--- a/hotspot/src/share/vm/gc_implementation/g1/g1PageBasedVirtualSpace.cpp	Mon Jan 12 12:51:53 2015 +0100
+++ b/hotspot/src/share/vm/gc_implementation/g1/g1PageBasedVirtualSpace.cpp	Mon Jan 12 15:24:29 2015 +0100
@@ -45,7 +45,8 @@
 #include "utilities/bitMap.inline.hpp"
 
 G1PageBasedVirtualSpace::G1PageBasedVirtualSpace() : _low_boundary(NULL),
-  _high_boundary(NULL), _committed(), _page_size(0), _special(false), _executable(false) {
+  _high_boundary(NULL), _committed(), _page_size(0), _special(false),
+  _dirty(), _executable(false) {
 }
 
 bool G1PageBasedVirtualSpace::initialize_with_granularity(ReservedSpace rs, size_t page_size) {
@@ -66,6 +67,9 @@
   assert(_committed.size() == 0, "virtual space initialized more than once");
   uintx size_in_bits = rs.size() / page_size;
   _committed.resize(size_in_bits, /* in_resource_area */ false);
+  if (_special) {
+    _dirty.resize(size_in_bits, /* in_resource_area */ false);
+  }
 
   return true;
 }
@@ -84,6 +88,7 @@
   _executable             = false;
   _page_size              = 0;
   _committed.resize(0, false);
+  _dirty.resize(0, false);
 }
 
 size_t G1PageBasedVirtualSpace::committed_size() const {
@@ -120,34 +125,43 @@
   return num * _page_size;
 }
 
-MemRegion G1PageBasedVirtualSpace::commit(uintptr_t start, size_t size_in_pages) {
+bool G1PageBasedVirtualSpace::commit(uintptr_t start, size_t size_in_pages) {
   // We need to make sure to commit all pages covered by the given area.
   guarantee(is_area_uncommitted(start, size_in_pages), "Specified area is not uncommitted");
 
-  if (!_special) {
+  bool zero_filled = true;
+  uintptr_t end = start + size_in_pages;
+
+  if (_special) {
+    // Check for dirty pages and update zero_filled if any found.
+    if (_dirty.get_next_one_offset(start,end) < end) {
+      zero_filled = false;
+      _dirty.clear_range(start, end);
+    }
+  } else {
     os::commit_memory_or_exit(page_start(start), byte_size_for_pages(size_in_pages), _executable,
                               err_msg("Failed to commit pages from "SIZE_FORMAT" of length "SIZE_FORMAT, start, size_in_pages));
   }
-  _committed.set_range(start, start + size_in_pages);
+  _committed.set_range(start, end);
 
-  MemRegion result((HeapWord*)page_start(start), byte_size_for_pages(size_in_pages) / HeapWordSize);
   if (AlwaysPreTouch) {
-    os::pretouch_memory((char*)result.start(), (char*)result.end());
+    os::pretouch_memory(page_start(start), page_start(end));
   }
-  return result;
+  return zero_filled;
 }
 
-MemRegion G1PageBasedVirtualSpace::uncommit(uintptr_t start, size_t size_in_pages) {
+void G1PageBasedVirtualSpace::uncommit(uintptr_t start, size_t size_in_pages) {
   guarantee(is_area_committed(start, size_in_pages), "checking");
 
-  if (!_special) {
+  if (_special) {
+    // Mark that memory is dirty. If committed again the memory might
+    // need to be cleared explicitly.
+    _dirty.set_range(start, start + size_in_pages);
+  } else {
     os::uncommit_memory(page_start(start), byte_size_for_pages(size_in_pages));
   }
 
   _committed.clear_range(start, start + size_in_pages);
-
-  MemRegion result((HeapWord*)page_start(start), byte_size_for_pages(size_in_pages) / HeapWordSize);
-  return result;
 }
 
 bool G1PageBasedVirtualSpace::contains(const void* p) const {
@@ -157,7 +171,7 @@
 #ifndef PRODUCT
 void G1PageBasedVirtualSpace::print_on(outputStream* out) {
   out->print   ("Virtual space:");
-  if (special()) out->print(" (pinned in memory)");
+  if (_special) out->print(" (pinned in memory)");
   out->cr();
   out->print_cr(" - committed: " SIZE_FORMAT, committed_size());
   out->print_cr(" - reserved:  " SIZE_FORMAT, reserved_size());

--- a/hotspot/src/share/vm/gc_implementation/g1/g1PageBasedVirtualSpace.hpp	Mon Jan 12 12:51:53 2015 +0100
+++ b/hotspot/src/share/vm/gc_implementation/g1/g1PageBasedVirtualSpace.hpp	Mon Jan 12 15:24:29 2015 +0100
@@ -49,6 +49,12 @@
   // Bitmap used for verification of commit/uncommit operations.
   BitMap _committed;
 
+  // Bitmap used to keep track of which pages are dirty or not for _special
+  // spaces. This is needed because for those spaces the underlying memory
+  // will only be zero filled the first time it is committed. Calls to commit
+  // will use this bitmap and return whether or not the memory is zero filled.
+  BitMap _dirty;
+
   // Indicates that the entire space has been committed and pinned in memory,
   // os::commit_memory() or os::uncommit_memory() have no function.
   bool _special;
@@ -71,12 +77,11 @@
  public:
 
   // Commit the given area of pages starting at start being size_in_pages large.
-  MemRegion commit(uintptr_t start, size_t size_in_pages);
+  // Returns true if the given area is zero filled upon completion.
+  bool commit(uintptr_t start, size_t size_in_pages);
 
   // Uncommit the given area of pages starting at start being size_in_pages large.
-  MemRegion uncommit(uintptr_t start, size_t size_in_pages);
-
-  bool special() const { return _special; }
+  void uncommit(uintptr_t start, size_t size_in_pages);
 
   // Initialization
   G1PageBasedVirtualSpace();

--- a/hotspot/src/share/vm/gc_implementation/g1/g1RegionToSpaceMapper.cpp	Mon Jan 12 12:51:53 2015 +0100
+++ b/hotspot/src/share/vm/gc_implementation/g1/g1RegionToSpaceMapper.cpp	Mon Jan 12 15:24:29 2015 +0100
@@ -67,9 +67,9 @@
   }
 
   virtual void commit_regions(uintptr_t start_idx, size_t num_regions) {
-    _storage.commit(start_idx * _pages_per_region, num_regions * _pages_per_region);
+    bool zero_filled = _storage.commit(start_idx * _pages_per_region, num_regions * _pages_per_region);
     _commit_map.set_range(start_idx, start_idx + num_regions);
-    fire_on_commit(start_idx, num_regions, true);
+    fire_on_commit(start_idx, num_regions, zero_filled);
   }
 
   virtual void uncommit_regions(uintptr_t start_idx, size_t num_regions) {
@@ -117,8 +117,7 @@
       uint old_refcount = _refcounts.get_by_index(idx);
       bool zero_filled = false;
       if (old_refcount == 0) {
-        _storage.commit(idx, 1);
-        zero_filled = true;
+        zero_filled = _storage.commit(idx, 1);
       }
       _refcounts.set_by_index(idx, old_refcount + 1);
       _commit_map.set_bit(i);