UBC parameters

All the existing parameters are listed in the below table.

By importance, the parameters are divided into 3 groups: primary parameters, secondary parameters and auxiliary parameters. More detailed description of the parameters and the resource control mechanisms governed by the parameters is provided below.

General information about all parameters

All resource control parameters have some common properties and some differences.

1. Most parameters provide both accounting of some system resource and allow controlling its consumption. The exceptions are physpages (accounting only) and vmguarpages (no accounting, control only), explained below.
2. Each parameter has 2 configuration variables, called barrier and limit. Although both 2 variables are changeable, only one or none of them may be effectively used for the resource control for some parameters. For example, physpages is an accounting-only parameter and both its configuration variables are not effectively used in the current OpenVZ version. The description of each parameter explains the meaning of the barrier and the limit and what they should be set to if they are not effectively used. In general, for all parameters the barrier should not be greater than the limit.
3. The parameters control how the resources are distributed between Virtual Environments in terms of
   • limits, i.e. upper boundaries on what this Virtual Environment can consume, and
   • guarantees, i.e. mechanisms ensuring that this Virtual Environment can get the assigned “resources” regardless of the activity and the amount of resources required by other Virtual Environments.
   The parameters containing “guar” in their names, i.e. vmguarpages and oomguarpages are Virtual Environment's guarantees. They guarantee availability of resources and certain service level up to the value, specified by the barrier, and do not guarantee above the barrier. However, these parameters do not impose usage restrictions. The guarantees are discussed in more detail in the paragraphs describing these parameters. The limit of vmguarpages and oomguarpages should be set to the maximal value (i.e. 2147483647 on a 32-bit architecture).
4. For some resource limiting parameters, such as kmemsize, both barrier and limit settings are effectively used. If the resource usage exceeds the barrier but doesn't exceed the limit, vital operations (such as process stack expansion) are still allowed to allocate new resources, and other ones are not allowed. A gap between the barrier and the limit gives applications better chances to handle resource shortage gracefully. For other resource limiting parameters, such as numproc, barrier and limit should be set to the same value.
5. Each parameter has “natural units of measurement” — the units of measurement of values shown via /proc/user_beancounters interface and accepted by vzctl. Values related to parameters with names starting with num are measured in pieces. Values related to parameters with names ending with pages are measured in memory pages (memory page is equal to 4 kilobytes on IA-32 hardware). The remaining values (parameters ending with size and buf) are measured in bytes.