mbuf_jumbo_9k & iSCSI failing

[Andrey V. Elsukov]

On 25.06.2017 18:32, Ryan Stone wrote:
> Having looking at the original email more closely, I see that you showed an
> mlxen interface with a 9020 MTU.  Seeing allocation failures of 9k mbuf
> clusters increase while you are far below the zone's limit means that
> you're definitely running into the bug I'm describing, and this bug could
> plausibly cause the iSCSI errors that you describe.
> 
> The issue is that the newer version of the driver tries to allocate a
> single buffer to accommodate an MTU-sized packet.  Over time, however,
> memory will become fragmented and eventually it can become impossible to
> allocate a 9k physically contiguous buffer.  When this happens the driver
> is unable to allocate buffers to receive packets and is forced to drop
> them.  Presumably, if iSCSI suffers too many packet drops it will terminate
> the connection.  The older version of the driver limited itself to
> page-sized buffers, so it was immune to issues with memory fragmentation.

I think it is not mlxen specific problem, we have the same symptoms with
ixgbe(4) driver too. To avoid the problem we have patches that are
disable using of 9k mbufs, and instead only use 4k mbufs.

-- 
WBR, Andrey V. Elsukov

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