OpenRC Extended cgroups support
Openrc has extended cgroups support
Staring with openrc-0.12 (not released ATM) openrc supports cgroup limit configuration. The simpliest and most reasonable way to configure it is use a multiline per-process values:
At first I should note that openrc has optional cgroup support to add it you need to set:
rc_controller_cgroups="YES"Otherwise one of the option will be applied and openrc “plugin” will not be loaded. As always settings can be set in rc.conf file and can be overloaded in ‘/etc/conf.d/foo’ file for service foo.
Each option is specified by name of the limit and value. Each option may be a multivalue, e.g.
# rc_cgroup_cpu="
# cpu.shares 512
# "For more information about the adjustments that can be made with cgroups, see Documentation/cgroups/* in the linux kernel source tree.
Currently next controllers are supported:
- blkio – block io controller
- cpu – cpu controller
- cpuacct – cpu accounting information
- cpuset – extended cpu configuration
- devices – devices access control
- memory – memory management
- net_prio – network priority options
Why do I ever need cgroups?
You can check kernel documentation. But roughly speaking you can monitor service processes, and manage resources much better.
Differences with other system managers
There are some differences between how systemd works, systemd creates hierarchies for system daemons and users in each controller. Openrc uses it’s own cgroup to monitor daemons, and create a group called ‘openrc_
So you can easily use other cgroup daemons like libcgroup with openrc without any problem
Future work
There are some work that can be done to make cgroup support better:
- configure controller merging
- cgroup-cleanup, i.e. destroy all childs when stopping service (there are some pathes but they were not applied upstream). We will wait for the real use cases here
- cgroup-watchdog, we can monitor if service is dead either by notify_agent (will not require any resources but will not restart service with childs alive) or by inotify (will require a watchdog service running but will have no such problems)
- notify-agent callbacks, currently we use notify agent only on openrc cgroup and there is no callback, but it can be fixed
- there is an abitify to make an api for freezer, but we’d wait for the real use case before implementing it.
Usefull links:
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