Object-level management of tiered memory has been studied to address the inefficiencies in page-based systems. However, object-level management for CXL-tiered memory remains underexplored due to CXL's tight performance budget and load/store interface. As a result, existing approaches remain limited in scope, primarily targeting unmanaged-language applications with bespoke runtimes or compiler support. This paper identifies and explores a new design point for object-level CXL management: managed languages and their runtimes. The key observation is that existing managed runtimes already provide highly optimized mechanisms for problems closely related to object-level management, including object relocation and dynamic code generation. However, they still lack the features needed for tiered memory management, such as hotness tracking and relocation policies, and thus must be carefully extended to fully realize this direction. We present Clove, a system that extends existing managed runtimes to support object-level CXL management for managed-language applications. Clove combines profile-guided object hotness tracking with object relocation techniques and policies. Our JVM prototype demonstrates that this extension enables high utilization of fast-tier memory while bounding runtime overhead, reducing application slowdown by 22-84% compared to page-based systems.

翻译：分层内存的对象级管理已被研究用以解决基于页面的系统中存在的低效问题。然而，由于CXL严格的性能预算与加载/存储接口，针对CXL分层内存的对象级管理仍未被充分探索。因此，现有方法范围受限，主要针对采用定制运行时或编译器支持的非托管语言应用。本文识别并探索了一个对象级CXL管理的新设计点：托管语言及其运行时。关键观察在于，现有托管运行时已为对象级管理密切相关的核心问题（包括对象重定位与动态代码生成）提供了高度优化的机制。然而，它们仍缺乏分层内存管理所需的功能（如热度追踪与重定位策略），因此必须谨慎扩展以充分实现这一方向。我们提出Clove，一个扩展现有托管运行时以支持托管语言应用的对象级CXL管理的系统。Clove将基于配置文件的对象热度追踪与对象重定位技术及策略相结合。我们的JVM原型证明，该扩展能够在限制运行时开销的同时实现快速层内存的高利用率，相较于基于页面的系统，应用性能降级减少了22–84%。