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emacs 27.1 From: Alistair Popple To: Jason Gunthorpe Cc: linux-mm@kvack.org, akpm@linux-foundation.org, linux-kernel@vger.kernel.org, "Sierra Guiza, Alejandro (Alex)" , Chaitanya Kulkarni , Dan Williams , Felix Kuehling , John Hubbard , Logan Gunthorpe , Miaohe Lin , Muchun Song , Pasha Tatashin , Ralph Campbell Subject: Re: [PATCH] mm/gup.c: Refactor check_and_migrate_movable_pages() Date: Fri, 05 Aug 2022 11:56:58 +1000 In-reply-to: Message-ID: <87v8r75ssf.fsf@nvdebian.thelocal> Content-Type: text/plain X-ClientProxiedBy: SJ0PR05CA0125.namprd05.prod.outlook.com (2603:10b6:a03:33d::10) To BYAPR12MB3176.namprd12.prod.outlook.com (2603:10b6:a03:134::26) MIME-Version: 1.0 X-MS-PublicTrafficType: Email X-MS-Office365-Filtering-Correlation-Id: 48d5615d-f675-435d-4d12-08da768a02ab X-MS-TrafficTypeDiagnostic: DM4PR12MB5867:EE_ 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:255.255.255.255;CTRY:;LANG:en;SCL:1;SRV:;IPV:NLI;SFV:NSPM;H:BYAPR12MB3176.namprd12.prod.outlook.com;PTR:;CAT:NONE;SFS:(13230016)(4636009)(346002)(396003)(136003)(39860400002)(376002)(366004)(83380400001)(66946007)(6506007)(5660300002)(38100700002)(66556008)(6862004)(4326008)(54906003)(6486002)(66476007)(2906002)(316002)(26005)(186003)(9686003)(6512007)(7416002)(107886003)(6666004)(6636002)(41300700001)(86362001)(478600001)(8936002)(8676002);DIR:OUT;SFP:1101; X-MS-Exchange-AntiSpam-MessageData-ChunkCount: 1 X-MS-Exchange-AntiSpam-MessageData-0: =?us-ascii?Q?e4VSHABe9aOUqCwkIVXOXf2hrWpbbrJrUOFo0mUQoFclgNo6U0N3QRz0zWo9?= =?us-ascii?Q?itZLHp9BeXoZYZ/WdXz0A1J1FcScx4UadDzWXpE4O8UTtQeQVZHxOkJdxWJ8?= =?us-ascii?Q?qgObcmMmBtzWeBXx+8t+CqFCduCN7nsc5IuniD91tVaSN9vZW6bv6mfkSRwD?= =?us-ascii?Q?P7yvhz0P6UepkJikMcnAMFExAfYc7yeiHReq8aXpaPjVzPD7Zs/pvCwxzzry?= =?us-ascii?Q?iwRMI9Y98ocvN6+1nbZwko0+dukcSOO56al3pOzXolsNi29OFlJdz2OIi3uZ?= =?us-ascii?Q?sRpkcp2jpfkCOKQJLEivsP7fAZZ28MQHmZbJItmupO18AQ9dQPUIi+OyCVZF?= =?us-ascii?Q?6SRyzpFOy1Kw4CuWjoBW0aBZAYaTPBfjZrjzpEBWvOMKAR5vmZoFu0uBXjo6?= =?us-ascii?Q?He4IlKn73/zLv8Sl/aozPcia4JWNJypirkA6upiznvKVN9RxhrhJHaDeg+ze?= =?us-ascii?Q?uIoclTlsay8WlXVy9Lyu8qAMqK6B7bY786chCOW5hZuH3WXdcqUUhhvmxdR8?= =?us-ascii?Q?xG7wqqJYuzPVR3M/0wR/RsjhUYF50g0XuAiMJ5M17VfrmlBDzMAFf3QSXqka?= =?us-ascii?Q?l4IdCEEoL1AT7voqFIPRaGIhpfXcVtLRnKS+VH3oI4SnWqtDsY6dB09LtZCC?= =?us-ascii?Q?ZaJ314nuPDm1lPzgQGDtrJluclB0v9FxGpWn6jVvoK6MD34VcBQsDT900IET?= =?us-ascii?Q?6/zuZdotHkLh8K/FpcGUiQXAsFv5iL2zREPXbNb0f1AsWVyjoN8QlEK6on9P?= =?us-ascii?Q?74tlZiZNimZGT65z4RpHhw3af8DjA1J8LA7KZDvHeKspDnFIippXc1ZJIRGQ?= =?us-ascii?Q?Yb7liUFAUbWjQVs4x2MROElBlS/VDZOFE7mCKd53tUlRMue2CK6T4iS5Mz5q?= =?us-ascii?Q?ZblnYKzQSEjJ+HszZEjaxHOmmB35MJSw+v3a7bfRvZG0p/UtENFDI8hAfzht?= =?us-ascii?Q?iswLYm57K1u+KSm+VZO45FL9Rf+bouT3RsfICQNx5EO0bw9/p0EA3ZoWOxQ8?= =?us-ascii?Q?AR3CWEolvNWsseaqr0IDvrJYu2kIyy72VApVZB3zwWUw0FIhvBAqHfZ+QoHP?= =?us-ascii?Q?7+AWKfDiVQ2xehJlY9XW9vP2KeucGrMBPQjR9QShG9eeMbxyoqBdbx87C1X9?= =?us-ascii?Q?6nQ5YvjhdMMDWfhNdPPXnTnr2n6eSpQBazdds7qOrxm1O5dbGVSqrGA2nfCh?= =?us-ascii?Q?gk2VSqn8aPtFMR7Y6YZubE+mFq4W97LkDs2Y/FOvncRjoy9yZF9lL1XegjLu?= =?us-ascii?Q?3kIhGK8LKYTEYOss6WOZiK5q9pmfzY/MVy4v3VZbcfBNeK8UlIQYXxBU1a4o?= =?us-ascii?Q?NsXPX856xlEOIQp4P0Lelf4tIh80pPQDr76btUyYkULVu8QnOv8Njm331g0y?= =?us-ascii?Q?XmBjxJiqdNhEtC7c9SVCq1m4gE0jlYGqZkp2LN/hBqniALtowGwvOz/7/XpG?