--- old/src/share/vm/gc/g1/g1Allocator.cpp	2015-08-17 17:07:17.771853035 +0200
+++ new/src/share/vm/gc/g1/g1Allocator.cpp	2015-08-17 17:07:17.692850669 +0200
@@ -232,7 +232,7 @@
                                                        AllocationContext_t context,
                                                        bool* plab_refill_failed) {
   size_t plab_word_size = G1CollectedHeap::heap()->desired_plab_sz(dest);
-  size_t required_in_plab = word_sz + PLAB::alignment_reserve();
+  size_t required_in_plab = PLAB::size_required_for_allocation(word_sz);
 
   // Only get a new PLAB if the allocation fits and it would not waste more than
   // ParallelGCBufferWastePct in the existing buffer.
@@ -245,13 +245,12 @@
     HeapWord* buf = _allocator->par_allocate_during_gc(dest, plab_word_size, context);
     if (buf != NULL) {
       // Otherwise.
-      alloc_buf->set_word_size(plab_word_size);
-      alloc_buf->set_buf(buf);
+      alloc_buf->set_buf(buf, plab_word_size);
 
       HeapWord* const obj = alloc_buf->allocate(word_sz);
       assert(obj != NULL, err_msg("PLAB should have been big enough, tried to allocate "
-                                  SIZE_FORMAT " with alignment reserve " SIZE_FORMAT " PLAB size " SIZE_FORMAT,
-                                  word_sz, PLAB::alignment_reserve(), plab_word_size));
+                                  SIZE_FORMAT " requiring " SIZE_FORMAT " PLAB size " SIZE_FORMAT,
+                                  word_sz, required_in_plab, plab_word_size));
       return obj;
     }
     // Otherwise.