range_tree_set
err = range_tree_set(&arena->rt, 0, attr->max_entries);
range_tree_set(&arena->rt, vmf->pgoff, 1);
range_tree_set(&arena->rt, vmf->pgoff, 1);
range_tree_set(&arena->rt, pgoff + mapped, page_cnt - mapped);
range_tree_set(&arena->rt, pgoff, page_cnt);
range_tree_set(&arena->rt, pgoff, page_cnt);
int range_tree_set(struct range_tree *rt, u32 start, u32 len);