netdev - Re: [PATCH v2 net-next 2/2] tcp: fix possible freeze in tx path under memory pressure

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Message-ID: <CALvZod5N-teApG8s0-DDRzoE0YOTfZe4P0r2R4boe_f_PJ60GA@mail.gmail.com>
Date:   Tue, 14 Jun 2022 13:31:55 -0700
From:   Shakeel Butt <shakeelb@...gle.com>
To:     Eric Dumazet <eric.dumazet@...il.com>
Cc:     "David S . Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>,
        Paolo Abeni <pabeni@...hat.com>,
        netdev <netdev@...r.kernel.org>,
        Soheil Hassas Yeganeh <soheil@...gle.com>,
        Wei Wang <weiwan@...gle.com>,
        Neal Cardwell <ncardwell@...gle.com>,
        Eric Dumazet <edumazet@...gle.com>
Subject: Re: [PATCH v2 net-next 2/2] tcp: fix possible freeze in tx path under
 memory pressure

On Tue, Jun 14, 2022 at 10:17 AM Eric Dumazet <eric.dumazet@...il.com> wrote:
>
> From: Eric Dumazet <edumazet@...gle.com>
>
> Blamed commit only dealt with applications issuing small writes.
>
> Issue here is that we allow to force memory schedule for the sk_buff
> allocation, but we have no guarantee that sendmsg() is able to
> copy some payload in it.
>
> In this patch, I make sure the socket can use up to tcp_wmem[0] bytes.
>
> For example, if we consider tcp_wmem[0] = 4096 (default on x86),
> and initial skb->truesize being 1280, tcp_sendmsg() is able to
> copy up to 2816 bytes under memory pressure.
>
> Before this patch a sendmsg() sending more than 2816 bytes
> would either block forever (if persistent memory pressure),
> or return -EAGAIN.
>
> For bigger MTU networks, it is advised to increase tcp_wmem[0]
> to avoid sending too small packets.
>
> v2: deal with zero copy paths.
>
> Fixes: 8e4d980ac215 ("tcp: fix behavior for epoll edge trigger")
> Signed-off-by: Eric Dumazet <edumazet@...gle.com>

Reviewed-by: Shakeel Butt <shakeelb@...gle.com>