Re: [PATCHv6 02/17] mm: Change the interface of prep_compound_tail()

David Hildenbrand (arm)
2026-02-04T16:14:21Z

On 2/2/26 16:56, Kiryl Shutsemau wrote:
> Instead of passing down the head page and tail page index, pass the tail
> and head pages directly, as well as the order of the compound page.
>
> This is a preparation for changing how the head position is encoded in
> the tail page.
>
> Signed-off-by: Kiryl Shutsemau <kas@kernel.org>
> Reviewed-by: Muchun Song <muchun.song@linux.dev>
> Reviewed-by: Zi Yan <ziy@nvidia.com>
> ---
> include/linux/page-flags.h | 4 +++-
> mm/hugetlb.c | 8 +++++---
> mm/internal.h | 12 ++++++------
> mm/mm_init.c | 2 +-
> mm/page_alloc.c | 2 +-
> 5 files changed, 16 insertions(+), 12 deletions(-)
>
> diff --git a/include/linux/page-flags.h b/include/linux/page-flags.h
> index f7a0e4af0c73..8a3694369e15 100644
> --- a/include/linux/page-flags.h
> +++ b/include/linux/page-flags.h
> @@ -865,7 +865,9 @@ static inline bool folio_test_large(const struct folio *folio)
> return folio_test_head(folio);
> }
>
> -static __always_inline void set_compound_head(struct page *page, struct page *head)
> +static __always_inline void set_compound_head(struct page *page,
> + const struct page *head,
> + unsigned int order)

Two tab indents please on second+ parameter list whenever you touch code.

> {
> WRITE_ONCE(page->compound_head, (unsigned long)head + 1);
> }
> diff --git a/mm/hugetlb.c b/mm/hugetlb.c
> index 6e855a32de3d..54ba7cd05a86 100644

[...]

> diff --git a/mm/internal.h b/mm/internal.h
> index d67e8bb75734..037ddcda25ff 100644
> --- a/mm/internal.h
> +++ b/mm/internal.h
> @@ -879,13 +879,13 @@ static inline void prep_compound_head(struct page *page, unsigned int order)
> INIT_LIST_HEAD(&folio->_deferred_list);
> }
>
> -static inline void prep_compound_tail(struct page *head, int tail_idx)
> +static inline void prep_compound_tail(struct page *tail,

Just wondering whether we should call this "struct page *page" for
consistency with set_compound_head().

Or alternatively, call it also "tail" in set_compound_head().

> + const struct page *head,
> + unsigned int order)

Two tab indent, then this fits into two lines in total.

> {
> - struct page *p = head + tail_idx;
> -
> - p->mapping = TAIL_MAPPING;
> - set_compound_head(p, head);
> - set_page_private(p, 0);
> + tail->mapping = TAIL_MAPPING;
> + set_compound_head(tail, head, order);
> + set_page_private(tail, 0);
> }
Only nits, in general LGTM

Acked-by: David Hildenbrand (arm) <david@kernel.org>

--
Cheers,

David