In windows mdl holds an association between the physical pages and virtual buffers
A scatter gather entry represents a contiguous physical memory
It can span multiple pages if the vm associated extends
mostly the first SGE will have this
in this case from the virtual address find the corresponding physical address
this physical address will be on a page boundry by default
then calculate the offset of vm by finding the nearest page rounded vm and taking the difference
apply this difference to physical address
then start calculating the pages till but the last one
find the offset of the last one
In linux the procedure is same but the skb contains SGL with SGE's
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