mempool: add unlikely and likely hints

Add unlikely and likely hints to the function mempool_free.  It lays out
the code in such a way that the common path is executed straighforward and
saves a cache line.

Signed-off-by: Mikulas Patocka <mpatocka@redhat.com>
Cc: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

mm/mempool.c

@@ -304,9 +304,9 @@ void mempool_free(void *element, mempool_t *pool)
 	 * ensures that there will be frees which return elements to the
 	 * pool waking up the waiters.
 	 */
-	if (pool->curr_nr < pool->min_nr) {
+	if (unlikely(pool->curr_nr < pool->min_nr)) {
 		spin_lock_irqsave(&pool->lock, flags);
-		if (pool->curr_nr < pool->min_nr) {
+		if (likely(pool->curr_nr < pool->min_nr)) {
 			add_element(pool, element);
 			spin_unlock_irqrestore(&pool->lock, flags);
 			wake_up(&pool->wait);