tcp: tcp_sendmsg() page recycling

If our TCP_PAGE(sk) is not shared (page_count() == 1), we can set page
offset to 0.

This permits better filling of the pages on small to medium tcp writes.

"tbench 16" results on my dev server (2x4x2 machine) :

Before : 3072 MB/s
After  : 3146 MB/s  (2.4 % gain)

Signed-off-by: Eric Dumazet <eric.dumazet@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 6 insertions, 1 deletions

diff --git a/net/ipv4/tcp.c b/net/ipv4/tcp.c
index 45156be3abfd..a09fe253b917 100644
--- a/net/ipv4/tcp.c
+++ b/net/ipv4/tcp.c
@@ -1009,7 +1009,12 @@ new_segment:
                                 int merge = 0;
                                 int i = skb_shinfo(skb)->nr_frags;
                                 struct page *page = TCP_PAGE(sk);
-                                int off = TCP_OFF(sk);
+                                int off;
+
+                                if (page && page_count(page) == 1)
+                                        TCP_OFF(sk) = 0;
+
+                                off = TCP_OFF(sk);
 
                                 if (skb_can_coalesce(skb, i, page, off) &&
                                     off != PAGE_SIZE) {