Linux cgroups

External

• https://access.redhat.com/documentation/en-us/red_hat_enterprise_linux/6/html/resource_management_guide/ch01
• https://access.redhat.com/documentation/en-us/red_hat_enterprise_linux/7/html/resource_management_guide/chap-introduction_to_control_groups
• https://www.kernel.org/doc/Documentation/cgroup-v1/cgroups.txt
• https://en.wikipedia.org/wiki/Cgroups
• http://man7.org/linux/man-pages/man7/cgroups.7.html

Internal

• Docker Concepts

Overview

cgroups is a Linux kernel feature that allows allocation of resources (CPU, system memory, network bandwidth, or a combination of these) among user-defined groups of processes running on the system. cgroups not only track groups of processes, but they also expose metrics about CPU, memory and block I/O usage.

cgroups are exposed through a pseudo-filesystem available at /sys/fs/cgroup (older systems expose it at /cgroup). The sub-directories of the cgroup pseudo-filesystem root correspond to different cgroups hierarchies: devices, freezer, blkio.

cgroups are organized hierarchically, child cgroups inheriting certain attributes from their parent group. Many different hierarchies of cgroups can exist simultaneously on a system. Each hierarchy is attached to one or more subsystem, where a subsystem represents a single resource like CPU time or memory.

cgroups can be configured via the cgconfig service.

cgroups Subsystems

• blkio - sets limits on input/output access from and to block devices.
• cpu - uses the scheduler to provide cgroup tasks access to the CPU.
• cpuacct - generates automatic reports on CPU resources.
• cpuset - assigns individual CPUs and memory nodes to tasks in a cgroup.
• devices.
• freezer.
• memory.
• net_cls - tags network packets with a tag identifier (classid) that allow the Linux traffic controller (tc) to identify packets.
• net_prio.
• ns - the namespace subsystem.
• perf_event.

Operations

The recommended location for cgroup hierarchies:

/sys/fs/cgroup