linux-kernel - Re: [PATCH 2/2] mm: madvise: make MADV

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Message-ID: <ba332040-cc8f-444b-8091-52bb6dba57e3@lucifer.local>
Date: Fri, 16 May 2025 16:43:41 +0100
From: Lorenzo Stoakes <lorenzo.stoakes@...cle.com>
To: "Liam R. Howlett" <Liam.Howlett@...cle.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        James Houghton <jthoughton@...gle.com>,
        Christian Borntraeger <borntraeger@...ux.ibm.com>,
        Ignacio Moreno Gonzalez <Ignacio.MorenoGonzalez@...a.com>,
        Yang Shi <yang@...amperecomputing.com>,
        David Hildenbrand <david@...hat.com>,
        Matthew Wilcox <willy@...radead.org>,
        Janosch Frank <frankja@...ux.ibm.com>,
        Heiko Carstens <hca@...ux.ibm.com>, Vasily Gorbik <gor@...ux.ibm.com>,
        Alexander Gordeev <agordeev@...ux.ibm.com>,
        Sven Schnelle <svens@...ux.ibm.com>, pbonzini@...hat.com,
        kvm@...r.kernel.org, linux-s390@...r.kernel.org, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/2] mm: madvise: make MADV_NOHUGEPAGE a no-op if !THP

On Fri, May 16, 2025 at 11:40:23AM -0400, Liam R. Howlett wrote:
> * Lorenzo Stoakes <lorenzo.stoakes@...cle.com> [250515 16:15]:
> > 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>
> > Reviewed-by: Yang Shi <yang@...amperecomputing.com>
> > Acked-by: David Hildenbrand <david@...hat.com>
> > Reviewed-by: Lorenzo Stoakes <lorenzo.stoakes@...cle.com>
>
> Nice to see you review this for yourself :)

Haha yeah... this is a Lorenzo-getting-confused-by-kernel-process situation
again, this is 100% Ignacio's patch, I just bundled it up in this series to
enforce ordering.

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

...But of course I did format-patch -s so I signed it off as well :P

At any rate the From: field and Ignacio's S-o-b should make everything correct
in the wash. I think.

Andrew - this is Ignacio's patch for avoidance of doubt :P

>
> Reviewed-by: Liam R. Howlett <Liam.Howlett@...cle.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
> >
>