[PATCH] page migration: use allocator function for migrate_pages()
Instead of passing a list of new pages, pass a function to allocate a new
page. This allows the correct placement of MPOL_INTERLEAVE pages during page
migration. It also further simplifies the callers of migrate pages.
migrate_pages() becomes similar to migrate_pages_to() so drop
migrate_pages_to(). The batching of new page allocations becomes unnecessary.