slub: add missed accounting

With per-cpu partial list, slab is added to partial list first and then moved
to node list. The __slab_free() code path for add/remove_partial is almost
deprecated(except for slub debug). But we forget to account add/remove_partial
when move per-cpu partial pages to node list, so the statistics for such events
are always 0. Add corresponding accounting.

This is against the patch "slub: use correct parameter to add a page to
partial list tail"
Acked-by: Christoph Lameter <cl@linux.com>
Signed-off-by: Shaohua Li <shaohua.li@intel.com>
Signed-off-by: Pekka Enberg <penberg@kernel.org>

mm/slub.c

@@ -1901,11 +1901,14 @@ static void unfreeze_partials(struct kmem_cache *s)
 			}
 
 			if (l != m) {
-				if (l == M_PARTIAL)
+				if (l == M_PARTIAL) {
 					remove_partial(n, page);
-				else
+					stat(s, FREE_REMOVE_PARTIAL);
+				} else {
 					add_partial(n, page,
 						DEACTIVATE_TO_TAIL);
+					stat(s, FREE_ADD_PARTIAL);
+				}
 
 				l = m;
 			}