Linux – See which directory takes space without considering other mountpoints

I often find myself having to clean up some directories because they are too full. Let's take /var as an example, as it is a common one, for obvious reasons.

In order to see which sub-directories takes a lot of space, I use du -sh /var/*. Unfortunately, I have some huge data in sub-directories of /var, which happen to be hosted on other partitions than /var (e.g. /var/chroot) and greatly slow the process for nothing.

Now du has a -x flag which excludes other mountpoints. It works fine when doing a du -shx /var but not with du -shx /var/* since * is expanded by the shell so /var/chroot is explicitely sent to du.

Another option I was proposed was to use find /var -xdev -mindepth 1 -maxdepth 1 -exec du -sh {} \+ but again, even though find does not follow other mountpoints, it still prints them and passes them to du, hence failing again to achieve my goal.

Before I end up writing a horrible bash function (or a perl/python program) that parses df or mount in a loop, does anyone know of a clean way to achieve what I'm trying to do?