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Howlett" , Nico Pache , Dev Jain , Barry Song , Lance Yang , Jonathan Corbet , Shuah Khan , Usama Arif , Andi Kleen Subject: Re: [PATCH v1] docs: filesystems: clarify KernelPageSize vs. MMUPageSize in smaps Date: Wed, 04 Mar 2026 11:04:35 -0500 X-Mailer: MailMate (2.0r6290) Message-ID: <6DDF4B32-4AC3-42E6-8791-B063FCC9C9C4@nvidia.com> In-Reply-To: <20260304155636.77433-1-david@kernel.org> References: <20260304155636.77433-1-david@kernel.org> Content-Type: text/plain X-ClientProxiedBy: BYAPR08CA0010.namprd08.prod.outlook.com (2603:10b6:a03:100::23) To DS7PR12MB9473.namprd12.prod.outlook.com (2603:10b6:8:252::5) 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: DS7PR12MB9473:EE_|DS5PPF482CFEB7D:EE_ X-MS-Office365-Filtering-Correlation-Id: a55ee953-046e-4fa7-48c9-08de7a07bdd4 X-MS-Exchange-SenderADCheck: 1 X-MS-Exchange-AntiSpam-Relay: 0 X-Microsoft-Antispam: BCL:0;ARA:13230040|7416014|376014|366016|1800799024|7053199007; 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X-MS-Exchange-AntiSpam-MessageData-ChunkCount: 1 X-MS-Exchange-AntiSpam-MessageData-0: =?us-ascii?Q?1zDxu+T4Na1jusY77ugohL/CN71LlyEKm37K3ieBV6Ir+yiwtQbzleH98Wed?= =?us-ascii?Q?ZhnGU2gHn+usA+sFYQ+MbyH4QTI+yeKl4up1AqHSlpA2/qhlgZWyIhk6ws8/?= =?us-ascii?Q?isHj7faNVJUabADa+ywnb9nv5XiBV6yrH7CRmRMiLB2Y9MBGW2N5wKZI5Ckr?= =?us-ascii?Q?KfCu6BFxFcoIWQwLWxVAHg0d675SQPn3uDE3ye5KIP9yvpY/5XP8gIh8iSWv?= =?us-ascii?Q?lQIGic/Wn3/VQwf69KHJDs9wQweaiiTMQRZcV6ZBsmWx9SnX9QuYQplOWoL1?= =?us-ascii?Q?Iv9B1z8MGI36rxQDFBmTi43IS/yNi7WWd0RV8bVujdG0mt1b1rjZFyYFTG00?= =?us-ascii?Q?FKlE8QSS0Kb9QIEa+MrhKa+cw7bmTpXayebgKWMnuiVgRCRkH94jGBqBY+rr?= =?us-ascii?Q?IXOVhXC1+galX7sKi8e7yIsT6zuBvq5IbTBwjNTMx06zRVQaNqgDYq7Tyta7?= =?us-ascii?Q?cP/ekJrXACvwbKY/xI1vpGJEAaEvMm0ofEyvAn2aWgkq04cVb22jvs57M8Vf?= =?us-ascii?Q?86fRznIx5G4zQuxThln1g0Ov/FnMsxJLZPu6rpm91SLeWuS0JRGXxP9FH0bu?= =?us-ascii?Q?JD1Ls8GtBHmP7m33WOx2mnpVZ11aqnM9Gm2ByqWfDLcrEOjw0Ux7xnk4vhNy?= =?us-ascii?Q?PcAnmBwws6X7+Vpr+WswDnFNDGlnlBj8z6aUUCHr/PaWSB65z/h3ERy7/oPO?= =?us-ascii?Q?GS3wpZYRPpHSTd6ORgY/TKJVcvn3ElECGYLvsOEQ/ChE6re+58SuBcThGP2a?= =?us-ascii?Q?D478FyuaE/w+2pAo74VUXAjZAAUHPCWFp827ElfnEicbKJiaaHIMKe2GadkP?= =?us-ascii?Q?d8cdtHGa0MCVql8+63GB/A3qlbdJZHn3gYp3FEUdqPQEjtCEinEllKuH5d1t?= =?us-ascii?Q?6zWuGaDA28EnNFpKyirBs7nWwn9aiB5O6voD0IbWVWtqu/5+E4qVrdhtaisf?= =?us-ascii?Q?Hr1/FG5vSIL9YfzsKUYC5clJoS5lGaZuVrDKCyPddgXwyH38jiDLcPGYovbq?= =?us-ascii?Q?M7T3hsg5GmnDfNLVA3j4Duj4iMIGLiFKfB83XkLzdwVEKi+wSb+r8gnvtLIu?= =?us-ascii?Q?PMXGeLl8c0v6WWtNBUNaOdEwesxooeoGazEPHKwjmOGMLEKcoAkfS9JEND85?= =?us-ascii?Q?UjS7eMeN+BCSMudXUybTmHBsuUW5N1ZAGVOz8PrChspJabeTCyncjSK5vt8g?= =?us-ascii?Q?a4tNkM5lzy6BmIeqSu9B2zd/Xx6Z5zOQfWKmYPEHZmqxowlNPrjshceurMoD?= =?us-ascii?Q?yPgCcbnH1wKX+RceAl+VDcypiHCwuwvwakLTnqg11Agv8H+Q5KnBjOiYa+3/?= =?us-ascii?Q?YXYiyw7Qf5PwRrpqWjTwOgrh/02SZPPdWPyRuZ+xroiJHvVvFwyzqUq50OOm?