posmaster failed under high load

Today I run http_load to do some benchmark of my Web-DB application
and found that under high load (it was about 18 postgres running ) postsmaster failed.
Restarting postmaster produces error:

IpcMemoryCreate: shmget failed (Identifier removed) key=5432010, size=24588, permission=700
IpcMemoryIdGet: shmget failed (Identifier removed) key=5432010, size=24588, permission=0
IpcMemoryAttach: shmat failed (Invalid argument) id=-2
FATAL 1: AttachSLockMemory: could not attach segment

I checked shared memory:
23:27[zeus]:~>ipcs -a

------ Shared Memory Segments --------
shmid owner perms bytes nattch status
10496 postgres 700 24588 5 dest
10497 postgres 600 8852184 5 dest
10498 postgres 600 96804 5 dest

------ Semaphore Arrays --------
semid owner perms nsems status

------ Message Queues --------
msqid owner perms used-bytes messages

Does this error means I need to increase shared memory ?
My setup: Linux 2.0.36, Dual PPRO, 256 Mb RAM
Postgres 6.4.2

Regards,

Oleg

_____________________________________________________________
Oleg Bartunov, sci.researcher, hostmaster of AstroNet,
Sternberg Astronomical Institute, Moscow University (Russia)
Internet: oleg(at)sai(dot)msu(dot)su, http://www.sai.msu.su/~megera/
phone: +007(095)939-16-83, +007(095)939-23-83