On 10/31/2013 10:26 PM, Eric Dumazet wrote:

On Thu, 2013-10-31 at 19:47 +0800, Jason Wang wrote:

quoted

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 <redacted>
Cc: Michael S. Tsirkin <mst@redhat.com>
Cc: Michael Dalton <redacted>
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;

quoted

+	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

quoted

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

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