[linux-next,3/6] memcontrol-v1: introduce ksm_stat at cgroup level

Commit Message

[e-mail] April 3, 2025, 5:31 a.m. UTC

From: xu xin <[e-mail]>

With the enablement of container-level KSM (e.g., via prctl), there is a
growing demand for container-level observability of KSM behavior. However,
current cgroup implementations lack support for exposing KSM-related
metrics.

This patch introduces a new interface named ksm_stat
at the cgroup hierarchy level, enabling users to monitor KSM merging
statistics specifically for containers where this feature has been
activated, eliminating the need to manually inspect KSM information for
each individual process within the cgroup.

Users can obtain the KSM information of a cgroup just by:

        `cat /sys/fs/cgroup/memory.ksm_stat`

Current implementation supports cgroup v1 temporarily; cgroup v2
compatibility is planned for future versions.

Co-developed-by: Haonan Chen <[e-mail]>
Signed-off-by: Haonan Chen <[e-mail]>
Signed-off-by: xu xin <[e-mail]>
---
 mm/memcontrol-v1.c | 40 ++++++++++++++++++++++++++++++++++++++++
 1 file changed, 40 insertions(+)

Patch

diff --git a/mm/memcontrol-v1.c b/mm/memcontrol-v1.c
index 8660908850dc..95da877d5516 100644
--- a/mm/memcontrol-v1.c
+++ b/mm/memcontrol-v1.c
@@ -1821,6 +1821,40 @@  static int memcg_numa_stat_show(struct seq_file *m, void *v)
 }
 #endif /* CONFIG_NUMA */

+#ifdef CONFIG_KSM
+struct memcg_ksm_stat {
+	unsigned long ksm_rmap_items;
+};
+
+static int evaluate_memcg_ksm_stat(struct task_struct *task, void *arg)
+{
+	struct mm_struct *mm;
+	struct memcg_ksm_stat *ksm_stat = arg;
+
+	mm = get_task_mm(task);
+	if (mm) {
+		ksm_stat->ksm_rmap_items += mm->ksm_rmap_items;
+		mmput(mm);
+	}
+
+	return 0;
+}
+
+static int memcg_ksm_stat_show(struct seq_file *m, void *v)
+{
+	struct memcg_ksm_stat ksm_stat;
+	struct mem_cgroup *memcg = mem_cgroup_from_seq(m);
+
+	/* Initialization */
+	ksm_stat.ksm_rmap_items = 0;
+	/* summing all processes'ksm statistic items of this cgroup hierarchy */
+	mem_cgroup_scan_tasks(memcg, evaluate_memcg_ksm_stat, &ksm_stat);
+	seq_printf(m, "ksm_rmap_items %lu\n", ksm_stat.ksm_rmap_items);
+
+	return 0;
+}
+#endif
+
 static const unsigned int memcg1_stats[] = {
 	NR_FILE_PAGES,
 	NR_ANON_MAPPED,
@@ -2079,6 +2113,12 @@  struct cftype mem_cgroup_legacy_files[] = {
 		.name = "numa_stat",
 		.seq_show = memcg_numa_stat_show,
 	},
+#endif
+#ifdef CONFIG_KSM
+	{
+		.name = "ksm_stat",
+		.seq_show = memcg_ksm_stat_show,
+	},
 #endif
 	{
 		.name = "kmem.limit_in_bytes",