[PATCH 1/6] swap: Add comments to lock_cluster_or_swap_info()

["Huang, Ying" <ying.huang@intel.com>]

From: Huang Ying <ying.huang@intel.com>

To improve the code readability.

Signed-off-by: "Huang, Ying" <ying.huang@intel.com>
Suggested-by: Dave Hansen <dave.hansen@linux.intel.com>
Cc: Michal Hocko <mhocko@suse.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Shaohua Li <shli@kernel.org>
Cc: Hugh Dickins <hughd@google.com>
Cc: Minchan Kim <minchan@kernel.org>
Cc: Rik van Riel <riel@redhat.com>
Cc: Daniel Jordan <daniel.m.jordan@oracle.com>
Cc: Dan Williams <dan.j.williams@intel.com>
---
 mm/swapfile.c | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/mm/swapfile.c b/mm/swapfile.c
index d8fddfb000ec..e31aa601d9c0 100644
--- a/mm/swapfile.c
+++ b/mm/swapfile.c
@@ -297,6 +297,12 @@ static inline void unlock_cluster(struct swap_cluster_info *ci)
 		spin_unlock(&ci->lock);
 }
 
+/*
+ * At most times, fine grained cluster lock is sufficient to protect
+ * the operations on sis->swap_map.  No need to acquire gross grained
+ * sis->lock.  But cluster and cluster lock isn't available for HDD,
+ * so sis->lock will be instead for them.
+ */
 static inline struct swap_cluster_info *lock_cluster_or_swap_info(
 	struct swap_info_struct *si,
 	unsigned long offset)
-- 
2.16.4