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]) by smtp.lore.kernel.org (Postfix) with ESMTP id F3747C48BEB for ; Fri, 16 Feb 2024 12:34:12 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id 7E96F6B00A6; Fri, 16 Feb 2024 07:34:12 -0500 (EST) Received: by kanga.kvack.org (Postfix, from userid 40) id 799396B00A7; Fri, 16 Feb 2024 07:34:12 -0500 (EST) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 687EC6B00A9; Fri, 16 Feb 2024 07:34:12 -0500 (EST) X-Delivered-To: linux-mm@kvack.org Received: from relay.hostedemail.com (smtprelay0015.hostedemail.com [216.40.44.15]) by kanga.kvack.org (Postfix) with ESMTP id 5AE866B00A6 for ; Fri, 16 Feb 2024 07:34:12 -0500 (EST) Received: from smtpin04.hostedemail.com (a10.router.float.18 [10.200.18.1]) by unirelay01.hostedemail.com (Postfix) with ESMTP id 272D41C0623 for ; Fri, 16 Feb 2024 12:34:12 +0000 (UTC) X-FDA: 81797609544.04.F944F2E Received: from dfw.source.kernel.org (dfw.source.kernel.org [139.178.84.217]) by imf26.hostedemail.com (Postfix) with ESMTP id 83969140003 for ; Fri, 16 Feb 2024 12:34:10 +0000 (UTC) Authentication-Results: imf26.hostedemail.com; dkim=none; spf=pass (imf26.hostedemail.com: domain of cmarinas@kernel.org designates 139.178.84.217 as permitted sender) smtp.mailfrom=cmarinas@kernel.org; dmarc=fail reason="SPF not aligned (relaxed), No valid DKIM" header.from=arm.com (policy=none) ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=hostedemail.com; s=arc-20220608; t=1708086850; 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: in-reply-to:in-reply-to:references:references; bh=+szfn7FTsCeayUieX57QJgh0t4LRwBC3rP//HGUA5Ho=; b=Tf4d4l5dNJzhzm5hlaOTZhbpN9x5J2l5R0hmQjctlkTUUCaVNB6PJ2fZymShfGaW08vQIn 5n6XM14uMwnK7OVhci7GJc/Zfmm558vuTCxVOl4Hz0fxlMzXOmP3XuVd6hWlwh8YYy5u+J OpPbo3KwCR5vVNPpWa2BNjgl+obxpQs= ARC-Seal: i=1; s=arc-20220608; d=hostedemail.com; t=1708086850; a=rsa-sha256; cv=none; b=ZwEZMuslSEFbCEyUkEc1vSS/g9BybJ9kVwABbOqtrsze7uPHg948erlZFiZmWZa6vMbBCm iwlLuoXOF76NeIFdpc0LhCuUxy5TYX31bCO74aTCzwoHr2G4zXpbXAdPa4lVmrXj3WflL7 2ikJLN2nHCf99A13sfy13ZhtlFf5ous= ARC-Authentication-Results: i=1; imf26.hostedemail.com; dkim=none; spf=pass (imf26.hostedemail.com: domain of cmarinas@kernel.org designates 139.178.84.217 as permitted sender) smtp.mailfrom=cmarinas@kernel.org; dmarc=fail reason="SPF not aligned (relaxed), No valid DKIM" header.from=arm.com (policy=none) Received: from smtp.kernel.org (transwarp.subspace.kernel.org [100.75.92.58]) by dfw.source.kernel.org (Postfix) with ESMTP id 8DD0C614FA; Fri, 16 Feb 2024 12:34:09 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 4F9B9C433C7; Fri, 16 Feb 2024 12:34:04 +0000 (UTC) Date: Fri, 16 Feb 2024 12:34:02 +0000 From: Catalin Marinas To: Ryan Roberts Cc: Will Deacon , Ard Biesheuvel , Marc Zyngier , James Morse , Andrey Ryabinin , Andrew Morton , Matthew Wilcox , Mark Rutland , David Hildenbrand , Kefeng Wang , John Hubbard , Zi Yan , Barry Song <21cnbao@gmail.com>, Alistair Popple , Yang Shi , Thomas Gleixner , Ingo Molnar , Borislav Petkov , Dave Hansen , "H. Peter Anvin" , linux-arm-kernel@lists.infradead.org, x86@kernel.org, linuxppc-dev@lists.ozlabs.