netdev - Re: [PATCH net-next 2/2] virtio-net: fix the XDP truesize calculation for mergeable buffers

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Date:   Wed, 6 May 2020 16:21:15 +0800
From:   Jason Wang <jasowang@...hat.com>
To:     "Michael S. Tsirkin" <mst@...hat.com>
Cc:     virtualization@...ts.linux-foundation.org, netdev@...r.kernel.org,
        linux-kernel@...r.kernel.org, bpf@...r.kernel.org,
        Jesper Dangaard Brouer <brouer@...hat.com>
Subject: Re: [PATCH net-next 2/2] virtio-net: fix the XDP truesize calculation
 for mergeable buffers


On 2020/5/6 下午3:37, Michael S. Tsirkin wrote:
> 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@...hat.com>
>> Signed-off-by: Jason Wang<jasowang@...hat.com>
> Seems too aggressive, we do not use up the whole page for the size.
>
>
>

For XDP yes, we do:

static unsigned int get_mergeable_buf_len(struct receive_queue *rq,
                       struct ewma_pkt_len *avg_pkt_len,
                       unsigned int room)
{
     const size_t hdr_len = sizeof(struct virtio_net_hdr_mrg_rxbuf);
     unsigned int len;

     if (room)
         return PAGE_SIZE - room;

...

Thanks