linux-kernel - Re: [PATCH RFC] mm: madvise: use walk_page_range_vma() for madvise_free_single

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Message-ID: <bd61e018-5fbb-4aac-8672-0c16254ba09e@lucifer.local>
Date: Tue, 3 Jun 2025 10:41:35 +0100
From: Lorenzo Stoakes <lorenzo.stoakes@...cle.com>
To: Barry Song <21cnbao@...il.com>
Cc: Dev Jain <dev.jain@....com>, akpm@...ux-foundation.org, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org, Barry Song <v-songbaohua@...o.com>,
        "Liam R. Howlett" <Liam.Howlett@...cle.com>,
        David Hildenbrand <david@...hat.com>, Vlastimil Babka <vbabka@...e.cz>,
        Jann Horn <jannh@...gle.com>, Suren Baghdasaryan <surenb@...gle.com>,
        Lokesh Gidra <lokeshgidra@...gle.com>,
        Tangquan Zheng <zhengtangquan@...o.com>
Subject: Re: [PATCH RFC] mm: madvise: use walk_page_range_vma() for
 madvise_free_single_vma()

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@....com> wrote:
> >
> >
> > On 03/06/25 7:01 am, Barry Song wrote:
> > > From: Barry Song <v-songbaohua@...o.com>
> > >
> > > 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@...cle.com>
> > > Cc: Lorenzo Stoakes <lorenzo.stoakes@...cle.com>
> > > Cc: David Hildenbrand <david@...hat.com>
> > > Cc: Vlastimil Babka <vbabka@...e.cz>
> > > Cc: Jann Horn <jannh@...gle.com>
> > > Cc: Suren Baghdasaryan <surenb@...gle.com>
> > > Cc: Lokesh Gidra <lokeshgidra@...gle.com>
> > > Cc: Tangquan Zheng <zhengtangquan@...o.com>
> > > Signed-off-by: Barry Song <v-songbaohua@...o.com>
> > > ---
> > >   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?

>
> >
>
> Thanks
> Barry

Cheers!