From mboxrd@z Thu Jan 1 00:00:00 1970 From: Jarek Poplawski Subject: Re: [PATCH net-next-2.6] net: pskb_expand_head() optimization Date: Sun, 12 Sep 2010 12:45:34 +0200 Message-ID: <20100912104534.GA2056@del.dom.local> References: <1283852248.2338.160.camel@edumazet-laptop> <20100910.125449.235704956.davem@davemloft.net> <20100911123140.GA1939@del.dom.local> <20100911.203002.193707453.davem@davemloft.net> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Cc: eric.dumazet@gmail.com, netdev@vger.kernel.org To: David Miller Return-path: Received: from mail-wy0-f174.google.com ([74.125.82.174]:61576 "EHLO mail-wy0-f174.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751842Ab0ILKpl (ORCPT ); Sun, 12 Sep 2010 06:45:41 -0400 Received: by wyf22 with SMTP id 22so4962750wyf.19 for ; Sun, 12 Sep 2010 03:45:40 -0700 (PDT) Content-Disposition: inline In-Reply-To: <20100911.203002.193707453.davem@davemloft.net> Sender: netdev-owner@vger.kernel.org List-ID: On Sat, Sep 11, 2010 at 08:30:02PM -0700, David Miller wrote: > From: Jarek Poplawski > Date: Sat, 11 Sep 2010 14:31:40 +0200 > > > Otherwise seems OK, but I still would like to know the scenario > > demanding this change. > > I want to make sk_buff use list_head, including all uses such as > frag_list et al. > > If the frag_list chain can be shared, a doubly linked list cannot be > used. > > This is someting I've been gradually working on now for more than 2 > years :) Hmm... Then the first message/changelog in this thread seems to describe the future bug, only with doubly linked lists. If so, it was a bit misleading to me ;-) Then a few more questions: 1) if doubly linked lists really require such pskb_copying, isn't it all too costly? 2) why skb_clone isn't enough instead of pskb_copy? 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? Jarek P.