openvz add/change/adjunt memory for a container

example :
512MB Guaranteed, 1024MB Burstable

vzctl set CONTAINER_ID --vmguarpages 512M --save
vzctl set CONTAINER_ID --oomguarpages 512M --save
vzctl set CONTAINER_ID --privvmpages 512M:1024M --save

CONTAINER_ID should be replaced with the container (or vps) to add or change the ram size.

vmguarpages: This parameter controls how much memory is available to the Virtual Environment (i.e. how much memory its applications can allocate by malloc(3) or other standard Linux memory allocation mechanisms). The more clients are served or the more “heavy” the application is, the more memory it needs.

oomguarpages: this parameter is related to vmguarpages. If applications start to consume more memory than the computer has, the system faces an out-of-memory condition. In this case the operating system will start to kill container's processes to free some memory and prevent the total death of the system. Although it happens very rarely in typical system loads, killing processes in out-of-memory situations is a normal reaction of the system, and it is built into every Linux kernel.

privvmpages: The barrier and the limit of privvmpages parameter control the upper boundary of the total size of allocated memory.