RE: [Xen-users] Guidelines for Dom0 memory

["JHJE (Jan Holst Jensen)" <jhje@xxxxxxxxxxxxxxx>]

> Is anybody aware of any work on guidelines for Dom0 memory settings -
> the dom0_mem  parameter for the Dom0 boot? Is there an easy way to
> determine a minimum value?

I run with 128 MB for dom0. Don't think it is worth adjusting it more
down. I have 5 guest domains that run via LVM and dom0 uses about 60 MB
itself. You will need something for the python stuff etc. (using xen
2.0.6).

> Does virtual I/O and sharing of memory pages with Dom0 have an effect
> that needs to be accounted for?

Definitely. If you use loopback devices for hosting guest file systems,
dom0 caches all that I/O and that loads dom0 considerably mem-wise. I
started using loopback devices and found that whenever I wanted to login
to dom0 there would be a noticeable delay (about one second) before
getting a login prompt (ssh access). After having switched to LVM I see
no more delay and memory load is much less in dom0.

> There doesn't seem to be a lot about this in the Xen 
> documentation. I'd
> really rather not allocate memory to Dom0 that isn't needed.

Me too. Haven't looked for much more docs since I brought this up on the
mailing list some time ago though.

Cheers
-- Jan Holst Jensen, Novo Nordisk, Denmark

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