The pair of get/set_freepage_migratetype() functions are used to cache
pageblock migratetype for a page put on a pcplist, so that it does not
have to be retrieved again when the page is put on a free list (e.g.
when pcplists become full).  Historically it was also assumed that the
value is accurate for pages on freelists (as the functions' names
unfortunately suggest), but that cannot be guaranteed without affecting
various allocator fast paths.  It is in fact not needed and all such
uses have been removed.

The last remaining (but pointless) usage related to pages of freelists
is in move_freepages(), which this patch removes.

To prevent further confusion, rename the functions to
get/set_pcppage_migratetype() and expand their description.  Since all
the users are now in mm/page_alloc.c, move the functions there from the
shared header.
Signed-off-by: NVlastimil Babka <vbabka@suse.cz>
Acked-by: NDavid Rientjes <rientjes@google.com>
Acked-by: NJoonsoo Kim <iamjoonsoo.kim@lge.com>
Cc: Minchan Kim <minchan@kernel.org>
Acked-by: NMichal Nazarewicz <mina86@mina86.com>
Cc: Laura Abbott <lauraa@codeaurora.org>
Reviewed-by: NNaoya Horiguchi <n-horiguchi@ah.jp.nec.com>
Cc: Seungho Park <seungho1.park@lge.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>
Acked-by: NMel Gorman <mgorman@techsingularity.net>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>