8053998: Hot card cache flush chunk size too coarse grained

Changed the chunk size to a smaller fixed number.

Reviewed-by: tschatzl, mgerdin

hotspot/src/share/vm/gc_implementation/g1/g1HotCardCache.hpp

@@ -70,6 +70,9 @@ class G1HotCardCache: public CHeapObj<mtGC> {
 
   G1CardCounts _card_counts;
 
+  // The number of cached cards a thread claims when flushing the cache
+  static const int ClaimChunkSize = 32;
+
   bool default_use_cache() const {
     return (G1ConcRSLogCacheSize > 0);
   }