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b=k/s9h5WpvqfmGi5vf7ltu+UCKQ1khGhtNwrVnOm3KPtz5dUUMCU0ugI8Uufk7SpTa g9jUaGJKKiYA0cJPk9NU0mOb3POQ3vVHQ3zpE+O26L3Rwg41uryfh8PZvgKUQq07H6 WWZ8THi0a7XpQxYReuxVNzW9RDT9su+QIB78LsvxbCUWhzf30xuIzKtQW/FB6nXxwe Lf6Uro0PiUn1VNYpQQue19jFId6oa4jgToyF4MIYoj2E+aBZR8Ch/s3zoEooOK77di jGOT5aY+lscwjLSIGTW41RfnrymzmAq2sPpe2bNyXimhpv/1R4+7GO2d4sve4NSjWz ztibZYwvWqqfQ== Message-ID: Date: Fri, 5 Jun 2026 17:54:11 +0200 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v7 2/6] tools/testing: add rmap walk latency benchmark To: xu.xin16@zte.com.cn, akpm@linux-foundation.org Cc: chengming.zhou@linux.dev, hughd@google.com, wang.yaxin@zte.com.cn, linux-mm@kvack.org, linux-kernel@vger.kernel.org, ljs@kernel.org, corbet@lwn.net References: <20260530170404509QpJmBtpSjn3uQHeVKA2iA@zte.com.cn> 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: <20260530170404509QpJmBtpSjn3uQHeVKA2iA@zte.com.cn> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit X-Rspamd-Server: rspam07 X-Rspam-User: X-Stat-Signature: kwjyoy7fcs6ibwpwya3hfz7a8e87afkk X-Rspamd-Queue-Id: E858E100009 X-HE-Tag: 1780674856-600530 X-HE-Meta: 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 H958G+Qq 0CAVlQ7har3mfA1UOlrcdOmDgLtCYAkJJD7br4lEwWRUeub1Fa035GMdWVYM9DY0A9pEQOuCS+FddYzEWdmUx8aoFLz0UpX+pa+ktGErVcns/oCxiAkbC4VvfuRADyZyvmCbOCWnZFnGwSpUB2NoyLOr3IkOH1K4SC3GPFcDnLiG2jAenYZg5HR4XZJLbLGjFY9hVWL356YKJki8L3fkKtGtiwnvWEVLVYOHz/qMY2nmhPSn9iQmR2b5cBr2ttUS7CKiKlpzKyayQwaLCHm9S99LlgM54hiS8BIefsVvQMgQ0SZPL7LZu7liXaOELJVwBAfiTFxzwNHtKpWrKxH0CaswzEwawhE3zpfGtDxnS0BDD42E= Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On 5/30/26 11:04, xu.xin16@zte.com.cn wrote: > From: xu xin > > Add a benchmark to measure rmap_walk latency for KSM, anonymous, > and file-backed pages under high sharing. > > For KSM, the sysfs file "max_page_sharing" is set as 256 to make > sure that every KSM page can be shared by 256 original pages. A > large region is split into 20000 VMAs via mprotect then merged by > KSM, whose purpose is to construct a lot of unrelated VMAs > sharing its anon_vma to reproduce the issue proposed at > https://lore.kernel.org/all/20260503205013850sym7UO0jvKJzyRiTYmO8V@zte.com.cn/. > > For anon and file pages, 256 (equal to KSM's max_page_sharing) > child processes are forked to share a single physical page (COW > not broken). The benchmark uses move_pages() to trigger migration, > collects rmap_walk_start/end trace events, and reports max/average > latency. The tool also saves/restores KSM config and filters trace > events by PID to avoid noise. > > For each test, the program prints the number of captured events and > the maximum / average latency in milliseconds. > > This benchmark helps developers evaluate optimizations in the reverse > mapping code, such as limiting max_page_sharing or improving tree > traversal efficiency. > > Usage (must be run as root): > '# cd tools/testing/rmap/ && make > ’# sudo ./rmap_benchmark > KSM rmap_walk latency (Shared by 256 VMAs via mprotect and KSM merge): > Max: 839.00 ms (838998 us) > Avg: 605.80 ms (605799 us) > Count: 4 events > Anonymous page rmap_walk latency (Shared by 256 VMAs via fork, COW not broken): > Max: 4.05 ms (4055 us) > Avg: 2.86 ms (2858 us) > Count: 2 events > File page rmap_walk latency (Shared by 256 VMAs via fork, MAP_SHARED): > Max: 2.57 ms (2572 us) > Avg: 1.25 ms (1250 us) > Count: 4 events > > Signed-off-by: xu xin > --- And that benchmark would then also have to be carried OOT I guess. -- Cheers, David