netdev - Re: [PATCH net-next-2.6] net: pskb_expand

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Message-Id: <20100912.085833.226777368.davem@davemloft.net>
Date:	Sun, 12 Sep 2010 08:58:33 -0700 (PDT)
From:	David Miller <davem@...emloft.net>
To:	jarkao2@...il.com
Cc:	eric.dumazet@...il.com, netdev@...r.kernel.org
Subject: Re: [PATCH net-next-2.6] net: pskb_expand_head() optimization

From: Jarek Poplawski <jarkao2@...il.com>
Date: Sun, 12 Sep 2010 12:45:34 +0200

> Then a few more questions:
> 1) if doubly linked lists really require such pskb_copying, isn't it
>    all too costly?

In the common case the data reference will be one, so we will not
copy.

> 2) why skb_clone isn't enough instead of pskb_copy?

Can't share the metadata.

> 3) since skb_clone has some cost too, why e.g. saving only the pointer
>    to the tail of the list in skb_shared_info isn't enough?

Then we won't get the rest of the advantages of using list_head such
as prefetching during traversals, automatic debugging facilities, et al.
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