zsmalloc: use class->pages_per_zspage

There is no need to recalcurate pages_per_zspage in runtime.  Just use
class->pages_per_zspage to avoid unnecessary runtime overhead.
Signed-off-by: Minchan Kim <minchan@kernel.org>
Acked-by: Sergey Senozhatsky <sergey.senozhatsky@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

mm/zsmalloc.c

@@ -1723,7 +1723,7 @@ static unsigned long zs_can_compact(struct size_class *class)
 	obj_wasted /= get_maxobj_per_zspage(class->size,
 			class->pages_per_zspage);
 
-	return obj_wasted * get_pages_per_zspage(class->size);
+	return obj_wasted * class->pages_per_zspage;
 }
 
 static void __zs_compact(struct zs_pool *pool, struct size_class *class)
@@ -1761,8 +1761,7 @@ static void __zs_compact(struct zs_pool *pool, struct size_class *class)
 
 		putback_zspage(pool, class, dst_page);
 		if (putback_zspage(pool, class, src_page) == ZS_EMPTY)
-			pool->stats.pages_compacted +=
-				get_pages_per_zspage(class->size);
+			pool->stats.pages_compacted += class->pages_per_zspage;
 		spin_unlock(&class->lock);
 		cond_resched();
 		spin_lock(&class->lock);