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Howlett" , Nico Pache , Ryan Roberts , Dev Jain , Barry Song , Lance Yang , Usama Arif , Kiryl Shutsemau , Vlastimil Babka , Mike Rapoport , Suren Baghdasaryan , Michal Hocko , Brendan Jackman , Johannes Weiner , Hugh Dickins , Nirmoy Das , Dragos Tatulea , linux-mm@kvack.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH v3] mm: remove min_free_kbytes adjustment for THP Date: Tue, 01 Sep 2026 16:01:59 -0400 X-Mailer: MailMate (3.0r7024) Message-ID: In-Reply-To: <20260901190123.3511535-1-noren@nvidia.com> References: <20260901190123.3511535-1-noren@nvidia.com> Content-Type: text/plain X-MS-Reactions: disallow X-ClientProxiedBy: CH3P220CA0019.NAMP220.PROD.OUTLOOK.COM (2603:10b6:610:1e8::18) 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_|CH3PR12MB7692:EE_ X-MS-Office365-Filtering-Correlation-Id: c0ece55b-550e-40a3-6e01-08df0863e375 X-MS-Exchange-SenderADCheck: 1 X-MS-Exchange-AntiSpam-Relay: 0 X-Microsoft-Antispam: BCL:0;ARA:13230040|366016|7416014|376014|1800799024|23010399003|10067099003|11063799006|56012099006|13003099007|18002099003|22082099003; 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X-MS-Exchange-AntiSpam-MessageData-ChunkCount: 1 X-MS-Exchange-AntiSpam-MessageData-0: =?us-ascii?Q?rPK5/PgL02uvRKgnA6xFxB5dY4HN/AH27d48fmK4zUMd+THMRgOfc72H/+aG?= =?us-ascii?Q?gWpLWmmtBcppnV8ymh5Zn36bAtAtR2HjPXdrXJoYdxQEtSxZXIVpixaubtB8?= =?us-ascii?Q?E8MG4g3CnNBDyCayl1oOEabbJJxr4QLxBZOgOUF7wzn1m2BZ5ZzC0ehILKd/?= =?us-ascii?Q?xi/rY4j+DRYPzmMAI6jh/g6M3jI6m1E9cqPNAPdG5ENY7PSEw8o6S9zNEX4y?= =?us-ascii?Q?UrIN+H2uvW3nR1RS7Ft8iyldXDkGpmBRougpbD6pAnUi11HvQWtGlUUBZ1t2?= =?us-ascii?Q?H/OF0Zzn9pgOL1A4wswKBiUTUrBxBy9zzLP6rraPk5vgq0BCguJpNa5TEd4H?= =?us-ascii?Q?0w0zfsIs2nWS6uOx2B9DlCh81RBQn3TPq/wT8kdCTO/IaKxwuDcL6YH3VU+3?= =?us-ascii?Q?wUK1HhcTMMIIE4QT9bxW4+fnlYnxxJGwpLDBFIpBRuknM3iVOsYpLfKY2AsH?= =?us-ascii?Q?vZyqmXbvk9xxNXCuRoqWmMPUvbwaNlX/3KUSXHZavU6Wu2SVno2Nh1Uvxe6M?= =?us-ascii?Q?c5hXOzDOKwNx1e3RLxdf+D1DsPI2HRHunLbQCglWlqgsQHfSEhwc5WtL0zzL?= =?us-ascii?Q?YW8r8pDZ38X2pG9L5fo9IjEm3g9Nz/NhZUW6vEOQo2QMjvRchjqJL6H0THn/?= =?us-ascii?Q?0CmuqXbfjl4B8G0z649jY22b/kLXP0jxK0C22X4UL7wdo9mDnIl35XkI13lc?= =?us-ascii?Q?uOASNTrJ4mSlcr3/xiAhuITTYa4AoINfpulN4Gz4Rwx4/EWViOd+uu4B67Kq?= =?us-ascii?Q?ViGSXPoZftQidhq886ecuM45FXpXTcIBBusVp2WMt1CfQ7v49wGZpqxs8CNw?= =?us-ascii?Q?0AA+zX81Fx2BRwVjDXp5UcMEt8/NB8hMkxaMo2GARMWkVke1YCfOHsP/FisF?= =?us-ascii?Q?eNpDIeccuPcBHF2SbNknjZZCXrYOqqJHtLxfRNFqChiONHML//IcrO2GxUDl?= =?us-ascii?Q?ZPr4FqE8LByqqcw7cljh1bXtISNMlMQH7fUhbFOnngYMII4k4EGmXuXZV6EM?= =?us-ascii?Q?vkNblarlkSYjFmh5w4HN08uHI0zy+wpefA9QsjqM9/beOu6+RousVZWQB+gF?= =?us-ascii?Q?Jf0VXLSzMnOwgD0GTVhFYzL4OMmo+7M7dDjDZyYNd8fl4dye1K48rWK9VjAm?= =?us-ascii?Q?PC7K9C3t5G8D4Xa4oaCEj7T2Hoo8LTdZKfDPGXXAhzb/YzG2xaDyJT4dEWte?= =?us-ascii?Q?2j/blOO69dR5RXX9EjwVCxaHnoWMPQ74TstnZrf0ztB+12l7/aSzxzGAbJ6m?= =?us-ascii?Q?UR0BSD1/Zg9XlmlEW7Ms/HdrJlkwMJfD6LNCRdfyPoyIBKeBE283L9E4NkqK?= =?us-ascii?Q?qJtDMoG2bb3vDHk1P6EvStyJi4QXDKNe6qvrj3jB6D4bbqbEmUbS2/EfIj+n?= =?us-ascii?Q?uhXx4pr7AkbCKwHu+yb7Oq48CkjqppndcDqcFPI+UsTtyruiVqgHOYDzba0N?= =?us-ascii?Q?vLEvAT6gctinQZWhNQLgLNe/qVKkfW81HE1Fvz56JgDvhJ6r0J9lYfR3xXux?= =?us-ascii?Q?Ojfb1/+YI7ItI1STqhk9cE9S2+bPUP1V5Ake3R/+w3WjRLVAxFUJ1Rq5eRh3?