Re: nosh version 1.31

From: Guillermo <gdiazhartusch_at_gmail.com>
Date: Sun, 29 Jan 2017 15:46:41 -0300

2017-01-22 14:29 GMT-03:00 Guillermo:
>
> $ tai64nlocal /run/system-manager/log/current
> [...]
> 2017-01-21 22:11:17.709678664 system-manager: ERROR:
> /sys/fs/cgroup/systemd//cgroup.subtree_control: No such file or
> directory
> 2017-01-21 22:11:17.709683364 system-manager: ERROR:
> /sys/fs/cgroup/systemd//service-manager.slice/cgroup.subtree_control:
> No such file or directory

Yeah, writing to cgroup.subtree_control to enable or disable
controllers for a hierarchy is v2-only; for cgroups v1, controllers
are attached to a hierarchy by passing their names as mount options.
And that creates a related issue: system-manager does the C++
equivalent of 'mount -t cgroup -o none,name=systemd cgroup
/sys/fs/cgroup/systemd', i.e. the hierarchy rooted in
/sys/fs/cgroup/systemd doesn't have cgroup controllers attached, so
subdirectories won't have any 'knobs' for set-control-group-knob(1) to
act on:

$ cat /proc/self/cgroup
1:name=systemd:/service-manager.slice/ttylogin_at_.service/ttylogin_at_tty1.service

$ ls /sys/fs/cgroup/systemd/service-manager.slice/ttylogin\_at_.service/ttylogin\@tty1.service
cgroup.clone_children
cgroup.procs
notify_on_release
tasks

If one mounts another cgroup hierarchy with attached controllers, for
example with 'mount -t cgroup -o cpu cgroup /sys/fs/cgroup/cpu', the
corresponding knobs won't be in the directory set-control-group-knob
expects to find them:

$ cat /proc/self/cgroup
2:cpu:/cgroup-in-cpu-hierarchy
1:name=systemd:/service-manager.slice/ttylogin_at_.service/ttylogin_at_tty1.service

$ ls /sys/fs/cgroup/cpu/cgroup-in-cpu-hierarchy
cgroup.clone_children
cgroup.procs
cpu.shares
notify_on_release
tasks

$ cat /sys/fs/cgroup/cpu/cgroup-in-cpu-hierarchy/cpu.shares
1024

$ set-control-group-knob cpu.shares 2048
set-control-group-knob: FATAL:
/service-manager.slice/ttylogin_at_.service/ttylogin_at_tty1.service/cpu.shares:
No such file or directory

One could instead attach controllers to the hierarchy rooted in
/sys/fs/cgroup/systemd, for example by mounting it with 'mount -t
cgroup -o cpu,name=systemd cgroup /sys/fs/cgroup/systemd' (not with
system-manager as process 1), and things would appear to be OK:

$ ls /sys/fs/cgroup/systemd/service-manager.slice/ttylogin\_at_.service/ttylogin\@tty1.service
cgroup.clone_children
cgroup.procs
cpu.shares
notify_on_release
tasks

(i.e. there is now a 'cpu.shares' file)

But then set-control-group-knob (and also move-to-control-group I
believe) becomes a no-operation because it can't find the cgroups
hierarchy; function calls like read_my_control_group(self_cgroup,
"name=systemd", current) in source/set-control-group-knob.cpp and
source/move-to-control-group.cpp will return false because
/proc/self/cgroup doesn't have the expected format:

$ cat /proc/self/cgroup
1:cpu,name=systemd:/service-manager.slice/ttylogin_at_.service/ttylogin_at_tty1.service

(The text between the colons now also contains the cgroup controller
name, not just the 'name=systemd' part)

$ set-control-group-knob cpu.shares 2048
$ cat /sys/fs/cgroup/systemd/service-manager.slice/ttylogin_at_.service/ttylogin_at_t.service/cpu.shares
1024

$ set-control-group-knob non-existent-knob 2048

(No output, not even a 'No such file or directory' error).

G.
Received on Sun Jan 29 2017 - 18:46:41 UTC