The application performance is as important as the resource utilization when we allocate memory for guest operating systems in virtualized environments.This paper presents a memory-balancing method for virtual machines

named GOSBMB(Guest Operating System Behaviors based Memory Balancer).It aims to minimize the performance loss brought by balancing memory.The memory need of the guest operating system consists of two parts which respectively

cover the amount of the memory consumed by the process working sets

and the memory used as the page cache.GOSBMB estimates the memory need by observing VMM architecturally visible events transparently.Then it allocates the memory resource for the guest operating systems on demand.We have implemented a working prototype of GOSBMB on Xen platform.The memory can be saved up to 69.6% with only 7.6% performance loss when we use GOSBMB to balance memory dynamically.