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

[Leon Hwang]

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/

Thanks,
Leon