Re: [Xen-users] Contending RAM

[tbrown@xxxxxxxxxxxxx]

AFAIK, having xen do virtual memory is out of the question... it would
need all sorts of device drivers etc that are (as I understand it)
purposely not part of xen. (e.g. xen doesn't know what a disk is, let
alone a SCSI/IDE/SATA driver is...)

However. It seems to me, that you might be able to get dom0 to do this...
How about creating a big tmpfs filesystem in dom0, putting some big files
on that and exporting those to the various domU to use as swapdevices?

Assuming it works, the effect should be something close to swapping to a
ramdisk. Slower than running on real memory, but faster than swapping to
disk.

I don't generally have much cause to work with sparse files, but I image
the swapfiles could be initialized as sparse files, which would save
a number of resources on startup.

Anyone care to experiment and report back?

-Tom

On Wed, 31 May 2006, Anthony Liguori wrote:

> Andy Davidson wrote:
> >
> > On 31 May 2006, at 20:37, Anthony Liguori wrote:
> >
> >> Andy Davidson wrote:
> >>> Ideally, we'd like to content system ram - so each machine is
> >>> configured to have 1GB available.  This obviously means we need to
> >>> contend memory .. probably 3:1 (including the requirements of the
> >>> Dom-0). Is this possible ?
> >> maxmem = 1024
> >> memory = 256
> >> When it comes time to use the VM you care about, use xm mem-set to
> >> increase it's memory to 1G (and after you're finished, decrease it
> >> back down to 256).
> >
> > Many thanks for replying.
> >
> > I see; this isn't possible to do dynamically ?
>
> It requires manual intervention.  As someone has previously mentioned,
> Xen does not support any concept of overcommit.
>
> Regards,
>
> Anthony Liguori
>
> > -a
> >
>
>
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