Don't understand vm_page_prot

[Timur Tabi <timur.tabi@xxxxxxxxxxx>]

I'm reading about vm_area_struct in Mel Gorman's book on the Linux VM, 
and he says that the vm_page_prot field in structure vm_area_struct 
contains "protection flags that are set for each PTE in this VMA". 
These are the _PAGE_xxx flags in pgtable.h.

The problem I have is that these flags describe individual pages.  For 
instance, _PAGE_DIRTY says that this particular page is dirty.  So what 
does it mean if _PAGE_DIRTY is set in vm_page_prot?  Does that mean that 
every page in this VMA is dirty?  What if only some of the pages are dirty?

--
Timur Tabi
Staff Software Engineer
timur.tabi@xxxxxxxxxxx

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