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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: [RFC PATCH 02/11] mm/khugepaged: remove READ_ONLY_THP_FOR_FS code in collapse_file() Date: Mon, 23 Mar 2026 16:24:26 -0400 X-Mailer: MailMate (2.0r6290) Message-ID: In-Reply-To: <71148f2e-cceb-418e-b762-c8dbd7a7eb1f@kernel.org> References: <20260323190644.1714379-1-ziy@nvidia.com> <20260323190644.1714379-3-ziy@nvidia.com> <7382046f-7c58-4a3e-ab34-b2704355b7d5@kernel.org> <71148f2e-cceb-418e-b762-c8dbd7a7eb1f@kernel.org> Content-Type: text/plain X-ClientProxiedBy: BL1P223CA0015.NAMP223.PROD.OUTLOOK.COM (2603:10b6:208:2c4::20) 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_|PH0PR12MB8008:EE_ X-MS-Office365-Filtering-Correlation-Id: 6179d64a-dc98-46d8-591e-08de891a3014 X-MS-Exchange-SenderADCheck: 1 X-MS-Exchange-AntiSpam-Relay: 0 X-Microsoft-Antispam: BCL:0;ARA:13230040|366016|1800799024|7416014|376014|18002099003|22082099003|56012099003; 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X-MS-Exchange-AntiSpam-MessageData-ChunkCount: 1 X-MS-Exchange-AntiSpam-MessageData-0: =?us-ascii?Q?/6ZXgzP9fm0SITOzvLgx/rPvhGy4wY2hPxD3WqTLgtAEdHs3HDH59kZU6cvp?= =?us-ascii?Q?/3QbsWInu8kbVd8uzlONbgvSeQ+D3nAXHuyQF1IVFvGR39Susk9HxwvrmQBj?= =?us-ascii?Q?B8UatDmur4qrPcVGy7gpuwYGg/J63q0yZcDQWRZWjIMW1Q3HRgIVwBmd+6Sm?= =?us-ascii?Q?HaTF42pebMx4gYbxtxg8ruOA5GpMmuXkSp8E1D1oXMOEi3Z0sPFdKv2n7KVz?= =?us-ascii?Q?d4XCXqCuzmYUfmJ2NFDNH7kbKQ1FXX2C7x30GH/UfPrqSIaA8oUeMziIUmRF?= =?us-ascii?Q?sSjsWQki4uzP1Pig0OgutTHQQxF5pzV8JvhxanFTJVJxkR8shZMAfTxaModK?= =?us-ascii?Q?uiNYPPI+mpWYx/U4QHLZnJfAiGlBY/5vv0aS6dN2lfRBUiIpg4R9eY8KxuLt?= =?us-ascii?Q?NsaSOzWqfq3b7qpc4h3I3ohyt7/fdcf8qVkVzBuan7wzf8ry0L+0wmqU/HqJ?= =?us-ascii?Q?CqTSPhYPRvelgsg04mT7PdHAks+sDVC7SVlIfjGS1Y1um7XqsI2vhzIZc63P?= =?us-ascii?Q?LvktqJmGRLhh/iK7BI/7EhA0yuRqB9aTWGNawfr/0XGHUv3XpHkaJ9pE9H/X?= =?us-ascii?Q?4ou852NbOxRo19Bj2BzeUyeUJsD0B1ypW4HzpXsVpYtZnbaFE1+Hqgr/kJZN?= =?us-ascii?Q?qk5lGgM6OKqFPy1XOx/aQ3RWhltLr4v9q7uWVKgIgSqc886WGe0WHaNWmzqD?= =?us-ascii?Q?Lx2Jv7z9Z+fSo3y9Hv2Gh2htHpQEeplL9b2CcbXrxu6DVuExEAQLlvrReCpg?= =?us-ascii?Q?hJJyjvsBZtfkcTwIWJe8vagmzM2HcPr9e6Ep0eInYnuoXNiLWixNCipp7nSH?= =?us-ascii?Q?ThmlvmQ9RLmgvJPqtO1noF4hM1+kZ3iPmX8KskOJv96LhHbQHlS1CKhHI6lp?= =?us-ascii?Q?8NkuHPKk0xUe3Sy7aX23H04Y+iZhB6a6b8Dif5VL+akticQRbWRXEDdEjPSx?= =?us-ascii?Q?PqNzMnVjmNS/HQhMsu0joLoyKnie84zVsGJJvAPxIJt2kWouj5tmV8SXJk9f?= =?us-ascii?Q?fveE5lDx4I5snhmuokrbc0vJ9PWPuh5kJv+FQHUw4K73lsai0irSDHnrzOBs?= =?us-ascii?Q?bOp1hJpAuvBvusMPkfp561CPguiVCufoTvJ7dXJ94dkOmj+qyddaM6GYw/uZ?= =?us-ascii?Q?RbzURD+0GyTwc6wXAvaUofXIrMdnW5i3WVkuee9DCEoDovbmOgTAxLKOqmay?= =?us-ascii?Q?9wTaE5uQJzzaxmHTDJn8Qk3jeGGgaUZy43UU2w/pcsYVJ/D4ZfiHL7LAOK8b?