CITS2002 Systems Programming  
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The Principle of Referential Locality

Numerous studies of the memory accesses of processes have observed that memory references cluster in certain parts of the program: over long periods, the centres of the clusters move, but over shorter periods, they are fairly static.

For most types of programs, it is clear that:

  • Except for infrequent branches and function/procedure invocation, program execution is sequential. The next instruction to be fetched usually follows the last one executed.
  • Programs generally operate at the same "depth" of function-invocation. References to instructions cluster within (and between) a small collection of functions.
  • Most iterative control flow (looping) is over short instruction sequences. Instructions from the same memory locations are fetched several times in succession.
  • Access to memory locations holding data is, too, constrained to a few frequently required data structures, or sequential steps through memory (e.g. when traversing arrays).

With reference to paging schemes, this locality of reference suggests that, within a process, the next memory reference will very likely be from the same page as the last memory reference.

This will impact heavily on our next enhancement to memory management: the use of virtual memory.

 


CITS2002 Systems Programming, Lecture 14, p1, 8th September 2020.