linux-kernel - Re: [PATCH net-next 11/12] net: hns3: do not allocate linear data for fraglist skb

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Date:   Wed, 16 Oct 2019 10:18:17 -0700
From:   Jakub Kicinski <jakub.kicinski@...ronome.com>
To:     Huazhong Tan <tanhuazhong@...wei.com>
Cc:     <davem@...emloft.net>, <netdev@...r.kernel.org>,
        <linux-kernel@...r.kernel.org>, <salil.mehta@...wei.com>,
        <yisen.zhuang@...wei.com>, <linuxarm@...wei.com>,
        Yunsheng Lin <linyunsheng@...wei.com>
Subject: Re: [PATCH net-next 11/12] net: hns3: do not allocate linear data
 for fraglist skb

On Wed, 16 Oct 2019 15:17:10 +0800, Huazhong Tan wrote:
> From: Yunsheng Lin <linyunsheng@...wei.com>
> 
> Currently, napi_alloc_skb() is used to allocate skb for fraglist
> when the head skb is not enough to hold the remaining data, and
> the remaining data is added to the frags part of the fraglist skb,
> leaving the linear part unused.
> 
> So this patch passes length of 0 to allocate fraglist skb with
> zero size of linear data.
> 
> Fixes: 81ae0e0491f3 ("net: hns3: Add skb chain when num of RX buf exceeds MAX_SKB_FRAGS")
> Signed-off-by: Yunsheng Lin <linyunsheng@...wei.com>
> Signed-off-by: Huazhong Tan <tanhuazhong@...wei.com>

Is this really a fix? I just wastes memory, right?

> diff --git a/drivers/net/ethernet/hisilicon/hns3/hns3_enet.c b/drivers/net/ethernet/hisilicon/hns3/hns3_enet.c
> index 6172eb2..14111af 100644
> --- a/drivers/net/ethernet/hisilicon/hns3/hns3_enet.c
> +++ b/drivers/net/ethernet/hisilicon/hns3/hns3_enet.c
> @@ -2866,8 +2866,7 @@ static int hns3_add_frag(struct hns3_enet_ring *ring, struct hns3_desc *desc,
>  			return -ENXIO;
>  
>  		if (unlikely(ring->frag_num >= MAX_SKB_FRAGS)) {
> -			new_skb = napi_alloc_skb(&ring->tqp_vector->napi,
> -						 HNS3_RX_HEAD_SIZE);
> +			new_skb = napi_alloc_skb(&ring->tqp_vector->napi, 0);
>  			if (unlikely(!new_skb)) {
>  				hns3_rl_err(ring_to_netdev(ring),
>  					    "alloc rx fraglist skb fail\n");