netdev - RE: [net-next 03/12] i40e: Handle a single mss packet with more than 8 frags

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Message-ID: <063D6719AE5E284EB5DD2968C1650D6D1C9F1E87@AcuExch.aculab.com>
Date:	Mon, 17 Nov 2014 14:40:59 +0000
From:	David Laight <David.Laight@...LAB.COM>
To:	'Eric Dumazet' <eric.dumazet@...il.com>
CC:	Jeff Kirsher <jeffrey.t.kirsher@...el.com>,
	"davem@...emloft.net" <davem@...emloft.net>,
	Serey Kong <serey.kong@...el.com>,
	"netdev@...r.kernel.org" <netdev@...r.kernel.org>,
	"nhorman@...hat.com" <nhorman@...hat.com>,
	"sassmann@...hat.com" <sassmann@...hat.com>,
	"jogreene@...hat.com" <jogreene@...hat.com>,
	Shannon Nelson <shannon.nelson@...el.com>
Subject: RE: [net-next 03/12] i40e: Handle a single mss packet with more
 than 8 frags

From: Eric 
> On Mon, 2014-11-17 at 14:15 +0000, David Laight wrote:
> 
> > Didn't someone write a function that significantly reduces the
> > number of fragments without actually requiring a single linear block?
> 
> I presume you refer to alloc_skb_with_frags() : It does the allocation,
> but I was expecting some kind soul to continue my work and provide the
> companion code to do the copy.

Not that one.
IIRC is was done to reduce the number of fragments through xennet.

You really want to try to keep some of the old fragments, just adding
new ones to merge short sections.

OTOH 8 fragments isn't enough if the MAC supports TSO (dunno if it does).
The skb_linearize() is only likely to fail for TSO anyway.
Or rather, if it can't allocate a 4k page you are already stuffed.

	David.