mbuf_jumbo_9k & iSCSI failing

[Zaphod Beeblebrox]

Don't forget that, generally, as I understand it, the network stack suffers
from the same problem for 9k buffers.

On Sun, Jun 25, 2017 at 12:56 PM, Ben RUBSON <ben.rubson at gmail.com> wrote:

> > On 25 Jun 2017, at 17:32, Ryan Stone <rysto32 at gmail.com> 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.
>
> Thank you for your explanation Ryan.
> You say "over time", and you're right, I have to wait several days (here
> 88) before the problem occurs.
> Strange however that in 2500MB free memory system is unable to find 9k
> physically contiguous. But we never know :)
>
> Let's then wait for your patch !
> (and reboot for now)
>
> Many thx !
>
> Ben
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