[lxc-users] Strange CPUSET CGROUP behaviour

[Ben Green]

So apparently this is a known kernel issue. Solution is to write values
into cpuset.mems and cpuset.cpus.

https://serverfault.com/questions/579555/cgroup-no-space-left-on-device

Cheers,
Ben

On 03/09/2020 15:27, Ben Green wrote:
> Hi all,
>
> We are starting to use LXC in production here, after solving our final
> problem (inconsistent and disappearing cgroup space - Thread name
> "Disappearing Cgroups" on this list) completely with the help of Serge
> E. Hallyn.
>
> Now something odd has come up. I have one server on the Debian kernel
> 4.19.0-9-amd64 and another on 4.19.0-10-amd64. On the 4.19.0-9-amd64
> kernel we cat this:
>
> # cat /sys/fs/cgroup/cpuset/forcontainers/tasks
> 1216
> 5065
> 12372
> etc.
>
> But on the other one with the 4.19.0-10-amd64 we get this:
>
> #  cat /sys/fs/cgroup/cpuset/forcontainers/tasks
>
> No output! Also on the 4.19.0-10-amd64 machine it is not possible to add
> to the list of tasks:
>
> # echo $$ >> /sys/fs/cgroup/cpuset/forcontainers/tasks
> -bash: echo: write error: No space left on device
>
> However, we've had this happen before, and thought that adding
> 'swapaccount=1' to the grub command line arguments had fixed it. Seems
> it hadn't. I'm not even sure therefore that this is consistent between
> kernels. It appears it might be entirely random.
>
> Has anyone else experienced this phenomena? Any clues as to what might
> be happening?
>
> It seems that the cgroup has a messed up mount, but it looks fine to me:
>
>   cgroup on /sys/fs/cgroup/cpuset type cgroup
> (rw,nosuid,nodev,noexec,relatime,cpuset)
>
> Remove and remake the /sys/fs/cgroup/cpuset/forcontainers directory and
> the problem persists.
>
>
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-- 
Cheers,
Ben Green

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