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b=Uoks8aMONAGVPbnyVCd43r//Ov68jjgFFZfnckuXJWQKk+2WEYy+MXXY5LyYPsBJ1 b5unPiWEPRZYHOa0u8Y+WMzSiOIK+Vv+KHyk39Z5rUrF0sq4ZIHuA4+pzogLDyx0fC /tkzWLKSa+ZTN5mYXfapsS8x1NxtY6FQmFElOGOApOnTTGpQSF159Pq/jwurPBNN8G 1zwVqE4nhoTa5l6qyC/JHowXQmGppLu7ADKFqQlZNASZbHv1KB2cu8dXEiUgXiiNO5 j3J/xn5vXlU1vy6OT+cDbi2rZyavnadEjZn0HkiigvZuqs2F6GZ8hW81NfPcGVMWBg Ty03Zwiy7ZnCg== Message-ID: <59292ba2-e0cc-4e50-bb26-be9c15843a41@kernel.org> Date: Mon, 20 Jul 2026 10:44:17 +0100 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [RFC PATCH v3 0/3] mm/damon: introduce DAMOS_SPLIT action To: Lian Wang , damon@lists.linux.dev, linux-mm@kvack.org Cc: sj@kernel.org, akpm@linux-foundation.org, linux-kernel@vger.kernel.org, ljs@kernel.org, liam@infradead.org, vbabka@kernel.org, rppt@kernel.org, surenb@google.com, mhocko@suse.com, npache@redhat.com, ziy@nvidia.com, baolin.wang@linux.alibaba.com, ryan.roberts@arm.com, daichaobing@sangfor.com.cn, wangkefeng.wang@huawei.com, gutierrez.asier@huawei-partners.com, zengheng4@huawei.com, kasong@tencent.com, corbet@lwn.net, skhan@linuxfoundation.org, linux-doc@vger.kernel.org, linux-kselftest@vger.kernel.org, lianux.wang@processmission.com, kunwu.chan@linux.dev References: <20260720030327.80153-1-lianux.mm@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: <20260720030327.80153-1-lianux.mm@gmail.com> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit X-Stat-Signature: jwxf136rg1bz91eucb1r5rz55sos35me X-Rspamd-Queue-Id: 863D780008 X-Rspam-User: X-Rspamd-Server: rspam07 X-HE-Tag: 1784540666-558777 X-HE-Meta: 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 8bW7NLKF GjhHPAjj7BnyVbM4QWhcTuajWeD/iPTHRc5dX3tY9rQBeldlTG3iO9+HUe+dpXkqay5RX1qh0dWtFYSnn+vioOORrlmokFCo7pAeLb0Ghcjhks34jh0q67huL84UnY8snK/rqHaNZZB7Z4ZhMaQPKJi4ze/biSJqMasVB8il84a8f+n/CzFm37TKwCFgSn/pe8oN5SofM13lCSQOm6EpK2ZrDPg2DxbwEmF5FFEkt69jrebynFoIb9kGDj2tbxG4P1m9l/cCYGFP7Y8X8UoxsRSzmC9j9z9tkcPpNZ6jXbjM4FgPVRzvhBKwoDaVSVm1L121Vn9WPK6RhSyorOKGsOf7GzMt71gLPv8joTyf/6wjT6/Rk/E2Ozm5DOvjmGfIXxtfwJQgmRbckMWa4XVSypUMux3a088t1HCWxWfhmJbm8Dus= Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On 7/20/26 04:03, Lian Wang wrote: > DAMOS_SPLIT splits large folios in a target region down to a > configured target order, using the existing split_folio_to_order(). > No new core-mm code or exported symbols are introduced. > > Based on mm-unstable at 61cccb8363fc ("mm/swap, PM: hibernate: > atomically replace hibernation pin"). > > Different addresses within a PMD-mapped folio resolve to the same > PMD Accessed bit. Accesses to a small part of the folio can > therefore coarsen DAMON's observed hot set relative to the actual > working set. > > DAMOS already provides promotion actions (HUGEPAGE, COLLAPSE) but > has no corresponding demotion action. DAMOS_SPLIT fills this gap. > It is a mechanism, not a policy -- it does not decide which folios > to split. Selection is left to DAMON's existing access patterns, > filters, and future probe/PMU signals. > > target_order selects the split target: 0 for order-0 base pages, > or a supported smaller mTHP order. Both anonymous and file-backed > folios are supported. The locking follows split_huge_pages_in_pid() > in mm/huge_memory.c. > > Tests > ===== > > damos_split.py (VM + Kunpeng 920): > anon THP -> order-0 split: PASS > > sangfor_exp.py (Kunpeng 920, tmpfs, 4096 MiB): > > - Created a 4 GiB PMD-mapped tmpfs workload. > - Applied DAMOS_SPLIT with target_order=0. > - ShmemPmdMapped dropped from 4194304 KiB to 0 in every round. > - Repeated for five rounds without functional failures. > > The functional selftest (damos_split.py) is included in this series. > Additional experiment scripts and raw results are available on > request. Performance characterization using masim [1] and KMB [2] > is in progress. > > [1] https://github.com/sjp38/masim > [2] https://gitee.com/OpenCloudOS/kernel-multi-bench Hi, you give no real motivation and evaluation why this is required or why this gives the user any benefit. HUGEPAGE + COLLAPSE is clear: give me THPs in a size not controlled by user space, because the expectation is that this memory will be performance sensitive. A SPLIT with an explicit order is not really want we want and it does not fit the existing primitives. -- Cheers, David