The top commercial banks active in the mortgage banking business last year saw a 6.2 percent increase in the volume of loans serviced for other investors, typically through securitizations. But experience varied markedly from one institution to the next, with a number of relatively smaller players posting huge increases in their servicing volume. RBC Centura Bank, with a modest $4.97 billion in mortgage servicing for other investors, was up more than fivefold from the