1 files changed, 60 insertions, 0 deletions
diff --git a/mm/vmstat.c b/mm/vmstat.c
index a7de9ad..c831be3 100644
--- a/mm/vmstat.c
+++ b/mm/vmstat.c
@@ -1379,6 +1379,66 @@ static DEFINE_PER_CPU(struct delayed_work, vmstat_work);
 int sysctl_stat_interval __read_mostly = HZ;
 static cpumask_var_t cpu_stat_off;
 
+#ifdef CONFIG_PROC_FS
+static void refresh_vm_stats(struct work_struct *work)
+{
+	refresh_cpu_vm_stats(true);
+}
+
+int vmstat_refresh(struct ctl_table *table, int write,
+		   void __user *buffer, size_t *lenp, loff_t *ppos)
+{
+	long val;
+	int err;
+	int i;
+
+	/*
+	 * The regular update, every sysctl_stat_interval, may come later
+	 * than expected: leaving a significant amount in per_cpu buckets.
+	 * This is particularly misleading when checking a quantity of HUGE
+	 * pages, immediately after running a test.  /proc/sys/vm/stat_refresh,
+	 * which can equally be echo'ed to or cat'ted from (by root),
+	 * can be used to update the stats just before reading them.
+	 *
+	 * Oh, and since global_page_state() etc. are so careful to hide
+	 * transiently negative values, report an error here if any of
+	 * the stats is negative, so we know to go looking for imbalance.
+	 */
+	err = schedule_on_each_cpu(refresh_vm_stats);
+	if (err)
+		return err;
+	for (i = 0; i < NR_VM_ZONE_STAT_ITEMS; i++) {
+		val = atomic_long_read(&vm_stat[i]);
+		if (val < 0) {
+			switch (i) {
+			case NR_ALLOC_BATCH:
+			case NR_PAGES_SCANNED:
+				/*
+				 * These are often seen to go negative in
+				 * recent kernels, but not to go permanently
+				 * negative.  Whilst it would be nicer not to
+				 * have exceptions, rooting them out would be
+				 * another task, of rather low priority.
+				 */
+				break;
+			default:
+				pr_warn("%s: %s %ld\n",
+					__func__, vmstat_text[i], val);
+				err = -EINVAL;
+				break;
+			}
+		}
+	}
+	if (err)
+		return err;
+	if (write)
+		*ppos += *lenp;
+	else
+		*lenp = 0;
+	return 0;
+}
+#endif /* CONFIG_PROC_FS */
+
 static void vmstat_update(struct work_struct *w)
 {
 	if (refresh_cpu_vm_stats(true)) {