Abstract:
Embodiments of the present invention address deficiencies of the art in respect to virtualization and provide a novel and non-obvious method, system and computer program product for monitoring and managing memory used in a virtualized computing environment. In this regard, a method for monitoring and managing memory used by a virtual machine in a virtualized computing environment can include counting page fault occurrences in a guest operating system (OS) executing in the VM, pinning additional physical memory to the VM along with initiating a hot-add event to the guest OS executing in the VM, responsive to exceeding a page fault allowance threshold in order to mitigate system degradation in the VM based on page fault occurrences.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    1. Field of the Invention 
         [0002]    The present invention relates to the field of virtualization and more particularly to memory management of operating systems executing in virtualized computing environments. 
         [0003]    2. Description of the Related Art 
         [0004]    As processor power increased exponentially throughout the years, advanced forms of operating systems (OS) enabled both simulated and actual multi-tasking such that multiple applications could execute within the same host computing environment. Most applications have become co-dependent on the presence of other applications such that the requisite environment for an application includes not only the underlying operating system and supporting hardware platform, but also other key applications including application servers, database management servers, collaboration servers and communicative logic commonly referred to as middleware. 
         [0005]    Recently, virtualization has been able to offer the inherent advantage of environment portability. Further, more powerful computing environments can support the coexistence of multiple different virtual machine (VM) images, all the while maintaining a virtual separation between the VM images. Consequently, a failure condition in one VM image cannot jeopardize the integrity of other co-executing VM images in the same hardware platform. 
         [0006]    In a virtualized environment, a virtual machine monitor/manager (VMM) is the primary resource manager, capable of managing the interaction between each VM image and the underlying resources provided by the hardware platform. The VMM, also known as the hypervisor, can support the operation of different “guest operating system images”—known as VM images—the number of VM images being limited only by the processing resources of a VM container holding the VM images or the hardware platform itself. 
         [0007]    The hypervisor typically manages the resources of CPU, memory and storage. There are two main categories of memory regarding a VM image, virtual memory and physical memory. Virtual memory can be greater than physical memory. Typically, a guest OS running in a VM manages pages internally in a page table in its virtual memory. While processing memory, if a request is made for a memory page that is not currently within the set of pages visible to the process in memory, an event known as a “page fault” occurs when a program accesses a page that is mapped in address space, but not loaded in physical memory. Since a page fault is essentially an interrupt (or exception) to the software raised by the hardware, page faults in a VM can cause significant performance penalties that disadvantage the base resource consolidation benefit inherent in virtualization for enterprise production environments. 
         [0008]    Large resource rich systems meant for virtualization of production environments are more efficient when VM virtual memory does not exceed the physical memory attributed to that VM and the physical memory is additionally pinned to the specific VM. VM memory performance can be near optimal when virtual memory is equivalent to pinned (allocated) physical memory and the amount of virtual memory is sufficient to avoid paging outside the VM scope. 
         [0009]    For instance, when an operating system starts to run out of memory, it will start to page fault and typically on a bare metal system end up paging out to disk. Nevertheless, inside a VM that disk is virtual and could be either a physical system entity managed by the hypervisor or merely a large memory buffer managed by the hypervisor. Yet, the drawback still remains that paging will end up degrading the system even as the hypervisor attempts to manage page faults. In most cases the amount of memory allocated to a VM is generally static during runtime of the VM. Some hypervisors have the capability to manually add or remove memory runtime to the VM if the OS running in the VM has hot-add capability. While a hot-add event could be purely virtual, such a hot-add event does not address the large performance penalty due to page faulting and actually contributes to the degradation and therefore is of minimal interest. 
       BRIEF SUMMARY OF THE INVENTION 
       [0010]    Embodiments of the present invention address deficiencies of the art in respect to virtualization and provide a novel and non-obvious method, system and computer program product for monitoring and managing memory used in a virtualized computing environment. In this regard, a method for monitoring and managing memory used by a virtual machine in a virtualized computing environment can include counting page fault occurrences in a guest operating system (OS) executing in the VM, pinning additional physical memory to the VM along with initiating a hot-add event to the guest OS executing in the VM, responsive to exceeding a page fault allowance threshold in order to mitigate system degradation in the VM based on page fault occurrences. 
