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From:   Yang Shi <shy828301@gmail.com>
Date:   Fri, 17 Dec 2021 11:07:52 -0800
Message-ID: <CAHbLzkpgqu0HWtxRqf7vhVBmeMAP0OxXdidHeM8NRjC_uUwo=A@mail.gmail.com>
Subject: Re: [PATCH v1 03/11] mm: simplify hugetlb and file-THP handling in __page_mapcount()
To:     David Hildenbrand <david@redhat.com>
Cc:     Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        Andrew Morton <akpm@linux-foundation.org>,
        Hugh Dickins <hughd@google.com>,
        Linus Torvalds <torvalds@linux-foundation.org>,
        David Rientjes <rientjes@google.com>,
        Shakeel Butt <shakeelb@google.com>,
        John Hubbard <jhubbard@nvidia.com>,
        Jason Gunthorpe <jgg@nvidia.com>,
        Mike Kravetz <mike.kravetz@oracle.com>,
        Mike Rapoport <rppt@linux.ibm.com>,
        "Kirill A . Shutemov" <kirill.shutemov@linux.intel.com>,
        Matthew Wilcox <willy@infradead.org>,
        Vlastimil Babka <vbabka@suse.cz>, Jann Horn <jannh@google.com>,
        Michal Hocko <mhocko@kernel.org>,
        Nadav Amit <namit@vmware.com>, Rik van Riel <riel@surriel.com>,
        Roman Gushchin <guro@fb.com>,
        Andrea Arcangeli <aarcange@redhat.com>,
        Peter Xu <peterx@redhat.com>,
        Donald Dutile <ddutile@redhat.com>,
        Christoph Hellwig <hch@lst.de>,
        Oleg Nesterov <oleg@redhat.com>, Jan Kara <jack@suse.cz>,
        Linux MM <linux-mm@kvack.org>, linux-kselftest@vger.kernel.org,
        linux-doc@vger.kernel.org
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On Fri, Dec 17, 2021 at 3:33 AM David Hildenbrand <david@redhat.com> wrote:
>
> Let's return early for hugetlb, which really only relies on the compound
> mapcount so far and does not support PageDoubleMap() yet. Use the chance
> to cleanup the file-THP case to make it easier to grasp. While at it, use
> head_compound_mapcount().
>
> This is a preparation for further changes.
>
> Reviewed-by: Peter Xu <peterx@redhat.com>
> Signed-off-by: David Hildenbrand <david@redhat.com>

Reviewed-by: Yang Shi <shy828301@gmail.com>

> ---
>  mm/util.c | 11 +++++++----
>  1 file changed, 7 insertions(+), 4 deletions(-)
>
> diff --git a/mm/util.c b/mm/util.c
> index 741ba32a43ac..3239e75c148d 100644
> --- a/mm/util.c
> +++ b/mm/util.c
> @@ -732,15 +732,18 @@ int __page_mapcount(struct page *page)
>  {
>         int ret;
>
> -       ret = atomic_read(&page->_mapcount) + 1;
> +       if (PageHuge(page))
> +               return compound_mapcount(page);
>         /*
>          * For file THP page->_mapcount contains total number of mapping
>          * of the page: no need to look into compound_mapcount.
>          */
> -       if (!PageAnon(page) && !PageHuge(page))
> -               return ret;
> +       if (!PageAnon(page))
> +               return atomic_read(&page->_mapcount) + 1;
> +
> +       ret = atomic_read(&page->_mapcount) + 1;
>         page = compound_head(page);
> -       ret += atomic_read(compound_mapcount_ptr(page)) + 1;
> +       ret += head_compound_mapcount(page);
>         if (PageDoubleMap(page))
>                 ret--;
>         return ret;
> --
> 2.31.1
>