RFR: 8165443: Free Collection Set serial phase takes very long on large heaps

[Kim Barrett]

> On Dec 6, 2019, at 4:53 AM, Stefan Johansson <stefan.johansson at oracle.com> wrote:
> Yes, I mentioned that I didn’t add any heuristic for this and I agree that one worker per region is to much, and in most cases we will already have fewer active workers for small heaps, this clamp was just a way to make sure we don’t have more workers than ever needed. 
> 
> I also agree that we could do some experiments and see if we can come up with a better way to size the number of threads here, but for now I think this is ok.
> 
> New webrev, full one also contain a change to work with latest WorkerDataArray changes:
> Full: http://cr.openjdk.java.net/~sjohanss/8165443/03/
> Inc: http://cr.openjdk.java.net/~sjohanss/8165443/02-03/

Looks good.