Snort mailing list archives

Re: PCAP_MEMORY issue


From: "Jefferson, Shawn" <Shawn.Jefferson () bcferries com>
Date: Tue, 3 Mar 2009 10:29:42 -0700

Hi,

Tasks:  74 total,   2 running,  72 sleeping,   0 stopped,   0 zombie
Cpu(s): 14.6%us,  0.4%sy,  0.0%ni, 83.4%id,  0.0%wa,  0.0%hi,  1.5%si,  0.0%st
Mem:   3115832k total,  1349952k used,  1765880k free,     9468k buffers
Swap:  2939852k total,        0k used,  2939852k free,   137108k cached

Linux <servername> 2.6.24-23-server #1 SMP Mon Jan 26 00:55:21 UTC 2009 i686 GNU/Linux

Ubuntu 8.04, which I think has slab (??).  I googled some on memory fragmentation, and found some commands to check for 
memory fragmentation, but I'm not totally sure what I'm looking at.

root@server:~# vmstat -s
      3115832 K total memory
      1343616 K used memory
       397572 K active memory
        68328 K inactive memory
      1772216 K free memory
         8872 K buffer memory
       131760 K swap cache
      2939852 K total swap
            0 K used swap
      2939852 K free swap
     18577114 non-nice user cpu ticks
            0 nice user cpu ticks
       473536 system cpu ticks
    185481446 idle cpu ticks
       134474 IO-wait cpu ticks
       144290 IRQ cpu ticks
       358175 softirq cpu ticks
            0 stolen cpu ticks
       670958 pages paged in
     31155560 pages paged out
            0 pages swapped in
            0 pages swapped out
   1751057950 interrupts
   1437711074 CPU context switches
   1235604996 boot time
        25810 forks

root@server:~# grep Normal /var/log/messages | tail -1
Mar  3 09:19:04 servername kernel: [495516.650157] Normal: 651*4kB 5*8kB 1*16kB 1*32kB 1*64kB 1*128kB 1*256kB 1*512kB 
1*1024kB 0*2048kB 0*4096kB = 4676kB

I only have 3GB total memory in this machine at the moment.

-----Original Message-----
From: Stephen John Smoogen [mailto:smooge () gmail com] 
Sent: February 26, 2009 12:27 PM
To: Jefferson, Shawn
Cc: Snort-users () lists sourceforge net
Subject: Re: [Snort-users] PCAP_MEMORY issue

On Tue, Feb 24, 2009 at 1:49 PM, Jefferson, Shawn
<Shawn.Jefferson () bcferries com> wrote:
I'm using PCAP_MEMORY, and the highest I can seem to go is:
PCAP_MEMORY=800000

If I try to increase it, I get error messages when snort is starting:
Error: setsockopt(PACKET_RX_RING): Cannot allocate memory

However, running top shows I've got 1.8 GB of memory left available on this
machine.  Is there something else I need to tweak to allow a higher amount
of memory for libpcap?

PS. I'm using Phil Wood's libpcap.


What is the system stats? CPU, kernel version, total memory, and does
the system have slab, slub, or some other memory allocation in use? [I
don't know how to tell this myself.. my systems are old enough to only
have slab.. but the new kernels would have access to different memory
allocations.] My guess is that one of the following is occuring:

Not enough continguous memory.
Contiguous Memory is not in a directly mappable zone. (If you have a
4+GB machine and you are trying to do this on a 32 bit architecture)

-- 
Stephen J Smoogen. -- BSD/GNU/Linux
How far that little candle throws his beams! So shines a good deed
in a naughty world. = Shakespeare. "The Merchant of Venice"

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