On 5/28/25 11:23 AM, Waiman Long wrote:
On 5/27/25 4:53 AM, Vishal Chourasia wrote:
The documentation for cgroup controller management has been updated to
be more consistent regarding following concepts:
What does it mean to have controllers
1) available in a cgroup, vs.
2) enabled in a cgroup
Which has been clearly defined below in the documentation.
"Enabling a controller in a cgroup indicates that the distribution of
the target resource across its immediate children will be controlled.
Consider the following sub-hierarchy"
As an example, consider
/sys/fs/cgroup # cat cgroup.controllers
cpuset cpu io memory hugetlb pids misc
/sys/fs/cgroup # cat cgroup.subtree_control # No controllers by default
/sys/fs/cgroup # echo +cpu +memory > cgroup.subtree_control
/sys/fs/cgroup # cat cgroup.subtree_control
cpu memory # cpu and memory enabled in /sys/fs/cgroup
/sys/fs/cgroup # mkdir foo_cgrp
/sys/fs/cgroup # cd foo_cgrp/
/sys/fs/cgroup/foo_cgrp # cat cgroup.controllers
cpu memory # cpu and memory available in 'foo_cgrp'
/sys/fs/cgroup/foo_cgrp # cat cgroup.subtree_control # empty by default
/sys/fs/cgroup/foo_cgrp # ls
cgroup.controllers cpu.max.burst memory.numa_stat
cgroup.events cpu.pressure memory.oom.group
cgroup.freeze cpu.stat memory.peak
cgroup.kill cpu.stat.local memory.pressure
cgroup.max.depth cpu.weight memory.reclaim
cgroup.max.descendants cpu.weight.nice memory.stat
cgroup.pressure io.pressure memory.swap.current
cgroup.procs memory.current memory.swap.events
cgroup.stat memory.events memory.swap.high
cgroup.subtree_control memory.events.local memory.swap.max
cgroup.threads memory.high memory.swap.peak
cgroup.type memory.low memory.zswap.current
cpu.idle memory.max memory.zswap.max
cpu.max memory.min memory.zswap.writeback
Once a controller is available in a cgroup it can be used to resource
control processes of the cgroup.
Signed-off-by: Vishal Chourasia <vishalc@xxxxxxxxxxxxx>
---
Documentation/admin-guide/cgroup-v2.rst | 4 ++--
1 file changed, 2 insertions(+), 2 deletions(-)
diff --git a/Documentation/admin-guide/cgroup-v2.rst
b/Documentation/admin-guide/cgroup-v2.rst
index 1a16ce68a4d7..0e1686511c45 100644
--- a/Documentation/admin-guide/cgroup-v2.rst
+++ b/Documentation/admin-guide/cgroup-v2.rst
@@ -438,8 +438,8 @@ Controlling Controllers
Enabling and Disabling
~~~~~~~~~~~~~~~~~~~~~
-Each cgroup has a "cgroup.controllers" file which lists all
-controllers available for the cgroup to enable::
+Each cgroup has a cgroup.controllers file, which lists all the
controllers
+available for that cgroup and which can be enabled for its children.
I believe breaking the sentence into two separate components is
actually making it less correct. There are implicit controllers that
are always enabled and do not show up in cgroup.controllers. Prime
examples are perf_event and freezer. IOW, only controllers that are
available and need to be explicitly enabled will show up.
A correction: The cgroup.controllers file shows the controllers that are
available in the current cgroup and which have to be explicitly enabled
in cgroup.subtree_control to make them available in the child cgroups.
Cheers,
Longman
