troubleshooting sudden memory spikes

Zbigniew Szalbot z.szalbot at
Fri Jun 26 15:34:25 UTC 2009


I have a 7.2 FreeBSD server that has recently started to exhibit some 
strange behaviour. For a few days (since Monday) the number of inactive 
memory is constantly on the rise. When it gets to a certain level 
(around 1300-1400M), the system will start swapping, the inactvie memory 
gets released and free memory jumps to about 1300-1500M.

You can see some graphs here to better realise what I am trying to describe:

I was once able to see the memory spike occuring and I noticed that 
proftpd was intensively being used at that time. We have implemented 
some changes to proftpd setup to make sure it does not cause trouble. 
However, the spikes still occur.

I am wondering how to troubleshoot it. Where would you start looking to 
solve the problem?

I am suspecting:
1/ proftpd still causes some kind of a problem on one jail
2/ at least one website is quite buggy and generates a lot of entries in 
error.log so maybe it is the site?
3/ something about the jail system which was added about two weeks ago?

As of writing this email...
last pid: 85820;  load averages:  0.20,  0.17,  0.17   up 16+00:10:51 
73 processes:  1 running, 72 sleeping
CPU:  2.5% user,  0.0% nice,  0.8% system,  0.2% interrupt, 96.5% idle
Mem: 256M Active, 1393M Inact, 234M Wired, 61M Cache, 112M Buf, 50M Free
Swap: 4492M Total, 285M Used, 4207M Free, 6% Inuse

The system is not very busy (load average above is quite typical for 
that machine) and prior to Monday it has never swapped. For the whole 
year I haven't managed to use more than 2MB of swap space. But this 
changed this Monday.

I would like to find out what causes such behaviour so your suggestions 
are very much appreciated!

Thank you and have a nice weekend!

Zbigniew Szalbot

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