tcp: makes tcp_try_coalesce aware of skb->head_frag

TCP coalesce can check if skb to be merged has its skb->head mapped to a
page fragment, instead of a kmalloc() area.

We had to disable coalescing in this case, for performance reasons.

We 'upgrade' skb->head as a fragment in itself.

This reduces number of cache misses when user makes its copies, since a
less sk_buff are fetched.

This makes receive and ofo queues shorter and thus reduce cache line
misses in TCP stack.

This is a followup of patch "net: allow skb->head to be a page fragment"

Tested with tg3 nic, with GRO on or off. We can see "TCPRcvCoalesce"
counter being incremented.

Signed-off-by: Eric Dumazet <[email protected]>
Cc: Ilpo Järvinen <[email protected]>
Cc: Herbert Xu <[email protected]>
Cc: Maciej Żenczykowski <[email protected]>
Cc: Neal Cardwell <[email protected]>
Cc: Tom Herbert <[email protected]>
Cc: Jeff Kirsher <[email protected]>
Cc: Ben Hutchings <[email protected]>
Cc: Matt Carlson <[email protected]>
Cc: Michael Chan <[email protected]>
Signed-off-by: David S. Miller <[email protected]>

0 files changed, 0 insertions, 0 deletions