mm/swapfile.c: use memset to fill the swap_map with SWAP_HAS_CACHE

We could use helper memset to fill the swap_map with SWAP_HAS_CACHE instead
of a direct loop here to simplify the code. Also we can remove the local
variable i and map this way.

Link: https://lkml.kernel.org/r/20200921122224.7139-1-linmiaohe@huawei.comSigned-off-by: Miaohe Lin <linmiaohe@huawei.com>
Cc: Hugh Dickins <hughd@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

mm/swapfile.c

@@ -975,8 +975,7 @@ static int swap_alloc_cluster(struct swap_info_struct *si, swp_entry_t *slot)
 {
 	unsigned long idx;
 	struct swap_cluster_info *ci;
-	unsigned long offset, i;
-	unsigned char *map;
+	unsigned long offset;
 
 	/*
 	 * Should not even be attempting cluster allocations when huge
@@ -996,9 +995,7 @@ static int swap_alloc_cluster(struct swap_info_struct *si, swp_entry_t *slot)
 	alloc_cluster(si, idx);
 	cluster_set_count_flag(ci, SWAPFILE_CLUSTER, CLUSTER_FLAG_HUGE);
 
-	map = si->swap_map + offset;
-	for (i = 0; i < SWAPFILE_CLUSTER; i++)
-		map[i] = SWAP_HAS_CACHE;
+	memset(si->swap_map + offset, SWAP_HAS_CACHE, SWAPFILE_CLUSTER);
 	unlock_cluster(ci);
 	swap_range_alloc(si, offset, SWAPFILE_CLUSTER);
 	*slot = swp_entry(si->type, offset);