[PATCH -V7 RESEND 02/21] swap: Add __swap_duplicate_locked()

[Huang Ying <ying.huang@xxxxxxxxx>]

The part of __swap_duplicate() with lock held is separated into a new
function __swap_duplicate_locked().  Because we will add more logic
about the PMD swap mapping into __swap_duplicate() and keep the most
PTE swap mapping related logic in __swap_duplicate_locked().

Just mechanical code refactoring, there is no any functional change in
this patch.

Signed-off-by: "Huang, Ying" <ying.huang@xxxxxxxxx>
Cc: "Kirill A. Shutemov" <kirill.shutemov@xxxxxxxxxxxxxxx>
Cc: Andrea Arcangeli <aarcange@xxxxxxxxxx>
Cc: Michal Hocko <mhocko@xxxxxxxxxx>
Cc: Johannes Weiner <hannes@xxxxxxxxxxx>
Cc: Shaohua Li <shli@xxxxxxxxxx>
Cc: Hugh Dickins <hughd@xxxxxxxxxx>
Cc: Minchan Kim <minchan@xxxxxxxxxx>
Cc: Rik van Riel <riel@xxxxxxxxxx>
Cc: Dave Hansen <dave.hansen@xxxxxxxxxxxxxxx>
Cc: Naoya Horiguchi <n-horiguchi@xxxxxxxxxxxxx>
Cc: Zi Yan <zi.yan@xxxxxxxxxxxxxx>
Cc: Daniel Jordan <daniel.m.jordan@xxxxxxxxxx>
---
 mm/swapfile.c | 63 ++++++++++++++++++++++++++++-----------------------
 1 file changed, 35 insertions(+), 28 deletions(-)

diff --git a/mm/swapfile.c b/mm/swapfile.c
index ec210be02c3b..f3c175d830b1 100644
--- a/mm/swapfile.c
+++ b/mm/swapfile.c
@@ -3441,32 +3441,12 @@ void si_swapinfo(struct sysinfo *val)
 	spin_unlock(&swap_lock);
 }
 
-/*
- * Verify that a swap entry is valid and increment its swap map count.
- *
- * Returns error code in following case.
- * - success -> 0
- * - swp_entry is invalid -> EINVAL
- * - swp_entry is migration entry -> EINVAL
- * - swap-cache reference is requested but there is already one. -> EEXIST
- * - swap-cache reference is requested but the entry is not used. -> ENOENT
- * - swap-mapped reference requested but needs continued swap count. -> ENOMEM
- */
-static int __swap_duplicate(swp_entry_t entry, unsigned char usage)
+static int __swap_duplicate_locked(struct swap_info_struct *p,
+				   unsigned long offset, unsigned char usage)
 {
-	struct swap_info_struct *p;
-	struct swap_cluster_info *ci;
-	unsigned long offset;
 	unsigned char count;
 	unsigned char has_cache;
-	int err = -EINVAL;
-
-	p = get_swap_device(entry);
-	if (!p)
-		goto out;
-
-	offset = swp_offset(entry);
-	ci = lock_cluster_or_swap_info(p, offset);
+	int err = 0;
 
 	count = p->swap_map[offset];
 
@@ -3476,12 +3456,11 @@ static int __swap_duplicate(swp_entry_t entry, unsigned char usage)
 	 */
 	if (unlikely(swap_count(count) == SWAP_MAP_BAD)) {
 		err = -ENOENT;
-		goto unlock_out;
+		goto out;
 	}
 
 	has_cache = count & SWAP_HAS_CACHE;
 	count &= ~SWAP_HAS_CACHE;
-	err = 0;
 
 	if (usage == SWAP_HAS_CACHE) {
 
@@ -3508,11 +3487,39 @@ static int __swap_duplicate(swp_entry_t entry, unsigned char usage)
 
 	p->swap_map[offset] = count | has_cache;
 
-unlock_out:
+out:
+	return err;
+}
+
+/*
+ * Verify that a swap entry is valid and increment its swap map count.
+ *
+ * Returns error code in following case.
+ * - success -> 0
+ * - swp_entry is invalid -> EINVAL
+ * - swp_entry is migration entry -> EINVAL
+ * - swap-cache reference is requested but there is already one. -> EEXIST
+ * - swap-cache reference is requested but the entry is not used. -> ENOENT
+ * - swap-mapped reference requested but needs continued swap count. -> ENOMEM
+ */
+static int __swap_duplicate(swp_entry_t entry, unsigned char usage)
+{
+	struct swap_info_struct *p;
+	struct swap_cluster_info *ci;
+	unsigned long offset;
+	int err = -EINVAL;
+
+	p = get_swap_device(entry);
+	if (!p)
+		goto out;
+
+	offset = swp_offset(entry);
+	ci = lock_cluster_or_swap_info(p, offset);
+	err = __swap_duplicate_locked(p, offset, usage);
 	unlock_cluster_or_swap_info(p, ci);
+
+	put_swap_device(p);
 out:
-	if (p)
-		put_swap_device(p);
 	return err;
 }
 
-- 
2.18.1