RFR (M): 8077144: Concurrent mark initialization takes too long

[Thomas Schatzl]

Hi all,

  there is a new webrev at
http://cr.openjdk.java.net/~tschatzl/8077144/webrev.1 (full)
http://cr.openjdk.java.net/~tschatzl/8077144/webrev.0_to_1 (diff)

which addresses all but one of the presented issues: there are no
provisions to deal with deallocating that memory.

This is a pre-existing issue I do not like to address as part of this
change; the existing destructor just calls ShouldNotReachHere() too.
When fixing this, support for releasing the data structures touched
here can be added as well.

A few of them will move out of G1ConcurrentMark in the near future
anyway (JDK-8151386) or modify the data structures significantly (JDK
-8151215).

Also, the name of the flag changed to be more generic, as there are
plans to not only implement pre-touching of bitmaps.

This change is based on the changes StefanK sent out for review today.

Thanks,
  Thomas