PSS
also: Proportional Set Size
PSS (Proportional Set Size) is a memory metric that fairly distributes shared memory among processes by dividing each shared page's size proportionally among all processes that use it.
PSS improves upon RSS (Resident Set Size) by accounting for shared memory in a more equitable way. When multiple processes share the same memory pages (common with shared libraries), RSS counts the full page size for each process, leading to overcounting. PSS divides the shared page size by the number of processes sharing it.
For example, if a 4KB page is shared by 2 processes, each process's PSS contribution is 2KB rather than the full 4KB counted in RSS. This gives a more accurate picture of actual per-process memory consumption.
PSS is commonly viewed through /proc/[pid]/smaps or tools like pss and smem, making it valuable for understanding real memory usage in systems with many shared libraries.