Query related to special pte mappings

[ravali pullela]

These questions got raised while I was going through vm_normal_page -

1) Why are there some special pte_mappings? [when i went through
mm/memory.c, ]
2) why is [is_zero_pfn] zero pfn used?

I followed the code path, but could not understand semantically what is a
special pte mapping used for and this zer_pfn? It would be great if you can
please point me to resources.

Thanks !
-------------- next part --------------
An HTML attachment was scrubbed...
URL: http://lists.kernelnewbies.org/pipermail/kernelnewbies/attachments/20140908/6953d2e9/attachment.html