Virtual Memory

Resident Set

The resident set of a process the portion of a process that is actually in main memory at any time.

Important factors:

• The smaller the amount, the more processes
• Too small $\to$ high page fault rate
• Too big $\to$ no real gain

Resident Set Management

How to determine the resident set size for a process?

Two kinds of policies exist:

1. Fixed-Allocation policy
2. Variable-Allocation policy

Fixed-allocation

• Gives a process a fixed number of pages within which to execute
• When a page fault occurs, one of the pages of that process must be replaced

Variable-allocation

• Number of pages allocated to a process varies over the lifetime of the process

Variable allocation, global scope is the easiest to implement and adopted in a number of operating systems.

The Working Set can be used to determine the resident set size in variable allocation.

Related

• Working Set