netdev - Re: [V2 PATCH 2/9] macvtap: zerocopy: fix truesize underestimation

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Date:	Tue, 15 May 2012 10:26:49 -0700
From:	Shirley Ma <mashirle@...ibm.com>
To:	Jason Wang <jasowang@...hat.com>
Cc:	eric.dumazet@...il.com, mst@...hat.com, netdev@...r.kernel.org,
	linux-kernel@...r.kernel.org, ebiederm@...ssion.com,
	davem@...emloft.net
Subject: Re: [V2 PATCH 2/9] macvtap: zerocopy: fix truesize underestimation

On Wed, 2012-05-02 at 11:41 +0800, Jason Wang wrote:
> As the skb fragment were pinned/built from user pages, we should
> account the page instead of length for truesize.
> 
> Signed-off-by: Jason Wang <jasowang@...hat.com>
> ---
>  drivers/net/macvtap.c |    6 ++++--
>  1 files changed, 4 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/net/macvtap.c b/drivers/net/macvtap.c
> index bd4a70d..7cb2684 100644
> --- a/drivers/net/macvtap.c
> +++ b/drivers/net/macvtap.c
> @@ -519,6 +519,7 @@ static int zerocopy_sg_from_iovec(struct sk_buff
> *skb, const struct iovec *from,
>                 struct page *page[MAX_SKB_FRAGS];
>                 int num_pages;
>                 unsigned long base;
> +               unsigned long truesize;
> 
>                 len = from->iov_len - offset;
>                 if (!len) {
> @@ -533,10 +534,11 @@ static int zerocopy_sg_from_iovec(struct sk_buff
> *skb, const struct iovec *from,
>                     (num_pages > MAX_SKB_FRAGS -
> skb_shinfo(skb)->nr_frags))
>                         /* put_page is in skb free */
>                         return -EFAULT;
> +               truesize = size * PAGE_SIZE;

Here should be truesize = size * PAGE_SIZE - offset, right?

>                 skb->data_len += len;
>                 skb->len += len;
> -               skb->truesize += len;
> -               atomic_add(len, &skb->sk->sk_wmem_alloc);
> +               skb->truesize += truesize;
> +               atomic_add(truesize, &skb->sk->sk_wmem_alloc);
>                 while (len) {
>                         int off = base & ~PAGE_MASK;
>                         int size = min_t(int, len, PAGE_SIZE - off);
> 
> 

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