linux-kernel - Re: [PATCH] mm: madvise: make MADV

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Message-ID: <c4431944-3db8-4c64-b6c4-aedd1f965083@lucifer.local>
Date: Thu, 8 May 2025 12:49:05 +0100
From: Lorenzo Stoakes <lorenzo.stoakes@...cle.com>
To: Ignacio.MorenoGonzalez@...a.com
Cc: Andrew Morton <akpm@...ux-foundation.org>,
        "Liam R. Howlett" <Liam.Howlett@...cle.com>,
        yang@...amperecomputing.com, willy@...radead.org, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] mm: madvise: make MADV_NOHUGEPAGE a no-op if !THP

On Thu, May 08, 2025 at 12:20:27PM +0200, Ignacio Moreno Gonzalez via B4 Relay wrote:
> From: Ignacio Moreno Gonzalez <Ignacio.MorenoGonzalez@...a.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@...radead.org>
> Signed-off-by: Ignacio Moreno Gonzalez <Ignacio.MorenoGonzalez@...a.com>

LGTM, so:

Reviewed-by: Lorenzo Stoakes <lorenzo.stoakes@...cle.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 */
> +	if (advice == MADV_NOHUGEPAGE)
> +		return 0;
>  	return -EINVAL;
>  }
>
>
> ---
> base-commit: fc96b232f8e7c0a6c282f47726b2ff6a5fb341d2
> change-id: 20250508-madvise-nohugepage-noop-without-thp-e0721b973d82
>
> Best regards,
> --
> Ignacio Moreno Gonzalez <Ignacio.MorenoGonzalez@...a.com>
>
>