In the chromium tree, there is now 3600 OWNERS files and 800 noparent rules. The owners system will only load those it think it needs, but if a patch is large enough to trigger many of those, the owners system will become very slow.

Looking at the OWNERS files in chromium/src, this probably started to become a problem when we got the noparent rules in every directory that uses mojom files because the security group want to look at certain things. There is not many other noparent rules.

I ran a test with a patch that changed hundreds of folders and the owners system basically froze up. I aborted after 10-15 minutes.

The reason is that we run iterate over all loaded rules and all loaded noparent directives for every changed file, and we get the dreaded O(n^2) in number of affected dirs with OWNERS files.

I have a rather small patch that fixes this by changing DataBase._paths_to_owners and DataBase._stop_looking to group rules by their longest glob-free path.