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SubjectRe: [PATCH net-next 2/2] virtio-net: fix the XDP truesize calculation for mergeable buffers
On Wed, May 06, 2020 at 02:16:33PM +0800, Jason Wang wrote:
> We should not exclude headroom and tailroom when XDP is set. So this
> patch fixes this by initializing the truesize from PAGE_SIZE when XDP
> is set.
>
> Cc: Jesper Dangaard Brouer <brouer@redhat.com>
> Signed-off-by: Jason Wang <jasowang@redhat.com>

Seems too aggressive, we do not use up the whole page for the size.



> ---
> drivers/net/virtio_net.c | 6 ++++--
> 1 file changed, 4 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
> index 98dd75b665a5..3f3aa8308918 100644
> --- a/drivers/net/virtio_net.c
> +++ b/drivers/net/virtio_net.c
> @@ -1184,7 +1184,7 @@ static int add_recvbuf_mergeable(struct virtnet_info *vi,
> char *buf;
> void *ctx;
> int err;
> - unsigned int len, hole;
> + unsigned int len, hole, truesize;
>
> /* Extra tailroom is needed to satisfy XDP's assumption. This
> * means rx frags coalescing won't work, but consider we've
> @@ -1194,6 +1194,7 @@ static int add_recvbuf_mergeable(struct virtnet_info *vi,
> if (unlikely(!skb_page_frag_refill(len + room, alloc_frag, gfp)))
> return -ENOMEM;
>
> + truesize = headroom ? PAGE_SIZE : len;
> buf = (char *)page_address(alloc_frag->page) + alloc_frag->offset;
> buf += headroom; /* advance address leaving hole at front of pkt */
> get_page(alloc_frag->page);

Is this really just on the XDP path? Looks like a confusing way to
detect that.


> @@ -1205,11 +1206,12 @@ static int add_recvbuf_mergeable(struct virtnet_info *vi,
> * the current buffer.
> */
> len += hole;
> + truesize += hole;
> alloc_frag->offset += hole;
> }
>
> sg_init_one(rq->sg, buf, len);
> - ctx = mergeable_len_to_ctx(len, headroom);
> + ctx = mergeable_len_to_ctx(truesize, headroom);
> err = virtqueue_add_inbuf_ctx(rq->vq, rq->sg, 1, buf, ctx, gfp);
> if (err < 0)
> put_page(virt_to_head_page(buf));
> --
> 2.20.1

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