On Tue, Jul 15, 2025 at 3:36 AM Pavel Begunkov <asml.silence@xxxxxxxxx> wrote:
>
> On 7/14/25 20:37, Mina Almasry wrote:
> > On Mon, Jul 14, 2025 at 5:01 AM Byungchul Park <byungchul@xxxxxx> wrote:
> ...>> +static inline struct netmem_desc *pp_page_to_nmdesc(struct page *page)
> >> +{
> >> + DEBUG_NET_WARN_ON_ONCE(!page_pool_page_is_pp(page));
> >> +
> >> + /* XXX: How to extract netmem_desc from page must be changed,
> >> + * once netmem_desc no longer overlays on page and will be
> >> + * allocated through slab.
> >> + */
> >> + return (struct netmem_desc *)page;
> >> +}
> >> +
> >
> > Same thing. Do not create a generic looking pp_page_to_nmdesc helper
> > which does not check that the page is the correct type. The
> > DEBUG_NET... is not good enough.
> >
> > You don't need to add a generic helper here. There is only one call
> > site. Open code this in the callsite. The one callsite is marked as
> > unsafe, only called by code that knows that the netmem is specifically
> > a pp page. Open code this in the unsafe callsite, instead of creating
> > a generic looking unsafe helper and not even documenting it's unsafe.
> >
> >> /**
> >> * __netmem_get_pp - unsafely get pointer to the &page_pool backing @netmem
> >> * @netmem: netmem reference to get the pointer from
> >> @@ -280,7 +291,7 @@ static inline struct net_iov *__netmem_clear_lsb(netmem_ref netmem)
> >> */
> >> static inline struct page_pool *__netmem_get_pp(netmem_ref netmem)
> >> {
> >> - return __netmem_to_page(netmem)->pp;
> >> + return pp_page_to_nmdesc(__netmem_to_page(netmem))->pp;
> >> }
> >
> > This makes me very sad. Casting from netmem -> page -> nmdesc...
>
> The function is not used, and I don't think the series adds any
> new users? It can be killed then. It's a horrible function anyway,
> would be much better to have a variant taking struct page * if
> necessary.
>
> > Instead, we should be able to go from netmem directly to nmdesc. I
> > would suggest rename __netmem_clear_lsb to netmem_to_nmdesc and have
> > it return netmem_desc instead of net_iov. Then use it here.
>
> Glad you liked the diff I suggested :) In either case, seems
> like it's not strictly necessary for this iteration as
> __netmem_get_pp() should be killed, and the rest of patches work
> directly with pages.
Good catch, in that case lets just delete __netmem_get_pp and there is
no need to add a netmem_nmdesc unless we find some other call site
that needs it.
--
Thanks,
Mina
