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, 12th September 2023.
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CITS2002