netdev - Re: [net-next 01/11] ixgbe: Support using build_skb in the case that jumbo frames are disabled

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Message-ID: <1365773465.4459.21.camel@edumazet-glaptop>
Date:	Fri, 12 Apr 2013 06:31:05 -0700
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Jeff Kirsher <jeffrey.t.kirsher@...el.com>
Cc:	davem@...emloft.net, Alexander Duyck <alexander.h.duyck@...el.com>,
	netdev@...r.kernel.org, gospo@...hat.com, sassmann@...hat.com
Subject: Re: [net-next 01/11] ixgbe: Support using build_skb in the case
 that jumbo frames are disabled

On Fri, 2013-04-12 at 06:10 -0700, Eric Dumazet wrote:

> Strange. I feel you overestimate the final skb->truesize
> 
> The name 'truesize' is a bit misleading here, as its the size of
> skb->head. A better name would have been frag_size, and you should not
> include in it the struct skb_shared_info overhead because build_skb()
> does it :
> 

Oh well, build_skb() does :

size -= SKB_DATA_ALIGN(sizeof(struct skb_shared_info)); 

so your patch is fine, only the @truesize name is misleading.

> skb->truesize will be set to SKB_TRUESIZE(frag_size)
> 
> #define SKB_TRUESIZE(X) ((X) +                                          \
>                          SKB_DATA_ALIGN(sizeof(struct sk_buff)) +       \
>                          SKB_DATA_ALIGN(sizeof(struct skb_shared_info)))
> 
> 



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