M visa lengh of stay overall.

Hi I have a M type which is valid up to a year, multiple entry with 60 day duration at any one time. Is there a restriction on how many days over the course of a year I can stay? For example, under 183 days? I spend weeks at a time in China and need to do this throughout the year. Am I able to stay as long as I need to, within the restrictions mentioned?

Thanks