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

[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

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
Signed-off-by: default avatarDavid S. Miller <>
parent b8259d9a
......@@ -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;
......@@ -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) {
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) {
TCP_PAGE(sk) = page = NULL;
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