基于headroom的假装:动态地假装存在“足够长”的对象

Andreas Sewe, Dingwen Yuan, Jan Sinschek, M. Mezini
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引用次数: 7

摘要

许多现代垃圾收集器都是分代的,在“大多数对象在年轻时就会死亡”的假设下运行。这样的收集器将经常收集的托儿所中的所有对象分配给不经常收集的老一代,并仅将幸存的对象保留给不经常收集的老一代。但这些幸存者在获得终身教职后会产生复制成本。为了避免这些成本,假装方案构建分类器来预测对象是长寿命还是短寿命;因此,它是终身或不立即分配。然而,到目前为止,这些预测并没有考虑到一个重要的事实:下一个藏品的距离。相比之下,基于净空的假装确实考虑到了这一点;因此,只要对象存在的时间“足够长”,它就可以动态地预占有对象。我们设计了两种方法来根据垃圾收集痕迹估计对象的生命周期。这导致了我们在Jikes RVM和MMTk的基础上实现了两个基于净空的预终身计划。我们的实验表明,动态的、基于净空的假装方案在收集器性能方面优于静态方案,尽管代价是增加了突变器开销。
本文章由计算机程序翻译,如有差异,请以英文原文为准。
Headroom-based pretenuring: dynamically pretenuring objects that live "long enough"
Many modern garbage collectors are generational, operating under the assumption that "most objects die young." Such collectors allocate all objects in a frequently collected nursery and tenure only surviving objects to a less-frequently collected, older generation. But these survivors induce copying costs upon tenuring. To avoid these costs, pretenuring schemes construct classifiers to predict whether an object will be long-lived or short-lived; accordingly, it is tenured or not immediately upon allocation. Up to now, however, these predictions did not account for one important fact: the proximity of the next collection. In contrast, headroom-based pretenuring does take this into account; thus, it can dynamically pretenure objects whenever they live "long enough." We devised two ways to estimate an object's lifetime from garbage collection traces. This led to two headroom-based pre-tenuring schemes, which we implemented on top of Jikes RVM and MMTk. Our experiments show that the dynamic, headroom-based pretenuring schemes outperform static schemes in terms of collector performance, albeit at the cost of increased mutator overhead.
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