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Subject: [BUG/RFC] write-open file THP cache purge can discard dirty page cache Cc: "To: Alexander Viro" , "Christian Brauner" , "Cc: Jan Kara" , "Andrew Morton" , "Song Liu" , , , , "Eric Hagberg" To: "Matthew Wilcox" , "Gregg Leventhal" From: "Zi Yan" X-Mailer: aerc 0.21.0 References: In-Reply-To: X-ClientProxiedBy: DS7PR03CA0091.namprd03.prod.outlook.com (2603:10b6:5:3b7::6) To IA0PR12MB8374.namprd12.prod.outlook.com (2603:10b6:208:40e::7) MIME-Version: 1.0 X-MS-PublicTrafficType: Email X-MS-TrafficTypeDiagnostic: IA0PR12MB8374:EE_|CH3PR12MB7524:EE_ X-MS-Office365-Filtering-Correlation-Id: a527ec0a-0a1a-4ec2-edb3-08ded6da879d X-MS-Exchange-SenderADCheck: 1 X-MS-Exchange-AntiSpam-Relay: 0 X-Microsoft-Antispam: BCL:0;ARA:13230040|1800799024|366016|376014|7416014|23010399003|22082099003|18002099003|4143699003|11063799006|56012099006; X-Microsoft-Antispam-Message-Info: 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Nvidia.com X-MS-Exchange-CrossTenant-Network-Message-Id: a527ec0a-0a1a-4ec2-edb3-08ded6da879d X-MS-Exchange-CrossTenant-AuthSource: IA0PR12MB8374.namprd12.prod.outlook.com X-MS-Exchange-CrossTenant-AuthAs: Internal X-MS-Exchange-CrossTenant-OriginalArrivalTime: 30 Jun 2026 19:05:20.0943 (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: HEH8Jco0Pqg5LV6lkoqOoZV7E60locBELZB/GxCUrnMXD/jZmnVSiOog80ZHV1d0 X-MS-Exchange-Transport-CrossTenantHeadersStamped: CH3PR12MB7524 X-Rspam-User: X-Stat-Signature: 7niswjod34d3wf1pren3fdg13z1gd1h3 X-Rspamd-Server: rspam10 X-Rspamd-Queue-Id: D4ECB1C0003 X-HE-Tag: 1782846328-505589 X-HE-Meta: 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QGNfl/nxRxIHx2f0b7u9URYqaqWNrwxX/VvdfC1IWDVjfhU9e3OzhAUAwtWOUAMbIofkmrioJYQvB+Zgr0GdafPQoEpelugDbh2w12S5V5Kt+VgMNqkpB3gdRey+UixWrvbAMgVe2rLyW1pA2bW4GnS2j0gow2k4dX8y8oHuv/6Zda0kzDYCpHh4WN2I8kpnJ+av3y7IDrhBeGgpFESmpenOFcE0RKtTBnmsOES5xRxrVI+IB2/oBMPl/7uALSTkIBfKfw2246v+e+8M0FL7SAvfVDx6pGx+JCloJxAwl/TYzaGt3PqA0GqG7vUihxffZA70TLSAHT0L1RtAcuFWZ6mPvdc7HZJkkaW/7MlFL1AoPb18MtwYWH8zYPcLPb4vqEXbIl+mFHGFFEqZYFs4E6sDC1fm0WbRyznkN4E5MNbbFxT8= Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Tue Jun 30, 2026 at 2:36 PM EDT, Matthew Wilcox wrote: > On Tue, Jun 30, 2026 at 01:01:53PM -0400, Gregg Leventhal wrote: >> On an affected 6.12 kernel with CONFIG_READ_ONLY_THP_FOR_FS=3Dy, a file = can >> contain read-only file THPs installed by khugepaged / MADV_COLLAPSE. Whe= n that >> same file is later opened for write, do_dentry_open() notices >> filemap_nr_thps() and drops the page cache: > [...] >>=20 >> This is unsafe if the mapping also contains dirty folios. > > But there shouldn't be any. It should not be possible to have > dirty folios and THPs in the same file unless the filesystem > supports large folios natively. > > If the file is open for writing, the attempt to create THPs should fail. Maybe he means order-0 dirty folios? --=20 Best Regards, Yan, Zi