[PATCH v4 1/8] swap: Add comments to lock_cluster_or_swap_info()

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

To improve the code readability.

Signed-off-by: "Huang, Ying" <ying.huang@intel.com>
Suggested-and-acked-by: Dave Hansen <dave.hansen@linux.intel.com>
Reviewed-by: Daniel Jordan <daniel.m.jordan@oracle.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: Dan Williams <dan.j.williams@intel.com>
---
 mm/swapfile.c | 9 +++++++--
 1 file changed, 7 insertions(+), 2 deletions(-)

diff --git a/mm/swapfile.c b/mm/swapfile.c
index d8fddfb000ec..d101e044efbf 100644
--- a/mm/swapfile.c
+++ b/mm/swapfile.c
@@ -297,13 +297,18 @@ static inline void unlock_cluster(struct swap_cluster_info *ci)
 		spin_unlock(&ci->lock);
 }
 
+/*
+ * Determine the locking method in use for this device.  Return
+ * swap_cluster_info if SSD-style cluster-based locking is in place.
+ */
 static inline struct swap_cluster_info *lock_cluster_or_swap_info(
-	struct swap_info_struct *si,
-	unsigned long offset)
+		struct swap_info_struct *si, unsigned long offset)
 {
 	struct swap_cluster_info *ci;
 
+	/* Try to use fine-grained SSD-style locking if available: */
 	ci = lock_cluster(si, offset);
+	/* Otherwise, fall back to traditional, coarse locking: */
 	if (!ci)
 		spin_lock(&si->lock);
 
-- 
2.16.4