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dkim=none (message not signed) header.d=none;dmarc=none action=none header.from=nvidia.com; Received: from IA0PR12MB8374.namprd12.prod.outlook.com (2603:10b6:208:40e::7) by LV3PR12MB9439.namprd12.prod.outlook.com (2603:10b6:408:20e::16) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id 15.21.546.21; Tue, 27 Oct 2026 02:34:51 +0000 Received: from IA0PR12MB8374.namprd12.prod.outlook.com ([fe80::d85f:4c87:ae84:3f16]) by IA0PR12MB8374.namprd12.prod.outlook.com ([fe80::d85f:4c87:ae84:3f16%6]) with mapi id 15.21.0546.021; Tue, 27 Oct 2026 02:34:51 +0000 Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset=UTF-8 Date: Mon, 26 Oct 2026 22:34:50 -0400 Message-Id: Subject: Re: [PATCH 11/16] mm/shmem: rescan after nonuniform folio splitting Cc: "Andrew Morton" , "Gregory Price" , "Joshua Hahn" , "Rakie Kim" , "Ying Huang" , "Johannes Weiner" , "Vladimir Davydov" , "Michal Hocko" , "Hugh Dickins" , "Baolin Wang" , "Lukas Czerner" , "Carlos Maiolino" , "Christian Brauner" , "Jan Kara" , "Daniel Verkamp" , "Jeff Xu" , "Muchun Song" , "Oscar Salvador" , "David Stevens" , "Matthew Wilcox (Oracle)" , "William Kucharski" , "Chris Li" , "Kairui Song" , "Nhat Pham" , "Miaohe Lin" , "Naoya Horiguchi" , , , To: "Kiryl Shutsemau" , "David Hildenbrand (Arm)" From: "Zi Yan" X-Mailer: aerc 0.22.0 References: <20261026-fixes_shmem-v1-0-703206d5fa0c@kernel.org> <20261026-fixes_shmem-v1-11-703206d5fa0c@kernel.org> In-Reply-To: X-ClientProxiedBy: BL1PR13CA0176.namprd13.prod.outlook.com (2603:10b6:208:2bd::31) To IA0PR12MB8374.namprd12.prod.outlook.com (2603:10b6:208:40e::7) X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Post: List-Help: List-Subscribe: List-Unsubscribe: List-Owner: Precedence: list MIME-Version: 1.0 X-MS-PublicTrafficType: Email X-MS-TrafficTypeDiagnostic: IA0PR12MB8374:EE_|LV3PR12MB9439:EE_ X-MS-Office365-Filtering-Correlation-Id: a08dab7d-6b84-4a74-62ac-08df33d2e097 X-MS-Exchange-SenderADCheck: 1 X-MS-Exchange-AntiSpam-Relay: 0 X-Microsoft-Antispam: BCL:0;ARA:13230040|1800799024|23010399003|376014|7416014|366016|261026121527099003|11063799006|4143699003|56012099006|261009223027099003|261021135927099003|261021121427099003|261022105027099003|10067099003|22082099003|18002099003|6133799003|261026140227099003; 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A nonuniform split can >> leave that folio large, so the scan skips the newly created folios. >> Hole punching then leaves pages within the hole allocated even though >> they could be discarded. >>=20 >> For example, a fault below the hole can allocate a 2 MiB folio after >> boundary handling. Punching a 1 MiB hole at offset 64 KiB splits the >> folio successfully but leaves the original folio at order 4. The scan >> continues past all 512 pages, leaving 2 MiB allocated instead of 1 MiB. >> The hole reads as zero, but the pages and their block charges remain. >>=20 >> Restart when the original folio is still in the mapping after partial >> truncation, identified by checking folio->mapping. If the helper >> removed the whole folio, no rescan is needed. >>=20 >> Fixes: 7460b470a131f ("mm/truncate: use folio_split() in truncate operat= ion") >> Cc: stable@vger.kernel.org >> Signed-off-by: David Hildenbrand (Arm) > > Acked-by: Kiryl Shutsemau (Meta) > > Do we want split state after truncate_inode_partial_folio() to be > communicated more explicit? ->mapping check works, but it might not be > obvious why. Just an idea for a follow up. Zhang Yi's truncate fix has done that. truncate_inode_partial_folio() returns true only if the folio is split[1]. His patches are in mm-stable but not upstreamed yet. [1] https://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm.git/tree/mm/tru= ncate.c?h=3Dmm-stable#n248 --=20 Best Regards, Yan, Zi