Peter

@nalimilan The problem this PR tries to address is that we will calculate the `mean` in the function no matter we have the mean value beforehand. They called `something` on...

~There was an issue on julialang discussing about allowing julia to be built with jemalloc, but iirc they got a conclusion that we didn't benefit from using it. Would that...

I double checked that issue and found that I didn't remember it correctly. It would definitely be interesting to have (though I don't really have a test case)