Sun Solaris Zones virtualisation creates isolated execution environments for operating system instances within a single host. The instances appear separate to applications, but actually share a number of core resources. One of the side effects is that they also use a common virtual memory pool and necessarily only have single instances of shared objects (page 21 of Solaris Containers Technology Architecture Guide at http://www.sun.com/blueprints/0506/819-6186.pdf).

This software virtualisation permits sharing between instances with no performance impact, reduce the overall memory footprint and introduce economies of scale to the hosting companies. I'd doubt that they would pass this saving on to customers as there seems to be a major problem in accounting for the shared use of these resources by the standard tools.