This is a code clean up patch without functionality changes.  The
swap_cluster_list data structure and its operations are introduced to
provide some better encapsulation for the free cluster and discard
cluster list operations.  This avoid some code duplication, improved the
code readability, and reduced the total line number.

[akpm@linux-foundation.org: coding-style fixes]
Link: http://lkml.kernel.org/r/1472067356-16004-1-git-send-email-ying.huang@intel.comSigned-off-by: N"Huang, Ying" <ying.huang@intel.com>
Acked-by: NMinchan Kim <minchan@kernel.org>
Acked-by: NRik van Riel <riel@redhat.com>
Cc: Tim Chen <tim.c.chen@intel.com>
Cc: Hugh Dickins <hughd@google.com>
Cc: Shaohua Li <shli@kernel.org>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>