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b=Cb4kQ1JADpegZqRJjJv6ho55cCfXaFkJ62EGyLUFZNx1QtUudOHPIQ3I0aLOZXju6 3XsmebWYwmT63NLyArWBYnqAyclbz92AXcEsAcB93ZXm3E9xdOx1n17hDeAyK27eMR WcBawrb5B0Du5RPvAX5AD51OjQVzIR+VZF1ovKlpYiC4+9fH9R6F5Pre0+iB1dOMUy 1Jv4MOabbDRbYarm3B2aQYf6mRH6J6oH+ZdA7fPr4B2vJJWCcsTNFfRqRgV4tFtstp H4E1XEmy3faB709NrUttcJ9ThEfkVTsIx/624RH4/XfFAYz4x1QudZPklaBgbfJ7cS 3oL2ta1G6znrQ== Message-ID: Date: Thu, 5 Mar 2026 19:59:14 +0100 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [GIT PULL] tracing: Fixes for 7.0 To: Linus Torvalds Cc: Steven Rostedt , Jason Gunthorpe , Leon Romanovsky , Masami Hiramatsu , Mathieu Desnoyers , Huiwen He , Jerome Marchand , Qing Wang , Shengming Hu , Linux-MM , linux-rdma , Lorenzo Stoakes References: <20260305103941.11f1b27d@gandalf.local.home> 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: 7bit X-Stat-Signature: 5nucngit8j95diq6r47xxcb4n4gdgy9a X-Rspamd-Server: rspam09 X-Rspam-User: X-Rspamd-Queue-Id: C69AF100007 X-HE-Tag: 1772737163-337013 X-HE-Meta: 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 OxpxCb7N cseBmUuuqGnpL3fz3ZGyTCVdxyUCNVv80qmguyBYOYa7vx5zlhyvIdRsiZUfVp56nkYFoorWV4nWFNSHzxMiWRHWnBq6/D72pU9qG6O7N3wgItR4xxAC69UGmV5PPelZKa3kITMjyIrl6/6anE20d50biirt+XFRtg0MEKgJWNRQfVX0NtgCggfasuX3k8kDaTgtUQTmzrIklgnEDluFAPXNHwOSP6H5lneXRz0un6AZ9PIX1Gp+omSm0Ej0VObDQA4cCeJnNZ63sTkBossjUsog1tA== Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On 3/5/26 18:17, Linus Torvalds wrote: > On Thu, 5 Mar 2026 at 09:00, David Hildenbrand (Arm) wrote: >> >> QEMU traditionally sets MADV_DONTFORK on guest RAM. One reason is to >> speed up fork(), because it doesn't need all the guest RAM in fork'ed >> child processes. > > Yes, I think the MADV_DONTFORK thing makes sense on its own - more so > than MADV_DOFORK does. > > Because it's a very valid thing for user space to do exactly for that > "speed up fork()" case. > > It's similar to how we also export a MADV_WIPEONFORK - for a different > use-case, where we don't want the copying behavior (typically because > we want the child to re-create its own set of data: I thin the main > reason tends to be for things like reseeding random number generation > after fork etc). > > So it's just MADV_DOFORK I don't particularly like, because it had > pre-existing kernel semantics (the VM_DONTCOPY bit predates the MADV_* > bits by many many years). > > Not copying on fork is always safe. But copying something that the > kernel has said "don't copy" just sounds *wrong*. > >>> But I get the feeling that maybe we should at least limit MADV_DOFORK >>> only to the case where the *source* of the DONTFORK was the user, not >>> some kernel mapping. >> >> ... that makes sense. Forbid toggling it on something that has >> VM_SPECIAL set, maybe. CCing Lorenzo. > > Yeah, I think VM_SPECIAL would be a better match than just checking > VM_IO. At least it would also catch things like that VM_DONTEXPAND, > and PFN mappings. > > So just changing the existing VM_IO test to cover all the VM_SPECIAL > bits would be a simple improvement. Ack. > > Maybe I should just do that and see if anybody even notices (and > revert and re-think if somebody does) Agreed. We could think about letting it sit a bit in -next before moving it to mainline. -- Cheers, David