mbuf_jumbo_9k & iSCSI failing

[Ben RUBSON]

> 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