  We consider the possibility that massive primordial black holes are the
dominant form of dark matter. Black hole formation generates entropy
fluctuations that adds a Poisson noise to the matter power spectrum. We use
Lyman-alpha forest observations to constrain this Poisson term in matter power
spectrum, then we constrain the mass of black holes to be less than few times
10^4 solar mass. We also find that structures with less than ~ 10^3 primordial
black holes evaporate by now.
