After I have Googled and the solution for this issue you try to use "rsync" command.
rsync -a --delete /tmp/empty /tmp/session/Wonderful, I removed more a milion files smoothly....
Which is the fastest?
rm: deleting millions of file is a no-can-do!
find -exec: an option, but slower!
find -delete: fast and easy way to remove loads of files.
rsync --delete: without doubt the quickest!