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emacs 27.1 From: Alistair Popple To: Andrew Morton Cc: linux-mm@kvack.org, jgg@nvidia.com, minchan@kernel.org, linux-kernel@vger.kernel.org, jhubbard@nvidia.com, pasha.tatashin@soleen.com, david@redhat.com Subject: Re: [PATCH v2] mm/gup.c: Simplify and fix check_and_migrate_movable_pages() return codes Date: Thu, 04 Aug 2022 10:12:59 +1000 In-reply-to: <20220802171215.3c909e1984ec345ff94af155@linux-foundation.org> Message-ID: <87czdg7tlt.fsf@nvdebian.thelocal> Content-Type: text/plain X-ClientProxiedBy: SYBPR01CA0140.ausprd01.prod.outlook.com (2603:10c6:10:5::32) 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: bb94e1d7-0cf5-4f10-189f-08da75ae4bc1 X-MS-TrafficTypeDiagnostic: DM6PR12MB3737: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)(39860400002)(346002)(396003)(366004)(136003)(376002)(6512007)(6916009)(6666004)(9686003)(26005)(86362001)(6506007)(41300700001)(316002)(478600001)(6486002)(38100700002)(186003)(83380400001)(5660300002)(2906002)(66556008)(4326008)(66946007)(8676002)(66476007)(8936002);DIR:OUT;SFP:1101; X-MS-Exchange-AntiSpam-MessageData-ChunkCount: 1 X-MS-Exchange-AntiSpam-MessageData-0: =?us-ascii?Q?3gjWGpYBDNdbkSDCGxakn8ph0spUYyVFCDYbKj2LiH3bXHJCjuJFi7dVVYjF?= =?us-ascii?Q?poDkTLN7oPFGZzG76VGJIWqDE7LQ3yEVEUp21S9bFfozl+u0pGvS+FKdxFdJ?= =?us-ascii?Q?Up9dAA+qRqFisxZ/Lv5reofPE5lCnSRsnwo7BanOD0B3hgjv9UxYIp1Al8qV?= =?us-ascii?Q?tIngYg20vekqMP7fPPR909MeHPhSFk36qjKY10AO1Q9tmHyDchRKpsKOQULy?= =?us-ascii?Q?RjX19bsJTg9yNSsJd8Fdk5SNkQrh+uWxI0FoYfE4nc+LeLNVQ1pjX/2DhpjY?= =?us-ascii?Q?XvjsdJ8Iz25rjJ9I9WDAEqb8NiOsq9YQ4GS0MFI8JHVp8SZ7MvlFp4l93kak?= =?us-ascii?Q?EHvqs2iWJMVh1X8EMcZs+bV5FiiVKAOMQfQkfQZjgqoTWM89VfdjWxPnBnoZ?= =?us-ascii?Q?tMJaKGsnBzHGtW0nhvRgo+ZvHdK8ooJnyV6gMhBIviE390vthE9cSK4A4dil?= =?us-ascii?Q?R/3Dny29SCMCKkxMKbpBv5BsrwzP7aU0yoIjAFAFNafcUEeJqvnOYb4nUc+q?= =?us-ascii?Q?P1QFF7T2PVSJgKkivUa4rDL37g1uJiSYW37SJ+yYdLlXr2hjvUAMdaqS70Jq?= =?us-ascii?Q?FifWsByQ/WaSD+f3ZRsvBjb8tWuPfj+oRAQ+0UYjoUoV+jz9gLAsKFaVYqhF?= =?us-ascii?Q?coNyk0NIFe+1BMAlb9MnsqrIHOuaxh5ub1juEr4lKo8PnKwkTobaLL17Ktgi?= =?us-ascii?Q?0WC1EHSUBZ918ZD3GHNa4aEFqQg/WoX2Q/5fOBQHbIjtz3P6a3wiqLiqpqUs?= =?us-ascii?Q?MM32MCT71CWsBGWkqx5YxvM7uOlarNcXqeiWmvwfl3rQuR6/85POD/wc7gEu?= =?us-ascii?Q?HcdJw/fv1KMmIIgfiLptxDxYU4x59lnA3ndnwTyAUtB1c9J1TkpyZCyosyQz?= =?us-ascii?Q?dg2T4Qm+/j1jZyKTG+HdT8dBVJs50PtmAMckZUmApi+7ILjv5wliCW4w1qNM?= =?us-ascii?Q?G76hmyT+o3HiuNuv3AVLqmbrONsEFFxBHExyTIspffaBvGzzJ3frWU4/pMR0?