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    Subject[PATCH AUTOSEL 4.19 010/209] tcp: up initial rmem to 128KB and SYN rwin to around 64KB
    Date
    From: Yuchung Cheng <ycheng@google.com>

    [ Upstream commit a337531b942bd8a03e7052444d7e36972aac2d92 ]

    Previously TCP initial receive buffer is ~87KB by default and
    the initial receive window is ~29KB (20 MSS). This patch changes
    the two numbers to 128KB and ~64KB (rounding down to the multiples
    of MSS) respectively. The patch also simplifies the calculations s.t.
    the two numbers are directly controlled by sysctl tcp_rmem[1]:

    1) Initial receiver buffer budget (sk_rcvbuf): while this should
    be configured via sysctl tcp_rmem[1], previously tcp_fixup_rcvbuf()
    always override and set a larger size when a new connection
    establishes.

    2) Initial receive window in SYN: previously it is set to 20
    packets if MSS <= 1460. The number 20 was based on the initial
    congestion window of 10: the receiver needs twice amount to
    avoid being limited by the receive window upon out-of-order
    delivery in the first window burst. But since this only
    applies if the receiving MSS <= 1460, connection using large MTU
    (e.g. to utilize receiver zero-copy) may be limited by the
    receive window.

    With this patch TCP memory configuration is more straight-forward and
    more properly sized to modern high-speed networks by default. Several
    popular stacks have been announcing 64KB rwin in SYNs as well.

    Signed-off-by: Yuchung Cheng <ycheng@google.com>
    Signed-off-by: Wei Wang <weiwan@google.com>
    Signed-off-by: Neal Cardwell <ncardwell@google.com>
    Signed-off-by: Eric Dumazet <edumazet@google.com>
    Reviewed-by: Soheil Hassas Yeganeh <soheil@google.com>
    Signed-off-by: David S. Miller <davem@davemloft.net>
    Signed-off-by: Sasha Levin <sashal@kernel.org>
    ---
    net/ipv4/tcp.c | 4 ++--
    net/ipv4/tcp_input.c | 25 ++-----------------------
    net/ipv4/tcp_output.c | 25 ++++---------------------
    3 files changed, 8 insertions(+), 46 deletions(-)

    diff --git a/net/ipv4/tcp.c b/net/ipv4/tcp.c
    index 611ba174265c8..1a1fcb32c4917 100644
    --- a/net/ipv4/tcp.c
    +++ b/net/ipv4/tcp.c
    @@ -3910,8 +3910,8 @@ void __init tcp_init(void)
    init_net.ipv4.sysctl_tcp_wmem[2] = max(64*1024, max_wshare);

    init_net.ipv4.sysctl_tcp_rmem[0] = SK_MEM_QUANTUM;
    - init_net.ipv4.sysctl_tcp_rmem[1] = 87380;
    - init_net.ipv4.sysctl_tcp_rmem[2] = max(87380, max_rshare);
    + init_net.ipv4.sysctl_tcp_rmem[1] = 131072;
    + init_net.ipv4.sysctl_tcp_rmem[2] = max(131072, max_rshare);

    pr_info("Hash tables configured (established %u bind %u)\n",
    tcp_hashinfo.ehash_mask + 1, tcp_hashinfo.bhash_size);
    diff --git a/net/ipv4/tcp_input.c b/net/ipv4/tcp_input.c
    index 14a6a489937c1..0e2b07be08585 100644
    --- a/net/ipv4/tcp_input.c
    +++ b/net/ipv4/tcp_input.c
    @@ -426,26 +426,7 @@ static void tcp_grow_window(struct sock *sk, const struct sk_buff *skb)
    }
    }

