SIMPLE_RB_LINK_MASK
switch (link & ~SIMPLE_RB_LINK_MASK) {
link &= SIMPLE_RB_LINK_MASK;
unsigned long old = (*link & SIMPLE_RB_LINK_MASK) | SIMPLE_RB_LINK_HEAD;
WRITE_ONCE(bpage->link.next, (struct list_head *)(link & SIMPLE_RB_LINK_MASK));
unsigned long ptr = (unsigned long)link & SIMPLE_RB_LINK_MASK;