src/share/vm/memory/collectorPolicy.cpp

@@ -46,10 +46,14 @@
 #endif // INCLUDE_ALL_GCS
 
 // CollectorPolicy methods.
 
 void CollectorPolicy::initialize_flags() {
+  if (MaxHeapSize < InitialHeapSize) {
+    vm_exit_during_initialization("Incompatible initial and maximum heap sizes specified");
+  }
+    
   if (MetaspaceSize > MaxMetaspaceSize) {
     MaxMetaspaceSize = MetaspaceSize;
   }
   MetaspaceSize = MAX2(min_alignment(), align_size_down_(MetaspaceSize, min_alignment()));
   // Don't increase Metaspace size limit above specified.

@@ -231,13 +235,10 @@
 
 void TwoGenerationCollectorPolicy::initialize_flags() {
   GenCollectorPolicy::initialize_flags();
 
   OldSize = align_size_down(OldSize, min_alignment());
-  if (NewSize + OldSize > MaxHeapSize) {
-    MaxHeapSize = NewSize + OldSize;
-  }
 
   if (FLAG_IS_CMDLINE(OldSize) && FLAG_IS_DEFAULT(NewSize)) {
     // NewRatio will be used later to set the young generation size so we use
     // it to calculate how big the heap should be based on the requested OldSize
     // and NewRatio.

@@ -248,10 +249,31 @@
     MaxHeapSize = calculated_heapsize;
     InitialHeapSize = calculated_heapsize;
   }
   MaxHeapSize = align_size_up(MaxHeapSize, max_alignment());
 
+  // adjust max heap size if necessary
+  if (NewSize + OldSize > MaxHeapSize) {
+    if (FLAG_IS_CMDLINE(MaxHeapSize)) {
+      // somebody set a maximum heap size with the intention that we should not
+      // exceed it. Adjust New/OldSize as necessary.
+      uintx calculated_size = NewSize + OldSize;
+      double shrink_factor = (double) MaxHeapSize / calculated_size;
+      // align
+      NewSize = align_size_down((uintx) (NewSize * shrink_factor), min_alignment());
+      // OldSize is already aligned because above we aligned MaxHeapSize to
+      // max_alignment(), and we just made sure that NewSize is aligned to
+      // min_alignment(). In initialize_flags() we verified that max_alignment()
+      // is a multiple of min_alignment().
+      OldSize = MaxHeapSize - NewSize;
+    } else {
+      MaxHeapSize = NewSize + OldSize;
+    }
+  }
+  // need to do this again
+  MaxHeapSize = align_size_up(MaxHeapSize, max_alignment());
+
   always_do_update_barrier = UseConcMarkSweepGC;
 
   // Check validity of heap flags
   assert(OldSize     % min_alignment() == 0, "old space alignment");
   assert(MaxHeapSize % max_alignment() == 0, "maximum heap alignment");