mm/swapfile.c: call free_swap_slot() in __swap_entry_free()

This is a code cleanup patch without functionality change.

Originally, when __swap_entry_free() is called, and its return value is 0,
free_swap_slot() will always be called to free the swap entry to the
per-CPU pool.  So move the call to free_swap_slot() to __swap_entry_free()
to simplify the code.

Link: http://lkml.kernel.org/r/20180827075535.17406-3-ying.huang@intel.com
Signed-off-by: "Huang, Ying" <ying.huang@intel.com>
Reviewed-by: Andrew Morton <akpm@linux-foundation.org>
Cc: 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>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

mm/swapfile.c

@@ -1182,6 +1182,8 @@ static unsigned char __swap_entry_free(struct swap_info_struct *p,
 	ci = lock_cluster_or_swap_info(p, offset);
 	usage = __swap_entry_free_locked(p, offset, usage);
 	unlock_cluster_or_swap_info(p, ci);
+	if (!usage)
+		free_swap_slot(entry);
 
 	return usage;
 }
@@ -1212,10 +1214,8 @@ void swap_free(swp_entry_t entry)
 	struct swap_info_struct *p;
 
 	p = _swap_info_get(entry);
-	if (p) {
-		if (!__swap_entry_free(p, entry, 1))
-			free_swap_slot(entry);
-	}
+	if (p)
+		__swap_entry_free(p, entry, 1);
 }
 
 /*
@@ -1637,8 +1637,6 @@ int free_swap_and_cache(swp_entry_t entry)
 		    !swap_page_trans_huge_swapped(p, entry))
 			__try_to_reclaim_swap(p, swp_offset(entry),
 					      TTRS_UNMAPPED | TTRS_FULL);
-		else if (!count)
-			free_swap_slot(entry);
 	}
 	return p != NULL;
 }