修改登录页面设计以使登录按钮始终可见

I have the following layout for login page,i need to reduce the spacing between each element,in short i need to move username,password and login button upwards of the screen ,that is when we open virtual keyboard the login button should be visible always,i tried using 'margintop=-negative value',its not working out.I have the following layout for login page,i ne