If My process allocates some big memory and then deallocates, would top or gnome-system-monitor show that my memory usage of that process decreased ? or kernel will still reserve that memory for that process ?

What I see is I am deallocating memory. But I still see gnome-system-monitor displaying growing memory for my program. I don't find memory leak in my end. I want to know whether its not displaying released memory ? or there is really a memory leak at my end ?