Since Lustre 2.12, the MAINTAINERS file contains a list of developers that are available for code review. It allows flexible selection of reviewers, by directory, filename, or regular expression. Developers are strongly encouraged to add themselves as reviewers for areas that they are knowledgeable in.
For developers looking for reviewers, they can look at the MAINTAINERS file, or run the contrib/scripts/get_maintainer.pl script against a specific file or patch to generate a list of reviewers. In addition to looking at the MAINTAINERS file, the get_maintainer.pl script will also search recent git commit history to find the list of people who have recently reviewed and/or modified this code the most. Since this is based on lines of code modified, it can sometimes be confused by patches that are making trivial changes (e.g. code style changes), so some discretion is needed when using the results.