Currently in order to support submodules all the directories are included (but not all files) when building the whitelist. This is done because we need the `.git` files (or directories) the contain to be present when we run `git ls-files --recurse-submodules`. Including every directory causes two performance issues: * Creating a directory in your repo (even empty one not added to git at all) will require the whitelist to be recalculated. * Recalculation of the whiltelist may be slowed down if there are a large number of directories. In particular `lstat` is called on every file (probably to get the right `type` to pass to the filter function). The fix is to use `git submodule status --recursive` to get a list of all the submodule directories. Then the `.git` files (or directories) in them can be included. This has to be repeated until all the submodules are known (as `--recursive` will not see the submodules until the parent module is included).