Dynamic memory paravirtualization transparent to guest OS

Abstract

has shown that a novel Dynamic Memory Mapping (DMM) model brings about additional flexibility to virtual resource management, leading to the feature-adjustable design of a virtual machine monitor (VMM). The study is reported in Issue 53 (June, 2010) of SCIENCE CHINA Information Sciences because of its significant research value. Memory is one of the most frequently accessed components in virtual machine (VM) systems. Because a VM's memory requirement varies according to the running applications, disregarding the dynamic changes can result in suboptimal use of memory resources, which negatively affects the VM's performance. However, because the infrastructures of current technologies are usually independent of each other, they exhibit poor extensibility, integrity, and maintainability. To improve the flexibility and extensibility of the VMM, we need to implement a dynamic memory management mechanism in the VMM, while preserving the high efficiency of memory accesses from virtual machines. To resolve these problems, this work proposes a DMM model [1]. The DMM model is a low-level memory management mechanism, which allows dynamic change of the mapping between the pseudo-physical memory as seen from VMs and the machine memory, while the virtual machine is running. On one hand, DMM is independent of, yet compatible with, various virtualization architectures, while on the other, it presents a uniform upward interface for supporting high-level memory management policies. As a result, the DMM layer incorporates high-level policies and low-level implementations by making both of them adjustable. In this work, Prof. Wang, Prof. Luo and their group present the principle of the DMM model, and explain the procedures of various memory management policies under this model, such as demand paging, virtual memory and memory sharing. They also implement the DMM model in KVM, an open source VMM. They first designed a memory pool, a set of machine pages provided by the VMM to a particular virtual machine whose size could be expanded or shrunk while operating. To make the model work in a real system, they manipulated a page-level protection mechanism to propagate memory-mapping updates to the shadow page tables, which is the only way for a VM to access its virtualized memory. They also utilized reverse mapping, a data structure that maps a machine page back to all the shadow page table entries that have mapped it, to facilitate the mapping propagation. The DMM model has several advantages over the current memory management mechanism in VMMs. The first is platform independ-ency-the model is defined abstractly, thus is independent of implementations and computer architectures. The second is flexibility-the DMM model provides a uniform interface for integrating advanced memory management policies. Through the general mechanism, they can work together without conflict. Last but not least, the modular and layered design of the DMM reduces the complexity of a VMM's code base, and therefore improves the security and dependability of the sys...

Evaluating industrial applicability of virtualization on a distributed multicore platform

“…The knowledge of current and future memory requirements of a virtual machine is an important input to the memory controller so that it can efficiently manage system memory. Several memory optimization techniques are implemented in the xen hypervisor, such as xen memory paging [3], paravirtualized paging [18] and dynamic memory virtualization [19]. However, these techniques do not estimate accurate memory consumption of a virtual machine over time.…”

Selective hardware/software memory virtualization

“…As another attempt, Wang et al propose Dynamic Memory Para-virtualization (DMP) to improve the performance of memory virtualization in [13]. For a VM in SP mode, DMP instruments the VMM to dynamically modify the Guest OS kernel binary code, so as to make use of the guest page table to find machine addresses.…”

“…The performance of a VM is often much inferior to the underlying native machine performance. Much effort has been made recently to reduce virtualization overhead in both software and hardware sides [1,4,11,13]. This paper focuses on one major overhead caused by memory or page table virtualization.…”

Selective hardware/software memory virtualization

“…The performance of a VM is often much inferior to the underlying native machine performance. Much effort has been made recently to reduce virtualization overhead in both software and hardware sides [1,4,11,13]. This paper focuses on one major overhead caused by memory or page table virtualization.…”