out of memory error while file uploading

Hi,
I have file upload functionality in my application, so am using formFile.
I am getting out of memory with that formFile element, even when am not uploading any file and simply trying to move onto next screen, its showing out of memory error.
I came to know that we can use 'controller' element in struts-config.xml for these type of issues. How can we do it? Waht about 'org.apache.struts.config.ControllerConfig' class? we need to use this class if we have specified 'controller' element in struts-config.xml?

whats the use of 'ContollerConfig' class and 'controller' element in xml?
we need to use both or what? any code snippest will be helpful..
Plz reply ASAP.
Thanks in advance.