linux-kernel - Re: [PATCH 1/4] mm: hugetlb: use flush_hugetlb_tlb_range() in move_hugetlb_page

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Message-ID: <CAHS8izM=_TWVhu9OcEFBg=MDYrh4BFmzM8a3=tSRPRBmkuAUuQ@mail.gmail.com>
Date:   Wed, 2 Aug 2023 17:26:17 -0700
From:   Mina Almasry <almasrymina@...gle.com>
To:     Mike Kravetz <mike.kravetz@...cle.com>,
        James Houghton <jthoughton@...gle.com>
Cc:     Kefeng Wang <wangkefeng.wang@...wei.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will@...nel.org>,
        Muchun Song <muchun.song@...ux.dev>, kirill@...temov.name,
        joel@...lfernandes.org, william.kucharski@...cle.com,
        kaleshsingh@...gle.com, linux-mm@...ck.org,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/4] mm: hugetlb: use flush_hugetlb_tlb_range() in move_hugetlb_page_tables()

On Mon, Jul 31, 2023 at 4:40 PM Mike Kravetz <mike.kravetz@...cle.com> wrote:
>
> On 07/31/23 15:48, Kefeng Wang wrote:
> > Archs may need to do special things when flushing hugepage tlb,
> > so use the more applicable flush_hugetlb_tlb_range() instead of
> > flush_tlb_range().
> >
> > Fixes: 550a7d60bd5e ("mm, hugepages: add mremap() support for hugepage backed vma")
> > Signed-off-by: Kefeng Wang <wangkefeng.wang@...wei.com>
>
> Thanks!
>
> Reviewed-by: Mike Kravetz <mike.kravetz@...cle.com>
>

Sorry for jumping in late, but given the concerns raised around HGM
and the deviation between hugetlb and the rest of MM, does it make
sense to try to make an incremental effort towards avoiding hugetlb
specialization?

In the context of this patch, I would prefer that the arch upgrade
flush_tlb_range() to handle hugetlb correctly, instead of adding more
hugetlb specific deviations, ala flush_hugetlb_tlb_range. While it's
at it, maybe replace flush_hugetlb_tlb_range() in the code with
flush_tlb_range().

Although, I don't have the expertise to judge if upgrading
flush_tlb_range() to handle hugetlb is easy or feasible at all.

> Although, I missed this in 550a7d60bd5e :(
>
> Looks like only powerpc provides an arch specific flush_hugetlb_tlb_range
> today.
> --
> Mike Kravetz
>
> > ---
> >  mm/hugetlb.c | 4 ++--
> >  1 file changed, 2 insertions(+), 2 deletions(-)
> >
> > diff --git a/mm/hugetlb.c b/mm/hugetlb.c
> > index 64a3239b6407..ac876bfba340 100644
> > --- a/mm/hugetlb.c
> > +++ b/mm/hugetlb.c
> > @@ -5281,9 +5281,9 @@ int move_hugetlb_page_tables(struct vm_area_struct *vma,
> >       }
> >
> >       if (shared_pmd)
> > -             flush_tlb_range(vma, range.start, range.end);
> > +             flush_hugetlb_tlb_range(vma, range.start, range.end);
> >       else
> > -             flush_tlb_range(vma, old_end - len, old_end);
> > +             flush_hugetlb_tlb_range(vma, old_end - len, old_end);
> >       mmu_notifier_invalidate_range_end(&range);
> >       i_mmap_unlock_write(mapping);
> >       hugetlb_vma_unlock_write(vma);
> > --
> > 2.41.0
> >



-- 
Thanks,
Mina