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[EP-tech] Eprints Server Freezes Often

Dear Members, Our eprints server freezes (stops responding) almost every week or so. The only solution to bring up the server again is to do a hard boot.
I have looked into the Web Server error log file and find that around the time the system freezes, the following error is recorded in the error log file:
[Thu May 18 06:10:05 2012] [error] (12)Cannot allocate memory: fork: Unable to fork new process
So, the obvious reason for the system freeze is, the system is running out of main memory. Once the server is re-booted, everything is back to normal, but with the passage of time, the free memory keeps gradually dropping.
The 'top' command issued right ofter the re-boot, gives the following output: 

top - 12:41:49 up 2 days, 55 min,  1 user,  load average: 0.90, 0.52, 0.35
Tasks: 167 total,   1 running, 166 sleeping,   0 stopped,   0 zombie
Cpu(s): 1.1%us, 0.2%sy, 0.0%ni, 97.3%id, 1.3%wa, 0.0%hi, 0.0%si, 0.0%st 
Mem:   4051536k total,  1162736k used,  2888800k free,    23300k buffers
Swap:  8193108k total,   378836k used,  7814272k free,   438404k cached
Over the period of few hours, the the usage of the main memory gradually goes up. 

The output of the 'top' command after 3 hours is:

top - 15:42:07 up 2 days,  4:02,  1 user,  load average: 0.23, 0.22, 0.18
Tasks: 173 total,   1 running, 172 sleeping,   0 stopped,   0 zombie
Cpu(s): 0.0%us, 0.0%sy, 0.0%ni, 99.6%id, 0.4%wa, 0.0%hi, 0.0%si, 0.0%st 
Mem:   4051536k total,  3048740k used,  1002796k free,   129020k buffers
Swap:  8193108k total,   378828k used,  7814280k free,   796732k cached
For a time gap of 3 hours, the free memory size has come down from 2888800k to 1002796k. The drop will continue over the period of time and eventually, the system freezes.
I restarted the apache server after about 3 hours and the output of the 'top' command is: 

top - 15:52:59 up 2 days,  4:07,  1 user,  load average: 0.11, 0.14, 0.16
Tasks: 168 total,   1 running, 167 sleeping,   0 stopped,   0 zombie
Cpu(s): 0.0%us, 0.0%sy, 0.0%ni, 99.6%id, 0.4%wa, 0.0%hi, 0.0%si, 0.0%st 
Mem:   4051536k total,  1686412k used,  2365124k free,   130712k buffers
Swap:  8193108k total,   378820k used,  7814288k free,   801620k cached
More than 1.3 GB of memory has been freed after restarting the apache server.
How do I ensure that memory level doesn't gradually drop and eventually cause the server to freeze? Should something be done at the apache configuration level? 

Any help/pointers to overcome the said problem will of great help to us.
We have recently upgraded our eprints software from eprints-3.2.8 to eprints-3.3.9. The above behaviour was very much there with the 3.2.8 version as well. 

Apache Server version: Apache/2.2.3 on 64-bit RHES

Many thanks in advance for your attention.


 - Francis

JRD Tata Memorial Library
IISc, Bengaluru, India

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