Virtualization essentially enables multiple operating systems and applications to run on one physical computer by multiplexing hardware resources. A key motivation for applying virtualization is to improve hardware resource utilization while maintaining reasonable quality of service. However, such a goal cannot be achieved without efficient resource management. Though most physical resources, such as processor cores and I/O devices, are shared among virtual machines using time slicing and can be scheduled flexibly based on priority, allocating an appropriate amount of main memory to virtual machines is more challenging. Different applications have different memory requirements. Even a single application shows varied working set sizes during its execution. An optimal memory management strategy under a virtualized environment thus needs to dynamically adjust memory allocation for each virtual machine, which further requires a prediction model that forecasts its host physical memory needs on the fly. This paper introduces MEmory Balancer (MEB) which dynamically monitors the memory usage of each virtual machine, accurately predicts its memory needs, and periodically reallocates host memory. MEB uses two effective memory predictors which, respectively, estimate the amount of memory available for reclaiming without a notable performance drop, and additional memory required for reducing the virtual machine paging penalty. Our experimental results show that our prediction schemes yield high accuracy and low overhead. Furthermore, the overall system throughput can be significantly improved with MEB.
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