Date:   Mon, 3 Jan 2022 16:44:43 -0800
From:   Stephen Hemminger <stephen@networkplumber.org>
To:     Ivan Babrou <ivan@cloudflare.com>
Cc:     netdev@vger.kernel.org, linux-kernel@vger.kernel.org,
        kernel-team@cloudflare.com,
        "David S . Miller" <davem@davemloft.net>,
        Jakub Kicinski <kuba@kernel.org>,
        Jonathan Corbet <corbet@lwn.net>,
        Eric Dumazet <edumazet@google.com>
Subject: Re: [PATCH net] tcp: note that tcp_rmem[1] has a limited range
Message-ID: <20220103164443.53b7b8d5@hermes.local>
In-Reply-To: <20220104003722.73982-1-ivan@cloudflare.com>
References: <20220104003722.73982-1-ivan@cloudflare.com>
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On Mon,  3 Jan 2022 16:37:22 -0800
Ivan Babrou <ivan@cloudflare.com> wrote:

> The value of rcv_ssthresh is limited to tcp_rwin, which is limited
> to 64k at the handshake time, since window scaling is not allowed there.
> 
> Let's add a note to the docs that increasing tcp_rmem[1] does not have
> any effect on raising the initial value of rcv_ssthresh past 64k.
> 
> Link: https://lkml.org/lkml/2021/12/22/652
> Signed-off-by: Ivan Babrou <ivan@cloudflare.com>
> ---
>  Documentation/networking/ip-sysctl.rst | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
> 
> diff --git a/Documentation/networking/ip-sysctl.rst b/Documentation/networking/ip-sysctl.rst
> index 2572eecc3e86..16528bc92e65 100644
> --- a/Documentation/networking/ip-sysctl.rst
> +++ b/Documentation/networking/ip-sysctl.rst
> @@ -683,7 +683,8 @@ tcp_rmem - vector of 3 INTEGERs: min, default, max
>  	default: initial size of receive buffer used by TCP sockets.
>  	This value overrides net.core.rmem_default used by other protocols.
>  	Default: 131072 bytes.
> -	This value results in initial window of 65535.
> +	This value results in initial window of 65535. Increasing this value
> +	won't raise the initial advertised window above 65535.
>  
>  	max: maximal size of receive buffer allowed for automatically
>  	selected receiver buffers for TCP socket. This value does not override

Why not add error check or warning in write to sysctl?