is accumulated via folio_size(folio). >>> >>> Fixes: a1a0dfd56f97 ("mm: handle THP in swap_*page_fs()") >>> Signed-off-by: David Carlier >> >> The patch seems theoretically correct, but I’m wondering >> where we can swap in mTHP for filesystem-based swap？ >> >> In both do_swap_page() and shmem_swapin_folio(), we check >> data_race(si->flags & SWP_SYNCHRONOUS_IO) before allocating >> large folios. Am I missing something? > > ▎ The patch seems theoretically correct, but I'm wondering > ▎ where we can swap in mTHP for filesystem-based swap? > > ▎ In both do_swap_page() and shmem_swapin_folio(), we check > ▎ data_race(si->flags & SWP_SYNCHRONOUS_IO) before allocating > ▎ large folios. Am I missing something? > > You're right, I missed that. SWP_FS_OPS is only set by NFS and > SMB which have no bdev, so SWP_SYNCHRONOUS_IO can never be set > alongside it. Large folios can't currently reach this path since > both do_swap_page() and shmem_swapin_folio() gate mTHP allocation > on SWP_SYNCHRONOUS_IO. > > That said, sio_read_complete() already calls count_mthp_stat() > and the per-memcg accounting uses folio_nr_pages(), so the code > seems written with large folios in mind even if the path is > currently unreachable. Using sio->pages (bvec entry count) for > a base-page count is still semantically wrong, but I understand > the practical impact is nil today. > > Happy to either drop this or keep it as a correctness cleanup, > whatever you and Andrew prefer. Best to rework the patch description (clarify that it's a cleanup) and drop the Fixes: I guess. -- Cheers, David