[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: David S. Miller <davem@davemloft.net>
diff --git a/net/ipv4/tcp.c b/net/ipv4/tcp.c
index 882436d..be35415 100644
--- a/net/ipv4/tcp.c
+++ b/net/ipv4/tcp.c
@@ -756,13 +756,9 @@
{
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 @@
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;