I'v a Linux server running under Debian Lenny with 4Go of RAM. It doesn't run a large number of stuffs:

Postfix/spamassassin (daemon mode) Bind9 KVM (one guest - 1Go of RAM for it) Every day at exactly 3:05 UTC, the server completely drop to ground floor almost all of its memory. After that, I'v more than 2 G used by buffer and never cleaned up (unless I manually tell the kernel to drop the cache).

I'v searched the web a lot and, at the begining, I though this was due to NFS buffer usage. I do backup over an NFS share drive using gzip/tar and the backup occured at 3:05.

However, I'm now in a very strange situation because I moved the backup task at 1:40 (it completes in 2 mins) and I still drop all the RAM at 3:05.

In my logs, nothing particular, except that at 03:05:01, cron open a session as root and immediately close it at 03:05:02 without doing anything. Of course, cron has been restarted and I checked the timing of the tasks - again, nothing particular.

Any idea why this happens? Or, any idea about how to track what's using all those buffers?

Thanks for your help,

  • Are you running low on memory? What does free -m report? – Steven Monday Apr 30 '11 at 14:48
  • What kind of cron job is it that runs at 3:05? Could you check your root's crontab? – Axel Knauf Apr 30 '11 at 18:25
  • to Steven:free -m will report ~2G used for buffer, 100M free, 100M for cache and the rest is in use by apps – Henry-Nicolas Tourneur Apr 30 '11 at 21:06
  • to Axel: it used to be a perl script that performs backup on an NFS share drive using gzip. Now the same script runs at 1:40 but still the same issue at 3:05. – Henry-Nicolas Tourneur Apr 30 '11 at 21:07
  • Here you can see what happens: img13.imageshack.us/i/snapshot2u.png <br> At the begining of the free space increase, the backup script is runned. At the end of the space (return to 100M free), it is 03:05. Some times ago, that script used to run at 03:05 but now it runs at 01:40. The script is mounting an NFS drive, gzipping folder of the server on the NFS share then it umount the share and exit. This is strange, in the first place, I though the script was the cause of the memory usage but now it's more like it's somehow forcing some internal clean-up. – Henry-Nicolas Tourneur Apr 30 '11 at 21:16

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