What is VSwap ? or How to Convert non-VSwap CT to VSwap?
A) What is VSwap?
vSwap, or Virtual Swap, is a new memory management feature in RHEL 6 (CentOS 6.0) that allows an Open VZ container to use RAM similar to a swap file. The performance is slightly reduced compared to RAM to mimic actual swapping without impacting disk I/O.
Please see the OpenVZ documentation: http://wiki.openvz.org/VSwap
B) How to Convert non-VSwap CT to VSwap?
An existing container with usual UBC parameters set, and you want to convert this one into VSwap enabled config, here’s what you need to do.
1) Decide on how much RAM and swap you want this CT to have. Generally, sum of your new RAM+swap should be more or less equal to sum of old PRIVVMPAGES and KMEMSIZE.
2) Manually remove all UBC parameters from config. This is optional, you can still have UBC limits applied if you want.
3) Add PHYSPAGES and SWAPPAGES parameters to config. Easiest way is to use vzctl set $CTID –ram N –swap M –save
Then config is vswap enabled, and start it (or use –reset_ub), vswap mechanism will be used by the kernel for this CT.