What is the name of this kung fu movie?

it's at least 7 years old. there was two brothers, one of them turned bad and the other turned good. there was a scene where the good brother was fighting a blow up punching bag i think. the good brother got amnesia i think. the good brother kills the bad brother in the end. there was also a scene where it showed the two brothers as kids in the martial arts school. i can't remember the name for sh!t.