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

[Ivan Khoronzhuk]

On Fri, Apr 19, 2019 at 11:31:56AM +0300, Ilias Apalodimas wrote:
> 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?
It's compensation substitution for page_pool support in skb netsack.
And should be considered in combine with:

skb = build_skb(xmeta, cpsw_rxbuf_total_len(pkt_size));
...
page_pool_recycle_direct(pool, page);
page_ref_inc(page);
netif_receive_skb(skb);

Here order is important.

I will correct comments in final version (w/o overloading) ofc, leaving
thinking environment for people. I think it's fair enough about this.

> > +		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

--
Regards,
Ivan Khoronzhuk