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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 11:45:08 -0400 X-Mailer: MailMate (3.0r7022) Message-ID: In-Reply-To: <56468737-471c-4d92-af01-a0c93cafdb1d@amd.com> 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> <19F47514-EBC4-4659-8252-EC3765D9B601@nvidia.com> <56468737-471c-4d92-af01-a0c93cafdb1d@amd.com> Content-Type: text/plain X-MS-Reactions: disallow X-ClientProxiedBy: BN0PR04CA0092.namprd04.prod.outlook.com (2603:10b6:408:ec::7) 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_|SA0PR12MB7091:EE_ X-MS-Office365-Filtering-Correlation-Id: 2c165a84-e127-4e52-ded0-08dee675e248 X-MS-Exchange-SenderADCheck: 1 X-MS-Exchange-AntiSpam-Relay: 0 X-Microsoft-Antispam: BCL:0;ARA:13230040|1800799024|23010399003|366016|376014|7416014|18002099003|22082099003|10067099003|11063799006|56012099006|4143699003; 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X-MS-Exchange-AntiSpam-MessageData-ChunkCount: 1 X-MS-Exchange-AntiSpam-MessageData-0: =?us-ascii?Q?z2CmmKiiKDJO7KTse3yFURLGsx9fbZHI90jISBD0/EFzuL5X2kBFa9zE7E5q?= =?us-ascii?Q?mTv0L3SThRgNbVbgJgZyxmwUS7e4JFpzZXVHpaptjdhBO2mq5x3z8jnzMlSR?= =?us-ascii?Q?BhedhvNuB297YJPViXvt33b/Ye2rh5448U4L8ei5DHwwmu3Ens00E9ZE1nB9?= =?us-ascii?Q?CH+Dz5D+fGD/gylXbao092IMiJGEDeXCz8emzN6u5axpHMfwW9Qmi2YZ5qOE?= =?us-ascii?Q?jfjVZflE4bzoo+SW5eckppcl2/OoeeIZPuMvj87PXQqXMPZJ0Eu1GheKmwZx?= =?us-ascii?Q?F4btv3UDlmaKlMmImvw6zgbafESEVmw0Dbyo+YT8xsPwLlZHCyq5vR+74hmm?= =?us-ascii?Q?uGUaB6Alhqc7HTxqhwq9Vgtarye68IqbI8sB4tWo3B1R7X7agsrDiMBFM1H9?= =?us-ascii?Q?Za2h2QjSjkYBjJjZzDB9xwd2D8x2z5VdVAhL/3NEEA5Xg2MmamRxA1X4EpLD?= =?us-ascii?Q?wLVS8p7m3KWuOavGoSHySqjkC7xNuEVdO9NrxhdppB+3oykj1k64233BmFl5?= =?us-ascii?Q?f3l77bqoxbBAx4TbCI5SBHMGOomyFFjhD8s2UpwJrqw3C646e1/IcDZH5AgU?= =?us-ascii?Q?kDNGhttz15apq/aQl7QFrKBNiDIoKn70UgcAKJA+25rerx/tbr+x5KgHXwju?= =?us-ascii?Q?/lsTy+9kifiw/p5V4HFJ9WPM0Avd+huXRlFBZBK9eZODbFaK5WND8N9NlXMR?= =?us-ascii?Q?Z6HICu4czbDho7/IEVNDNdDy0FJ5V54CA28neHpqsJvIuoaL284M3BnTwMMw?= =?us-ascii?Q?02VZlOqpOR21arpy/W3CJyXoyy/E1Ubw65rwe0fgQfAzWxq6Tw9fEUCnaZ6T?= =?us-ascii?Q?3c/kKGckk9F9M+pkQSvnCn/Ra95ETN76tUXfwlEIW1Q92IyQxAPJ0OCdLuKl?= =?us-ascii?Q?xJelFnT/thakzLl4nFykhmsBZ0xnZixsTgqPHEpOCFwEJl+HsuojOv6t272J?= =?us-ascii?Q?Q34zzFV/UM1yj1KwYddJv3pxbaKQXP/f7jNJJ45L5+o3QyCIvf6tBlU+dvhw?= =?us-ascii?Q?gaRRn2r0tvGQEIoG8BITE5A616NQ2RF/LIPYihd6PKHHZ7FMEZM7yiuoYlJf?