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Mercier" , Isaac Manjarres Subject: Re: [RFC PATCH] mm/page_alloc: Add PCP list for THP CMA Date: Mon, 04 Aug 2025 15:00:27 -0400 X-Mailer: MailMate (2.0r6272) Message-ID: <8A3D2D44-DCE9-48FC-A684-C43006B3912F@nvidia.com> In-Reply-To: References: Content-Type: text/plain Content-Transfer-Encoding: quoted-printable X-ClientProxiedBy: BL1PR13CA0205.namprd13.prod.outlook.com (2603:10b6:208:2be::30) To DS7PR12MB9473.namprd12.prod.outlook.com (2603:10b6:8:252::5) 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: DS7PR12MB9473:EE_|BN5PR12MB9510:EE_ X-MS-Office365-Filtering-Correlation-Id: 017c7657-774f-4cbe-5e7c-08ddd3892eb8 X-MS-Exchange-SenderADCheck: 1 X-MS-Exchange-AntiSpam-Relay: 0 X-Microsoft-Antispam: BCL:0;ARA:13230040|366016|1800799024|7416014|376014; X-Microsoft-Antispam-Message-Info: =?us-ascii?Q?UMU2mA0H5igYGj4zTGk2b6MF0Rwif6Zy1JcmudmCE5pnp98EtWkq4Tz7Q4vB?= =?us-ascii?Q?1+8AqF3hTj3hD+w+g1PSJiq44nLf2Wzndb2NztQztzI0tAKYAU50w/gKu6Tk?= =?us-ascii?Q?MwhvgV2nO1rkHunmowuflE2qohRnt8cWLYidcmCXEabp3R3MjZr8xdsL6mtD?= =?us-ascii?Q?cpu5a9xEtOZrsJdbNlvlA7+qQkZCqEJtoTyndKfFXBO6T2PFu9RMnBrgYEkz?= =?us-ascii?Q?Z1B4qec1J1SInvra7nOXEBKeuUXghiIC4U/LRG81o/yuvbclF79AFCAvMsg8?= =?us-ascii?Q?CGf0k+yn8CTVEsgBrF9QJ/ynBtEKrhHaStiIZHW1aQGNzDMNwi72a1waSbII?= =?us-ascii?Q?Ec12AJY4Vu3B8rEDFHVIxviU2VMFzSEY0J4QiLTkD1WYDXxtIpHK54+EWfD8?= =?us-ascii?Q?KB0ZgFgAwZECPqRNsuFeRm9a3frWmBXoqNvq2pRjiQ0ht0WDvORlG3uFVh6b?= =?us-ascii?Q?5E3V3zd5+81sx3gVazsrdWRuP+OvkKjRZWhcSlAEOpIwH9kZAbUaYuUh+cmr?= =?us-ascii?Q?Mo5XkUHLBrlm3htXLImcERcS7B7fuLqEV1Zj66CRX+3XICe0hheBZDv5RDF6?= =?us-ascii?Q?lYlitKH3MMG/S0XKLfD0HIRw6rSFs4JI5DKgQU2/n2cOnY+0LOFpco2DRM7h?= =?us-ascii?Q?3XbYFxdS3z/g8eAx/RtquUOVuV0oImpC3474O9HijSznL12/EswABg4R1tGu?= =?us-ascii?Q?1PKTO5RSQBM4ZrTtx1MUeyMVYC+HOBBIRIC5LEZkS0YO4DddKJmhqDYcjvIY?= =?us-ascii?Q?UCAZulJN1+2nukwXHprij3TmMi7oz1b1A3fxG8MfYfAMG+em7+kofeyVNruw?= =?us-ascii?Q?ldx2XNNG572lbWRFYsQJgIHJ3HJ3SCjJI6Td+XMm3YAGTKd4iwhw7m4bMCgm?= =?us-ascii?Q?Vh2ro9ga/72FQdT6Qwz2gQf+pTsdgUj472C1r9oMzomDHsodCU68aeEmGzUy?= =?us-ascii?Q?Us9y1MOdGdO07kGiATYGQwJZSxHz3UzF09eaI0W1ZUjN/XsYHFnm8zd7Ozl/?= =?us-ascii?Q?fJtRwlTrNeSIobfRYleQVmV8E3GI++/ciIcvkiQB0WrRFsaG57yBn+dWJl+v?= =?us-ascii?Q?/0w7s5I/OEoyXPe1JqsjNc/Fj8M277vMpmFuf5BBGIk0J/N903/JpDJm5TCO?= =?us-ascii?Q?QWfjjfmxHg7UmnO0ItmfDU5cio630CVqG8zAcMjpv+hi/nXVw8Ihe69iKcTM?= =?us-ascii?Q?AyBNsQwPE+Sq/cT7ES6LjC0J0wlAJApiahARGSpmk2JEfUoYv5Q8ehoklmqq?