Master P Wife ... There IS a Limit -- Files for Divorce

Master P's wife has had it with the rap mogul ... she's filed for divorce.

Sonya Miller filed divorce docs -- obtained by TMZ -- in which she seeks to end her 24-year marriage based on the standard "irreconcilable differences."

The couple has 4 minor children -- she wants full custody.  They also have famous adult son, Romeo.

Sonya wants spousal support.

This one's a little weird.  Back in 2011, Sonya went to court to get child support.  At the time we thought they were already divorced, but now we learn no one ever pulled the trigger and filed divorce documents.  So she did it now, but we're told they've been separated for a long time.