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b=l9kMZD3aeiJBKU0WkHAx5I6MX+3fTECuET2RPs5ZfkfhBFFuxuups0ATW43dLBgfr MA8SuwN45QMbMDt2MLAYDHXWuuWapUDwbzv2esKaalR3SKu/TwKPNUqrH33OWxGsSh a9T4iaWnbVHCc2mvkCyJnA9Pu3HDtk6DoM+50EtAYaFDL2bGDlibekBeSplbGJvq3e 13u6gzvS0jMkHy6Yo5iyQ4dr1cAsqT1bDrxyrbNSNQS7we5WDNvo7SbZBeotCeeWBp 3flujOFuDIj7SnIzZy81DXRsiZtDTiuz1M4VUHbNUKEScaOelwuMxptTNG6Wq1mXI5 PuQRzHQGGhXaA== Message-ID: <794e7270-c91d-42eb-b2a6-67929198a1da@kernel.org> Date: Thu, 9 Apr 2026 19:31:44 +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: Zi Yan Cc: John Hubbard , Andrew Morton , Jason Gunthorpe , Peter Xu , Mike Rapoport , LKML , linux-mm@kvack.org, Sourab Gupta , "Matthew Wilcox (Oracle)" References: <20260409014647.397515-1-jhubbard@nvidia.com> <4d6c1af0-dee5-4f1b-b74c-2ebc23de7baf@kernel.org> <1A7433E5-C8C1-45EC-A0B7-2BDC7D065B1A@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: <1A7433E5-C8C1-45EC-A0B7-2BDC7D065B1A@nvidia.com> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit X-Rspamd-Queue-Id: 63E224000D X-Stat-Signature: abq7tfdhaec4jazbqtaqkpgxkz8m1zd8 X-Rspam-User: X-Rspamd-Server: rspam08 X-HE-Tag: 1775755910-235745 X-HE-Meta: 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 30TjSsn6 DA8aaNuecP/4QmEon/kWYypnlL/mI1AWsb7gm3HKXM5by8o8GXVgZ4Aj6PaWFB77wn3FEhwHbQdFbbaKsSOpNAvmysDCc/eKFCBZZ1dT90Qd4o5RARAMcCAzquf52cdFqb68iyI2+3WBSdG72u9GGeRdhttAjwc8QAFKnlbKhc8hNXWMoWwJ0aWOrTVzA8SUbSAN5Wo1/+reahokmOzkPD2lCe6no4V/9wVFH0k0qP9gIWa84SH77/gmWgfwj2RLiNBpI Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On 4/9/26 18:55, Zi Yan wrote: > On 9 Apr 2026, at 11:11, David Hildenbrand (Arm) wrote: > >> On 4/9/26 17:05, Zi Yan wrote: >>> >>> >>> The idea is to give every allocated page a NotRmappable page_type and >>> 1) let page_rmappable_folio() remove the page_type by setting mapcount >>> to 0, since page_type overlaps with mapcount; >>> 2) allow callers of alloc_page*() to change page_type from NotRmappable >>> to other types. >> >> Could we instead just set the special type in vm_insert_page(), after >> verifying that it does not have any other type? > > You mean in validate_page_before_insert() we set the page to NotRmappable > if it can be inserted, then in the rmap code we reject NotRmappable > page/folios? And NotRmappable will remain until the page/folio is freed. > That should work. So the purpose is to avoid setting the page_type if > a page/folio is never going through vm_insert_page()? Yes, only these non-folio pages will show up process page tables. We would add a safety check that the mapcount really is 0 (-1) or already the proper type (NotRmappable). Rmap code would then simply skip any such thing. -- Cheers, David