RSS, PSS and USS

#os/linux/memory

We can use smem to see physical memory and swap usage of each processes. Install smem under ubuntu is easy:

sudo apt update
sudo apt install smem

Basically this tool collect informations from /proc/<pid>/maps

There are 3 metrics: RSS, PSS and USS[1]:

RSS

RSS = resident set size

It counts process's memory usage include shared libraries multiple times if they are used by different processes.

PSS

PSS = proportional set size

PSS is an enhanced metric that accounts for shared memory more accurately than RSS. It divides the shared memory by the number of processes sharing it and adds this fraction to the USS to provide a more realistic figure.

It helps in understanding the memory distribution among processes more fairly.

USS

USS = unique set size

It counts process's memory usage exclude shared libraries. This metrics is helpful how this process consumes physical memory at runtime.

  1. https://elinux.org/Android_Memory_Usage ↩︎