VSS, RSS, USS, PSS

• VSS: process virtual set size
• RSS: Resident Set Size
      process에 연관된 physical page 수
      shared page frame은 확인할 수 없음
• USS: Unique Set Size
      process만의 고유 page 수 
      shared는 제외한 private한 memory size
• PSS: proportional set size
      = USS + (shared page 크기 / shared process 수)
      좀 더 실제 사용 size에 근접한 값을 출력