tn_asize
if (tp->tn_asize >= np)
tp->tn_asize = tp->tn_anon->size;
tp->tn_asize = anon_grow(tp->tn_anon, NULL, tp->tn_asize,
np - tp->tn_asize, ANON_SLEEP);
ASSERT(tp->tn_asize >= np);
anon_release(tp->tn_anon, tp->tn_asize);
tp->tn_asize = 0;