Re: [PATCH v1 06/10] mm/huge_memory: remove folio split check for READ_ONLY_THP_FOR_FS

[Lance Yang <lance.yang@linux.dev>]

On Thu, Mar 26, 2026 at 09:42:51PM -0400, Zi Yan wrote:
>Without READ_ONLY_THP_FOR_FS, large file-backed folios cannot be created by
>a FS without large folio support. The check is no longer needed.
>
>Signed-off-by: Zi Yan <ziy@nvidia.com>
>---
> mm/huge_memory.c | 22 ----------------------
> 1 file changed, 22 deletions(-)
>
>diff --git a/mm/huge_memory.c b/mm/huge_memory.c
>index 1da1467328a3..30eddcbf86f1 100644
>--- a/mm/huge_memory.c
>+++ b/mm/huge_memory.c
>@@ -3732,28 +3732,6 @@ int folio_check_splittable(struct folio *folio, unsigned int new_order,
> 		/* order-1 is not supported for anonymous THP. */
> 		if (new_order == 1)
> 			return -EINVAL;

While you're at it, could we also collapse this block above into a
single condition:

	/* order-1 is not supported for anonymous THP. */
	if (folio_test_anon(folio) && new_order == 1)
		return -EINVAL;

Just saying. LGTM.

Reviewed-by: Lance Yang <lance.yang@linux.dev>


>-	} else if (split_type == SPLIT_TYPE_NON_UNIFORM || new_order) {
>-		if (IS_ENABLED(CONFIG_READ_ONLY_THP_FOR_FS) &&
>-		    !mapping_large_folio_support(folio->mapping)) {
>-			/*
>-			 * We can always split a folio down to a single page
>-			 * (new_order == 0) uniformly.
>-			 *
>-			 * For any other scenario
>-			 *   a) uniform split targeting a large folio
>-			 *      (new_order > 0)
>-			 *   b) any non-uniform split
>-			 * we must confirm that the file system supports large
>-			 * folios.
>-			 *
>-			 * Note that we might still have THPs in such
>-			 * mappings, which is created from khugepaged when
>-			 * CONFIG_READ_ONLY_THP_FOR_FS is enabled. But in that
>-			 * case, the mapping does not actually support large
>-			 * folios properly.
>-			 */
>-			return -EINVAL;
>-		}
> 	}
> 
> 	/*