cgroups

cgroups (control groups) provide a process hierarchy for distribution of resources (CPU, memory, disk I/O, network) introduced in 2006 under the name "process containers" and merged in 2.6.24 in 2008.

It builds on Linux namespaces.

Versions

• v1:
  • Multiple process hierarchies, one per controller.
  • Thread level, not process.
• v2:
  • No longer possible to assign different threads of the same process different cgroups.
  • Subgroups created within a single hierarchy.
  • Propagation of parameters to immediate subgroups

Both versions are supported in-kernel, and it possible, though confusing, to use both concurrently.

Implementation

• /sys/fs/cgroups exposes a VFS
• libcgroup provides an API interface to the filesystem.
• cgrulesengd moves processes into cgroups based on a set of rules loaded at startup.
• A process may inspect its own cgroups via /proc/self/cgroup.

Resources

• TLDR Understanding the new groups v2 API
• Control Groups v1
• Control Group v2

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Backlinks

• Greybeard Qualification (Linux Internals) (public)
• Namespaces (public)