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

[Paolo Abeni <pabeni@redhat.com>]

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.

/P