TLB Coalescing for Multi-Grained Page Migration in Hybrid Memory Systems

Superpages have long been proposed to enlarge the coverage of translation lookaside buffer (TLB). They are extremely beneficial for reducing address translation overhead in big memory systems, such as hybrid memory systems that composed of DRAM and non-volatile memories (NVMs). However, superpages conflict with fine-grained memory migration, one of the key techniques in hybrid memory systems to improve performance and energy efficiency. Fine-grained page migrations usually require to splinter superpages, mitigating the benefit of TLB hardware for superpages. In this paper, we present Tamp, an efficient memory management mechanism to support multiple page sizes in hybrid memory systems. We manage large-capacity NVM using superpages, and use a relatively small size of DRAM to cache hot base pages within the superpages. We find that there are remarkable contiguity exist for hot base pages in superpages. In response, we bind those contiguous hot pages together and migrate them to DRAM. We also propose multi-grained TLBs to coalesce multiple page address translations into a single TLB entry. Our experimental results show that Tamp can significantly reduce TLB misses by 62.4% on average, and improve application performance (IPC) by 16.2%, compared to a page migration policy without TLB coalescing support.