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Howlett" , Mike Rapoport , Suren Baghdasaryan , Vlastimil Babka , David Hildenbrand , Jonathan Corbet , Michal Hocko , Shuah Khan , Randy Dunlap , Baolin Wang , Nico Pache , Ryan Roberts , Dev Jain , Barry Song , Usama Arif , Kiryl Shutsemau , Nirmoy Das , Dragos Tatulea , linux-mm@kvack.org, linux-doc@vger.kernel.org, linux-kernel@vger.kernel.org, Lorenzo Stoakes , Andrew Morton Subject: Re: [PATCH v2] mm/khugepaged: cap min_free_kbytes recommendation at 1 GiB Date: Mon, 31 Aug 2026 11:01:16 -0400 X-Mailer: MailMate (3.0r7024) Message-ID: <28FC994B-F63D-493A-B86E-F87E37B303B1@nvidia.com> In-Reply-To: <8411e51c-92fe-41b0-9de0-e9cfc5a50301@linux.dev> References: <20260831075635.2244437-1-noren@nvidia.com> <8411e51c-92fe-41b0-9de0-e9cfc5a50301@linux.dev> Content-Type: text/plain X-MS-Reactions: disallow X-ClientProxiedBy: BN9PR03CA0254.namprd03.prod.outlook.com (2603:10b6:408:ff::19) To IA0PR12MB8374.namprd12.prod.outlook.com (2603:10b6:208:40e::7) 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: IA0PR12MB8374:EE_|DS8PR12MB333896:EE_ X-MS-Office365-Filtering-Correlation-Id: 400cbac5-27b5-4248-e42b-08df0770b61e X-MS-Exchange-SenderADCheck: 1 X-MS-Exchange-AntiSpam-Relay: 0 X-Microsoft-Antispam: BCL:0;ARA:13230040|1800799024|23010399003|366016|376014|7416014|4143699003|10067099003|11063799006|56012099006|6133799003|18002099003|22082099003; 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X-MS-Exchange-AntiSpam-MessageData-ChunkCount: 1 X-MS-Exchange-AntiSpam-MessageData-0: =?us-ascii?Q?kXA3+4wByRiGFgm+IE/eRRe5mr14BVlRIIQEP/ASQdb4gHSO+c4u8Maf483b?= =?us-ascii?Q?WTvXYiuSTp3FQ3MIXFQAW0WuhPeDxufqcRam5Edij2XWiShpaHTW3soRP5+m?= =?us-ascii?Q?HcIqNFGd9uc7GbCyPCp9zztflUK+eGu+Cv+r+Yr1NqQvvuBjazijM/zzR0wL?= =?us-ascii?Q?e2BFaNNFqVbkFA+KY0P0vHxjxpwpIW7aSDaM9lkq/Tc3MzZabC72fsfVIMg1?= =?us-ascii?Q?/VqpE9MNOiMucPmUfsSt65m7X82WhppyCUxmzUhA6VYpzEeinuQFdJ5KbpY0?= =?us-ascii?Q?WZw0kXRTcbHFe+scdhQJjaRQfG8kNUOBNw7DhKG7CafnnR9uvHTqDKFVbDOC?= =?us-ascii?Q?s72xPo72R03gZAvSOPfstGBpPyETcm5tb/X/vDbnorSPj8HcndOxQ9Mfn1sX?= =?us-ascii?Q?QTkeXghkMVoLZiV4a2r+YL8E0slYvsWWMD29r57NGLDoXXZdCU9jOveSaVpF?= =?us-ascii?Q?juuKEiDEQSW1vvFv1muA+Lekr3KFUz5wOvyBTJmArM1kNf0bWnX0nJrlhsQU?= =?us-ascii?Q?/nPUUsC7003+/OJ6TUOdY/rXBqyO96ZaDU0fKzPDTV1X2chW6CAQsol4dhY7?= =?us-ascii?Q?RDOMbEEm5Xq/OKfsNxkNiF/5oqVfG17u/myr4RpWTunm0yC+U5Yi+YOB9+8T?= =?us-ascii?Q?mPnkSa80WHv1/3U2DK5KW0RShec2KNHZGbHiyzOnaRP3ckm3QGqcbtLDOlo9?= =?us-ascii?Q?VOog5d4ePiX7SuVlwJ+vqixIk/3oU6pQixEoZdMp1HlD5+PhTk3nQmVk8+o6?= =?us-ascii?Q?DyUt/2XsFudRwjFcTJzn866mim3zbdN1WdtDxEYo4Rpi+bYd+HGoy7B7mpUj?= =?us-ascii?Q?xUYpVriHEWyT1NOVdUMWO762jAw7uKqnSV/sMO6o8G8HJvmce9CMfGOfdrek?= =?us-ascii?Q?t50CQbUx49SM9MYBROunNo0ewHaJJbPFWDeslsSHNe/l8AJ1M5tV+EE4fWXF?