RFR (XS): -8064865: Remove the debug funciontality RotateCMSCollectionTypes for CMS

[Bengt Rutisson]

Hi all,

Can I have a couple of reviews for this small change to remove a debug 
flag from CMS?

http://cr.openjdk.java.net/~brutisso/8064865/webrev.00/

https://bugs.openjdk.java.net/browse/JDK-8064865

Background:

During the review of "8064702: Remove the CMS foreground collector" it 
was discussed how to handle the RotateCMSCollectionTypes feature. It was 
suggested to remove this feature in a separate change. This is the 
change to remove that feature.

 From the bug description:

The RotateCMSCollectionTypes flag is used in CMS to rotate between the 
three different kinds of collections of the old generation that CMS has; 
background collection, foreground collection and full compacting serial GC.

The functionality is only available in non-product builds.

With JDK-8064702 the foreground collector is being removed. This means 
that there are only two types left. The RotateCMSCollectionTypes flag is 
not being automatically tested and it is very rarely used. Rather than 
maintaining it we should remove this functionality. If we need this for 
debugging in the future it is a pretty simple patch to add back. But for 
the most part it should be possible to debug in other ways, by for 
example using ExplicitGCInvokesConcurrent flag and similar.

Thanks,
Bengt