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Howlett" , Nico Pache , Ryan Roberts , Dev Jain , Barry Song , Lance Yang , Usama Arif , , , Nimrod Oren Subject: [PATCH] mm/khugepaged: cap min_free_kbytes recommendation at 1 GiB Date: Tue, 28 Jul 2026 23:20:14 +0300 Message-ID: <20260728202014.2517142-1-noren@nvidia.com> X-Mailer: git-send-email 2.45.0 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Content-Type: text/plain X-NV-OnPremToCloud: ExternallySecured X-EOPAttributedMessage: 0 X-MS-PublicTrafficType: Email X-MS-TrafficTypeDiagnostic: BN3PEPF0000B071:EE_|IA1PR12MB7592:EE_ X-MS-Office365-Filtering-Correlation-Id: 3ae5c903-2ee5-4881-20eb-08deece5a10e X-MS-Exchange-SenderADCheck: 1 X-MS-Exchange-AntiSpam-Relay: 0 X-Microsoft-Antispam: BCL:0;ARA:13230040|1800799024|376014|23010399003|7416014|36860700016|82310400026|10067099003|18002099003|11063799006|56012099006|13003099007|6133799003; X-Microsoft-Antispam-Message-Info: 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 X-Forefront-Antispam-Report: CIP:216.228.117.161;CTRY:US;LANG:en;SCL:1;SRV:;IPV:NLI;SFV:NSPM;H:mail.nvidia.com;PTR:dc6edge2.nvidia.com;CAT:NONE;SFS:(13230040)(1800799024)(376014)(23010399003)(7416014)(36860700016)(82310400026)(10067099003)(18002099003)(11063799006)(56012099006)(13003099007)(6133799003);DIR:OUT;SFP:1101; X-MS-Exchange-AntiSpam-MessageData-ChunkCount: 1 X-MS-Exchange-AntiSpam-MessageData-0: gqig14HUTZSHUnUQzeSrpsxNylQsbHfHcfWWX1Ed3k5qvAI09rUPUfzYS+gk5zgHanWiSUIP6lBlCVjvtB5PBtyYQFAPfIt8T7O/CJyyRJ+Fg0AqymKlmX5uVotPEu5jPsIPhdv0utRpDiHp2kOx0VB52seE4VNWJWQmvnPEdwDWYwtsz/dEj/Q9iVot16GPkdXM3VRKSlIvvqU42YMCtwThtkJcI+7+2cEd3SKIKHlMKizg5ez0IKj8u4uuHAHnrXm85V3/CzA6wgNMA1Z1QCdnQYnf2rghj9rALxCKg0soamFDFSA8Aas/95DZjO7U4m2FkAFT8FIGNL5Or6kvJ12cl893MP8v3LcJ3t9BW0O9bMglGWVFHeWCShzHdxZAPYjRX4ElDEdW/niIjf/ERQqIhF/D4ehYfDmHBJmOQX9B9gjSolYJWuuCMEi48Cen X-OriginatorOrg: Nvidia.com X-MS-Exchange-CrossTenant-OriginalArrivalTime: 28 Jul 2026 20:20:12.5055 (UTC) X-MS-Exchange-CrossTenant-Network-Message-Id: 3ae5c903-2ee5-4881-20eb-08deece5a10e X-MS-Exchange-CrossTenant-Id: 43083d15-7273-40c1-b7db-39efd9ccc17a X-MS-Exchange-CrossTenant-OriginalAttributedTenantConnectingIp: TenantId=43083d15-7273-40c1-b7db-39efd9ccc17a;Ip=[216.228.117.161];Helo=[mail.nvidia.com] X-MS-Exchange-CrossTenant-AuthSource: BN3PEPF0000B071.namprd04.prod.outlook.com X-MS-Exchange-CrossTenant-AuthAs: Anonymous X-MS-Exchange-CrossTenant-FromEntityHeader: HybridOnPrem X-MS-Exchange-Transport-CrossTenantHeadersStamped: IA1PR12MB7592 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. Link: https://lore.kernel.org/r/20260716173504.760369-1-noren@nvidia.com/ Suggested-by: Lorenzo Stoakes (ARM) Signed-off-by: Nimrod Oren --- v1: * Cap the final recommendation at 1 GiB as suggested by Lorenzo. RFC v1: https://lore.kernel.org/r/20260716173504.760369-1-noren@nvidia.com/ --- mm/khugepaged.c | 7 ++++++- 1 file changed, 6 insertions(+), 1 deletion(-) diff --git a/mm/khugepaged.c b/mm/khugepaged.c index 27e8f3077e80..d9caf10e05b5 100644 --- a/mm/khugepaged.c +++ b/mm/khugepaged.c @@ -23,6 +23,7 @@ #include #include #include +#include #include #include "internal.h" @@ -3096,9 +3097,13 @@ void set_recommended_min_free_kbytes(void) recommended_min += pageblock_nr_pages * nr_zones * MIGRATE_PCPTYPES * MIGRATE_PCPTYPES; - /* don't ever allow to reserve more than 5% of the lowmem */ + /* + * Don't ever allow to reserve more than 5% of lowmem or 1 GiB, + * whichever is smaller. + */ recommended_min = min(recommended_min, (unsigned long) nr_free_buffer_pages() / 20); + recommended_min = min(recommended_min, SZ_1G / PAGE_SIZE); recommended_min <<= (PAGE_SHIFT-10); if (recommended_min > min_free_kbytes) { -- 2.45.0