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Shutemov" , David Hildenbrand , Yang Shi , Miaohe Lin , Kefeng Wang , Yu Zhao , John Hubbard , Baolin Wang , linux-kselftest@vger.kernel.org, linux-kernel@vger.kernel.org, Kairui Song Subject: Re: [PATCH v10 2/8] mm/huge_memory: add two new (not yet used) functions for folio_split() Date: Mon, 10 Mar 2025 12:39:57 -0400 X-Mailer: MailMate (2.0r6233) Message-ID: In-Reply-To: References: <20250307174001.242794-1-ziy@nvidia.com> <20250307174001.242794-3-ziy@nvidia.com> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit X-ClientProxiedBy: BL1PR13CA0251.namprd13.prod.outlook.com (2603:10b6:208:2ba::16) To DS7PR12MB9473.namprd12.prod.outlook.com (2603:10b6:8:252::5) Precedence: bulk X-Mailing-List: linux-kselftest@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 X-MS-PublicTrafficType: Email X-MS-TrafficTypeDiagnostic: DS7PR12MB9473:EE_|CY5PR12MB6204:EE_ X-MS-Office365-Filtering-Correlation-Id: f9cf8f9f-c16f-400c-3c20-08dd5ff2330c X-MS-Exchange-SenderADCheck: 1 X-MS-Exchange-AntiSpam-Relay: 0 X-Microsoft-Antispam: BCL:0;ARA:13230040|1800799024|366016|376014|7416014; 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index < nr_pages; index += new_nr_pages) { >> + struct page *head = &folio->page; >> + struct page *new_head = head + index; >> + >> + /* >> + * Careful: new_folio is not a "real" folio before we cleared PageTail. >> + * Don't pass it around before clear_compound_head(). >> + */ >> + struct folio *new_folio = (struct folio *)new_head; > [...] >> + /* ->mapping in first and second tail page is replaced by other uses */ >> + VM_BUG_ON_PAGE(new_nr_pages > 2 && new_head->mapping != TAIL_MAPPING, >> + new_head); >> + new_head->mapping = head->mapping; >> + new_head->index = head->index + index; > > Why are you using new_head->mapping and ->index instead of new_folio? Because of the “Careful” comment. But new_folio->* should be fine, since it is the same as new_head. So I probably can replace all new_head with new_folio except those VM_BUG_ON_PAGE checks? Best Regards, Yan, Zi