Merge-Tree: Visualizing the Integration of Commits into Linux

With an average of more than 900 top-level merges into the Linux kernel per release, many containing hundreds of commits and some containing thousands, maintenance of older versions of the kernel becomes nearly impossible. Various commercial products, such as the Android platform, run older versions of the kernel. Due to security, performance, and changing hardware needs, maintainers must understand what changes (commits) are added to the current version of the kernel since the last time they inspected it in order to make the necessary patches. Current tools provide information about repositories through the directed acyclic graph (DAG) of the repository, which is helpful for smaller projects. However, with the scale and number of branches in the kernel the DAG becomes overwhelming very quickly. Furthermore, the DAG contains every ancestor of every commit, while maintainers are more interested in how and when a commit arrives to the official Linux repository. In this paper, we propose the merge-tree, a simplified transformation of the DAG of the Linux git repository that shows the way in which commits are merged into the master branch of Linux. Using the merge-tree, we build Linvis, a tool that is designed to allow users to explore how commits are merged into the Linux kernel.