Fwd: [Xen-users] Why limit dom0's memory?

["Gastón Keller" <gastonkeller@xxxxxxxxx>]

---------- Forwarded message ----------
From: Gastón Keller <gastonkeller@xxxxxxxxx>
Date: Sat, 14 Jun 2008 08:34:56 -0400
Subject: Re: [Xen-users] Why limit dom0's memory?
To: "Sandor W. Sklar" <ssklar@xxxxxxxxxxxx>

On 6/14/08, Sandor W. Sklar <ssklar@xxxxxxxxxxxx> wrote:
>
> Could someone explain why it is recommended to limit the amount of
> memory on the Dom0 via setting dom0_mem=XXX in grub.conf?  Are there
> situations where the dom0 would grab onto more memory then it needs?
>
> I've got two systems (RHEL5.1) running with the Xen kernel; each
> system (X86-64) has 8 GB of RAM.
>
> On one system, as reported by "xm list", the dom0 is using 4978 MiB,
> while the sum of the five domU's memory usage is 2075 MiB, which
> roughly equals full usage of the 8 GB.
>
> On the other, the dom0 is using 2943 MiB, while the sum of the six
> domUs is 5114 MiB, again with a rough total of 8 GB.
>
> So, it appears that the dom0 basically just consumes all memory not
> used by domUs, and will release that memory when it is needed by a new
> guest.  If that is true, then I don't see the advantage of forcing the
> dom0 to a hard memory limit, but there must be one, since the option
> is there and people are using it (or so google tells me.)
>
> Do I have this wrong, or am I not understanding something?

AFAIK what some people is doing is setting a level of memory for Dom0
for it to never go down that level (giving memory to the guests). That
is, if you set the memory to 1 GB, Dom0 will allocate all your memory
except for that 1 GB. It's a way of ensuring that Dom0 will never run
out of memory.

 Gaston
>
> Thanks,
>       -s-
>
>
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>


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La única verdad es la realidad.



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La única verdad es la realidad.

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