Reducing Host Load, Network Load and Latency in a Distributed Shared Memory

Mether is a Distributed Shared Memory (DSM) that runs on Sun¹ workstations under the SunOS 4.0 operating system. User programs access the Mether address space in a way indistinguishable from other memory. Mether had a number of performance problems which we had also seen on a distributed shared memory called Memnet[2]. In this paper we discuss changes we made to Mether and protocols we developed to use Mether that minimize host load, network load, and latency. An interesting (and unexpected) result was that for one problem we studied the same best protocol for Mether is identical to the best protocol for MemNet[6]. The changes to Mether involve exposing an inconsistent store to the application and making access to the consistent and inconsistent versions very convenient; providing both demand-driven and data-driven semantics for updating pages; and allowing the user to specify that only a small subset of a page need be transferred. All of these operations are encoded in a few address bits in the Mether virtual address