netdev - Re: [PATCH net-next] net: increase LL_MAX_HEADER if HYPERV

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Date:	Sun, 01 Nov 2015 14:36:20 -0800
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	David Miller <davem@...emloft.net>
Cc:	haiyangz@...rosoft.com, edumazet@...gle.com,
	netdev@...r.kernel.org, kys@...rosoft.com
Subject: Re: [PATCH net-next] net: increase LL_MAX_HEADER if HYPERV_NET is
 enabled

On Sun, 2015-11-01 at 15:58 -0500, David Miller wrote:
> From: Eric Dumazet <eric.dumazet@...il.com>
> Date: Sun, 01 Nov 2015 09:20:59 -0800
> 
> > From: Eric Dumazet <edumazet@...gle.com>
> > 
> > My recent commit, attaching SYNACK messages to request sockets
> > exposed a too small LL_MAX_HEADER when netvsc_drv.c is in use,
> > because this driver sets a needed_headroom of 220 bytes.
> > 
> > Increase LL_MAX_HEADER in this case, to avoid a realloc of all
> > TCP frames.
> > 
> > In another patch, I'll make skb_set_owner_w() more robust.
> > 
> > Fixes: ca6fb0651883 ("tcp: attach SYNACK messages to request sockets instead of listener")
> > Signed-off-by: Eric Dumazet <edumazet@...gle.com>
> > Bisected-by: Haiyang Zhang <haiyangz@...rosoft.com>
> 
> Using a value of 256 just because HYPER-V is crazy imposes a huge
> unnecessary burdon upon the rest of the stack.
> 
> I rejected a previous attempt to use such a huge value for
> LL_MAX_HEADER, and I will do so again here.  We need a different fix
> for this issue, one that doesn't hurt everyone.

Sure, I was planning to send the skb_set_owner_w() fix as well.

I was not aware you already objected to LL_MAX_HEADER increase.




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