I've attained a multiple entry tourist L type with a 90 day limit.

Does this mean I can enter China multiple times, 90 days max each time or multiple times WITHIN the 90 day limit. It's valid for a few years, but I'll only be using it in 2017.

Essentially, If I'm here in May (which I am currently) and I want to return for 4 30day trips over the next 8 months or so, will this become an issue or am I cool just to turn up in china and float through immigration with my multiple, 90 day limit visa?