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

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Date:	Fri, 25 Jun 2010 10:07:34 +0800
From:	"Xin, Xiaohui" <xiaohui.xin@...el.com>
To:	Herbert Xu <herbert@...dor.apana.org.au>,
	"Dong, Eddie" <eddie.dong@...el.com>
CC:	Stephen Hemminger <shemminger@...tta.com>,
	"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>,
	"jdike@...ux.intel.com" <jdike@...ux.intel.com>
Subject: RE: [RFC PATCH v7 01/19] Add a new structure for skb buffer from
	external.

Herbert,
That's why I have sent you the patch for guest virtio-net driver. I reserved 512 bytes in each page, then I can always have the space to copy and avoid the backend memory used up issue.

Thanks
Xiaohui

>-----Original Message-----
>From: Herbert Xu [mailto:herbert@...dor.apana.org.au]
>Sent: Thursday, June 24, 2010 6:09 PM
>To: Dong, Eddie
>Cc: Xin, Xiaohui; Stephen Hemminger; netdev@...r.kernel.org; kvm@...r.kernel.org;
>linux-kernel@...r.kernel.org; mst@...hat.com; mingo@...e.hu; davem@...emloft.net;
>jdike@...ux.intel.com
>Subject: Re: [RFC PATCH v7 01/19] Add a new structure for skb buffer from external.
>
>On Wed, Jun 23, 2010 at 06:05:41PM +0800, Dong, Eddie wrote:
>>
>> I mean once the frontend side driver post the buffers to the backend driver, the backend
>driver will "immediately" use that buffers to compose skb or gro_frags and post them to the
>assigned host NIC driver as receive buffers. In that case, if the backend driver recieves a
>packet from the NIC that requires to do copy, it may be unable to find additional free guest
>buffer because all of them are already used by the NIC driver. We have to reserve some guest
>buffers for the possible copy even if the buffer address is not identified by original skb :(
>
>OK I see what you mean.  Can you tell me how does Xiaohui's
>previous patch-set deal with this problem?
>
>Thanks,
>--
>Visit Openswan at http://www.openswan.org/
>Email: Herbert Xu ~{PmV>HI~} <herbert@...dor.apana.org.au>
>Home Page: http://gondor.apana.org.au/~herbert/
>PGP Key: http://gondor.apana.org.au/~herbert/pubkey.txt
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