New RHEL6-based OpenVZ kernel has a new memory management model, which supersedes User beancounters. It is called VSwap. When physpages limit is reached, memory pages belonging to the container are pushed out to so called virtual swap (vswap). The difference between normal swap and vswap is that with vswap no actual disk I/O usually occurs. Instead, a container is artificially slowed down, to emulate the effect of the real swapping. Actual swap out occurs only if there is a global memory shortage on the system. VSwap is designed to replace User beancounters and it is built into the RHEL6-based kernel.
When should VSwap be enabled
Vswap should be enabled if your host operating system is RHEL6-based or uses 2.6.32 kernel . The 2.6.18 kernel and RHEL5 does not support VSwap and will never be supported .
NOTE : Virtualizor ENABLES VSwap by default if the HOST NODE is an Enterprise Linux 6
How to calcuate VSwap memory
VSwap is calculated by the amount of burst memory you have added to a virtual server. For example, if you specify 256 MB Ram and 512 MB Burst the VSwap size would be 512MB (512MB - 256MB = 256MB).
How to enable VSwap memory in centos 6
You can enable VSwap from your Virtualizor Admin -> Configuration -> General settings .
Then click on save configuration to enable VSwap .