src/share/vm/memory/collectorPolicy.cpp

rev 4560 : 8006088: Incompatible heap size flags accepted by VM
Summary: Make processing of minimum, initial and maximum heap size more intiutive by removing previous limitations on allowed values, and make error reporting consistent. Further, fix errors in ergonomic heap sizing.
Reviewed-by: johnc, jwilhelm, tamao

@@ -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.

@@ -69,25 +73,13 @@
     vm_exit_during_initialization("Too small initial Metaspace size");
   }
 }
 
 void CollectorPolicy::initialize_size_info() {
-  // User inputs from -mx and ms are aligned
-  set_initial_heap_byte_size(InitialHeapSize);
-  if (initial_heap_byte_size() == 0) {
-    set_initial_heap_byte_size(NewSize + OldSize);
-  }
-  set_initial_heap_byte_size(align_size_up(_initial_heap_byte_size,
-                                           min_alignment()));
-
-  set_min_heap_byte_size(Arguments::min_heap_size());
-  if (min_heap_byte_size() == 0) {
-    set_min_heap_byte_size(NewSize + OldSize);
-  }
-  set_min_heap_byte_size(align_size_up(_min_heap_byte_size,
-                                       min_alignment()));
-
+  // User inputs from -mx and ms must be aligned
+  set_min_heap_byte_size(align_size_up(Arguments::min_heap_size(), min_alignment()));
+  set_initial_heap_byte_size(align_size_up(InitialHeapSize, min_alignment()));
   set_max_heap_byte_size(align_size_up(MaxHeapSize, max_alignment()));
 
   // Check heap parameter properties
   if (initial_heap_byte_size() < M) {
     vm_exit_during_initialization("Too small initial heap");

@@ -231,13 +223,10 @@
 
 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 +237,31 @@
     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");