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From: Lance Yang <ioworker0@gmail.com>
Date: Thu, 13 Jun 2024 16:54:39 +0800
Message-ID: <CAK1f24mZk8hKDSPk+y7fP=cLoTuWxGaju_JqnKd_6BYQbZr6zg@mail.gmail.com>
Subject: Re: [PATCH v7 2/4] mm/rmap: add helper to restart pgtable walk on changes
To: David Hildenbrand <david@redhat.com>
Cc: akpm@linux-foundation.org, willy@infradead.org, sj@kernel.org, 
	baolin.wang@linux.alibaba.com, maskray@google.com, ziy@nvidia.com, 
	ryan.roberts@arm.com, 21cnbao@gmail.com, mhocko@suse.com, 
	fengwei.yin@intel.com, zokeefe@google.com, shy828301@gmail.com, 
	xiehuan09@gmail.com, libang.li@antgroup.com, wangkefeng.wang@huawei.com, 
	songmuchun@bytedance.com, peterx@redhat.com, minchan@kernel.org, 
	linux-mm@kvack.org, linux-kernel@vger.kernel.org
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On Thu, Jun 13, 2024 at 4:30=E2=80=AFPM David Hildenbrand <david@redhat.com=
> wrote:
>
> On 10.06.24 14:02, Lance Yang wrote:
> > Introduce the page_vma_mapped_walk_restart() helper to handle scenarios
> > where the page table walk needs to be restarted due to changes in the p=
age
> > table, such as when a PMD is split. It releases the PTL held during the
> > previous walk and resets the state, allowing a new walk to start at the
> > current address stored in pvmw->address.
> >
> > Suggested-by: David Hildenbrand <david@redhat.com>
> > Signed-off-by: Lance Yang <ioworker0@gmail.com>
> > ---
> >   include/linux/rmap.h | 22 ++++++++++++++++++++++
> >   1 file changed, 22 insertions(+)
> >
> > diff --git a/include/linux/rmap.h b/include/linux/rmap.h
> > index 7229b9baf20d..5f18509610cc 100644
> > --- a/include/linux/rmap.h
> > +++ b/include/linux/rmap.h
> > @@ -710,6 +710,28 @@ static inline void page_vma_mapped_walk_done(struc=
t page_vma_mapped_walk *pvmw)
> >               spin_unlock(pvmw->ptl);
> >   }
> >
> > +/**
> > + * page_vma_mapped_walk_restart - Restart the page table walk.
> > + * @pvmw: Pointer to struct page_vma_mapped_walk.
> > + *
> > + * It restarts the page table walk when changes occur in the page
> > + * table, such as splitting a PMD. Ensures that the PTL held during
> > + * the previous walk is released and resets the state to allow for
> > + * a new walk starting at the current address stored in pvmw->address.
> > + */
> > +static inline void
> > +page_vma_mapped_walk_restart(struct page_vma_mapped_walk *pvmw)
> > +{
> > +     WARN_ON_ONCE(!pvmw->pmd);
>
> Can we have this more general, like
>
> WARN_ON_ONCE(!pvmw->pmd && !pvmw->pte);

Sure, let=E2=80=99s make it more general.

>
> And then setting both to NULL below?
>
>
> > +     WARN_ON_ONCE(!pvmw->ptl);
>
> This is confusing: you check for ptl below. What would be clearer is
>
> if (likely(pvmw->ptl))
>         spin_unlock(pvmw->ptl);
> else
>         WARN_ON_ONCE(1);

Will adjust as you suggested, thanks!

>
>
> > +
> > +     if (pvmw->ptl)
> > +             spin_unlock(pvmw->ptl);
> > +
> > +     pvmw->ptl =3D NULL;
> > +     pvmw->pmd =3D NULL;
> > +}
> > +
> >   bool page_vma_mapped_walk(struct page_vma_mapped_walk *pvmw);
> >
> >   /*
>
> I'd suggest squashing that into the next patch.

Got it.

Thanks,
Lance

>
> --
> Cheers,
>
> David / dhildenb
>