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b=LYG6CnCEItvZ1t1f0fNdIfFH2mgnPJbb9AqdB7VhYKVsu39rSOmUgAmG/clAtfthW vSzhfhgtykCg3u9tj10zNhGIdH8SzlZseFkVnb4QNHDJR8IfnV21np3aiuMDg1p03A mvYL1VxU1p/cNMwiSgXaoDERPwg/F09NKkTDrk8YCR4RDwA/xbawGp8Bc/fHlbLwMY 3gYjch89ARZNLG18rZH1y9xcKaIdh4HBo9xE1p190YRP7bP5N3OCKEMm9p1bweCANc bZaWN4C0EBhJHSFUakxRzsxmfBV+rfdLVs/5SeFCwaRW/G4xamXt4KkExx1YySTy81 GGOPFr0FvFZ0w== Message-ID: Date: Sat, 7 Feb 2026 23:25:27 +0100 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH mm-new v7 4/5] mm: khugepaged: skip lazy-free folios To: Barry Song <21cnbao@gmail.com> Cc: Lance Yang , Vernon Yang , akpm@linux-foundation.org, lorenzo.stoakes@oracle.com, ziy@nvidia.com, dev.jain@arm.com, linux-mm@kvack.org, linux-kernel@vger.kernel.org, Vernon Yang References: <20260207081613.588598-1-vernon2gm@gmail.com> <20260207081613.588598-5-vernon2gm@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: 8bit X-Stat-Signature: edawes46g6h8b5ou8e34cfk9snnr48rg X-Rspam-User: X-Rspamd-Server: rspam08 X-Rspamd-Queue-Id: F28CE18000C X-HE-Tag: 1770503133-713411 X-HE-Meta: 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 /7j+E+q7 dICR4ZRfC6OdeJuZuN7rlxSrdDS3FMAlaqhwhICXf7y1a68TA1hYrvKgbXfypMKkmCBvqABp6EyOTgrum8GSJjFDns00VAx6uyajlBuH4O4T4+xeBEAe6NxZz2/hU81cHlaQkvTZ7nm2QNzjR5vzyjO0IsccMqevoqzKS7OJOflBsvOITbNOueBFl4zaAdtnr7DxYUH7bGtAy8T4eABKx0dTliy3phddcPcShHXJr5GAkebxaXUoUaB+qm/sN6ZlVq+YB0EmdcMtv2pq+jJVXtfT8lyzZ9ClX5/MTGqb+Wex3pQd2mP5RfLA6kg== 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 2/7/26 23:17, Barry Song wrote: > On Sun, Feb 8, 2026 at 6:05 AM David Hildenbrand (Arm) wrote: >> >> On 2/7/26 23:01, Barry Song wrote: >>> >>> Maybe change “just not skip” to “just skip”? >>> >>> If the goal is to avoid the collapse overhead for folios that are >>> about to be dropped, we might consider skipping collapse for the >>> entire VMA？ >> If there is no memory pressure in the system, why wouldn't you just want >> to collapse in a VM_DROPPABLE region? >> >> "about to be dropped" only applies once there is actual memory pressure. >> If not, these pages stick around forever. > > agree. But this brings us back to the philosophy of the original patch. > If there is no memory pressure, lazyfree folios won’t be dropped, so > collapsing them might also be reasonable. It's about memory pressure in the future. > > Just collapsing fully lazyfree folios with VM_DROPPABLE while > skipping partially lazyfree VMAs seems a bit confusing to me :-) Think of it like this: All folios in VM_DROPPABLE are lazyfree. Collapsing maintains that property. So you can just collapse and memory pressure in the future will free it up. In contrast, collapsing in !VM_DROPPABLE does not maintain that property. The collapsed folio will not be lazyfree and memory pressure in the future will not be able to free it up. -- Cheers, David