The idea was to lazily map pages only when needed. In practice, this doesn't work that well--too many mapping types are fallible in practice, and we need to get that feedback to the user. And mapping changes are rare, so there's not much benefit.
The main place where we still want this is something like virtio-fs DAX support, where mappings are added and removed often and are unlikely to fail. We might just say that multi-process memory access with virtio-fs+DAX is just slow. Or we might preserve lazy mapping for this case.
The idea was to lazily map pages only when needed. In practice, this doesn't work that well--too many mapping types are fallible in practice, and we need to get that feedback to the user. And mapping changes are rare, so there's not much benefit.
The main place where we still want this is something like virtio-fs DAX support, where mappings are added and removed often and are unlikely to fail. We might just say that multi-process memory access with virtio-fs+DAX is just slow. Or we might preserve lazy mapping for this case.