UniMem: Redesigning Disaggregated Memory within A Unified Local-Remote Memory Hierarchy

Disaggregated memory (DM) has been proposed as a feasible solution towards scaling memory capacity. A variety of memory disaggregation approaches have been introduced to facilitate the practical use of DM. The cache-coherent-based DM system, which relies on cache-coherent accelerator, can offer network-attached memory as NUMA memory. However, the current cache-coherent-based DM system introduces an extra address translation for each remote memory access. Meanwhile, the local cache mechanism of existing approaches overlooks the inherent issues of cache thrashing and pollution that arise from DM system. This paper presents UniMem, a cache-coherent-based DM system that proposes a unified local-remote memory hierarchy to remove extra indirection layer on remote memory access path. To optimize local memory utilization, UniMem redesigns the local cache mechanism to prevent cache thrashing and pollution. Furthermore, UniMem puts forth a page migration mechanism that promotes frequently used pages from device-attached memory to host memory based not only on page hotness but also on hotness fragmentation. Compared to state-of-the-art systems, UniMem reduces the average memory access time by up to 76.4% and offers substantial improvement in terms of data amplification.