men's room vs small room

men's room

noun
  • A lavatory intended for use by men, often including urinals in addition to toilets. 

  • Other rooms intended for use by men, as waiting rooms, dressing rooms, locker rooms, etc. 

small room

noun
  • A lavatory: a room intended for urination and defecation. 

  • Used other than figuratively or idiomatically: see small, room. 

How often have the words men's room and small room occurred in a corpus of books? (source: Google Ngram Viewer )