vm/swap used until exhausted

Different memory usage 7.4.3 vs 8.0.0beta1

client does:

begin
bulk inserts into single table via PQexecParams (1.2 million records)
commit

under 7.4.3 memory usage is static
under 8.0.0beta1 server used increasing memory untill depletion of vm/swap

7.4.3
last pid: 974; load averages: 1.44, 1.12, 0.68 up 0+00:24:08
19:05:08
65 processes: 3 running, 62 sleeping
CPU states: 88.0% user, 0.0% nice, 9.7% system, 2.3% interrupt, 0.0% idle
Mem: 96M Active, 16M Inact, 31M Wired, 7008K Cache, 28M Buf, 28M Free
Swap: 357M Total, 37M Used, 319M Free, 10% Inuse

PID USERNAME PRI NICE SIZE RES STATE TIME WCPU CPU COMMAND
923 pgsql 115 0 16712K 11792K RUN 8:06 65.82% 65.82% postgres
921 pgsql 96 0 2292K 1320K RUN 0:01 0.00% 0.00% top
904 pgsql 4 0 16016K 1204K select 0:00 0.00% 0.00% postgres
877 pgsql 8 0 916K 0K wait 0:00 0.00% 0.00% <sh>
906 pgsql 4 0 6808K 12K select 0:00 0.00% 0.00% postgres
905 pgsql 4 0 7764K 12K select 0:00 0.00% 0.00% postgres

8.0.0 beta1

last pid: 11448; load averages: 1.00, 0.35, 0.23 up 0+04:57:28
23:38:28
64 processes: 2 running, 62 sleeping
CPU states: 77.0% user, 0.0% nice, 15.6% system, 7.4% interrupt, 0.0% idle
Mem: 115M Active, 15M Inact, 42M Wired, 7540K Cache, 28M Buf, 564K Free
Swap: 357M Total, 57M Used, 300M Free, 15% Inuse, 932K Out

PID USERNAME PRI NICE SIZE RES STATE TIME WCPU CPU COMMAND
11448 pgsql 130 0 83564K 78732K RUN 0:58 72.08% 70.56% postgres
11438 pgsql 96 0 13960K 10156K select 0:00 0.00% 0.00% postgres
11436 pgsql 96 0 13952K 0K select 0:00 0.00% 0.00% <postgres>
877 pgsql 5 0 920K 0K ttyin 0:00 0.00% 0.00% <sh>
11440 pgsql 4 0 4552K 0K select 0:00 0.00% 0.00% <postgres>
11439 pgsql 96 0 5480K 2028K select 0:00 0.00% 0.00% postgres