netdev - Re: [RFC PATCH] net, gro: fix the truesize of all fragments

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Message-ID: <1387549695.19078.430.camel@edumazet-glaptop2.roam.corp.google.com>
Date:	Fri, 20 Dec 2013 06:28:15 -0800
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Zhi Yong Wu <zwu.kernel@...il.com>
Cc:	netdev@...r.kernel.org, Zhi Yong Wu <wuzhy@...ux.vnet.ibm.com>
Subject: Re: [RFC PATCH] net, gro: fix the truesize of all fragments

On Fri, 2013-12-20 at 19:45 +0800, Zhi Yong Wu wrote:
> From: Zhi Yong Wu <wuzhy@...ux.vnet.ibm.com>
> 
> When the truesize of all fragments was calculated, it didn't take
> the first small piece of data into account.
> 
> Signed-off-by: Zhi Yong Wu <wuzhy@...ux.vnet.ibm.com>
> ---
>  net/core/skbuff.c |   10 +++++++---
>  1 files changed, 7 insertions(+), 3 deletions(-)
> 
> diff --git a/net/core/skbuff.c b/net/core/skbuff.c
> index 2b6b863..0665bd6 100644
> --- a/net/core/skbuff.c
> +++ b/net/core/skbuff.c
> @@ -3027,9 +3027,12 @@ int skb_gro_receive(struct sk_buff **head, struct sk_buff *skb)
>  		frag->page_offset += offset;
>  		skb_frag_size_sub(frag, offset);
>  
> -		/* all fragments truesize : remove (head size + sk_buff) */
> +		/**
> +		 * all fragments truesize :
> +		 * remove (head size + sk_buff + offset)
> +		 */
>  		delta_truesize = skb->truesize -
> -				 SKB_TRUESIZE(skb_end_offset(skb));
> +				 SKB_TRUESIZE(skb_end_offset(skb) + offset);
>  
>  		skb->truesize -= skb->data_len;
>  		skb->len -= skb->data_len;
> @@ -3060,7 +3063,8 @@ int skb_gro_receive(struct sk_buff **head, struct sk_buff *skb)
>  		memcpy(frag + 1, skbinfo->frags, sizeof(*frag) * skbinfo->nr_frags);
>  		/* We dont need to clear skbinfo->nr_frags here */
>  
> -		delta_truesize = skb->truesize - SKB_DATA_ALIGN(sizeof(struct sk_buff));
> +		delta_truesize = skb->truesize -
> +			SKB_DATA_ALIGN(sizeof(struct sk_buff)) - offset;
>  		NAPI_GRO_CB(skb)->free = NAPI_GRO_FREE_STOLEN_HEAD;
>  		goto done;
>  	}


Nope, this patch is not needed.

truesize is about tracking the memory we allocated, not the memory we
really use.

What exact issue do you have ? I suspect a bug in a driver.



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