RFR: Convert magic value to ShenandoahPacingSurcharge

[Aleksey Shipilev]

The change speaks for itself:

diff -r b3dae83fdf52 src/hotspot/share/gc/shenandoah/shenandoahPacer.cpp
--- a/src/hotspot/share/gc/shenandoah/shenandoahPacer.cpp       Tue Aug 14 09:53:21 2018 +0200
+++ b/src/hotspot/share/gc/shenandoah/shenandoahPacer.cpp       Tue Aug 14 10:47:33 2018 +0200
@@ -69,3 +69,3 @@
   tax *= 3;                          // mark is phase 1 of 3, claim 1/3 of free for it
-  tax *= 1.1;                        // additional surcharge to help unclutter heap
+  tax *= ShenandoahPacingSurcharge;  // additional surcharge to help unclutter heap

@@ -98,3 +98,3 @@
   tax = MAX2<double>(1, tax);        // never allocate more than GC processes during the phase
-  tax *= 1.1;                        // additional surcharge to help unclutter heap
+  tax *= ShenandoahPacingSurcharge;  // additional surcharge to help unclutter heap

@@ -119,3 +119,3 @@
   tax = MAX2<double>(1, tax);        // never allocate more than GC processes during the phase
-  tax *= 1.1;                        // additional surcharge to help unclutter heap
+  tax *= ShenandoahPacingSurcharge;  // additional surcharge to help unclutter heap

@@ -143,3 +143,3 @@
   double tax = 1.0 * live / taxable; // base tax for available free space
-  tax *= 1.1;                        // additional surcharge to help unclutter heap
+  tax *= ShenandoahPacingSurcharge;  // additional surcharge to help unclutter heap

@@ -168,3 +168,3 @@
   tax = MAX2<double>(1, tax);              // never allocate more than GC collects during the cycle
-  tax *= 1.1;                              // additional surcharge to help unclutter heap
+  tax *= ShenandoahPacingSurcharge;        // additional surcharge to help unclutter heap

diff -r b3dae83fdf52 src/hotspot/share/gc/shenandoah/shenandoah_globals.hpp
--- a/src/hotspot/share/gc/shenandoah/shenandoah_globals.hpp    Tue Aug 14 09:53:21 2018 +0200
+++ b/src/hotspot/share/gc/shenandoah/shenandoah_globals.hpp    Tue Aug 14 10:47:33 2018 +0200
@@ -406,2 +406,9 @@
                                                                             \
+  experimental(double, ShenandoahPacingSurcharge, 1.1,                      \
+          "Additional pacing tax surcharge to help unclutter the heap. "    \
+          "Larger values makes the pacing more aggressive. Lower values "   \
+          "risk GC cycles finish with less memory than were available at "  \
+          "the beginning of it.")                                           \
+          range(1, 100)                                                     \
+                                                                            \
   experimental(uintx, ShenandoahCriticalFreeThreshold, 1,                   \


Testing: tier3_gc_shenandoah

Thanks,
-Aleksey