"Jeremy C. Reed" <reed@reedmedia.net> writes:

> Has anyone noticed problems or had success with mount_null on mount_mfs?

This is a known problem of nullfs (or layerfs) cache.  This occurs
since layerfs cache keeps reference to underlying vnode.  Reclaiming
the space is defered until top vnode is recycled.

There is an incorrect work around in PR#15555.  No real fix yet.  Some
recent discuss with Bill Stuldenmund and me will be found in
source-changes.

enami.