What is burstable RAM? What is privvmpages?

Each Virtual Private Server has a guaranteed amount of RAM that can be used at any time no matter what. Yet there is always certain amount of RAM still available on the server and not used by any VPS. As long as those resources are available, you will be able to go over that limit of guaranteed RAM.

privvmpages is your burstable limit and if you are going over the limit, it is time to upgrade your plan to next one or reduce your memory requirements by fixing the code that is trying to use more RAM.