[8u] RFR Backport 8057003: Large reference arrays cause extremely long synchronization times

[Liang Mao]

Hi,

I'm requesting the backport of 8057003 into 8u. As the description in the bug,
it's a serious G1 issue which leads to 10X longer concurrent mark time and hang
the Java threads for seconds. We encounter the problem in several applications.
Since G1 is widely used in 8u, we need to fix it.

Original bug:
 https://bugs.openjdk.java.net/browse/JDK-8057003
 http://hg.openjdk.java.net/jdk9/jdk9/hotspot/rev/a67614dce6cd

The JDK9 patch did not apply cleanly. Although it is not a small patch, I
 didn't change much except some assertions. One assertion in taskqueue.hpp
 is removed. It should be ok because it's no longer there as well since JDK9.

8u webrev:
http://cr.openjdk.java.net/~ddong/liangmao/8057003/webrev.00/

Testing:
gc/g1, specjbb2015 with fastdebug

Could someone please have a look and sponsor?

Thanks,
Liang