    -/* 3. Tuning rcvbuf, when connection enters established state. */
    -static void tcp_fixup_rcvbuf(struct sock *sk)
    -{
    - u32 mss = tcp_sk(sk)->advmss;
    - int rcvmem;
    -
    - rcvmem = 2 * SKB_TRUESIZE(mss + MAX_TCP_HEADER) *
    - tcp_default_init_rwnd(mss);
    -
    - /* Dynamic Right Sizing (DRS) has 2 to 3 RTT latency
    - * Allow enough cushion so that sender is not limited by our window
    - */
    - if (sock_net(sk)->ipv4.sysctl_tcp_moderate_rcvbuf)
    - rcvmem <<= 2;
    -
    - if (sk->sk_rcvbuf < rcvmem)
    - sk->sk_rcvbuf = min(rcvmem, sock_net(sk)->ipv4.sysctl_tcp_rmem[2]);
    -}
    -
    -/* 4. Try to fixup all. It is made immediately after connection enters
    +/* 3. Try to fixup all. It is made immediately after connection enters
    * established state.
    */
    void tcp_init_buffer_space(struct sock *sk)
    @@ -454,8 +435,6 @@ void tcp_init_buffer_space(struct sock *sk)
    struct tcp_sock *tp = tcp_sk(sk);
    int maxwin;

    - if (!(sk->sk_userlocks & SOCK_RCVBUF_LOCK))
    - tcp_fixup_rcvbuf(sk);
    if (!(sk->sk_userlocks & SOCK_SNDBUF_LOCK))
    tcp_sndbuf_expand(sk);

    @@ -485,7 +464,7 @@ void tcp_init_buffer_space(struct sock *sk)
    tp->snd_cwnd_stamp = tcp_jiffies32;
    }

    -/* 5. Recalculate window clamp after socket hit its memory bounds. */
    +/* 4. Recalculate window clamp after socket hit its memory bounds. */
    static void tcp_clamp_window(struct sock *sk)
    {
    struct tcp_sock *tp = tcp_sk(sk);
    diff --git a/net/ipv4/tcp_output.c b/net/ipv4/tcp_output.c
    index 2697e4397e46c..53f910bb55087 100644
    --- a/net/ipv4/tcp_output.c
    +++ b/net/ipv4/tcp_output.c
    @@ -179,21 +179,6 @@ static inline void tcp_event_ack_sent(struct sock *sk, unsigned int pkts,
    inet_csk_clear_xmit_timer(sk, ICSK_TIME_DACK);
    }

    -
    -u32 tcp_default_init_rwnd(u32 mss)
    -{
    - /* Initial receive window should be twice of TCP_INIT_CWND to
    - * enable proper sending of new unsent data during fast recovery
    - * (RFC 3517, Section 4, NextSeg() rule (2)). Further place a
    - * limit when mss is larger than 1460.
    - */
    - u32 init_rwnd = TCP_INIT_CWND * 2;
    -
    - if (mss > 1460)
    - init_rwnd = max((1460 * init_rwnd) / mss, 2U);
    - return init_rwnd;
    -}
    -
    /* Determine a window scaling and initial window to offer.
    * Based on the assumption that the given amount of space
    * will be offered. Store the results in the tp structure.
    @@ -228,7 +213,10 @@ void tcp_select_initial_window(const struct sock *sk, int __space, __u32 mss,
    if (sock_net(sk)->ipv4.sysctl_tcp_workaround_signed_windows)
    (*rcv_wnd) = min(space, MAX_TCP_WINDOW);
    else
    - (*rcv_wnd) = space;
    + (*rcv_wnd) = min_t(u32, space, U16_MAX);
    +
    + if (init_rcv_wnd)
    + *rcv_wnd = min(*rcv_wnd, init_rcv_wnd * mss);

    (*rcv_wscale) = 0;
    if (wscale_ok) {
    @@ -241,11 +229,6 @@ void tcp_select_initial_window(const struct sock *sk, int __space, __u32 mss,
    (*rcv_wscale)++;
    }
    }
    -
    - if (!init_rcv_wnd) /* Use default unless specified otherwise */
    - init_rcv_wnd = tcp_default_init_rwnd(mss);
    - *rcv_wnd = min(*rcv_wnd, init_rcv_wnd * mss);
    -
    /* Set the clamp no higher than max representable value */
    (*window_clamp) = min_t(__u32, U16_MAX << (*rcv_wscale), *window_clamp);
    }
    --
    2.20.1
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