From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from shelob.surriel.com (shelob.surriel.com [96.67.55.147]) (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 794DE4949FA for ; Fri, 11 Sep 2026 16:04:16 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=96.67.55.147 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1789142658; cv=none; b=g9kzrh5tJvV7/QRoH7UQTcmdLQ019ItbaoU/QhRCp50uDh/QtZvfh7t5nvF2T7n7ZCqCgp4G7bgvz7Mv7LPhE/qWbclUJI6tQ5VHZMQcvBJ4iARv+wB8Fx5AS+ECtLkJ+1rVvjVqncAcdi7yoixXijx5+p1n4PHnOUm3l0Ay8bs= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1789142658; c=relaxed/simple; bh=rR1Bx7fi8xYmaqwM12Cl5cmpcBittw/5vU9eYvMxtCA=; h=Message-ID:Subject:From:To:Cc:Date:In-Reply-To:References: Content-Type:MIME-Version; b=lS/EhNAsLmHnqli5O8LW+v5WaYBxCCD8IF9DB1UwEfxWEs647H0++6t5x92TzpyyRXCbWlkg/VIt1nFyOOqgS5H+s/xOiZKSg4iPWo0c9Yxai727WAYXNsYQPlV/explqw9vxm1zYHMpZ8CCkVfnLFzLGtG31rauJBVncF3Moy4= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=quarantine dis=none) header.from=surriel.com; spf=pass smtp.mailfrom=surriel.com; dkim=pass (2048-bit key) header.d=surriel.com header.i=@surriel.com header.b=WnlsB0ID; arc=none smtp.client-ip=96.67.55.147 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=quarantine dis=none) header.from=surriel.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=surriel.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=surriel.com header.i=@surriel.com header.b="WnlsB0ID" DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=surriel.com ; s=mail; h=MIME-Version:Content-Transfer-Encoding:Content-Type:References: In-Reply-To:Date:Cc:To:From:Subject:Message-ID:Sender:Reply-To:Content-ID: Content-Description:Resent-Date:Resent-From:Resent-Sender:Resent-To:Resent-Cc :Resent-Message-ID; bh=rR1Bx7fi8xYmaqwM12Cl5cmpcBittw/5vU9eYvMxtCA=; b=WnlsB0 IDbzhjdBLketBrAColocv1cck0fpkaLFQAjJHI4hr87M4LisybioWrfUTth+BFqJX/WWHTNcWtxbc 7NLv6WxJdEVsCMSeBk0VASNfbMqjho2THp070kDqJHdh4JcULIUxaaYNuIdfbIUC5qRbMg3tFPsOq E8CIBgyOGHjHQBQNymfwJLmBQZGqSAiPMJc1KY4r6XRK7ZuBrmCm33kVrVIsfA6bsL33gyj5UaaQX OcaI4z+ZJMhm8ZDdS8vBvSduyu36pyDDNlK97xHiat8ONcbVxMrol2Nh19vhqVDWKt53yVgv7lZO2 Tcf7YK7kPCeaFunp9YjXR6i2Khmg==; Received: from [2601:18c:8100:a0e0:5a47:caff:fe78:8708] by shelob.surriel.com with esmtpsa (TLS1.3) tls TLS_AES_256_GCM_SHA384 (Exim 4.99.5) (envelope-from ) id 1x53j7-000000080lY-3ueh; Fri, 11 Sep 2026 16:03:45 +0000 Message-ID: <7c7b028ae93f0551e07e9e09468954e76ad072ee.camel@surriel.com> Subject: Re: [PATCH RFC v4 0/12] mm: use per-VMA lock in __access_remote_vm for improved monitoring reliability From: Rik van Riel To: "David Hildenbrand (Arm)" , 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 