[PATCH 3/4] proc: Report process NUMA balancing mode

["Li Zhe" <lizhe.67@bytedance.com>]

Add NumaB_mode to /proc/<pid>/status so users can inspect the configured
process automatic NUMA balancing mode without issuing a prctl() from the
target process.

The field reports the process mode as enabled or disabled when automatic
NUMA balancing is supported, and unsupported when the kernel is built
without CONFIG_NUMA_BALANCING. Effective behavior still depends on the
global numa_balancing sysctl and memory policy.

Signed-off-by: Li Zhe <lizhe.67@bytedance.com>
---
 fs/proc/array.c                      | 16 ++++++++++++++++
 include/linux/sched/numa_balancing.h |  5 +++++
 2 files changed, 21 insertions(+)

diff --git a/fs/proc/array.c b/fs/proc/array.c
index f6f75d206762..a27a6a57e8b2 100644
--- a/fs/proc/array.c
+++ b/fs/proc/array.c
@@ -425,6 +425,21 @@ static inline void task_thp_status(struct seq_file *m, struct mm_struct *mm)
 	seq_printf(m, "THP_enabled:\t%d\n", thp_enabled);
 }
 
+#ifdef CONFIG_NUMA_BALANCING
+static inline void task_numa_balancing_status(struct seq_file *m,
+					      struct task_struct *task)
+{
+	seq_printf(m, "NumaB_mode:\t%s\n",
+		   task_numa_balancing_mode_name(task));
+}
+#else
+static inline void task_numa_balancing_status(struct seq_file *m,
+					      struct task_struct *task)
+{
+	seq_puts(m, "NumaB_mode:\tunsupported\n");
+}
+#endif
+
 static inline void task_untag_mask(struct seq_file *m, struct mm_struct *mm)
 {
 	seq_printf(m, "untag_mask:\t%#lx\n", mm_untag_mask(mm));
@@ -453,6 +468,7 @@ int proc_pid_status(struct seq_file *m, struct pid_namespace *ns,
 		task_untag_mask(m, mm);
 		mmput(mm);
 	}
+	task_numa_balancing_status(m, task);
 	task_sig(m, task);
 	task_cap(m, task);
 	task_seccomp(m, task);
diff --git a/include/linux/sched/numa_balancing.h b/include/linux/sched/numa_balancing.h
index bc413aae5915..69e79359fa22 100644
--- a/include/linux/sched/numa_balancing.h
+++ b/include/linux/sched/numa_balancing.h
@@ -47,6 +47,11 @@ static inline int task_numa_balancing_get_current(void)
 {
 	return task_numa_process_mode_enabled(current);
 }
+
+static inline const char *task_numa_balancing_mode_name(struct task_struct *p)
+{
+	return task_numa_process_mode_enabled(p) ? "enabled" : "disabled";
+}
 bool should_numa_migrate_memory(struct task_struct *p, struct folio *folio,
 				int src_nid, int dst_cpu);
 #else
-- 
2.20.1