         [0011]    In yet another embodiment, specifying requisite access to physical memory allocated to the VM, in a configuration file, wherein the configuration file includes a page fault threshold of the VM can be included. In another embodiment, the method can include monitoring page faults based on a pre-specified threshold level. 
         [0012]    In another embodiment of the invention, a virtualization data processing system can be provided. The system can include a hypervisor configured for execution in a host computing platform, a VM image managed by the hypervisor, and, system degradation mitigation logic coupled to the hypervisor, the logic comprising program code enabled to count page fault occurrences in a guest operating system (OS) running in the VM, pin additional physical memory to the VM and initiate a hot-add event to the guest OS running in the VM responsive to exceeding a page fault allowance threshold. 
         [0013]    Additional aspects of the invention will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The aspects of the invention will be realized and attained by means of the elements and combinations particularly pointed out in the appended claims. It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory only and are not restrictive of the invention, as claimed. 
     
    
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS 
         [0014]    The accompanying drawings, which are incorporated in and constitute part of this specification, illustrate embodiments of the invention and together with the description, serve to explain the principles of the invention. The embodiments illustrated herein are presently preferred, it being understood, however, that the invention is not limited to the precise arrangements and instrumentalities shown, wherein: 
           [0015]      FIG. 1  is pictorial illustration of a virtualization data processing system configured to monitor and manage memory used by a hypervisor; 
           [0016]      FIG. 2  is a schematic illustration of a virtualization data processing system configured to monitor and manage memory used by a hypervisor; and 
           [0017]      FIG. 3  is a flow chart illustrating a process for monitoring and managing memory used by a hypervisor. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0018]    Embodiments of the present invention provide a method, system and computer program product for monitoring and managing memory used in a virtual machine environment. In accordance with an embodiment of the present invention, the number of page fault occurrences in a guest OS running in a VM can be counted. Responsive to the counted page faults exceeding a page fault threshold, additional physical memory can be pinned to the VM. Thereafter, a hot-add event can be initiated to the guest OS executing in the VM controlled by a hypervisor. 
         [0019]      FIG. 1  is a pictorial illustration of a virtualization data processing system configured to monitor and manage memory used by a hypervisor. As shown in  FIG. 1 , a host computing platform  110  can support the operation of a virtual machine monitor, also known as a hypervisor  120 , managing multiple different VM images  130 . Each of the VM images  130  can provide a computing environment, including a guest operating system  160 , for one or more corresponding applications  170 . As such, the hypervisor  120  can establish a configuration  140  for each different one of the VM images  130  specifying requisite access to computing resources provided by the host computing platform  110 , for instance processor, physical memory pool  190 , file system, communications and even other ones of the VM images  160 . The requisite access specified in each configuration  140  can support the intended amount of internal memory  150  in each VM image  130 . 
         [0020]    Initially, a VM image  160  can be configured to use internal memory  150  linked to the physical memory pool  190  of the host computing platform. The hypervisor  120  can be configured to monitor the VM and count a number of page fault occurrences in a guest OS  160  executing in the VM  130 . Thereafter, based on detecting a threshold count of page fault occurrences, the hypervisor  120  can be configured to mitigate system degradation. In order to mitigate system degradation, the hypervisor  120  can be configured to pin additional physical memory  190  to the VM once the page fault threshold  125  has been exceeded, and initiate a hot-add event  195 , providing an on-demand increase in virtual memory  180 . A hot-add event notifies the guest OS  160  that a memory module is about to be added and the guest OS  160  can remap data in the memory module prior to the addition of physical memory. Since the hot-added virtual memory  180  allocated to the VM  130  is pinned to physical memory  190 , the page faulting will eventually abate the system degradation. 
         [0021]    In further illustration,  FIG. 2  is a schematic illustration of a virtualization data processing system configured to monitor and manage memory used by a hypervisor. The system can include a host computing platform  210  coupled to a hypervisor  220 . Furthermore, the system can also include a physical memory pool  280  coupled to the host computing platform  210 . The hypervisor  220  can be configured to manage one or more VM images  230 . A VM image  230  can notably include a guest OS  240 , application instances, middleware, and/or an application server within the VM image. The guest OS  240  inside of the VM  230  can be encapsulated in a virtual environment. The hypervisor  220  is the layer between the VMs  230  and the physical hardware to maintain safe and transparent interactions between the VMs and the physical hardware. Notably, each VM session can be a separate entity that is isolated from other VMs by the hypervisor. If one VM crashes or otherwise becomes unstable, the other VMs, as well as the hypervisor, should not be adversely affected. Thus, the guest OS  240  can lack any awareness of the surrounding physical resources and even the hypervisor  220 . 
