netdev - Re: [PATCH v2 17/24] page_pool: Convert page_pool_return_skb

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Date:   Fri, 6 Jan 2023 16:53:00 +0000
From:   Matthew Wilcox <willy@...radead.org>
To:     Jesper Dangaard Brouer <jbrouer@...hat.com>
Cc:     Jesper Dangaard Brouer <hawk@...nel.org>,
        Ilias Apalodimas <ilias.apalodimas@...aro.org>,
        brouer@...hat.com, netdev@...r.kernel.org, linux-mm@...ck.org,
        Shakeel Butt <shakeelb@...gle.com>
Subject: Re: [PATCH v2 17/24] page_pool: Convert page_pool_return_skb_page()
 to use netmem

On Fri, Jan 06, 2023 at 04:49:12PM +0100, Jesper Dangaard Brouer wrote:
> On 05/01/2023 22.46, Matthew Wilcox (Oracle) wrote:
> > This function accesses the pagepool members of struct page directly,
> > so it needs to become netmem.  Add page_pool_put_full_netmem() and
> > page_pool_recycle_netmem().
> > 
> > Signed-off-by: Matthew Wilcox (Oracle) <willy@...radead.org>
> > ---
> >   include/net/page_pool.h | 14 +++++++++++++-
> >   net/core/page_pool.c    | 13 ++++++-------
> >   2 files changed, 19 insertions(+), 8 deletions(-)
> > 
> > diff --git a/include/net/page_pool.h b/include/net/page_pool.h
> > index fbb653c9f1da..126c04315929 100644
> > --- a/include/net/page_pool.h
> > +++ b/include/net/page_pool.h
> > @@ -464,10 +464,16 @@ static inline void page_pool_put_page(struct page_pool *pool,
> >   }
> >   /* Same as above but will try to sync the entire area pool->max_len */
> > +static inline void page_pool_put_full_netmem(struct page_pool *pool,
> > +		struct netmem *nmem, bool allow_direct)
> > +{
> > +	page_pool_put_netmem(pool, nmem, -1, allow_direct);
> > +}
> > +
> >   static inline void page_pool_put_full_page(struct page_pool *pool,
> >   					   struct page *page, bool allow_direct)
> >   {
> > -	page_pool_put_page(pool, page, -1, allow_direct);
> > +	page_pool_put_full_netmem(pool, page_netmem(page), allow_direct);
> >   }
> >   /* Same as above but the caller must guarantee safe context. e.g NAPI */
> > @@ -477,6 +483,12 @@ static inline void page_pool_recycle_direct(struct page_pool *pool,
> >   	page_pool_put_full_page(pool, page, true);
> >   }
> > +static inline void page_pool_recycle_netmem(struct page_pool *pool,
> > +					    struct netmem *nmem)
> > +{
> > +	page_pool_put_full_netmem(pool, nmem, true);
>                                               ^^^^
> 
> It is not clear in what context page_pool_recycle_netmem() will be used,
> but I think the 'true' (allow_direct=true) might be wrong here.
> 
> It is only in limited special cases (RX-NAPI context) we can allow
> direct return to the RX-alloc-cache.

Mmm.  It's a c'n'p of the previous function:

static inline void page_pool_recycle_direct(struct page_pool *pool,
                                            struct page *page)
{
        page_pool_put_full_page(pool, page, true);
}

so perhaps it's just badly named?