Re: [PATCH net-next 2/2] net/sched: fq_codel: local packets no longer count against memory limit

[Paolo Abeni <pabeni@redhat.com>]

On 5/14/26 10:49 AM, Eric Dumazet wrote:
> On Thu, May 14, 2026 at 1:24 AM Paolo Abeni <pabeni@redhat.com> wrote:
>> On 5/12/26 11:48 AM, Eric Dumazet wrote:
>>> Commit 95b58430abe7 ("fq_codel: add memory limitation per queue")
>>> claimed that the 32Mb default was "reasonable even for heavy duty usages."
>>>
>>> In practice, this is not the case.
>>>
>>> Packets that are associated with local sockets sk_wmem_alloc
>>> do not really need additional memory control.
>>>
>>> Signed-off-by: Eric Dumazet <edumazet@google.com>
>>> ---
>>>  net/sched/sch_fq_codel.c | 2 +-
>>>  1 file changed, 1 insertion(+), 1 deletion(-)
>>>
>>> diff --git a/net/sched/sch_fq_codel.c b/net/sched/sch_fq_codel.c
>>> index 1b1de693d4c64a1f5f4e9e788371829dea91740e..71107dc52be799a14f370f2ad74d2eadd93992c1 100644
>>> --- a/net/sched/sch_fq_codel.c
>>> +++ b/net/sched/sch_fq_codel.c
>>> @@ -212,7 +212,7 @@ static int fq_codel_enqueue(struct sk_buff *skb, struct Qdisc *sch,
>>>               q->new_flow_count++;
>>>               WRITE_ONCE(flow->deficit, q->quantum);
>>>       }
>>> -     get_codel_cb(skb)->mem_usage = skb->truesize;
>>> +     get_codel_cb(skb)->mem_usage = is_skb_wmem(skb) ? 0 : skb->truesize;
>>>       q->memory_usage += get_codel_cb(skb)->mem_usage;
>>>       memory_limited = q->memory_usage > q->memory_limit;
>>>       qdisc_qlen_inc(sch);
>>
>> I *think* this patch is causing TDC self-tests failures:
>>
>> # not ok 704 a4bb - Test FQ_CODEL with HTB parent - force packet drop with empty queue
>> # Could not match regex pattern. Verify command output:
>> # qdisc fq_codel 10: parent 1:10 limit 10240p flows 1 quantum 1514 target 99us interval 999us memory_limit 1b ecn drop_batch 64
>> #  Sent 490 bytes 5 pkt (dropped 0, overlimits 0 requeues 0)
>> #  backlog 0b 0p requeues 0
>> #   maxpacket 98 drop_overlimit 0 new_flow_count 1 ecn_mark 0
>> #   new_flows_len 1 old_flows_len 0
>>
>> whole log at:
>>
>> https://github.com/p4tc-dev/tc-executor/tree/storage/artifacts/645644/1-tdc-sh
>>
>> Looking at the test code, I think the patch broke it, but the failures
>> started a little afterward the patch merge, so I'm possibly
>> misunderstanding something here.
>>
>> Thanks,
>>
>> Paolo
>>
> 
> It seems this test uses a memory limit of 1 byte.
> 
> $TC qdisc add dev $DUMMY parent 1:10 handle 10: fq_codel memory_limit
> 1 flows 1 target 0.1ms interval 1ms
> 
> This might be a typo, I think they expected a limit of 0 packet.

FTR, I think/agree a change to the self-tests would be preferable.

/P