RFR(S): 8072434: 8064457: introduces performance regressions in 9-b47

[Lindenmaier, Goetz]

Hi,

There is a performance regression after my change 8064457.
30G heaps do not displace the CompressedClassSpace from the lower memory
region and instead are allocated in upper regions.
This webrev should fix the Problem.

http://cr.openjdk.java.net/~goetz/webrevs/8072434-css/webrev.01/
I verified that it works now and ran runtime/CompressedOops jtreg tests on linuxx86_64.
I'll get a comprehensive test run by tomorrow.

Best regards,
  Goetz.