Re: [PATCH v2 3/5] mm: add static PMD zero page

["Pankaj Raghav (Samsung)" <kernel@pankajraghav.com>]

> > Then, we'd only need a config option to allow for that to happen.
> 
> Something incomplete and very hacky just to give an idea. It would try allocating
> it if there is actual code running that would need it, and then have it
> stick around forever.
> 
Thanks a lot for this David :) I think this is a much better idea and
reduces the amount code and reuse the existing infrastructure.

I will try this approach in the next version.

<snip>
> +       /*
> +        * Our raised reference will prevent the shrinker from ever having
> +        * success -> static.
> +        */
> +       if (atomic_read(&huge_zero_folio_is_static))
> +               return huge_zero_folio;
> +       /* TODO: memblock allocation if buddy is not up yet? Or Reject that earlier. */

Do we need memblock allocation? At least the use cases I forsee for
static pmd zero page are all after the mm is up. So I don't see why we
need to allocate it via memblock.

> +       if (!get_huge_zero_page())
> +               return NULL;
> +       if (atomic_cmpxchg(&huge_zero_folio_is_static, 0, 1) != 0)
> +               put_huge_zero_page();
> +       return huge_zero_folio;
> +
> +}
> +#endif /* CONFIG_STATIC_HUGE_ZERO_FOLIO */
> +
>  static unsigned long shrink_huge_zero_page_count(struct shrinker *shrink,
>                                         struct shrink_control *sc)
>  {
> 

--
Pankaj