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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 15:47:02 -0400 X-Mailer: MailMate (2.0r6290) Message-ID: In-Reply-To: <7382046f-7c58-4a3e-ab34-b2704355b7d5@kernel.org> References: <20260323190644.1714379-1-ziy@nvidia.com> <20260323190644.1714379-3-ziy@nvidia.com> <7382046f-7c58-4a3e-ab34-b2704355b7d5@kernel.org> Content-Type: text/plain Content-Transfer-Encoding: quoted-printable X-ClientProxiedBy: BL1P221CA0035.NAMP221.PROD.OUTLOOK.COM (2603:10b6:208:5b5::8) To DS7PR12MB9473.namprd12.prod.outlook.com (2603:10b6:8:252::5) MIME-Version: 1.0 X-MS-PublicTrafficType: Email X-MS-TrafficTypeDiagnostic: DS7PR12MB9473:EE_|CH3PR12MB9028:EE_ X-MS-Office365-Filtering-Correlation-Id: d0a15440-f285-49a5-e766-08de8914f661 X-MS-Exchange-SenderADCheck: 1 X-MS-Exchange-AntiSpam-Relay: 0 X-Microsoft-Antispam: BCL:0;ARA:13230040|7416014|376014|366016|1800799024|56012099003|22082099003|18002099003; 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>> bool is_shmem =3D shmem_file(file); >> >> - VM_BUG_ON(!IS_ENABLED(CONFIG_READ_ONLY_THP_FOR_FS) && !is_shmem); >> + VM_WARN_ON_ONCE(!is_shmem); > > Oh, but if that means that khugepaged cannot collapse large folios in > FSes anymore, then this is the wrong approach I suppose? > > I would have assumed that we would now collapse for any files that > support large folios (in PMD size), not stopping to collapse entirely. 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(). Best Regards, Yan, Zi