Flowtables -- any tuning hints?

Hello Freebsd-current_at_ folks,

I see with the commit "svn commit: r191259 - head/sys/netinet"
flowtables have been added..  Cool!

Does anyone have any tuning hints for this addition -- specifically
how much memory does the hash table consume?   Or better yet does any
documentation exist for this newly added feature?

Looking for an easy way to calculate max flows for the amount of
memory installed in a FreeBSD machine.

Thanks in advance,

Scott