From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from NAM12-MW2-obe.outbound.protection.outlook.com (mail-mw2nam12on2105.outbound.protection.outlook.com [40.107.244.105]) (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 0EEE71D514B for ; Fri, 29 Aug 2025 22:11:20 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=fail smtp.client-ip=40.107.244.105 ARC-Seal:i=2; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1756505482; cv=fail; b=aqxlqQjJmKxzOL9Jpsq/umWkVgGQUMhTWTF3xFY9yXXazIJEpPbGyhAM4WdD/LsTf1nNJ8Knc1uML2T6tZvG5xsinvkZtWh0MP+dMOr0owo/vWVTwEYCPxD0KHEFzRHTArS28bTQDNeu9Lzywf69Ln6Wn5NQMkEuMX7pf/HKqoU= ARC-Message-Signature:i=2; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1756505482; c=relaxed/simple; bh=O6+61oyv8KufkwrxZ09L0rL3S5iPT7GxBHhXcYSn8W8=; h=Message-ID:Date:Subject:To:Cc:References:From:In-Reply-To: Content-Type:MIME-Version; b=O6Gm8talbYxbeg6suLi5tUZ22Rszywuowd8ITShc46W7rH6y5fP74G2UsFh9OCTCDEFjDJoE0BOAZgPo2ttnOXYk4wpMm1i/i+BDn7Sc+2XQFbatIbZZGz3k1yZbXpV8I+ASrG7bH4E45wyB+aVxF4gtgrOSf3Bh5j3LFWUvwBs= ARC-Authentication-Results:i=2; smtp.subspace.kernel.org; dmarc=pass (p=quarantine dis=none) header.from=os.amperecomputing.com; spf=pass smtp.mailfrom=os.amperecomputing.com; dkim=pass (1024-bit key) header.d=os.amperecomputing.com header.i=@os.amperecomputing.com header.b=Sqd2/1zc; arc=fail smtp.client-ip=40.107.244.105 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=quarantine dis=none) header.from=os.amperecomputing.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=os.amperecomputing.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=os.amperecomputing.com header.i=@os.amperecomputing.com header.b="Sqd2/1zc" ARC-Seal: i=1; a=rsa-sha256; s=arcselector10001; d=microsoft.com; cv=none; b=XQz8elbsxsnLR7x11ouHLxNPRQ+YwN+wNDSiu+0Dn9MOV3J8oO3Dn3SiN3FNYFQKpzGu7+kRqi26bHwqETbGyZxmA7YWpdCw1KMER8GmBSS4MbIK3OwPhukLAuzmDReaJFtpcQIc0gtwDO9LYq8JIXVq2WPATza026y6DXYtBBdqktSsFImd6EBYDZHvkW41Yp3yrl3aB8JH/uGlXwu1wZ1QZrz8Dmncb5emGCTa1CFgCQG9RpLtmtejnESeckNRlhZmseUtKd6M+q09bsqBUhxFI8FrKN0f+W2+aVjKOxCt19K+rcjtVmZOQVlQ99yU6pOGZxVRrG/rXI2L35nc5w== ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=microsoft.com; s=arcselector10001; h=From:Date:Subject:Message-ID:Content-Type:MIME-Version:X-MS-Exchange-AntiSpam-MessageData-ChunkCount:X-MS-Exchange-AntiSpam-MessageData-0:X-MS-Exchange-AntiSpam-MessageData-1; bh=MMB59pMOOUKrtw+f6n8uSoIV7MrtbzoGdzscsB72pec=; b=cNKE2zo8resMsGwUCY8voWBjFFVXFxc7gpBOIgcs4sxSgF4yGpBbInb+HWYc/yl5pLZDAhAzfNwTQQAX02uror9NJvBEb7cQPfcvVmlHxzg8bOR+V81fgyv+1CABJ+V/v4+HuWb1jXyiyFVhANMmg8zeM491vOkz8LvzuZMLznn9cEAHd7XGzVE3nETUlEQnosggK/so56QmVAtRnm2YFHwgitvl0lN4wXrZj9DJRK9iCGyyzm6eN/oiJLkCtSykF91v4ioJL0KjO1egQcXNlPP9T07iBuHUet90rS/hS8nmDRXaXpyd7xxuV4xG3AjYgUNHGVjs3mYd+ZdNbXApFw== ARC-Authentication-Results: i=1; mx.microsoft.com 1; spf=pass smtp.mailfrom=os.amperecomputing.com; dmarc=pass action=none header.from=os.amperecomputing.com; dkim=pass header.d=os.amperecomputing.com; arc=none DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=os.amperecomputing.com; s=selector2; h=From:Date:Subject:Message-ID:Content-Type:MIME-Version:X-MS-Exchange-SenderADCheck; bh=MMB59pMOOUKrtw+f6n8uSoIV7MrtbzoGdzscsB72pec=; b=Sqd2/1zcICHVretgcQiNyj/UlS8MIlDlX3axv4PN2sw8JC/9vYFpr9fZYdqDQeFalD7aHeZ3e3nIpZHOj0iUl3WgkCg2HV4eEe6nXNLakfBaRb7F+xAOSlIjuQTOzAxOXN024qwN6bLu0IHpkSLh0jKGrCJ0fTJ4ejEkBikfQYg= Authentication-Results: dkim=none (message not signed) header.d=none;dmarc=none action=none header.from=os.amperecomputing.com; Received: from BN0PR01MB6877.prod.exchangelabs.com (2603:10b6:408:161::22) by LV2PR01MB7693.prod.exchangelabs.com (2603:10b6:408:176::9) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id 15.20.9073.21; Fri, 29 Aug 2025 22:11:15 +0000 Received: from BN0PR01MB6877.prod.exchangelabs.com ([fe80::91fc:9877:8a2a:d4e0]) by BN0PR01MB6877.prod.exchangelabs.com ([fe80::91fc:9877:8a2a:d4e0%7]) with mapi id 15.20.9052.023; Fri, 29 Aug 2025 22:11:15 +0000 Message-ID: Date: Fri, 29 Aug 2025 15:11:11 -0700 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v7 4/6] arm64: mm: Optimize split_kernel_leaf_mapping() To: Ryan Roberts , Catalin Marinas , Will Deacon , Andrew Morton , David Hildenbrand , Lorenzo Stoakes , Ard Biesheuvel , Dev Jain , scott@os.amperecomputing.com, cl@gentwo.org Cc: linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org References: <20250829115250.2395585-1-ryan.roberts@arm.com> <20250829115250.2395585-5-ryan.roberts@arm.com> Content-Language: en-US From: Yang Shi