diff --git a/include/linux/vmstat.h b/include/linux/vmstat.h
index 773135fc6e19..506d625163a1 100644
--- a/include/linux/vmstat.h
+++ b/include/linux/vmstat.h
@@ -313,6 +313,12 @@ static inline void __mod_node_page_state(struct pglist_data *pgdat,
 			enum node_stat_item item, int delta)
 {
 	if (vmstat_item_in_bytes(item)) {
+		/*
+		 * Only cgroups use subpage accounting right now; at
+		 * the global level, these items still change in
+		 * multiples of whole pages. Store them as pages
+		 * internally to keep the per-cpu counters compact.
+		 */
 		VM_WARN_ON_ONCE(delta & (PAGE_SIZE - 1));
 		delta >>= PAGE_SHIFT;
 	}
diff --git a/mm/vmstat.c b/mm/vmstat.c
index 0b0fc3b77789..e60b36f5f0a9 100644
--- a/mm/vmstat.c
+++ b/mm/vmstat.c
@@ -342,6 +342,12 @@ void __mod_node_page_state(struct pglist_data *pgdat, enum node_stat_item item,
 	long t;
 
 	if (vmstat_item_in_bytes(item)) {
+		/*
+		 * Only cgroups use subpage accounting right now; at
+		 * the global level, these items still change in
+		 * multiples of whole pages. Store them as pages
+		 * internally to keep the per-cpu counters compact.
+		 */
 		VM_WARN_ON_ONCE(delta & (PAGE_SIZE - 1));
 		delta >>= PAGE_SHIFT;
 	}
@@ -551,6 +557,12 @@ static inline void mod_node_state(struct pglist_data *pgdat,
 	long o, n, t, z;
 
 	if (vmstat_item_in_bytes(item)) {
+		/*
+		 * Only cgroups use subpage accounting right now; at
+		 * the global level, these items still change in
+		 * multiples of whole pages. Store them as pages
+		 * internally to keep the per-cpu counters compact.
+		 */
 		VM_WARN_ON_ONCE(delta & (PAGE_SIZE - 1));
 		delta >>= PAGE_SHIFT;
 	}