= =?us-ascii?Q?V++WWlNWpx7EnHpGQYegL2KsUcnbyw8xw6+GZuEqxjretASOli8zTgm7dlUq?= =?us-ascii?Q?fnGetBZJSkmr+vmU0doSb49WzLF6yeuNpLxLTXGixlmLnjYp7ZLSpT0PWcCJ?= =?us-ascii?Q?BxNrnjP4Rh1dWO8gKnagntGC9inlx1XpuwM5GYxhl8WFfrnzrwPf8s4SDg/j?= =?us-ascii?Q?GTm5W05X9sgWreKuReqnvEcwPDBArPCG290N0xLWpQV7xa+eKfPtLHF6vKaN?= =?us-ascii?Q?PfA8D83pYneej2f+SwxcdED1/CqgdS77DpTPQ7v67l6mg2QcO9knf4+jpxGf?= =?us-ascii?Q?T6otc8+KSQCemg0sycSlQdq6EuctSWt/TarR7sJJN71VNPL+6pDjuxMIKBOS?= =?us-ascii?Q?mR5fry4Jriiw2j2PaUPG0FJhlx85zhgEwFPOgQ4oiFj1hs8AaTmUNFEAsN7P?= =?us-ascii?Q?mVGsdZNJ4ZJBGKzvk11BnTomp8GvgiUjCLMEb+UDmBybD3Mg0TIFQljphofq?= =?us-ascii?Q?kuuH3xpWBg=3D=3D?= X-OriginatorOrg: Nvidia.com X-MS-Exchange-CrossTenant-Network-Message-Id: 6179d64a-dc98-46d8-591e-08de891a3014 X-MS-Exchange-CrossTenant-AuthSource: DS7PR12MB9473.namprd12.prod.outlook.com X-MS-Exchange-CrossTenant-AuthAs: Internal X-MS-Exchange-CrossTenant-OriginalArrivalTime: 23 Mar 2026 20:24:30.3582 (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: AlQUG5GPaHrz7UyJYtc4vonlBTAQsffznDzRRMd7oyYNpjDrftvlY4IhPtiCqdRV X-MS-Exchange-Transport-CrossTenantHeadersStamped: PH0PR12MB8008 On 23 Mar 2026, at 16:13, David Hildenbrand (Arm) wrote: > On 3/23/26 20:59, Zi Yan wrote: >> On 23 Mar 2026, at 15:53, David Hildenbrand (Arm) wrote: >> >>> On 3/23/26 20:47, Zi Yan wrote: >>>> >>>> >>>> My understanding is that collapse_file() is only used for >>>> READ_ONLY_THP_FOR_FS. If FSes with large folio support also use it, >>>> I can replace IS_ENABLE with mapping_large_folio_support(). >>> >>> Otherwise we'd be losing support for THP collapse in files? We'd have to >>> cross fingers that readahead gives us some. >>> >>> So we have to be a bit careful here. We want khugepaged to collapse THPs >>> in filesystems that support large folios even without READ_ONLY_THP_FOR_FS. >> >> Based on[1], collapse_file() only works on read-only fd. So it is not >> as general as all files. If we do what you suggested, the function >> will be collapse read-only folios from FSes with large folio support. > > Right, I think that's the first step to keep the existing use case > working. Long term, I suspect we might want to extend that to writable > files etc. > >> >> BTW, has anyone used/relied on collapse_file() on any FS with large folio >> support? > > I assume so, because for executables you would have to be lucky to get a > PMD THP? So I don't see the non-khugepaged large folio support on par > with khugepaged support. It is more like turning on READ_ONLY_THP_FOR_FS by default for FS with large folio support instead of removing it. OK, I will give it another try. Best Regards, Yan, Zi