test_keep_probing
test_keep_probing(slab, cfg, one, onelen, zone, zonelen, &now, 0, default_max_rtt);
test_keep_probing(slab, cfg, one, onelen, zone, zonelen, &now, 1, default_max_rtt);
test_keep_probing(slab, cfg, one, onelen, zone, zonelen, &now, 0, 3000);
test_keep_probing(slab, cfg, one, onelen, zone, zonelen, &now, 1, 3000);