Scalability Challenges in Current MPI One-Sided Implementations

MPI one-sided or remote memory access (RMA) communication provides a different execution model from traditional two-sided or group communication and is better suited for some classes of applications. However, current implementations of MPI RMA are notorious for their inability to scale to large systems or problem sizes. In this paper, we present a study of the RMA infrastructure in popular open-source MPI implementations. Our objective is to identify critical scalability limitations with respect to memory usage in these implementations. We then perform a thorough evaluation on two cluster computers to demonstrate those scalability limitations, and we provide suggestions on how they can be alleviated.