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH v6 16/18] arm64/mm: Implement pte_batch_hint() Message-ID: References: <20240215103205.2607016-1-ryan.roberts@arm.com> <20240215103205.2607016-17-ryan.roberts@arm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20240215103205.2607016-17-ryan.roberts@arm.com> X-Rspamd-Queue-Id: 83969140003 X-Rspam-User: X-Rspamd-Server: rspam11 X-Stat-Signature: i1qbftf56md96kk3ged619mrkayftx9f X-HE-Tag: 1708086850-6663 X-HE-Meta: U2FsdGVkX1+Uu8hjCvATfa2cp4+YN/1dSalWEp0Hxvf9+9R7Vjw4EJuevJWzl2zPA98oEwL2vzk85hh4AehWGCBCmek3v4t+Vz3+HeCmHGaiQESgjwruGxODAPezpMAF30jJ3mUo9XP/yupsN8T0rNE0oEug+hYCw71KyniYJdhkzq5P0IsVXJ6Rpy8g21qWZjlBKQen5bNFYjCxKKQQFN3U9JKsERzTrvi8FPFKiXcyyMNfecbnGRB9NR5KZNey4emHg8JzduzEErzpOMrbFSE3KDVuBoktRA+hcbYT0Hzy/HNWgPDJ5UJgTU7K69dQ26pRewOtq7wkpe6acD4KQ8xQz/A+46G5RXeaRsmeZQ4+D9eRWVHsM6qzK/WNUBF0JMXEmMU/JaT6YOImHlg6oBmHacxE5ah5feEj9brof8T6BySlH44ucZ8lcyrU72rcwnhTQbDoj1aKzB0iXxw+XG8o3FaMleTIe5GIjjBLVGYLd2X7hFZ3+WBQ81h3qfJ/gA9kUFStSG0qXsaWDyKowNBRcjiMeht5UiWx4Fec466Hr5YhjM3ryHesAy+b70MwIdHWK9t2ulqyw1g3mHwjesOiSWjqpiJ4vxxKyy6v4p6pt8Bm+8X+lMJ8MJV9sLIueRRDLKUuh6UUabB6vyTiqSMDdb18UNOGV3+UpxSLelhz2HpKGWrst3xp+Va1W+UHZ7fhUNU5dwxD7MGDK7aMWBalQ39gj8Ric98rRe74qx6YOIT2VZ1rjITEJIyLTcYYZhYRYLjfESblHMhkqulKKkgqrR6j3YhY9hec2+7gTfhJknZ+RZ3dXLWTkcMQ3f0ueaU+96AD8B8N9o26cQ1oh1ZzR1qE9DyKSgS2eFs/EDpec61gp8RBs8sYAwITySi6kbcXWwK7Y16mv7u0BHonNiKjq4a0KWdTyjV9GCWgLVKfOumq456zqbA5KzUn64pLxmY6+TtCqhTNcbFjwog +0Lfkjvg QYNleekxU9po0yIw5l0fXfQMeeUQ3T96JUYPgLnc3qWUUlBUliX1Low5WqkQLGt4PRJuAjaO0UkRT9IcVu0r/r9ATqFXcQejPS0FQXtuqXh8ypNvoRj+hOO5W9A== X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Thu, Feb 15, 2024 at 10:32:03AM +0000, Ryan Roberts wrote: > When core code iterates over a range of ptes and calls ptep_get() for > each of them, if the range happens to cover contpte mappings, the number > of pte reads becomes amplified by a factor of the number of PTEs in a > contpte block. This is because for each call to ptep_get(), the > implementation must read all of the ptes in the contpte block to which > it belongs to gather the access and dirty bits. > > This causes a hotspot for fork(), as well as operations that unmap > memory such as munmap(), exit and madvise(MADV_DONTNEED). Fortunately we > can fix this by implementing pte_batch_hint() which allows their > iterators to skip getting the contpte tail ptes when gathering the batch > of ptes to operate on. This results in the number of PTE reads returning > to 1 per pte. > > Acked-by: Mark Rutland > Reviewed-by: David Hildenbrand > Tested-by: John Hubbard > Signed-off-by: Ryan Roberts Acked-by: Catalin Marinas