Efficient migration of large-memory VMS using private virtual memory

Abstract

Recently, Infrastructure-as-a-Service clouds provide virtual machines (VMs) with a large amount of memory. Such large-memory VMs can be migrated to other hosts on host maintenance, but it is costly to always preserve hosts with sufficient free memory as the destination of VM migration. Using virtual memory in destination hosts is a possible solution, but the performance of VM migration largely degrades because traditional general-purpose virtual memory causes frequent paging during the migration. This paper proposes VMemDirect, which achieves efficient migration of large-memory VMs using private virtual memory. VMemDirect creates private swap space for each VM on fast NVMe SSDs. Then it transfers likely accessed memory data to physical memory and the other data to the private swap space directly. This direct memory transfer can completely avoid paging during VM migration. We have implemented VMemDirect in KVM and showed that the performance of VM migration and the migrated VM was improved dramatically.