> on a filesystem that has... memfd_create's whole selling point is that it isn't backed by a filesystem; it isn't "on" one in the first place, so there is now

> on a filesystem that has... memfd_create's whole selling point is that it isn't backed by a filesystem; it isn't "on" one in the first place, so there is nowhere for it to inherit such restrictions from. The consequences of that can be surprising though, I agree, and are worth exploring and writing about.