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From: Lance Yang <ioworker0@gmail.com>
Date: Mon, 3 Jun 2024 12:27:09 +0800
Message-ID: <CAK1f24=30RmJ2s0pqVNyj--BuB78k3P_2tXNsezAFQOnmqoa7w@mail.gmail.com>
Subject: Re: [PATCH 1/1] mm/mlock: implement folio_mlock_step() using folio_pte_batch()
To: Barry Song <21cnbao@gmail.com>
Cc: akpm@linux-foundation.org, ryan.roberts@arm.com, david@redhat.com, 
	baolin.wang@linux.alibaba.com, ziy@nvidia.com, fengwei.yin@intel.com, 
	ying.huang@intel.com, libang.li@antgroup.com, linux-mm@kvack.org, 
	linux-kernel@vger.kernel.org
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Hi Barry,

Thanks for taking time to review!

On Mon, Jun 3, 2024 at 12:14=E2=80=AFPM Barry Song <21cnbao@gmail.com> wrot=
e:
>
> On Mon, Jun 3, 2024 at 3:31=E2=80=AFPM Lance Yang <ioworker0@gmail.com> w=
rote:
> >
> > Let's make folio_mlock_step() simply a wrapper around folio_pte_batch()=
,
> > which will greatly reduce the cost of ptep_get() when scanning a range =
of
> > contptes.
> >
> > Signed-off-by: Lance Yang <ioworker0@gmail.com>
> > ---
> >  mm/mlock.c | 23 ++++++-----------------
> >  1 file changed, 6 insertions(+), 17 deletions(-)
> >
> > diff --git a/mm/mlock.c b/mm/mlock.c
> > index 30b51cdea89d..1ae6232d38cf 100644
> > --- a/mm/mlock.c
> > +++ b/mm/mlock.c
> > @@ -307,26 +307,15 @@ void munlock_folio(struct folio *folio)
> >  static inline unsigned int folio_mlock_step(struct folio *folio,
> >                 pte_t *pte, unsigned long addr, unsigned long end)
> >  {
> > -       unsigned int count, i, nr =3D folio_nr_pages(folio);
> > -       unsigned long pfn =3D folio_pfn(folio);
> > -       pte_t ptent =3D ptep_get(pte);
> > -
> > -       if (!folio_test_large(folio))
> > +       if (likely(!folio_test_large(folio)))
> >                 return 1;
> >
> > -       count =3D pfn + nr - pte_pfn(ptent);
> > -       count =3D min_t(unsigned int, count, (end - addr) >> PAGE_SHIFT=
);
> > -
> > -       for (i =3D 0; i < count; i++, pte++) {
> > -               pte_t entry =3D ptep_get(pte);
> > -
> > -               if (!pte_present(entry))
> > -                       break;
> > -               if (pte_pfn(entry) - pfn >=3D nr)
> > -                       break;
> > -       }
> > +       const fpb_t fpb_flags =3D FPB_IGNORE_DIRTY | FPB_IGNORE_SOFT_DI=
RTY;
> > +       int max_nr =3D (end - addr) / PAGE_SIZE;
> > +       pte_t ptent =3D ptep_get(pte);
> >
> > -       return i;
> > +       return folio_pte_batch(folio, addr, pte, ptent, max_nr, fpb_fla=
gs, NULL,
> > +                              NULL, NULL);
> >  }
>
> what about a minimum change as below?

Nice, that makes sense to me ;)
I'll adjust as you suggested.

Thanks again for your time!
Lance

> index 30b51cdea89d..e8b98f84fbd2 100644
> --- a/mm/mlock.c
> +++ b/mm/mlock.c
> @@ -307,26 +307,15 @@ void munlock_folio(struct folio *folio)
>  static inline unsigned int folio_mlock_step(struct folio *folio,
>                 pte_t *pte, unsigned long addr, unsigned long end)
>  {
> -       unsigned int count, i, nr =3D folio_nr_pages(folio);
> -       unsigned long pfn =3D folio_pfn(folio);
> +       unsigned int count =3D (end - addr) >> PAGE_SHIFT;
>         pte_t ptent =3D ptep_get(pte);
> +       const fpb_t fpb_flags =3D FPB_IGNORE_DIRTY | FPB_IGNORE_SOFT_DIRT=
Y;
>
>         if (!folio_test_large(folio))
>                 return 1;
>
> -       count =3D pfn + nr - pte_pfn(ptent);
> -       count =3D min_t(unsigned int, count, (end - addr) >> PAGE_SHIFT);
> -
> -       for (i =3D 0; i < count; i++, pte++) {
> -               pte_t entry =3D ptep_get(pte);
> -
> -               if (!pte_present(entry))
> -                       break;
> -               if (pte_pfn(entry) - pfn >=3D nr)
> -                       break;
> -       }
> -
> -       return i;
> +       return folio_pte_batch(folio, addr, pte, ptent, count, fpb_flags,=
 NULL,
> +                              NULL, NULL);
>  }
>
>
>
> >
> >  static inline bool allow_mlock_munlock(struct folio *folio,
> > --
> > 2.33.1
> >