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

[Leon Hwang]

On 3/3/26 11:55, Eric Dumazet wrote:
> 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

This ss command is acceptable in an emergency.

A sysctl option would be better for persistent SRE operations.

Thanks,
Leon