linux-kernel - Re: [PATCH v2 1/3] virtio_net: Split receive buffer alloc/add

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Message-ID: <8739bn6n66.fsf@rustcorp.com.au>
Date:	Wed, 11 Jan 2012 12:00:25 +1030
From:	Rusty Russell <rusty@...tcorp.com.au>
To:	Mike Waychison <mikew@...gle.com>,
	"Michael S. Tsirkin" <mst@...hat.com>
Cc:	netdev@...r.kernel.org, earhart@...gle.com,
	virtualization@...ts.linux-foundation.org, digitaleric@...gle.com,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 1/3] virtio_net: Split receive buffer alloc/add

On Tue, 10 Jan 2012 09:41:01 -0800, Mike Waychison <mikew@...gle.com> wrote:
> In preparation for allocating receive buffers in the slow path without
> disabling NAPI, split the allocation and addition of receive buffers
> apart into two separate functions (per receive buffer type).
> 
> While here, move the vi->num accounting into the add functions.
> 
> Signed-off-by: Mike Waychison <mikew@...gle.com>

Hi Mike...

        This exposes a nasty ugliness in the way virtio_net works.  We
allocate an skbuff for the small packet case, and just allocate the
pages for the large packet cases, and alloc the skbuff when we fill the
pages.

        I think all the allocators should return a populated skbuff;
this uses a bit more memory in theory, but should make the code simpler.
As an added bonus, your life should get much simpler for these patches.

I'll try to create such a patch tonight, but I'm busy finalizing my
linux.conf.au presentation, so it might take longer :(

Thanks,
Rusty.
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