----- 原始邮件 -----
> On Wed, Nov 20, 2013 at 07:08:50AM -0500, Jason Wang wrote:
> >
> >
> > ----- 原始邮件 -----
> > > On Wed, Nov 20, 2013 at 05:07:26PM +0800, Jason Wang wrote:
> > > > We need decrease the rq->num after we can get a buf through
> > > > virtqueue_get_buf() even if we could not allocate frag skb. Otherwise,
> > > > the
> > > > refill routine won't be triggered under heavy memory stress since the
> > > > driver may
> > > > still think there's enough room.
> > > >
> > > > This bug was introduced by commit
> > > > 2613af0ed18a11d5c566a81f9a6510b73180660a
> > > > (virtio_net: migrate mergeable rx buffers to page frag allocators).
> > > >
> > > > Cc: Rusty Russell <rusty@xxxxxxxxxxxxxxx>
> > > > Cc: Michael S. Tsirkin <mst@xxxxxxxxxx>
> > > > Cc: Michael Dalton <mwdalton@xxxxxxxxxx>
> > > > Cc: Eric Dumazet <edumazet@xxxxxxxxxx>
> > > > Signed-off-by: Jason Wang <jasowang@xxxxxxxxxx>
> > >
> > > So let's wrap virtqueue_get_buf to make sure we get it right?
> > >
> >
> > Ok. good idea.
>
> So I did this (below) but the compiler is not smart enough to
> avoid two branches on data path.
> So I'm not sure anymore: with my patch it's pretty clear how
> the code works.
>
> Signed-off-by: Michael S. Tsirkin <mst@xxxxxxxxxx>
>
> but I don't think we need to apply this.
>
True, another point is we'd better to handle both increasing and decreasing in the
same way. We do not increase it in a helper.
> diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
> index 11d9cc9..1cc2e43 100644
> --- a/drivers/net/virtio_net.c
> +++ b/drivers/net/virtio_net.c
> @@ -296,6 +296,14 @@ static struct sk_buff *page_to_skb(struct receive_queue
> *rq,
> return skb;
> }
>
> +static void *rq_get_buf(struct receive_queue *rq, unsigned int *len)
> +{
> + void *buf = virtqueue_get_buf(rq->vq, len);
> + if (buf)
> + rq->num--;
> + return buf;
> +}
> +
> static struct sk_buff *receive_mergeable(struct net_device *dev,
> struct receive_queue *rq,
> void *buf,
> @@ -315,7 +323,7 @@ static struct sk_buff *receive_mergeable(struct
> net_device *dev,
> while (--num_buf) {
> int num_skb_frags;
>
> - buf = virtqueue_get_buf(rq->vq, &len);
> + buf = rq_get_buf(rq, &len);
> if (unlikely(!buf)) {
> pr_debug("%s: rx error: %d buffers out of %d missing\n",
> dev->name, num_buf, hdr->mhdr.num_buffers);
> @@ -329,7 +337,6 @@ static struct sk_buff *receive_mergeable(struct
> net_device *dev,
> }
>
> page = virt_to_head_page(buf);
> - --rq->num;
>
> num_skb_frags = skb_shinfo(curr_skb)->nr_frags;
> if (unlikely(num_skb_frags == MAX_SKB_FRAGS)) {
> @@ -370,7 +377,7 @@ err_buf:
> dev->stats.rx_dropped++;
> dev_kfree_skb(head_skb);
> while (--num_buf) {
> - buf = virtqueue_get_buf(rq->vq, &len);
> + buf = rq_get_buf(rq, &len);
> if (unlikely(!buf)) {
> pr_debug("%s: rx error: %d buffers missing\n",
> dev->name, num_buf);
> @@ -379,7 +386,6 @@ err_buf:
> }
> page = virt_to_head_page(buf);
> put_page(page);
> - --rq->num;
> }
> return NULL;
> }
> @@ -675,9 +681,8 @@ static int virtnet_poll(struct napi_struct *napi, int
> budget)
>
> again:
> while (received < budget &&
> - (buf = virtqueue_get_buf(rq->vq, &len)) != NULL) {
> + (buf = rq_get_buf(rq, &len)) != NULL) {
> receive_buf(rq, buf, len);
> - --rq->num;
> received++;
> }
>
> --
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