Memory organization based on data temperature

内存管理是任何软件系统的重要组成部分。编程语言提供不同程度的支持。内存中分配的对象具有不同的生命周期。可从根集或从另一个活动对象访问的对象称为活动对象。相比之下，不能再访问的对象被认为是死的。在一些语言中，例如C语言，程序员负责在死对象变得不可访问之前释放它们的内存。在其他语言中，例如Java，垃圾收集器负责收集死对象。有些对象会持续很长时间，但很少被访问；这些对象被认为是冷的。已经表明，将冷对象移动到垃圾收集器未触及的区域是有利的。由于这些区域不经常被访问，因此可以将它们调出到磁盘。将冷对象隔离到特定区域将有助于实际内存占用和高速缓存一致性。随着永久存储器的激增，在这样的存储器中存储具有冷对象的区域是可能的。用于永久存储的术语是NVRAM(非易失性随机存取存储器)。与动态RAM相比，NVRAM的成本更低，访问时间稍长。NVRAM的主要应用一直是数据库事务领域。在这里，我们计划用它来隔离NVRAM中的冷物体。提出的研究的主要目标是通过使用持久存储来提高垃圾收集的有效性。我们将研究冷物体的一些性质。如何检测到冰冷的物体？他们应该什么时候被转移到寒冷的地区？他们应该什么时候从寒冷的地区搬回来？他们应该在什么时候被垃圾收集？这些问题的答案将指导生成的软件的开发、实现和测试，这些软件将包含在IBM J9产品和OMR Eclipse项目的垃圾收集策略中。

Memory management is an essential part of any software system. Programming languages offer different degrees of support. Objects allocated in memory have varying life times. Objects that are accessible from the rootset or from another live object are said to be alive. In contrast, objects that can no longer be accessed are said to be dead. In some languages, for example C, the programmer is responsible to free the memory of dead objects before they become unreachable. In other languages, for example Java, a garbage collector is responsible for collecting dead objects. Some objects persist for a long time but they are seldom accessed; these objects are said to be cold. It has been shown that it is advantageous to move cold object to regions that are not touched by the garbage collector. Since these regions are infrequently accessed, they can be paged out to disk. Sequestering cold objects into special areas will help both the real memory footprint as well as cache coherence.With the proliferation of persistent memory it is possible to store regions with cold objects in such memory. The term used for persistent storage is NVRAM (Non-Volatile Random Access Memory). NVRAM is less costly than dynamic RAM with slightly higher access time. The main application for NVRAM has been in the area of database transactions. Here, we plan to use it to sequester cold objects in NVRAM. The main objective of the proposed research is to increase the effectiveness of garbage collection by making use of persistent memory. Some properties of cold objects will be investigated. How are cold objects detected? When should they be moved to a cold area? When should they move back from the cold area? When shouldthey be garbage collected? The answer to these questions will guide the development, implementation, and testing of software generated for inclusion in the garbage collection strategies of the IBM J9 product as well as the OMR Eclipse project.