In-Reply-To: <20250829115250.2395585-5-ryan.roberts@arm.com> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-ClientProxiedBy: BYAPR11CA0072.namprd11.prod.outlook.com (2603:10b6:a03:80::49) To BN0PR01MB6877.prod.exchangelabs.com (2603:10b6:408:161::22) Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 X-MS-PublicTrafficType: Email X-MS-TrafficTypeDiagnostic: BN0PR01MB6877:EE_|LV2PR01MB7693:EE_ X-MS-Office365-Filtering-Correlation-Id: 50e7d43f-bee0-4564-67af-08dde748f824 X-MS-Exchange-AtpMessageProperties: SA X-MS-Exchange-SenderADCheck: 1 X-MS-Exchange-AntiSpam-Relay: 0 X-Microsoft-Antispam: BCL:0;ARA:13230040|1800799024|7416014|376014|366016|921020|7053199007; X-Microsoft-Antispam-Message-Info: =?utf-8?B?S2s2Mmt6Wk1GODN2ZHRaT2ZRVmZYNFhSdnhTK1dTR29yYlpoY1k0QUhCTFJM?= =?utf-8?B?RTVKamFneWoxQ1ZUcXAybGpMTFBBWjBQSi9DcEcwSUp4RjNUZ1BCUnlndkJY?= =?utf-8?B?SzZrNG1Gd0JVSGdOZ1BFWVQrZVp4Z1QxakpWSkY5RURwMTc4SXp3K0dtMWZW?= =?utf-8?B?Ym0va1llc2Z0WmlLcHFqVWZCaFk1S01zSGlZcDJKZVR3bzJyQ2YrV2crc0wx?= =?utf-8?B?cGFsQUtGQmRpaTFhYXhyRzNtRm9lTU9HWWMzaDJWdWEyQnh4YzBPUkM1Umtk?= =?utf-8?B?RXlUa3Z5aSt3cVJhTGZ0ZzBsWHA5ZGwvbDVwMGlyMkovQWtVRkZZeGVBbFN4?= =?utf-8?B?TDh2am5iTlN4bzgxaFA2bGFzbXlkTU54dnBQUEJhOEEyZ040WG15ZHpka0Jl?= =?utf-8?B?ZVppc1FZYlpWTkFUN0FHbC8xeUsrY2RnRnQreDJPWDNjeUl6NnA0eW0xeU5y?= =?utf-8?B?THVPUE0zVGYzbzRIRlVFakM4d1BVNEc1bnRwQll3dFlPSjRrL1BWMWhpNGJD?= =?utf-8?B?a3NEK3djWDEydE1BLzN2QWNpVnhNSGQxQ0F5NHI5SDQwak1ZOHJVUlZJbnVK?= =?utf-8?B?U3dudVl5NlU4TktPYnJQb3hvQ0o2c1NkSWxuY245VGFaODl2RFpYVVJ6a0th?= =?utf-8?B?OWJ4SFhqK0gwVVRoQk9kR3UvdVFGOGZLRUNXMnBOZU1oNm4rMXhlSGQyZ0RH?= =?utf-8?B?d1VyYThyQzJZRWhmN3JtemFWLzluSmducExNRHBZaHBBMkdJenR5NlpXK0lN?= =?utf-8?B?cVFIT20zQk5HSFBldGtXalROdlcvMmcrRUxUZnlPd09DaVg3WEhSYk04aHJp?= =?utf-8?B?Ui9PbmVOZ1ovMHNlRjQyRTNPdmFsVEhUUXR3MHVUNnoyTi91ZW9DOEFENmla?= =?utf-8?B?ZEtidkVwdEhmT2tiejNGZXZpZm01V2ZkZ0E2d3FjZk5ycE8vTEswTVJzMlNG?= =?utf-8?B?Y2ZyTFlySHJDUVUwQmNRWDFOY2RPbFdnSFg2YnVVTFhmRWRiSFk4NEMrS2xx?= =?utf-8?B?S3JEdTk2bTVNODdaalpSdnNkMzA0VjdLdDRPRllVR1Jsa2N6alRpVjBrRVFk?= =?utf-8?B?emJrMS9LV2ZxRHA4MnduR29wRlA0Y3QxYXZocEQzMVE5S2s3anFVcHp0TGZV?= =?utf-8?B?RlYwc1FTRGM2dlU2Tzd3VXlCZTlYZ2ZvU1kzSjl2UWExSi9iZlluNTJLLzRp?= =?utf-8?B?ZWVDckVNcktoSkY0YVIrOEJRQk16eUVwSzhCUEhWeENjSUJzRzh3WUM4ZDRQ?