The measures Commonwealth Bank took over the past couple of years to manage changed regulatory requirements around home lending caused the bank's mortgage lending growth to fall to close to half system growth during June half last year.CBA chief executive Matt Comyn said that with the necessary adjustments in place, the bank's mortgage business is getting back to system growth. After falling to 60 per cent of system growth in the six months to June, it was back up to 90 per cent of system during the December half."We have had a focus to get to system," Comyn told analysts at yesterday's half-year results briefing.Since 2015 the bank has made a number of changes to its loan underwriting process. They include: increased serviceability buffers on income and debt; limits on lending in high-risk areas and to non-residents; LVR limits on interest-only and investment loans; interest-only terms limited to five years, removing low doc loans from sale; limits on high debt-to-income ratios; and the introduction of data-driven liability verification tools, including comprehensive credit reporting.Comyn said: "For customers there has been a lot more inquiry into expenditure and more rigorous assessments."Over the past two years applications for interest-only loans have been flat and investor applications have fallen 25 to 30 per cent. "That is what you would expect," he said.However, he stressed that there was no less supply, borrowing capacity had not changed much, approval rates were about the same, time to decision was down a little and loan sizes were up. From the bank's perspective, availability of credit is not a constraint.Capacity fell by as much as 10 per cent during 2016 for some groups of borrowers but has been stable over the past year. "In any case, few borrowers borrow at capacity," Comyn says. Despite the fall in house prices over the past year, the average loan-to-valuation ratio of the mortgage portfolio has only risen from 50 per cent to 51 per cent.Borrowers have big payment buffers in place. Thirty-one per cent of home loan accounts have more than two years of payments in advance.