Re: [PATCH v1 02/11] mm/page_alloc: split prep_compound_page into head and tail subparts

[Dan Williams <dan.j.williams@intel.com>]

On Thu, Mar 25, 2021 at 4:10 PM Joao Martins <joao.m.martins@oracle.com> wrote:
>
> Split the utility function prep_compound_page() into head and tail
> counterparts, and use them accordingly.

To make this patch stand alone better lets add another sentence:

"This is in preparation for sharing the storage for / deduplicating
compound page metadata."

Other than that, looks good to me.

>
> Signed-off-by: Joao Martins <joao.m.martins@oracle.com>
> ---
>  mm/page_alloc.c | 32 +++++++++++++++++++++-----------
>  1 file changed, 21 insertions(+), 11 deletions(-)
>
> diff --git a/mm/page_alloc.c b/mm/page_alloc.c
> index c53fe4fa10bf..43dd98446b0b 100644
> --- a/mm/page_alloc.c
> +++ b/mm/page_alloc.c
> @@ -692,24 +692,34 @@ void free_compound_page(struct page *page)
>         __free_pages_ok(page, compound_order(page), FPI_NONE);
>  }
>
> +static void prep_compound_head(struct page *page, unsigned int order)
> +{
> +       set_compound_page_dtor(page, COMPOUND_PAGE_DTOR);
> +       set_compound_order(page, order);
> +       atomic_set(compound_mapcount_ptr(page), -1);
> +       if (hpage_pincount_available(page))
> +               atomic_set(compound_pincount_ptr(page), 0);
> +}
> +
> +static void prep_compound_tail(struct page *head, int tail_idx)
> +{
> +       struct page *p = head + tail_idx;
> +
> +       set_page_count(p, 0);
> +       p->mapping = TAIL_MAPPING;
> +       set_compound_head(p, head);
> +}
> +
>  void prep_compound_page(struct page *page, unsigned int order)
>  {
>         int i;
>         int nr_pages = 1 << order;
>
>         __SetPageHead(page);
> -       for (i = 1; i < nr_pages; i++) {
> -               struct page *p = page + i;
> -               set_page_count(p, 0);
> -               p->mapping = TAIL_MAPPING;
> -               set_compound_head(p, page);
> -       }
> +       for (i = 1; i < nr_pages; i++)
> +               prep_compound_tail(page, i);
>
> -       set_compound_page_dtor(page, COMPOUND_PAGE_DTOR);
> -       set_compound_order(page, order);
> -       atomic_set(compound_mapcount_ptr(page), -1);
> -       if (hpage_pincount_available(page))
> -               atomic_set(compound_pincount_ptr(page), 0);
> +       prep_compound_head(page, order);
>  }
>
>  #ifdef CONFIG_DEBUG_PAGEALLOC
> --
> 2.17.1
>