Linux memory metrics: does PSS include USS?

Question

As I know, because of memory sharing, there're several metrics for measuring the memory usage of a Linux process (VSS, RSS, PSS, USS). PSS means proportional set size, and USS means unique set size.

But I have 2 interpretations about the PSS: 1) PSS doesn't include USS, it's only about the proportionally shared memory; 2) PSS = USS + proportionally shared memory.

Which interpretation is correct?

Answer 1

1) is correct. PSS = USS + proportionally shared memory.

You can find the explanation on smem's man page.