diff --git a/fs/nilfs2/bmap.h b/fs/nilfs2/bmap.h
index fae83cf9c009..a20569b19929 100644
--- a/fs/nilfs2/bmap.h
+++ b/fs/nilfs2/bmap.h
@@ -105,6 +105,7 @@ static inline int nilfs_bmap_is_new_ptr(unsigned long ptr)
  * @b_last_allocated_ptr: last allocated ptr for data block
  * @b_ptr_type: pointer type
  * @b_state: state
+ * @b_nchildren_per_block: maximum number of child nodes for non-root nodes
  */
 struct nilfs_bmap {
 	union {
@@ -118,6 +119,7 @@ struct nilfs_bmap {
 	__u64 b_last_allocated_ptr;
 	int b_ptr_type;
 	int b_state;
+	__u16 b_nchildren_per_block;
 };
 
 /* pointer type */
diff --git a/fs/nilfs2/btree.c b/fs/nilfs2/btree.c
index 829e145f1353..7089d9041146 100644
--- a/fs/nilfs2/btree.c
+++ b/fs/nilfs2/btree.c
@@ -154,7 +154,7 @@ static inline int nilfs_btree_node_size(const struct nilfs_bmap *btree)
 
 static int nilfs_btree_nchildren_per_block(const struct nilfs_bmap *btree)
 {
-	return NILFS_BTREE_NODE_NCHILDREN_MAX(nilfs_btree_node_size(btree));
+	return btree->b_nchildren_per_block;
 }
 
 static inline __le64 *
@@ -2218,10 +2218,14 @@ static const struct nilfs_bmap_operations nilfs_btree_ops_gc = {
 int nilfs_btree_init(struct nilfs_bmap *bmap)
 {
 	bmap->b_ops = &nilfs_btree_ops;
+	bmap->b_nchildren_per_block =
+		NILFS_BTREE_NODE_NCHILDREN_MAX(nilfs_btree_node_size(bmap));
 	return 0;
 }
 
 void nilfs_btree_init_gc(struct nilfs_bmap *bmap)
 {
 	bmap->b_ops = &nilfs_btree_ops_gc;
+	bmap->b_nchildren_per_block =
+		NILFS_BTREE_NODE_NCHILDREN_MAX(nilfs_btree_node_size(bmap));
 }