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Howlett" , Nico Pache , Ryan Roberts , Dev Jain , Barry Song , Lance Yang , Vlastimil Babka , Mike Rapoport , Suren Baghdasaryan , Michal Hocko , Shuah Khan , linux-btrfs@vger.kernel.org, linux-kernel@vger.kernel.org, linux-fsdevel@vger.kernel.org, linux-mm@kvack.org, linux-kselftest@vger.kernel.org Subject: Re: [PATCH 7.2 v2 05/12] mm/khugepaged: remove READ_ONLY_THP_FOR_FS check in hugepage_pmd_enabled() Date: Mon, 13 Apr 2026 16:42:37 -0400 X-Mailer: MailMate (2.0r6290) Message-ID: <05F00072-7E06-47C9-BC26-FE3736F557FC@nvidia.com> In-Reply-To: References: <20260413192030.3275825-1-ziy@nvidia.com> <20260413192030.3275825-6-ziy@nvidia.com> Content-Type: text/plain X-ClientProxiedBy: MN0P220CA0002.NAMP220.PROD.OUTLOOK.COM (2603:10b6:208:52e::31) To DS7PR12MB9473.namprd12.prod.outlook.com (2603:10b6:8:252::5) Precedence: bulk X-Mailing-List: linux-btrfs@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 X-MS-PublicTrafficType: Email X-MS-TrafficTypeDiagnostic: DS7PR12MB9473:EE_|CH3PR12MB8727:EE_ X-MS-Office365-Filtering-Correlation-Id: a21175ec-86d2-45eb-ecb4-08de999d3503 X-MS-Exchange-SenderADCheck: 1 X-MS-Exchange-AntiSpam-Relay: 0 X-Microsoft-Antispam: BCL:0;ARA:13230040|366016|1800799024|7416014|376014|22082099003|56012099003|18002099003; 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X-MS-Exchange-AntiSpam-MessageData-ChunkCount: 1 X-MS-Exchange-AntiSpam-MessageData-0: =?us-ascii?Q?FpW1Wf2Ajty79E/OFmmU4cFneeqNTSr+upBCEAeGW49c36eqSYGHBL9qfOw6?= =?us-ascii?Q?2InDIfzrkztRhzUW9DdW0wtqLUdyLWj8YBBNIlUESp1njMtiSMds1HC7SJRE?= =?us-ascii?Q?oUZvx96u8cCNPirvbdVg7tfav6uHFQVxH2gwq1zQRPTHXPyH7izGfk6Iv4hg?= =?us-ascii?Q?17c9FYigDdz4jZttZ5fHO6Gz7KGL9sYSmvMSOregTeaiOjkJlnrbMWsa0kpx?= =?us-ascii?Q?Ixq45XsjEvuUqdEVQnyVIWi5716/2+Sx4zv176CV0ouwLyf8fspaDsMYm5vS?= =?us-ascii?Q?Um0ke6qgruQjKKHSBVp1bCu6QgfiP27EKQzUuW4Sut9HvOpZizyihjxdKe9S?= =?us-ascii?Q?8XwkrxtP6hKvpC1e+2iLO+b81jOKOEqrYn1KtIbnB0JkfxRLLZuiJuibWYES?= =?us-ascii?Q?CwbeSF1ZuJ43r5dJxWjR3np29+OY4B8SneTzmmSXU8NIfE/bTrEG99x/rGi4?= =?us-ascii?Q?2TRYbrdAo7VxlyKx/hNrJw1Mn8TvvB5mqwfLHgkPirHKD6SqlqvUBl7tyMdR?= =?us-ascii?Q?hShMV/qSCRq65N817/g2sJRBtfkZjAW/o/sNwlfNmicf8e4rw4OQXsek3vwT?= =?us-ascii?Q?YSbMdf1JJKswkY1+53P2rPxdqaZspOQyjr21s/H/ss/F/kwJS28Jn93URpl/?= =?us-ascii?Q?JziBHiQ84dOQcNkTU104rLhGn9JVfrYocy1mqZtS5lJg0IfxplvVyKwBox5Z?= =?us-ascii?Q?PzTlq+/n2uWwtwOneCJ45rjvc8GHUIiRfNnDrjWk9Zecz7FdpgfWZnuBPKUM?= =?us-ascii?Q?YpJ88YIJwECmXNiUmeui2R7Pl5wY92mZSL1QTq6JE5dk3dzcqlzqxhb+O/rT?= =?us-ascii?Q?iShQX61Ne5fnQ1d0nkRRiZoHyUHKHsLXVUSTM7VP708ehX4ege/MGEElKOoD?= =?us-ascii?Q?hb59lED7R81CCGDEyK3svGKednepZhWkZfs/ggib8PxPzIu4NEJlUAkSuhz1?= =?us-ascii?Q?UPIHm/Gc7E4QAgws+EnYaUwMlv9gKrgKD2gSedkx7SB+bDu1vNJki94oK/kw?= =?us-ascii?Q?bszf+4uLIe9CsRoPVFoS6VE07yOEvBrqoYlsL8mipkrHNJaSKmzeJ4jbkQ2i?= =?us-ascii?Q?pQJs+HTtJdlOVyfU9REQhBYlM50Ym21H8vyzIrr7PGE0QwU3XZNzLyabZjK0?