gwtExt panel to fill the page

While using gwtExt tools, I wanted the panel to occupy the entire screen. Found that Viewport is the component to use. However I didnt see the required effect in spite of using the Viewport as per the guide. I just got a small, shrinked panel as it used to be. After couple of trial and error, the culprit turned out to be an auto-height method called by the main panel. Commenting this statement cured the problem.

// panel.setAutoHeight(true);