mbuf_jumbo_9k & iSCSI failing

[Edward Napierala]

2017-06-25 16:32 GMT+01:00 Ryan Stone <rysto32 at gmail.com>:

> 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.  [..]


More specifically, it will terminate the connection when there's no "ping
reply"
from the other side for the configured amount of time, which defaults to
five
seconds.  It can be changed using the kern.iscsi.ping_timeout sysctl, as
described in iscsi(4).