Thanks, that totally makes sense. I also wanted to not miss stuff, such as remounting the lower file system, or that it somehow will still do some unnecessary writes if the upper FS doesn't have the noatime flag, set, when the lower one does have it set.
I kind of would have expected that the upper FS would also get this flag (in the mount command output) or something.
Anyway, if the "limits" of the flags are essentially defined by the underlying file system that's pretty clear.
