[RFC 0/2] migrate: convert migrate_pages()/unmap_and_move() to use folios

[Huang Ying]

The conversion is quite straightforward, just replace the page API to
the corresponding folio API.  migrate_pages() and unmap_and_move()
mostly work with folios (head pages) only.

One question is about THP.  Which is converted to large folio in the
patchset.  This is generally OK, because the code can work with
arbitrary order large folio at most times.  But some THP related
statistics (such as THP_MIGRATION_SUCCESS, etc.) are converted for
large folio with arbitrary order too.  Do we really care about the
order of large folio?  Do we need to be backward compatible strictly?

Best Regards,
Huang, Ying