= =?us-ascii?Q?IXUPLY1pLN6s41Dp7J7lxFoKxPkkAG9rxV0gMoyip5D5BmpaPkhzTUZHIYPH?= =?us-ascii?Q?d39B0o7bpsoPiP8UwMDgxndm3ojgbUAxB02j+q35Lgr9Tl+VQdfknP6CkLw6?= =?us-ascii?Q?+TULtHU3pneWdnCqL+URg68KzXlmqC7xVG5RoHOGNOR9YW+TCXKRLIrXxyWw?= =?us-ascii?Q?dhTmpYgt6L8=3D?= X-Forefront-Antispam-Report: CIP:255.255.255.255;CTRY:;LANG:en;SCL:1;SRV:;IPV:NLI;SFV:NSPM;H:DS7PR12MB9473.namprd12.prod.outlook.com;PTR:;CAT:NONE;SFS:(13230040)(366016)(1800799024)(7416014)(376014);DIR:OUT;SFP:1101; X-MS-Exchange-AntiSpam-MessageData-ChunkCount: 1 X-MS-Exchange-AntiSpam-MessageData-0: =?us-ascii?Q?gLjVPctGu/FbVtsGURHarDkWHQXnkxpSMs9H76U9CO7lctLgT81gqsOn/t7g?= =?us-ascii?Q?C8rNLWiaA8lFRNXqEs3usy2b+svOOu/wqN8myM+mdgXHfZZrHSO2L5eTsjg0?= =?us-ascii?Q?BupvohYqBDyNNaCBwRWrzP2W2qof5uIBdtUASkqdIfxe3Ae/mNDy7oczyAii?= =?us-ascii?Q?xfYEjFe5mx/tHvLg0HjNx4HhJTr2mV6b9h/3ky0uTgHDeX5fsJgGlWWWJQpl?= =?us-ascii?Q?4e3IA4zj2PwXzsnHbHK5GvP/0KTQjimwHCSefZ0KK/SDJShctERFwsXCPXzp?= =?us-ascii?Q?PHVpb7uxJbQKg9OG59JJzhA9PWDiV+TOjLM7Vk/QEdsjoPNBfzdOX6UUc440?= =?us-ascii?Q?0CuUc1bCkN4kuOFtXtGuLevOaTYMRCMLkX7z1EbhzLp+Hb4wRQHIAMccbEI2?= =?us-ascii?Q?Vp0+MD0Mvl8ZPk5Kjm9okfhe7Upb83SPEw/eTtzDG/RFfFLptKi9UHxAALEJ?= =?us-ascii?Q?JLmC43tWZS40w3t71RBLALigGTQ7PZQuiQQqO5cdWyt+FsGxQurhVw8asFq8?= =?us-ascii?Q?ijaQGPsZtBjPso2FjAHpx0zP4svAt2F37fAnv/EF/I4/wDQWgnFvNk/VWO7m?= =?us-ascii?Q?44wTIj7YcUd3jh8tvUc5AHxwD1qJyAu3EwvfpLdWwVa03Ne4dKUV3i17LFk6?= =?us-ascii?Q?iD2j24lCglMqa/TvMBgDB8hhbi5yWPXjYSVrbjMmuqx5Q3vXdJvjSleMXRdp?= =?us-ascii?Q?WujmYXZ/8tTRe5Zi1gGjObvckXTfAdQNL/Y4YQj++7prbFiLMNcYaBeG4Nao?= =?us-ascii?Q?nyndDPqjgX4T1WuQbbdRLmKtQYi6/7lSLDGIa8fKadFTLyaSDrwWGwEyhexn?= =?us-ascii?Q?Fd/1JkqZVHQIQZjN71kWrOt3EFTIeatuLyPnRTDIYf+UfunAC6lMyfxQAbso?= =?us-ascii?Q?v+PK0hLc3hjHisu3Th3z7R51WozhMuCqXGA9D/Omr54JIDMLcQm3XOaYUvLs?= =?us-ascii?Q?FFYYTaTBOIAFoiKDdpK1mMorAGxZvgIp+OUizTsfUkYuQUeCwExxKKp3GgS4?= =?us-ascii?Q?OUDxejLgD84exA74DUNR/l5iJZL5PkKyqjalwimZziqNpQXKhgFFOUeckQNF?= =?us-ascii?Q?35CRwKoGLKPtCh1HGpO5BhhoHvMsbCX8WmjWQtlsMCkqfKImJnd3UcL4of7N?= =?us-ascii?Q?qxZPcD7wjGmJp+Jer8gcF4maQ58Jzy4sIgLtmwRSzQVZAQd3WudKnxD02XFt?= =?us-ascii?Q?GneVBtsrE6ioIjLYMjin1umTpsRumjXkaX06lJJQOfpud78OdPHphWhhGZ2t?= =?us-ascii?Q?UYwzIZre2wj0P840GmJeczXgkaJ4tNoKlgqYypNln9pjt94LBNlKJFufgaW4?= =?us-ascii?Q?aDULGiBDqnugBH9GYbfGXGp0icfN4VHW3AE9SQYCzf1tSz4wftfujr6GwZyg?= =?us-ascii?Q?IQkHG6lpQhbZiPUhG21evqEGoBXyFAqCtkgVRKei1Mxy19uzA8cxFuxwrpH/?