= =?us-ascii?Q?q18DjRVc6b1nMJl3YanZyXZ7N5+VfNdJqbYTpx5PJCZof+3+nTyiIZbRV/5B?= =?us-ascii?Q?UfFwiqJfgUwtB06vQe+sGe6GRt7HV8nUoYLzGSzPKEzcyU8JswoiTqECRvrW?= =?us-ascii?Q?Gq6ONKI+qQ+y1uwA045SumsTB3K9zweUqayYJ0v0HceQXeuaWpDGgDAtmgT6?= =?us-ascii?Q?rkxl5oe2m2kTSn/bmjOhOrsYVi7m97RLHMHHX/Vkn8AXATb6ZhGThMCAJluU?= =?us-ascii?Q?ri8UUinlDDMGGPwVUgPVU5Ei3K+7YeQk4ANOVTfHc3cdGQCnpidW1wxtsajv?= =?us-ascii?Q?CgDC024M2UxQszv8i2C/hQix2mzyc4Ljo0MjsLlDiSo8PUEPCidxLc3QVBM3?= =?us-ascii?Q?NRim9m2tI10oV103drZZAG20hbr8Vt44lnDEICBWxMIuyZQlZqQQW6cifnoa?= =?us-ascii?Q?4m2rSMcxbA9bys+fxBrzXAXlFaYPGFG2c2t7/s5SIdLv8I4gyFLyhun9Y4B7?= =?us-ascii?Q?vbgqKfka+eTVgN6+Al0PSWzV3nlKPduEAw0VjNwTgAABW2wFF7BjJLaoFeV/?= =?us-ascii?Q?2IqnlOevyRHuNVN78H0InHPCD2Q5qsNgrMOsx7RJ/gTvm4U+Utoxe5NrijDZ?= =?us-ascii?Q?FeK62cGUbQ=3D=3D?= X-OriginatorOrg: Nvidia.com X-MS-Exchange-CrossTenant-Network-Message-Id: a21175ec-86d2-45eb-ecb4-08de999d3503 X-MS-Exchange-CrossTenant-AuthSource: DS7PR12MB9473.namprd12.prod.outlook.com X-MS-Exchange-CrossTenant-AuthAs: Internal X-MS-Exchange-CrossTenant-OriginalArrivalTime: 13 Apr 2026 20:42:41.2466 (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: ICc2eUsNxA8nXHqFy7a4AyZcTQeluNkksDkFbtP/4KoSybkSoA4+ZDjrpOxoae6w X-MS-Exchange-Transport-CrossTenantHeadersStamped: CH3PR12MB8727 On 13 Apr 2026, at 16:33, Matthew Wilcox wrote: > On Mon, Apr 13, 2026 at 03:20:23PM -0400, Zi Yan wrote: >> After READ_ONLY_THP_FOR_FS Kconfig is removed, this check becomes dead >> code. >> >> This changes hugepage_pmd_enabled() semantics. Previously, with >> READ_ONLY_THP_FOR_FS enabled, hugepage_pmd_enabled() returned true whenever >> /sys/kernel/mm/transparent_hugepage/enabled was set to "always" or >> "madvise". >> >> After this change, hugepage_pmd_enabled() is governed only by the anon and >> shmem PMD THP controls. As a result, khugepaged collapse for file-backed >> folios no longer runs unconditionally under the top-level THP setting, and >> now depends on the anon/shmem PMD configuration. > > This seems like it'll turn off khugepaged too easily. I would have > thought we'd want: > > - if (IS_ENABLED(CONFIG_READ_ONLY_THP_FOR_FS) && > - hugepage_global_enabled()) > + if (hugepage_global_enabled()) > return true; I thought about this, but it means khugepaged is turned on regardless of anon and shmem configs. I tend to think the original code was a bug, since enabling CONFIG_READ_ONLY_THP_FOR_FS would enable khugepaged all the time. > > ... or maybe this whole thing could be simplified? Alternatives could be: 1. to add a file-backed khhugepaged config, but another sysfs? 2. to replace hugepage_pmd_enabled() with hugepage_global_enabled() and let thp_vma_allowable_order() in collapse_scan_mm_slot() skip not qualified VMAs, but that would waste extra CPU cycles for scanning. Maybe not too much waste. Best Regards, Yan, Zi