Re: [PATCH net] netpoll: bound the deferred transmit queue

[Breno Leitao <leitao@debian.org>]

On Mon, Sep 14, 2026 at 12:12:21AM -0400, Zack Gomez wrote:
> A producer that outruns that drain therefore grows the queue until the
> host is out of memory.
...
> Observed with netconsole forwarding a GPU driver
> that logged one line at ~1e5/s after a firmware hang.

I know what you mean, I'm seeing the same issue on my side.

> Cap it at 1024 skbs and drop new skbs beyond that.

I don't think netpoll should be the one doing rate limiting here.

I think the rate limiting should live on the netconsole side, not
netpoll.

I have a patchset that does exactly that, which I wrote after
hitting a similar issue in production. Would you mind having a test?

https://lore.kernel.org/all/20260910-netcons_ratelimit-v2-0-ebf0dd91e26e@debian.org/

> @@ -314,6 +322,10 @@ static netdev_tx_t __netpoll_send_skb(struct netpoll *np, struct sk_buff *skb)
>  	}
>  
>  	if (!dev_xmit_complete(status)) {
> +		if (skb_queue_len(&npinfo->txq) >= NETPOLL_TXQ_MAX) {
> +			dev_kfree_skb_irq(skb);
> +			goto out;

If we do end up also rate limiting at the netpoll side, I'd like to
see a WARN_ON_ONCE() here, since it shouldn't be the main ratelimit
path, but rather something to flag that something is off.

--breno