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Howlett" , "Vlastimil Babka" , "Mike Rapoport" , "Suren Baghdasaryan" , "Michal Hocko" , "Baolin Wang" , "Nico Pache" , "Ryan Roberts" , "Dev Jain" , "Barry Song" , "Lance Yang" , "Usama Arif" , "Gregory Price" , "Ying Huang" , "Alistair Popple" , "Johannes Weiner" , "Qi Zheng" , "Shakeel Butt" , "Kairui Song" From: "Zi Yan" Subject: Re: [PATCH v3 08/14] erofs: use folio_attach/detach_private() instead of direct assignment X-Mailer: aerc 0.22.0 References: <20260907-remove-pg_private-v3-0-6ae22f9d9272@nvidia.com> <20260907-remove-pg_private-v3-8-6ae22f9d9272@nvidia.com> <5b02f5de-00b6-4f8e-9e30-6d0acedafaf4@kernel.org> <6a465ff3-21ff-435d-963b-385e7e5174fa@kernel.org> In-Reply-To: <6a465ff3-21ff-435d-963b-385e7e5174fa@kernel.org> X-ClientProxiedBy: YQZPR01CA0150.CANPRD01.PROD.OUTLOOK.COM (2603:10b6:c01:8c::9) To IA0PR12MB8374.namprd12.prod.outlook.com (2603:10b6:208:40e::7) Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 X-MS-PublicTrafficType: Email X-MS-TrafficTypeDiagnostic: IA0PR12MB8374:EE_|CH2PR12MB4183:EE_ X-MS-Office365-Filtering-Correlation-Id: 02225031-74d8-41fe-88fa-08df0ee02583 X-MS-Exchange-SenderADCheck: 1 X-MS-Exchange-AntiSpam-Relay: 0 X-Microsoft-Antispam: BCL:0;ARA:13230040|366016|1800799024|23010399003|7416014|376014|10067099003|56012099006|4143699003|11063799006|22082099003|18002099003|921020; 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But after PG_pri= vate >>>> is replaced by checking folio->private in a future commit, it can brea= k >>>> folio_expected_ref_count(), since the folio has private data without >>>> elevated refcount. Change them to use folio_attach/detach_private(). >>> >>> Freezing the folio will properly work I assume, as we'd always freeze w= ith that >>> refcount in mind or remove the reference (detach private) early? >>=20 >> Yes. >>=20 >>> >>> I'm thinking of folio_ref_freeze() in __folio_freeze_and_split_unmapped= (). >>> >>> Or is the ref only very short-lived either way such that we don't care? >>=20 >> The folios here are locked since they are in the process of >> readahead, which requires all folios locked. So they are not reachable >> from folio split code. In additio, the private is deatched and ref is >> decreased before the folio lock is dropped. > > It would be great to summarize this interaction with core-mm (migration/s= plit) > in the patch description. Will update the commit message. --=20 Best Regards, Yan, Zi