Had anyone succeed in looking up the motivation behind the reserved space idea in ext filesystems, e.g a commit message from the time this feature was introduce

Had anyone succeed in looking up the motivation behind the reserved space idea in ext filesystems, e.g a commit message from the time this feature was introduced? I've tried but failed miserably, got lost in many different git repositories. One fun fact I learned though - one of the reasons is "for quota file". Since ext stores quota information in an ordinary file, there could be an issue where user fills up a disk but the information about it isn't written in quota file due to lack of space.