--- old/src/share/vm/runtime/commandLineFlagConstraintsGC.cpp	2016-03-29 11:56:35.802007312 -0700
+++ new/src/share/vm/runtime/commandLineFlagConstraintsGC.cpp	2016-03-29 11:56:35.658007317 -0700
@@ -386,21 +386,21 @@
 #if INCLUDE_ALL_GCS
   if (UseConcMarkSweepGC) {
     // ParGCCardsPerStrideChunk shoule be compared with card table size.
-    // As CardTableModRefBS::_last_valid_index is 'protected', calculate it in a same way.
     size_t heap_size = Universe::heap()->reserved_region().word_size();
-    size_t card_table_size = align_size_up(heap_size, CardTableModRefBS::card_size_in_words);
-    card_table_size /= (CardTableModRefBS::card_size_in_words + 1);
-    card_table_size -= 1;
+    CardTableModRefBS* bs = (CardTableModRefBS*)GenCollectedHeap::heap()->rem_set()->bs();
+    size_t card_table_size = bs->cards_required(heap_size) - 1; // Valid card table size
 
     if ((size_t)value > card_table_size) {
       CommandLineError::print(verbose,
-                              "ParGCCardsPerStrideChunk (" INTX_FORMAT ") must be "
-                              "less than or equal to card table size (" SIZE_FORMAT ")\n",
+                              "ParGCCardsPerStrideChunk (" INTX_FORMAT ") is too large for the heap size and "
+                              "must be less than or equal to card table size (" SIZE_FORMAT ")\n",
                               value, card_table_size);
       return Flag::VIOLATES_CONSTRAINT;
     }
 
-    // If n_strides which is used with ParGCCardsPerStrideChunk is really large, we would face an overflow.
+    // ParGCCardsPerStrideChunk is used with n_strides(ParallelGCThreads*ParGCStridesPerThread)
+    // from CardTableModRefBSForCTRS::process_stride(). However, ParGCStridesPerThread is already checked
+    // not to make an overflow with ParallelGCThreads from its constraint function.
     uintx n_strides = ParallelGCThreads * ParGCStridesPerThread;
     uintx ergo_max = max_uintx / n_strides;
     if ((uintx)value > ergo_max) {