Re: [PATCH 2/2] mm: madvise: make MADV_NOHUGEPAGE a no-op if !THP

["Liam R. Howlett" <Liam.Howlett@oracle.com>]

* Lorenzo Stoakes <lorenzo.stoakes@oracle.com> [250515 16:15]:
> 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>
> Reviewed-by: Yang Shi <yang@os.amperecomputing.com>
> Acked-by: David Hildenbrand <david@redhat.com>
> Reviewed-by: Lorenzo Stoakes <lorenzo.stoakes@oracle.com>

Nice to see you review this for yourself :)

> Signed-off-by: Lorenzo Stoakes <lorenzo.stoakes@oracle.com>

Reviewed-by: Liam R. Howlett <Liam.Howlett@oracle.com>

> ---
>  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 2f190c90192d..1a8082c61e01 100644
> --- a/include/linux/huge_mm.h
> +++ b/include/linux/huge_mm.h
> @@ -506,6 +506,8 @@ 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;
> @@ -595,6 +597,9 @@ 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_HUGEPAGE is not supported */
> +	if (advice == MADV_NOHUGEPAGE)
> +		return 0;
>  	return -EINVAL;
>  }
>  
> -- 
> 2.49.0
>