Resource management

A container's CPU and memory usage, IO throttling, network priorities and access to devices is managed using cgroups.


osctld is managing all cgroup subsystems and lets you configure individual cgroup parameters. Since cgroups are hierarchic, but spread into multiple subsystems, osctld provides a concept of unified groups. These groups are defined once using osctl, but they are created in all cgroup subsystems, so each subsystem has the same hierarchy. Every container belongs to one of the groups.

There are always two groups present: the root group and the default group. The root group is the parent of all groups, it's called /. The default group is where new containers are put, unless a different group is specified. Its name is /default.

cgroup parameters can be configured both for groups and containers. This lets you to put several containers into one group and set shared limits, or limit entire group hierarchies.

Groups are managed by osctl group commands:

osctl group ls
tank   /          -        -
tank   /default   -        -

Configuring limits

Two of the most frequently wanted limits are for memory and CPU usage.

Memory limits

Memory limits can be set using osctl group/ct set memory, depending on whether you wish to configure limits for entire groups or specific containers. When you set a limit on a group, no child group or container can exceed it.

Let's set a limit on the root group, which will limit the total amount of memory your containers can use. The command below will let all containers together use up to 16 GB memory and 4 GB swap:

osctl group set memory / 16G 4G

You can also set limits on your containers:

osctl ct set memory myct01 2G 1G

You could create many such containers, even if the sum of their memory limits exceed that of the root group, i.e. >16 GB. But the sum of the used memory couldn't go over 16 GB.

Configured limits can be removed using osctl group/ct unset memory.

CPU limits

Similar to memory limits, it is possible to limit CPU usage in percents, where 100 % means that the group/container can utilize one CPU core. Let's configure some CPU limits:

osctl group set cpu-limit / 800
osctl ct set cpu-limit myct01 200

The commands above will ensure that all containers use 8 cores at max and container myct01 can use up to 2 cores.

CPU limits can be removed using osctl group/ct unset cpu-limit.

Other cgroup parameters

Configuration of memory and CPU limits as described on this page is actually just an abstraction on top of osctl group/ct cgparams commands, using which you can configure individual cgroup parameters. osctl group/ct set memory is configuring parameters memory.limit_in_bytes and memory.memsw.limit_in_bytes, where as CPU limits configure cpu.cfs_period_us and cpu.cfs_quota_us. If you'd like to configure other cgroup parameters, see resource management.

Note that access to devices using the device cgroup is managed independently, see device management.