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 3ED9ECD98E4 for ; Wed, 17 Jun 2026 09:42:52 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id 3D15B6B008A; Wed, 17 Jun 2026 05:42:51 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id 3820E6B0093; Wed, 17 Jun 2026 05:42:51 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 29A296B0095; Wed, 17 Jun 2026 05:42:51 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from relay.hostedemail.com (smtprelay0017.hostedemail.com [216.40.44.17]) by kanga.kvack.org (Postfix) with ESMTP id EF4096B008A for ; Wed, 17 Jun 2026 05:42:50 -0400 (EDT) Received: from smtpin12.hostedemail.com (lb01a-stub [10.200.18.249]) by unirelay07.hostedemail.com (Postfix) with ESMTP id 7D895165904 for ; Wed, 17 Jun 2026 09:42:50 +0000 (UTC) X-FDA: 84888915300.12.D5C5A3C Received: from sea.source.kernel.org (sea.source.kernel.org [172.234.252.31]) by imf23.hostedemail.com (Postfix) with ESMTP id AB19E140002 for ; Wed, 17 Jun 2026 09:42:48 +0000 (UTC) Authentication-Results: imf23.hostedemail.com; dkim=pass header.d=kernel.org header.s=k20260515 header.b=e00WLGFJ; spf=pass (imf23.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=1781689368; 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=MM09kvmX/Dy87FUT0EyogMRDLec0+XBI8U1zURJrec8=; b=gQk1+FTWVCqjQZVNCIsHT4FMPf4V+gmZ1XGAzYGQUaLdi8LraBs5EUyHJE1a1IuU5F922L TeC3fsp4Y+00nYCmXjxtDNOX4d+ShaV8NSxT4OItNqCPqtFe0EoGD73JhaNdz43k1+86yK N/lX1vI+y/9RLan/HMGZpTeWngGyheQ= ARC-Authentication-Results: i=1; imf23.hostedemail.com; dkim=pass header.d=kernel.org header.s=k20260515 header.b=e00WLGFJ; spf=pass (imf23.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; a=rsa-sha256; d=hostedemail.com; s=arc-20220608; cv=none; t=1781689368; b=zadCzoridGYpjfXZQ1kNft3VNj8riPQrZ7V8hjRbe6ZDc1nHU9+zhtiECv8sCUqTAInoVI Zu7AEayOVXjq1ME1wevBBhJZTZAldOf7it5gMKGI4PU36pNm5iIGX8GvAT6r6LHoO1o7ZQ Ih2WaCvYpFAVyMA67Y+Hy3tBjRF2ioA= Received: from smtp.kernel.org (quasi.space.kernel.org [100.103.45.18]) by sea.source.kernel.org (Postfix) with ESMTP id DCE41431F8; Wed, 17 Jun 2026 09:42:47 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 360961F000E9; Wed, 17 Jun 2026 09:42:45 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1781689367; bh=MM09kvmX/Dy87FUT0EyogMRDLec0+XBI8U1zURJrec8=; h=Date:Subject:To:Cc:References:From:In-Reply-To; b=e00WLGFJlnwL6SU8u5diDh8unAwZ6/h1/bvYyV++QY16qBZUTQxmnZFAemrs5+gJp RXEUtVLdX3ob02F5tJXKXeRGp8XAou+qPomHFwhWsqTdyTmr7EuHG75bYKDRuPqPip +lmbC3x+8Jgf83A1vD7ootg3sxoLIR1fcJOoF4Jpy2lYwZ0QJ7fM53tVEjHeKN9XPM eXk7Xqypr/g++fkO6mLdR1I0KfRc21FRljosw56wGadXRb2bFlqEuSzTmRWten1BLn Cmmtp0Sq28bRwp8vkgGCSwO9QkqZ0EM3FHjye74zSXEUglsBcevZNvD904lOr/sCkL FTFh6FB+xlQ6A== Message-ID: Date: Wed, 17 Jun 2026 11:42:44 +0200 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH 0/3] mm: __access_remote_vm with per-VMA lock To: Suren Baghdasaryan , Rik van Riel Cc: linux-kernel@vger.kernel.org, x86@kernel.org, linux-mm@kvack.org, Thomas Gleixner , Ingo Molnar , Dmitry Ilvokhin , Borislav Petkov , Dave Hansen , Andrew Morton , Lorenzo Stoakes , "Liam R. Howlett" , Vlastimil Babka References: <20260616190300.1509639-1-riel@surriel.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 X-Rspamd-Server: rspam04 X-Rspamd-Queue-Id: AB19E140002 X-Stat-Signature: nk6t7gqu8xge5e69atdqmzzg495uhrit X-Rspam-User: X-HE-Tag: 1781689368-641970 X-HE-Meta: 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 nm4hWzKz exYAxk5kdh3zIvI9ostvB/ZoXxdvGkCNuV+t3pxkk07pSjXH09t33obmmNLw4J7J8R2xUePkWuXmox4dkB8dHuQPoTRvBKSWLGvRudg2uv8p4uECXZC0DbTrOVBg1nFNt8r7loYBMKL17sVMndr/P2XgUw5XJe2UIAbEn9WkhjDKXb82jsHfZxyBp4oIknPf9dPHIouzk3SyQhcUGjhuli7g5ch8eol6xz2g1/Zpjvg8jWo5dnLMf1SISkepBfeyi7xGBhXzC7CRfo8E/AES/Nv+ya9jhxHCRiYEEV4uu4ZJ3KJihlzu12pX8G5Y2VjKTq55qjRimJ4hYUXrz5gNw9BvAkze3zRKv8kXCjvqh/LIcjtZEbl0w0fStqiSsZLKbtvT+AqEcRDOMzAg= Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On 6/17/26 03:10, Suren Baghdasaryan wrote: > On Tue, Jun 16, 2026 at 12:04 PM Rik van Riel wrote: >> >> Sometimes processes can get stuck with the mmap_lock held for >> a long time. This slows down, and can even prevent system monitoring >> tools from assessing and logging the situation, because they themselves >> end up getting stuck on the mmap_lock. >> >> However, with the introduction of per-VMA locks, we can improve the >> reliability of system monitoring, and generally speed up __access_remote_vm >> under mmap_loc contention, by adding a fast path that does not require >> the process-wide mmap_lock. >> >> This fast path is only compiled in and used when it is safe to do so, >> meaning a kernel with per-VMA locks, RCU pgae table freeing, the VMA >> is not hugetlbfs, iomap, pfnmap, etc... >> >> The code seems to work, but could still use some more cleaning up >> and benchmarking. > > Thanks for the patchset Rik! > Previously when I looked into using per-VMA locks in > access_remote_vm(), the biggest hurdle was get_user_pages_remote(), > which required mmap_lock. Your implementation avoids altogether and > keeps the code much simpler than what I expected. But, wouldn't we, in general, also want to teach GUP to just work with per-VMA locks? -- Cheers, David