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Memory Ballooning
In computing, memory ballooning is a technique used to eliminate the need to overprovision host memory used by a virtual machine (VM). To implement it, the virtual machine's kernel implements a "balloon driver" which allocates unused memory within the VM's address space into a reserved memory pool (the "balloon") so that it is unavailable to other processes on the VM. However, rather than being reserved for other uses within the VM, the physical memory mapped to those pages within the VM is actually unmapped from the VM by the host operating system's hypervisor, making it available for other uses by the host machine. Depending on the amount of memory required by the VM, the size of the "balloon" may be increased or decreased dynamically, mapping and unmapping physical memory as required by the VM. References See also *Memory overcommitment *Thin provisioning In computing, thin provisioning involves using virtualization technology to give the appearance of having more physical ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Computing
Computing is any goal-oriented activity requiring, benefiting from, or creating computing machinery. It includes the study and experimentation of algorithmic processes, and development of both hardware and software. Computing has scientific, engineering, mathematical, technological and social aspects. Major computing disciplines include computer engineering, computer science, cybersecurity, data science, information systems, information technology and software engineering. The term "computing" is also synonymous with counting and calculating. In earlier times, it was used in reference to the action performed by mechanical computing machines, and before that, to human computers. History The history of computing is longer than the history of computing hardware and includes the history of methods intended for pen and paper (or for chalk and slate) with or without the aid of tables. Computing is intimately tied to the representation of numbers, though mathematical conc ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Virtual Machine
In computing, a virtual machine (VM) is the virtualization/emulation of a computer system. Virtual machines are based on computer architectures and provide functionality of a physical computer. Their implementations may involve specialized hardware, software, or a combination. Virtual machines differ and are organized by their function, shown here: * '' System virtual machines'' (also termed full virtualization VMs) provide a substitute for a real machine. They provide functionality needed to execute entire operating systems. A hypervisor uses native execution to share and manage hardware, allowing for multiple environments which are isolated from one another, yet exist on the same physical machine. Modern hypervisors use hardware-assisted virtualization, virtualization-specific hardware, primarily from the host CPUs. * Process virtual machines are designed to execute computer programs in a platform-independent environment. Some virtual machine emulators, such as QEMU and video ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Hypervisor
A hypervisor (also known as a virtual machine monitor, VMM, or virtualizer) is a type of computer software, firmware or hardware that creates and runs virtual machines. A computer on which a hypervisor runs one or more virtual machines is called a ''host machine'', and each virtual machine is called a ''guest machine''. The hypervisor presents the guest operating systems with a virtual operating platform and manages the execution of the guest operating systems. Unlike an emulator, the guest executes most instructions on the native hardware. Multiple instances of a variety of operating systems may share the virtualized hardware resources: for example, Linux, Windows, and macOS instances can all run on a single physical x86 machine. This contrasts with operating-system–level virtualization, where all instances (usually called ''containers'') must share a single kernel, though the guest operating systems can differ in user space, such as different Linux distributions with the s ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Memory Overcommitment
Memory overcommitment is a concept in computing that covers the assignment of more memory to virtual computing devices (or processes) than the physical machine they are hosted, or running on, actually has. This is possible because virtual machines (or processes) do not necessarily use as much memory at any one point as they are assigned, creating a buffer. If four virtual machines each have 1 GB of memory on a physical machine with 4 GB of memory, but those virtual machines are only ''using'' 500 MB, it is possible to create additional virtual machines that take advantage of the 500 MB each existing machine is leaving free. Memory swapping is then used to handle spikes in memory usage. The disadvantage of this approach is that memory swap files are slower to read from than 'actual' memory, which can lead to performance drops. While memory overcommitment is usually talked about in the context of virtualization, it is actually a generalised concept; Windows NT cont ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Thin Provisioning
In computing, thin provisioning involves using virtualization technology to give the appearance of having more physical resources than are actually available. If a system always has enough resource to simultaneously support all of the virtualized resources, then it is not thin provisioned. The term thin provisioning is applied to disk layer in this article, but could refer to an allocation scheme for any resource. For example, real memory in a computer is typically thin-provisioned to running tasks with some form of address translation technology doing the virtualization. Each task acts as if it has real memory allocated. The sum of the allocated virtual memory assigned to tasks typically exceeds the total of real memory. The efficiency of thin or thick/fat provisioning is a function of the use case, not of the technology. Thick provisioning is typically more efficient when the amount of resource used very closely approximates to the amount of resource allocated. Thin provisio ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Virtual Machines
In computing, a virtual machine (VM) is the virtualization/emulation of a computer system. Virtual machines are based on computer architectures and provide functionality of a physical computer. Their implementations may involve specialized hardware, software, or a combination. Virtual machines differ and are organized by their function, shown here: * '' System virtual machines'' (also termed full virtualization VMs) provide a substitute for a real machine. They provide functionality needed to execute entire operating systems. A hypervisor uses native execution to share and manage hardware, allowing for multiple environments which are isolated from one another, yet exist on the same physical machine. Modern hypervisors use hardware-assisted virtualization, virtualization-specific hardware, primarily from the host CPUs. * Process virtual machines are designed to execute computer programs in a platform-independent environment. Some virtual machine emulators, such as QEMU and video ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
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