Apologies that this is more of a Linux cgroup question than specific to systemd, but I was wondering if someone here might be able to enlighten me...
Two questions:
- Why on cgroups v1 do the cpuset controller's
cpuset.effective_{cpus,mems}seem to simply not work? - Is there any way to check effective cgroup memory or hugetlb limits? (cgroups v1 or v2)
Cpuset effective limits
root@ubuntu:~# podman run --rm -it --privileged -w /sys/fs/cgroup fedora
[root@7b9b67c7e1d4 cgroup]# mkdir cpuset/my-group
[root@7b9b67c7e1d4 cgroup]# cat cpuset/cpuset.cpus
0-5
[root@7b9b67c7e1d4 cgroup]# cat cpuset/my-group/cpuset.cpus
[root@7b9b67c7e1d4 cgroup]# cat cpuset/my-group/cpuset.effective_cpus
Expected cpuset/my-group/cpuset.effective_cpus to give 0-5 as set in the parent cgroup. Works as expected on cgroups v2.
[root@7b9b67c7e1d4 cgroup]# echo 0-5 > cpuset/my-group/cpuset.cpus
[root@7b9b67c7e1d4 cgroup]# cat cpuset/my-group/cpuset.{effective_,}cpus
0-5
0-5
[root@7b9b67c7e1d4 cgroup]# echo 0-4 > cpuset/cpuset.cpus
bash: echo: write error: Device or resource busy
Didn't expect this to fail - shouldn't it automatically impose a stricter limit on any child cgroups? Do I need to manually update all child cgroups first?
[root@7b9b67c7e1d4 cgroup]# echo 0-4 > cpuset/my-group/cpuset.cpus
[root@7b9b67c7e1d4 cgroup]# cat cpuset/my-group/cpuset.{effective_,}cpus
0-4
0-4
Can impose a stricter limit on child cgroups, as expected.
[root@7b9b67c7e1d4 cgroup]# echo 0-4 > cpuset/cpuset.cpus
[root@7b9b67c7e1d4 cgroup]# echo 0-5 > cpuset/my-group/cpuset.cpus
bash: echo: write error: Permission denied
But can't relax the child's cgroup restriction (i.e. need awareness of CPU restrictions already imposed above - how are you supposed to check this in a private cgroup namespace?).
Memory/Hugetlb effective limits
On cgroups v1:
[root@7b9b67c7e1d4 cgroup]# ls memory/
cgroup.clone_children memory.kmem.failcnt memory.kmem.tcp.limit_in_bytes memory.max_usage_in_bytes memory.soft_limit_in_bytes notify_on_release
cgroup.event_control memory.kmem.limit_in_bytes memory.kmem.tcp.max_usage_in_bytes memory.move_charge_at_immigrate memory.stat tasks
cgroup.procs memory.kmem.max_usage_in_bytes memory.kmem.tcp.usage_in_bytes memory.numa_stat memory.swappiness
memory.failcnt memory.kmem.slabinfo memory.kmem.usage_in_bytes memory.oom_control memory.usage_in_bytes
memory.force_empty memory.kmem.tcp.failcnt memory.limit_in_bytes memory.pressure_level memory.use_hierarchy
There is a memory.limit_in_bytes file, but no memory.effective_limit_in_bytes to reflect parent cgroup restrictions.
Similarly on cgroups v2:
[root@0c0d71230663 cgroup]# ls memory.*
memory.current memory.events.local memory.low memory.min memory.oom.group memory.stat memory.swap.events memory.swap.max
memory.events memory.high memory.max memory.numa_stat memory.pressure memory.swap.current memory.swap.high
There is a memory.max file, but not memory.max.effective (corresponding to cpuset.cpus.effective).
I guess you could traverse up the cgroup hierarchy to find the smallest limit being imposed... But this isn't possible inside a private cgroup namespace. Is there any way to find the actual cgroup limit imposed?
Any insights welcome!
Thanks,
Lewis
