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

[Tony Printezis]

..and of course the webrev url is wrong. This is the right one:

http://cr.openjdk.java.net/~tonyp/7046182/webrev.0/

Apologies!

Tony

Tony Printezis wrote:
> 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
>