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Tue, 22 Apr 2025 23:28:02 +0000 Message-ID: Date: Wed, 23 Apr 2025 07:27:48 +0800 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v3 1/2] sched/numa: Skip VMA scanning on memory pinned to one NUMA node via cpuset.mems To: Libo Chen CC: , , , , , , , , , , , , , , , , , , , , References: <20250417191543.1781862-1-libo.chen@oracle.com> <20250417191543.1781862-2-libo.chen@oracle.com> <244cb537-7d43-4795-9cb6-fc10234c68a1@intel.com> <2ce24cae-12fc-4a28-8396-c5b46a5f76d3@oracle.com> Content-Language: en-US From: "Chen, Yu C" In-Reply-To: <2ce24cae-12fc-4a28-8396-c5b46a5f76d3@oracle.com> Content-Type: text/plain; charset="UTF-8"; format=flowed Content-Transfer-Encoding: 8bit X-ClientProxiedBy: KL1P15301CA0044.APCP153.PROD.OUTLOOK.COM (2603:1096:820:6::32) To DM4PR11MB6020.namprd11.prod.outlook.com (2603:10b6:8:61::19) 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: DM4PR11MB6020:EE_|LV8PR11MB8698:EE_ X-MS-Office365-Filtering-Correlation-Id: 3c4b99e0-4f6e-4450-e455-08dd81f55350 X-MS-Exchange-SenderADCheck: 1 X-MS-Exchange-AntiSpam-Relay: 0 X-Microsoft-Antispam: BCL:0;ARA:13230040|376014|7416014|366016|1800799024|7053199007; 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X-MS-Exchange-AntiSpam-MessageData-ChunkCount: 1 X-MS-Exchange-AntiSpam-MessageData-0: =?utf-8?B?ZTl4cEw1cnZaajRUcXNWNE8xYTIrVU9BdU5GSFRVWDF1OXZlQllaRjd6UXNW?= =?utf-8?B?dHhYM2dNODFnRVVqR3dsV1JUMWxlMVJwcFBaMkxZbEZtckJxMjNSWnZDL2RY?= =?utf-8?B?TnFjSWJ5NmlvZVVkSTZEWGloSUhqUEFzTldOZ01hMGxVVndPSi9Jem1OMGJ6?= =?utf-8?B?M1FSVWpSbnJjSTRpRWFBaExxcjd6V0trYnlDUnZ2Q1FZa1F3WkhBTUlaajRi?= =?utf-8?B?aHkwRzhGWGNESmdwdW03c1hvQS9MUWIzN2o1ZUVHc1lUWGVnTFlEQ0U3a0Zh?= =?utf-8?B?NFlOQmJFbGV3WGg5UUlYYzZCd2FBd29iMzBhZS8xT09ZMjc0eGhtY2NkbjFl?= =?utf-8?B?YmRYSlNGK25ZMzNkRDdLRFFRZXg0SkZyMTFGUHFkVlpTOUFyY3RET0Z6VmRa?= =?utf-8?B?OEg1R3R3RnBGNjk3VWJPZ2xjUHZKaENjcG0zQzBkdWxGSHdCaEhhdzVCcTFx?= =?utf-8?B?b25IbGc2VldoRjFiOXY3N2EwTldyS1VDNFV3djFQNUdZWnFTUG9mRFBYQVRy?= =?utf-8?B?S0pHd21EMEdhTlIveloyZWlVc29oRy9zZGVTajZJQ3NZbXlMcGRjQlNPcHFM?= =?utf-8?B?OGYrR0gydlFuNUp0MnJEd1JYWTFsTlEwR2JuZWVzZWdWK3lIbkRIZ2plT3Zt?= =?utf-8?B?amN0cVI3MzVQMG5zTWF4YkJON1ZuNFdTUzdZVUF6aUszejdGOWdKWG9CUFJB?= =?utf-8?B?TW9aak1uWHJxMTAvQldoZWtVTGdmbmZKendQODZjRi9sQ20wdHp2OEd5cGlE?= =?utf-8?B?WXNNN0JpSkt1TjM2Z202UVpGK2xhOWtNVXNXcmxXYXdSSjB1SERKZFFxNk1x?= =?utf-8?B?MjJXUUhKWi9nbk9RN3FObzU5S3RpWUxhODJUTzlTbVBCMnZvY1hZanI5Ylgz?= =?utf-8?B?RFdqb2VzcWUwQVFyZ0VOT3loSk5UbEJTNlBCYVIyWS9UNG1kY3V3ODlueFc3?