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any modern machine I've seen has a BIOS that will tell you how much memory
is in the box... I don't know what XEN itself uses, but it shouldn't be
much (looks like maybe 2-5 meg) ... so take 10 or 20 meg off what the
machine has... as long as you don't spec more than that to dom0 you should
be ok... obviously you can't give dom0 256 meg on a 256 meg machine...

once you get xen up and running "xm info" should give you some numbers on
what is in the box.

-Tom

On Mon, 11 Apr 2005, Sunny Dubey wrote:

> hey guys
>
> I've tried specifying the 256MB to dom0_mem= and it panics saying it couldn't
> allocate enough memory. So I tried looking for the memory availability in
> 'dmesg' and 'free', and none of those values work either, the kernel still
> panics.
>
> dom0_mem=262144
>
> The Xen dom0 kernel works fine when I do something drastic like specifying
> only 128MB.
>
> dom0_mem=131072
>
> What is the correct way for figuring how much memory I have and such ?
>
> thanks
>
> Sunny Dubey




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Reformatted, text below.

Am Montag, den 11.04.2005, 18:33 -0700 schrieb Tom Brown:
> On Mon, 11 Apr 2005, Sunny Dubey wrote:
> > I've tried specifying the 256MB to dom0_mem= and it panics saying it couldn't
> > allocate enough memory. So I tried looking for the memory availability in
> > 'dmesg' and 'free', and none of those values work either, the kernel still
> > panics.
> >
> > dom0_mem=262144
> >
> > The Xen dom0 kernel works fine when I do something drastic like specifying
> > only 128MB.
> >
> > dom0_mem=131072
> >
> > What is the correct way for figuring how much memory I have and such ?

Without Xen:
dmesg | grep ^Memory
cat /proc/meminfo

within Xen dom0:
xm info | grep ^memory

> any modern machine I've seen has a BIOS that will tell you how much memory
> is in the box... I don't know what XEN itself uses, but it shouldn't be
> much (looks like maybe 2-5 meg)

On my machine it's ~30MB ("xm info" total minus free memory minus sum of
all "xm list" mems) with 7 domUs running.

> ... so take 10 or 20 meg off what the
> machine has... as long as you don't spec more than that to dom0 you should
> be ok... obviously you can't give dom0 256 meg on a 256 meg machine...

Since you run xen you may plan to run at least one domU. Let's say you
have 256MB RAM installed, and xen itself uses 30MB (probably less), then
you could start with dom0_mem=241664 (236MB), but then there is no
memory left for domUs!

> once you get xen up and running "xm info" should give you some numbers on
> what is in the box.

/nils.



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