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b=LYgK2zjMS2/60iBvFKXAn0KYpMT6XMLbnhrdo+aV5QAjiDzMsMFz4pGREkqYWj96w I6LvtG9NLWdEabLJIyQl3Aj1XneN4fVw0T7/jyiAJp6pipk/Gkb+gmOGitbn65eLQb urOqtm8YjZlAJuqo38ozvQE/PshPN0agxtm9wGx1s/TLk4y80Usmajwvyutf3mObsI K77oF/jSMYLEoSbJ725v5zeKIzBIATPFV7CnAK0vvG/vZICtDD/k9aS1c1gyqmOhem iBXeY1n8f/KB0KWHZQI6+MvDpIp7RMzyuxis5fe5RUkHKfIoO9DwlQuOPcZ9Zk1HX8 SWbtRzF0eIQgg== Message-ID: <658903fb-cf3a-43c3-b8c0-d47b63d10782@kernel.org> Date: Mon, 23 Feb 2026 14:16:52 +0100 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH mm-new v8 4/4] mm: khugepaged: skip lazy-free folios To: Vernon Yang , Barry Song <21cnbao@gmail.com> Cc: akpm@linux-foundation.org, lorenzo.stoakes@oracle.com, ziy@nvidia.com, dev.jain@arm.com, lance.yang@linux.dev, linux-mm@kvack.org, linux-kernel@vger.kernel.org, Vernon Yang References: <20260221093918.1456187-1-vernon2gm@gmail.com> <20260221093918.1456187-5-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-Rspam-User: X-Rspamd-Server: rspam07 X-Rspamd-Queue-Id: E41B91C0011 X-Stat-Signature: 634snsz9fmaeqexbwbhoi3kk4aa3m7cr X-HE-Tag: 1771852617-17563 X-HE-Meta: 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 bE/fbRCL zcSJ29WRFIC4Ic1qxHajiESuvRuomytZJ4J1enrPTOsXFSjPCtFPB7buHbmeI+SjBINQ3SQJPFVJbkoCJHC41XjZOqEDMGJThy5z2AVYncyyEDUnngr0XoSBw+FesBSH9J3TbWM2bNbVJD6824qD3xzDBsu0l/gG5I92L4xxs8/zUfASC6UAVgVOo6UHqyjkwm3+5PUUm7PmVm/y/pbL4RzkL/o5gUPdulkzdzvLRg7u40N3lIZlCLwt9zVxNKHQRyhKxZvgDjNcLxykeeG2zKP5FcCRHKFnel5jBiTOfHHRtaF7xF1Iog0r07g== 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 2/21/26 14:38, Vernon Yang wrote: > On Sat, Feb 21, 2026 at 06:27:36PM +0800, Barry Song wrote: >> On Sat, Feb 21, 2026 at 5:40 PM Vernon Yang wrote: >>> >>> From: Vernon Yang >>> >>> For example, create three task: hot1 -> cold -> hot2. After all three >>> task are created, each allocate memory 128MB. the hot1/hot2 task >>> continuously access 128 MB memory, while the cold task only accesses >>> its memory briefly and then call madvise(MADV_FREE). However, khugepaged >>> still prioritizes scanning the cold task and only scans the hot2 task >>> after completing the scan of the cold task. >>> >>> And if all folios in VM_DROPPABLE are lazyfree, Collapsing maintains >>> that property, so we can just collapse and memory pressure in the future >> >> I don’t think this is accurate. A VMA without VM_DROPPABLE >> can still have all folios marked as lazyfree. Therefore, having >> all folios lazyfree is not the reason why collapsing preserves >> the property. > > In folio_add_new_anon_rmap(), we know that the vma has the VM_DROPPABLE > attribute, which is the root reason why Collapsing maintains that property. > The above commit log clearly states "all folios in VM_DROPPABLE are lazyfree" > ^^^^^^^^^^^^^^^ > (the "if" is redundant and should be removed), not "all folios are lazyfree". Exactly. folio_add_new_anon_rmap() makes sure that all folios (except the shared zero folios ;) ) in VM_DROPPABLE are lazyfree. In fact, MADV_FREE should be a NOP on VM_DROPPABLE, as folio_mark_lazyfree() doesn't do anything. > >> This raises a question: if a VMA without VM_DROPPABLE has >> many contiguous lazyfree folios that can be collapsed, and >> none of those folios are non-lazyfree, should we collapse >> them and pass the lazyfree state to the new folio? I'd assume we'd only want to add support for that when there are actual known use cases that can trigger that + benefit from it. Adds complexity. -- Cheers, David