Subject: Re: [RFC PATCH 3/3] net: ethernet: ti: cpsw: add XDP support

From: Ilias Apalodimas <[email-masked]>
Date: Fri, 19 Apr 2019 11:31:56 +0300

Hi Ivan, 

> +static struct page *cpsw_alloc_page(struct cpsw_common *cpsw)
> +{
> +	struct page_pool *pool = cpsw->rx_page_pool;
> +	struct page *page;
> +	int i = 0;
> +
> +	do {
> +		page = page_pool_dev_alloc_pages(pool);
> +		if (!page)
> +			return NULL;
> +
> +		/* skip pages used by skb netstack */
I think the comment here is wrong and might confuse people.
The page ref cnt is 1, which means the packet was *processed* and netstack is
done with it, hence you can re-use it.
If it's !=1 then you correctly unmap the buffer and decrease the ref cnt, so it
will eventually be freed and not returned to the pool, right?
> +		if (page_ref_count(page) == 1)
> +			break;
> +
> +		/* it's a pitty, but free page */
> +		page_pool_recycle_direct(pool, page);
> +	} while (++i < descs_pool_size);
> +
> +	return page;
> +}
> +
 
 /Ilias