Bridging the performance gap for copy-based garbage collectors atop non-volatile memory

Abstract

Non-volatile memory (NVM) is expected to revolutionize the memory hierarchy with not only non-volatility but also large capacity and power efficiency. Memory-intensive applications, which are often written in managed languages like Java, would run atop NVM for better cost-efficiency. Unfortunately, such applications may suffer from performance slowdown due to the unmanaged performance gap between DRAM and NVM. This paper studies the performance of a series of Java applications atop NVM and uncovers that the copy-based garbage collection (GC), the mainstream GC algorithm, is an NVM-unfriendly component in JVM. GC becomes a severe performance bottleneck especially when memory resource is scarce. To this end, this paper analyzes the memory behavior of copy-based GC and uncovers that its inappropriate usage on NVM bandwidth is the main reason for its performance slowdown. This paper thus proposes two NVM-aware optimizations: write cache and header map, to effectively manage the limited NVM bandwidth. It further improves the GC performance with hardware instructions like non-temporal memory accesses and prefetching. We have implemented the optimizations on two mainstream copy-based garbage collectors in OpenJDK. Evaluation with various memory-intensive applications shows that our optimizations can improve the GC time, application execution time, application tail latency by up to 2.69×, 11.0%, and 5.09×, respectively. CCS Concepts: • Software and its engineering → Runtime environments; • Hardware → Memory and dense storage.