Re: [PATCH] mm: madvise: make MADV_NOHUGEPAGE a no-op if !THP

[James Houghton <jthoughton@google.com>]

On Thu, May 8, 2025 at 3:20 AM Ignacio Moreno Gonzalez via B4 Relay
<devnull+Ignacio.MorenoGonzalez.kuka.com@kernel.org> wrote:
>
> From: Ignacio Moreno Gonzalez <Ignacio.MorenoGonzalez@kuka.com>
>
> VM_NOHUGEPAGE is a no-op if CONFIG_TRANSPARENT_HUGEPAGE is disabled. So
> it makes no sense to return an error when calling madvise() with
> MADV_NOHUGEPAGE in that case.
>
> Suggested-by: Matthew Wilcox <willy@infradead.org>
> Signed-off-by: Ignacio Moreno Gonzalez <Ignacio.MorenoGonzalez@kuka.com>
> ---
> https://lore.kernel.org/linux-mm/20250502-map-map_stack-to-vm_nohugepage-only-if-thp-is-enabled-v1-1-113cc634cd51@kuka.com
>
> Here it is presented as a separate thread to avoid mixing stable and
> non-stable patches.
>
> This change makes calling madvise(addr, size, MADV_NOHUGEPAGE) on !THP
> kernels to return 0 instead of -EINVAL.
> ---
>  include/linux/huge_mm.h | 5 +++++
>  1 file changed, 5 insertions(+)
>
> diff --git a/include/linux/huge_mm.h b/include/linux/huge_mm.h
> index e893d546a49f464f7586db639fe216231f03651a..5fca742dc5ba784ffccea055b07247707d16cc67 100644
> --- a/include/linux/huge_mm.h
> +++ b/include/linux/huge_mm.h
> @@ -509,6 +509,8 @@ bool unmap_huge_pmd_locked(struct vm_area_struct *vma, unsigned long addr,
>
>  #else /* CONFIG_TRANSPARENT_HUGEPAGE */
>
> +#include <uapi/asm/mman.h>
> +
>  static inline bool folio_test_pmd_mappable(struct folio *folio)
>  {
>         return false;
> @@ -598,6 +600,9 @@ static inline bool unmap_huge_pmd_locked(struct vm_area_struct *vma,
>  static inline int hugepage_madvise(struct vm_area_struct *vma,
>                                    unsigned long *vm_flags, int advice)
>  {
> +       /* On a !THP kernel, MADV_NOHUGEPAGE is a no-op, but MADV_NOHUGEPAGE is not supported */

Do you mean "but MADV_HUGEPAGE is not supported"? Just want to make
sure; it seems like no one else has asked about this yet.

> +       if (advice == MADV_NOHUGEPAGE)
> +               return 0;
>         return -EINVAL;
>  }