Re: [Qemu-devel] RAM overcomittment

[Bill C. Riemers]

I would suggest just the opposite, under  commit your ram.  If your base operating system is Linux, you can create your swap partitions under a host linux tmpfs directory.  You can then safely over commit the amount of tmpfs swap space.  The guest linux system will expect he swap to be slow, so it won't use it for buffering disk IO or such.  However, until you actually exhaust the amount of physical ram available the tmpfs swap will actually be very fast.

Bill

On 9/28/06, James Oakley <address@hidden> wrote:

On Wednesday 27 September 2006 6:59 pm, The MoonSeeker wrote:
> Le 27 sept. 06 à 23:41, Paul Brook a écrit :
> > 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.
>
> Ok but some virtual solution like openVZ allow you run more VM than
> the memory installed. By example, with openVZ I can create 10 Virtual
> Machine who have a limite fixe to 200 MB but have guaranteed RAM of
> 20MB. With qemu I need to have 10 X 200MB for VM's + 128 MB host of
> RAM installed on the work station...
>
> I think we can Save ressource because in the most case, the VM's will
> never use the 200MB. I think it will be a nice if qemu implemented a
> tool that let use exceed this limitation.

Only Windows guests. The Virtuozzo guys don't advertise the fact that Linux
*uses all available RAM*.

Overselling RAM for Linux guests as a terrible idea.

--
James Oakley
Engineering - SolutionInc Ltd.
address@hidden
http://www.solutioninc.com

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