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client-ip=165.204.84.17; helo=satlexmb07.amd.com; pr=C Received: from satlexmb07.amd.com (165.204.84.17) by SJ5PEPF000001C9.mail.protection.outlook.com (10.167.242.37) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id 15.20.9564.3 via Frontend Transport; Thu, 29 Jan 2026 14:45:29 +0000 Received: from BLR-L-BHARARAO.amd.com (10.180.168.240) by satlexmb07.amd.com (10.181.42.216) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id 15.2.2562.17; Thu, 29 Jan 2026 08:45:22 -0600 From: Bharata B Rao To: , CC: , , , , , , , , , , , , , , , , , , , , , , , , , , , Bharata B Rao Subject: [RFC PATCH v5 09/10] mm: klruscand: use mglru scanning for page promotion Date: Thu, 29 Jan 2026 20:10:42 +0530 Message-ID: <20260129144043.231636-10-bharata@amd.com> X-Mailer: git-send-email 2.34.1 In-Reply-To: <20260129144043.231636-1-bharata@amd.com> References: <20260129144043.231636-1-bharata@amd.com> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable X-ClientProxiedBy: satlexmb08.amd.com (10.181.42.217) To satlexmb07.amd.com (10.181.42.216) X-EOPAttributedMessage: 0 X-MS-PublicTrafficType: Email X-MS-TrafficTypeDiagnostic: SJ5PEPF000001C9:EE_|CH2PR12MB4136:EE_ X-MS-Office365-Filtering-Correlation-Id: a61017e7-f960-49fb-d3e5-08de5f450c85 X-MS-Exchange-SenderADCheck: 1 X-MS-Exchange-AntiSpam-Relay: 0 X-Microsoft-Antispam: BCL:0;ARA:13230040|7416014|82310400026|376014|1800799024|36860700013; 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X-OriginatorOrg: amd.com X-MS-Exchange-CrossTenant-OriginalArrivalTime: 29 Jan 2026 14:45:29.9321 (UTC) X-MS-Exchange-CrossTenant-Network-Message-Id: a61017e7-f960-49fb-d3e5-08de5f450c85 X-MS-Exchange-CrossTenant-Id: 3dd8961f-e488-4e60-8e11-a82d994e183d X-MS-Exchange-CrossTenant-OriginalAttributedTenantConnectingIp: TenantId=3dd8961f-e488-4e60-8e11-a82d994e183d;Ip=[165.204.84.17];Helo=[satlexmb07.amd.com] X-MS-Exchange-CrossTenant-AuthSource: SJ5PEPF000001C9.namprd05.prod.outlook.com X-MS-Exchange-CrossTenant-AuthAs: Anonymous X-MS-Exchange-CrossTenant-FromEntityHeader: HybridOnPrem X-MS-Exchange-Transport-CrossTenantHeadersStamped: CH2PR12MB4136 Content-Type: text/plain; charset="utf-8" From: Kinsey Ho Introduce a new kernel daemon, klruscand, that periodically invokes the MGLRU page table walk. It leverages the new callbacks to gather access information and forwards it to pghot sub-system for promotion decisions. This benefits from reusing the existing MGLRU page table walk infrastructure, which is optimized with features such as hierarchical scanning and bloom filters to reduce CPU overhead. As an additional optimization to be added in the future, we can tune the scan intervals for each memcg. Signed-off-by: Kinsey Ho Signed-off-by: Yuanchu Xie [Reduced the scan interval to 500ms, KLRUSCAND to default n in config] Signed-off-by: Bharata B Rao --- mm/Kconfig | 8 ++++ mm/Makefile | 1 + mm/klruscand.c | 110 +++++++++++++++++++++++++++++++++++++++++++++++++ 3 files changed, 119 insertions(+) create mode 100644 mm/klruscand.c diff --git a/mm/Kconfig b/mm/Kconfig index 07b16aece877..9e9eca8db8bf 100644 --- a/mm/Kconfig +++ b/mm/Kconfig @@ -1502,6 +1502,14 @@ config HWMEM_PROFILER rolled up to PGHOT sub-system for further action like hot page promotion or NUMA Balancing =20 +config KLRUSCAND + bool "Kernel lower tier access scan daemon" + default n + depends on PGHOT && LRU_GEN_WALKS_MMU + help + Scan for accesses from lower tiers by invoking MGLRU to perform + page table walks. + source "mm/damon/Kconfig" =20 endmenu diff --git a/mm/Makefile b/mm/Makefile index 89f999647752..c68df497a063 100644 --- a/mm/Makefile +++ b/mm/Makefile @@ -153,3 +153,4 @@ obj-$(CONFIG_PGHOT) +=3D pghot-precise.o else obj-$(CONFIG_PGHOT) +=3D pghot-default.o endif +obj-$(CONFIG_KLRUSCAND) +=3D klruscand.o diff --git a/mm/klruscand.c b/mm/klruscand.c new file mode 100644 index 000000000000..13a41b38d67d --- /dev/null +++ b/mm/klruscand.c @@ -0,0 +1,110 @@ +// SPDX-License-Identifier: GPL-2.0-only +#include +#include +#include +#include +#include +#include + +#include "internal.h" + +#define KLRUSCAND_INTERVAL 500 +#define BATCH_SIZE (2 << 16) + +static struct task_struct *scan_thread; +static unsigned long pfn_batch[BATCH_SIZE]; +static int batch_index; + +static void flush_cb(void) +{ + int i; + + for (i =3D 0; i < batch_index; i++) { + unsigned long pfn =3D pfn_batch[i]; + + pghot_record_access(pfn, NUMA_NO_NODE, PGHOT_PGTABLE_SCAN, jiffies); + + if (i % 16 =3D=3D 0) + cond_resched(); + } + batch_index =3D 0; +} + +static bool accessed_cb(unsigned long pfn) +{ + WARN_ON_ONCE(batch_index =3D=3D BATCH_SIZE); + + if (batch_index < BATCH_SIZE) + pfn_batch[batch_index++] =3D pfn; + + return batch_index =3D=3D BATCH_SIZE; +} + +static int klruscand_run(void *unused) +{ + struct lru_gen_mm_walk *walk; + + walk =3D kzalloc(sizeof(*walk), + __GFP_HIGH | __GFP_NOMEMALLOC | __GFP_NOWARN); + if (!walk) + return -ENOMEM; + + while (!kthread_should_stop()) { + unsigned long next_wake_time; + long sleep_time; + struct mem_cgroup *memcg; + int flags; + int nid; + + next_wake_time =3D jiffies + msecs_to_jiffies(KLRUSCAND_INTERVAL); + + for_each_node_state(nid, N_MEMORY) { + pg_data_t *pgdat =3D NODE_DATA(nid); + struct reclaim_state rs =3D { 0 }; + + if (node_is_toptier(nid)) + continue; + + rs.mm_walk =3D walk; + set_task_reclaim_state(current, &rs); + flags =3D memalloc_noreclaim_save(); + + memcg =3D mem_cgroup_iter(NULL, NULL, NULL); + do { + struct lruvec *lruvec =3D + mem_cgroup_lruvec(memcg, pgdat); + unsigned long max_seq =3D + READ_ONCE((lruvec)->lrugen.max_seq); + + lru_gen_scan_lruvec(lruvec, max_seq, accessed_cb, flush_cb); + cond_resched(); + } while ((memcg =3D mem_cgroup_iter(NULL, memcg, NULL))); + + memalloc_noreclaim_restore(flags); + set_task_reclaim_state(current, NULL); + memset(walk, 0, sizeof(*walk)); + } + + sleep_time =3D next_wake_time - jiffies; + if (sleep_time > 0 && sleep_time !=3D MAX_SCHEDULE_TIMEOUT) + schedule_timeout_idle(sleep_time); + } + kfree(walk); + return 0; +} + +static int __init klruscand_init(void) +{ + struct task_struct *task; + + task =3D kthread_run(klruscand_run, NULL, "klruscand"); + + if (IS_ERR(task)) { + pr_err("Failed to create klruscand kthread\n"); + return PTR_ERR(task); + } + + scan_thread =3D task; + return 0; +} +module_init(klruscand_init); --=20 2.34.1