[8u] RFR: 8135318: CMS wrong max_eden_size for check_gc_overhead_limit

[Severin Gehwolf]

Hi,

Could I please get a review for this OpenJDK 8u backport? It's
essentially the same patch as in JDK 9+, but it didn't apply cleanly
since the surrounding code is different and the files were moved
around.

Adjustments I've done:

JDK 8u uses a different file layout:

src/share/vm/gc/cms/concurrentMarkSweepGeneration.cpp =>
src/share/vm/gc_implementation/concurrentMarkSweep/concurrentMarkSweepGeneration.cpp

JDK 8u doesn't have JDK-8065972 and JDK-8065992, which account for the
surrounding code changes. Note that JDK-8065992 makes the _young_gen
instance variable ParNewGEneration* from Generation*.

Bug: https://bugs.openjdk.java.net/browse/JDK-8135318
webrev: http://cr.openjdk.java.net/~sgehwolf/webrevs/JDK-8135318/01/webrev/
JDK 9 change: http://hg.openjdk.java.net/jdk9/jdk9/hotspot/rev/dd0c55eac358

Testing: "tier1" testing of Linux x86_64 which showed no new regressions.

Thoughts?

Thanks,
Severin