(Issue A) -- 2 byte reduction: change _refcount from 4 bytes to 2 bytes. It's extremely unlikely that the reference count would be as high as 32767.

class Symbol : public MetaspaceObj {
 private:
  volatile int _refcount;
  int _identity_hash;
  unsigned short _length; // number of UTF8 characters in the symbol
  jbyte _body[1];

(Issue B) -- 1 byte reduction: size(int) function is incorrect. It assumes (pessimistically) that sizeof(Symbol) is 11, but in fact with most compilers sizeof(Symbol) is 12.

  static int size(int length) {
    size_t sz = heap_word_size(sizeof(Symbol) + (length > 0 ? length - 1 : 0));
    return align_object_size(sz);
  }


The fix for issue B is to split Symbol into two parts:

class SymbolBase {
    // all fields except _body[];
};

class Symbol: private SymbolBase {
    jbyte _body[1];

  static int size(int length) {
    size_t sz = heap_word_size(sizeof(SymbolBase) + (length > 0 ? length : 0));
    return align_object_size(sz);
  }

};