Generally the soloution for that amount of blowby is an engine rebuild. Possibly another problem, however the rings are probably worn out, especially if the engine seems to be running evenly on all cylinders. Your motor oil is probably getting dirty and diluted with diesel fuel fast too. Diesel diluted oil is not good on the engine, it does not lubricate well.
One other possibliity is that your injector pump is leaking diesel fuel into the crankcase causing you oil level to be overfull with diesel diluted oil and thereby creating blowby.
Good luck.