Increasing nofile limit

I have an issue where a mysql process in a vserver is running out of
filehandles, but I don't seem able to increase the limit.

I've added entries for the mysql and root users
in /etc/security/limits.conf, and I've tried creating rlimits/nofile in the
vserver's etc directory;  neither have any effect.  Is there a way to do
this with cgroups? I can't find any documentation on this.

Also, the nofile limit reported by ulimit is different if I log in to the
vserver remotely versus logging in with "vserver enter" from the host.

My environment:

Debian 8 (jessie)
util-vserver v.0.30.216-pre3126-jessie0.1-1
kernel 3.18.25-vs2.3.7.4-beng