Memory page sharing

Hi All, 

I have my RHEV 3 Beta environment running. On one of my server there are 2 virtual machines running where the 1 virtual machine has been assigned 1 GB memory and 2nd has been assigned 3 GB of memory however the Physical server has 6 GB of memory so whenever I try to create the 3rd machine on this server, I recieve the error "Cannot run VM. VM's swap percentage is above the threshold. (check your configuration parameters for Host Swap Percentage)." 

And on the Hosts tab, it shows under the General tab "Memory page sharing - Inactive"

As per my understanding I am not able to assign memory to new machine as my memory page sharing is not active however I am not able to find the way to enable the memory page sharing for my Hosts.

Kindly suggest.

Thanks,

Ashish