linux-kernel - Re: [PATCH v1 03/11] mm: simplify hugetlb and file-THP handling in __page

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Date:   Fri, 17 Dec 2021 11:07:52 -0800
From:   Yang Shi <shy828301@...il.com>
To:     David Hildenbrand <david@...hat.com>
Cc:     Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Hugh Dickins <hughd@...gle.com>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        David Rientjes <rientjes@...gle.com>,
        Shakeel Butt <shakeelb@...gle.com>,
        John Hubbard <jhubbard@...dia.com>,
        Jason Gunthorpe <jgg@...dia.com>,
        Mike Kravetz <mike.kravetz@...cle.com>,
        Mike Rapoport <rppt@...ux.ibm.com>,
        "Kirill A . Shutemov" <kirill.shutemov@...ux.intel.com>,
        Matthew Wilcox <willy@...radead.org>,
        Vlastimil Babka <vbabka@...e.cz>, Jann Horn <jannh@...gle.com>,
        Michal Hocko <mhocko@...nel.org>,
        Nadav Amit <namit@...are.com>, Rik van Riel <riel@...riel.com>,
        Roman Gushchin <guro@...com>,
        Andrea Arcangeli <aarcange@...hat.com>,
        Peter Xu <peterx@...hat.com>,
        Donald Dutile <ddutile@...hat.com>,
        Christoph Hellwig <hch@....de>,
        Oleg Nesterov <oleg@...hat.com>, Jan Kara <jack@...e.cz>,
        Linux MM <linux-mm@...ck.org>, linux-kselftest@...r.kernel.org,
        linux-doc@...r.kernel.org
Subject: Re: [PATCH v1 03/11] mm: simplify hugetlb and file-THP handling in __page_mapcount()

On Fri, Dec 17, 2021 at 3:33 AM David Hildenbrand <david@...hat.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@...hat.com>
> Signed-off-by: David Hildenbrand <david@...hat.com>

Reviewed-by: Yang Shi <shy828301@...il.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
>