= =?utf-8?B?eW5JZTBiRTdEMUNGblBxWU1yUGlIUUFub3pJd0pnSkc3UHNpOXZ6VUY3L3Iv?= =?utf-8?B?UkRZSG42UWJoNW9OUWVqK3hQRWJtc3MvVkRjZU41MXBFMzlaZEN0UEVnNWFT?= =?utf-8?B?L2tDL1JrY2dhd0QyeU5wc2tkbTRVUURxWWRKRFNkaW80bitvZXJ1L2hCRHhQ?= =?utf-8?B?S0NBZmFrVmVzamhkc2FJbU15ZERqUCtRWWNwa0xTY0ttSGZwUUJvUnloaklN?= =?utf-8?B?QVdjNjc4Skl0dVlkRnZlWEEzcTdNSE8xcFl4WUV6VkNxekszWnh6SXpuMmJz?= =?utf-8?B?UDE3Q1M5Um43bjRFaHZvYnY1M3dsOG8wYlFUR2RQS2hTL2s1Tk5IdlRSa3Rj?= =?utf-8?B?MGRuTDVkOWZBVGVzNTVScVREemZvekdHbmNFcGh4dmRQNFBwN0dJZHZqaHRK?= =?utf-8?B?Ry9YRm5OQU5PelVsSExhY2JlRTQ5bzZnVllxUXlYRWYyaDNHUXhFY25ZRS9I?= =?utf-8?B?Tld0NUY5V05zcEdIRUg2d0ZaaVpPamZheEhxYjYwdDdDOVoyM1lLeUY5dVFy?= =?utf-8?B?eE05MjYvTzlVTzJIejBXa3NsVklmVXpnV3BSb2J0U1kvOHEyZTljZG50SWVn?= =?utf-8?B?NHFIUEFjZVlvRUV4T0xudlNEbXdRYit1TS93NGwya1ltNkcyc05qcWRXTkp6?= =?utf-8?B?WjRjMlRzWkZxbDc0UjM5YW00VVVvUko0YWYvZ1JnVW9TdzMwVk12cnNadnBw?= =?utf-8?B?TzdTMWdFekFRPT0=?= X-Forefront-Antispam-Report: CIP:255.255.255.255;CTRY:;LANG:en;SCL:1;SRV:;IPV:NLI;SFV:NSPM;H:BN0PR01MB6877.prod.exchangelabs.com;PTR:;CAT:NONE;SFS:(13230040)(1800799024)(7416014)(376014)(366016)(921020)(7053199007);DIR:OUT;SFP:1102; X-MS-Exchange-AntiSpam-MessageData-ChunkCount: 1 X-MS-Exchange-AntiSpam-MessageData-0: =?utf-8?B?dFFSMC9kK2FBZFVCeDRVNXlYSzY2cDBRZDRkY2FNLyt4Q2R2c2hjUVpzU1FX?= =?utf-8?B?NjZncXBSaFdvbzhJNEdlSTllL1N2T1FRT3RlSDdwMmloOElqWHBYeGJRRXA0?= =?utf-8?B?aHRSOERmZENEVjduNE1tZ0JUaFVnYzg3SHlsb3JXZklSWHJkMTZYNFlWR2U2?= =?utf-8?B?TkFlbDQ0Y2g5V1RFVGFkVXd5aHRCVmxQUTVwYmdkSjB4VjVKTkNVaXk0bnpo?= =?utf-8?B?bTcrcEhtbmJ5ZTVKQ2hjSXVOZnB2dy9VdFlWVEFVSDVnVG1ObHlWQUNKRnBq?= =?utf-8?B?UWpWdXRoSlloNytlQ0MwbHFxRjMyLzRnU3NublZXTFRXdFlWZmJIK25JU3Za?= =?utf-8?B?Y3BTTFE2SUEwUFRzZjFVelFGMWNtZ0paMURaUzZMLzBYQ04vM0NSdlM0NUpX?= =?utf-8?B?NERwVU1pOFBhVXlFdWhJUHVMdjhYdTNjRE5uYkhWWVdOcVZIOHJYeFdrZWJv?= =?utf-8?B?T2UxSkdvRUY3UEgwaVZ6eUFXaXVsNEFUMmlTang3eU9jRnhQWlBrYVUrcGhY?= =?utf-8?B?R1JiREVYVGRHK0FNQXJDTTVmVFRIaXRUbWZXbm5GQUlmTlZJc0tUTStFdUds?= =?utf-8?B?b3JDTnJ3RjdwNHprWmY0K0pPZE5nN0dGWlQwN3NJOW1qMFRvck5kOVp3MGp1?= =?utf-8?B?S2ZwUjdscis0Rlp4SSsvVjJHWlJFSWVrcXFNQ3k5NXpFY2NZTXNsYmJ3bGpi?= =?utf-8?B?NEI5QmczM1dhSEE5Tmw5Rk1vZWdzekZEYzIrSE9BbE0vcVpvNnBRUnkxSjFV?= =?utf-8?B?ZFZlUy91YWdsNTVCbzlRME1TVjg5NUxpcHVqMlE0WFVXNUwwaGhreWpzekNa?