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

[Roman Kennke]

Good!

Am 24. August 2018 16:13:18 MESZ schrieb Aleksey Shipilev <shade at redhat.com>:
>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

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