= =?us-ascii?Q?vI//sA4QYgklXiDGXF/NZALhtGcoq3lHXX1kO/3yFKBqoMUaVrvbPJuJGHZl?= =?us-ascii?Q?SqxgT70ioccWVTx/A5tpA6usPirfZiSf9HZVa9ZPZWtQ8/JOmfYFh0xUPhHI?= =?us-ascii?Q?+cimEz8KWQLVP5gWMOBF5cETtffEOdAQpNgbyKIA?= X-OriginatorOrg: Nvidia.com X-MS-Exchange-CrossTenant-Network-Message-Id: 017c7657-774f-4cbe-5e7c-08ddd3892eb8 X-MS-Exchange-CrossTenant-AuthSource: DS7PR12MB9473.namprd12.prod.outlook.com X-MS-Exchange-CrossTenant-AuthAs: Internal X-MS-Exchange-CrossTenant-OriginalArrivalTime: 04 Aug 2025 19:00:30.5429 (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: e/l+Q1aN4rqh1Qsi+ktmAxktc4d9J9XhyevUww2sxPLZxXnZr8vngIdXtL53fpTp X-MS-Exchange-Transport-CrossTenantHeadersStamped: BN5PR12MB9510 On 4 Aug 2025, at 14:49, David Hildenbrand wrote: > On 04.08.25 20:20, Juan Yescas wrote: >> Hi David/Zi, >> >> Is there any reason why the MIGRATE_CMA pages are not in the PCP lists= ? >> >> There are many devices that need fast allocation of MIGRATE_CMA pages,= >> and they have to get them from the buddy allocator, which is a bit >> slower in comparison to the PCP lists. >> >> We also have cases where the MIGRATE_CMA memory requirements are big. >> For example, GPUs need MIGRATE_CMA memory in the ranges of 30MiB to 50= 0MiBs. >> These cases would benefit if we have THPs for CMAs. >> >> Could we add the support for MIGRATE_CMA pages on the PCP and THP list= s? > > Remember how CMA memory is used: > > The owner allocates it through cma_alloc() and friends, where the CMA a= llocator will try allocating *specific physical memory regions* using all= oc_contig_range(). It doesn't just go ahead and pick a random CMA page fr= om the buddy (or PCP) lists. Doesn't work (just imagine having different = CMA areas etc). Yeah, unless some code is relying on gfp_to_alloc_flags_cma() to get ALLO= C_CMA to try to get CMA pages from buddy. > > Anybody else is free to use CMA pages for MOVABLE allocations. So we tr= eat them as being MOVABLE on the PCP. > > Having a separate CMA PCP list doesn't solve or speedup anything, reall= y. It can be slower when small CMA pages are on PCP lists and large CMA page= s cannot be allocated, one needs to drain PCP lists. This assumes the code = is trying to get CMA pages from buddy, which is not how CMA memory is design= ed to be used like David mentioned above. > > I still have no clue what this patch here tried to solve: it doesn't ma= ke any sense. Best Regards, Yan, Zi