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Bug#878242: linux-image-4.12.0-2-marvell: flood of messages "mv643xx_eth_port mv643xx_eth_port.0 eth0: failed to linearize skb with tiny unaligned fragment"

Cross-posted to 2 groups.

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Hi, Ben.

On Oct 11 2017, Ben Hutchings wrote:
> On Wed, 2017-10-11 at 11:48 -0300, rbrito@ime.usp.br wrote:
> > I am using an armel system with only 128MB of RAM (a KuroBox Pro) running
> > Debian testing and, if my memory serves me well, I started seeing lots and
> > lots of messages like:
> > 
> >     mv643xx_eth_port mv643xx_eth_port.0 eth0: failed to linearize skb with tiny unaligned fragment
> > 
> > on my dmesg after I upgraded to kernel 4.12. I don't know if this is a
> > serious problem or only a cosmetic issue.
> [...]
> 
> This message and the code that generates it have been present in the
> mv643xx_eth driver for a long time.  The network interface hardware is
> generally capable of transmitting a packet that comes from multiple
> buffers in memory, but in some cases the driver copies all the data
> into a single buffer, probably to avoid a hardware bug.  If there is
> not enough memory to make that copy then it logs this message.

Oh, thanks for the explanation.

> I think the driver should drop the packet if this happens, but instead
> it just reports that the hardware is busy.  That will cause the kernel
> to try sending the packet again repeatedly, resulting in repetition of
> this log message until there is more memory available.

Hummm, that may be related to some lower performance that I have felt (but
not measured).

I see. Discarding the packet would flag congestion with TCP, if I understand
it correctly.

> If you haven't seen this error message before, it might be triggered by an
> application change.  But I think it's more likely to be caused by higher
> memory usage or fragmentation of memory.

Yes, I think that the problem is that the programs are getting bigger and
bigger.  Would setting vm.min_free_kbytes to a higher value worth it?

Anyway, I just upgraded to kernel 4.13 and I will report what I see.


Thanks,

-- 
Rogério Brito : rbrito@{ime.usp.br,gmail.com} : GPG key 4096R/BCFCAAAA
http://cynic.cc/blog/ : github.com/rbrito : profiles.google.com/rbrito
DebianQA: http://qa.debian.org/developer.php?login=rbrito%40ime.usp.br

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Bug#878242: linux-image-4.12.0-2-marvell: flood of messages "mv643xx_eth_port mv643xx_eth_port.0 eth0: failed to linearize skb with tiny unaligned fragment" Ben Hutchings <ben@decadent.org.uk> - 2017-10-13 00:10 +0200
  Bug#878242: linux-image-4.12.0-2-marvell: flood of messages "mv643xx_eth_port mv643xx_eth_port.0 eth0: failed to linearize skb with tiny unaligned fragment" Ben Hutchings <ben@decadent.org.uk> - 2017-10-13 00:20 +0200
    Bug#878242: linux-image-4.12.0-2-marvell: flood of messages "mv643xx_eth_port mv643xx_eth_port.0 eth0: failed to linearize skb with tiny unaligned fragment" Rogério Brito <rbrito@ime.usp.br> - 2017-10-19 20:50 +0200
  Bug#878242: linux-image-4.12.0-2-marvell: flood of messages "mv643xx_eth_port mv643xx_eth_port.0 eth0: failed to linearize skb with tiny unaligned fragment" Rogério Brito <rbrito@ime.usp.br> - 2017-10-13 00:30 +0200

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