Re: [PATCH RFC] mm: madvise: use walk_page_range_vma() for madvise_free_single_vma()

[David Hildenbrand]

On 03.06.25 11:41, Lorenzo Stoakes wrote:
> On Tue, Jun 03, 2025 at 08:47:04PM +1200, Barry Song wrote:
> > On Tue, Jun 3, 2025 at 6:11 PM Dev Jain <dev.jain@xxxxxxx> wrote:
> > > On 03/06/25 7:01 am, Barry Song wrote:
> > > > From: Barry Song <v-songbaohua@xxxxxxxx>
> > > >
> > > > We've already found the VMA before calling madvise_free_single_vma(),
> > > > so calling walk_page_range() and doing find_vma() again seems
> > > > unnecessary. It also prevents potential optimizations for MADV_FREE
> > > > to use a per-VMA lock.
> > > >
> > > > Cc: "Liam R. Howlett" <Liam.Howlett@xxxxxxxxxx>
> > > > Cc: Lorenzo Stoakes <lorenzo.stoakes@xxxxxxxxxx>
> > > > Cc: David Hildenbrand <david@xxxxxxxxxx>
> > > > Cc: Vlastimil Babka <vbabka@xxxxxxx>
> > > > Cc: Jann Horn <jannh@xxxxxxxxxx>
> > > > Cc: Suren Baghdasaryan <surenb@xxxxxxxxxx>
> > > > Cc: Lokesh Gidra <lokeshgidra@xxxxxxxxxx>
> > > > Cc: Tangquan Zheng <zhengtangquan@xxxxxxxx>
> > > > Signed-off-by: Barry Song <v-songbaohua@xxxxxxxx>
> > > > ---
> > > >    mm/madvise.c | 2 +-
> > > >    1 file changed, 1 insertion(+), 1 deletion(-)
> > > >
> > > > diff --git a/mm/madvise.c b/mm/madvise.c
> > > > index d408ffa404b3..c6a28a2d3ff8 100644
> > > > --- a/mm/madvise.c
> > > > +++ b/mm/madvise.c
> > > > @@ -826,7 +826,7 @@ static int madvise_free_single_vma(struct madvise_behavior *madv_behavior,
> > > >
> > > >        mmu_notifier_invalidate_range_start(&range);
> > > >        tlb_start_vma(tlb, vma);
> > > > -     walk_page_range(vma->vm_mm, range.start, range.end,
> > > > +     walk_page_range_vma(vma, range.start, range.end,
> > > >                        &madvise_free_walk_ops, tlb);
> > > >        tlb_end_vma(tlb, vma);
> > > >        mmu_notifier_invalidate_range_end(&range);
> > >
> > > Can similar optimizations be made in madvise_willneed(), madvise_cold_page_range(), etc?
> >
> > Yes, I think the same code flow applies to madvise_willneed,
> > madvise_cold_page_range, and similar functions, though my current
> > interest is more on madvise_free.
> >
> > Let me prepare a v2 that includes those as well.
>
> FWIW Dev makes a great point here and I agree wholeheartedly, let's fix all such
> cases...
>
> As an aside, I wonder if we previously didn't do this because we hadn't
> previously exposed the walk_page_range_vma() API or something?

IIRC, yes:

commit e07cda5f232fac4de0925d8a4c92e51e41fa2f6e
Author: David Hildenbrand <david@xxxxxxxxxx>
Date:   Fri Oct 21 12:11:39 2022 +0200

    mm/pagewalk: add walk_page_range_vma()
    
    Let's add walk_page_range_vma(), which is similar to walk_page_vma(),
    however, is only interested in a subset of the VMA range.
    
    To be used in KSM code to stop using follow_page() next.


--
Cheers,

David / dhildenb