--- old/share/gc/parallel/psVirtualspace.cpp	2018-06-15 09:47:39.238912477 -0700
+++ new/share/gc/parallel/psVirtualspace.cpp	2018-06-15 09:47:39.178912475 -0700
@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2003, 2015, Oracle and/or its affiliates. All rights reserved.
+ * Copyright (c) 2003, 2018, 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
@@ -98,6 +98,21 @@
   return result;
 }
 
+bool PSVirtualSpace::expand_by(size_t bytes, int fd) {
+  assert(is_aligned(bytes), "arg not aligned");
+  DEBUG_ONLY(PSVirtualSpaceVerifier this_verifier(this));
+  if (uncommitted_size() < bytes) {
+    return false;
+  }
+  char* const base_addr = committed_high_addr();
+  bool commit_result = os::commit_memory(base_addr, bytes, alignment(), !ExecMem, fd, committed_size());
+  bool result = special() || commit_result;
+  if (result) {
+    _committed_high_addr += bytes;
+  }
+  return result;
+}
+
 bool PSVirtualSpace::shrink_by(size_t bytes) {
   assert(is_aligned(bytes), "arg not aligned");
   DEBUG_ONLY(PSVirtualSpaceVerifier this_verifier(this));
@@ -176,6 +191,66 @@
   return bytes;
 }
 
+size_t
+PSVirtualSpace::expand_into(PSVirtualSpace* other_space, size_t bytes, int fd) {
+  assert(is_aligned(bytes), "arg not aligned");
+  assert(grows_up(), "this space must grow up");
+  assert(other_space->grows_down(), "other space must grow down");
+  assert(reserved_high_addr() == other_space->reserved_low_addr(),
+         "spaces not contiguous");
+  assert(special() == other_space->special(), "one space is special, the other is not");
+  DEBUG_ONLY(PSVirtualSpaceVerifier this_verifier(this));
+  DEBUG_ONLY(PSVirtualSpaceVerifier other_verifier(other_space));
+
+  size_t bytes_needed = bytes;
+
+  // First use the uncommitted region in this space.
+  size_t tmp_bytes = MIN2(uncommitted_size(), bytes_needed);
+  if (tmp_bytes > 0) {
+    if (expand_by(tmp_bytes)) {
+      bytes_needed -= tmp_bytes;
+    } else {
+      return 0;
+    }
+  }
+
+  // Next take from the uncommitted region in the other space, and commit it.
+  tmp_bytes = MIN2(other_space->uncommitted_size(), bytes_needed);
+  if (tmp_bytes > 0) {
+    char* const commit_base = committed_high_addr();
+    if (other_space->special() ||
+        os::commit_memory(commit_base, tmp_bytes, alignment(), !ExecMem, fd, committed_size())) {
+      // Reduce the reserved region in the other space.
+      other_space->set_reserved(other_space->reserved_low_addr() + tmp_bytes,
+                                other_space->reserved_high_addr(),
+                                other_space->special());
+
+      // Grow both reserved and committed in this space.
+      _reserved_high_addr += tmp_bytes;
+      _committed_high_addr += tmp_bytes;
+      bytes_needed -= tmp_bytes;
+    } else {
+      return bytes - bytes_needed;
+    }
+  }
+
+  // Finally take from the already committed region in the other space.
+  tmp_bytes = bytes_needed;
+  if (tmp_bytes > 0) {
+    // Reduce both committed and reserved in the other space.
+    other_space->set_committed(other_space->committed_low_addr() + tmp_bytes,
+                               other_space->committed_high_addr());
+    other_space->set_reserved(other_space->reserved_low_addr() + tmp_bytes,
+                              other_space->reserved_high_addr(),
+                              other_space->special());
+
+    // Grow both reserved and committed in this space.
+    _reserved_high_addr += tmp_bytes;
+    _committed_high_addr += tmp_bytes;
+  }
+  return bytes;
+}
+
 #ifndef PRODUCT
 bool PSVirtualSpace::is_aligned(size_t value, size_t align) {
   const size_t tmp_value = value + align - 1;