L2ARC_DEV_HDR_EVICT_FIRST
dev.l2ad_first = !!(l2dhdr.dh_flags & L2ARC_DEV_HDR_EVICT_FIRST);
dev->l2ad_first = !!(l2dhdr->dh_flags & L2ARC_DEV_HDR_EVICT_FIRST);
l2dhdr->dh_flags |= L2ARC_DEV_HDR_EVICT_FIRST;