Linux kernel - allocation failed

Hello,
I have problems with my system, it freezed after some days of working, only
thing I found in logs was:

May 14 20:29:57 X kernel: __alloc_pages: 0-order allocation failed
(gfp=0x1d2/0)
$ uptime
20:10:01 up 5 days, 6:29, 2 users, load average: 191.44, 187.64, 174.14

then I hardly managed to reboot it,and after about couple minutes from
reboot I got:

May 14 20:17:23 X kernel: __alloc_pages: 0-order allocation failed
(gfp=0xf0/0)
May 14 20:17:29 X kernel: __alloc_pages: 0-order allocation failed
(gfp=0xf0/0)
May 14 20:17:34 X kernel: __alloc_pages: 0-order allocation failed
(gfp=0xf0/0)
.......
May 14 20:20:27 X kernel: __alloc_pages: 0-order allocation failed
(gfp=0xf0/0)
May 14 20:20:28 X kernel: __alloc_pages: 0-order allocation failed
(gfp=0x1d2/0)
May 14 20:20:28 X kernel: __alloc_pages: 0-order allocation failed
(gfp=0x1d2/0)
May 14 20:20:29 X kernel: VM: killing process sshd
May 14 20:20:29 X kernel: __alloc_pages: 0-order allocation failed
(gfp=0x1d2/0)
May 14 20:20:29 X kernel: VM: killing process sh

then after second reboot its working,but for how long? Any ideas what could
be wrong
- kernel 2.4.30-grsec
- hardware: AMD Athlon, 512Mb RAM, Swap is 1GB big

Regards.