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b=NsnqMXpWB3QmA+klSyyaj1wBsJ2EFa0NbC9JvMCJmyntg4A8WexCuYa++cJWmW88Y jmxy1sXzIeUr8Tjay3Z08TnSORZy/Q8mVvLJiQJ18pReXFrjj7myDeDjVqsSbi+zP3 2fvQAz2KMe8JFL5/vduoqVVTmh3Iq+GYXn/HWfgHVQbK1TKpqCQhRhL86NY0PswiAI mAYOf+9Ikd5vngGUfiMLltxwrTKpverdAausN0GEowm7j0TkE41X0hLnfWAYBK/GZJ KoIMIwN8xl6BWrWTKpXZ1kWJn/UQNrv+Wdn3OTMPXjTYM05z+hQv6RDO98PsKo+AE3 wgudDjEWkO1nA== Message-ID: Date: Sat, 7 Feb 2026 23:05:44 +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-Rspamd-Server: rspam11 X-Stat-Signature: i33fusxetieweg8qe9jg7pqhx174csar X-Rspam-User: X-Rspamd-Queue-Id: 6CDA340014 X-HE-Tag: 1770501950-770918 X-HE-Meta: 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 fg2gQTmY uda+PQlKB9FWy6eIw3x6DTd7ZFfS18PjdA485yTbQblx+R8nQ3XX+6f7EuBf2TnE9FjEe78O9S5jFNh952CcmXuPq/F9kNZJ2p32kFiSEucOAHC9irfcz3eyqHh/fO//ZfhA7cY99QqSD31uLK+dnF9Cqzclxlx5V6L2vblBjZ2nOQb4lKhcMPv70Xi5cuFZ7fblE1cIakNHL8QPJZsY5Obiithv65zH55+0BPnx8OTHRxoYyXACZM56xASFytoctAroe2FZ/dEzhG2Jcel1FHoZs+XvMmBMDdO+7Z35SqxPgzqbt4V6fJx3UuQ== 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 23:01, Barry Song wrote: > On Sun, Feb 8, 2026 at 5:38 AM David Hildenbrand (Arm) wrote: >> >> On 2/7/26 14:51, Lance Yang wrote: >>> >>> >>> >>> Good catch! >>> >> >> Good point! >> >>> >>> Right. When the VMA has VM_DROPPABLE, we would drop the lazyfree folio >>> regardless of whether it (or the PTE) is dirty in try_to_unmap_one(). >>> >>> So, IMHO, we could go with: >>> >>> cc->is_khugepaged && folio_test_lazyfree(folio) && >>> (!pte_dirty(pteval) || (vma->vm_flags & VM_DROPPABLE)) >> >> Hm. In a VM_DROPPABLE mapping all folios should be marked as lazy-free >> (see folio_add_new_anon_rmap()). >> >> The new (collapse) folio will also be marked lazy (due to >> folio_add_new_anon_rmap()) free and can just get dropped any time. >> >> So likely we should just not skip collapse for lazyfree folios in >> VM_DROPPABLE mappings? > > 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. -- Cheers, David