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b=UZp7lfRv15shr5/jiCnRRh8gt6f7FZR2Voy9nBq1Wf7WL/bVFyoFGFdtnLtFZT/RW VlvsDgVXq1HJCUsIBprHl+OZ4v7RpuZmSGSgUXuJkExqqTQzP8wEri/PN+o6bct97h qFP4NRemhz/tESWdlkezBlOrw+I4SCdpLSWFkH6b8uXt2SWOCMhIuuhIm7d7aMIc9p KXEhTP01uiDoHqSd3QcZPkLToisJ6pOh0QzrjvR/VXWaDZZvF9qCpjvW4ug5Y88boy 88PB0wis58ArZBogah1C8iHnAGH8zDzCWCr75+deippDfJhEupejKo3Oe5xSmnsXgZ eMji33rOSG36w== Message-ID: Date: Mon, 6 Jul 2026 08:49:34 +0200 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v11 0/3] KSM: performance optimizations for rmap_walk_ksm 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 References: <20260706124039747M7gtCsrOvuzDyfLMXIJ2B@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: <20260706124039747M7gtCsrOvuzDyfLMXIJ2B@zte.com.cn> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit X-Rspam-User: X-Rspamd-Server: rspam09 X-Rspamd-Queue-Id: F198F40009 X-Stat-Signature: i3kf9ih3oi4nez41jzwgszf98or3wu5w X-HE-Tag: 1783320579-887698 X-HE-Meta: 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 JJgGZ0Rr r8JwUJVlLF1EVfosfgE5RCz4lmtsGfXwmgamqb7ORW7+OaxJlbBFVhQOyT0nPqYrhvXhcqQKRtHlsnYGpNwsX1CzaeIRTEE9ulbkt2tIzMtrnXsoFmbeGqr0dAjMi3482sCiOEIsLBuGPV7NU4pIaVYYwt+O8uePvS0APxGt4dSj8SZh4lzxzYs4ankm2+Vlf/r/UE7+HNVy7HUUNWBspJaJwRikWh4V0iw8r16NtfwMxnxcwDeCKtl4HPgegFBD844L6IuUbc4OPKSLT9X1vouMZPncGxGnC8KuEMoUWkbmootEuav+ieNArudT0uDRWD6a0Rf59WGn0GpT1Gwuf9ztrZGXed1uxyZuzlrgDqfS4NL+sZpdUjI3qTF9rMeuznVJ+dwPpMR2KBQ4WNtLH9GBwj7DLFvBAa86kEB01VhsraUM= Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On 7/6/26 06:40, xu.xin16@zte.com.cn wrote: >> Again, thanks for persisting with this. Great improvement and I'd love >> to see us get this finished off. >> >> Please have a look through the AI review: >> >> https://sashiko.dev/#/patchset/20260703162253688u8Str9eFLR8TGCmo7nIOF@zte.com.cn >> >> That 32-bit thing looks legit, kinda fatal but easy to address. >> > > Hi, Andrew, This is not a major issue. I think it's acceptable and detailed > analysis is as follows: > > The sashiko said: > " >> Looking at struct ksm_rmap_item in mm/ksm.c, the linear_page_index (unsigned >> long) is placed in a union with an anonymous struct containing oldchecksum >> (unsigned int), age (rmap_age_t, 1 byte), and remaining_skips (rmap_age_t, >> 1 byte). >> On 32-bit platforms, an unsigned long is only 4 bytes, while the anonymous >> struct is at least 6 bytes. When break_cow(), remove_node_from_stable_tree(), >> and remove_rmap_item_from_tree() assign rmap_item->linear_page_index = 0 to >> reset the age-related information, it appears this will only zero the first 4 >> bytes (clearing oldchecksum). The age and remaining_skips fields would retain >> their stale historical values from before the page was originally merged. > > Indeed, on 32-bit CPU, that patch doesn't clear age-related information, but it > doesn't introduce any issue because at this point the linear_page_index and > age-related information do not overlap, and there is no conflict between them. > This is clearly consistent with the logic before applying the patch, so there > won't be any problem. It keeps bringing that up, and we clearly document "might overlay age-related information". So just ignore this. -- Cheers, David