Memory used ??

I have a linux server (redhat9) and 512Mb Ram (upgrading to 1 gig Ram soon). My problem is, I have to reboot every 3-4 days because the memory used % gets too high and the server stops. This is really annoying and stressfull... When I look at my runnin process (SSH top). I get this:

20:58:58 up 5 days, 2:14, 1 user, load average: 0.22, 0.20, 0.13
89 processes: 86 sleeping, 2 running, 1 zombie, 0 stopped
CPU states: 2.0% user 1.0% system 0.0% nice 0.0% iowait 97.0% idle
Mem: 505716k av, 492384k used, 13332k free, 0k shrd, 1648k buff
58808k actv, 1468k in_d, 6880k in_c
Swap: 1052248k av, 59000k used, 993248k free 57476k cached

I've heard that I shouldn't worry and that my server's memory may be cahed but not really used!?! But the problem is still there, I have to reboot every 3 or 4 days and it sucks! What is the cached used for? Can I allow it less memory, and run as smoothly.

What can I do to fix this?

Thanks!

 

 

 

 

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