Duration: 1:11:04

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Programmers are increasingly choosing managed languages for modern applications, which rely on garbage collection to manage dynamically allocated objects. The garbage collector directly determines program performance by making a classic space-time tradeoff that seeks to provide space efficiency, fast reclamation, and mutator performance. The three canonical tracing garbage collectors: semi-space, mark-sweep, and mark-compact each sacrifice one objective. This talk describes a collector family, called mark-region and introduces opportunistic defragmentation, which mixes copying and marking in a single pass. Combining both, we implement immix, a novel high performance garbage collector that for the first time achieves all three performance objectives simultaneously. The key insight is to allocate and reclaim memory in contiguous regions, at a coarse block grain when possible and otherwise reclaim in groups of finer grain lines. We show that immix outperforms existing canonical algorithms, improving total application performance by 7 to 25. These innovations and the identification of a new family of collectors open new opportunities for garbage collector design.