--- a/hotspot/src/share/vm/memory/metaspace.cpp	Fri Aug 22 14:21:41 2014 -0700
+++ b/hotspot/src/share/vm/memory/metaspace.cpp	Mon Aug 25 00:13:36 2014 -0700
@@ -3126,6 +3126,8 @@
 
   if (DumpSharedSpaces) {
 #if INCLUDE_CDS
+    MetaspaceShared::estimate_regions_size();
+
     SharedReadOnlySize  = align_size_up(SharedReadOnlySize,  max_alignment);
     SharedReadWriteSize = align_size_up(SharedReadWriteSize, max_alignment);
     SharedMiscDataSize  = align_size_up(SharedMiscDataSize,  max_alignment);

--- a/hotspot/src/share/vm/memory/metaspaceShared.cpp	Fri Aug 22 14:21:41 2014 -0700
+++ b/hotspot/src/share/vm/memory/metaspaceShared.cpp	Mon Aug 25 00:13:36 2014 -0700
@@ -816,6 +816,7 @@
         //tty->print_cr("Preload failed: %s", class_name);
       }
     }
+    fclose(file);
   } else {
     char errmsg[JVM_MAXPATHLEN];
     os::lasterror(errmsg, JVM_MAXPATHLEN);
@@ -1086,3 +1087,49 @@
   }
   return true;
 }
+
+int MetaspaceShared::count_class(const char* classlist_file) {
+  if (classlist_file == NULL) {
+    return 0;
+  }
+  char class_name[256];
+  int class_count = 0;
+  FILE* file = fopen(classlist_file, "r");
+  if (file != NULL) {
+    while ((fgets(class_name, sizeof class_name, file)) != NULL) {
+      if (*class_name == '#') { // comment
+        continue;
+      }
+      class_count++;
+    }
+    fclose(file);
+  } else {
+    char errmsg[JVM_MAXPATHLEN];
+    os::lasterror(errmsg, JVM_MAXPATHLEN);
+    tty->print_cr("Loading classlist failed: %s", errmsg);
+    exit(1);
+  }
+
+  return class_count;
+}
+
+// the sizes are good for typical large applications that have a lot of shared
+// classes
+void MetaspaceShared::estimate_regions_size() {
+  int class_count = count_class(SharedClassListFile);
+  class_count += count_class(ExtraSharedClassListFile);
+
+  if (class_count > LargeThresholdClassCount) {
+    if (class_count < HugeThresholdClassCount) {
+      SET_ESTIMATED_SIZE(Large, ReadOnly);
+      SET_ESTIMATED_SIZE(Large, ReadWrite);
+      SET_ESTIMATED_SIZE(Large, MiscData);
+      SET_ESTIMATED_SIZE(Large, MiscCode);
+    } else {
+      SET_ESTIMATED_SIZE(Huge,  ReadOnly);
+      SET_ESTIMATED_SIZE(Huge,  ReadWrite);
+      SET_ESTIMATED_SIZE(Huge,  MiscData);
+      SET_ESTIMATED_SIZE(Huge,  MiscCode);
+    }
+  }
+}

--- a/hotspot/src/share/vm/memory/metaspaceShared.hpp	Fri Aug 22 14:21:41 2014 -0700
+++ b/hotspot/src/share/vm/memory/metaspaceShared.hpp	Mon Aug 25 00:13:36 2014 -0700
@@ -30,6 +30,19 @@
 #include "utilities/exceptions.hpp"
 #include "utilities/macros.hpp"
 
+#define LargeSharedArchiveSize    (300*M)
+#define HugeSharedArchiveSize     (800*M)
+#define ReadOnlyRegionPercentage  0.4
+#define ReadWriteRegionPercentage 0.55
+#define MiscDataRegionPercentage  0.03
+#define MiscCodeRegionPercentage  0.02
+#define LargeThresholdClassCount  5000
+#define HugeThresholdClassCount   40000
+
+#define SET_ESTIMATED_SIZE(type, region)                              \
+  Shared ##region## Size  = FLAG_IS_DEFAULT(Shared ##region## Size) ? \
+    (type ## SharedArchiveSize *  region ## RegionPercentage) : Shared ## region ## Size
+
 class FileMapInfo;
 
 // Class Data Sharing Support
@@ -112,5 +125,8 @@
   static void link_one_shared_class(Klass* obj, TRAPS);
   static void check_one_shared_class(Klass* obj);
   static void link_and_cleanup_shared_classes(TRAPS);
+
+  static int count_class(const char* classlist_file);
+  static void estimate_regions_size() NOT_CDS_RETURN;
 };
 #endif // SHARE_VM_MEMORY_METASPACE_SHARED_HPP