Re: [Xen-users] CentOS6 & Ubuntu12 PV domU Memory

[George Shuklin <george.shuklin@xxxxxxxxx>]

On 04.02.2013 22:59, Rushikesh Jadhav wrote:
> Hi Everyone,
>
> I'm not sure if I'm the only one facing it or is it a known issue.
> CentOS6 and Ubuntu12.04 domU report less memory than they actually have.
>
> Example, a CentOS6 VM with 512MB shows only 484 as total in free -m.
> A Ubuntu domU shows 284M as total if the static max is 8GB and target 
> memory is 512MB.
> Both domUs are 64bit.
>
> CentOS5 reports the exact same memory as its target.
> I would be thankful if someone can share a reason or their domU # free -m
User-friendly answer: linux specific. Not XCP issue.

Technical stuff: pv-ops version of linux kernel marks some used areas as 
reserved (you can see this in dmesg output in Memory: line). AFAIK (I'm 
not sure) -xen version of linux mark those areas as 'available', but 
'busy'. PV-ops kernel simply mark it as 'reserved'.
You can compare 'free' memory for -xen and pv-ops kernels - it same. But 
for -xen kernel TotalMem higher and Used is higher too,  and for pv-ops 
TotalMem is lower, but used is lower too.

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