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Linux x86_64; rv:102.0) Gecko/20100101 Thunderbird/102.5.1 Subject: Re: [PATCH mm-unstable] mm: clarify folio_set_compound_order() zero support Content-Language: en-US To: Sidhartha Kumar , , CC: , , , , , References: <20221207223731.32784-1-sidhartha.kumar@oracle.com> From: John Hubbard In-Reply-To: <20221207223731.32784-1-sidhartha.kumar@oracle.com> Content-Type: text/plain; charset="UTF-8"; format=flowed Content-Transfer-Encoding: 7bit X-Originating-IP: [10.126.231.37] X-ClientProxiedBy: rnnvmail201.nvidia.com (10.129.68.8) To rnnvmail201.nvidia.com (10.129.68.8) X-EOPAttributedMessage: 0 X-MS-PublicTrafficType: Email X-MS-TrafficTypeDiagnostic: CO1NAM11FT089:EE_|CY5PR12MB6575:EE_ X-MS-Office365-Filtering-Correlation-Id: cb35c5af-c518-4bec-3072-08dad8b488a2 X-MS-Exchange-SenderADCheck: 1 X-MS-Exchange-AntiSpam-Relay: 0 X-Microsoft-Antispam: BCL:0; X-Microsoft-Antispam-Message-Info: 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 X-Forefront-Antispam-Report: CIP:216.228.117.160;CTRY:US;LANG:en;SCL:1;SRV:;IPV:NLI;SFV:NSPM;H:mail.nvidia.com;PTR:dc6edge1.nvidia.com;CAT:NONE;SFS:(13230022)(4636009)(346002)(39860400002)(136003)(376002)(396003)(451199015)(40470700004)(46966006)(36840700001)(7636003)(2906002)(4326008)(16576012)(53546011)(478600001)(316002)(356005)(110136005)(54906003)(36756003)(40460700003)(70586007)(31696002)(8676002)(70206006)(40480700001)(86362001)(31686004)(186003)(83380400001)(26005)(47076005)(426003)(336012)(36860700001)(82740400003)(5660300002)(2616005)(41300700001)(8936002)(16526019)(82310400005)(43740500002)(2101003);DIR:OUT;SFP:1101; X-OriginatorOrg: Nvidia.com X-MS-Exchange-CrossTenant-OriginalArrivalTime: 08 Dec 2022 00:38:32.3452 (UTC) X-MS-Exchange-CrossTenant-Network-Message-Id: cb35c5af-c518-4bec-3072-08dad8b488a2 X-MS-Exchange-CrossTenant-Id: 43083d15-7273-40c1-b7db-39efd9ccc17a X-MS-Exchange-CrossTenant-OriginalAttributedTenantConnectingIp: TenantId=43083d15-7273-40c1-b7db-39efd9ccc17a;Ip=[216.228.117.160];Helo=[mail.nvidia.com] X-MS-Exchange-CrossTenant-AuthSource: CO1NAM11FT089.eop-nam11.prod.protection.outlook.com X-MS-Exchange-CrossTenant-AuthAs: Anonymous X-MS-Exchange-CrossTenant-FromEntityHeader: HybridOnPrem X-MS-Exchange-Transport-CrossTenantHeadersStamped: CY5PR12MB6575 Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 12/7/22 14:37, Sidhartha Kumar wrote: > Document hugetlb's use of a zero compound order so support for zero > orders is not removed from folio_set_compound_order(). > > Signed-off-by: Sidhartha Kumar > Suggested-by: Mike Kravetz > Suggested-by: Muchun Song > --- > This can be folded into f2b67a51d0ef6871d4fb0c3e8199f278112bd108 > mm: add folio dtor and order setter functions > > include/linux/mm.h | 7 +++++++ > 1 file changed, 7 insertions(+) > > diff --git a/include/linux/mm.h b/include/linux/mm.h > index 443d496949a8..cd8508d728f1 100644 > --- a/include/linux/mm.h > +++ b/include/linux/mm.h > @@ -999,9 +999,16 @@ static inline void set_compound_order(struct page *page, unsigned int order) > #endif > } > > +/* > + * folio_set_compound_order is generally passed a non-zero order to > + * initialize a large folio. However, hugetlb code abuses this by > + * passing in zero when 'dissolving' a large folio. > + */ Wouldn't it be better to instead just create a new function for that case, such as: dissolve_large_folio() ? > static inline void folio_set_compound_order(struct folio *folio, > unsigned int order) > { > + VM_BUG_ON_FOLIO(!folio_test_large(folio), folio); > + > folio->_folio_order = order; > #ifdef CONFIG_64BIT > folio->_folio_nr_pages = order ? 1U << order : 0; thanks, -- John Hubbard NVIDIA