From mboxrd@z Thu Jan 1 00:00:00 1970 Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.remote-ip=100.103.45.18 ARC-Seal: i=1; d=subspace.kernel.org; s=arc20261015; a=rsa-sha256; cv=none; t=1794081312; b=LYCMG9/JZEjdtnc2FbdEn+k61QEC8f93deozRdoOdmpP13bMpG2TckDdD9MvavLXuupb 19SsQ8t/Kt5W/YP7U4talQTc5j1rBL7Xm778aAV6d+okzNy+Kk4LscfACFsGXzi/2o/ef BdTenE/YVC9h4dh2Fb4+RH5SXPEQ1XmNiPiQJi6B9zrRyyxrj/1BmIk27cEIlvz9i2GwM T0l0Mw0HRS3Ddp9uQbsJHjaJe6h9rP9rAa/bwZguk7bWTsLLhomw1nz6iQZnTO3Uuo/fv 7x95D3MLi/unTg7hWt7J+nEP9SaETcpcsrom+tnNxEtRC69QjYoVZUOCdELic5nauog== ARC-Message-Signature: i=1; d=subspace.kernel.org; s=arc20261015; a=rsa-sha256; c=relaxed/relaxed; t=1794081312; h=Received:DKIM-Signature:Message-ID:Date:MIME-Version:User-Agent: Subject:To:Cc:References:From:Content-Language:Autocrypt:In-Reply-To: Content-Type:Content-Transfer-Encoding; bh=39+TUkTn71HtHvq6NpbancWTbHR1aQMzi3+k/eHDkII=; b=Ryylcz7OLtrGPhdRBs4T8p8ZtdbyiZJpgJlCBk4fl3/5oOoou9uKVVZUMRLVYjQ02XP0 tD7s97xzCkSLvc9UYVV7chGE9+dtqX74ey3ZCpw6up6A6FFofCSVwHaVH7daQx+LOu8wO Lc5o+/1t69/6fDz37YtKUuVZr4EDRAVyL7VfOjbf22pbo2FXYxeRZX6Kj6+wswtFjsMJr Rv5zCAnvfYSc40ksuzcaf3ooB6B4SKXdhFT2gSzbGUSAgwTbUbUQiCHHPu8FHtPKgJ9kf qxMuRhBqWx5WI3dBE7dfub/8lUDe94F921kk/rDnwh40fCa2DLGl86fzLllqOJzRkNA== ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dkim=pass header.d=kernel.org header.i=@kernel.org header.a=rsa-sha256 header.s=k20260515 header.b=XPjXjKD8; arc=none smtp.remote-ip=100.103.45.18 Received: from smtp.kernel.org (quasi.space.kernel.org [100.103.45.18]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature ECDSA (prime256v1)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id C700F606A32C; Sat, 7 Nov 2026 19:55:11 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.a=rsa-sha256 header.s=k20260515 header.b=XPjXjKD8 Received: by smtp.kernel.org (Postfix) with ESMTPSA id 11D291F0089F; Sat, 7 Nov 2026 19:55:04 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1794081311; bh=39+TUkTn71HtHvq6NpbancWTbHR1aQMzi3+k/eHDkII=; h=Date:Subject:To:Cc:References:From:In-Reply-To; b=XPjXjKD824HOWovf8zZKb5c7Cb7I3D6NAD/lB0a8I4g19WeIXtgm5YZyMR/Kiu++6 B4OWZfuSb0TuEbG5bmrG2bK+f6320HjkTn4eSxLkhPYPhJuAPI/Jh8ChZpPIFGLunD 0gzKkwqLlZI/nC5lfdscz6x4B0dc48SJXcDriiVIugJYxUjUYpWFyBPVUqiU7J53nT qFp9AzFPMSyoVTRSUkTWQiQs+YzS5oVk6erZmbjDuwzJEDle3ZhX+A1fth88v9z5+2 egk4SzjImL8w9uEXb6v3D2msUKCRpiL66AJ6Xjc38rUj2CfFgXhL+hTpCJYEeJMPhT 2gHXaIkgPZbVA== Message-ID: Date: Sat, 7 Nov 2026 20:55:01 +0100 X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Post: List-Help: List-Subscribe: List-Unsubscribe: List-Owner: Precedence: list MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v3 0/4] mm/ksm: keep smart scan from losing duplicate pages To: Qiliang Yuan , Andrew Morton , Xu Xin , Chengming Zhou , Stefan Roesch , Lorenzo Stoakes , "Liam R. Howlett" , Vlastimil Babka , Mike Rapoport , Suren Baghdasaryan , Michal Hocko , Shuah Khan , Jonathan Corbet , Shuah Khan , Randy Dunlap Cc: linux-mm@kvack.org, linux-kernel@vger.kernel.org, linux-kselftest@vger.kernel.org, linux-doc@vger.kernel.org References: <20261107-bug-mm-ksm-smart-scan-align-skips-v3-0-16d5ce8b5fd6@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: <20261107-bug-mm-ksm-smart-scan-align-skips-v3-0-16d5ce8b5fd6@gmail.com> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit On 11/7/26 17:56, Qiliang Yuan wrote: > With smart scan, which is on by default, two identical pages that become > mergeable some scans apart can stay unmerged for as long as they live: > each page times its skipped scans on its own, and once both are old they > may never be looked at in the same scan, which merging through the > unstable tree requires. This was first noticed as intermittent failures > of ksm_tests "KSM NUMA merging" in run_vmtests.sh. > > Patch 1 picks the skipped scans by the global scan number, so all old > pages are looked at together every eighth scan. Over 420 pairs made > mergeable 0 to 20 scans apart, 361 and 334 merged before on two boots > and all of them after, at the cost of about 10% more ksmd time on memory > that never merges. > > Patch 2 documents how smart scan picks the scans to skip. > > Patch 3 moves waiting for KSM full scans into a vm_util helper, and > patch 4 adds a ksm_functional_tests case that fails 20/20 without patch > 1 and 0/20 with it, on both boots. > > Signed-off-by: Qiliang Yuan > --- I'll wait a bit for more review before I queue this, thanks. -- Cheers, David