netdev - Re: [PATCH net-next] tcp: properly reset skb->truesize for tx recycling

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Message-Id: <20190419.164254.1552615935538141540.davem@davemloft.net>
Date:   Fri, 19 Apr 2019 16:42:54 -0700 (PDT)
From:   David Miller <davem@...emloft.net>
To:     edumazet@...gle.com
Cc:     netdev@...r.kernel.org, eric.dumazet@...il.com, soheil@...gle.com,
        willemb@...gle.com
Subject: Re: [PATCH net-next] tcp: properly reset skb->truesize for tx
 recycling

From: Eric Dumazet <edumazet@...gle.com>
Date: Fri, 19 Apr 2019 16:02:03 -0700

> tcp sendmsg() and sendpage() normally advance skb->data_len
> and skb->truesize by the payload added to an skb.
> 
> But sendmsg(fd, ..., MSG_ZEROCOPY) has to account for whole pages,
> even if a single byte of payload is used in the page.
> 
> This means that we can not assume skb->truesize can be adjusted
> by skb->data_len. We must instead overwrite its value.
> 
> Otherwise skb->truesize is too big and can hit socket sndbuf limit,
> especially if the skb is recycled multiple times :/
> 
> Fixes: 472c2e07eef0 ("tcp: add one skb cache for tx")
> Signed-off-by: Eric Dumazet <edumazet@...gle.com>

Applied, thanks Eric.