Galvin Edition 9 Exercise 9 Question 24 (Page No. 454)

Question

Discuss situations in which the least frequently used ($LFU$) page replacement algorithm generates fewer page faults than the least recently used ($LRU$) page-replacement algorithm. Also discuss under what circumstances the opposite holds.

Answer 1

Consider the following sequence of memory accesses in a system that can hold four pages in memory: 1 1 2 3 4 5 1. When page 5 is accessed, the least frequently used page-replacement algorithm would replace a page other than 1, and therefore would not incur a page fault when page 1 is accessed again. On the other hand, for the sequence “1 2 3 4 5 2,” the least recently used algorithm performs better.

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CHAPTER 9