* Longest runtime: This would be the movie with the most minutes of screen time. In this case, it would likely be a movie with an extended runtime like an epic historical film.
* Longest theatrical run: This would be the movie that stayed in theaters for the most consecutive weeks or months. This is a common way to measure a film's commercial success.
* Longest time in continuous re-releases: Some movies have been re-released in theaters over decades, even if they weren't consistently playing.
To give you the best answer, please clarify what you mean by "longest running."
Once you provide that information, I can help you find the specific Malayalam movie that fits that criteria.