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Howlett" , Vlastimil Babka , Mike Rapoport , Suren Baghdasaryan , Michal Hocko , Karim Manaouil , Frank van der Linden , Teja Vojjala , Pravin Tamkhane , Kinsey Ho , Wei Xu , Matthew Wilcox , Davidlohr Bueso , Vinod Koul , Bharata B Rao , SeongJae Park , David Rientjes , Xuezheng Chu , Yiannis Nikolakopoulos , Dave Hansen , Johannes Weiner , John Hubbard , Peter Xu , Rik van Riel , Shakeel Butt , Tejun Heo , Fan Ni , Jonathan Cameron , "Aneesh Kumar K.V" , Nathan Lynch , Frank Li , Dan Williams , linux-mm@kvack.org, linux-kernel@vger.kernel.org, Mike Day Subject: Re: [PATCH RFC v6 3/5] mm/migrate: add copy offload registration infrastructure Date: Mon, 20 Jul 2026 10:44:34 -0400 X-Mailer: MailMate (3.0r7022) Message-ID: <19F47514-EBC4-4659-8252-EC3765D9B601@nvidia.com> In-Reply-To: <87wlupx60s.fsf@DESKTOP-5N7EMDA> References: <20260630-shivank-batch-migrate-offload-v6-0-da95d7e8b8a2@amd.com> <20260630-shivank-batch-migrate-offload-v6-3-da95d7e8b8a2@amd.com> <87wlupx60s.fsf@DESKTOP-5N7EMDA> Content-Type: text/plain X-MS-Reactions: disallow X-ClientProxiedBy: BL1PR13CA0134.namprd13.prod.outlook.com (2603:10b6:208:2bb::19) To IA0PR12MB8374.namprd12.prod.outlook.com (2603:10b6:208:40e::7) Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 X-MS-PublicTrafficType: Email X-MS-TrafficTypeDiagnostic: IA0PR12MB8374:EE_|MW3PR12MB4379:EE_ X-MS-Office365-Filtering-Correlation-Id: 6d4da827-2225-4846-31e4-08dee66d6bef X-MS-Exchange-SenderADCheck: 1 X-MS-Exchange-AntiSpam-Relay: 0 X-Microsoft-Antispam: BCL:0;ARA:13230040|1800799024|23010399003|376014|7416014|366016|22082099003|18002099003|56012099006|4143699003|11063799006|10067099003; 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X-MS-Exchange-AntiSpam-MessageData-ChunkCount: 1 X-MS-Exchange-AntiSpam-MessageData-0: =?us-ascii?Q?NGGU51x+p4dyP8LLHvRPz0wHddGTS9CkMpHaRvhU0XbxdAajpvFNQj7EihOL?= =?us-ascii?Q?uZWMgkuTQT2vA78qsoazmLPg+EUxYFBy/W05cOe1kLd5MRCyIuPsMJdXL0hl?= =?us-ascii?Q?fee+Ttz49IoafHfdKoas0xX2ScL72omwf/6cYq4X0KOwUbZnTuaRl7/AO0b4?= =?us-ascii?Q?Kpus0cicRhGxXYYeObQ48Ru/CGyUI9c42dJQs6aU/ePjb2xycO8jVv7pDAme?= =?us-ascii?Q?wO6QYIt4nN9SVreOJhwMF8MciY9yT7XdiYIZ/grEXSW6yc4x6talAuCiFX24?= =?us-ascii?Q?dNbIBQ/s/dii38TQdiHmp40hXSFAwO0IThW1Zn5GXHqn7q4PUBJATe3aJ0o3?= =?us-ascii?Q?OcTBAa0vTWSOvCymjssCKvj1ae2K+rx6S8K74kN1f8Xcf5R97K9f6gBhPcup?= =?us-ascii?Q?e4m7S2xKW3c1PGCl4oTig4SKuUX0qpZn5irqatFKxoY7nS9LCE/3UjOegnmz?= =?us-ascii?Q?xbULni1VRHcdd5tIfTd1N2Fy7n14+cyj/wg/lInHsbjXllISsDfJpsmzv7uw?= =?us-ascii?Q?RwvtuFuzioxjC6i6Kah7nS/MWK2qdOtSbGcP30ZEyJ4sXggytjuDFo9dABxg?= =?us-ascii?Q?C5coWGITFvNMiJaZN2jAxRQlvF8eUEyiGejJfVKQ+AE5cH9NwxVPBTm38/Ef?= =?us-ascii?Q?9x+WNgQhijxQxPTbMoXY4/qeiBdpP5Rmroa5Xz9JMVEiFn2yynUbCP705OaZ?= =?us-ascii?Q?bhVuJwGzJzKMrgq0k+CuToV3O2x7yQXRW1E/5VZvbIoq0Lr7tPIQ5GYtkJ8Q?= =?us-ascii?Q?TKf4FFnttDAre3rPApwXie9VG2n+VW+9YrORTl2C+f3VM9aypYsW28NLqS0/?= =?us-ascii?Q?424UUvNYqrsw0TcHhZHi498nZ1VB2LZkUhDp+kKB8OeG6PSxszVMWqKpINQV?= =?us-ascii?Q?SlOe17jIl0G8FHkQMZfMAoKOO8UvuQgodtpjADH3PPJAbwmLWVa0KNqA9hiL?= =?us-ascii?Q?8nfhu7RQZQhzbG2RNpBPvy4yzluY3UvhCAZi494lyuV0S4laO+FpAQJ6B9jO?= =?us-ascii?Q?iSb2ADqFbHe/r0K/5uwzQRB7zfCnT8/FdR4f0mEc6Kuyii0WdM9HJtPPAdO2?= =?us-ascii?Q?/ZG6apUuaKWySmlliKMQ1EgzQthFxdmwYA5jb+HefJJSlKIvdj5LOdg3ixvP?= =?us-ascii?Q?F4MJixBN+2sYR32vLBbDkFEcISF1yYD0aTFOhhJKHnbtahXUCj/QvvyIUq54?= =?us-ascii?Q?eqWi4i0Se1ZgpipuR29ST0dcSfT7RMSFrfW+QH6keyNJFpDekkPECEAIj9up?