8316319: Generational ZGC: The SoftMaxHeapSize might be wrong when CDS decreases the MaxHeapSize

Reviewed-by: aboldtch, serb

src/hotspot/share/gc/x/xArguments.cpp

@@ -37,6 +37,10 @@ void XArguments::initialize_alignments() {
   HeapAlignment = SpaceAlignment;
 }
 
+void XArguments::initialize_heap_flags_and_sizes() {
+  // Nothing extra to do
+}
+
 void XArguments::initialize() {
   // Check mark stack size
   const size_t mark_stack_space_limit = XAddressSpaceLimit::mark_stack();

src/hotspot/share/gc/x/xArguments.hpp

@@ -31,6 +31,7 @@ class CollectedHeap;
 class XArguments : AllStatic {
 public:
   static void initialize_alignments();
+  static void initialize_heap_flags_and_sizes();
   static void initialize();
   static size_t heap_virtual_to_physical_ratio();
   static CollectedHeap* create_heap();

src/hotspot/share/gc/z/shared/zSharedArguments.cpp

@@ -38,6 +38,16 @@ void ZSharedArguments::initialize_alignments() {
   }
 }
 
+void ZSharedArguments::initialize_heap_flags_and_sizes() {
+  GCArguments::initialize_heap_flags_and_sizes();
+
+  if (ZGenerational) {
+    ZArguments::initialize_heap_flags_and_sizes();
+  } else {
+    XArguments::initialize_heap_flags_and_sizes();
+  }
+}
+
 void ZSharedArguments::initialize() {
   GCArguments::initialize();
 

src/hotspot/share/gc/z/shared/zSharedArguments.hpp

@@ -31,6 +31,7 @@ class CollectedHeap;
 class ZSharedArguments : public GCArguments {
 private:
   virtual void initialize_alignments();
+  virtual void initialize_heap_flags_and_sizes();
 
   virtual void initialize();
   virtual size_t conservative_max_heap_alignment();

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

@@ -37,6 +37,19 @@ void ZArguments::initialize_alignments() {
   HeapAlignment = SpaceAlignment;
 }
 
+void ZArguments::initialize_heap_flags_and_sizes() {
+  if (!FLAG_IS_CMDLINE(MaxHeapSize) &&
+      !FLAG_IS_CMDLINE(MaxRAMFraction) &&
+      !FLAG_IS_CMDLINE(MaxRAMPercentage) &&
+      !FLAG_IS_CMDLINE(SoftMaxHeapSize)) {
+    // We are really just guessing how much memory the program needs.
+    // When that is the case, we don't want the soft and hard limits to be the same
+    // as it can cause flakyness in the number of GC threads used, in order to keep
+    // to a random number we just pulled out of thin air.
+    FLAG_SET_ERGO(SoftMaxHeapSize, MaxHeapSize * 90 / 100);
+  }
+}
+
 void ZArguments::select_max_gc_threads() {
   // Select number of parallel threads
   if (FLAG_IS_DEFAULT(ParallelGCThreads)) {
@@ -126,16 +139,6 @@ void ZArguments::initialize() {
     FLAG_SET_ERGO_IF_DEFAULT(ZCollectionIntervalMajor, ZCollectionInterval);
   }
 
-  if (!FLAG_IS_CMDLINE(MaxHeapSize) &&
-      !FLAG_IS_CMDLINE(MaxRAMFraction) &&
-      !FLAG_IS_CMDLINE(MaxRAMPercentage)) {
-    // We are really just guessing how much memory the program needs.
-    // When that is the case, we don't want the soft and hard limits to be the same
-    // as it can cause flakyness in the number of GC threads used, in order to keep
-    // to a random number we just pulled out of thin air.
-    FLAG_SET_ERGO_IF_DEFAULT(SoftMaxHeapSize, MaxHeapSize * 90 / 100);
-  }
-
   if (FLAG_IS_DEFAULT(ZFragmentationLimit)) {
     FLAG_SET_DEFAULT(ZFragmentationLimit, 5.0);
   }

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

@@ -34,6 +34,7 @@ private:
 
 public:
   static void initialize_alignments();
+  static void initialize_heap_flags_and_sizes();
   static void initialize();
   static size_t heap_virtual_to_physical_ratio();
   static CollectedHeap* create_heap();