= =?us-ascii?Q?VhFNXKKbR2/Lw8AOVZYcIwAhBlVOhob19d857yOpZ7+8wdXrCX2qrAsxI46o?= =?us-ascii?Q?tM+WYpc/1QHQJzLhP68vqlzPDZtWozhw+G2eS1S8WAXlSH6uAAH9XTtZ+13h?= =?us-ascii?Q?C010pNa03KOXkfF0v4cKm28nTCvITz1vRbfTslp/ovfLeJee2KIH7S9noh+G?= =?us-ascii?Q?BcVVe6PZ70PdPVbneEg9HhvWMTfwv/tvoaQMa7zJojKjUV8lTEFC9ZrFzRAG?= =?us-ascii?Q?Zx9EUznzWVcXNdaTCdzhKJLRFJgJnPFmy5DXMOXF/JZmyabAZaTaSKlTr3W8?= =?us-ascii?Q?Skq9hWED0pRnlHc34PiyVgEifDWyZ4UBt4sC0UyyhV7GjVitO31kjbL+v8y1?= =?us-ascii?Q?pDlKZfCY8nAXWgOpcWYRDa1Y1nmc+O+VpuyCJRcYDocDQ1HJudIVagL75xbz?= =?us-ascii?Q?aqkym5hSRlnkmd9EVFa9WwXc8KCWFo4x88sikj23ZpWCURa3S4yzFfKRvLKy?= =?us-ascii?Q?tr5HqUJ99PQM2Kg47mB3Riz0+XHHRlripWVD4mmBgwvXOHhBUHSd01bMPVI1?= =?us-ascii?Q?scrdHju+W/bcvCI4/5BxYVunc7/m9h97H3TTfynAQxGdi8Suj6NvR0niNzAK?= =?us-ascii?Q?xEX1Uitd6/P10I7akBagDxJQG1vphl90RrwmURRSpLY0xz13?= X-OriginatorOrg: Nvidia.com X-MS-Exchange-CrossTenant-Network-Message-Id: 2c165a84-e127-4e52-ded0-08dee675e248 X-MS-Exchange-CrossTenant-AuthSource: IA0PR12MB8374.namprd12.prod.outlook.com X-MS-Exchange-CrossTenant-AuthAs: Internal X-MS-Exchange-CrossTenant-OriginalArrivalTime: 20 Jul 2026 15:45:11.8615 (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: ClYQmjZvvxvJ82NoGk0r51Ht/IHCepMLWJ8fn/IBYQ+OWQ9dz8iyAD1Z+urSI7Ru X-MS-Exchange-Transport-CrossTenantHeadersStamped: SA0PR12MB7091 On 20 Jul 2026, at 11:32, Garg, Shivank wrote: > On 7/20/2026 8:14 PM, Zi Yan wrote: >> 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/ >> >>> > It is not cause double copying. > migrate_should_offload() /and migrate_offload_enabled > gate if folio can be added to unmap_batch/dst_batch. So migrate_should_offload() is actually migrate_should_offload_batched_copy(). 32BIT does not get batched copy nor offloaded copy. > > migrate_offload_enabled branch is enabled from the offload driver like DCBM (which > again depends on 64_BIT) will call migrate_offload_register(). > > I think I can add a defensive 64_BIT check in migrate_should_offload() to prevent > any potential bugs. I think a better name would be helpful and sufficient. BTW, ideally, batched copy and offloaded copy are two separate features and could be enabled separately. But considering the hassle of finding a place to store FOLIO_CONTENT_COPIED on 32BIT, it might be fine to have a combined batched and offloaded copy. Best Regards, Yan, Zi