Cgroups for resource management in Linux

Take Control

Article from ADMIN 06/2011

By Ralf Spenneberg

The new cgroups feature provides an administrative approach to restricting resource use. This application is particularly interesting for virtualized systems.

A couple of years ago, I was teaching Linux at a large-scale IT service provider's office. Their administrators had plenty of experience with commercial Unix variants, such as HP-UX, and they asked me how they could implement resource management and controls on Linux. How could an administrator restrict the amount of RAM used by a single process or a group of processes?

At the time, I had to admit that Linux didn't offer this feature. But in 2006, Rohit Seth started to develop this functionality, and as of kernel 2.6.24, administrators can use it. Originally referred to as "process containers," control groups (cgroups for short) [1] can restrict, enumerate (for billing purposes), and isolate resources (e.g., RAM, CPU, I/O).

Although many administrators will not need to use this functionality on a standard server, this application is very interesting in environments with KVM-based virtualization. Cgroups let you restrict the resources used by a virtual guest or prioritize use compared with other guests.

A cgroup lets the administrator group multiple processes and then define parameters for specific subsystems for these processes and all of their child processes. A subsystem could be a resource controller that manages the amount of RAM available.

To use cgroups, you first need to define a hierarchy in which the groups will be managed. To do so, you edit the /etc/cgconfig.conf file, which you can see in Listing 1.

Listing 1

/etc/cgconfig.conf

01 mount {
02         cpuset  = /cgroup/cpuset;
03         cpu     = /cgroup/cpu;
04         cpuacct = /cgroup/cpuacct;
05         memory  = /cgroup/memory;
06         devices = /cgroup/devices;
07         freezer = /cgroup/freezer;
08

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