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(p200300d82f20da00b70ad5023b511f2d.dip0.t-ipconnect.de. [2003:d8:2f20:da00:b70a:d502:3b51:1f2d]) by smtp.gmail.com with ESMTPSA id ffacd0b85a97d-3e766659ea0sm3822008f8f.43.2025.09.12.10.13.49 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Fri, 12 Sep 2025 10:13:50 -0700 (PDT) Message-ID: <36bf71ea-f6aa-42fa-9fa2-53d00f351777@redhat.com> Date: Fri, 12 Sep 2025 19:13:48 +0200 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH] mm/khugepaged: Do not fail collapse_pte_mapped_thp() on SCAN_PMD_NULL To: Kiryl Shutsemau , Andrew Morton , Lorenzo Stoakes Cc: Zi Yan , Baolin Wang , "Liam R. Howlett" , Nico Pache , Ryan Roberts , Dev Jain , Barry Song , linux-mm@kvack.org, linux-kernel@vger.kernel.org References: From: David Hildenbrand Autocrypt: addr=david@redhat.com; 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 B3JfpUqcWwE7vUaYrHG1nw54pLUoPG6sAA7Mehl3nd4pZUALHwARAQABzSREYXZpZCBIaWxk ZW5icmFuZCA8ZGF2aWRAcmVkaGF0LmNvbT7CwZoEEwEIAEQCGwMCF4ACGQEFCwkIBwICIgIG FQoJCAsCBBYCAwECHgcWIQQb2cqtc1xMOkYN/MpN3hD3AP+DWgUCaJzangUJJlgIpAAKCRBN 3hD3AP+DWhAxD/9wcL0A+2rtaAmutaKTfxhTP0b4AAp1r/eLxjrbfbCCmh4pqzBhmSX/4z11 opn2KqcOsueRF1t2ENLOWzQu3Roiny2HOU7DajqB4dm1BVMaXQya5ae2ghzlJN9SIoopTWlR 0Af3hPj5E2PYvQhlcqeoehKlBo9rROJv/rjmr2x0yOM8qeTroH/ZzNlCtJ56AsE6Tvl+r7cW 3x7/Jq5WvWeudKrhFh7/yQ7eRvHCjd9bBrZTlgAfiHmX9AnCCPRPpNGNedV9Yty2Jnxhfmbv Pw37LA/jef8zlCDyUh2KCU1xVEOWqg15o1RtTyGV1nXV2O/mfuQJud5vIgzBvHhypc3p6VZJ lEf8YmT+Ol5P7SfCs5/uGdWUYQEMqOlg6w9R4Pe8d+mk8KGvfE9/zTwGg0nRgKqlQXrWRERv cuEwQbridlPAoQHrFWtwpgYMXx2TaZ3sihcIPo9uU5eBs0rf4mOERY75SK+Ekayv2ucTfjxr Kf014py2aoRJHuvy85ee/zIyLmve5hngZTTe3Wg3TInT9UTFzTPhItam6dZ1xqdTGHZYGU0O otRHcwLGt470grdiob6PfVTXoHlBvkWRadMhSuG4RORCDpq89vu5QralFNIf3EysNohoFy2A LYg2/D53xbU/aa4DDzBb5b1Rkg/udO1gZocVQWrDh6I2K3+cCs7BTQRVy5+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: X-Mimecast-Spam-Score: 0 X-Mimecast-MFC-PROC-ID: eLXfwmenv4goOlHBPF4TFXVtzA_oX9PmiQm3fd2uJ8k_1757697231 X-Mimecast-Originator: redhat.com Content-Language: en-US Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-Rspamd-Queue-Id: 371064000D X-Rspamd-Server: rspam05 X-Stat-Signature: 4b8d895zbyxjpjfd99br1xxmp3n8yu51 X-Rspam-User: X-HE-Tag: 1757697234-815588 X-HE-Meta: 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 1IFIBVf9 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 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 12.09.25 18:58, Kiryl Shutsemau wrote: > From: Kiryl Shutsemau > > MADV_COLLAPSE on a file mapping behaves inconsistently depending on if > PMD page table is installed or not. > > Consider following example: > > p = mmap(NULL, 2UL << 20, PROT_READ | PROT_WRITE, > MAP_SHARED, fd, 0); > err = madvise(p, 2UL << 20, MADV_COLLAPSE); > > fd is a populated tmpfs file. > > The result depends on the address that the kernel returns on mmap(). > If it is located in an existing PMD table, the madvise() will succeed. > However, if the table does not exist, it will fail with -EINVAL. > > This occurs because find_pmd_or_thp_or_none() returns SCAN_PMD_NULL when > a page table is missing, which causes collapse_pte_mapped_thp() to fail. > > SCAN_PMD_NULL and SCAN_PMD_NONE should be treated the same in > collapse_pte_mapped_thp(): install the PMD leaf entry and allocate page > tables as needed. > > Signed-off-by: Kiryl Shutsemau > --- Makes sense to me. Is this something we want a Fixes: or even Cc: stable for? I assume it doesn't really happen frequently, but could also happen after MADV_DONTNEED'ing the full range with pt reclaim I think after having faulted in some PTEs, for example. Acked-by: David Hildenbrand -- Cheers David / dhildenb