FaaSnap: FaaS made fast using snapshot-based VMs

FaaSnap is a VM snapshot-based platform that uses a set of complementary optimizations to improve function cold-start performance for Function-as-a-Service (FaaS) applications. Compact loading set files take better advantage of prefetching. Per-region memory mapping tailors page fault handling depending on the contents of different guest VM memory regions. Hierarchical overlapping memory-mapped regions simplify the mapping process. Concurrent paging allows the guest VM to start execution immediately, rather than pausing until the working set is loaded. Altogether, FaaSnap significantly reduces guest VM page fault handling time on the critical path and improves overall function loading performance. Experiments on serverless benchmarks show that it reduces end-to-end function execution by up to 3.5x compared to state-of-the-art, and on average is only 3.5% slower than snapshots cached in memory. Moreover, we show that FaaSnap is resilient to changes of working set and remains efficient under bursty workloads and when snapshots are located in remote storage.