From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 6C1503101A7 for ; Fri, 8 May 2026 10:58:40 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1778237920; cv=none; b=hSbrMtSVjDb30Q2ihiXFyeaQg7LF3z0i3dr1uLaAvNQPOH9NwnmYAPnMB694WWgiK/E9qWCqa0UU22i7cvKacrHfYwh5hTNAH0Edcp+vt2nnIDhjHvnsjPy8wILXNjZUIP6bQYv/7lx3DFfx94B9cJyeIKdejVNifUE1/tHlsr0= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1778237920; c=relaxed/simple; bh=S59UBbH+ZLEy2OAA811fhr/mLyBXtU8vtHsvcNkbvFY=; h=Message-ID:Date:MIME-Version:Subject:From:To:Cc:References: In-Reply-To:Content-Type; b=iOilAaML4yPWFdx5UPBBlA2c+WU6zTeEpu7YD2hU+tVEdvPT0LEChVQbuijMucpe/UsaRDRjof0DM4oJ2p7MhY9EQzNXh+NsC7n3wCnkovwRBTWAjdHu5LlLFxz8LEHV8d9sLCGIONM06X1k2IqU8+1XeeZdh1qneKoxn3Cd3jQ= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=QRnDcjoA; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="QRnDcjoA" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 55A2BC2BCB0; Fri, 8 May 2026 10:58:37 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1778237920; bh=S59UBbH+ZLEy2OAA811fhr/mLyBXtU8vtHsvcNkbvFY=; h=Date:Subject:From:To:Cc:References:In-Reply-To:From; b=QRnDcjoAmG5/ULzMWOY7X1jV0sSv+hOHKKEZsTR1f6QNKIQL69NBnChoUrj0Fucn6 7zvDZnDrD5itCv7Otgu+f0tse5KowMZFsfAA7v8hxAes/XxMioazCJYp9HN276d6P2 VkL8hWaUaXWW2/2IgHu1zzmdUQSvGoQqz2u+9nRef2KTnoIS/Sb/6rYgDnL2aLDuRt Xo67qYI7luSkDYF1cXk98Im+oQP/goggHCqOTfuUM9MJZcOi/97ZBremb78u0j0wUy Mm/qSkOZYMl0EAZHUynPW7nL8qfNvi9QJpGbeTCoU1q5mtuRWrC96JDUIkm30EllhJ nbA9u4QORLDqA== Message-ID: <36346c42-2557-431f-aef5-0f92b0828e76@kernel.org> Date: Fri, 8 May 2026 12:58:35 +0200 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH 1/6] mm: Make per-VMA locks available universally From: "David Hildenbrand (Arm)" To: Dave Hansen , linux-kernel@vger.kernel.org Cc: Andrew Morton , "Liam R. Howlett" , linux-mm@kvack.org, Lorenzo Stoakes , Shakeel Butt , Suren Baghdasaryan , Vlastimil Babka References: <20260429181954.F50224AE@davehans-spike.ostc.intel.com> <20260429181955.0C443845@davehans-spike.ostc.intel.com> 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: 7bit On 5/8/26 12:12, David Hildenbrand (Arm) wrote: > On 4/29/26 20:19, Dave Hansen wrote: >> From: Dave Hansen >> >> The per-VMA locks have been around for several years. They've had some >> bugs worked out of them and have seen quite wide use. However, they >> are still only available when architectures explicitly enable them. >> Remove the conditional compilation around the per-VMA locks, making >> them available on all architectures and configs. > > Yes, we should really just make it now just a fixed part of the kernel design. > >> >> The approach up to now seemed to be to add ARCH_SUPPORTS_PER_VMA_LOCK >> when the architecture started using per-VMA locks in the fault >> handler. But, contrary to the naming, the Kconfig option does not >> really indicate whether the architecture supports per-VMA locks or >> not. It is more of a marker for whether the architecture is likely to >> benefit from per-VMA locks. >> >> To me, the most important thing side-effect of universal availability >> is letting per-VMA locks be used in SMP=n configs. This lets us use >> per-VMA locking in all x86 code without fallbacks. >> >> Overall, this just generally makes the kernel simpler. Just look at >> the diffstat. It also opens the door to users that want to use the >> per-VMA locks in common code. Doing *that* can bring additional >> simplifications. >> >> The downside of this is adding some fields to vm_area_struct and >> mm_struct. > > I'd assume most distributions would already enable it. > > mm_struct is very likely not a problem. > > On x86-64, the smallest size for vma_area_struct possible (make allnoconfig) > seems to be 68bytes. The largest size (make allyesconfig) with lockdep and all > that is 256bytes. Without lockdep we are at 192 bytes: independent of per-VMA locks. > > I'd expect that on most 64bit configs we usually end up with 192 bytes today. > > Given that our slab sizes are ...32/64/96/128/192/..., I guess we'd have to be > lucky to jump between sizes on most configs. As Vlastimil reminded me, the have separate slab caches, so they are better packed. So I don't think a small increase there would really be a problem. -- Cheers, David