visibility map - what do i miss?

hi,
i tried to test new "visibility map" feature.

to do so i:
1. fetched postgresql sources from cvs
2. compiled
3. turned autovacuum off
4. started pg
5. ran this queries:
  - CREATE TABLE test_1 (i INT4);
  - CREATE TABLE test_2 (i INT4);
  - CREATE TABLE test_3 (i INT4);
  - CREATE TABLE test_4 (i INT4);
  - INSERT INTO test_1 SELECT generate_series(1, 100000000);
  - INSERT INTO test_2 SELECT generate_series(1, 100000000);
  - INSERT INTO test_3 SELECT generate_series(1, 100000000);
  - INSERT INTO test_4 SELECT generate_series(1, 100000000);
  - UPDATE test_2 SET i = i + 1 WHERE i < 10000000;
  - UPDATE test_3 SET i = i + 1 WHERE i < 50000000;
  - UPDATE test_4 SET i = i + 1 WHERE i < 90000000;
  - VACUUM test_1;
  - VACUUM test_2;
  - VACUUM test_3;
  - VACUUM test_4;

I did it 2 times, first with sources of pg from 1st of november, and
second - with head from yesterday evening (warsaw, poland time).

results puzzled me.

First run - without visibility maps, timing of vacuums:
Time: 267844.822 ms
Time: 138854.592 ms
Time: 305467.950 ms
Time: 487133.179 ms

Second run - on head:

Time: 252218.609 ms
Time: 234388.763 ms
Time: 334016.413 ms
Time: 575698.750 ms

Now - as I understand the change - visilibity maps should make second run much faster?

Tests were performed on laptop. During first test I used it to browse the web,
read mail. During second test - nobody used the laptop.

Relation forms seem to exist:
# select oid from pg_database where datname = 'depesz';
  oid
-------
 16389
(1 row)
# select relfilenode from pg_class where relname ~ 'test_';
 relfilenode
-------------
       26756
       26759
       26762
       26765
(4 rows)

=> ls -l {26756,26759,26762,26765}*
-rw------- 1 pgdba pgdba 1073741824 2008-12-06 01:31 26756
-rw------- 1 pgdba pgdba 1073741824 2008-12-06 01:33 26756.1
-rw------- 1 pgdba pgdba 1065066496 2008-12-06 01:34 26756.2
-rw------- 1 pgdba pgdba     811008 2008-12-06 01:34 26756_fsm
-rw------- 1 pgdba pgdba      57344 2008-12-06 01:34 26756_vm
-rw------- 1 pgdba pgdba 1073741824 2008-12-06 01:35 26759
-rw------- 1 pgdba pgdba 1073741824 2008-12-06 01:36 26759.1
-rw------- 1 pgdba pgdba 1073741824 2008-12-06 01:37 26759.2
-rw------- 1 pgdba pgdba  312582144 2008-12-06 01:39 26759.3
-rw------- 1 pgdba pgdba     892928 2008-12-06 01:39 26759_fsm
-rw------- 1 pgdba pgdba      57344 2008-12-06 01:39 26759_vm
-rw------- 1 pgdba pgdba 1073741824 2008-12-06 01:39 26762
-rw------- 1 pgdba pgdba 1073741824 2008-12-06 01:49 26762.1
-rw------- 1 pgdba pgdba 1073741824 2008-12-06 01:41 26762.2
-rw------- 1 pgdba pgdba 1073741824 2008-12-06 01:42 26762.3
-rw------- 1 pgdba pgdba  523862016 2008-12-06 01:43 26762.4
-rw------- 1 pgdba pgdba    1204224 2008-12-06 01:43 26762_fsm
-rw------- 1 pgdba pgdba      81920 2008-12-06 01:53 26762_vm
-rw------- 1 pgdba pgdba 1073741824 2008-12-06 02:01 26765
-rw------- 1 pgdba pgdba 1073741824 2008-12-06 02:08 26765.1
-rw------- 1 pgdba pgdba 1073741824 2008-12-06 02:18 26765.2
-rw------- 1 pgdba pgdba 1073741824 2008-12-06 01:50 26765.3
-rw------- 1 pgdba pgdba 1073741824 2008-12-06 01:51 26765.4
-rw------- 1 pgdba pgdba  735141888 2008-12-06 02:00 26765.5
-rw------- 1 pgdba pgdba    1523712 2008-12-06 02:00 26765_fsm
-rw------- 1 pgdba pgdba      98304 2008-12-06 02:18 26765_vm

What do I miss?

Best regards,

depesz

--
Linkedin: http://www.linkedin.com/in/depesz  /  blog: http://www.depesz.com/
jid/gtalk: depesz@depesz.com / aim:depeszhdl / skype:depesz_hdl / gg:6749007