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=1794247014; b=PS4DcC3RTwH3Fo34ePJxfnDRr58ztvg7pmBOQYQA+LR3WfbqYG+uRc+j0vgchU4NE/5V FVmiyP18cl6zm7brshe7VwZUvPmg6NdbdkF4jeMCvKpS1GoZ6Q01Htf+H/SmA8unzv05B RLzCxHHqXs4JBg2cM2NpJaMtNPs5S8q40jd6MJ+oj8VGS4QO4fHmvk5ayB1d9XW2UDlir 77bVL6lcVwkXSlDitPSIGSEyXGcz8wWd4PNTr/VKJYwX9+cPcQvV6cF3p9VJYj6O8vz7Z WEjexv/9lJw6Z6SkWevWd14u2bekcu8o1j8pJ+GP1+lMrWfqM2aoh1UPKSWtw+WUf9A== ARC-Message-Signature: i=1; d=subspace.kernel.org; s=arc20261015; a=rsa-sha256; c=relaxed/relaxed; t=1794247014; 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=YNhycM7i44D28IncIzykroZv4YkZR+2ZSE2Wf7GgLlw=; b=2cwjmCnrI8RfuCvRXArDWM5j0IsfaUKYiVXbCDFoXNoWF5Y7eqbrhN5kjizFzJLFSAy4 oKwQnZBk3Riz05q7g4EBQOiqmH1DDAxjP5zPZPY/HAyO6Uo3iMQAi6ju4X+WIC41KRtD4 HXCwoSpLWw0obC14y/xDJM8DSTZatgDqaxXhJT071RyH//HQmM5geau63wsbJbOw5OnEg PYlJvezLAQO9nUBfi8jtqkBVdAGDfonYb2+Uf+vFyFS5gCRFrrAkyFBslCNEj0dY4WlmL WfHTil+lSHufscBPlbB7LITYhrzBvk/QOoBCUjmieEu6oUgiIiYHB4dNwsTuK6/hAhg== 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=FlBYnBqf; 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 69BE8606A321 for ; Mon, 9 Nov 2026 17:56:54 +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=FlBYnBqf Received: by smtp.kernel.org (Postfix) with ESMTPSA id 508AC1F0089F; Mon, 9 Nov 2026 17:56:50 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1794247014; bh=YNhycM7i44D28IncIzykroZv4YkZR+2ZSE2Wf7GgLlw=; h=Date:Subject:To:Cc:References:From:In-Reply-To; b=FlBYnBqfZpkSaqKkRTnAoc7afDQSDdvqCa9MUzI6cuF9mNMxqvr1IAKmNkcC6ai03 lrPBfh4FuKT18GoykGxO2NN3CBz0rfQgKfhVtGCk2GmpY29bmxyRHvEzrNI9qfHoWZ WLj/rtNedM8B+hgbCKGsln1f8EmIWM5epY6UIh8hAnkqqkyRwL9fiordu85mVcjwsa P5D0OoIYOvUCnRmv1tVXikRgx14ns1TMzFYUHUd/ugeOicyVNwWML4r0z5j3jSyL8v Jz/EU+PReWuJaBROy647MQZz6o4Sq3cbSkdLBpX75Sf4QsP3wU7b0z4saRRrb720Jj 2kGTV0rgXr0eA== Message-ID: <2199b816-e3b0-4f1f-aef4-e79ce71fd07a@kernel.org> Date: Mon, 9 Nov 2026 18:56:47 +0100 X-Mailing-List: linux-doc@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 resend] ksm: add merge_only_zero_pages to merge only empty anonymous pages To: "Xu Xin (vivo)" , Jinjiang Tu Cc: Andrew Morton , Jonathan Corbet , Chengming Zhou , Lorenzo Stoakes , "Liam R . Howlett" , linux-mm@kvack.org, linux-doc@vger.kernel.org, Huan Yang , Wang Xiao References: <20261106034841.233085-1-xu.xin@linux.dev> <2a642af6-b97a-4f24-9889-1844812de4cc@huawei.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: Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit On 11/9/26 03:02, Xu Xin (vivo) wrote: > On Sat, Nov 07, 2026 at 04:13:40PM +0800, Jinjiang Tu wrote: >> >> 在 2026/11/6 11:48, xu.xin@linux.dev 写道: >>> From: "Xu Xin (vivo)" >>> >>> KSM side-channel exposure is desired. Many handset vendors may prefer >>> this knob, which can be used as a default fallback policy. >>> >>> - Not suitable for server and virtualization workloads containing many >>> non-zero duplicate pages, where vanilla KSM provides better memory >>> savings. >> >> It’s a coincidence that I’m also working on similar optimizations. >> In our scenario, we have a MySQL instance with over 700 GB of anonymous >> memory. Most of this memory belongs to the buffer pool, which caches >> data from storage; these pages cannot be merged. Of the remaining memory, >> around 15 GB is consumed by hashtables, which contain many zero-filled >> pages that are eligible for merging to reduce memory footprint. >> >> When we enabled KSM for the entire MySQL instance, ksmd created rmap_item >> metadata for each candidate page.The massive metadata overhead wiped out >> any gains from page merging, and even resulted in a negative benefit. >> >> For this reason, I’m trying to make ksmd merge only zero pages. The goal >> is to have ksmd skip scanning non-zero pages entirely, thereby avoiding >> the rmap_item metadata cost introduced by scanning non-mergeable pages. > > Skip generating ksm_rmap_item for non-zero pages ? That dose make sense to me. Yes, we should avoid any such memory overhead in that case. -- Cheers, David