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[80.187.83.189]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-46fab656554sm123876145e9.11.2025.10.13.02.52.38 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Mon, 13 Oct 2025 02:52:39 -0700 (PDT) Message-ID: <8e458538-69dc-4c0f-a25b-0c85ce1e866e@redhat.com> Date: Mon, 13 Oct 2025 11:52:37 +0200 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [Regerssion] [KSM] KSM CPU overhead in 6.16+ kernel compared to <=6.15 versions ("folio_walk_start" kernel object overhead) To: craftfever@murena.io, akpm@linux-foundation.org, xu.xin16@zte.com.cn, chengming.zhou@linux.dev Cc: linux-mm@kvack.org, linux-kernel@vger.kernel.org, regressions@lists.linux.dev References: <020cf8de6e773bb78ba7614ef250129f11a63781@murena.io> From: David Hildenbrand Autocrypt: addr=david@redhat.com; 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 B3JfpUqcWwE7vUaYrHG1nw54pLUoPG6sAA7Mehl3nd4pZUALHwARAQABzSREYXZpZCBIaWxk ZW5icmFuZCA8ZGF2aWRAcmVkaGF0LmNvbT7CwZoEEwEIAEQCGwMCF4ACGQEFCwkIBwICIgIG FQoJCAsCBBYCAwECHgcWIQQb2cqtc1xMOkYN/MpN3hD3AP+DWgUCaJzangUJJlgIpAAKCRBN 3hD3AP+DWhAxD/9wcL0A+2rtaAmutaKTfxhTP0b4AAp1r/eLxjrbfbCCmh4pqzBhmSX/4z11 opn2KqcOsueRF1t2ENLOWzQu3Roiny2HOU7DajqB4dm1BVMaXQya5ae2ghzlJN9SIoopTWlR 0Af3hPj5E2PYvQhlcqeoehKlBo9rROJv/rjmr2x0yOM8qeTroH/ZzNlCtJ56AsE6Tvl+r7cW 3x7/Jq5WvWeudKrhFh7/yQ7eRvHCjd9bBrZTlgAfiHmX9AnCCPRPpNGNedV9Yty2Jnxhfmbv Pw37LA/jef8zlCDyUh2KCU1xVEOWqg15o1RtTyGV1nXV2O/mfuQJud5vIgzBvHhypc3p6VZJ lEf8YmT+Ol5P7SfCs5/uGdWUYQEMqOlg6w9R4Pe8d+mk8KGvfE9/zTwGg0nRgKqlQXrWRERv cuEwQbridlPAoQHrFWtwpgYMXx2TaZ3sihcIPo9uU5eBs0rf4mOERY75SK+Ekayv2ucTfjxr Kf014py2aoRJHuvy85ee/zIyLmve5hngZTTe3Wg3TInT9UTFzTPhItam6dZ1xqdTGHZYGU0O otRHcwLGt470grdiob6PfVTXoHlBvkWRadMhSuG4RORCDpq89vu5QralFNIf3EysNohoFy2A LYg2/D53xbU/aa4DDzBb5b1Rkg/udO1gZocVQWrDh6I2K3+cCs7BTQRVy5+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: <020cf8de6e773bb78ba7614ef250129f11a63781@murena.io> X-Mimecast-Spam-Score: 0 X-Mimecast-MFC-PROC-ID: gLozfbGbYoRCTXr6lsdlBq27rTUfEVzu7aItKVlXkjs_1760349160 X-Mimecast-Originator: redhat.com Content-Language: en-US Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-Rspamd-Server: rspam10 X-Rspamd-Queue-Id: 4C98B1C0013 X-Stat-Signature: oygwz8pmrord6948godxgduuww4tzspg X-Rspam-User: X-HE-Tag: 1760349163-114633 X-HE-Meta: U2FsdGVkX19hYZMsf35lV/BZdAPK87KFWlBbTEl4EdHNqg2V6ypzklENBlhZyeXpStKnjx5sW10/PJ+SupT8ath2jef7hGi4YWIjW1rCMBSprhpgUUbuM5As415vL0wq2e2fNc6W6Qe0sgdgWnw/Dsg1HW/ZF399UlRPfhGDFAm4yZDcnejz7S69cHP5sQBM92aQoFmX3YNJHWWPYDrnJM574JV2krrg9BW9aLL8PizyitE+vBuHqswvSKiL2apQmGmIxORedjMhrc05jCRsHiJRHcUkRaXq7h7KnKBmJlGWY+JUrD0wYjnYev9UeVqZ628jsmQ+jgUvAVdl1jiH0M8zU/xJihonbCX7tY9QZfcMN5XpMPpYMZ+e7ucuEjc2EvF47dfLh8bxeQeWM5fJ9hftLlemInSTueFnGlWJfxLDGrEXAsMc3LgQ7mgLOsV2KGPdh2jkXqCnLBX0YyKwzMSoGk6DfFdG1/IFM1h6hPT2xnzzuB7Av6mWqPTlH177KBZ2MCcQhGEPf3EfVZFxTp1JU/YQb7mJNPFIlMsmBmv0nx6/2KzGunFqu/j777pE8AMyl5e82rWsam839xsO1J4alArygFTn3o6BVUeXclqP5Uqjr8D68So8IsdSLb8TKm/I1KkxRbbUuB+MACMegXldP1LRI+eoIZ0/dAqxuhmaBRrgM1BvI5RRvyR9yQlWQLGa5QtXnSV7Ir31QK0ovy8zIue1p9+Cxwcrwd3Bl26oSVVew828mQIiYq79jVkpNGC44VisTnExPNrn4PibGLroVMk6d2oSiU6oWFhF9i8f8/8gJ441wFzmx7PAT+0HH1aB1lPBs4wC+NlTLDDAbPdJFQfbHZH/RUL/dch00SK5CbpgdCKIqa3TpMdKn6/3e1dhtxGlZXrUFA6OloxLcJYu2QevrIkEvpbDCusacwcPvWSXSYJ8koFR1/TYXBg0NDUkmA1142chtISGaj0 1zXgzEFN 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 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 13.10.25 11:22, craftfever@murena.io wrote: Hi, > I've posted about that problem already on bigzilla (#220599), but maintainers asked to post issues on maillist. > The problem with freezes during KSM page scanning with certain processes like Chromium with huge virtual memory size amount was fized in 6.17.1 compared to 6.16.x/6.17, but problem with huge CPU overhead is present there. Compared to Linux <=6.15, where the overhead is much lighter anad there no much CPU consuming during KSM scanning, there is "folio_walk_start" kernel object is present (which I reviewed with "perf top" command) that is not present in versions <=6.15 during KSM work and which is in work starting from Linux 6.16. This method very resource-consuming compared to algorithm used in <=6.15 versions. Is there a kernel parameter to disable it or it needs more optimization? I doubt hat it has a lot to do with folio_walk_start(), that's just a simple page table walk replacing the previous walk based on follow_page(). So that's why you would suddenly spot it in perf top -- before commit b1d3e9bbccb4 ("mm/ksm: convert scan_get_next_rmap_item() from follow_page() to folio_walk") we would have used follow_page(). Do you see any kernel splats / soft-lockups? I can see that in commit b1d3e9bbccb4 I removed a cond_resched(). maybe that's why it's a problem in you kernel config. -- Cheers David / dhildenb