Memory organization based on data temperature

内存管理是任何软件系统的重要组成部分。编程语言提供了不同程度的支持。在内存中分配的对象具有不同的生命周期。可以从根集或其他活动对象访问的对象称为活动对象。相反，不能再访问的对象被称为死对象。在某些语言中，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；这些物体据说是冷的。已经证明，将冷对象移动到垃圾收集器不接触的区域是有利的。由于这些区域很少被访问，因此可以将它们分页到磁盘上。将冷对象隔离到特殊区域将有助于实际内存占用和缓存一致性。随着持久内存的扩散，在这种内存中存储具有冷对象的区域成为可能。用于持久存储的术语是NVRAM（非易失性随机存取存储器）。NVRAM比动态RAM成本更低，但访问时间稍长。NVRAM的主要应用是在数据库事务领域。在这里，我们计划使用它将冷对象隔离在NVRAM中。所提出的研究的主要目标是通过使用持久内存来提高垃圾收集的有效性。研究冷物体的一些性质。如何检测冷物体？什么时候应该把他们转移到寒冷的地区？他们应该什么时候从寒冷地区搬回来？什么时候应该收垃圾？这些问题的答案将指导为包含在IBM J9产品和OMR Eclipse项目的垃圾收集策略中而生成的软件的开发、实现和测试。

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 should**they 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.