mm: add swap cache interface for swap reference

In a following patch, the usage of swap cache is recorded into swap_map.
This patch is for necessary interface changes to do that.

2 interfaces:

  - swapcache_prepare()
  - swapcache_free()

are added for allocating/freeing refcnt from swap-cache to existing swap
entries.  But implementation itself is not changed under this patch.  At
adding swapcache_free(), memcg's hook code is moved under
swapcache_free().  This is better than using scattered hooks.

Signed-off-by: KAMEZAWA Hiroyuki <[email protected]>
Reviewed-by: Daisuke Nishimura <[email protected]>
Acked-by: Balbir Singh <[email protected]>
Cc: Hugh Dickins <[email protected]>
Cc: Johannes Weiner <[email protected]>
Cc: Li Zefan <[email protected]>
Cc: Dhaval Giani <[email protected]>
Cc: YAMAMOTO Takashi <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>

0 files changed, 0 insertions, 0 deletions