= =?us-ascii?Q?nbugbTTw/7CSeWSCUcINJyMlNbNG8MLZOgOOOeYo3vjFMjoFLY8FG4ZXNjGA?= =?us-ascii?Q?0IEGf9YK+mVk8zY9j/bcUUh47kdtz5NoX0Vqc5mlfFE/1K7JA3laNa4NRqTn?= =?us-ascii?Q?QQ0RlteXxpSnPcxcPjLwP7sHaAME8zaPCmMP+m+G9kQIuakW1HC+3EZoWO0Z?= =?us-ascii?Q?6wSPNBvVNN+gtnBzUmg9UJpvoxujmuP0IX/DJGTIQ1TXHuTIF12107W1pPf2?= =?us-ascii?Q?yjomAClB3Gl0BdWoBS+eu9B4fdqDJ5O2QIdSYoM5QYt2C/o+83ImcJwpCjBF?= =?us-ascii?Q?PpUQ9Q973qG4ZFqWkBcslhN2SL/I5YQJvCG3ZqcYW1nZa56iaqwjqP2lltxn?= =?us-ascii?Q?JI+xYKH3CJbP3vyZ+s2ZpSyB2tXuQNcW6j5RRyLQxHfAr7u73EJHYtc03iPV?= =?us-ascii?Q?gRnnB7UtkWeqrVS5RyrieePw5/1i/VO+5LqCaZew5ZeGpFIo1K+8gZgx9YeW?= =?us-ascii?Q?KQf3QNUT3WWwUhQjPC65VonmRz0VkUNUgvfOClM9a6i6KD/pgLdY5s9DAQDn?= =?us-ascii?Q?VkrAEPkx+uAMCi0J1TMHS86/dVdd2kXJ/kCYSeStCf8kJutF7DfdO+zeGVgR?= =?us-ascii?Q?WlyrQpJIr9kHR05kiudG3EWV6CRgWqzm3x9qefdlX44M2EzLhG6UGi/BZb7Z?= =?us-ascii?Q?5Cr0Kyg8QM0zj/v6DOAL1Rig6JZDPznZHLZ9EjVYBHnVpwS0dEfXD8VyrP6R?= =?us-ascii?Q?0esmn8/Plz9MCWsCJzlcX6xnralFWwCIvuRWc+57pD0cw/HZ?= X-OriginatorOrg: Nvidia.com X-MS-Exchange-CrossTenant-Network-Message-Id: 400cbac5-27b5-4248-e42b-08df0770b61e X-MS-Exchange-CrossTenant-AuthSource: IA0PR12MB8374.namprd12.prod.outlook.com X-MS-Exchange-CrossTenant-AuthAs: Internal X-MS-Exchange-CrossTenant-OriginalArrivalTime: 31 Aug 2026 15:01:18.4948 (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: Zvz67CQUdLLaCt3fYaSpHspW6AsJxOe3lpTxwJF5875FRBHkNkTs+Ew/CNzfwIcn X-MS-Exchange-Transport-CrossTenantHeadersStamped: DS8PR12MB333896 On 31 Aug 2026, at 5:00, Lance Yang wrote: > On 2026/8/31 15:56, Nimrod Oren wrote: >> When THP is enabled, set_recommended_min_free_kbytes() may raise >> min_free_kbytes using a heuristic that scales with pageblock_nr_pages. >> With MIGRATE_PCPTYPES equal to 3, the formula accounts for 11 >> pageblocks for every eligible populated zone before capping the result >> at 5% of low memory. >> >> This is reasonable when a pageblock is 2 MiB, as on common 4 KiB page >> configurations, but scales poorly with larger base page sizes. With >> the default arm64 pageblock sizes, the contribution per eligible zone >> before the 5% cap is: >> >> 4 KiB pages: 2 MiB pageblock, 22 MiB per zone >> 16 KiB pages: 32 MiB pageblock, 352 MiB per zone >> 64 KiB pages: 512 MiB pageblock, 5.5 GiB per zone >> >> Consequently, min_free_kbytes can reach excessive and unwanted levels. >> >> Add an absolute 1 GiB cap to the recommendation, in addition to the >> existing percentage cap. This bounds the automatic recommendation to a >> sane value on systems with large pageblocks while preserving existing >> behavior for typical systems with 2 MiB pageblocks. > > Sorry, I haven't been following the previous discussion. > > One nit: why 1 GiB? It feels a bit arbitrary to me ... It is. Just better than 5.5GiB in the existing configuration. Best Regards, Yan, Zi