Re: [Xen-users] Guidelines for Dom0 memory

["William Man" <williamman@xxxxxxxxxxxxxxxx>]

My box runs Debian Sarge with xen 2.0.7, LVM and 6 guest domains and seems
to be happy with just 64M.  Running top reveals that it is using zero swap
and still has 30MB of free ram.
However, my host domain is purely used for hosting xen and nothing else.

I started off with 32MB, but found it started to struggle a little then
up'ed it to 64.

W

----- Original Message ----- 
From: "JHJE (Jan Holst Jensen)" <jhje@xxxxxxxxxxxxxxx>
To: "Edwards, Nigel (Nigel Edwards)" <nigel.edwards@xxxxxx>;
<xen-users@xxxxxxxxxxxxxxxxxxx>
Sent: Friday, January 06, 2006 11:47 AM
Subject: RE: [Xen-users] Guidelines for Dom0 memory


> 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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