From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) (using TLSv1 with cipher DHE-RSA-AES256-SHA (256/256 bits)) (No client certificate requested) by smtp.lore.kernel.org (Postfix) with ESMTPS id D15EACD3447 for ; Fri, 8 May 2026 10:12:34 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id DB5E46B0137; Fri, 8 May 2026 06:12:33 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id D66756B0138; Fri, 8 May 2026 06:12:33 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id C2EC26B0139; Fri, 8 May 2026 06:12:33 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from relay.hostedemail.com (smtprelay0014.hostedemail.com [216.40.44.14]) by kanga.kvack.org (Postfix) with ESMTP id AD5AF6B0137 for ; Fri, 8 May 2026 06:12:33 -0400 (EDT) Received: from smtpin06.hostedemail.com (lb01a-stub [10.200.18.249]) by unirelay03.hostedemail.com (Postfix) with ESMTP id 57E34A07A4 for ; Fri, 8 May 2026 10:12:33 +0000 (UTC) X-FDA: 84743838186.06.BE70007 Received: from sea.source.kernel.org (sea.source.kernel.org [172.234.252.31]) by imf26.hostedemail.com (Postfix) with ESMTP id 824DD140005 for ; Fri, 8 May 2026 10:12:31 +0000 (UTC) Authentication-Results: imf26.hostedemail.com; dkim=pass header.d=kernel.org header.s=k20201202 header.b=R4dUvE+S; spf=pass (imf26.hostedemail.com: domain of david@kernel.org designates 172.234.252.31 as permitted sender) smtp.mailfrom=david@kernel.org; dmarc=pass (policy=quarantine) header.from=kernel.org ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=hostedemail.com; s=arc-20220608; t=1778235151; h=from:from:sender:reply-to:subject:subject:date:date: message-id:message-id:to:to:cc:cc:mime-version:mime-version: content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references:dkim-signature; bh=3M4BVUeod7EsE+qXOSOWLKWHoWslD2RxHgWBj0aiUmE=; b=gyD3QbhNE2iZqyr7VXC1ydm9vtHvKMBQ0Zu5jguE4NU4HaTpOzjrfp83x37kooqa3WPI8A aptfoQ33YxEaDcXx/LytV0YTJMn22Ae5yP+Dz76ROM31W2WL7yrWEMIHmIxwDL0H9D6Phv 2h8WgDPHFjD2kDGmgScVzAXn0jHHhtI= ARC-Authentication-Results: i=1; imf26.hostedemail.com; dkim=pass header.d=kernel.org header.s=k20201202 header.b=R4dUvE+S; spf=pass (imf26.hostedemail.com: domain of david@kernel.org designates 172.234.252.31 as permitted sender) smtp.mailfrom=david@kernel.org; dmarc=pass (policy=quarantine) header.from=kernel.org ARC-Seal: i=1; s=arc-20220608; d=hostedemail.com; t=1778235151; a=rsa-sha256; cv=none; b=h4lQf1Ti5PHArpFloPERN1j42C5Qpuwo4aTKJZMJ6ImFHCPirzanmVmbx9mFyyXqwvtlBq XzuOEzjQufIpHMxxC26OEoIpPyJHKneeqmvMInNWxTeMDcYXEs0HtZbhnF4DqH4FnJVyOu klZv4YxKnmbHxBecAh9ytvNtcvJBN+w= Received: from smtp.kernel.org (transwarp.subspace.kernel.org [100.75.92.58]) by sea.source.kernel.org (Postfix) with ESMTP id 892A743B59; Fri, 8 May 2026 10:12:30 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 79958C2BCB0; Fri, 8 May 2026 10:12:27 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1778235150; bh=mPW1suWcBNXHM4rmLBS8M3I/y4AtZZ/H0fZ1cIPIBKA=; h=Date:Subject:To:Cc:References:From:In-Reply-To:From; b=R4dUvE+Sl0M8nNwXwoA7TYhLb9H31T3bfqiWkk6bhraXAn0LTgx90vVyH8hPMsHAB Pw302qNkqO5xZnVmqdXEgGP543kejzukiSUl7/PNE7O9qnLirqV3T/d+lA4pfxW0gA 1TxAj3qOhgKKm1UPg0gboc2/zmPXFbbwtaZcFyMTnoYdsVUeIOvaPuxa2UlcGJ87pq j9KI9UJCZvpYoHgH9hCZXEHZ7kRAW6cDZn5Wa9JK+JrMFPqd8q1fcHJOjGcEbC3rWD pR5LH2+83uX9euGh20uGIFiNxBmKWw6Oo5jUsiinMl0wNzEg5rO88dYbhHawsSm/Vi vwZdYj/1vnl6Q== Message-ID: Date: Fri, 8 May 2026 12:12:25 +0200 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH 1/6] mm: Make per-VMA locks available universally 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> 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: <20260429181955.0C443845@davehans-spike.ostc.intel.com> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit X-Rspamd-Server: rspam02 X-Rspamd-Queue-Id: 824DD140005 X-Rspam-User: X-Stat-Signature: 49gmid8wsa6dqpbiciuknq3rqmjintjx X-HE-Tag: 1778235151-943529 X-HE-Meta: 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 X7/7dXrV DKTFeJLjCqY1faRtRzR4m0mgrnNq0Wiom73F2l2OZKZt4nNersaSnEdjYqlEc+ds886AqLDLnk933v+iLED9kPQcuR4iVM3nTSItVkuBNE+/5BkI5h1zPE1fCfPXZJI96FcHLeH8M9JiaJZHN6pNFBQFyvmf+EQAO23rWsbWke7KWM4UgiCwx9DJbL/jVx5CGTcGTysA0pPSNvJ9HkjLVyYE+4GSOJxOLmScjGQPS1/o+Z9FjQviRy68KdWXret6XKyvWpcB5xFcwMCit8fG15O2qNw== Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: 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. Maybe on 32bit? Not sure if anybody would really notice. > I suspect there are some very simple ways to implement the > per-VMA locks that don't require any additional fields, especially if > such an approach was limited to SMP=n configs*. For now, do the > simplest thing: use the same implementation everywhere. > > * For example, since SMP=n configs don't care much about scalability or > false sharing, there could be a single, global VMA seqcount that is > bumped when any VMA is modified instead of having space in each VMA > for a seqcount. I'd do that only if we actually determine this to be a problem. -- Cheers, David