mm/slab: Optimize the code logic in find_mergeable()

We can first assess the flags, if it's unmergeable, there's no need
to calculate the size and align.

Signed-off-by: Xavier <xavier_qy@163.com>
Signed-off-by: Vlastimil Babka <vbabka@suse.cz>

Author: Xavier

mm/slab_common.c

@@ -186,14 +186,15 @@ struct kmem_cache *find_mergeable(unsigned int size, unsigned int align,
 	if (ctor)
 		return NULL;
 
-	size = ALIGN(size, sizeof(void *));
-	align = calculate_alignment(flags, align, size);
-	size = ALIGN(size, align);
 	flags = kmem_cache_flags(flags, name);
 
 	if (flags & SLAB_NEVER_MERGE)
 		return NULL;
 
+	size = ALIGN(size, sizeof(void *));
+	align = calculate_alignment(flags, align, size);
+	size = ALIGN(size, align);
+
 	list_for_each_entry_reverse(s, &slab_caches, list) {
 		if (slab_unmergeable(s))
 			continue;