SA-PFRS: Semantics-Aware Page Frame Reclamation System in Virtualized Environments

Page reclamation is one compelling way to overcommit memory in modern operating systems. To achieve wise reclamation, the Linux kernels employ page frame reclamation algorithm (PFRA) to reclaim pages based on the page usage view. However, due to the semantic gap problem in virtualized environments, the native PFRA suffers three types of unwise evictions including false eviction, superficial eviction and omitted eviction. This will lead to high swapping I/O activity and consequently limits the ability to overcommit memory. We present SA-PFRS, a Semantics-Aware Page Frame Reclamation System, to address this problem. SA-PFRS separates the memory pages allocated for guests from reclaimable candidates in host, explores how the pages are being used by guest OS, and adjusts the reclamation order in the view of guest. Then, SA-PFRS re-arranges the reclamation sequence of guest pages and host pages, so as to reclaim the memory pages in a global semantics-aware manner. This enables SA-PFRS to eliminate a large number of swapping I/O operations when memory is overcommitted. We implement a prototype of SA-PFRS in Linux kernel, and show its effectiveness through a set of experiments.