Evaluation of a minimally synchronous algorithm for 2:1 octree balance

The p4est library implements octree-based adaptive mesh refinement (AMR) and has demonstrated parallel scalability beyond 100,000 MPI processes in previous weak scaling studies. This work focuses on the strong scalability of mesh adaptivity in p4est, where the communication pattern of the existing 2:1-balance is a latency bottleneck. The sorting-based algorithm of Malhotra and Biros has balanced communication, but synchronizes all processes. We propose an algorithm that combines sorting and neighbor-to-neighbor exchange to minimize the number of processes each process synchronizes with.