From mboxrd@z Thu Jan 1 00:00:00 1970 From: Eric Dumazet Subject: Re: [PATCH 02/11] net: add function to allocate skbuff head without data area Date: Mon, 20 Aug 2012 08:39:34 +0200 Message-ID: <1345444774.5158.241.camel@edumazet-glaptop> References: <1345443532-3707-1-git-send-email-kaber@trash.net> <1345443532-3707-3-git-send-email-kaber@trash.net> Mime-Version: 1.0 Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: 7bit Cc: Florian.Westphal@Sophos.com, netdev@vger.kernel.org, netfilter-devel@vger.kernel.org To: Patrick McHardy Return-path: Received: from mail-wi0-f172.google.com ([209.85.212.172]:34984 "EHLO mail-wi0-f172.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751333Ab2HTGjj (ORCPT ); Mon, 20 Aug 2012 02:39:39 -0400 In-Reply-To: <1345443532-3707-3-git-send-email-kaber@trash.net> Sender: netdev-owner@vger.kernel.org List-ID: On Mon, 2012-08-20 at 08:18 +0200, Patrick McHardy wrote: > Add a function to allocate a skbuff head without any data. This will be > used by memory mapped netlink to attached data from the mmaped area to > the skb. > > Additionally change skb_release_all() to check whether the skb has a > data area to allow the skb destructor to clear the data pointer in > case only a head has been allocated. * ... > > +struct sk_buff *__alloc_skb_head(gfp_t gfp_mask, int node) > +{ > + struct sk_buff *skb; > + > + /* Get the HEAD */ > + skb = kmem_cache_alloc_node(skbuff_head_cache, > + gfp_mask & ~__GFP_DMA, node); > + if (!skb) > + goto out; > + prefetchw(skb); > + This prefetch is probably not worth it, since you write on skb on the following memset(). Cpu wont have enough 'time' to take benefit from this hint. > + /* > + * Only clear those fields we need to clear, not those that we will > + * actually initialise below. Hence, don't put any more fields after > + * the tail pointer in struct sk_buff! > + */ > + memset(skb, 0, offsetof(struct sk_buff, tail));