"This reduces native kernel max memory support from around 127 TB to around 120 TB. We also limit the Xen hypervisor to ~7 TB of physical memory - is that wise in the long run? Sure, current CPUs support 40 physical bits [1 TB] for now so it's all theoretical at this moment. My guess is that CPU makers will first extend the physical lines all the way up to 46-47 bits before they are willing to touch the logical model and extend the virtual space beyond 48 bits (47 bits of that available to kernel-space in practice - i.e. 128 TB). So eventually, in a few years, we'll feel some sort of crunch when the # of physical lines approaches the # of logical bits - just like when 32-bit felt a crunch when physical lines went to 31 and beyond."