netdev - Re: [PATCH net] tcp: tcp_grow_window() needs to respect tcp

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Date:   Tue, 16 Apr 2019 21:48:13 -0700 (PDT)
From:   David Miller <davem@...emloft.net>
To:     edumazet@...gle.com
Cc:     netdev@...r.kernel.org, eric.dumazet@...il.com, soheil@...gle.com,
        ncardwell@...gle.com, weiwan@...gle.com
Subject: Re: [PATCH net] tcp: tcp_grow_window() needs to respect tcp_space()

From: Eric Dumazet <edumazet@...gle.com>
Date: Tue, 16 Apr 2019 10:55:20 -0700

> For some reason, tcp_grow_window() correctly tests if enough room
> is present before attempting to increase tp->rcv_ssthresh,
> but does not prevent it to grow past tcp_space()
> 
> This is causing hard to debug issues, like failing
> the (__tcp_select_window(sk) >= tp->rcv_wnd) test
> in __tcp_ack_snd_check(), causing ACK delays and possibly
> slow flows.
> 
> Depending on tcp_rmem[2], MTU, skb->len/skb->truesize ratio,
> we can see the problem happening on "netperf -t TCP_RR -- -r 2000,2000"
> after about 60 round trips, when the active side no longer sends
> immediate acks.
> 
> This bug predates git history.
> 
> Signed-off-by: Eric Dumazet <edumazet@...gle.com>
> Acked-by: Soheil Hassas Yeganeh <soheil@...gle.com>
> Acked-by: Neal Cardwell <ncardwell@...gle.com>
> Acked-by: Wei Wang <weiwan@...gle.com>

Applied and queued up for -stable, thanks Eric.