[ 103/221] xen/netfront: improve truesize tracking

Greg Kroah-Hartman
2013-01-15T22:31:21Z

From: Ian Campbell <Ian.Campbell@citrix.com>

commit d9a58a782e396a0f04e8445b7ba3763c8a48c7fe upstream.

Using RX_COPY_THRESHOLD is incorrect if the SKB is actually smaller
than that. We have already accounted for this in
NETFRONT_SKB_CB(skb)->pull_to so use that instead.

Fixes WARN_ON from skb_try_coalesce.

Signed-off-by: Ian Campbell <ian.campbell@citrix.com>
Cc: Sander Eikelenboom <linux@eikelenboom.it>
Cc: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
Cc: annie li <annie.li@oracle.com>
Cc: xen-devel@lists.xen.org
Cc: netdev@vger.kernel.org
Acked-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
drivers/net/xen-netfront.c | 27 ++++-----------------------
1 file changed, 4 insertions(+), 23 deletions(-)

--- a/drivers/net/xen-netfront.c
+++ b/drivers/net/xen-netfront.c
@@ -1015,29 +1015,10 @@ err:
i = xennet_fill_frags(np, skb, &tmpq);

/*
- * Truesize approximates the size of true data plus
- * any supervisor overheads. Adding hypervisor
- * overheads has been shown to significantly reduce
- * achievable bandwidth with the default receive
- * buffer size. It is therefore not wise to account
- * for it here.
- *
- * After alloc_skb(RX_COPY_THRESHOLD), truesize is set
- * to RX_COPY_THRESHOLD + the supervisor
- * overheads. Here, we add the size of the data pulled
- * in xennet_fill_frags().
- *
- * We also adjust for any unused space in the main
- * data area by subtracting (RX_COPY_THRESHOLD -
- * len). This is especially important with drivers
- * which split incoming packets into header and data,
- * using only 66 bytes of the main data area (see the
- * e1000 driver for example.) On such systems,
- * without this last adjustement, our achievable
- * receive throughout using the standard receive
- * buffer size was cut by 25%(!!!).
- */
- skb->truesize += skb->data_len - RX_COPY_THRESHOLD;
+ * Truesize is the actual allocation size, even if the
+ * allocation is only partially used.
+ */
+ skb->truesize += PAGE_SIZE * skb_shinfo(skb)->nr_frags;
skb->len += skb->data_len;

if (rx->flags & XEN_NETRXF_csum_blank)