= =?us-ascii?Q?sl6Svmtl2PBJyYVtl1VVaYwg5P0gUw34Cm15Wq8XJVTjKM1eZ0CtcqHLUlM0?= =?us-ascii?Q?v4nh/6mQeXZZBv4y3c4JPMB9e73cFZwvP6I2D4IJ0Hy2w/URCKJ8NabP+xME?= =?us-ascii?Q?vidaFeO3KTt4XhauHhKllcxS2N47Yg+0BHM4Vu6Fm0s7SirdoEza1hFwTWoC?= =?us-ascii?Q?Xsr57cX0ntJIeRxH02v2JX04CmP2+UItRd8bYzChrXoA2M6gHTjm8LVfsY1q?= =?us-ascii?Q?gsLMvhmx1yBPWEabYgMmXHPAVo5Twb2D8nwRzKFbSOceIDsRrRzBt63i9R1t?= =?us-ascii?Q?D4MZIEh2w/Gm4kxCqOLOekGqgdmV26i6Z5HterR2aqNXQg5zKCJ/JglUzurS?= =?us-ascii?Q?u2ewowbJHsyF9U+CZ2JTfhZNYKszfuxLswWMKXeDNZg9GTv2Kn92F7beHOT0?= =?us-ascii?Q?lia0yK1BxWfJVGFwZpbYMLNbBtiVFiAqvw9OxI2L1s8XNimNT/IRE/F5p1jG?= =?us-ascii?Q?gOlzRPDfHukz+tYlte2zpdp+7ANjKIanX0z7EXw87jnd6I+OKA4gVk6os2F7?= =?us-ascii?Q?aRvxs7KoAx9nVoIK1HhrGpkMujXY9YqnSAk/Geca?= X-OriginatorOrg: Nvidia.com X-MS-Exchange-CrossTenant-Network-Message-Id: bb94e1d7-0cf5-4f10-189f-08da75ae4bc1 X-MS-Exchange-CrossTenant-AuthSource: BYAPR12MB3176.namprd12.prod.outlook.com X-MS-Exchange-CrossTenant-AuthAs: Internal X-MS-Exchange-CrossTenant-OriginalArrivalTime: 04 Aug 2022 00:14:28.4551 (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: 4gOV8Hduo6jaivGQ8VcQlcIb2DYSW2ng4VD0Roaa8pRMTySErc6ZTw6IKjBQNzceJVxnfQjs+kTeLLS4zyCwMw== X-MS-Exchange-Transport-CrossTenantHeadersStamped: DM6PR12MB3737 Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Andrew Morton writes: > On Tue, 2 Aug 2022 10:30:12 +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. This is indicated by returning zero. When all pages >> are in the correct zone the number of pinned pages is returned. >> >> However migration can also fail, in which case pages are unpinned and >> -ENOMEM is returned. However if the failure was due to not being unable >> to isolate a page zero is returned. This leads to indefinite looping in >> __gup_longterm_locked(). >> >> Fix this by simplifying the return codes such that zero indicates all >> pages were successfully pinned in the correct zone while errors indicate >> either pages were migrated and pinning should be retried or that >> migration has failed and therefore the pinning operation should fail. >> >> This fixes the indefinite looping on page isolation failure by failing >> the pin operation instead of retrying indefinitely. >> > > Are we able to identify a Fixes: for this? Presumably something in the > series "Add MEMORY_DEVICE_COHERENT for coherent device memory mapping"? It seems the infinite loop was desired behaviour so I will re-spin this as a pure clean-up.