Maintainability of the Linux kernel

The authors have examined 365 versions of Linux. For every version, they counted the number of instances of common (global) coupling between each of the 17 kernel modules and all the other modules in that version of Linux. They found that the number of instances of common coupling grows exponentially with the version number. This result is significant at the 99.99% level, and no additional variables are needed to explain this increase. On the other hand, the number of lines of code in each kernel module grows only linearly with the version number. They conclude that, unless Linux is restructured with a bare minimum of common coupling, the dependencies induced by common coupling will, at some future date, make Linux exceedingly hard to maintain without inducing regression faults.