Cache-Conscious Coallocation of Hot Data Streams

The memory system performance of many programs can be improved by coallocating contemporaneously accessed heap objects in the same cache block. We present a novel profile-based analysis for producing such a layout. The analysis achieves cacheconscious coallocation of a hot data stream H (i.e., a regular data access pattern that frequently repeats) by isolating and combining allocation sites of object instances that appear in H such that intervening allocations coming from other sites are separated. The coallocation solution produced by the analysis is enforced by an automatic tool, cminstr, that redirects a program’s heap allocations to a run-time coallocation library comalloc. We also extend the analysis to coallocation at object field granularity. The resulting field coallocation solution generalizes common data restructuring techniques, such as field reordering, object splitting, and object merging, and allows their combination. Furthermore, it provides insight into object restructuring by breaking down the coallocation benefit on a per-technique basis, which provides the opportunity to pick the “sweet spot” for each program. Experimental results using a set of memory-performance-limited benchmarks, including a few SPECInt2000 programs, and Microsoft VisualFoxPro, indicate that programs possess significant coallocation opportunities. Automatic object coallocation improves execution time by 13% on average in the presence of hardware prefetching. Hand-implemented field coallocation solutions for two of the benchmarks produced additional improvements (12% and 22%) but the effort involved suggests implementing an automated version for type-safe languages, such as Java and C#.