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b=mKURoMZue+AtZNQKf0EPlAVQIq/zNoBQrF7LiX9aEP+WS86xWR6WnRLEn3wOeRgcA GC09liXgi2keglH9pGZYTeUF9WczP0XQjt43Gk5Muv62Pp+vQnum/z71pcd5eA4CBQ haOZ6ebeEstgl9txZF9Ew69ygrgHdb52t0J74yAwq7N8OUu5whr8zy4ct67eMXuF3B Ur+jh4Ka+PeVXepAPbzvpkrKRszkORT0Agwu4Y11HJwwOf5sdW13Gdnw1hAYqYdGuA 3a7TodSNgosYBiAerJETY1esejSTngZgpFSyJNMxxW9MXrXqxopBPZmnyrg1YI2vRr fB2UABqeIUcgw== Message-ID: <5aae8c80-e886-47b1-a1e1-4e91771f3492@kernel.org> Date: Fri, 5 Jun 2026 11:22:05 +0200 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH] mm/gup: fix GUP-fast fallback for NULL-mapping order-0 folios To: Alistair Popple , Balbir Singh Cc: John Hubbard , Andrew Morton , Jason Gunthorpe , Peter Xu , Mike Rapoport , LKML , linux-mm@kvack.org, Sourab Gupta , Zi Yan References: <20260409014647.397515-1-jhubbard@nvidia.com> <4d6c1af0-dee5-4f1b-b74c-2ebc23de7baf@kernel.org> <08afbec2-bbe7-4e8a-8d99-8a5eaecaeee7@nvidia.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: 7bit X-Rspamd-Server: rspam10 X-Rspam-User: X-Stat-Signature: wbmw1txb89hnzsohnhbc1tpb1cuor9jx X-Rspamd-Queue-Id: B059140011 X-HE-Tag: 1780651331-983927 X-HE-Meta: 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 I6pBNQwZ bfmk3F7bKhVmm/7r1nXw869dgy0NznyMknVWU4sS0IM12V14Tr8rnJ891orHtLhUF8CJlRnXa/QMS2usYmMfO8lH6Jc9etQIjCKjLaZYZNIHNs6GBkJygEpNIaZP1LLiSffhc8vVvvrmyXz718/+UzUK4sJJIOGyulfzrh3uMILfP33I3YUo+or70cgOGWe9/ivKEMcMb1ZH90c2fpEX6sjwdsiH726QQT7KhYmCUym/1Ku5fFPN9xl6wE9ANfiK5ekp0hGXs/hk+4GhpuUxXxqAXWQ== Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On 6/5/26 07:17, Alistair Popple wrote: > On 2026-05-15 at 10:09 +1000, Balbir Singh wrote... >> On 4/9/26 17:52, David Hildenbrand (Arm) wrote: >>> >>> Hm, what if secretmem folio just got truncated? I hate to rely on some >>> handling in the caller to detect truncation differently during GUP-fast, >>> but this function returning "true". >>> >> >> Can secretmem folios be truncated? I assume you are referring to >> ftruncate(), I am looking at the setattr implementation of secretmem >> and it does not seem like it can be truncated. >> >>> Zi is working on a way to distinguish folios from non-folio things: that >>> we can identify whatever was added through vm_insert_page(). >>> >>> Because that's really the key problem here: vm_insert_page() pages are >>> not actually folios, they just look like a folio today, but looking at >>> fields like ->mapping does not make any sense. >>> >> >> I still think this is a short term fix worth having until we get >> Zi's fixes > > Agreed - this clearly results in a performance regression and we have customers > reporting it as such. I think Zi might be out of the office atm but when I last > spoke to him he agreed this fix should go in for now and his approach will come > later. He should be back now. But yeah, let's get this fix in. -- Cheers, David