[PATCH v4 11/13] mm, swap: introduce a helper for retrieving cluster from offset

[Kairui Song <ryncsn@gmail.com>]

From: Kairui Song <kasong@tencent.com>

It's a common operation to retrieve the cluster info from offset,
introduce a helper for this.

Suggested-by: Chris Li <chrisl@kernel.org>
Signed-off-by: Kairui Song <kasong@tencent.com>
---
 mm/swapfile.c | 14 ++++++++++----
 1 file changed, 10 insertions(+), 4 deletions(-)

diff --git a/mm/swapfile.c b/mm/swapfile.c
index 6da2f3aa55fb..37d540fa0310 100644
--- a/mm/swapfile.c
+++ b/mm/swapfile.c
@@ -424,6 +424,12 @@ static inline unsigned int cluster_index(struct swap_info_struct *si,
 	return ci - si->cluster_info;
 }
 
+static inline struct swap_cluster_info *offset_to_cluster(struct swap_info_struct *si,
+							  unsigned long offset)
+{
+	return &si->cluster_info[offset / SWAPFILE_CLUSTER];
+}
+
 static inline unsigned int cluster_offset(struct swap_info_struct *si,
 					  struct swap_cluster_info *ci)
 {
@@ -435,7 +441,7 @@ static inline struct swap_cluster_info *lock_cluster(struct swap_info_struct *si
 {
 	struct swap_cluster_info *ci;
 
-	ci = &si->cluster_info[offset / SWAPFILE_CLUSTER];
+	ci = offset_to_cluster(si, offset);
 	spin_lock(&ci->lock);
 
 	return ci;
@@ -1480,10 +1486,10 @@ static void swap_entry_range_free(struct swap_info_struct *si, swp_entry_t entry
 	unsigned char *map_end = map + nr_pages;
 	struct swap_cluster_info *ci;
 
-	/* It should never free entries across different clusters */
-	VM_BUG_ON((offset / SWAPFILE_CLUSTER) != ((offset + nr_pages - 1) / SWAPFILE_CLUSTER));
-
 	ci = lock_cluster(si, offset);
+
+	/* It should never free entries across different clusters */
+	VM_BUG_ON(ci != offset_to_cluster(si, offset + nr_pages - 1));
 	VM_BUG_ON(cluster_is_empty(ci));
 	VM_BUG_ON(ci->count < nr_pages);
 
-- 
2.47.1