Tackling Memory Footprint Expansion During Live Migration of Virtual Machines
Roja Eswaran, Mingjie Yan, Kartik Gopalan · 2024
Live migration is widely used in cloud platforms to transfer Virtual Machines (VMs) from one physical machine to another. Live migration is useful for workload consolidation, load balancing, failure management, and energy savings. Copy-on-write (COW) page sharing allows identical pages to be shared both within a VM and across co-located VMs to reduce their collective memory footprint. Current live migration techniques are not aware of such page sharing; thus they do not preserve pre-existing page sharing when migrating VMs to a common destination machine. Consequently, each shared page is replicated at the destination multiple times as if they were separate pages. This expansion of the memory footprint of VMs during migration can lead to problems such as migration failure, increased network traffic, and longer migration times. We propose Sharing-aware Live Migration (SLM), which preserves pre-existing COW page sharing within and across VMs that are migrated to a common destination machine. The key idea is to identify guest pages that are mapped to the same physical page at the source machine and to map them to the same physical page at the destination. We present SLM technique for both pre-copy and post-copy live migration of multiple VMs and describe its implementation on the KVM/QEMU virtualization platform. Our evaluations show that SLM successfully preserves pre-existing COW page sharing during migration, eliminates the risk of migration failure due to memory expansion, and reduces total migration time and network traffic overhead.