cli options for young/old ShenandoahMinFreeThreshold

Reviewed-by: wkemper, ysr

Author: caojoshua

src/hotspot/share/gc/shenandoah/heuristics/shenandoahAdaptiveHeuristics.cpp

@@ -273,7 +273,7 @@ bool ShenandoahAdaptiveHeuristics::should_start_gc() {
   double rate = _allocation_rate.sample(allocated);
   _last_trigger = OTHER;
 
-  size_t min_threshold = capacity / 100 * ShenandoahMinFreeThreshold;
+  size_t min_threshold = min_free_threshold();
 
   if (allocation_headroom < min_threshold) {
     log_info(gc)("Trigger (%s): Free (" SIZE_FORMAT "%s) is below minimum threshold (" SIZE_FORMAT "%s)",

src/hotspot/share/gc/shenandoah/heuristics/shenandoahCompactHeuristics.cpp

@@ -55,7 +55,7 @@ bool ShenandoahCompactHeuristics::should_start_gc() {
   available = (available > soft_tail) ? (available - soft_tail) : 0;
 
   size_t threshold_bytes_allocated = capacity / 100 * ShenandoahAllocationThreshold;
-  size_t min_threshold = capacity / 100 * ShenandoahMinFreeThreshold;
+  size_t min_threshold = min_free_threshold();
 
   if (available < min_threshold) {
     log_info(gc)("Trigger: Free (" SIZE_FORMAT "%s) is below minimum threshold (" SIZE_FORMAT "%s)",

src/hotspot/share/gc/shenandoah/heuristics/shenandoahHeuristics.cpp

@@ -512,6 +512,14 @@ bool ShenandoahHeuristics::in_generation(ShenandoahHeapRegion* region) {
           || (_generation->generation_mode() == OLD && region->affiliation() == OLD_GENERATION));
 }
 
+size_t ShenandoahHeuristics::min_free_threshold() {
+  size_t min_free_threshold =
+      _generation->generation_mode() == GenerationMode::OLD
+          ? ShenandoahOldMinFreeThreshold
+          : ShenandoahMinFreeThreshold;
+  return _generation->soft_max_capacity() / 100 * min_free_threshold;
+}
+
 void ShenandoahHeuristics::save_last_live_memory(size_t live_memory) {
   _live_memory_penultimate_cycle = _live_memory_last_cycle;
   _live_memory_last_cycle = live_memory;

src/hotspot/share/gc/shenandoah/heuristics/shenandoahHeuristics.hpp

@@ -119,6 +119,8 @@ class ShenandoahHeuristics : public CHeapObj<mtGC> {
 
   bool in_generation(ShenandoahHeapRegion* region);
 
+  size_t min_free_threshold();
+
 public:
   ShenandoahHeuristics(ShenandoahGeneration* generation);
   virtual ~ShenandoahHeuristics();

src/hotspot/share/gc/shenandoah/heuristics/shenandoahStaticHeuristics.cpp

@@ -49,7 +49,7 @@ bool ShenandoahStaticHeuristics::should_start_gc() {
   size_t soft_tail = max_capacity - capacity;
   available = (available > soft_tail) ? (available - soft_tail) : 0;
 
-  size_t threshold_available = capacity / 100 * ShenandoahMinFreeThreshold;
+  size_t threshold_available = min_free_threshold();
 
   if (available < threshold_available) {
     log_info(gc)("Trigger: Free (" SIZE_FORMAT "%s) is below minimum threshold (" SIZE_FORMAT "%s)",

src/hotspot/share/gc/shenandoah/shenandoah_globals.hpp

@@ -111,10 +111,18 @@
           range(0,100)                                                      \
                                                                             \
   product(uintx, ShenandoahMinFreeThreshold, 10, EXPERIMENTAL,              \
-          "Percentage of free heap memory below which most heuristics "     \
-          "trigger collection independent of other triggers. Provides "     \
-          "a safety margin for many heuristics. In percents of (soft) "     \
-          "max heap size.")                                                 \
+          "Percentage of free heap memory (or young generation, in "        \
+          "generational mode) below which most heuristics trigger "         \
+          "collection independent of other triggers. Provides a safety "    \
+          "margin for many heuristics. In percents of (soft) max heap "     \
+          "size.")                                                          \
+          range(0,100)                                                      \
+                                                                            \
+  product(uintx, ShenandoahOldMinFreeThreshold, 5, EXPERIMENTAL,            \
+          "Percentage of free old generation heap memory below which most " \
+          "heuristics trigger collection independent of other triggers. "   \
+          "Provides a safety margin for many heuristics. In percents of "   \
+          "(soft) max heap size.")                                          \
           range(0,100)                                                      \
                                                                             \
   product(uintx, ShenandoahAllocationThreshold, 0, EXPERIMENTAL,            \