On 6/17/21 11:44 AM, Joao Martins wrote:
> Split the utility function prep_compound_page() into head and tail
> counterparts, and use them accordingly.
>
> This is in preparation for sharing the storage for / deduplicating
> compound page metadata.
>
> Signed-off-by: Joao Martins <joao.m.martins@xxxxxxxxxx>
> ---
> 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 8836e54721ae..95967ce55829 100644
> --- a/mm/page_alloc.c
> +++ b/mm/page_alloc.c
> @@ -741,24 +741,34 @@ void free_compound_page(struct page *page)
> free_the_page(page, compound_order(page));
> }
>
> +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);
When you rebase, you should notice this has been removed from
prep_compound_page as all tail pages should have zero ref count.
> + 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
>
I'll need something like this for demote hugetlb page fuinctionality
when the pages being demoted have been optimized for minimal vmemmap
usage.
Acked-by: Mike Kravetz <mike.kravetz@xxxxxxxxxx>
--
Mike Kravetz