= =?utf-8?B?bDFjTHFQdmdnNThsYWVWU21BOWhBTDdxTXZYU2NxYzlwZEhuREdPck4wYUtW?= =?utf-8?B?aG85RVVVZ3JGVSs0cmlrbFF6T09EVjBGSVlJTmE5Y3RybTAyWUZydTRWbVZP?= =?utf-8?B?R2FqUlBkTTFxRnNETUtsVWx1MlRlTDZBVUF4aVRWcUJPU2x3QW1CQjJLdTdR?= =?utf-8?B?blJjSExkdUp4eU1vZXEyVjlvSVowVC9wamZsUDlHTTRaS3I1Wk1EMkNGL0VR?= =?utf-8?B?RDhlS1ZYdC9XdENxZUtuRXc5NVArT2EvYWNPd2hva2g2MytGYVZmMFZ3QlZH?= =?utf-8?B?RzhSTXcyYmg1b0l0M1VoVnJZUEs5R3pKYlN6ck5EcnkzOTNFUFNsT08yRFpr?= =?utf-8?B?Zm1Uc0xlRXExYzVrZHhSYWhKeEErRVZSaWcvQzN5R3I5SDYwa25jSWZBeTcr?= =?utf-8?B?blZ6Zm9PekpxT2dMalBJVUQ1R0ZhQ3RabGd6c21GOWZKWllXVmVtaURkOTFW?= =?utf-8?B?d0FqMUdtNm1sQm9aenhSTWE0VlgvM2VUNU1Na0pibnQyMk9kMjZnZ3duTExF?= =?utf-8?B?M2FNMk9MYVgyb05PVVJHT3JMRjFnTUNqTnBUd0UrTnNuOUdOUnlkLzB0ZTdS?= =?utf-8?B?OEVIRVViNGVxdUpjWk1jWXpKRlBqVnpMeXNSMWZUa29ySlJvS3ZqeXhXb1ph?= =?utf-8?B?dHdWQ0hzZko4NDhCd2srWDR2U2FKUURxYUlxWk5jd211blVzdXdncmdwekdx?= =?utf-8?B?N0xBQTJmMmpZV2tmTUFJVWI3NjZDZE4vdmRxUzduTzF5YW5RMWRBeEpnOUpQ?= =?utf-8?B?Z3VLT1ZheWtNUU5UOEEwUmYvcURWNFhvZ3JUWWZmWHR5a1prbUszVkhic3o0?= =?utf-8?B?L0JocW5RVENqaTVycHF4aHFpNGU0bVRPaUlJUE9GVVhEMHpkUXFyQmhFdHJj?= =?utf-8?B?MVpFNkltM09kK3JsNWV0d09XTHdQSERmaEl4NEYwaHYyUDFsbE42SmNPblhL?= =?utf-8?B?djg4cGVzWVJnVnk4cnAybzFpbkZid3RsMjVuQjN0OTVjWXA0dDBXTXpWVWtY?= =?utf-8?B?YmZNb1ZTQis5QXg0NWI0b2Y1bVJSQzlrTlFIOUNSbUozL0FYQ3oxd28wQ3pB?= =?utf-8?B?QS9RMERxYno0MWMwK2pTa2k1N0x0ejNpcTJoNHY5K3gvVzEyaElVQ1VQTW5Z?= =?utf-8?B?QUxweC9yQXhWNFk3YkdITFNScG9LTWR1Q1BoakVwdnFhYThXcXZjd2dCNkxp?= =?utf-8?B?SFhEZ0xTL0ZVVTk3VUtPU1oxdGduMGhFd3A4c2plNXB1c2dCV3B5b0IwZ1I2?= =?utf-8?B?VlRZUFNQcDRPRnpQWDRRR2wxelpYa3NvbGpUZWg4NkZPOWhORHZoSmxxUHJn?= =?utf-8?B?elE9PQ==?= X-OriginatorOrg: os.amperecomputing.com X-MS-Exchange-CrossTenant-Network-Message-Id: 50e7d43f-bee0-4564-67af-08dde748f824 X-MS-Exchange-CrossTenant-AuthSource: BN0PR01MB6877.prod.exchangelabs.com X-MS-Exchange-CrossTenant-AuthAs: Internal X-MS-Exchange-CrossTenant-OriginalArrivalTime: 29 Aug 2025 22:11:15.2819 (UTC) X-MS-Exchange-CrossTenant-FromEntityHeader: Hosted X-MS-Exchange-CrossTenant-Id: 3bc2b170-fd94-476d-b0ce-4229bdc904a7 X-MS-Exchange-CrossTenant-MailboxType: HOSTED X-MS-Exchange-CrossTenant-UserPrincipalName: mHhacqlxvJoiB5BJiCXAndbcUZDZY40bd6wuO79nB9sB6dkfzTskXR9eikNGUzwiax3yVL2g5vYy9WPMVDrHVspKUV4/g0JOUoGZl+kbEA0= X-MS-Exchange-Transport-CrossTenantHeadersStamped: