On 2023/3/23 9:36, Xuan Zhuo wrote:
> On Wed, 22 Mar 2023 16:22:18 +0800, Yunsheng Lin <linyunsheng@xxxxxxxxxx> wrote:
>> On 2023/3/22 11:03, Xuan Zhuo wrote:
>>> In the xdp implementation of virtio-net mergeable, it always checks
>>> whether two page is used and a page is selected to release. This is
>>> complicated for the processing of action, and be careful.
>>>
>>> In the entire process, we have such principles:
>>> * If xdp_page is used (PASS, TX, Redirect), then we release the old
>>> page.
>>> * If it is a drop case, we will release two. The old page obtained from
>>> buf is release inside err_xdp, and xdp_page needs be relased by us.
>>>
>>> But in fact, when we allocate a new page, we can release the old page
>>> immediately. Then just one is using, we just need to release the new
>>> page for drop case. On the drop path, err_xdp will release the variable
>>> "page", so we only need to let "page" point to the new xdp_page in
>>> advance.
>>>
>>> Signed-off-by: Xuan Zhuo <xuanzhuo@xxxxxxxxxxxxxxxxx>
>>> ---
>>> drivers/net/virtio_net.c | 15 ++++++---------
>>> 1 file changed, 6 insertions(+), 9 deletions(-)
>>>
>>> diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
>>> index e2560b6f7980..4d2bf1ce0730 100644
>>> --- a/drivers/net/virtio_net.c
>>> +++ b/drivers/net/virtio_net.c
>>> @@ -1245,6 +1245,9 @@ static struct sk_buff *receive_mergeable(struct net_device *dev,
>>> if (!xdp_page)
>>> goto err_xdp;
>>> offset = VIRTIO_XDP_HEADROOM;
>>> +
>>> + put_page(page);
>>
>> the error handling of xdp_linearize_page() does not seems self contained.
>> Does it not seem better：
>> 1. if xdp_linearize_page() succesed, call put_page() for first buffer just
>> as put_page() is call for other buffer
>> 2. or call virtqueue_get_buf() and put_page() for all the buffer of the packet
>> so the error handling is not needed outside the virtqueue_get_buf().
>>
>> In that case, it seems we can just do below without xdp_page:
>> page = xdp_linearize_page(rq, num_buf, page, ...);
>
>
> This does look better.
>
> In fact, we already have vq reset, we can load XDP based on vq reset.
> In this way, we can run without xdp_linearize_page.
For compatibility, it is still needed, right?
>
>
>>
>>
>>> + page = xdp_page;
>>> } else if (unlikely(headroom < virtnet_get_headroom(vi))) {
>>> xdp_room = SKB_DATA_ALIGN(VIRTIO_XDP_HEADROOM +
>>> sizeof(struct skb_shared_info));
>>> @@ -1259,6 +1262,9 @@ static struct sk_buff *receive_mergeable(struct net_device *dev,
>>> page_address(page) + offset, len);
>>> frame_sz = PAGE_SIZE;
>>> offset = VIRTIO_XDP_HEADROOM;
>>> +
>>> + put_page(page);
>>> + page = xdp_page;
>>
>> It seems we can limit the scope of xdp_page in this "else if" block.
>>
>>> } else {
>>> xdp_page = page;
>>> }
>>
>> It seems the above else block is not needed anymore.
>
> Yes, the follow-up patch has this optimization.
Isn't refoctor patch supposed to be self-contianed too, instead of
depending on follow-up patch?
