Ioutil reports very high cpu usage and i/o-spinning for chown -R

My CPU usage is very high and the disk is running wild on docker run. I use chown -R uid:gid /some/dir at entrypoint in my containers. It takes about 2-3 minutes to change ownership for ~100 files.

  938 be/3 root        0.00 B/s   61.97 K/s  0.00 % 97.35 % [jbd2/sda3-8]
 7214 be/4 root       97.02 K/s   86.24 K/s  0.00 %  1.85 % chown -R bitbucket:bitbucket /opt/bitbucket
 7634 be/4 root        3.59 K/s    0.00 B/s  0.00 %  0.81 % chown -R fisheye:fisheye /opt/fisheye/

All containers are using docker volumes.

What can be the casue of this and how can this be fixed?

I am using Ubuntu 16.04.4 LTS and Docker version 17.12.1-ce.