mm: make per-memcg LRU lists exclusive

mm: make per-memcg LRU lists exclusive

Now that all code that operated on global per-zone LRU lists is
converted to operate on per-memory cgroup LRU lists instead, there is no
reason to keep the double-LRU scheme around any longer.

The pc->lru member is removed and page->lru is linked directly to the
per-memory cgroup LRU lists, which removes two pointers from a
descriptor that exists for every page frame in the system.

Signed-off-by: Johannes Weiner <[email protected]>
Signed-off-by: Hugh Dickins <[email protected]>
Signed-off-by: Ying Han <[email protected]>
Reviewed-by: KAMEZAWA Hiroyuki <[email protected]>
Reviewed-by: Michal Hocko <[email protected]>
Reviewed-by: Kirill A. Shutemov <[email protected]>
Cc: Daisuke Nishimura <[email protected]>
Cc: Balbir Singh <[email protected]>
Cc: Greg Thelen <[email protected]>
Cc: Michel Lespinasse <[email protected]>
Cc: Rik van Riel <[email protected]>
Cc: Minchan Kim <[email protected]>
Cc: Christoph Hellwig <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>