Adaptive Code Unloading for Resource-Constrained JVMs

Lingli Zhang and Chandra Krintz



Compile-only JVMs for resource-constrained embedded systems have the potential for using device resources more efficiently than interpreter-only systems since compilers can produce significantly higher quality code and code can be stored and reused for future invocations. However, this additional storage requirement for reuse of native code bodies, introduces memory overhead not imposed in interpreter-based systems.

In this paper, we present a Java Virtual Machine (JVM) extension for adaptive code unloading that significantly reduces the memory requirements imposed by a compile-only JVM. The extension features an unloader that uses execution behavior to adaptively determine *when* to unload as well as *what* code to unload. We implement and empirically identify a set of unloading strategies that enable significant code size reduction (43%-61%). This reduction translates into significant execution time benefits for the benchmarks and JVM configurations that we studied. As such, by using adaptive code unloading, we make compile-only JVMs for embedded devices more feasible.