8257901: ZGC: Take virtual memory usage into account when sizing heap

src/hotspot/share/gc/shared/gcArguments.cpp

@@ -172,3 +172,7 @@ void GCArguments::initialize_heap_flags_and_sizes() {
 
   DEBUG_ONLY(assert_flags();)
 }
+
+size_t GCArguments::max_virtual_memory_fraction() {
+  return MaxVirtMemFraction;
+}

src/hotspot/share/gc/shared/gcArguments.hpp

@@ -46,6 +46,7 @@ class GCArguments {
 public:
   virtual void initialize();
   virtual size_t conservative_max_heap_alignment() = 0;
+  virtual size_t max_virtual_memory_fraction();
   virtual CollectedHeap* create_heap() = 0;
 
   // Allows GCs to tell external code if it's supported or not in the current setup.

src/hotspot/share/gc/z/zAddressSpaceLimit.cpp

@@ -24,6 +24,7 @@
 #include "precompiled.hpp"
 #include "gc/z/zAddressSpaceLimit.hpp"
 #include "gc/z/zGlobals.hpp"
+#include "runtime/globals.hpp"
 #include "runtime/os.hpp"
 #include "utilities/align.hpp"
 
@@ -46,6 +47,6 @@ size_t ZAddressSpaceLimit::mark_stack() {
 
 size_t ZAddressSpaceLimit::heap_view() {
   // Allow all heap views to occupy 50% of the address space
-  const size_t limit = address_space_limit() / 2 / ZHeapViews;
+  const size_t limit = address_space_limit() / MaxVirtMemFraction / ZHeapViews;
   return align_up(limit, ZGranuleSize);
 }

src/hotspot/share/gc/z/zArguments.cpp

@@ -25,6 +25,7 @@
 #include "gc/z/zAddressSpaceLimit.hpp"
 #include "gc/z/zArguments.hpp"
 #include "gc/z/zCollectedHeap.hpp"
+#include "gc/z/zGlobals.hpp"
 #include "gc/z/zHeuristics.hpp"
 #include "gc/shared/gcArguments.hpp"
 #include "runtime/globals.hpp"
@@ -94,6 +95,13 @@ void ZArguments::initialize() {
   }
 }
 
+size_t ZArguments::max_virtual_memory_fraction() {
+  // Used by heap size heuristics to determine max amount of address
+  // space to use. Inflates the default MaxVirtMemFraction to account
+  // for all heap views and the virtual-to-physical ratio.
+  return MaxVirtMemFraction * ZHeapViews * ZVirtualToPhysicalRatio;
+}
+
 size_t ZArguments::conservative_max_heap_alignment() {
   return 0;
 }

src/hotspot/share/gc/z/zArguments.hpp

@@ -34,6 +34,7 @@ class ZArguments : public GCArguments {
 
   virtual void initialize();
   virtual size_t conservative_max_heap_alignment();
+  virtual size_t max_virtual_memory_fraction();
   virtual CollectedHeap* create_heap();
 
   virtual bool is_supported() const;

src/hotspot/share/runtime/arguments.cpp

@@ -1659,7 +1659,7 @@ julong Arguments::limit_by_allocatable_memory(julong limit) {
   julong max_allocatable;
   julong result = limit;
   if (os::has_allocatable_memory_limit(&max_allocatable)) {
-    result = MIN2(result, max_allocatable / MaxVirtMemFraction);
+    result = MIN2(result, max_allocatable / GCConfig::arguments()->max_virtual_memory_fraction());
   }
   return result;
 }