mm: free up PG_slab

mm: free up PG_slab

Reclaim the Slab page flag by using a spare bit in PageType.  We are
perennially short of page flags for various purposes, and now that the
original SLAB allocator has been retired, SLUB does not use the
mapcount/page_type field.  This lets us remove a number of special cases
for ignoring mapcount on Slab pages.

[[email protected]: update vmcoreinfo]
Link: https://lkml.kernel.org/r/[email protected]
Link: https://lkml.kernel.org/r/[email protected]
Signed-off-by: Matthew Wilcox (Oracle) <[email protected]>
Acked-by: David Hildenbrand <[email protected]>
Cc: Miaohe Lin <[email protected]>
Cc: Muchun Song <[email protected]>
Cc: Oscar Salvador <[email protected]>
Cc: Vlastimil Babka <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>