why is emacs using all my memory

[David Pleydell]

I have writen a program in C (called from a script in R) that I run inside 
emacs. The program is still in development phase so I have it spit out lots and 
lots and lots of text for monitorring progress. The program runs for several 
days. 

After half a day emacs is now using over 3Gb of RAM (almost half of my RAM). So 
I killed all the old text and purged the kill ring using M-:(setq kill-ring 
nil). But this hasn't freed the 3Gb. I have no idea what emacs is doing with 
this 3Gb, there are no other processes running. How can I diagnose what process 
within emacs is using this memory? Perhaps there is there some kind of "M-x 
top"?

thankx
David