Have some confusion about the pfn_valid() ?

[zhong jiang]

Hi

In my opinion, pfn_valid() is meant to be able to tell if a given PFN has valid
section, and That section can contain corresponding mem_map. but, the section can
be has holes, the corresponding mem_map also be allcoated, resulting in treating
the PFN as valid incorrect.

what's problem for the interpretation of the above?