Re: [PATCH net-next v12 06/13] page_pool: devmem support

[Pavel Begunkov]

On 6/21/24 19:48, Mina Almasry wrote:
> On Mon, Jun 17, 2024 at 7:17 AM Pavel Begunkov <asml.silence@xxxxxxxxx> wrote:
...
> > >    static inline unsigned long netmem_to_pfn(netmem_ref netmem)
> > >    {
> > > +     if (netmem_is_net_iov(netmem))
> > > +             return 0;
> >
> > IIRC 0 is a valid pfn. Not much of a concern since it's
> > used only for tracing, but might make sense to pass some
> > invalid pfn if there is one
>
> AFAIU all non-negative pfns are technically valid pfns if the machine
> is big enough.
>
> I could have this function return long long instead of unsigned long
> so I can return a negative number for errors, and then cast to
> unsigned long when I figure out it's actually a pfn. Seemed like such
> a hassle especially since the call site is just tracing that I figured
> it's not that worth it.

Yeah, sounds like an overkill for tracing

> > > +
> > >        return page_to_pfn(netmem_to_page(netmem));
> > >    }
> > ...
> > >    static inline netmem_ref netmem_compound_head(netmem_ref netmem)
> > >    {
> > > +     /* niov are never compounded */
> > > +     if (netmem_is_net_iov(netmem))
> > > +             return netmem;
> > > +
> > >        return page_to_netmem(compound_head(netmem_to_page(netmem)));
> > >    }
> > >
> > > +static inline void *netmem_address(netmem_ref netmem)
> >
> > I don't think it's used anywhere, do I miss it?
>
> Ah, It's used by the GVE devmem implementation:
> https://github.com/mina/linux/commit/da89baa81873d457cbf7b49ee6b4f0d66855b205
>
> I could leave it out of this patch, then add it with the follow up GVE
> devmem implementation, but I figured almost for sure drivers are going
> to need this eventually, and it's small, so just put it here.

Either way is fine by me, checking the function is not leftovers


--
Pavel Begunkov