[PATCH] speed up pte_chain locking on uniprocessors

ifdef out some operations in pte_chain_lock() which are not necessary
on uniprocessor.

include/linux/page-flags.h

@@ -240,16 +240,20 @@ static inline void pte_chain_lock(struct page *page)
 	 * attempt to acquire the lock bit.
 	 */
 	preempt_disable();
+#ifdef CONFIG_SMP
 	while (test_and_set_bit(PG_chainlock, &page->flags)) {
 		while (test_bit(PG_chainlock, &page->flags))
 			cpu_relax();
 	}
+#endif
 }
 
 static inline void pte_chain_unlock(struct page *page)
 {
+#ifdef CONFIG_SMP
 	smp_mb__before_clear_bit();
 	clear_bit(PG_chainlock, &page->flags);
+#endif
 	preempt_enable();
 }