mm/mremap: calculate extent in one place

mm/mremap: calculate extent in one place

Page tables is moved on the base of PMD.  This requires both source and
destination range should meet the requirement.

Current code works well since move_huge_pmd() and move_normal_pmd() would
check old_addr and new_addr again.  And then return to move_ptes() if the
either of them is not aligned.

Instead of calculating the extent separately, it is better to calculate in
one place, so we know it is not necessary to try move pmd.  By doing so,
the logic seems a little clear.

Signed-off-by: Wei Yang <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Tested-by: Dmitry Osipenko <[email protected]>
Acked-by: Kirill A. Shutemov <[email protected]>
Cc: Aneesh Kumar K.V <[email protected]>
Cc: Anshuman Khandual <[email protected]>
Cc: Matthew Wilcox <[email protected]>
Cc: Peter Xu <[email protected]>
Cc: Sean Christopherson <[email protected]>
Cc: Thomas Hellstrom <[email protected]>
Cc: Thomas Hellstrom (VMware) <[email protected]>
Cc: Vlastimil Babka <[email protected]>
Cc: Yang Shi <[email protected]>
Link: http://lkml.kernel.org/r/[email protected]
Signed-off-by: Linus Torvalds <[email protected]>