[Grml] Limit tmpfs RAM across mount points

[Mark]

What is the preferred grml way to limit total tmpfs RAM usage across all
mount points.  By default tmpfs takes 50% of RAM before swapout.  We
want a lower threshold of 20% RAM.  With fstab syntax it's possible to
limit one mount at a time, but is that the best one can do?  It would be
easier to limit the whole tmpfs subsystem and leave fstab entries
"unlimited."  Where is the 50% limit set, for example.

        M