Re: [PATCH net-next] net: mana: Add page pool for RX buffers

[Jesper Dangaard Brouer]

On 14/07/2023 14.51, Haiyang Zhang wrote:
> > -----Original Message-----
> > From: Jesper Dangaard Brouer <jbrouer@xxxxxxxxxx>
> > On 14/07/2023 05.53, Jakub Kicinski wrote:
> > > On Thu, 13 Jul 2023 14:48:45 +0000 Haiyang Zhang wrote:
> > > > Add page pool for RX buffers for faster buffer cycle and reduce CPU
> > > > usage.
> > > >
> > > > Get an extra ref count of a page after allocation, so after upper
> > > > layers put the page, it's still referenced by the pool. We can reuse
> > > > it as RX buffer without alloc a new page.
> > >
> > > Please use the real page_pool API from include/net/page_pool.h
> > > We've moved past every driver reinventing the wheel, sorry.
> >
> > +1
> >
> > Quoting[1]: Documentation/networking/page_pool.rst
> >
> >    Basic use involves replacing alloc_pages() calls with the
> > page_pool_alloc_pages() call.
> >    Drivers should use page_pool_dev_alloc_pages() replacing
> > dev_alloc_pages().
>   
> Thank Jakub and Jesper for the reviews.
> I'm aware of the page_pool.rst doc, and actually tried it before this
> patch, but I got lower perf. If I understand correctly, we should call
> page_pool_release_page() before passing the SKB to napi_gro_receive().
>
> I found the page_pool_dev_alloc_pages() goes through the slow path,
> because the page_pool_release_page() let the page leave the pool.
>
> Do we have to call page_pool_release_page() before passing the SKB
> to napi_gro_receive()? Any better way to recycle the pages from the
> upper layer of non-XDP case?

Today SKB "upper layers" can recycle page_pool backed packet data/page.

Just use skb_mark_for_recycle(skb), then you don't need 
page_pool_release_page().

I guess, we should update the documentation, mentioning this.

--Jesper