MongoDB journal - how to keep from getting too big?


I had a web app come crashing down because the MongoDB journal got too large:

2015-11-04T21:24:21.073+0000 E JOURNAL  [initandlisten] Insufficient free space for journal files
2015-11-04T21:24:21.073+0000 I JOURNAL  [initandlisten] Please make at least 3379MB available in /data/db/journal or use --smallfiles

How exactly do I fix this? Can I wipe out the journal? I’m using mupx to deploy, so I don’t exactly have fine-grained control over booting up mongod with the --smallfiles option.