mm/frontswap.c: use non-atomic '__set_bit()' when possible

The 'a' and 'b' bitmaps are local to this function, so no concurrent
access can occur.  So the non-atomic '__set_bit()' can be used to save a
few cycles.

Link: https://lkml.kernel.org/r/e52476da5cee57151745c5c3c934a69798dc6fa4.1638132190.git.christophe.jaillet@wanadoo.fr
Signed-off-by: Christophe JAILLET <christophe.jaillet@wanadoo.fr>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

mm/frontswap.c

@@ -127,7 +127,7 @@ void frontswap_register_ops(struct frontswap_ops *ops)
 	spin_lock(&swap_lock);
 	plist_for_each_entry(si, &swap_active_head, list) {
 		if (!WARN_ON(!si->frontswap_map))
-			set_bit(si->type, a);
+			__set_bit(si->type, a);
 	}
 	spin_unlock(&swap_lock);
 
@@ -149,7 +149,7 @@ void frontswap_register_ops(struct frontswap_ops *ops)
 	spin_lock(&swap_lock);
 	plist_for_each_entry(si, &swap_active_head, list) {
 		if (si->frontswap_map)
-			set_bit(si->type, b);
+			__set_bit(si->type, b);
 	}
 	spin_unlock(&swap_lock);