3.12. Common Tunable Parameters
The following parameters are present in every created cgroup, regardless of the subsystem that the cgroup is using:
- tasks
- contains a list of processes, represented by their PIDs, that are running in a cgroup. The list of PIDs is not guaranteed to be ordered or unique (that is, it may contain duplicate entries). Writing a PID into the
tasksfile of a cgroup moves that process into that cgroup. - cgroup.procs
- contains a list of thread groups, represented by their TGIDs, that are running in a cgroup. The list of TGIDs is not guaranteed to be ordered or unique (that is, it may contain duplicate entries). Writing a TGID into the
cgroup.procsfile of a cgroup moves that thread group into that cgroup. - cgroup.event_control
- along with the cgroup notification API, allows notifications to be sent about a changing status of a cgroup.
- notify_on_release
- contains a Boolean value,
1or0, that either enables or disables the execution of the release agent. If thenotify_on_releaseparameter is enabled, the kernel executes the contents of therelease_agentfile when a cgroup no longer contains any tasks (that is, the cgroup'stasksfile contained some PIDs and those PIDs were removed, leaving the file empty). A path to the empty cgroup is provided as an argument to the release agent.The default value of thenotify_on_releaseparameter in the root cgroup is0. All non-root cgroups inherit the value innotify_on_releasefrom their parent cgroup. - release_agent (present in the root cgroup only)
- contains a command to be executed when a “notify on release” is triggered. Once a cgroup is emptied of all processes, and the
notify_on_releaseflag is enabled, the kernel runs the command in therelease_agentfile and supplies it with a relative path (relative to the root cgroup) to the emptied cgroup as an argument. The release agent can be used, for example, to automatically remove empty cgroups; for more information, see Example 3.4, “Automatically removing empty cgroups”.Example 3.4. Automatically removing empty cgroups
Follow these steps to configure automatic removal of any emptied cgroup from thecpucgroup:- Create a shell script that removes empty
cpucgroups, place it in, for example,/usr/local/bin, and make it executable.~]#
cat /usr/local/bin/remove-empty-cpu-cgroup.sh#!/bin/sh rmdir /cgroup/cpu/$1 ~]#chmod +x /usr/local/bin/remove-empty-cpu-cgroup.shThe$1variable contains a relative path to the emptied cgroup. - In the
cpucgroup, enable thenotify_on_releaseflag:~]#
echo 1 > /cgroup/cpu/notify_on_release - In the
cpucgroup, specify a release agent to be used:~]#
echo "/usr/local/bin/remove-empty-cpu-cgroup.sh" > /cgroup/cpu/release_agent - Test your configuration to make sure emptied cgroups are properly removed:
cpu]#
pwd; ls/cgroup/cpu cgroup.event_control cgroup.procs cpu.cfs_period_us cpu.cfs_quota_us cpu.rt_period_us cpu.rt_runtime_us cpu.shares cpu.stat libvirt notify_on_release release_agent tasks cpu]#cat notify_on_release1 cpu]#cat release_agent/usr/local/bin/remove-empty-cpu-cgroup.sh cpu]#mkdir blue; lsblue cgroup.event_control cgroup.procs cpu.cfs_period_us cpu.cfs_quota_us cpu.rt_period_us cpu.rt_runtime_us cpu.shares cpu.stat libvirt notify_on_release release_agent tasks cpu]#cat blue/notify_on_release1 cpu]#cgexec -g cpu:blue dd if=/dev/zero of=/dev/null bs=1024k &[1] 8623 cpu]#cat blue/tasks8623 cpu]#kill -9 8623cpu]#lscgroup.event_control cgroup.procs cpu.cfs_period_us cpu.cfs_quota_us cpu.rt_period_us cpu.rt_runtime_us cpu.shares cpu.stat libvirt notify_on_release release_agent tasks
