[Xen-users] Calculate free memory

[Muriel <mucawhite@xxxxxxxxx>]

Hi all,
can be a stupid question, but there is a method to calculate the free
memory in a system that counts also the memory reserved for the Dom0?
I tried using xm info and free comand but there is something wrong.
A simple example, host with 4 GB, kernel 2.6.32.39, xen 4.0.2,
scientific linux 6:

--------------------------------------------
xm info
total_memory           : 4094
free_memory            : 1046

free -m
total       used       free     shared    buffers     cached
3456       1090       2365          0          8        127

So from "xm info" i have 3048 MB reserved, but 3456 are for dom0 (
difference -408)
------------------------------------------

Now a system with 16GB, xen 4.1, centos 5:
xm info:
total_memory           : 16381
free_memory            : 13633

free -m
total       used       free     shared    buffers     cached
3072       2196        875          0        160        338

For xm info i have 2748 MB reserved, but 3072 are for dom0 (diff -324)
If I set the dom0 memory but the difference between xm info data and
free remain constant.
------------------------------------------

I have thought of memory reserved for the hypervisor, but then I tried
with this configuration:
host with 8GB, kernel 2.6.32.39, xen 4.0.2, scientific linux 6:
xm info
total_memory           : 8190
free_memory            : 5006

free -m
total       used       free     shared    buffers     cached
3072       2454        617          0        194        338

For xm info i have 3190 MB reserved, but 3072 are for dom0 (diff +112).
------------------------------------------

Someone can explain what happens?
There is a simple and reliable way to get as much ram I have available for domU?

Thanks,
Muriel

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