linux-kernel - Re: [PATCH 1/7] mm/hugetlb: Handle FOLL_DUMP well in follow_page

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Date:   Wed, 14 Jun 2023 16:24:59 -0700
From:   Mike Kravetz <mike.kravetz@...cle.com>
To:     Peter Xu <peterx@...hat.com>
Cc:     linux-kernel@...r.kernel.org, linux-mm@...ck.org,
        Matthew Wilcox <willy@...radead.org>,
        Andrea Arcangeli <aarcange@...hat.com>,
        John Hubbard <jhubbard@...dia.com>,
        Mike Rapoport <rppt@...nel.org>,
        David Hildenbrand <david@...hat.com>,
        Vlastimil Babka <vbabka@...e.cz>,
        "Kirill A . Shutemov" <kirill@...temov.name>,
        Andrew Morton <akpm@...ux-foundation.org>,
        James Houghton <jthoughton@...gle.com>,
        Hugh Dickins <hughd@...gle.com>
Subject: Re: [PATCH 1/7] mm/hugetlb: Handle FOLL_DUMP well in
 follow_page_mask()

On 06/13/23 17:53, Peter Xu wrote:
> Firstly, the no_page_table() is meaningless for hugetlb which is a no-op
> there, because a hugetlb page always satisfies:
> 
>   - vma_is_anonymous() == false
>   - vma->vm_ops->fault != NULL
> 
> So we can already safely remove it in hugetlb_follow_page_mask(), alongside
> with the page* variable.
> 
> Meanwhile, what we do in follow_hugetlb_page() actually makes sense for a
> dump: we try to fault in the page only if the page cache is already
> allocated.  Let's do the same here for follow_page_mask() on hugetlb.
> 
> It should so far has zero effect on real dumps, because that still goes
> into follow_hugetlb_page().  But this may start to influence a bit on
> follow_page() users who mimics a "dump page" scenario, but hopefully in a
> good way.  This also paves way for unifying the hugetlb gup-slow.
> 
> Signed-off-by: Peter Xu <peterx@...hat.com>
> ---
>  mm/gup.c     | 9 ++-------
>  mm/hugetlb.c | 9 +++++++++
>  2 files changed, 11 insertions(+), 7 deletions(-)

Thanks Peter!

Reviewed-by: Mike Kravetz <mike.kravetz@...cle.com>
-- 
Mike Kravetz