BTRFS_SPACE_INFO_SUB_GROUP_MAX
for (int i = 0; i < BTRFS_SPACE_INFO_SUB_GROUP_MAX; i++) {
for (int i = 0; i < BTRFS_SPACE_INFO_SUB_GROUP_MAX; i++) {
for (int i = 0; i < BTRFS_SPACE_INFO_SUB_GROUP_MAX; i++)
struct btrfs_space_info *sub_group[BTRFS_SPACE_INFO_SUB_GROUP_MAX];