Re: [PATCH net-next V2 1/2] net: introduce skb_coalesce_rx_frag()

[Jason Wang <jasowang@redhat.com>]

On 10/31/2013 10:26 PM, Eric Dumazet wrote:
> On Thu, 2013-10-31 at 19:47 +0800, Jason Wang wrote:
>> Sometimes we need to coalesce the rx frags to avoid frag list. One example is
>> virtio-net driver which tries to use small frags for both MTU sized packet and
>> GSO packet. So this patch introduce skb_coalesce_rx_frag() to do this.
>>
>> Cc: Rusty Russell <rusty@rustcorp.com.au>
>> Cc: Michael S. Tsirkin <mst@redhat.com>
>> Cc: Michael Dalton <mwdalton@google.com>
>> Cc: Eric Dumazet <edumazet@google.com>
>> Acked-by: Michael S. Tsirkin <mst@redhat.com>
>> Signed-off-by: Jason Wang <jasowang@redhat.com>
>> ---
>> Changes from V1:
>> - remove the useless off parameter.
>> ---
>>  include/linux/skbuff.h |  3 +++
>>  net/core/skbuff.c      | 13 +++++++++++++
>>  2 files changed, 16 insertions(+)
>>
>> diff --git a/include/linux/skbuff.h b/include/linux/skbuff.h
>> index 2c15497..fffaeaf 100644
>> --- a/include/linux/skbuff.h
>> +++ b/include/linux/skbuff.h
>> @@ -1372,6 +1372,9 @@ static inline void skb_fill_page_desc(struct sk_buff *skb, int i,
>>  void skb_add_rx_frag(struct sk_buff *skb, int i, struct page *page, int off,
>>  		     int size, unsigned int truesize);
>>  
>> +void skb_coalesce_rx_frag(struct sk_buff *skb, int i, int size,
>> +			  unsigned int truesize);
>> +
>>  #define SKB_PAGE_ASSERT(skb) 	BUG_ON(skb_shinfo(skb)->nr_frags)
>>  #define SKB_FRAG_ASSERT(skb) 	BUG_ON(skb_has_frag_list(skb))
>>  #define SKB_LINEAR_ASSERT(skb)  BUG_ON(skb_is_nonlinear(skb))
>> diff --git a/net/core/skbuff.c b/net/core/skbuff.c
>> index 0ab32fa..87670e1 100644
>> --- a/net/core/skbuff.c
>> +++ b/net/core/skbuff.c
>> @@ -476,6 +476,19 @@ void skb_add_rx_frag(struct sk_buff *skb, int i, struct page *page, int off,
>>  }
>>  EXPORT_SYMBOL(skb_add_rx_frag);
>>  
>> +void skb_coalesce_rx_frag(struct sk_buff *skb, int i, int size,
>> +			  unsigned int truesize)
>> +{
>> +	skb_frag_t *frag = &skb_shinfo(skb)->frags[i];
>> +
>> +	skb_frag_size_add(frag, size);
>> +	skb->len += size;
>> +	skb->data_len += size;
>> +	skb->truesize += truesize;
>
>> +	skb_frag_unref(skb, i);
> This unref is not logical, or should at least be
>
> __skb_frag_unref(frag);
>
> But I do think this is best done in the caller.
>
> In virtio_net this would be a :
>
> put_page(page);
>
> In tcp stack we do almost the same, but we take the reference on the
> page if we could not coalesce with prio frag, instead of doing a get and
> put in the other case.
>
>         if (can_coalesce) {
>                 skb_frag_size_add(&skb_shinfo(skb)->frags[i - 1], copy);
>         } else {
>                 get_page(page);
>                 skb_fill_page_desc(skb, i, page, offset, copy);
>         }
>

Ok, get it. Will do a put_page() in V3.

Thanks
>> +}
>> +EXPORT_SYMBOL(skb_coalesce_rx_frag);
>> +
>>  static void skb_drop_list(struct sk_buff **listp)
>>  {
>>  	kfree_skb_list(*listp);
>
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