The Working Set

• A set of pages a program frequently references
• To run efficiently, most of the program's working set must be in primary memory - else we get thrashing (program frequently requests pages from primary storage)
• Whether to add a new process would imply checking whether most of its working set can be maintained in primary memory
• Working set could change over the process lifetime, as it changes phases
• The working set size if a major design criteria for the OS designer