netdev - Re: Increasing skb->mark size

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Message-ID: <20151202025835.GL15533@two.firstfloor.org>
Date:	Wed, 2 Dec 2015 03:58:35 +0100
From:	Andi Kleen <andi@...stfloor.org>
To:	Daniel Borkmann <daniel@...earbox.net>
Cc:	Andi Kleen <andi@...stfloor.org>,
	Lorenzo Colitti <lorenzo@...gle.com>,
	Matt Bennett <Matt.Bennett@...iedtelesis.co.nz>,
	"netdev@...r.kernel.org" <netdev@...r.kernel.org>,
	Luuk Paulussen <Luuk.Paulussen@...iedtelesis.co.nz>,
	davem@...emloft.net
Subject: Re: Increasing skb->mark size

> >This would be be great. I've recently ran into some issues with
> >the overhead of the Android firewall setup.
> >
> >So basically you need 4 extra bytes in sk_buff. How about:
> >
> >- shrinking skb->priority to 2 byte
> 
> That wouldn't work, see SO_PRIORITY and such (4 bytes) ...

But does anybody really use the full 4 bytes for the priority?
SO_PRIORITY could well truncate the value.

> 
> >- skb_iff is either skb->dev->iff or 0. so it could be replaced with a
> >single bit flag for the 0 case.
> 
> ... and that one wouldn't work on ingress.

Please explain.

-Andi
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