netdev - Re: [PATCH net-next] tcp: fix zerocopy and notsent

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Date:   Mon, 25 Mar 2019 16:46:51 -0400
From:   Soheil Hassas Yeganeh <soheil@...gle.com>
To:     Eric Dumazet <edumazet@...gle.com>
Cc:     "David S . Miller" <davem@...emloft.net>,
        netdev <netdev@...r.kernel.org>,
        Eric Dumazet <eric.dumazet@...il.com>,
        Willem de Bruijn <willemb@...gle.com>
Subject: Re: [PATCH net-next] tcp: fix zerocopy and notsent_lowat issues

On Mon, Mar 25, 2019 at 4:44 PM Eric Dumazet <edumazet@...gle.com> wrote:
>
> My recent patch had at least two problems :
>
> 1) TX zerocopy wants notification when skb is acknowledged,
>    thus we need to call skb_zcopy_clear() if the skb is
>    cached into sk->sk_tx_skb_cache
>
> 2) Some applications might expect precise EPOLLOUT notifications,
>    so we need to update sk->sk_wmem_queued and call
>    sk_mem_uncharge() from sk_wmem_free_skb() in all cases.
>    The SOCK_QUEUE_SHRUNK flag must also be set.
>
> Fixes: 472c2e07eef0 ("tcp: add one skb cache for tx")
> Signed-off-by: Eric Dumazet <edumazet@...gle.com>
> Cc: Willem de Bruijn <willemb@...gle.com>
> Cc: Soheil Hassas Yeganeh <soheil@...gle.com>

Acked-by: Soheil Hassas Yeganeh <soheil@...gle.com>

Thank you for the fix!

> ---
>  include/net/sock.h | 9 +++++----
>  net/ipv4/tcp.c     | 2 --
>  2 files changed, 5 insertions(+), 6 deletions(-)
>
> diff --git a/include/net/sock.h b/include/net/sock.h
> index 577d91fb56267371c6bc5ae65f7454deba726bd6..7fa2232785226bcafd46b230559964fd16f3c4f4 100644
> --- a/include/net/sock.h
> +++ b/include/net/sock.h
> @@ -1465,13 +1465,14 @@ static inline void sk_mem_uncharge(struct sock *sk, int size)
>
>  static inline void sk_wmem_free_skb(struct sock *sk, struct sk_buff *skb)
>  {
> -       if (!sk->sk_tx_skb_cache) {
> -               sk->sk_tx_skb_cache = skb;
> -               return;
> -       }
>         sock_set_flag(sk, SOCK_QUEUE_SHRUNK);
>         sk->sk_wmem_queued -= skb->truesize;
>         sk_mem_uncharge(sk, skb->truesize);
> +       if (!sk->sk_tx_skb_cache) {
> +               skb_zcopy_clear(skb, true);
> +               sk->sk_tx_skb_cache = skb;
> +               return;
> +       }
>         __kfree_skb(skb);
>  }
>
> diff --git a/net/ipv4/tcp.c b/net/ipv4/tcp.c
> index 29b94edf05f9357d3a33744d677827ce624738ae..77fa3d26fb88c42a0b3152d4408081083c893b2a 100644
> --- a/net/ipv4/tcp.c
> +++ b/net/ipv4/tcp.c
> @@ -871,8 +871,6 @@ struct sk_buff *sk_stream_alloc_skb(struct sock *sk, int size, gfp_t gfp,
>
>                 fclones = container_of(skb, struct sk_buff_fclones, skb1);
>                 if (refcount_read(&fclones->fclone_ref) == 1) {
> -                       sk->sk_wmem_queued -= skb->truesize;
> -                       sk_mem_uncharge(sk, skb->truesize);
>                         skb->truesize -= skb->data_len;
>                         sk->sk_tx_skb_cache = NULL;
>                         pskb_trim(skb, 0);
> --
> 2.21.0.392.gf8f6787159e-goog
>