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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: Muchun Song CC: Sidhartha Kumar , Mike Kravetz , Matthew Wilcox , , Linux Memory Management List , Andrew Morton , Muchun Song , , David Hildenbrand References: <20221207223731.32784-1-sidhartha.kumar@oracle.com> <92965844-c430-8b8e-d9f1-705d7578bceb@nvidia.com> <0187f9c2-e80a-9cde-68bc-c9bdbd96b6fe@oracle.com> <2723541a-79aa-c6b5-d82c-53db76b78145@oracle.com> <36ddac45-ecd0-e2d2-e974-8c85ca503053@oracle.com> <20cc2088-b66e-28d1-a529-414e82146336@nvidia.com> <434a111c-7f1a-0018-6bd2-561cb382deea@oracle.com> <7d72778e-7305-18e9-edf4-ed55a98aa7e2@nvidia.com> <00222280-DBDD-49A3-92A5-05112359AE30@linux.dev> From: John Hubbard In-Reply-To: <00222280-DBDD-49A3-92A5-05112359AE30@linux.dev> Content-Type: text/plain; charset="UTF-8"; format=flowed Content-Transfer-Encoding: 7bit X-Originating-IP: [10.126.230.37] 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: DM6NAM11FT038:EE_|PH7PR12MB7966:EE_ X-MS-Office365-Filtering-Correlation-Id: aa91f9c5-f5de-4998-bddc-08dada29db81 X-MS-Exchange-SenderADCheck: 1 X-MS-Exchange-AntiSpam-Relay: 0 X-Microsoft-Antispam: BCL:0; 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X-OriginatorOrg: Nvidia.com X-MS-Exchange-CrossTenant-OriginalArrivalTime: 09 Dec 2022 21:10:53.6167 (UTC) X-MS-Exchange-CrossTenant-Network-Message-Id: aa91f9c5-f5de-4998-bddc-08dada29db81 X-MS-Exchange-CrossTenant-Id: 43083d15-7273-40c1-b7db-39efd9ccc17a X-MS-Exchange-CrossTenant-OriginalAttributedTenantConnectingIp: TenantId=43083d15-7273-40c1-b7db-39efd9ccc17a;Ip=[216.228.117.161];Helo=[mail.nvidia.com] X-MS-Exchange-CrossTenant-AuthSource: DM6NAM11FT038.eop-nam11.prod.protection.outlook.com X-MS-Exchange-CrossTenant-AuthAs: Anonymous X-MS-Exchange-CrossTenant-FromEntityHeader: HybridOnPrem X-MS-Exchange-Transport-CrossTenantHeadersStamped: PH7PR12MB7966 X-Rspamd-Server: rspam07 X-Rspamd-Queue-Id: 0FB9C40008 X-Rspam-User: X-Stat-Signature: g4x33ug5sc3w4kqsj3u4u6ncq5t358ph X-HE-Tag: 1670620255-108543 X-HE-Meta: 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 Vj7Zw2Mr f3U3MMDGW1xjDOMgcewFv9r9MLw== X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On 12/9/22 06:27, Muchun Song wrote: > From you advise, I think we can remove VM_BUG_ON and handle non-zero > order page, something like: Yes, and thanks for summarizing all the individual feedback into a proposed solution. If we go this route, then I'd suggest a little note above the function, such as: /* * For non-large folios, this will have no effect, other than possibly * generating a warning, if the caller attempts to set a non-zero folio order * for a non-large folio. */ > static inline void folio_set_order(struct folio *folio, > unsigned int order) > { > if (!folio_test_large(folio)) { > WARN_ON(order); Better make that a WARN_ON_ONCE(), to avoid taking the machine down with excessive warnings in the log. > return; > } > > folio->_folio_order = order; > #ifdef CONFIG_64BIT > folio->_folio_nr_pages = order ? 1U << order : 0; > #endif > } > > In this case, > > 1) we can handle both non-zero and zero (folio_order() works as well > for this case) order page. > 2) it can prevent OOB for non-large folio and warn unexpected users. > 3) Do not BUG. > 4) No need to rename folio_set_order. > > What do you think? If the new behavior is OK with everyone, it seems good to me. thanks, -- John Hubbard NVIDIA