Re: [PATCH v5 01/14] mm/khugepaged: remove READ_ONLY_THP_FOR_FS check

[Zi Yan <ziy@nvidia.com>]

On 29 Apr 2026, at 23:29, Zi Yan wrote:

> collapse_file() requires FSes supporting large folio with at least
> PMD_ORDER, so replace the READ_ONLY_THP_FOR_FS check with that.
> MADV_COLLAPSE ignores shmem huge config, so exclude the check for shmem.
>
> While at it, replace VM_BUG_ON with VM_WARN_ON_ONCE.
>
> Add a helper function mapping_pmd_folio_support() for FSes supporting large
> folio with at least PMD_ORDER.
>
> Signed-off-by: Zi Yan <ziy@nvidia.com>
> Reviewed-by: Lance Yang <lance.yang@linux.dev>
> Reviewed-by: Baolin Wang <baolin.wang@linux.alibaba.com>
> ---
>  include/linux/pagemap.h | 26 ++++++++++++++++++++++++++
>  mm/khugepaged.c         | 10 ++++++++--
>  2 files changed, 34 insertions(+), 2 deletions(-)
>
> diff --git a/include/linux/pagemap.h b/include/linux/pagemap.h
> index 1f50991b43e3b..1fed3414fe9b8 100644
> --- a/include/linux/pagemap.h
> +++ b/include/linux/pagemap.h
> @@ -513,6 +513,32 @@ static inline bool mapping_large_folio_support(const struct address_space *mappi
>  	return mapping_max_folio_order(mapping) > 0;
>  }
>
> +/**
> + * mapping_pmd_folio_support() - Check if a mapping support PMD-sized folio
> + * @mapping: The address_space
> + *
> + * Some file supports large folio but does not support as large as PMD order.
> + * If a PMD-sized pagecache folio is attempted to be created on a filesystem,
> + * this check needs to be performed first.
> + *
> + * Return: true - PMD-sized folio is supported, false - PMD-sized folio is not
> + * supported.
> + */
> +#ifdef CONFIG_TRANSPARENT_HUGEPAGE
> +static inline bool mapping_pmd_folio_support(const struct address_space *mapping)
> +{
> +	/* AS_FOLIO_ORDER is only reasonable for pagecache folios */
> +	VM_WARN_ON_ONCE((unsigned long)mapping & FOLIO_MAPPING_ANON);
> +
> +	return mapping_max_folio_order(mapping) >= PMD_ORDER;

Hi Andrew,

Can you help apply the fixup below? It addresses the concern raised by
Nico and Lance[1]. Thanks.

[1] https://lore.kernel.org/all/aa778cfc-b7f8-4100-89bb-d2b2ef8e1138@redhat.com/

From 9c1749df6516c06b1628ac7804bc7a6ab5709f37 Mon Sep 17 00:00:00 2001
From: Zi Yan <ziy@nvidia.com>
Date: Thu, 7 May 2026 02:02:28 -0400
Subject: [PATCH] fix mapping_pmd_folio_support() to represent its exact
 meaning

Signed-off-by: Zi Yan <ziy@nvidia.com>
---
 include/linux/pagemap.h | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/include/linux/pagemap.h b/include/linux/pagemap.h
index c6a4ecd3d6ed1..52895896f3357 100644
--- a/include/linux/pagemap.h
+++ b/include/linux/pagemap.h
@@ -530,7 +530,8 @@ static inline bool mapping_pmd_folio_support(const struct address_space *mapping
 	/* AS_FOLIO_ORDER is only reasonable for pagecache folios */
 	VM_WARN_ON_ONCE((unsigned long)mapping & FOLIO_MAPPING_ANON);

-	return mapping_max_folio_order(mapping) >= PMD_ORDER;
+	return mapping_min_folio_order(mapping) <= PMD_ORDER &&
+	       mapping_max_folio_order(mapping) >= PMD_ORDER
 }
 #else
 static inline bool mapping_pmd_folio_support(const struct address_space *mapping)
-- 
2.53.0


Best Regards,
Yan, Zi