B_AGE
pribp->b_flags |= B_AGE;
bp->b_flags |= B_AGE;
supbp->b_flags |= B_AGE;
bp->b_flags |= B_AGE;
bp->b_flags &= ~(B_AGE | B_REUSE);
if (bp->b_flags & B_AGE) {
bp->b_flags &= ~(B_AGE | B_REUSE);
bp->b_flags |= B_AGE;
bp->b_flags &= ~(B_ASYNC | B_NOCACHE | B_AGE | B_RELBUF);