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Howlett" , "Matthew Wilcox" , "Ryan Roberts" , "William Kucharski" , "Andrew Morton" X-Mailer: aerc 0.22.0 References: <20260904022657.2656810-1-ziy@nvidia.com> <2026-09-05-daily-reply-0043-folio-split-memcg-6-6-bounce-v2@kernel.org> In-Reply-To: <2026-09-05-daily-reply-0043-folio-split-memcg-6-6-bounce-v2@kernel.org> X-ClientProxiedBy: MN0PR05CA0023.namprd05.prod.outlook.com (2603:10b6:208:52c::14) To IA0PR12MB8374.namprd12.prod.outlook.com (2603:10b6:208:40e::7) Precedence: bulk X-Mailing-List: stable@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 X-MS-PublicTrafficType: Email X-MS-TrafficTypeDiagnostic: IA0PR12MB8374:EE_|CH1PR12MB9621:EE_ X-MS-Office365-Filtering-Correlation-Id: 5c454490-bd96-4f6b-2472-08df0c68c105 X-MS-Exchange-SenderADCheck: 1 X-MS-Exchange-AntiSpam-Relay: 0 X-Microsoft-Antispam: BCL:0;ARA:13230040|366016|1800799024|23010399003|376014|7416014|10067099003|22082099003|18002099003|5023799004|11063799006|56012099006|4143699003; X-Microsoft-Antispam-Message-Info: BJjAmo9keyz0UaevPrx0OQLRVb3IF+8t4FcACBINu/xBByFOffdGZyNa7BT/qJiLppGeO2jlAUyRxmju5O1ARGyEOcc20N20U6F3gxyS4RGk0lAAbP9a9kHsdcz13Vjh4JMxBHCbeervR/biUidTVD6i+OZkB93iGqQ8Kc97R7J2neSUG46/X0pPx6dvvrpF3ks1v7J2beShD+oE4lJatshxwWFH55uezyBsv4eSBM5tqISREi5/Xdskp9rC2rW2vaUuK5EkOB/atHlRFnQ5CiLIUMmqViHV4S/GQXyWGh3Gp0w/zklplP8xx+rQBoe45Jin8KvRb4tGgpmJhiJM2E3jDB27fnW55QGSA6jaGYj64//CSQmQTXh8FoRAfaUKnV1K8qgUr+630xMGnPUPRehrWBPcTWapUY9KOFIl7QToJy+YdmsBIK+MQlt+03OtjNWGZGeGfEuBESCeM+tpLYyci5UWH8HKsIpZNKRKij03p0BJiHQ1CwkMpTqd3c46DVivoJBFA/Z+TxyO5qGN3HQpezD3Egf/D9Q9SxmH0OJGKRFF76+3WuYT/qASzN/q5eTrB7YNfmoTcyqsecDQJ7ooiGngnqNVAz+neD5euUHlNsA7jkRc9OBqAGbjdUn6p8nwCa7cvoF6BW+GRJAYLuYDvaAgAS9JbkJ8ja/+xlM= X-Forefront-Antispam-Report: CIP:255.255.255.255;CTRY:;LANG:en;SCL:1;SRV:;IPV:NLI;SFV:NSPM;H:IA0PR12MB8374.namprd12.prod.outlook.com;PTR:;CAT:NONE;SFS:(13230040)(366016)(1800799024)(23010399003)(376014)(7416014)(10067099003)(22082099003)(18002099003)(5023799004)(11063799006)(56012099006)(4143699003);DIR:OUT;SFP:1101; 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Commit 7b785645e8f13 ("mm: fix page cache >> convergence regression") fixed a workingset regression with it. >> xas_split_alloc() does not have it and needs to be fixed. > > Mainline's c299a2285d9d takes a reference on the folio's memcg with > get_mem_cgroup_from_folio() and holds it in current->active_memcg for the > duration of __folio_split() - rcu_read_lock()+css_tryget(), released with > mem_cgroup_put() afterwards. This 6.6.y version instead holds a bare > folio_memcg(folio) pointer across the same window, which includes a TLB > shootdown and several lock acquisitions - exactly the kind of window the > upstream refcount exists to close. > > 6.6 already has rcu_read_lock(), css_tryget() and mem_cgroup_put() availa= ble, > so nothing's missing to do this the same way upstream does. Could you re= send a > v2 that takes and drops the reference (under CONFIG_MEMCG, as upstream do= es)? No, this is not needed. Before commit f1cf8d2f36dc3 ("mm: memcontrol: eliminate the problem of dying memory cgroup for LRU folios"), like v6.6, a charged folio take a ref on its memcg. During split, the folio is locked, so will not be uncharged. As a result, its memcg will not go away. According to Claude, adding a ref there might cause a deadlock when a to-be-split folio has a dying memcg, where css_tryget() keeps failing and folio_memcg() keeps returning the same memcg. This should also apply to v6.1. I will send my version for 6.1 backport. --=20 Best Regards, Yan, Zi