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What is PSS of a process?


The “proportional set size” or PSS of process is the sum of the unshared memory of a process and the proportion of memory shared with other processes.

Formula: unshared memory of a process + (memory shared with other processes /number of processes that share memory)

We’ll understand through an example


  • Process A has 100 KiB of unshared memory
  • Process B has 200 KiB of unshared memory
  • Both process A and process B have 150 KiB of the same shared memory region
  • There are 2 processes

Now, the PSS for these two processes are as follows:

  • PSS of process A = 100 KiB + (150 KiB / 2) = 175 KiB
  • PSS of process B = 200 KiB + (150 KiB / 2) = 275 KiB


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