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

Xin, Xiaohui
2010-06-09T08:48:48Z

>-----Original Message-----
>From: kvm-owner@vger.kernel.org [mailto:kvm-owner@vger.kernel.org] On Behalf Of Andi
>Kleen
>Sent: Monday, June 07, 2010 3:51 PM
>To: Stephen Hemminger
>Cc: Xin, Xiaohui; netdev@vger.kernel.org; kvm@vger.kernel.org;
>linux-kernel@vger.kernel.org; mst@redhat.com; mingo@elte.hu; davem@davemloft.net;
>herbert@gondor.apana.org.au; jdike@linux.intel.com
>Subject: Re: [RFC PATCH v7 01/19] Add a new structure for skb buffer from external.
>
>Stephen Hemminger <shemminger@vyatta.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@linux.intel.com -- Speaking for myself only.
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