Low-latency, high-throughput garbage collection

Wenyu Zhao, S. Blackburn, K. McKinley
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引用次数: 4

Abstract

To achieve short pauses, state-of-the-art concurrent copying collectors such as C4, Shenandoah, and ZGC use substantially more CPU cycles and memory than simpler collectors. They suffer from design limitations: i) concurrent copying with inherently expensive read and write barriers, ii) scalability limitations due to tracing, and iii) immediacy limitations for mature objects that impose memory overheads. This paper takes a different approach to optimizing responsiveness and throughput. It uses the insight that regular, brief stop-the-world collections deliver sufficient responsiveness at greater efficiency than concurrent evacuation. It introduces LXR, where stop-the-world collections use reference counting (RC) and judicious copying. RC delivers scalability and immediacy, promptly reclaiming young and mature objects. RC, in a hierarchical Immix heap structure, reclaims most memory without any copying. Occasional concurrent tracing identifies cyclic garbage. LXR introduces: i) RC remembered sets for judicious copying of mature objects; ii) a novel low-overhead write barrier that combines coalescing reference counting, concurrent tracing, and remembered set maintenance; iii) object reclamation while performing a concurrent trace; iv) lazy processing of decrements; and v) novel survival rate triggers that modulate pause durations. LXR combines excellent responsiveness and throughput, improving over production collectors. On the widely-used Lucene search engine in a tight heap, LXR delivers 7.8× better throughput and 10× better 99.99% tail latency than Shenandoah. On 17 diverse modern workloads in a moderate heap, LXR outperforms OpenJDK’s default G1 on throughput by 4% and Shenandoah by 43%.
低延迟、高吞吐量的垃圾收集
为了实现短停顿,最先进的并发复制收集器(如C4、Shenandoah和ZGC)比简单的收集器使用更多的CPU周期和内存。它们受到设计限制:i)并发复制具有固有的昂贵的读写障碍,ii)由于跟踪而产生的可伸缩性限制,以及iii)对施加内存开销的成熟对象的即时性限制。本文采用了一种不同的方法来优化响应性和吞吐量。它使用的洞察力,定期,短暂的停止世界收集提供足够的响应效率更高的同时疏散。它介绍了LXR,其中停止世界集合使用引用计数(RC)和明智的复制。RC提供可伸缩性和即时性,及时回收年轻和成熟的对象。在分层混合堆结构中,RC无需任何复制即可回收大部分内存。偶尔并发跟踪识别循环垃圾。LXR引入:i) RC记忆集,用于明智地复制成熟对象;Ii)结合了合并引用计数、并发跟踪和记忆集维护的新型低开销写屏障;Iii)执行并发跟踪时的对象回收;Iv)惰性处理减量;v)调节暂停持续时间的新存活率触发器。LXR结合了出色的响应能力和吞吐量,改进了生产收集器。在密集堆中广泛使用的Lucene搜索引擎上,LXR比Shenandoah提供了7.8倍的吞吐量和10倍的99.99%的尾部延迟。在中等堆中的17种不同现代工作负载上,LXR的吞吐量比OpenJDK的默认G1高4%,比Shenandoah高43%。
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