Commit c65f7f00 authored by David S. Miller's avatar David S. Miller
Browse files

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



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: default avatarDavid S. Miller <davem@davemloft.net>
parent b8259d9a

include/net/sock.h

+5 −2
Original line number Diff line number Diff line
@@ -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);

net/ipv4/tcp.c

+2 −11
Original line number Diff line number Diff line
@@ -756,13 +756,9 @@ static inline int select_size(struct sock *sk, struct tcp_sock *tp) 
{

	int tmp = tp->mss_cache_std;



	if (sk->sk_route_caps & NETIF_F_SG) {

		int pgbreak = SKB_MAX_HEAD(MAX_TCP_HEADER);

	if (sk->sk_route_caps & NETIF_F_SG)

		tmp = 0;



		if (tmp >= pgbreak &&

		    tmp <= pgbreak + (MAX_SKB_FRAGS - 1) * PAGE_SIZE)

			tmp = pgbreak;

	}

	return tmp;

}
@@ -872,11 +868,6 @@ new_segment: 
					tcp_mark_push(tp, skb);

					goto new_segment;

				} else if (page) {

					/* If page is cached, align

					 * offset to L1 cache boundary

					 */

					off = (off + L1_CACHE_BYTES - 1) &

					      ~(L1_CACHE_BYTES - 1);

					if (off == PAGE_SIZE) {

						put_page(page);

						TCP_PAGE(sk) = page = NULL;

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