netdev - Re: [net-next 1/1] tipc: fall back to smaller MTU if allocation of local send skb fails

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Date:   Fri, 01 Dec 2017 15:22:19 -0500 (EST)
From:   David Miller <davem@...emloft.net>
To:     jon.maloy@...csson.com
Cc:     netdev@...r.kernel.org,
        mohan.krishna.ghanta.krishnamurthy@...csson.com,
        tung.q.nguyen@...tech.com.au, hoang.h.le@...tech.com.au,
        canh.d.luu@...tech.com.au, ying.xue@...driver.com,
        tipc-discussion@...ts.sourceforge.net
Subject: Re: [net-next 1/1] tipc: fall back to smaller MTU if allocation of
 local send skb fails

From: Jon Maloy <jon.maloy@...csson.com>
Date: Thu, 30 Nov 2017 16:47:25 +0100

> 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@...csson.com>
> Signed-off-by: Jon Maloy <jon.maloy@...csson.com>

Applied, thanks Jon.