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

Dan Williams
2021-04-24T00:16:22Z

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