netdev - Re: [PATCH] tcp: avoid order-1 allocations on wifi and tx path

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Date:	Wed, 11 Apr 2012 09:38:02 +0200
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Marc MERLIN <marc@...lins.org>, David Miller <davem@...emloft.net>
Cc:	Larry.Finger@...inger.net, bhutchings@...arflare.com,
	linux-wireless@...r.kernel.org, netdev@...r.kernel.org
Subject: Re: [PATCH] tcp: avoid order-1 allocations on wifi and tx path

On Wed, 2012-04-11 at 08:30 +0200, Eric Dumazet wrote:
> Marc Merlin reported many order-1 allocations failures in TX path on its
> wireless setup, that dont make any sense with MTU=1500 network, and non
> SG capable hardware.
> 
> After investigation, it turns out TCP uses sk_stream_alloc_skb() and
> used as a convention skb_tailroom(skb) to know how many bytes of data
> payload could be put in this skb (for non SG capable devices)
> 
...
> 
> Reported-by: Marc MERLIN <marc@...lins.org>
> Tested-by: Marc MERLIN <marc@...lins.org>
> Signed-off-by: Eric Dumazet <eric.dumazet@...il.com>

David, I forgot to say this should be backported to 3.2 & 3.3

commit 87fb4b7b533073 (net: more accurate skb truesize) did the
placement of skb_shared_info at the end of skb head, so
sk_stream_alloc_skb() had to reserve more room so that tailroom stayed
at MSS



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