For experimentation: Incremental-update

[Roman Kennke]

This patch replaces the current SATB based marking with Incremental-
update. In short: instead of marking through the old graph and ensuring
consistency at the beginning of marking (i.e. snapshot-at-the-
beginning), incremental update is kindof the reverse: it marks through
the new graph and ensures consistency at the end.

I would like to throw out this patch for people to experiment with.
Currently it does not match SATB in performance, but I may be
overlooking something, or maybe heuristics need to be changed or
something like that.

The idea of the benefit of i-u is that we'd get less float and would
collect more efficiently by not treating all new objects as implicitely
live (which can easily amount to 1/3rd of the heap during one marking).
I-u instead marks through new objects too, and should give us a more
precise idea of liveness of the heap.


Please give it a shot. Partial collection might require i-u.

http://cr.openjdk.java.net/~rkennke/incremental-update/webrev.00/


Roman