VUSECOUNT_GATE
if (__predict_false((use & VUSECOUNT_GATE) == 0)) {
bool gated = (atomic_load_relaxed(&vp->v_usecount) & VUSECOUNT_GATE);
atomic_or_uint(&vp->v_usecount, VUSECOUNT_GATE);
atomic_and_uint(&vp->v_usecount, ~VUSECOUNT_GATE);
atomic_or_uint(&vp->v_usecount, VUSECOUNT_GATE);
atomic_and_uint(&vp->v_usecount, ~VUSECOUNT_GATE);