= =?us-ascii?Q?himxIMCgbw0FtEdc4iP2h5qWdBG2LyKNyu2J1R1c0r/DliFkr17+l0OzGk9f?= =?us-ascii?Q?QPqdocG2roXsXIGt/hB5+1R1nUa4rjFWoIDoxttUxX+iTWOqFLjOxmb+VyN5?= =?us-ascii?Q?THOFRhMhQqJGvMbyKgZD0WNTS8XCPoOfvdrif3dX?= X-OriginatorOrg: Nvidia.com X-MS-Exchange-CrossTenant-Network-Message-Id: 48d5615d-f675-435d-4d12-08da768a02ab X-MS-Exchange-CrossTenant-AuthSource: BYAPR12MB3176.namprd12.prod.outlook.com X-MS-Exchange-CrossTenant-AuthAs: Internal X-MS-Exchange-CrossTenant-OriginalArrivalTime: 05 Aug 2022 02:27:15.1347 (UTC) X-MS-Exchange-CrossTenant-FromEntityHeader: Hosted X-MS-Exchange-CrossTenant-Id: 43083d15-7273-40c1-b7db-39efd9ccc17a X-MS-Exchange-CrossTenant-MailboxType: HOSTED X-MS-Exchange-CrossTenant-UserPrincipalName: sV/ajf4Cx90YaJ3e24Eh7cqcF7ZVV40W5gk9j3kbATLvZ6BKQYPUax+jTw4myl73G9JipY7Twsa6X6YTXCzVdA== X-MS-Exchange-Transport-CrossTenantHeadersStamped: DM4PR12MB5867 Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Jason Gunthorpe writes: > On Thu, Aug 04, 2022 at 01:22:41PM +1000, Alistair Popple wrote: >> When pinning pages with FOLL_LONGTERM check_and_migrate_movable_pages() >> is called to migrate pages out of zones which should not contain any >> longterm pinned pages. >> >> When migration succeeds all pages will have been unpinned so pinning >> needs to be retried. Migration can also fail, in which case the pages >> will also have been unpinned but the operation should not be retried. If >> all pages are in the correct zone nothing will be unpinned and no retry >> is required. >> >> The logic in check_and_migrate_movable_pages() tracks unnecessary state >> and the return codes for each case are difficult to follow. Refactor the >> code to clean this up. No behaviour change is intended. >> >> Signed-off-by: Alistair Popple >> Cc: "Sierra Guiza, Alejandro (Alex)" >> Cc: Chaitanya Kulkarni >> Cc: Dan Williams >> Cc: Felix Kuehling >> Cc: Jason Gunthorpe >> Cc: John Hubbard >> Cc: Logan Gunthorpe >> Cc: Miaohe Lin >> Cc: Muchun Song >> Cc: Pasha Tatashin >> Cc: Ralph Campbell >> >> --- >> >> Originally posted as "mm/gup.c: Simplify and fix >> check_and_migrate_movable_pages() return codes"[1]. >> >> Changes from that version: >> >> - Restore the original isolation failure behaviour and don't fail the >> pup. Instead retry indefinitely. >> - Unpin all pages on retry or failure rather than just failure. >> >> Jason - I dropped your Reviewed-by. I had to remove the changes to make >> error handling follow convention as we need to always unpin the pages. >> We also need the list_empty() checks because we may or may not have >> pages in the list if we found coherent pages. So there isn't much I >> could see to simplify, but let me know if you spot some. > > I don't quite understand this, if the point is to loop on the LRU > indefinately, why not just code that? Why do we need to go around the > big loop? I assume by "big loop" you mean calling check_and_migrate_movable_pages() again? We have to do that after the migration anyway. Looping on the LRU indefinitely inside check_and_migrate_movable_pages() doesn't remove that requirement so I'm not convinced it would simplify things much. It could also lead to deadlock because we may already have other pages isolated from the LRU. - Alistair > Jason