Oracle VM - Why does the guest show less memory than allocated?

Hello,

I allocated certain amount of memory in the VM manager for the guest, but the guest, when started, shows somewhat less memory. Not sure why. I started seeing this issue only recently, I believe. Previously I am pretty sure the memory on the guest was exactly what was allocated in the VM manager during the guest creation. The last change I remember is the upgrade of VM server. As far as the guests, there were all newly created.

For example, from my VM Server, the xentop shows 4825052k (both MEM and MAXMEM) for one of the guests, and the top on the guest machine shows: Mem:   4670520k total.