The fifty percent rule revisited
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Combinatorial reasoning is applied to the analysis of two kinds of dynamic storage allocation system to derive results about the degree and characteristics of memory fragmentation. The simple first-fit scheme with immediate replacement, discussed by Knuth, is analyzed further, providinginter alia a new derivation of the “fifty percent rule”. Next a system with garbage collections is considered, and the mean and variance of the number of holes following a garbage collection are determined, along with other results. The cell distributions resulting from these two idealized policies are contrasted.
KeywordsDynamic storage allocation garbage collection memory fragmentation fifty percent rule
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