Shared Heap Management for Memory-Limited Java Virtual Machines

摘要

One scarce resource in embedded systems is memory. Multitasking makes the lack of memory problem even worse. Most current embedded systems, which do not provide virtual memory, simply divide physical memory and evenly assign, contiguous memory chunks to multiple applications. Such simple memory management can frequently cause the lack of available memory for some applications, while others are not using the full amount of assigned memory. To overcome inefficiency in current memory management, we present an efficient heap management scheme that allows multiple applications to share heap space. To reduce overall heap memory usage, applications adaptively acquire subheaps out of shared pool of memory and release surplus subheaps to shared pool. As a result, applications see noncontiguous multiple subheaps as a heap in their address space. We target Java applications to implement our heap-sharing scheme in the KVM from Sun Microsystems. To protect fragmented heap space with a limited number of regions in memory protection unit (MPU), we maintain only a limited number of subheaps. We experimentally evaluate our heap management scheme with J2ME MIDP applications. Our static and dynamic schemes reduce heap memory usage, on average, by 30 and 27%, respectively. For both schemes, overheads are kept low. The execution times in our schemes are increased only by 0.01% for static scheme and 0.35% for dynamic scheme, on average.