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emacs 27.1 From: Alistair Popple To: Jason Gunthorpe Cc: Alex Williamson , David Hildenbrand , akpm@linux-foundation.org, minchan@kernel.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org, paulmck@kernel.org, jhubbard@nvidia.com, joaodias@google.com Subject: Re: [PATCH] mm: Re-allow pinning of zero pfns Date: Fri, 24 Jun 2022 11:55:25 +1000 In-reply-to: <20220624013415.GI4147@nvidia.com> Message-ID: <874k0ax1s0.fsf@nvdebian.thelocal> Content-Type: text/plain X-ClientProxiedBy: SJ0PR13CA0013.namprd13.prod.outlook.com (2603:10b6:a03:2c0::18) 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: 0a1e2cf2-8280-4f0f-1833-08da5584bade X-MS-TrafficTypeDiagnostic: DM5PR1201MB2521: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)(366004)(346002)(376002)(39860400002)(136003)(396003)(6506007)(66476007)(66556008)(4326008)(66946007)(38100700002)(8676002)(5660300002)(86362001)(41300700001)(6486002)(478600001)(6512007)(6666004)(316002)(9686003)(54906003)(6636002)(26005)(186003)(8936002)(2906002)(6862004);DIR:OUT;SFP:1101; X-MS-Exchange-AntiSpam-MessageData-ChunkCount: 1 X-MS-Exchange-AntiSpam-MessageData-0: =?us-ascii?Q?Vcf4CFPVW8WV7+H2RDXfFho9xQuXvhIQLTgTLDOGE0bund7FKaoJA+eAHQzy?= =?us-ascii?Q?QYocX9DO5n2eiU3jy8SJondUoEUqvcdyP69AoYEOcwF7d6ifo1tiUa/Jc6Sp?= =?us-ascii?Q?HkqpNHTGZWzPP3+WMhp+O1kH5G1jbuBbCN/DirSOxvyrcgY5RVVcCWzzyrpF?= =?us-ascii?Q?s9yOLKhCjSBffrfTISOtlczRdXIuWQQ6Gxc17kxKgHsADRHIemIaZ4EmQOpI?= =?us-ascii?Q?g7KOTi6SLXyyZWy76b3JsB/3ZmBSGwGPhMXHa488Uj1wImcMDjOQ8ARsxezF?= =?us-ascii?Q?3CIXHd/rScPGnkEpZGHOMOetWCffpTUYu1WlwfUy8ZsGaz+ApUuGz2K/e+tP?= =?us-ascii?Q?8/1nXXETxVHMqmyM5odCfYV9Xil42dlTyuEXFx+IvHAXvX04YhLLGxpoUwIQ?= =?us-ascii?Q?T3IeQL4SD2ZMC8F/or1uzAzscwqwulA864YmbK42HeThAFu2nfEB+W9w79OP?= =?us-ascii?Q?Z5vGUJQTY/1PMx0VStllhhkjtKZiwanXQmKLID856rRgTAwtisVALi4f5+2V?= =?us-ascii?Q?qG8eIUfG1eH8aj5491UCBT7Re1TetrKU7Mh31NKhfmarllvPkLENXQDsYGZ7?= =?us-ascii?Q?RvCPiiFfK7PaNBopxe3iNeSOUkzo9fFOlVNvbM5e5qWonoX8Y203WGYa+j5X?= =?us-ascii?Q?pqD2Vz7MOVrASlrF8v5KjDtKOjLQnlL2HsEmN5BHAc8K+Fz39RWNR/o0A08A?= =?us-ascii?Q?GMiQthxVOxAZCE0XQO9ZuUzIzjg6fwjnAETysonuxCUeOeplMx4cqe46Kogi?= =?us-ascii?Q?/9bcnif7hA2prQ+N+fbG5KamYJRTyPgfZzhE/zv0PRlH0jwO0KSM3m9Gu6Ym?= =?us-ascii?Q?WfJ5aVuTb3WJR+rWtpOEd1jlv5ZnfBJYcGapoP/Ug0IRkQ54gkJ3vaDPBf3i?= =?us-ascii?Q?AzQS1iBFk0PvJx81jlUD6Y+d5c/Mv5QljHZfF6JfYgudfkbl4kdG7RAj5sCx?= =?us-ascii?Q?r/iu6B8RXF+9bvkEqLqybeOJ1oprunbrSmcdjZuTZMXsLCj2fdsDlGCnPQOs?