netdev - RE: [RFC PATCH v7 01/19] Add a new structure for skb buffer from external.

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Date:	Wed, 9 Jun 2010 16:48:48 +0800
From:	"Xin, Xiaohui" <xiaohui.xin@...el.com>
To:	Andi Kleen <andi@...stfloor.org>,
	Stephen Hemminger <shemminger@...tta.com>
CC:	"netdev@...r.kernel.org" <netdev@...r.kernel.org>,
	"kvm@...r.kernel.org" <kvm@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"mst@...hat.com" <mst@...hat.com>, "mingo@...e.hu" <mingo@...e.hu>,
	"davem@...emloft.net" <davem@...emloft.net>,
	"herbert@...dor.apana.org.au" <herbert@...dor.apana.org.au>,
	"jdike@...ux.intel.com" <jdike@...ux.intel.com>
Subject: RE: [RFC PATCH v7 01/19] Add a new structure for skb buffer from
 external.

>-----Original Message-----
>From: kvm-owner@...r.kernel.org [mailto:kvm-owner@...r.kernel.org] On Behalf Of Andi
>Kleen
>Sent: Monday, June 07, 2010 3:51 PM
>To: Stephen Hemminger
>Cc: Xin, Xiaohui; netdev@...r.kernel.org; kvm@...r.kernel.org;
>linux-kernel@...r.kernel.org; mst@...hat.com; mingo@...e.hu; davem@...emloft.net;
>herbert@...dor.apana.org.au; jdike@...ux.intel.com
>Subject: Re: [RFC PATCH v7 01/19] Add a new structure for skb buffer from external.
>
>Stephen Hemminger <shemminger@...tta.com> writes:
>
>> Still not sure this is a good idea for a couple of reasons:
>>
>> 1. We already have lots of special cases with skb's (frags and fraglist),
>>    and skb's travel through a lot of different parts of the kernel.  So any
>>    new change like this creates lots of exposed points for new bugs. Look
>>    at cases like MD5 TCP and netfilter, and forwarding these SKB's to ipsec
>>    and ppp and ...
>>
>> 2. SKB's can have infinite lifetime in the kernel. If these buffers come from
>>    a fixed size pool in an external device, they can easily all get tied up
>>    if you have a slow listener. What happens then?
>
>3. If they come from an internal pool what happens when the kernel runs
>low on memory? How is that pool balanced against other kernel
>memory users?
>
The size of the pool is limited by the virtqueue capacity now.
If the virtqueue is really huge, then how to balance on memory is a problem.
I did not consider it clearly how to tune it dynamically currently...

>-Andi
>
>--
>ak@...ux.intel.com -- Speaking for myself only.
>--
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