Re: [PATCH v2] mm: remove PageTransCompound()

["David Hildenbrand (Arm)" <david@kernel.org>]

On 6/18/26 13:35, Kefeng Wang wrote:
> Remove the last user of PageTransCompound() in ksm and
> get rid of PageTransCompound().
> 
> Signed-off-by: Kefeng Wang <wangkefeng.wang@huawei.com>
> ---
> v2:
> - use more folio in cmp_and_merge_page(), suggested by David
> 
>  include/linux/page-flags.h | 14 --------------
>  mm/ksm.c                   | 17 +++++++++--------
>  2 files changed, 9 insertions(+), 22 deletions(-)
> 
> diff --git a/include/linux/page-flags.h b/include/linux/page-flags.h
> index 7223f6f4e2b4..7a863572adce 100644
> --- a/include/linux/page-flags.h
> +++ b/include/linux/page-flags.h
> @@ -879,20 +879,6 @@ FOLIO_FLAG_FALSE(partially_mapped)
>  
>  #define PG_head_mask ((1UL << PG_head))
>  
> -#ifdef CONFIG_TRANSPARENT_HUGEPAGE
> -/*
> - * PageTransCompound returns true for both transparent huge pages
> - * and hugetlbfs pages, so it should only be called when it's known
> - * that hugetlbfs pages aren't involved.
> - */
> -static inline int PageTransCompound(const struct page *page)
> -{
> -	return PageCompound(page);
> -}
> -#else
> -TESTPAGEFLAG_FALSE(TransCompound, transcompound)
> -#endif
> -
>  #if defined(CONFIG_MEMORY_FAILURE) && defined(CONFIG_TRANSPARENT_HUGEPAGE)
>  /*
>   * PageHasHWPoisoned indicates that at least one subpage is hwpoisoned in the
> diff --git a/mm/ksm.c b/mm/ksm.c
> index 7d5b76478f0b..41ab25aa2a82 100644
> --- a/mm/ksm.c
> +++ b/mm/ksm.c
> @@ -2327,23 +2327,24 @@ static void cmp_and_merge_page(struct page *page, struct ksm_rmap_item *rmap_ite
>  	tree_rmap_item =
>  		unstable_tree_search_insert(rmap_item, page, &tree_page);
>  	if (tree_rmap_item) {
> +		struct folio *tree_folio;
>  		bool split;
>  
>  		kfolio = try_to_merge_two_pages(rmap_item, page,
>  						tree_rmap_item, tree_page);
> +		tree_folio = page_folio(tree_page);
>  		/*
> -		 * If both pages we tried to merge belong to the same compound
> -		 * page, then we actually ended up increasing the reference
> -		 * count of the same compound page twice, and split_huge_page
> -		 * failed.
> +		 * If both pages we tried to merge belong to the same (large)
> +		 * folio, then we actually ended up increasing the reference
> +		 * count of the same folio twice, and split_huge_page failed.
> +		 *
>  		 * Here we set a flag if that happened, and we use it later to
> -		 * try split_huge_page again. Since we call put_page right
> +		 * try split_huge_page again. Since we call folio_put() right
>  		 * afterwards, the reference count will be correct and
>  		 * split_huge_page should succeed.
>  		 */
> -		split = PageTransCompound(page)
> -			&& compound_head(page) == compound_head(tree_page);
> -		put_page(tree_page);
> +		split = folio == tree_folio;
> +		folio_put(tree_folio);
>  		if (kfolio) {
>  			/*
>  			 * The pages were successfully merged: insert new

Thanks!

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

-- 
Cheers,

David