quoted

Exactly. But for hugetlbfs/shmem ("!RAM-backed files") this is not what we
want.

OK, then I must have misread your requirements. Maybe I just got lost in
all the combinations you have listed.

Another special case could be dax/pmem I think. You might want to fault 
it in readable/writable but not perform an actual read/write unless 
really required.

QEMU phrases this as "don't cause wear on the storage backing".

-- 
Thanks,

David / dhildenb