Minimum 23,439 (15.4%) Low 55,133 (36.3%)
https://www.bop.gov/about/statistics/statistics_inmate_sec_l...
Also consider that there are inmates that didn't actually commit violent crimes that are labeled as such because they received gun enhancements to their sentence for the ownership of a firearm even if not on their person during the "furtherance of the crime". Yes, there are people who are sitting in prison longer than they should be because they had legally owned firearms at their house while they were growing a plant.
That article you linked tries to paint an invalid picture of how prison populations are kept artificially high to protect the jobs and industries that surround correction institutions. There are union groups across different sectors that rally hard to ensure that humans are warehoused to pay the bills.
To illustrate how full the low/minimum prisons are with drug offenders your first day there everyone will greet you and if you're there for drug related crimes the second anyone hears "drug" they just wave their hand because they have heard the story so many times and there is almost never any variation. I'm not a drug offender, I was there for a computer-hacking related charge, but I basically got to the point where I could guess all the different elements of their story like how much they were getting paid per drug run (it seems to be about $2,000 per run for the low level mules, if anyone is curious)