Re: [PATCH] mm/huge_memory: merge uniform_split_supported() and non_uniform_split_supported()

Dev Jain
2025-11-03T09:05:03Z

On 01/11/25 7:41 am, Wei Yang wrote:
> The functions uniform_split_supported() and
> non_uniform_split_supported() share significantly similar logic.
>
> The only functional difference is that uniform_split_supported()
> includes an additional check on the requested @new_order before
> proceeding with further validation.
>
> This commit unifies the logic by introducing a new variable,
> @need_check, which is conditionally set based on whether a uniform
> split is requested. This allows us to merge the two functions into
> a single, combined helper, removing redundant code and simplifying
> the split support checking mechanism.
>
> Signed-off-by: Wei Yang <richard.weiyang@gmail.com>
> Cc: Zi Yan <ziy@nvidia.com>
> ---
> include/linux/huge_mm.h | 8 +++---
> mm/huge_memory.c | 55 +++++++++++------------------------------
> 2 files changed, 18 insertions(+), 45 deletions(-)
>
> diff --git a/include/linux/huge_mm.h b/include/linux/huge_mm.h
> index cbb2243f8e56..79343809a7be 100644
> --- a/include/linux/huge_mm.h
> +++ b/include/linux/huge_mm.h
> @@ -369,10 +369,8 @@ int __split_huge_page_to_list_to_order(struct page *page, struct list_head *list
> unsigned int new_order, bool unmapped);
> int min_order_for_split(struct folio *folio);
> int split_folio_to_list(struct folio *folio, struct list_head *list);
> -bool uniform_split_supported(struct folio *folio, unsigned int new_order,
> - bool warns);
> -bool non_uniform_split_supported(struct folio *folio, unsigned int new_order,
> - bool warns);
> +bool folio_split_supported(struct folio *folio, unsigned int new_order,
> + bool uniform_split, bool warns);
> int folio_split(struct folio *folio, unsigned int new_order, struct page *page,
> struct list_head *list);
>
> @@ -403,7 +401,7 @@ static inline int split_huge_page_to_order(struct page *page, unsigned int new_o
> static inline int try_folio_split_to_order(struct folio *folio,
> struct page *page, unsigned int new_order)
> {
> - if (!non_uniform_split_supported(folio, new_order, /* warns= */ false))
> + if (!folio_split_supported(folio, new_order, /* uniform_split = */ false, /* warns= */ false))
> return split_huge_page_to_order(&folio->page, new_order);
> return folio_split(folio, new_order, page, NULL);
> }
> diff --git a/mm/huge_memory.c b/mm/huge_memory.c
> index d1fa0d2d9b44..f6d2cb2a5ca0 100644
> --- a/mm/huge_memory.c
> +++ b/mm/huge_memory.c
> @@ -3673,55 +3673,34 @@ static int __split_unmapped_folio(struct folio *folio, int new_order,
> return 0;
> }
>
> -bool non_uniform_split_supported(struct folio *folio, unsigned int new_order,
> - bool warns)
> +bool folio_split_supported(struct folio *folio, unsigned int new_order,
> + bool uniform_split, bool warns)
> {
> - if (folio_test_anon(folio)) {
> - /* order-1 is not supported for anonymous THP. */
> - VM_WARN_ONCE(warns && new_order == 1,
> - "Cannot split to order-1 folio");
> - return new_order != 1;
> - } else if (IS_ENABLED(CONFIG_READ_ONLY_THP_FOR_FS) &&
> - !mapping_large_folio_support(folio->mapping)) {
> - /*
> - * No split if the file system does not support large folio.
> - * Note that we might still have THPs in such mappings due to
> - * CONFIG_READ_ONLY_THP_FOR_FS. But in that case, the mapping
> - * does not actually support large folios properly.
> - */
> - VM_WARN_ONCE(warns,
> - "Cannot split file folio to non-0 order");
> - return false;
> - }
> -
> - /* Only swapping a whole PMD-mapped folio is supported */
> - if (folio_test_swapcache(folio)) {
> - VM_WARN_ONCE(warns,
> - "Cannot split swapcache folio to non-0 order");
> - return false;
> - }
> + bool need_check = uniform_split ? new_order : true;
>
> - return true;
> -}
> -
> -/* See comments in non_uniform_split_supported() */
> -bool uniform_split_supported(struct folio *folio, unsigned int new_order,
> - bool warns)
> -{
> if (folio_test_anon(folio)) {
> + /* order-1 is not supported for anonymous THP. */
> VM_WARN_ONCE(warns && new_order == 1,
> "Cannot split to order-1 folio");
> return new_order != 1;
> - } else if (new_order) {
> + } else if (need_check) {
> if (IS_ENABLED(CONFIG_READ_ONLY_THP_FOR_FS) &&
> !mapping_large_folio_support(folio->mapping)) {
> + /*
> + * No split if the file system does not support large
> + * folio. Note that we might still have THPs in such
> + * mappings due to CONFIG_READ_ONLY_THP_FOR_FS. But in
> + * that case, the mapping does not actually support
> + * large folios properly.
> + */
> VM_WARN_ONCE(warns,
> "Cannot split file folio to non-0 order");
> return false;
> }
> }
>
> - if (new_order && folio_test_swapcache(folio)) {
> + /* Only swapping a whole PMD-mapped folio is supported */
> + if (need_check && folio_test_swapcache(folio)) {
> VM_WARN_ONCE(warns,
> "Cannot split swapcache folio to non-0 order");
> return false;
> @@ -3779,11 +3758,7 @@ static int __folio_split(struct folio *folio, unsigned int new_order,
> if (new_order >= old_order)
> return -EINVAL;
>
> - if (uniform_split && !uniform_split_supported(folio, new_order, true))
> - return -EINVAL;
> -
> - if (!uniform_split &&
> - !non_uniform_split_supported(folio, new_order, true))
> + if (!folio_split_supported(folio, new_order, uniform_split, /* warn = */ true))
> return -EINVAL;
>
> is_hzp = is_huge_zero_folio(folio);

@Zi, I am confused on the code. Is there something stopping us from passing a zero new_order to
non_uniform_split_supported()?