LV2PR01MB7693 On 8/29/25 4:52 AM, Ryan Roberts wrote: > The common case for split_kernel_leaf_mapping() is for a single page. > Let's optimize this by only calling split_kernel_leaf_mapping_locked() > once. > > Since the start and end address are PAGE_SIZE apart, they must be > contained within the same contpte block. Further, if start is at the > beginning of the block or end is at the end of the block, then the other > address must be in the _middle_ of the block. So if we split on this > middle-of-the-contpte-block address, it is guaranteed that the > containing contpte block is split to ptes and both start and end are > therefore mapped by pte. > > This avoids the second call to split_kernel_leaf_mapping_locked() > meaning we only have to walk the pgtable once. > > Signed-off-by: Ryan Roberts > --- > arch/arm64/mm/mmu.c | 18 +++++++++++++++--- > 1 file changed, 15 insertions(+), 3 deletions(-) > > diff --git a/arch/arm64/mm/mmu.c b/arch/arm64/mm/mmu.c > index 114b88216b0c..8b5b19e1154b 100644 > --- a/arch/arm64/mm/mmu.c > +++ b/arch/arm64/mm/mmu.c > @@ -740,9 +740,21 @@ int split_kernel_leaf_mapping(unsigned long start, unsigned long end) > mutex_lock(&pgtable_split_lock); > arch_enter_lazy_mmu_mode(); > > - ret = split_kernel_leaf_mapping_locked(start); > - if (!ret) > - ret = split_kernel_leaf_mapping_locked(end); > + /* > + * Optimize for the common case of splitting out a single page from a > + * larger mapping. Here we can just split on the "least aligned" of > + * start and end and this will guarantee that there must also be a split > + * on the more aligned address since the both addresses must be in the > + * same contpte block and it must have been split to ptes. > + */ > + if (end - start == PAGE_SIZE) { > + start = __ffs(start) < __ffs(end) ? start : end; > + ret = split_kernel_leaf_mapping_locked(start); This makes sense to me. I suggested the same thing in the discussion with Dev for v5. I'd like to have this patch squashed into patch #3. Thanks, Yang > + } else { > + ret = split_kernel_leaf_mapping_locked(start); > + if (!ret) > + ret = split_kernel_leaf_mapping_locked(end); > + } > > arch_leave_lazy_mmu_mode(); > mutex_unlock(&pgtable_split_lock);