RFR: Set ShenandoahMaxCSetFactor >50% to unclutter dense heaps better

[Aleksey Shipilev]

Before the refactoring for allocation rate, this option was at 75%:
  http://hg.openjdk.java.net/shenandoah/jdk/rev/846a1f988366#l1.19

It was like that for a reason. LRUFragger survives on very dense heap more reliably when this option
is restored at >50%. Other benchmarks are not affected, because they have enough headroom to never
hit the max-cset.

diff -r 1278eeea1a96 src/hotspot/share/gc/shenandoah/shenandoah_globals.hpp
--- a/src/hotspot/share/gc/shenandoah/shenandoah_globals.hpp    Thu Aug 23 11:33:51 2018 -0400
+++ b/src/hotspot/share/gc/shenandoah/shenandoah_globals.hpp    Fri Aug 24 16:10:13 2018 +0200
@@ -178,14 +178,16 @@
   experimental(uintx, ShenandoahLearningSteps, 5,                           \
                "Number of GC cycles to run in order to learn application "  \
                "and GC performance for adaptive heuristics.")               \
           range(0,100)                                                      \
                                                                             \
-  experimental(uintx, ShenandoahMaxCSetFactor, 25,                          \
+  experimental(uintx, ShenandoahMaxCSetFactor, 60,                          \
                "Maximum amount of free space to reserve for collection set "\
                "allocations. Larger values make GC more aggressive, while " \
                "leaving less headroom for application to allocate in. "     \
+               "For dense heaps, should be more than 50 to clean up more "  \
+               "space than application allocates in left-over heap. "       \
                "In percents of free space available.")                      \
           range(0,100)                                                      \
                                                                             \
   experimental(uintx, ShenandoahAllocSpikeFactor, 5,                        \
                "The amount of heap space to reserve for absorbing the "     \

Testing: tier1_gc_shenandoah, benchmarks, LRUFragger

Thanks,
-Aleksey