= =?us-ascii?Q?K8LroN2gPyqb6oXyNWIw/MLiy2guhHzsHCZwq6/PHHgSPYDPzGvyO4s13+NC?= =?us-ascii?Q?Zq8121wiYwwhcB8r1yUc71xSlSMwKJ1bPm/J319+sqch0PyMVhSm4yzK5wz4?= =?us-ascii?Q?h6Z8XSJuG05qxHwpyJAFxGCwfq+nj/K6Euua/WfquXirPFRN+y+2gNBKpPNA?= =?us-ascii?Q?kv77HWXlXg=3D=3D?= X-OriginatorOrg: Nvidia.com X-MS-Exchange-CrossTenant-Network-Message-Id: c0ece55b-550e-40a3-6e01-08df0863e375 X-MS-Exchange-CrossTenant-AuthSource: IA0PR12MB8374.namprd12.prod.outlook.com X-MS-Exchange-CrossTenant-AuthAs: Internal X-MS-Exchange-CrossTenant-OriginalArrivalTime: 01 Sep 2026 20:02:02.3899 (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: UzQi4YI3MMP50RXAMeVivKqDbOjEnoFuko5QayCbCLndmfCVDZd02zfcif4PH3UH X-MS-Exchange-Transport-CrossTenantHeadersStamped: CH3PR12MB7692 On 1 Sep 2026, at 15:01, 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. > Commit f000565adb77 ("thp: set recommended min free kbytes") added this > heuristic to help keep pageblocks free and reduce fragmentation for THP > allocations. > > The recommendation scales poorly with larger base page sizes. With the > default arm64 pageblock sizes, the contribution per eligible zone > before applying the existing cap of 5% of low memory 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 > > Even with that cap, min_free_kbytes can reach excessive levels. > > The automatic min_free_kbytes increase predates proactive compaction > and many subsequent changes to compaction. Given those changes, > increasing min_free_kbytes for THP by default is no longer clearly > justified. > > Remove set_recommended_min_free_kbytes() and all associated > recalculation paths. With this policy gone, min_free_kbytes is > controlled only by the page allocator's default calculation and the > vm.min_free_kbytes sysctl. Users who want additional headroom may set a > higher value via that sysctl. > > Link: https://lore.kernel.org/r/20260831075635.2244437-1-noren@nvidia.com/ > Suggested-by: Michal Hocko > Signed-off-by: Nimrod Oren > --- > v3: > * Replace the 1 GiB cap with removal of the THP-driven min_free_kbytes > increase as suggested by Michal. > * Remove all associated recalculation paths. > * Make min_free_kbytes, user_min_free_kbytes, > calculate_min_free_kbytes(), and setup_per_zone_wmarks() static. > * Drop the now-unused declarations and khugepaged's page_alloc.h include. > * Drop the obsolete v2 documentation addition. > > v2: > * Use a named constant for the cap. > * Drop explicit linux/sizes.h include. > * Update min_free_kbytes documentation. > https://lore.kernel.org/r/20260831075635.2244437-1-noren@nvidia.com/ > > v1: > * Cap the final recommendation at 1 GiB as suggested by Lorenzo. > https://lore.kernel.org/r/20260728202014.2517142-1-noren@nvidia.com/ > > RFC v1: > https://lore.kernel.org/r/20260716173504.760369-1-noren@nvidia.com/ > --- > include/linux/khugepaged.h | 5 ---- > mm/huge_memory.c | 14 --------- > mm/internal.h | 8 ----- > mm/khugepaged.c | 60 -------------------------------------- > mm/page_alloc.c | 11 +++---- > mm/page_alloc.h | 2 -- > mm/shmem.c | 7 ----- > 7 files changed, 4 insertions(+), 103 deletions(-) > The stats look nice. Like you said in the commit message, user can still have the old behavior by increasing vm.min_free_kbytes. Thanks. Acked-by: Zi Yan Best Regards, Yan, Zi