= =?us-ascii?Q?2MaYGwii6Kanjm0YTghree0hhbw2mUv0atWcrD+YW86TY+NV3NOMfCOSFTFF?= =?us-ascii?Q?0oQ2et0YXN7eK5ZjYvPM/l7QIgP8uFRObwU5MICsoeAse5FHhBRxu9Gu6k4g?= =?us-ascii?Q?OduaC6nVVilOg28P/Y6823LKLr+MlidLdWZgVlMUazXJ4M0Bpmj3Iv0RaVbT?= =?us-ascii?Q?+0ZQmaADbUtsJavexLe5BM8kdWN0eEm+27zCjxKGOli9uqlIN5UHpc3hCVRc?= =?us-ascii?Q?W1tlSlwFx00daXFxMNbvp5OpCv8/wZ1n+9ZiArIMCOgf7tBzCMW3DXk3okAt?= =?us-ascii?Q?KSJgrbm3Gs5jqpWQ4g5bQ2vu1z39dvoohb537NONJh3bbBfEwjjV6UVA8JlP?= =?us-ascii?Q?Rjj886S4dFqMUPA1GbIJcSLEeWOR2joN4C3bXd00e2YP4xkq+/KrZEjNHQ8c?= =?us-ascii?Q?OijzCmLcYFMUrr6px4W/ApkZk2VJxNH2240ysAK33H08ZGCeNmJ/wEP7sGE7?= =?us-ascii?Q?rzfBzcTu6yhRD4H9VXJue+wW9NhMeL0gkOdxEjZqERiJQQ4Ys2psf0DnHMf6?= =?us-ascii?Q?xYOzO8w9Bf1gcl8eFZHKzXC5gQulhZeJKjyzaI1W?= X-OriginatorOrg: Nvidia.com X-MS-Exchange-CrossTenant-Network-Message-Id: 0a1e2cf2-8280-4f0f-1833-08da5584bade X-MS-Exchange-CrossTenant-AuthSource: BYAPR12MB3176.namprd12.prod.outlook.com X-MS-Exchange-CrossTenant-AuthAs: Internal X-MS-Exchange-CrossTenant-OriginalArrivalTime: 24 Jun 2022 01:56:18.7070 (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: s+AgW4nh2t5PwXlN1Bs4gZ+XCsHKTEKKxZfvgOdOTOcM/dFf5PPfdltI2aVFo3Ml478cqZN43jG2mmDmJwNxNQ== X-MS-Exchange-Transport-CrossTenantHeadersStamped: DM5PR1201MB2521 Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Jason Gunthorpe writes: > On Fri, Jun 24, 2022 at 10:11:01AM +1000, Alistair Popple wrote: > >> > Hum.. Alistair, maybe you should look at this as well, I'm struggling >> > alot to understand how it is safe to drop the reference on the page >> > but hold a pointer to it on the movable_page_list - sure it was >> > isolated - but why does that mean it won't be concurrently unmapped >> > and freed? >> >> folio_isolate_lru() takes a reference on the page so you're safe from it >> being freed. If it gets unmapped it will be freed when the matching >> putback_movable_pages() is called. > > Hm, I guess I didn't dig deep enough into that call chain.. > >> > Anyhow, it looks like the problem is the tortured logic in this >> > function, what do you think about this: >> >> At a glance it seems reasonable, although I fear it might conflict with >> my changes for device coherent migration. Agree the whole >> check_and_migrate_movable_pages() logic is pretty tortured though, and I >> don't think I'm making it better so would be happy to try cleaning it up >> futher once the device coherent changes are in. > > OK, can I leave this patch with you then? I have no way to test it.. Yep, no worries. > Thanks, > Jason