Date: Fri, 11 Sep 2026 12:03:45 -0400 In-Reply-To: <9e902c8e-c825-45ee-89a1-85923453e43d@kernel.org> References: <20260724222934.1463812-1-riel@surriel.com> <9e902c8e-c825-45ee-89a1-85923453e43d@kernel.org> Autocrypt: addr=riel@surriel.com; prefer-encrypt=mutual; keydata=mQENBFIt3aUBCADCK0LicyCYyMa0E1lodCDUBf6G+6C5UXKG1jEYwQu49cc/gUBTTk33A eo2hjn4JinVaPF3zfZprnKMEGGv4dHvEOCPWiNhlz5RtqH3SKJllq2dpeMS9RqbMvDA36rlJIIo47 Z/nl6IA8MDhSqyqdnTY8z7LnQHqq16jAqwo7Ll9qALXz4yG1ZdSCmo80VPetBZZPw7WMjo+1hByv/ lvdFnLfiQ52tayuuC1r9x2qZ/SYWd2M4p/f5CLmvG9UcnkbYFsKWz8bwOBWKg1PQcaYHLx06sHGdY dIDaeVvkIfMFwAprSo5EFU+aes2VB2ZjugOTbkkW2aPSWTRsBhPHhV6dABEBAAG0HlJpayB2YW4gU mllbCA8cmllbEByZWRoYXQuY29tPokBHwQwAQIACQUCW5LcVgIdIAAKCRDOed6ShMTeg05SB/986o gEgdq4byrtaBQKFg5LWfd8e+h+QzLOg/T8mSS3dJzFXe5JBOfvYg7Bj47xXi9I5sM+I9Lu9+1XVb/ r2rGJrU1DwA09TnmyFtK76bgMF0sBEh1ECILYNQTEIemzNFwOWLZZlEhZFRJsZyX+mtEp/WQIygHV WjwuP69VJw+fPQvLOGn4j8W9QXuvhha7u1QJ7mYx4dLGHrZlHdwDsqpvWsW+3rsIqs1BBe5/Itz9o 6y9gLNtQzwmSDioV8KhF85VmYInslhv5tUtMEppfdTLyX4SUKh8ftNIVmH9mXyRCZclSoa6IMd635 Jq1Pj2/Lp64tOzSvN5Y9zaiCc5FucXtB9SaWsgdmFuIFJpZWwgPHJpZWxAc3VycmllbC5jb20+iQE +BBMBAgAoBQJSLd2lAhsjBQkSzAMABgsJCAcDAgYVCAIJCgsEFgIDAQIeAQIXgAAKCRDOed6ShMTe g4PpB/0ZivKYFt0LaB22ssWUrBoeNWCP1NY/lkq2QbPhR3agLB7ZXI97PF2z/5QD9Fuy/FD/jddPx KRTvFCtHcEzTOcFjBmf52uqgt3U40H9GM++0IM0yHusd9EzlaWsbp09vsAV2DwdqS69x9RPbvE/Ne fO5subhocH76okcF/aQiQ+oj2j6LJZGBJBVigOHg+4zyzdDgKM+jp0bvDI51KQ4XfxV593OhvkS3z 3FPx0CE7l62WhWrieHyBblqvkTYgJ6dq4bsYpqxxGJOkQ47WpEUx6onH+rImWmPJbSYGhwBzTo0Mm G1Nb1qGPG+mTrSmJjDRxrwf1zjmYqQreWVSFEt26tBpSaWsgdmFuIFJpZWwgPHJpZWxAZmIuY29tP okBPgQTAQIAKAUCW5LbiAIbIwUJEswDAAYLCQgHAwIGFQgCCQoLBBYCAwECHgECF4AACgkQznneko TE3oOUEQgAsrGxjTC1bGtZyuvyQPcXclap11Ogib6rQywGYu6/Mnkbd6hbyY3wpdyQii/cas2S44N cQj8HkGv91JLVE24/Wt0gITPCH3rLVJJDGQxprHTVDs1t1RAbsbp0XTksZPCNWDGYIBo2aHDwErhI omYQ0Xluo1WBtH/UmHgirHvclsou1Ks9jyTxiPyUKRfae7GNOFiX99+ZlB27P3t8CjtSO831Ij0Ip QrfooZ21YVlUKw0Wy6Ll8EyefyrEYSh8KTm8dQj4O7xxvdg865TLeLpho5PwDRF+/mR3qi8CdGbkE c4pYZQO8UDXUN4S+pe0aTeTqlYw8rRHWF9TnvtpcNzZw== Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable User-Agent: Evolution 3.60.2 (3.60.2-1.fc44) Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 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. > >=20 > > This results in system monitoring tools getting stuck, right when > > system information would be the most helpful. >=20 > 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? >=20 > 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.=C2=A0 This series gives a speedup as well, by removing=C2=A0 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? --=20 All Rights Reversed.