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Byungchul Park , Gregory Price , Ying Huang , Alistair Popple , linux-mm@kvack.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH v2] mm/migrate: rename PAGE_ migration flags to FOLIO_ Date: Wed, 25 Mar 2026 11:05:44 -0400 X-Mailer: MailMate (2.0r6290) Message-ID: <925CC2D7-D525-4272-A01D-2A1E50127401@nvidia.com> In-Reply-To: <218144c5-6f51-44c9-bd70-e171005d3606@kernel.org> References: <20260324114720.864478-2-shivankg@amd.com> <54398FC0-2F68-410C-B9C4-2802810C119B@nvidia.com> <41cd005e-3702-4c67-8d32-0c09274194e9@amd.com> <857B5E73-94AC-41B9-A3BE-953E59A5DB40@nvidia.com> <27b1b602-129f-4bc5-a553-386e8d1f5d90@kernel.org> <539EA481-9CA0-4B2A-B0B4-C254E34BA7EC@nvidia.com> <218144c5-6f51-44c9-bd70-e171005d3606@kernel.org> Content-Type: text/plain X-ClientProxiedBy: SJ0PR13CA0093.namprd13.prod.outlook.com (2603:10b6:a03:2c5::8) To DS7PR12MB9473.namprd12.prod.outlook.com (2603:10b6:8:252::5) MIME-Version: 1.0 X-MS-PublicTrafficType: Email X-MS-TrafficTypeDiagnostic: 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bx0enmITtkHJKFaZxXCRHp487woEHnAk37X/sTRq3t0KRmID/m23nXwIGj693XubAlWAe8TEeu0zKphUmM25MnLOp8WuqYv1Z9QciuACmbi0QJabFH4i7iIQ/wIlF8Z02KdBGTx8kh0VNnY9U/2/sjfE7Pp72DsITgCquODqzmuK1PnmuaR4UJoSfHWa8mh6p2Ltz2kxSwtyDu79RmsOL6kdHrW44W5FeBE8ZjLVfhUhFY/bm5seaEo4EXH6h32GTonxDa2dUlQQptP64Pq69a/p4xy4HLqy9b/z5ZShDY+CXjdggBO4h5PkgKwXdUMr3Ycp3L3lTYu67fdh3o23bo5v0wxFEuL4sx5A4tMVTOYIfCvXVp8vJHHOm4fULSjU0qbcwCrb5RI/a2gK9RORd2iUhKNnpPQxlUEnIXsc3a2NC/lgEf7VzbG6v1SDXZWl48w2V Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On 25 Mar 2026, at 11:04, David Hildenbrand (Arm) wrote: > On 3/25/26 16:00, Zi Yan wrote: >> On 25 Mar 2026, at 10:53, David Hildenbrand (Arm) wrote: >> >>> On 3/25/26 15:21, Zi Yan wrote: >>>> >>>> >>>> Hi David, >>> >>> Hi, >>> >>>> >>>> In terms of folio_change_private(), I did not think it is related to >>>> folio_{attach,detach}_private(), since the latter change folio refcount during >>>> the operation. If folio_change_private() is related to attach/detach, >>>> I imagine it would check folio refcount before touches ->private. But >>>> that is my interpretation. >>> >>> I mean, given that >>> >>> a) It's located in pagemap.h in between folio_attach_private() and >>> folio_detach_private() >>> >>> b) It clearly states that "The page must previously have had data >>> attached and the data must be detached before the folio will be freed." >>> >>> This is the wrong API to use? >>> >>> Sure, it sets folio->private but in different context. >>> >>> I can spot one user in mm/hugetlb.c, that likely also should not be >>> using this API, because there likely was no previous attach/detach. >>> >>>> >>>> BTW, do you know why we have set_page_private() but no folio_set_private()? >>>> I would suggest folio_set_private() if it exists. >>> >>> folio_set_private() sets ... PG_private. :) >>> >>> folio_test_private() checks PG_private and folio_get_private() returns >>> page->private. >>> >>> A cursed interface. >> >> Oh man. folio_get_private() should be renamed to folio_get_private_data(), >> so that we can have folio_set_private_data(). > > Likely we should strive towards only using folio->private (and the API) > really for fs-private data (i.e., the pagemap.h interface), and add > proper custom members for all other use cases. > > For page->private it's a different discussion (requires more work I > guess, because there are many more use cases. > Makes sense to me. Best Regards, Yan, Zi