+
+ /*
+ * THP can not break up slab pages so avoid taking
+ * compound_lock(). Slab performs non-atomic bit ops
+ * on page->flags for better performance. In particular
+ * slab_unlock() in slub used to be a hot path. It is
+ * still hot on arches that do not support
+ * this_cpu_cmpxchg_double().
+ */
+ if (PageSlab(page_head)) {
+ if (PageTail(page)) {
+ if (put_page_testzero(page_head))
+ VM_BUG_ON(1);
+
+ atomic_dec(&page->_mapcount);
+ goto skip_lock_tail;
+ } else
+ goto skip_lock;
+ }