= =?utf-8?B?QnNOWHRBQ1ZOOURCWXdOQlhsVklyKy9kOHBrbGVtMGJpd0I5YXpOOU5hdUp3?= =?utf-8?B?NlVHL0tYY3VJaXVSWHF5RGkvWXBNQ3lCdHhETjhWcDVzd2ExWmpzWjFNa3NP?= =?utf-8?B?cllHdTJjWkQyOWNvdWhoOTZnNk1lQUwwZS83aTRWdUI3eXN5OVg0U2hWZlcw?= =?utf-8?B?aDBvSlNOaWF6UmdxcnpZTkM4OGNkaktjcVJoZnRQZzVTNXg0YUVpYkhhMDhI?= =?utf-8?B?a2FOdUM3Mzd6amg1aWtPSjlac1ZDeTJqQ3hEa2RGTkZqeCtvZjVkS25TbWR3?= =?utf-8?B?dXFBMlpGZ2d6ZTN4Ymh3NVYxSmkrd3FpRWFBczVnS0paUEtrQXk3QzZKZXlK?= =?utf-8?B?dVRIVlpIb3dteHU1YzAvUUJoZnNKSy9vMTFIbUtBallyMHdSWHhPd2p6REwx?= =?utf-8?B?RmNIUUlVZnNkZWgxMTJGcUMyWGg3UW01ZDE5UXNJcURNcnNEU2JhbFU2dkNx?= =?utf-8?B?OFozNDFhYXhsMlI0WWZDNUlkb3lOSnk0SHBpaDFDbDJsYm5yTFNEYU1kL25k?= =?utf-8?B?QjJjVzhhbjA1eFlwZnhQRjBrd3JJOTZrUmxxNENYNmZYdkdxN1Y4UFlxWXhM?= =?utf-8?B?UHVwdEp2dENhenBVVTJyWUxFejA5NDJIcS96amZJdytXYytIV2R4RU9mSDFk?= =?utf-8?B?M0RKZG9FK0N2UFA0bHBUMlVrcUVNZnJEQ0JHNlVRNjNIK1loWUY5QmZGOFc4?= =?utf-8?B?ZkVRUlZGMDhDbFQ4c2huUnNKQ2hGZGVzMlVpUC84WTlRcVYxWWJjajZNVXpw?= =?utf-8?B?Ylo2SWs5bGJwVmhFUFlkemplQzNhUjJYNE14YkhFbE9DaE9FTmdUNWtFRi9h?= =?utf-8?B?dmRhR2VQNnRWUEx1K2QyeWpBbDJaZFNwcWZjdUgvVFRDa1RqVTM0bERPTHVJ?= =?utf-8?B?V1RSS29BZHh2aStHT3IwNCtuQU8vTkF4VHdQQ2lxRzF6V3YrRVBpQzhBQXd1?= =?utf-8?B?a2FrcU9BL1RpSDM0WVZpemRjMFlQbWt0Ly9UaFNLQXhrVFNYS0YrWWtBY0wr?= =?utf-8?B?TDI0TFdYdEh4MmIrZjFXSzUzMDNDaExXcUE5TW1qZi9WSlg5NnpmUTdSZkpi?= =?utf-8?B?Z3lvMDQ3VTExSy9FRTFySlFYbHRuMWtnUDlVbTA2VnlEY2VuTW5qR2syNnpE?= =?utf-8?Q?YJc4rrgBO+iXhaHhGxkx95R/8?= X-MS-Exchange-CrossTenant-Network-Message-Id: 3c4b99e0-4f6e-4450-e455-08dd81f55350 X-MS-Exchange-CrossTenant-AuthSource: DM4PR11MB6020.namprd11.prod.outlook.com X-MS-Exchange-CrossTenant-AuthAs: Internal X-MS-Exchange-CrossTenant-OriginalArrivalTime: 22 Apr 2025 23:28:02.6242 (UTC) X-MS-Exchange-CrossTenant-FromEntityHeader: Hosted X-MS-Exchange-CrossTenant-Id: 46c98d88-e344-4ed4-8496-4ed7712e255d X-MS-Exchange-CrossTenant-MailboxType: HOSTED X-MS-Exchange-CrossTenant-UserPrincipalName: /1boi+bHfP1wlAwqZx4+EJ97vx58Z++3fcApwtgMRk91n2GyiCH1Efep+IV09dpzMG37pfreDrRYT/0tuFuR2A== X-MS-Exchange-Transport-CrossTenantHeadersStamped: LV8PR11MB8698 X-OriginatorOrg: intel.com On 4/23/2025 6:20 AM, Libo Chen wrote: > Hi Yu > > On 4/19/25 04:16, Chen, Yu C wrote: >> Hi Libo, >> >> On 4/18/2025 3:15 AM, Libo Chen wrote: >>> When the memory of the current task is pinned to one NUMA node by cgroup, >>> there is no point in continuing the rest of VMA scanning and hinting page >>> faults as they will just be overhead. With this change, there will be no >>> more unnecessary