tipc: fall back to smaller MTU if allocation of local send skb fails

When sending node local messages the code is using an 'mtu' of 66060
bytes to avoid unnecessary fragmentation. During situations of low
memory tipc_msg_build() may sometimes fail to allocate such large
buffers, resulting in unnecessary send failures. This can easily be
remedied by falling back to a smaller MTU, and then reassemble the
buffer chain as if the message were arriving from a remote node.

At the same time, we change the initial MTU setting of the broadcast
link to a lower value, so that large messages always are fragmented
into smaller buffers even when we run in single node mode. Apart from
obtaining the same advantage as for the 'fallback' solution above, this
turns out to give a significant performance improvement. This can
probably be explained with the __pskb_copy() operation performed on the
buffer for each recipient during reception. We found the optimal value
for this, considering the most relevant skb pool, to be 3744 bytes.

Acked-by: Ying Xue <ying.xue@ericsson.com>
Signed-off-by: Jon Maloy <jon.maloy@ericsson.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 1 insertions, 1 deletions

diff --git a/net/tipc/link.c b/net/tipc/link.c
index 6bce0b1117bd..2d6b2aed30e0 100644
--- a/net/tipc/link.c
+++ b/net/tipc/link.c
@@ -483,7 +483,7 @@ bool tipc_link_create(struct net *net, char *if_name, int bearer_id,
 /**
  * tipc_link_bc_create - create new link to be used for broadcast
  * @n: pointer to associated node
- * @mtu: mtu to be used
+ * @mtu: mtu to be used initially if no peers
  * @window: send window to be used
  * @inputq: queue to put messages ready for delivery
  * @namedq: queue to put binding table update messages ready for delivery