mm: introduce zone_reclaim struct

mm: introduce zone_reclaim struct

Add zone_reclam_stat struct for later enhancement.

A later patch uses this.  This patch doesn't any behavior change (yet).

Reviewed-by: KAMEZAWA Hiroyuki <[email protected]>
Signed-off-by: KOSAKI Motohiro <[email protected]>
Acked-by: Rik van Riel <[email protected]>
Cc: Balbir Singh <[email protected]>
Cc: Daisuke Nishimura <[email protected]>
Cc: Hugh Dickins <[email protected]>
Cc: KOSAKI Motohiro <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>