PTE updates or page faults in this scenario. >>> >>> We have seen up to a 6x improvement on a typical java workload running on >>> VMs with memory and CPU pinned to one NUMA node via cpuset in a two-socket >>> AARCH64 system. With the same pinning, on a 18-cores-per-socket Intel >>> platform, we have seen 20% improvment in a microbench that creates a >>> 30-vCPU selftest KVM guest with 4GB memory, where each vCPU reads 4KB >>> pages in a fixed number of loops. >>> >>> Signed-off-by: Libo Chen >> >> I think this is a promising change that we can perform fine-grain NUMA >> balance control on a per-cgroup basis rather than system-wide NUMA >> balance for every task, which is costly. >> > > Yes indeed, the cost, from we have seen, can be quite astonishing > >>> --- >>>   kernel/sched/fair.c | 7 +++++++ >>>   1 file changed, 7 insertions(+) >>> >>> diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c >>> index e43993a4e5807..c9903b1b39487 100644 >>> --- a/kernel/sched/fair.c >>> +++ b/kernel/sched/fair.c >>> @@ -3329,6 +3329,13 @@ static void task_numa_work(struct callback_head *work) >>>       if (p->flags & PF_EXITING) >>>           return; >>>   +    /* >>> +     * Memory is pinned to only one NUMA node via cpuset.mems, naturally >>> +     * no page can be migrated. >>> +     */ >>> +    if (cpusets_enabled() && nodes_weight(cpuset_current_mems_allowed) == 1) >>> +        return; >>> + >> >> I found that you had a proposal in V1 to address Peter's concern[1]: >> Allow the task to be migrated to its preferred Node, even if the task's >> memory policy is restricted to 1 Node. In your previous proposal, only if the task's cpumask is bound to the same Node as its memory policy node, the NUMA balance scanning is skipped, because a cgroup usually binds its tasks and memory allocation policy to the same node. Not sure if that could be turned into: >> >> If the task's memory policy node's CPU mask is a subset of the task's cpumask, the NUMA balance scan is allowed. >> > > I guess fundamentally is this really worth it? Do the benefits of NUMA task migrations only outweigh the overheads of VMA scanning, PTE updates and page faults etc? I suppose this is workload-dependent, but what about the best-case scenario? I think we probably need more data. Also if we do that, we also need to do the same for other VMA skipping scenarios. > Overall that can be a future work and I agree for now this patch is simple enough and feel free to add: Tested-by: Chen Yu thanks, Chenyu