Clove: Object-Level CXL Memory Management in Managed Runtimes

TL;DR

Clove is a system that extends managed runtimes to enable efficient object-level CXL memory management, improving fast-tier memory utilization with bounded overhead.

Contribution

It introduces Clove, a novel approach that integrates hotness tracking and object relocation into managed runtimes for CXL memory management.

Findings

Reduces application slowdown by 22-84% compared to page-based systems.

Enables high utilization of fast-tier memory.

Extends existing managed runtimes with minimal overhead.

Abstract

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.