Resource Management: Beancounters

The paper outlines various means of resource management available in the Linux kernel, such as per-process limits (the setrlimit(2) interface), shows their shortcomings, and illustrares the need for another resource control mechanism: beancounters. Beancounters are a set of per-process group parameters (proposed and implemented by Alan Cox and Andrey Savochkin and further developed for OpenVZ) which can be used with or without containers. Beancounters history, architecture, goals, efficiency, and some in-depth implementation details are given. 1 Current state of resource management in the Linux kernel Currently the Linux kernel has only one way to control resource consumption of running processes – it is UNIX-like resource limits (rlimits). Rlimits set upper bounds for some resource usage parameters. Most of these limits apply to a single process, except for the limit for the number of processes, which applies to a user. The main goal of these limits is to protect processes from an accidental misbehavior (like infinite memory consumption) of other processes. A better way to organize such a protection would be to set up a minimal amount of resources that are always available to the process. But the old way (specifying upper limits to catch some cases of excessive consumption) may work, too. It is clear that the reason for introducing limits was the protection against an accidental misbehavior of processes. For example, there are separate limits for the data and stack size, but the limit on the total memory consumed by the stack, data, BSS, and memory mapped regions does not exist. Also, it is worth to note that the RLIMIT_CORE and RLIMIT_RSS limits are mostly ignored by the Linux kernel. Again, most of these resource limits apply to a single process, which means, for example, that all the memory may be consumed by a single user running the appropriate number of processes. Setting the limits in such a way as to have the value of multiplying the per-process limit by the number of processes staying below the available values is impractical.