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=1793179386; b=H8AqYuyHhHHha5dD39ewEz5j/Zeyk0jK1stBICXlF3W4LmDHpSysAHnV9A2cKa2ICnj6 R4vU3jY5H8Pv76lAZIz5brnqT30nHiPVx93JDdM2+n3s4gVkeP1k04T1s7iSFGVd4mAwN LOGH/w30RrinY2RsZCcT4tFFFyIgnAfXBDQdDtKPIVGpZ+6ypkzavdOXYV2/eqvVHNmw8 BsQALuPltXYlGRC14jcUg7IauKKBqzvH/2kOmjenpoTVY8fDtxmIkZgdic7VGBxBm8QPF WOM4O57I+GYuSrhdU7aWNwLw+dc9MuazTAToJIwa1OzkSXuJx41/cXUUK2SVvgzGn/w== ARC-Message-Signature: i=1; d=subspace.kernel.org; s=arc20261015; a=rsa-sha256; c=relaxed/relaxed; t=1793179386; 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=9UoZu4LOCR+P05LgNRjZiBqAG2n8MlC20pukDWQyPU0=; b=CvT0Ha9dxZVMUhm2jxm55L8KkkG61PE9Ey8ARF7CI4/6Bv750JG3vOkuLkNpQoHIUOQb O8jK2IGhKb/K6ihSFlRwlJo2dBoKs1krJ7jSxuQM+ny/4b0f7WrChS5G1Vc3sZRqUgoQv sG5ZcMV3bcH+zc/C9jx8sc40v8uhpXtTeSqTScU348H+mqvQU4tYVfqF/1M2DZoNc3Sjd 3sun53UFdZod02KeddadNZ3nN//3zYWV3k9Xr/iJidKGPF1NUZC++IyEI8o68QmnpX1o0 xOjjiTcHfD9h4rjnmhJ55L3j4qQPGeRrjwJvE3q71zWNdSGuqqQOpfLqV1/+ytQ7uRw== 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=cAXWT2+g; 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 0BF1F606A31A; Wed, 28 Oct 2026 09:23:05 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key, unprotected) header.d=kernel.org header.i=@kernel.org header.a=rsa-sha256 header.s=k20260515 header.b=cAXWT2+g Received: by smtp.kernel.org (Postfix) with ESMTPSA id B91C71F01825; Wed, 28 Oct 2026 09:23:01 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1793179385; bh=9UoZu4LOCR+P05LgNRjZiBqAG2n8MlC20pukDWQyPU0=; h=Date:Subject:To:Cc:References:From:In-Reply-To; b=cAXWT2+gQZ82YrnQOeJbjSRGKbLs4lfRW7FFfRDFxaAIOAcI4PS6NZOiYSiQh2wc9 ITBa/gneOaJViW5esoOnJCwEcBKOfo1xiqPXthg+nrjWIGQK76SW6iRT2OED/Ur+Hr YO1v0tBq4zVTyMrYanGNSo9ygjAxbsg8ys+lkbNQJ0sMWk/2B1cd/TxH9kJXmuYczB fHeT+XC3xNAsG9jOxXmBISGFZ8/MI/c1HSnRE6QaXrU0mkggDtJZOjhA45fS2YuYCW /GaiUfORHM8nA7PDRof6B1mGieA1UXqwMLFNKtwKia2QqGujtPi5qqFZ/09HjIz+So 4+3VTWZH2D/1g== Message-ID: <25f5cbed-9126-4870-a81e-65099155bc9d@kernel.org> Date: Wed, 28 Oct 2026 10:22:58 +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 4/4] mm: pass the number of PTEs to move_pte() To: Imre Kaloz Cc: "David S. Miller" , Andreas Larsson , "Matthew Wilcox (Oracle)" , "Mike Rapoport (IBM)" , Andrew Morton , "Liam R. Howlett" , Lorenzo Stoakes , Vlastimil Babka , Jann Horn , Pedro Falcato , Suren Baghdasaryan , Michal Hocko , sparclinux@vger.kernel.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org, Magnus Lindholm References: <2bc50d2a6829b49ee909e5bb943244859661a40b.1792609488.git.kaloz@kernel.org> <409079fe-ab52-4389-9fe0-d7246eb27bad@kernel.org> <20261027212610.6798-1-kaloz@kernel.org> <20261028091631.8072-1-kaloz@kernel.org> 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: <20261028091631.8072-1-kaloz@kernel.org> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit On 10/28/26 10:16, Imre Kaloz wrote: > Hi David, > > On 10/28/26 09:49, David Hildenbrand (Arm) wrote: >> But that's too complicated, requiring page table walks .... >> People running museum piece hardware and complaining about performance of mremap >> or memory reclaim should reconsider life choices. > > I'm one of the museum folks myself, though more the kind who loves > running a modern kernel on old hardware than the kind who complains > about it :) A lot of these machines are still doing real work, and > these days not everyone can, or wants to, just buy a new computer. > > Some of us spend our time keeping these platforms working, and I'm > not asking anyone else to carry that, which is why I tried to keep > all of it in sparc. Okay, so mremap() and reclaim memory performance concerns make you sleep bad at night? :) Don't get me wrong, I know that running new kernels on old HW is fun. Last week a got upstream Linux running on a 32bit x86 notebook from 2007 with the snap of a finger. Everything just works (using Alpine). I couldn't care less about performance. Nobody should. The biggest problem all of us with supporting old hardware is the maintanance cost. Not just core-mm, but also things like ad-hoc page table walkers you are adding we (from core-mm) might have to touch at some point. If there is no good reason for the complexity, out it goes. Because otherwise people will push more and more for removing legacy support completely, and that's not what you want, right? > >> So I'd say, make it as slow as you want while reducing core-MM complexity and >> not adding more arch complexity. > > With C, move_pte() and __HAVE_ARCH_MOVE_PTE go away from > include/linux/pgtable.h and mm/mremap.c just like with A and B. The > walk lives in sparc's own flush_cache_range() and only runs on the > CPUs that need it. > > B would be less sparc code, but every UltraSPARC I-IV machine would > pay 13-18% on reclaim for it, so I'd still lean towards C. If you feel > strongly about B, though, I'm happy to send that instead. You know my answer :) -- Cheers, David