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[Xen-users] Out of SKBUFF ?

To: xen-users@xxxxxxxxxxxxxxxxxxx
Subject: [Xen-users] Out of SKBUFF ?
From: Georg Glas <georg-xen@xxxxxxxxxxx>
Date: Thu, 22 Nov 2007 15:11:47 +0100
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i am constantly facing a problem with a domU running out of SKBUFF.

I see the message "Attempt to allocate order 5 skbuff. Increase
MAX_SKBUFF_ORDER." in domU 400-500 times/minute

The domU contains a PCI Network Card (tg3), three netloop devices (the
domU acts as perimeter Firewall) and some tun devices.

I have tried playing around with net.core Parameter but did not find a
way to avoid this ... any hints ?
The domU is receiving about 570 packets/sec and forwarding about 26
packets/sec (peak is at 2000 packets/sec) however the problem occures

dom0 is running 2.6.19-4-generic-amd64 (2.6.19-2ubuntu7.1)
domU is running 2.6.18-4-xen-vserver-amd64 (2.6.18.dfsg.1-12etch2)
xen-utils/xen-tools 3.0.3 from ubuntu ..

what sideeffects might cause an increase of MAX_SKBUFF_ORDER in the
code (im pretty short on memory in domU, 512MB currently). Any other
ways to workaround this ?
It seams when running out of buffers, i currently loose tcp
connections ... e.g. postfix complains about lost connections ..

Georg Glas

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