Memory overcommitment is a concept in

computing Computing is any goal-oriented activity requiring, benefiting from, or creating computer, computing machinery. It includes the study and experimentation of algorithmic processes, and the development of both computer hardware, hardware and softw ...

that covers the assignment of more

memory Memory is the faculty of the mind by which data or information is encoded, stored, and retrieved when needed. It is the retention of information over time for the purpose of influencing future action. If past events could not be remembe ...

to virtual computing devices (or processes) than the physical machine they are hosted, or running on, actually has. This is possible because

virtual machine In computing, a virtual machine (VM) is the virtualization or emulator, emulation of a computer system. Virtual machines are based on computer architectures and provide the functionality of a physical computer. Their implementations may involve ...

s (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. Another disadvantage is that, when running out of real memory, the system is relying on the applications to not use the additional memory despite it being allocated to them. Should a program do so anyway, it or another has to be killed in order to free up memory to prevent the system from freezing. The OOM Killer is what performs this task. While memory overcommitment is usually talked about in the context of

virtualization In computing, virtualization (abbreviated v12n) is a series of technologies that allows dividing of physical computing resources into a series of virtual machines, operating systems, processes or containers. Virtualization began in the 1960s wit ...

, it is actually a generalised concept;

Windows NT Windows NT is a Proprietary software, proprietary Graphical user interface, graphical operating system produced by Microsoft as part of its Windows product line, the first version of which, Windows NT 3.1, was released on July 27, 1993. Original ...

contained overcommitment features, as do most modern generalised operating systems, including the

Linux kernel The Linux kernel is a Free and open-source software, free and open source Unix-like kernel (operating system), kernel that is used in many computer systems worldwide. The kernel was created by Linus Torvalds in 1991 and was soon adopted as the k ...

References

Virtual machines Hardware virtualization {{compsci-stub

See also

References