aoe: for performance support larger packet payloads

tAdd adds the ability to work with large packets composed of a number of
segments, using the scatter gather feature of the block layer (biovecs)
and the network layer (skb frag array).  The motivation is the performance
gained by using a packet data payload greater than a page size and by
using the network card's scatter gather feature.

Users of the out-of-tree aoe driver already had these changes, but since
early 2011, they have complained of increased memory utilization and
higher CPU utilization during heavy writes.[1] The commit below appears
related, as it disables scatter gather on non-IP protocols inside the
harmonize_features function, even when the NIC supports sg.

  commit f01a5236bd4b140198fbcc550f085e8361fd73fa
  Author: Jesse Gross <jesse@nicira.com>
  Date:   Sun Jan 9 06:23:31 2011 +0000

      net offloading: Generalize netif_get_vlan_features().

With that regression in place, transmits always linearize sg AoE packets,
but in-kernel users did not have this patch.  Before 2.6.38, though, these
changes were working to allow sg to increase performance.

1. http://www.spinics.net/lists/linux-mm/msg15184.html

Signed-off-by: Ed Cashin <ecashin@coraid.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 1 insertions, 0 deletions

diff --git a/drivers/block/aoe/aoedev.c b/drivers/block/aoe/aoedev.c
index 6b5110a47458..b2d1fd354eac 100644
--- a/drivers/block/aoe/aoedev.c
+++ b/drivers/block/aoe/aoedev.c
@@ -182,6 +182,7 @@ skbfree(struct sk_buff *skb)
 			"cannot free skb -- memory leaked.");
 		return;
 	}
+	skb->truesize -= skb->data_len;
 	skb_shinfo(skb)->nr_frags = skb->data_len = 0;
 	skb_trim(skb, 0);
 	dev_kfree_skb(skb);