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

[Jason Wang]

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 
>> Cc: Michael S. Tsirkin 
>> Cc: Michael Dalton 
>> Cc: Eric Dumazet 
>> Acked-by: Michael S. Tsirkin 
>> Signed-off-by: Jason Wang 
>> ---
>> 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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Re: [PATCH net-next V2 1/2] net: introduce skb_coalesce_rx_frag()

[Eric Dumazet]

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 
> Cc: Michael S. Tsirkin 
> Cc: Michael Dalton 
> Cc: Eric Dumazet 
> Acked-by: Michael S. Tsirkin 
> Signed-off-by: Jason Wang 
> ---
> 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);
}


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


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

[Jason Wang]

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 
Cc: Michael S. Tsirkin 
Cc: Michael Dalton 
Cc: Eric Dumazet 
Acked-by: Michael S. Tsirkin 
Signed-off-by: Jason Wang 
---
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);
+}
+EXPORT_SYMBOL(skb_coalesce_rx_frag);
+
 static void skb_drop_list(struct sk_buff **listp)
 {
kfree_skb_list(*listp);
-- 
1.8.1.2

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