heap-and-size indexed overflow-sub-trees using prio_tree->index_bits.
Instead the overflow sub-trees are indexed using full BITS_PER_LONG bits
of size_index. This may lead to skewed sub-trees because most of the
-higher significant bits of the size_index are likely to be be 0 (zero). In
+higher significant bits of the size_index are likely to be 0 (zero). In
the example above, all 3 overflow-sub-trees are skewed. This may marginally
affect the performance. However, processes rarely map many vmas with the
same start_vm_pgoff but different end_vm_pgoffs. Therefore, we normally