Re: [RFC PATCH net-next] tcp: Add net.ipv4.tcp_purge_receive_queue sysctl

[Eric Dumazet]

On Tue, Mar 3, 2026 at 3:12 AM Leon Hwang <leon.hwang@xxxxxxxxx> wrote:
>
>
>
> On 3/3/26 08:22, Jakub Kicinski wrote:
> > On Mon, 2 Mar 2026 17:55:59 +0800 Leon Hwang wrote:
> >> On 26/2/26 09:43, Jakub Kicinski wrote:
> >>> On Wed, 25 Feb 2026 15:46:33 +0800 Leon Hwang wrote:
> >>>> Issue:
> >>>> When a TCP socket in the CLOSE_WAIT state receives a RST packet, the
> >>>> current implementation does not clear the socket's receive queue. This
> >>>> causes SKBs in the queue to remain allocated until the socket is
> >>>> explicitly closed by the application. As a consequence:
> >>>>
> >>>> 1. The page pool pages held by these SKBs are not released.
> >>>
> >>> On what kernel version and driver are you observing this?
> >>
> >> # uname -r
> >> 6.19.0-061900-generic
> >>
> >> # ethtool -i eth0
> >> driver: mlx5_core
> >> version: 6.19.0-061900-generic
> >> firmware-version: 26.43.2566 (MT_0000000531)
> >
> > Okay... this kernel + driver should just patiently wait for the page
> > pool to go away.
> >
> > What is the actual, end user problem that you're trying to solve?
> > A few kB of data waiting to be freed is not a huge problem..
>
> Yes, it is not a huge problem.
>
> The actual end-user issue was discussed in
> "page_pool: Add page_pool_release_stalled tracepoint" [1].
>
> I think it would be useful to provide a way for SREs to purge the
> receive queue when CLOSE_WAIT TCP sockets receive RST packets. If the
> NIC, e.g., Mellanox, flaps, the underlying page pool and pages can be
> released at the same time.
>
> Links:
> [1]
> https://lore.kernel.org/netdev/b676baa0-2044-4a74-900d-f471620f2896@xxxxxxxxx/

Perhaps SRE could use this in an emergency?

ss -t -a state close-wait -K