About XenHVM network driver and mbuf tagging

[Egoitz Aurrekoetxea]

Hi all,

If you’re running FreeBSD 9.1 or greater (release versions tested only) under Xen 4.1 in HVM mode (xen-detect is saying "Running in HVM context on Xen v4.1.”) AND if you use some (in combination of both, and trying to see if with any other network drivers not involving virtualization and using too the LRO piece of code of the FreeBSD kernel) kind of software involving mbuf tagging too (Mac Framework, vlan tagging, ipsec….) AND you move an important amount of traffic with that driver (the net hvm driver in this case) you will see wired memory starts increasing pretty fast and never being released. This seems to be due to a problem with the LRO code of the FreeBSD kernel which causes mbuf_tags not being properly released after the own mbuf chains have been properly released. So as a temporary workaround (and really as valid workaround without involving any kind of limitation) you can just disable LRO flag in you interfaces running this driver (ifconfig xn0-1-2…. -lro) and you’re done.

This is a message for just trying to avoid people to waste time in trying to find some workaround for the issue. For more info, I’m moving this topic at freebsd-hackers list with egoitz(at)ramattack.net email address and with thread subject "mbuf_tag memory freeing issues with LRO enabled on the XENHVM driver”.

Best regards,


Egoitz Aurrekoetxea
Departamento de sistemas
944 209 470
Parque Tecnológico. Edificio 103
48170 Zamudio (Bizkaia)
egoitz at sarenet.es
www.sarenet.es

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