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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: Matthew Wilcox , Sidhartha Kumar CC: , , , , , , References: <20221207223731.32784-1-sidhartha.kumar@oracle.com> <92965844-c430-8b8e-d9f1-705d7578bceb@nvidia.com> <0187f9c2-e80a-9cde-68bc-c9bdbd96b6fe@oracle.com> From: John Hubbard In-Reply-To: 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: BN8NAM11FT032:EE_|SA0PR12MB4542:EE_ X-MS-Office365-Filtering-Correlation-Id: f8a6a2f1-fb85-4f09-a0eb-08dad9563f25 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:216.228.117.161;CTRY:US;LANG:en;SCL:1;SRV:;IPV:NLI;SFV:NSPM;H:mail.nvidia.com;PTR:dc6edge2.nvidia.com;CAT:NONE;SFS:(13230022)(4636009)(376002)(136003)(346002)(39860400002)(396003)(451199015)(36840700001)(40470700004)(46966006)(31696002)(31686004)(36756003)(86362001)(316002)(7636003)(356005)(70206006)(70586007)(83380400001)(8676002)(4326008)(8936002)(2906002)(41300700001)(478600001)(2616005)(110136005)(16576012)(54906003)(36860700001)(40460700003)(82740400003)(16526019)(26005)(53546011)(40480700001)(82310400005)(5660300002)(47076005)(336012)(426003)(186003)(43740500002);DIR:OUT;SFP:1101; X-OriginatorOrg: Nvidia.com X-MS-Exchange-CrossTenant-OriginalArrivalTime: 08 Dec 2022 19:56:07.4160 (UTC) X-MS-Exchange-CrossTenant-Network-Message-Id: f8a6a2f1-fb85-4f09-a0eb-08dad9563f25 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: BN8NAM11FT032.eop-nam11.prod.protection.outlook.com X-MS-Exchange-CrossTenant-AuthAs: Anonymous X-MS-Exchange-CrossTenant-FromEntityHeader: HybridOnPrem X-MS-Exchange-Transport-CrossTenantHeadersStamped: SA0PR12MB4542 X-Rspam-User: X-Rspamd-Server: rspam04 X-Rspamd-Queue-Id: 38F5B4001D X-Stat-Signature: dnpohgj5z9gn8ucn11hctcthhgw71fdc X-HE-Tag: 1670529370-485616 X-HE-Meta: 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 IlA/h4dl jHqsePa2vUwQLbYUtqyHJ3a405A== 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 12/8/22 11:33, Matthew Wilcox wrote: > None of the above! > > Whatever we're calling this function *it does not belong* in mm.h. > Anything outside the MM calling it is going to be a disaster -- can you > imagine what will happen if a filesystem or device driver is handed a > folio and decides "Oh, I'll just change the size of this folio"? It is > an attractive nuisance and should be confined to mm/internal.h *at best*. > > Equally, we *must not have* separate folio_set_order() and > folio_set_nr_pages(). These are the same thing! They must be kept > in sync! If we are to have a folio_set_order() instead of open-coding > it, then it should also update nr_pages. > > So, given that this is now an internal-to-mm, if not internal-to-hugetlb > function, I see no reason that it should not handle the case of 0. > I haven't studied what hugetlb_dissolve does, or why it can't use the > standard split_folio(), but I'm sure there's a good reason. Sure, perhaps I overreacted to the "abuse of this function" comment, and the whole thing could be fixed up with a clean name, hiding it from the public mm.h API, and...removing comments about abuse! haha :) thanks, -- John Hubbard NVIDIA