RE: [Xen-users] Attempt to allocate order 5 skbuff. Increase MAX_SKBUFF_ORDER

[Steven Timm <timm@xxxxxxxx>]

> > very few ports from accessing our site.
> >
> > I am not sure why the iptables_nat module would be loaded
> > because we are not using NAT in our network configuration, at least we
> > are
> > not intending to do so.
> Well if you don't need it then just try and remove the NAT module using "modprobe -r 
> iptable_nat". And see if that makes any difference.
Can't remove it, get the message
"module is in use".. not sure by what.

> > > Now the issue about MAX_SKBUFF_ORDER should only show up when you are
> > trying to send large packets. Do you use jumbo frames or something like
> > that? What MTU sizes are set for the interfaces? As far as I know the
> > message you get means that Xen is trying to allocate a buffer for the
> > packet to send, but the packet size is too big for the buffer
> > allocator.
> > >
> > [root@fg3x3 ~]# ifconfig
> > eth0      Link encap:Ethernet  HWaddr 00:16:3E:05:03:03
> >            inet addr:131.225.107.144  Bcast:131.225.107.255
> > Mask:255.255.255.0
> >            inet6 addr: fe80::216:3eff:fe05:303/64 Scope:Link
> >            UP BROADCAST RUNNING MULTICAST  MTU:1500  Metric:1
> >            RX packets:2971214615 errors:0 dropped:0 overruns:0 frame:0
> >            TX packets:1576876803 errors:0 dropped:0 overruns:0
> > carrier:0
> >            collisions:0 txqueuelen:1000
> >            RX bytes:2428856680 (2.2 GiB)  TX bytes:4068069258 (3.7 GiB)
> >
> > No--no jumbo frames anywhere. MTU size is the standard 1500.
> This is on all Dom0/DomU frontend and backend interfaces?
That's right.

> > > In general, you can configure the Xen kernel to use a Xen-specific
> > buffer allocator, or the kernel's default buffer allocator. There is a
> > kernel configuration option for that and it is called
> > CONFIG_XEN_SKBUFF. You could try and switch that off, and recompile the
> > kernel.
> > >
> > So CONFIG_XEN_SKBUFF is by default on?
CONFIG_XEN_SKBUFF is on in my config.
There is no MAX_SKBUFF_ORDER parameter anywhere in my source tree,
much less the config file.

Steve Timm


> I don't know for sure. It depends on your distro and whatever kernel you use. 
> You can check this in your kernel config files or eventually by looking at 
> /proc/config.gz. It depends on the Xen version etc, I don't know that by heart.
>
> Also, the value of MAX_SKBUFF_ORDER depends on your kernel configuration and 
> memory options.
>
>
> > > Looking at your megasas error message, I suspect that this is simply
> > because your system is running under high load and it is probably
> > running out of memory in various places. Maybe that is also the root
> > cause for the skbuff problem. What does Xen tell you about the memory
> > utilization, and how do you allocate your memory to DomU/Dom0?
> > >
> > This is a dell poweredge 2950 with 16 GB of RAM overall.  2GB for dom0,
> > [root@fermigrid3 ~]# free
> >               total       used       free     shared    buffers
> > cached
> > Mem:       2156544    1218036     938508          0     242084
> > 434092
> > -/+ buffers/cache:     541860    1614684
> > Swap:     24579440          0   24579440
> >
> > 4GB for this domU.
> >
> > [root@fg3x3 ~]# free
> >               total       used       free     shared    buffers
> > cached
> > Mem:       4096176    4073044      23132          0      33024
> > 3130072
> > -/+ buffers/cache:     909948    3186228
> > Swap:      8191992         48    8191944
> >
> > 4 other domU's on this system but they are mostly idle.
> Can you post an output of /proc/slabinfo of your DomU/Dom0 under high load?
Kernel config and slabinfo are posted.
--
------------------------------------------------------------------
Steven C. Timm, Ph.D  (630) 840-8525
timm@xxxxxxxx  http://home.fnal.gov/~timm/
Fermilab Computing Division, Scientific Computing Facilities,
Grid Facilities Department, FermiGrid Services Group, Assistant Group Leader.

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Attachment: slabinfo.fg3x3
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Attachment: fg3x3.config
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