With the most recent update of Debian squeeze’s kernel I finally made it into the changelog*, as this excerpt shows:

 * [openvz] proc: Fix extreme memory use for /proc/self/mountinfo in
   container, thanks to Andrew Vagin, Christoph Lechleitner (Closes: #655385)

PS: The changelog link above is dead, but the Debian Bug report logs still have the discussion of #655385