[Xen-users] Strange memory issue

[Flavio <fbcyborg@xxxxxxxxx>]

Hello,

I would like to ask you some clarification about the memory management in the
XEN hypervisor, because I had some bad experiences using my PC when the dom0
is running.

I have 4GB of RAM on my system, and they are absolutely not faulty, so, when I
boot with a "traditional" kernel, I can see them all if I perform a
"cat /proc/meminfo"
or "free", as regard the total amount of available memory.

What happens here is that when I boot the same kernel, but using the xen.gz
hypervisor, the total amount of RAM is less than 4 GB. The main reason why I am
curious is that this value randomly changes. In practise, when booting
the dom0,
one time I can see 1,5GB of TOTAL RAM, once 1GB, once 3GB, and so on.

For instance, this is what I see now:
$ free
             total       used       free     shared    buffers     cached
Mem:       3225484    1669384    1556100

$ cat /proc/meminfo |grep MemTotal
MemTotal:        3225484 kB

Furthermore, the amount of free RAM is making me worried, because, sometime
if I perform some heavy load processing (e.g. kernel compilations) my system
freezes, especially if Mozilla Firefox is open.

Talking with a friend of mine, I deduced that the dom0 takes
(reserves) a certain amount
of RAM. Is it that correct? How does it work?
Is there a way to rule this behaviour? Is it possible to tell the dom0
how much RAM to
take?

I'm running Gentoo Linux x86_64 kernel 3.1.3.

Thanks,

-- 
Flavio

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