Improving host swapping using adaptive prefetching and paging notifier

In a virtualized system, the hypervisor may be forced to reclaim memory by swapping out pages of guest operating systems (OSes) when the regular memory balancing mechanisms, such as page sharing and ballooning, fail to revoke enough memory for reallocation purpose, which always leads to serious performance degradation. In this paper, we introduce Adaptive Swap Prefetcher (ASP) and Host Swapping Notifier (HSN), the effective and lightweight solutions to gracefully reduce the degradation in system performance when host swapping is triggered. ASP smartly prefetches more pages from the host swap file as long as the good spatial locality persists so as to reduce disk transfers. The guest OS will be notified by HSN when the hypervisor evicts pages, which then hides those pages from its memory reclamation routines to eliminate unnecessary guest swapping and to prevent the occurrence of double paging anomaly. Currently ASP and HSN are implemented in KVM, experimental results show that guest performance can be improved by a factory of 1.4x and 2x respectively using ASP and HSN.