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The FIFO Page Replacement Policy

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• In the FIFO page replacement policy, the page that is brought in the earliest will be replaced.

  As you will see in the next example, the FIFO policy will replace the pages in a round-robin manner (i.e., cyclicly).

• Implementing the FIFO page replacement policy:
  • Use an index variable to point to the memory frame that will be replaced

  • Set this index variable to 0 initially

  • Increase index by ONE each time a page is brought in from disk. The page will be store in the memory frame pointed to by the index variable

• In all the examples of the different page replacement policies, I will use the following page request summary:

  

  and 3 memory frames.

• The following figure shows the behavior of the program in paging using the FIFO page replacement policy:

  

  • We can see notably bad replacement decisions made in this short example (see figure above).

    Due to the program locality, it is not a good idea to replace a page that was used last....

  • There are a total of 11 page read operations to satisfy the total of 18 page requests.

• Advantage of FIFO replacement policy:
  • Easy to implement (round robin)

• Disadvantage of FIFO replacement policy:
  • Can sometimes make dumb replcament decisions...

• Let's see if there are better replacement policies....