My docker containers have some data generated from applications running in the container. 
Even when I delete those files inside container system I can still see them existing on host system at 
var/lib/docker/devicemapper/mnt/c76a6e7874bbfb7d18c7f8aeaed154460ca5b8a18e1823d813b621bc7c42afa8/rootfs/var/www/html/etc/app/files

This is not freeing up space on host system. Any thoughts on this ?

Appreciate your help.