Re: [PATCH net-next v9] virtio_net: add page_pool support for buffer allocation

[Vishwanath Seshagiri <vishs@meta.com>]

On 3/2/26 3:57 PM, Michael S. Tsirkin wrote:
>> @@ -2666,32 +2603,25 @@ static void receive_buf(struct virtnet_info *vi, struct receive_queue *rq,
>>   static int add_recvbuf_small(struct virtnet_info *vi, struct receive_queue *rq,
>>   			     gfp_t gfp)
>>   {
>> -	char *buf;
>>   	unsigned int xdp_headroom = virtnet_get_headroom(vi);
>>   	void *ctx = (void *)(unsigned long)xdp_headroom;
>> -	int len = vi->hdr_len + VIRTNET_RX_PAD + GOOD_PACKET_LEN + xdp_headroom;
>> +	unsigned int len = vi->hdr_len + VIRTNET_RX_PAD + GOOD_PACKET_LEN + xdp_headroom;
>> +	char *buf;
>>   	int err;
>>   
>>   	len = SKB_DATA_ALIGN(len) +
>>   	      SKB_DATA_ALIGN(sizeof(struct skb_shared_info));
>>   
>> -	if (unlikely(!skb_page_frag_refill(len, &rq->alloc_frag, gfp)))
>> -		return -ENOMEM;
>> -
>> -	buf = virtnet_rq_alloc(rq, len, gfp);
>> +	buf = page_pool_alloc_va(rq->page_pool, &len, gfp);
> 
> So this can increase len (for end of page accounting).
> 
>>   	if (unlikely(!buf))
>>   		return -ENOMEM;
>>   
>>   	buf += VIRTNET_RX_PAD + xdp_headroom;
>>   
>> -	virtnet_rq_init_one_sg(rq, buf, vi->hdr_len + GOOD_PACKET_LEN);
>> -
>> -	err = virtqueue_add_inbuf_premapped(rq->vq, rq->sg, 1, buf, ctx, gfp);
>> -	if (err < 0) {
>> -		virtnet_rq_unmap(rq, buf, 0);
>> -		put_page(virt_to_head_page(buf));
>> -	}
>> +	err = virtnet_rq_submit(rq, buf, vi->hdr_len + GOOD_PACKET_LEN, ctx, gfp);
>>   
>> +	if (err < 0)
>> +		page_pool_put_page(rq->page_pool, virt_to_head_page(buf), -1, false);
>>   	return err;
> 
> 
> But len is ignored in the rest of the function.
> Will this not under-account truesize?
> 
> 
> If it's intentional maybe add a comment explaining why?

It isn't intentional. I will add a separate alloc_len variable for the
page_pool_alloc_va() in v10.

> 
>>   }
>>