Resident Set Size and Ssh-agent

[yuenlok]

I use ssh-agent to do scp jobs from crontab without typing password. But the RSS(Resident Set Size) used by the ssh-agent process increase after each scp operation, so in a couple of days, the ssh-agent process becomes a "huge" process that uses around 10M resident set size, and it continue to increase.
Anybody knows why? Is it normal or there's something wrong with my setting? How can I restrict the resource used by the process?

Any help will be appreciated.