Everything does pathname lookups all the time, it’s hugely performance-critical, and it’s very much one of those areas where you also want to scale well in SMP environments, and it has lots of complexity in locking. And you very much do not want to do any IO, so caching is very important. In fact, pathname lookup is so important that you can’t leave it to the low-level filesystem, because we have 20+ different filesystems, and having each of them do their own caching and their own locking would be a complete disaster. - linus about the VFS