= =?us-ascii?Q?rLboFSLsIgWskLuyrvgJ6VXV4nFoS5klfDEjyrro6Ufl6SS5pHAfYfk87cg2?= =?us-ascii?Q?0ZNnws1IP7U0k+g+LFs4skgqx4x8FD1ZxZ7nkaY3XaFbzWon5H9AeT0u25wy?= =?us-ascii?Q?m0wYAOu2cNEk4bL17LpZSutihkF5YgcJa/42Gm+10eoosIkvofrlGViy1zZP?= =?us-ascii?Q?gqpB4hamX5obz66EzRaVwexQFIC0sK/+XBWEqn1+o1S/KVsIYa4LtJFuB/cB?= =?us-ascii?Q?UYdxErG7K/SMc9T3TYMvjTCnA+0Oi+UXL/f2dZojA3heAXQhEjExod18HZ1S?= =?us-ascii?Q?1VjChZzvcnfae4MNsVGqrb+8tQSe1tKwFWy/J8jzFQz/ns519vubWad25U7J?= =?us-ascii?Q?sg5yob1NHw=3D=3D?= X-OriginatorOrg: Nvidia.com X-MS-Exchange-CrossTenant-Network-Message-Id: a55ee953-046e-4fa7-48c9-08de7a07bdd4 X-MS-Exchange-CrossTenant-AuthSource: DS7PR12MB9473.namprd12.prod.outlook.com X-MS-Exchange-CrossTenant-AuthAs: Internal X-MS-Exchange-CrossTenant-OriginalArrivalTime: 04 Mar 2026 16:04:40.2530 (UTC) X-MS-Exchange-CrossTenant-FromEntityHeader: Hosted X-MS-Exchange-CrossTenant-Id: 43083d15-7273-40c1-b7db-39efd9ccc17a X-MS-Exchange-CrossTenant-MailboxType: HOSTED X-MS-Exchange-CrossTenant-UserPrincipalName: hQNaLOu0gy7ehH7WSzyuP/u6uP62gRRGWI3YjIuSzXEycy2u0hF1f88LpQIxL8E9 X-MS-Exchange-Transport-CrossTenantHeadersStamped: DS5PPF482CFEB7D On 4 Mar 2026, at 10:56, David Hildenbrand (Arm) wrote: > There was recently some confusion around THPs and the interaction with > KernelPageSize / MMUPageSize. Historically, these entries always > correspond to the smallest size we could encounter, not any current > usage of transparent huge pages or larger sizes used by the MMU. > > Ever since we added THP support many, many years ago, these entries > would keep reporting the smallest (fallback) granularity in a VMA. > > For this reason, they default to PAGE_SIZE for all VMAs except for > VMAs where we have the guarantee that the system and the MMU will > always use larger page sizes. hugetlb, for example, exposes a custom > vm_ops->pagesize callback to handle that. Similarly, dax/device > exposes a custom vm_ops->pagesize callback and provides similar > guarantees. > > Let's clarify the historical meaning of KernelPageSize / MMUPageSize, > and point at "AnonHugePages", "ShmemPmdMapped" and "FilePmdMapped" > regarding PMD entries. > > While at it, document "FilePmdMapped", clarify what the "AnonHugePages" > and "ShmemPmdMapped" entries really mean, and make it clear that there > are no other entries for other THP/folio sizes or mappings. > > Link: https://lore.kernel.org/all/20260225232708.87833-1-ak@linux.intel.com/ > Cc: Andrew Morton > Cc: Lorenzo Stoakes > Cc: Zi Yan > Cc: Baolin Wang > Cc: Liam R. Howlett > Cc: Nico Pache > Cc: Ryan Roberts Cc: Dev Jain > Cc: Barry Song > Cc: Lance Yang > Cc: Jonathan Corbet > Cc: Shuah Khan > Cc: Usama Arif > Cc: Andi Kleen > Signed-off-by: David Hildenbrand (Arm) > --- > Documentation/filesystems/proc.rst | 37 ++++++++++++++++++++++-------- > 1 file changed, 27 insertions(+), 10 deletions(-) > LGTM. Reviewed-by: Zi Yan Best Regards, Yan, Zi