= =?us-ascii?Q?ZjMM7meTPEx2xK7S6n6tBR6BqolKF5yFB5/tqe6ErksRGL4wJyoqYOg+8uPj?= =?us-ascii?Q?pXUd6w1GStdRRwtzm4VhD/i+T6h3TK05JDUUa75JwH/HivpjAsh+7KlwaNvB?= =?us-ascii?Q?oRd+IcZNsEx6pm9FABzQvnzbc90nHxEMlR+DfagoaaFPDT5/803EmXB5IEuI?= =?us-ascii?Q?QGiS7tziiu1JOqAhdfPZtWp82Gx/jAUfAknahcQQ0wEdkysxCRQ5M8fcr2Uo?= =?us-ascii?Q?qxMeUk3i1gBlWD6yDQkfL4yZ14q1wtMuTSBHXtlqqKhXT48Rzjx0quvTPgLn?= =?us-ascii?Q?DsXUE2iPuc+M1YZ4T6oLVp77VS5m80CXCQ/w/2sJWkqwRvipAeMD7sA4b9ae?= =?us-ascii?Q?Teb9rrC1ceULMjZXlez1ZIzhPT/TMPaHnvi5VUYM6G9keAggaKTQOr4gh3Hk?= =?us-ascii?Q?J/r32/iUAFxt98FuJRgRRrFoliqI/qNasCcqKqhhFCVwZAP0?= X-OriginatorOrg: Nvidia.com X-MS-Exchange-CrossTenant-Network-Message-Id: 6d4da827-2225-4846-31e4-08dee66d6bef X-MS-Exchange-CrossTenant-AuthSource: IA0PR12MB8374.namprd12.prod.outlook.com X-MS-Exchange-CrossTenant-AuthAs: Internal X-MS-Exchange-CrossTenant-OriginalArrivalTime: 20 Jul 2026 14:44:37.1708 (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: J8R2VzyxaFTtqmD8KcmVbsXNJKEeGm8iW35zD8U9VSvXVnqsiUtgLhF2tKi9la2c X-MS-Exchange-Transport-CrossTenantHeadersStamped: MW3PR12MB4379 On 20 Jul 2026, at 7:19, Huang, Ying wrote: > Shivank Garg writes: > > [snip] > >> diff --git a/mm/migrate.c b/mm/migrate.c >> index 41b732e78a67..4fed3110ca0a 100644 >> --- a/mm/migrate.c >> +++ b/mm/migrate.c >> @@ -43,6 +43,7 @@ >> #include >> #include >> #include >> +#include >> >> #include >> >> @@ -51,12 +52,6 @@ >> #include "internal.h" >> #include "swap.h" >> >> -/* For now, never offload. Wired up in later patch. */ >> -static bool migrate_should_offload(int reason) >> -{ >> - return false; >> -} >> - >> static const struct movable_operations *offline_movable_ops; >> static const struct movable_operations *zsmalloc_movable_ops; >> >> @@ -2050,7 +2045,7 @@ static int migrate_pages_batch(struct list_head *from, >> >> /* Batch-copy eligible folios before the move phase */ >> if (!list_empty(&unmap_batch)) >> - migrate_folios_mc_copy(&dst_batch, &unmap_batch, nr_batch); >> + migrate_offload_batch_copy(&dst_batch, &unmap_batch, nr_batch); >> >> retry = 1; >> for (pass = 0; pass < nr_pass && retry; pass++) { > > Found a difference between v5 and v6 here. In v5, migrate_pages_batch() > checks the return value of migrate_offload_batch_copy() and acts > accordingly. While in v6, it does not. Why was this changed? > > IIUC, FOLIO_CONTENT_COPIED is now used to indicate a copy failure. Is > this necessary? Is it possible that some (but not all) folios fail to > be copied? Based on the discussion[1], FOLIO_CONTENT_COPIED is used to indicate both 1. folio is copied via offloading, and 2. MC copy failure. So the code no longer needs to store the return value of migrate_offload_batch_copy() and can just check dst->migrate_info & FOLIO_CONTENT_COPIED. For 32bit, FOLIO_CONTENT_COPIED is always 0, so all folios are always copied in the serialized path. Hmm, that might be causing double copying, since migrate_folios_mc_copy() copies batched folios and later migrate_folios_move() copies them again since dst->migrate_info & FOLIO_CONTENT_COPIED is always false. Maybe we could make migrate_folios_mc_copy() return immediately in 32bit, otherwise, we will need to find somewhere else to store FOLIO_CONTENT_COPIED. [1] https://lore.kernel.org/all/c2bfdf39-8caa-43bd-b1ad-2285b4cc767a@amd.com/ > > [snip] > > --- > Best Regards, > Huang, Ying Best Regards, Yan, Zi