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From:   Yang Shi <shy828301@gmail.com>
Date:   Fri, 17 Dec 2021 11:12:17 -0800
Message-ID: <CAHbLzkrY3MBsr+xKp_6zr8jwe=d1ua_5tpgVHjBgU90srW2Srw@mail.gmail.com>
Subject: Re: [PATCH v1 04/11] mm: thp: simlify total_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 simplify a bit, returning for PageHuge() early and using
> head_compound_page() as we are only getting called for HEAD pages.
>
> Note the VM_BUG_ON_PAGE(PageTail(page), page) check at the beginning of
> total_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/huge_memory.c | 7 +++----
>  1 file changed, 3 insertions(+), 4 deletions(-)
>
> diff --git a/mm/huge_memory.c b/mm/huge_memory.c
> index 4751d03947da..826cabcad11a 100644
> --- a/mm/huge_memory.c
> +++ b/mm/huge_memory.c
> @@ -2506,12 +2506,11 @@ int total_mapcount(struct page *page)
>
>         if (likely(!PageCompound(page)))
>                 return atomic_read(&page->_mapcount) + 1;
> +       if (PageHuge(page))
> +               return head_compound_mapcount(page);
>
> -       compound = compound_mapcount(page);
>         nr = compound_nr(page);
> -       if (PageHuge(page))
> -               return compound;
> -       ret = compound;
> +       ret = compound = head_compound_mapcount(page);
>         for (i = 0; i < nr; i++)
>                 ret += atomic_read(&page[i]._mapcount) + 1;
>         /* File pages has compound_mapcount included in _mapcount */
> --
> 2.31.1
>