NAT gives error: couldn't allocate queue item

[myce]

After some running time I start getting these errors:

02:22:29.522 NAT: 64 messages suppressed about dropping package (couldn't allocate queue item)
02:22:29.524 NAT: 64 messages suppressed about dropping package (couldn't allocate queue item)
02:22:29.525 NAT: 64 messages suppressed about dropping package (couldn't allocate queue item)

When this happens, network access from the guest slows down and eventually stops completely.
Since the guest is generating quite a bit of network load, I guess some resource (memory pool used for queue items?) is used up.
Is there any config setting I should increase? Anything else I can do?

Regards,
Mike

[Perryg]

Try dropping the MTU on the guest that is generating the most load. Do it a little at a time until you stop seeing errors.

[myce]

Doing a bit of research in the source showed that the queue which generates this error has a (hardcoded) length of 50 items. I opened a ticket (3875) asking to raise this limit or make it user-configurable.