diff -r fa357420e7d2 -r 6aa7255741f3 src/share/vm/memory/barrierSet.inline.hpp
--- a/src/share/vm/memory/barrierSet.inline.hpp	Tue Nov 24 15:19:30 2009 -0800
+++ b/src/share/vm/memory/barrierSet.inline.hpp	Thu Dec 03 15:01:57 2009 -0800
@@ -43,6 +43,8 @@
 }
 
 void BarrierSet::write_ref_array(MemRegion mr) {
+  assert((HeapWord*)align_size_down((uintptr_t)mr.start(), HeapWordSize) == mr.start() , "Unaligned start");
+  assert((HeapWord*)align_size_up  ((uintptr_t)mr.end(),   HeapWordSize) == mr.end(),    "Unaligned end"  );
   if (kind() == CardTableModRef) {
     ((CardTableModRefBS*)this)->inline_write_ref_array(mr);
   } else {
@@ -50,6 +52,34 @@
   }
 }
 
+// count is number of array elements being written
+void BarrierSet::write_ref_array(HeapWord* start, size_t count) {
+  assert(count <= (size_t)max_intx, "count too large");
+  HeapWord* end = (HeapWord*)((char*)start + (count*heapOopSize));
+  // In the case of compressed oops, start and end may potentially be misaligned;
+  // so we need to conservatively align the first downward (this is not
+  // strictly necessary for current uses, but a case of good hygiene and,
+  // if you will, aesthetics) and the second upward (this is essential for
+  // current uses) to a HeapWord boundary, so we mark all cards overlapping
+  // this write. In the event that this evolves in the future to calling a
+  // logging barrier of narrow oop granularity, like the pre-barrier for G1
+  // (mentioned here merely by way of example), we will need to change this
+  // interface, much like the pre-barrier one above, so it is "exactly precise"
+  // (if i may be allowed the adverbial redundancy for emphasis) and does not
+  // include narrow oop slots not included in the original write interval.
+  HeapWord* aligned_start = (HeapWord*)align_size_down((uintptr_t)start, HeapWordSize);
+  HeapWord* aligned_end   = (HeapWord*)align_size_up  ((uintptr_t)end,   HeapWordSize);
+  // If compressed oops were not being used, these should already be aligned
+  assert(UseCompressedOops || (aligned_start == start && aligned_end == end),
+         "Expected heap word alignment of start and end");
+#if 0
+  warning("Post:\t" INTPTR_FORMAT "[" SIZE_FORMAT "] : [" INTPTR_FORMAT","INTPTR_FORMAT")\t",
+                   start,            count,              aligned_start,   aligned_end);
+#endif
+  write_ref_array_work(MemRegion(aligned_start, aligned_end));
+}
+
+
 void BarrierSet::write_region(MemRegion mr) {
   if (kind() == CardTableModRef) {
     ((CardTableModRefBS*)this)->inline_write_region(mr);