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b=lHionywGxDyubOlbZk8DN8Xy578RDJsEfrSCaGl3Cp11wK07buKXQadWsIpZkvqBZ LPA3baWtj7dYXkCyCPCYEIbvjN3CpJpph8flrnIkKEEJi4nqvIiSxli0s3Z2uauNqN wGDwvOE+VrBHjcP6Y75rSdJxG7VWjGl6KTtlZ49zJD+uvHv3vTWrJ2/o3zaASbX9Sm 6s1lUJ7TSE1a9VGwGzD4fQi2KDzwKmPzbgyKX9j3Chc0sjibjfVBsRD5/ZOOQcrfik zuqF4zO/rJVZ4HthPS4m2KeudY4PFOO7U6ezhzHTS7tp/CG4B8up4FZrEFUvcmfXzt +G7Y9CTiNJc5Q== Message-ID: <21a9b331-58ec-4c04-a09e-545ac31f2eca@kernel.org> Date: Thu, 12 Feb 2026 13:47:34 +0100 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH] mm/userfaultfd: fix likely/unlikely annotation in move_pages() To: Matthew Wilcox , Aswin Kumar Cc: linux-mm@kvack.org, andrew.morton@linux-foundation.org, linux-kernel@vger.kernel.org References: <20260204142350.1642-1-aswinkumar3301@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; format=flowed Content-Transfer-Encoding: 7bit X-Stat-Signature: wx7dqu3prr57gte7n1dok6sx4tsi3mkw X-Rspamd-Queue-Id: 61FFE1A000D X-Rspam-User: X-Rspamd-Server: rspam04 X-HE-Tag: 1770900460-449770 X-HE-Meta: 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 iRIlY7ah qSiRtIAQ7w/ETemIIkvWFfaV3RZCHVCqbfSqjrLlhsInmVbWTHiOHKPECRfRQ70dwhDae9i4/U04S5Uz5eEJwWC8JWPipzddNgTHRvptNIc3gXU66WOGAohv8Zdmw5H/gG6Iq/s2BVDC36pUXivTsiz+AScN+ZUgQWrkUwHPQ7S0NdmQVUOpY4LYs4FLLFDJvfzvv0ERXJm6PAmbqTr/dHAbya+WVX0P2YXxkBjct6Bukq22AWXlKbtu/HPOC4IHNcW0Uor0hYFyfXe1Md+UyYp8UHFrvPlUtCejQ0SaJZduQDF0= X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On 2/4/26 15:58, Matthew Wilcox wrote: > On Wed, Feb 04, 2026 at 02:23:50PM +0000, Aswin Kumar wrote: >> All other userfaultfd paths use unlikely() for the mmap_changing check, > > No they don't? > > $ git grep mmap_changing mm > mm/userfaultfd.c: if (atomic_read(&ctx->mmap_changing)) > mm/userfaultfd.c: if (atomic_read(&ctx->mmap_changing)) > mm/userfaultfd.c: if (atomic_read(&ctx->mmap_changing)) > mm/userfaultfd.c: if (likely(atomic_read(&ctx->mmap_changing))) > >> This is a performance-only fix - the logic is correct but the branch >> prediction annotation is wrong, potentially causing a minor performance >> penalty on the fast path. > > Can you measure it? Bet you can't. > > Honestly, I'd just remove the likely() annotation, not change it to > unlikely(). Agreed. -- Cheers, David