Re: [PATCH v2 2/4] Defer skb allocation -- new skb_set calls & chain pages in virtio_net

Rusty Russell
2009-12-14T06:54:48Z

On Fri, 11 Dec 2009 11:13:02 pm Shirley Ma wrote:
> Signed-off-by: Shirley Ma <xma@us.ibm.com>

I don't think there's a good way of splitting this change across multiple
patches. And I don't think this patch will compile; I don't think we can
get rid of trim_pages yet.

We *could* first split the receive paths into multiple parts as you have
(eg. add_recvbuf_big etc), then actually rewrite them, but that's too much
work to refactor the code twice.

So just roll all the driver changes into one patch; so you will have two
patches: one which creates the destroy_bufs API for virtio, and one which
uses it in the virtio_net driver.

> +static struct sk_buff *skb_goodcopy(struct virtnet_info *vi, struct page **page,
> + unsigned int *len)

This actually allocates an skb, and transfers the first page to it (via copy
and possibly the first fragment). skb_from_page() perhaps?

> + hdr_len = sizeof(hdr->hdr);
> + offset = sizeof(struct padded_vnet_hdr);
> + }
> +
> + memcpy(hdr, p, hdr_len);
> +
> + *len -= hdr_len;

Perhaps you should return NULL here as an error if *len was < hdr_len?

Thanks,
Rusty.