Grindstone + painter's servant + gitrog

Player A controls a [[Grindstone]] and a [[Painter's Servant]]. Player B controls [[The Gitrog Monster]]. When player A activates grindstone targeting player B, when would the Gitrog draws for any milled lands resolve?

Grindstone just says "repeat this process" so it makes me thing it would all be the resolution of the 1 ability, so assuming no responses or anything player B would mill their whole library and then any Gitrog draw triggers would then begin to resolve once the library is empty? Or would it be mill 2, resolve Gitrog triggers if any, mill 2 again?

Thanks in advance.