CRR (S): 7046182: G1: remove unnecessary iterations over the collection set

[Tony Printezis]

Hi all,

Could I have a couple of code reviews for this change?

http://syros.us.oracle.com/local_ws/hotspot-g1-cset-iter/webrev/

Basically, we (unnecessarily) iterate over the collection set a couple 
of times during each GC to reset two fields on the RSet data structure. 
It's better to make sure that those fields are reset when the region is 
freed (so it's "ready to go" when it's re-allocated) to avoid those two 
iterations.

I added some extra code to assert that these two fields are in the 
correct state before each GC and I also added an extra verification step 
on the master free list to also check that condition on all the regions 
on it (since the two fields in question should be reset before the 
region is added to the master free list).

I'm piggy-backing the removal of the G1_REM_SET_LOGGING code on this 
(it's kinda related as it also iterates over the collection set - so, we 
remove more collection set iterations!). We haven't used it for a while 
and it's helpfulness is marginal.

Thanks,

Tony