         [0022]    The system can further include system degradation mitigation logic  250  coupled to the hypervisor  220 . The system degradation mitigation logic  250  can include program code enabled to monitor VM images  230  for page fault system degradation based on the currently allocated resources of the VM images  230 . Furthermore, the system degradation mitigation logic can be enabled to count a number of page fault occurrences in a guest OS  240  running in a VM, and determine whether the page fault threshold has been exceeded. If the number of page faults exceeds the page fault threshold, the system degradation mitigation logic  250  can be enabled to pin more physical memory from the physical memory pool  280  to the VM image  230  and initiate a hot-add event  260  based on exceeding the page fault threshold. 
         [0023]    In yet further illustration,  FIG. 3  is a flow chart illustrating a process for monitoring and managing memory used by a hypervisor. The process can begin in block  310  in which a configuration file from a VM can be read. The configuration file can specify requisite access to computing resources, such as initial physical memory allocated to the VM at startup, provided by the host computing platform. Additionally, the configuration file can specify a page fault threshold for a VM image. In block  320 , physical memory can be allocated to the VM as designated in the configuration file. In block  330  the VM image can be monitored and the number of page fault occurrences in the VM image can be counted. Notably, monitoring page faults to a threshold level can be a matter of policy, including determining what threshold level to specify for a VM image. 
         [0024]    In decision block  340 , if the page fault count is greater than the page fault threshold, additional physical memory can be pinned from the host computing platform&#39;s physical memory pool to the VM in block  350 . Thereafter, a hot-add event can be initiated to the OS inside the VM in block  360 . Hot-add memory allows ranges of physical memory to be added to a running operating system without requiring the system to be shut down. 
         [0025]    Notably, it should be recognized by one skilled in the art that the process of removing memory can be implemented based on low page fault occurrences. For example, a low water mark where paging is significantly low from the guest OS that the hypervisor via a policy definition can be enabled to initiate a removal of memory from the guest OS&#39; internal usage. In other words, the hypervisor can initiate a hot remove event triggered to the guest OS running in the VM and subsequently deallocate corresponding physical memory back to the physical memory pool of the host computing platform. 
         [0026]    Embodiments of the invention can take the form of an entirely hardware embodiment, an entirely software embodiment or an embodiment containing both hardware and software elements. In a preferred embodiment, the invention is implemented in software, which includes but is not limited to firmware, resident software, microcode, and the like. Furthermore, the invention can take the form of a computer program product accessible from a computer-usable or computer-readable medium providing program code for use by or in connection with a computer or any instruction execution system. 
         [0027]    For the purposes of this description, a computer-usable or computer readable medium can be any apparatus that can contain, store, communicate, propagate, or transport the program for use by or in connection with the instruction execution system, apparatus, or device. The medium can be an electronic, magnetic, optical, electromagnetic, infrared, or semiconductor system (or apparatus or device) or a propagation medium. Examples of a computer-readable medium include a semiconductor or solid state memory, magnetic tape, a removable computer diskette, a random access memory (RAM), a read-only memory (ROM), a rigid magnetic disk and an optical disk. Current examples of optical disks include compact disk-read only memory (CD-ROM), compact disk-read/write (CD-R/W) and DVD. 
         [0028]    A data processing system suitable for storing and/or executing program code will include at least one processor coupled directly or indirectly to memory elements through a system bus. The memory elements can include local memory employed during actual execution of the program code, bulk storage, and cache memories which provide temporary storage of at least some program code in order to reduce the number of times code must be retrieved from bulk storage during execution. Input/output or I/O devices (including but not limited to keyboards, displays, pointing devices, etc.) can be coupled to the system either directly or through intervening I/O controllers. Network adapters may also be coupled to the system to enable the data processing system to become coupled to other data processing systems or remote printers or storage devices through intervening private or public networks. Modems, cable modem and Ethernet cards are just a few of the currently available types of network adapters.