We need an event for estimating the live set reasonably well, without causing a rather long and unpleasant safe pointing VM operation. This would open up all kind of neat applications, like figuring out when we're getting closer to OOME.

It would also be nice to be able to get an estimate of the class histogram (number of instances and (and possibly space) occupied by class), but that could be an optional event (using the same mechanism).

Perhaps one way of accomplishing this would be to simply do a concurrent mark, and collect some statistics whilst marking (skip re-marks etc), and report what we ended up with.

The event could happen once in a blue moon (once every N minutes) and still be very useful.