pretty much every lifter I've ever met in olympic weightlifting starts with the bar, then 40kgs and then increases by 10 or 15 or 20 kgs each warm up depending on his max and proficiency with the lifts
if your working set is going to be 100kgs
a longer warm up for me would be
20, 50, 60, 70, 80, 85, 90, 95, 100. Maybe skip the 85.
always though ramp up, you want at least 4 sets and probably less than 8 although I wouldn't mind even 10.
The sure thing is that you want to have good technique on a certain set. If you just warmed up with a crappy set with 50 don't go up to 60, warm up again with 50 till it looks good and is fast
also do your warm ups with little rest inbetween. 2 mins tends to be a lot. I keep the rest in my warm ups 1-2 mins(maybe not any at all when bar -> 40 or 50 kgs) and working sets 1-3 mins