Re: [PATCH v2 mptcp-next 7/7] mptcp: implemented OoO queue pruning

[Matthieu Baerts <matttbe@kernel.org>]

On 06/08/2026 18:42, Paolo Abeni wrote:
> On 8/6/26 4:45 PM, Paolo Abeni wrote:
>> When moving incoming skbs in the msk receive queue and the latter
>> is above limits, prune it as needed quite alike what TCP is doing
>> at the subflow level. The main difference relies in the stop condition:
>> since MPTCP does not perform collapsing, it's better off dropping the
>> bare minimum to fit the (newer) incoming packet.
>>
>> Signed-off-by: Paolo Abeni <pabeni@redhat.com>
>> Tested-by: Gang Yan <yangang@kylinos.cn>
>> Reviewed-by: Matthieu Baerts (NGI0) <matttbe@kernel.org>
>> ---
>> v<n> -> v<n+1>:
>>   - prune only for new data
>>   - reorganize the code to follow more closely TCP
>> ---
>>  net/mptcp/mib.c      |  1 +
>>  net/mptcp/mib.h      |  1 +
>>  net/mptcp/protocol.c | 81 ++++++++++++++++++++++++++++++++++++++------
>>  3 files changed, 73 insertions(+), 10 deletions(-)
>>
>> diff --git a/net/mptcp/mib.c b/net/mptcp/mib.c
>> index ef65e2df709f..2569385bab7c 100644
>> --- a/net/mptcp/mib.c
>> +++ b/net/mptcp/mib.c
>> @@ -87,6 +87,7 @@ static const struct snmp_mib mptcp_snmp_list[] = {
>>  	SNMP_MIB_ITEM("WinProbe", MPTCP_MIB_WINPROBE),
>>  	SNMP_MIB_ITEM("BacklogDrop", MPTCP_MIB_BACKLOGDROP),
>>  	SNMP_MIB_ITEM("RcvPruned", MPTCP_MIB_RCVPRUNED),
>> +	SNMP_MIB_ITEM("OFOPruned", MPTCP_MIB_OFOPRUNED),
>>  };
>>  
>>  /* mptcp_mib_alloc - allocate percpu mib counters
>> diff --git a/net/mptcp/mib.h b/net/mptcp/mib.h
>> index 9271205f682e..3a3425e258a7 100644
>> --- a/net/mptcp/mib.h
>> +++ b/net/mptcp/mib.h
>> @@ -90,6 +90,7 @@ enum linux_mptcp_mib_field {
>>  	MPTCP_MIB_WINPROBE,		/* MPTCP-level zero window probe */
>>  	MPTCP_MIB_BACKLOGDROP,		/* Backlog over memory limit */
>>  	MPTCP_MIB_RCVPRUNED,		/* Dropped due to memory constraints */
>> +	MPTCP_MIB_OFOPRUNED,		/* MPTCP-level OoO queue pruned */
>>  	__MPTCP_MIB_MAX
>>  };
>>  
>> diff --git a/net/mptcp/protocol.c b/net/mptcp/protocol.c
>> index 63f2c18bc01f..ec874d2ead6a 100644
>> --- a/net/mptcp/protocol.c
>> +++ b/net/mptcp/protocol.c
>> @@ -242,6 +242,65 @@ static bool mptcp_rcvbuf_grow(struct sock *sk, u32 newval)
>>  	return false;
>>  }
>>  
>> +/* "Inspired" from the TCP version; main difference: stop as soon as the MPTCP
>> + * socket is under memory limit.
>> + */
>> +static void mptcp_prune_ofo_queue(struct sock *sk,
>> +				  const struct sk_buff *in_skb)
>> +{
>> +	struct mptcp_sock *msk = mptcp_sk(sk);
>> +	struct rb_node *node, *prev;
>> +	bool pruned = false;
>> +	u64 mem;
>> +
>> +	if (RB_EMPTY_ROOT(&msk->out_of_order_queue))
>> +		return;
>> +
>> +	node = &msk->ooo_last_skb->rbnode;
>> +
>> +	do {
>> +		struct sk_buff *skb = rb_to_skb(node);
>> +
>> +		/* Stop pruning if the incoming skb would land in OoO tail. */
>> +		if (after64(MPTCP_SKB_CB(in_skb)->map_seq,
>> +			    MPTCP_SKB_CB(skb)->map_seq))
>> +			break;
>> +
>> +		pruned = true;
>> +		prev = rb_prev(node);
>> +		rb_erase(node, &msk->out_of_order_queue);
>> +		mptcp_drop(sk, skb);
>> +		msk->ooo_last_skb = rb_to_skb(prev);
>> +
>> +		mem = (unsigned int)sk_rmem_alloc_get(sk);
>> +		if (mem <= sk->sk_rcvbuf)
>> +			break;
>> +
>> +		node = prev;
>> +	} while (node);
>> +
>> +	if (pruned)
>> +		MPTCP_INC_STATS(sock_net(sk), MPTCP_MIB_OFOPRUNED);
>> +}
>> +
>> +/* The stack can't drop packets for fallback socket at the msk level, or the
>> + * stream will break.
>> + */
>> +static bool mptcp_can_ingest(const struct sock *sk)
>> +{
>> +	return unlikely(sk_rmem_alloc_get(sk) <= READ_ONCE(sk->sk_rcvbuf)) ||
>> +			__mptcp_check_fallback(mptcp_sk(sk));
> The above should obviously be: 'likely(...)'
> 
> @Matttbe: please LMK if you prefer a repost or you could adjust that
> while applying to the export branch.
No problem, I can adjust them when applying them (if there are no other
big modifications required, but I guess no).

Cheers,
Matt
-- 
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