Re: [Qemu-devel] RAM overcomittment

[Paul Brook <paul@codesourcery.com>]

On Wednesday 27 September 2006 22:31, The MoonSeeker wrote:
> Hello,
>
> I'd like to know if qemu have a tool that let a VM to use more RAM
> than it have (when initialised).
>
> Another question is  : Can we run run many VM using more RAM than the
> RAM installed (on the workstation)? For example I'd like to create 5
> VM's who have 256MB (can use 256MB but only for a slice of time) but
> normally one VM use only 50MB. On the workstation I have only 512MB
> RAM. Is it possible to create these VM's or have we to have 5 X 256
> RAM + HOST RAM = 1.5 GB installed on the workstation?
>
> I think we can save ressource by using RAM overcomittment. What do
> you think? Is this implemented on qemu? Or will be implemented?

qemu is just like any other application. It is only limited by how much 
virtual memory your OS can provide. ie. if you have sufficient swap you can 
have as many qemu instances using as much memory as you want.

qemu is currently limits each guest to 2Gb ram. This is independent of how 
much physical memory the host has.

Note that modern OS (everything except DOS) generally use all available ram.  
Telling qemu to use more memory than you have physical ram is liable to cause 
heavy swapping.

Paul