Predicting the availability of contiguous memory

Abstract

In a memory allocation algorithm with variable-size segments, checkerboarding (external fragmentation) distributes the unused memory space into a number of relatively small fragments, so that the largest fragment is considerably smaller than the total. For some computer architectures, garbage collection is impossible or unfeasible at an arbitrary memory allocation decision. Hence it is necessary to consider the individual sizes of fragments (and, in particular, the largest one) rather than the sum total available. A simulation model is used to develop empirical probability distributions for the size of the largest fragment of available memory at a given instant, conditional only on the number of allocated blocks. A predictor developed from such distributions is presented, and example distributions for a job scheduling system are presented and discussed.