What is VSwap?
The new CentOS 6 OpenVZ kernel has a new memory management model, which supersedes User beancounters. It is called VSwap.
When the Guaranteed Ram 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.
When should I enable VSwap?
You SHOULD enable VSwap if your host operating system is CentOS 6 or uses the 2.6.32 kernel. VSwap has been designed to replace User beancounters and is built into the CentOS 6 kernel.
When should I NOT enable VSwap?
Do NOT enable VSwap if you are using CentOS 5 as your host operating system. The 2.6.18 kernel does not support VSwap.
How is VSwap calculated?
VSwap is calculated from the amount of burst memory you add to a virtual server. For example, if you specify 512MB Ram and 1024MB Burst the VSwap would be 512MB (1024MB - 512MB = 512MB).
How can we enable VSwap?
Enable it by edit your Node settings.
List Nodes >>> Edit Node >>>> VSwap
You should enable it for existing VPS from the Resources page
Virtual Servers >>>> Manage Virtual Server >>>> Resources >>>>VSwap
No need to reboot the VPS!!