--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/src/hotspot/share/gc/z/zHeuristics.cpp	Wed Nov 20 10:37:46 2019 +0100
@@ -0,0 +1,64 @@
+/*
+ * Copyright (c) 2019, Oracle and/or its affiliates. All rights reserved.
+ * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
+ *
+ * This code is free software; you can redistribute it and/or modify it
+ * under the terms of the GNU General Public License version 2 only, as
+ * published by the Free Software Foundation.
+ *
+ * This code is distributed in the hope that it will be useful, but WITHOUT
+ * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
+ * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
+ * version 2 for more details (a copy is included in the LICENSE file that
+ * accompanied this code).
+ *
+ * You should have received a copy of the GNU General Public License version
+ * 2 along with this work; if not, write to the Free Software Foundation,
+ * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
+ *
+ * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
+ * or visit www.oracle.com if you need additional information or have any
+ * questions.
+ */
+
+#include "precompiled.hpp"
+#include "gc/z/zCPU.inline.hpp"
+#include "gc/z/zGlobals.hpp"
+#include "gc/z/zHeuristics.hpp"
+#include "gc/z/zUtils.inline.hpp"
+#include "logging/log.hpp"
+#include "runtime/globals.hpp"
+#include "runtime/os.hpp"
+
+void ZHeuristics::set_medium_page_size() {
+  // Set ZPageSizeMedium so that a medium page occupies at most 3.125% of the
+  // max heap size. ZPageSizeMedium is initially set to 0, which means medium
+  // pages are effectively disabled. It is adjusted only if ZPageSizeMedium
+  // becomes larger than ZPageSizeSmall.
+  const size_t min = ZGranuleSize;
+  const size_t max = ZGranuleSize * 16;
+  const size_t unclamped = MaxHeapSize * 0.03125;
+  const size_t clamped = MIN2(MAX2(min, unclamped), max);
+  const size_t size = ZUtils::round_down_power_of_2(clamped);
+
+  if (size > ZPageSizeSmall) {
+    // Enable medium pages
+    ZPageSizeMedium             = size;
+    ZPageSizeMediumShift        = log2_intptr(ZPageSizeMedium);
+    ZObjectSizeLimitMedium      = ZPageSizeMedium / 8;
+    ZObjectAlignmentMediumShift = ZPageSizeMediumShift - 13;
+    ZObjectAlignmentMedium      = 1 << ZObjectAlignmentMediumShift;
+
+    log_info(gc, init)("Medium Page Size: " SIZE_FORMAT "M", ZPageSizeMedium / M);
+  } else {
+    log_info(gc, init)("Medium Page Size: N/A");
+  }
+}
+
+bool ZHeuristics::use_per_cpu_shared_small_pages() {
+  // Use per-CPU shared small pages only if these pages occupy at most 3.125%
+  // of the max heap size. Otherwise fall back to using a single shared small
+  // page. This is useful when using small heaps on large machines.
+  const size_t per_cpu_share = (MaxHeapSize * 0.03125) / ZCPU::count();
+  return per_cpu_share >= ZPageSizeSmall;
+}