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[TCP]: Simplify SKB data portion allocation with NETIF_F_SG.

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The ideal and most optimal layout for an SKB when doing
scatter-gather is to put all the headers at skb->data, and
all the user data in the page array.

This makes SKB splitting and combining extremely simple,
especially before a packet goes onto the wire the first
time.

So, when sk_stream_alloc_pskb() is given a zero size, make
sure there is no skb_tailroom().  This is achieved by applying
SKB_DATA_ALIGN() to the header length used here.

Next, make select_size() in TCP output segmentation use a
length of zero when NETIF_F_SG is true on the outgoing
interface.

Signed-off-by: David S. Miller <davem@davemloft.net>
This commit is contained in:
David S. Miller
2005-07-05 15:17:25 -07:00
parent b8259d9ad1
commit c65f7f00c5
2 changed files with 7 additions and 13 deletions
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7
include/net/sock.h
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@@ -1134,13 +1134,16 @@ static inline void sk_stream_moderate_sndbuf(struct sock *sk)
static inline struct sk_buff *sk_stream_alloc_pskb(struct sock *sk,
int size, int mem, int gfp)
{
struct sk_buff *skb = alloc_skb(size + sk->sk_prot->max_header, gfp);
struct sk_buff *skb;
int hdr_len;
hdr_len = SKB_DATA_ALIGN(sk->sk_prot->max_header);
skb = alloc_skb(size + hdr_len, gfp);
if (skb) {
skb->truesize += mem;
if (sk->sk_forward_alloc >= (int)skb->truesize ||
sk_stream_mem_schedule(sk, skb->truesize, 0)) {
skb_reserve(skb, sk->sk_prot->max_header);
skb_reserve(skb, hdr_len);
return skb;
}
__kfree_skb(skb);