netdev - Re: optimizations to sk_buff handling in rds_tcp_data

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Message-ID: <20160407192946.GA10957@oracle.com>
Date:	Thu, 7 Apr 2016 15:29:46 -0400
From:	Sowmini Varadhan <sowmini.varadhan@...cle.com>
To:	Eric Dumazet <eric.dumazet@...il.com>
Cc:	alexei.starovoitov@...il.com, tom@...bertland.com,
	netdev@...r.kernel.org
Subject: Re: optimizations to sk_buff handling in rds_tcp_data_ready

On (04/07/16 07:16), Eric Dumazet wrote:
> Use skb split like TCP in output path ?

That almost looks like what I want, but skb_split modifies both
skb and skb1, and I want to leave skb untouched (otherwise 
I will mess up the book-keeping in tcp_read_sock). But skb_split 
is a good template- I think it could even be extended to avoid copying
the frags that we'd later trim off in rds_tcp_data_recv anyway, 
let me see what I can come up with, based on that code.

> Really, pskb_expand_head() is not supposed to copy payload ;)

That would make my world very easy! But it has callers from all
over the kernel, e.g., skb_realloc_headroom, and changing it is
obviously risky