mm: migrate: add hugepage migration code to move_pages()

mm: migrate: add hugepage migration code to move_pages()

Extend move_pages() to handle vma with VM_HUGETLB set.  We will be able to
migrate hugepage with move_pages(2) after applying the enablement patch
which comes later in this series.

We avoid getting refcount on tail pages of hugepage, because unlike thp,
hugepage is not split and we need not care about races with splitting.

And migration of larger (1GB for x86_64) hugepage are not enabled.

Signed-off-by: Naoya Horiguchi <[email protected]>
Acked-by: Andi Kleen <[email protected]>
Reviewed-by: Wanpeng Li <[email protected]>
Cc: Hillf Danton <[email protected]>
Cc: Mel Gorman <[email protected]>
Cc: Hugh Dickins <[email protected]>
Cc: KOSAKI Motohiro <[email protected]>
Cc: Michal Hocko <[email protected]>
Cc: Rik van Riel <[email protected]>
Cc: "Aneesh Kumar K.V" <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>