netdev - Re: [PATCH net] vxlan: update skb dst pmtu on tx path

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Date:   Mon, 22 Jan 2018 23:35:49 +0100
From:   Roman Kapl <code@...pl.cz>
To:     Xin Long <lucien.xin@...il.com>,
        network dev <netdev@...r.kernel.org>
Cc:     davem@...emloft.net, Jiri Benc <jbenc@...hat.com>
Subject: Re: [PATCH net] vxlan: update skb dst pmtu on tx path

On 12/18/2017 07:20 AM, Xin Long wrote:
> Unlike ip tunnels, now vxlan doesn't do any pmtu update for
> upper dst pmtu, even if it doesn't match the lower dst pmtu
> any more.
>
> The problem can be reproduced when reducing the vxlan lower
> dev's pmtu when running netperf. In jianlin's testing, the
> performance went to 1/7 of the previous.
>
> This patch is to update the upper dst pmtu to match the lower
> dst pmtu on tx path so that packets can be sent out even when
> lower dev's pmtu has been changed.
>
> It also works for metadata dst.
Sorry for resurrecting the conversation, but what exactly was meant by 
this "works metadata dst" remark? I am currently having kernel crashes 
related to ops->update_pmtu == NULL on VXLAN xmit and I am using tunnel 
metadata set by act_tunnel_key. Before this patch, it was OK.

My first thought was to add `if (ops->update_pmtu != NULL)`, but it 
appears some thought was given to this. Or maybe md_dst_ops should have 
update pmtu?

Thanks, Roman Kapl