Explicit Management of Memory Hierarchy

All scalable parallel computers feature a memory hierarchy, in which some locations are “closer” to a particular processor than others. The hardware in a particular system may support a shared memory or message passing programming model, but these factors effect only the relative costs of local and remote accesses, not the system’s fundamental Non-Uniform Memory Access (NUMA) characteristics. Yet while the efficient management of memory hierarchies is fundamental to high performance in scientific computing, existing parallel languages and tools provide only limited support for this management task. Recognizing this deficiency, we propose abstractions and programming tools that can facilitate the explicit management of memory hierarchies by the programmer, and hence the efficient programming of scalable parallel computers. The abstractions comprise local arrays, global (distributed) arrays, and disk resident arrays located on secondary storage. The tools comprise the Global Arrays library, which supports the transfer of data between local and global arrays, and the Disk Resident Arrays (DRA) library, for transferring data between global and disk resident arrays. We describe the shared memory NUMA model implemented in the tools, discuss extensions for wide area computing environments, and review major applications of the tools, which currently total over one million lines of code.