illumos gate

On Illumos there is no statistic output that properly indicates the potentially free memory
I would like such a kstat that can be used in monitoring systems/scripts to trigger alerts if it is low.
We have the used memory statistic per zone but none for available.
It should exclude ARC contrary to the free memory statistic.
It should be readable without root permissions.
The only way to gather data to calculate this easily is through "echo ::memstats | mdb -k" which takes 4 seconds to compile th data and must be run as root.