From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-alma10-1.taild15c8.ts.net [100.103.45.18]) (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 482394A3D41 for ; Fri, 11 Sep 2026 16:44:12 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=100.103.45.18 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1789145054; cv=none; b=OmgCIg3+sCqdTCX7R+vV2BxWAm4F7jZGdhb2j3cINcdtSVuNsdtvMTKcSlna1SRTaddLSm4KHXqt0krcbwGeLMZa2upJ99RfxQoO60MsDhJSfrfVXlZav4yVl+G+zCSe3+Ud3DlXNQxqQlip41TujdYznxl2YHUtJZ6RLiPoBgk= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1789145054; c=relaxed/simple; bh=PMgKtl8zUoM6gfxbBHwRSP8q6IH3cUZp18QA+Ka/09Q=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=aUK/u8h0L6eVIlNmiNFXzIiNeDfuro56hHnUuGABFnS+Nn5SaSTpi555BpTyWkpfL30d+dXY3CSxebobx++fa5L9xfhqpuAmhbUzD/Iv0WJxCs7zIPvtQbL7WoAlb28OI56K7MqHGS0nu1W4ujXfZtaIqsd/YGVaMwg7kDufasQ= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=JNlZ0Vfr; arc=none smtp.client-ip=100.103.45.18 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="JNlZ0Vfr" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 9ACDE1F000FF; Fri, 11 Sep 2026 16:44:07 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1789145052; bh=64/u24ltheFG+IRwvDX3qmiVM9rNvR3qqwc5FQ5UhyE=; h=Date:Subject:To:Cc:References:From:In-Reply-To; b=JNlZ0VfryvP9EzKmXHTr9w/lIf2axf3au0kadcGsERGODueey6Tw/YYQ7c4bG5XsO V2fZ50m7qORqDc5hsVlmwsbqMJOHGILSx+sty1t6GluygCYQzS6LqtByMeNe/AuX3S uJH/gJXDtT/BWS5LWoQOQQsn4WjyWZ7sCqbL8Y1fNlYzfYl/t20Lh0mooj4F/ua59Z R+wClSZRMp1xfQNZvdk9FLadg65f5VV6DMzkmx42VpRAyuTdkQZRqntDswfi8F9QxC Y/j+PuTJ3KMm+bhmrV7LDhA1KznGr8n7Uuft0S+5jxWqdiVFkulT0d3baNTZG9oA6I V5q80ufL8r/cA== Message-ID: <6882373c-f76f-41ee-be62-cd910d07efce@kernel.org> Date: Fri, 11 Sep 2026 18:44:04 +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 RFC v4 0/12] mm: use per-VMA lock in __access_remote_vm for improved monitoring reliability To: Rik van Riel , Andrew Morton Cc: linux-kernel@vger.kernel.org, linux-mm@kvack.org, kernel-team@meta.com, Dave Hansen , Peter Zijlstra , Suren Baghdasaryan , Lorenzo Stoakes , Vlastimil Babka , "Liam R. Howlett" , Mike Rapoport , Michal Hocko , Jason Gunthorpe , John Hubbard , Peter Xu , Matthew Wilcox , Usama Arif References: <20260724222934.1463812-1-riel@surriel.com> <9e902c8e-c825-45ee-89a1-85923453e43d@kernel.org> <7c7b028ae93f0551e07e9e09468954e76ad072ee.camel@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: <7c7b028ae93f0551e07e9e09468954e76ad072ee.camel@surriel.com> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit On 9/11/26 18:03, Rik van Riel wrote: > On Fri, 2026-09-11 at 17:11 +0200, David Hildenbrand (Arm) wrote: >> On 7/25/26 00:29, Rik van Riel wrote: >>> __access_remote_vm() holds mmap_read_lock() for the whole transfer. >>> On >>> large machines, with large multi-threaded applications, the >>> mmap_lock >>> is often contended, leading to things like reads of >>> /proc/PID/cmdline >>> stalling. >>> >>> This results in system monitoring tools getting stuck, right when >>> system information would be the most helpful. >> >> Rik, what's the status of this, and which series do you consider more >> relevant: >> the pure per-VMA lock change or the pure page-table walking + folio >> batching? >> >> I'd assume the page-table walking would result in more speedup and >> the per-VMA >> in mostly less contention. So likely we'd want the page-table walking >> optimization first. > > We can merge them in either order.  > > This series gives a speedup as well, by removing  > the double VMA lookup. > > If you want to merge the page table walking and > folio batching change first, I can easily rebase > this per-VMA lock series on top of that. > > Do you have additional feedback on changes you > want me to make to get the page table walking > and folio batching thing in a merge-ready shape? I'll go through one patch set next week, I'm trying to figure out which one to prioritize :) -- Cheers, David