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References: <20210526201239.3351-1-shy828301@gmail.com> <20210526201239.3351-2-shy828301@gmail.com>
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From:   Shakeel Butt <shakeelb@google.com>
Date:   Wed, 26 May 2021 16:03:23 -0700
Message-ID: <CALvZod7AXsky5ojvc_4E8=vK3eaBmto0XHcc41fBLFuWHUA4+g@mail.gmail.com>
Subject: Re: [v4 PATCH 2/2] mm: rmap: make try_to_unmap() void function
To:     Yang Shi <shy828301@gmail.com>
Cc:     Hugh Dickins <hughd@google.com>, Zi Yan <ziy@nvidia.com>,
        "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>,
        Minchan Kim <minchan@kernel.org>, naoya.horiguchi@nec.com,
        wangyugui@e16-tech.com, Andrew Morton <akpm@linux-foundation.org>,
        Linux MM <linux-mm@kvack.org>,
        LKML <linux-kernel@vger.kernel.org>
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On Wed, May 26, 2021 at 1:12 PM Yang Shi <shy828301@gmail.com> wrote:
>
> Currently try_to_unmap() return bool value by checking page_mapcount(),
> however this may return false positive since page_mapcount() doesn't
> check all subpages of compound page.  The total_mapcount() could be used
> instead, but its cost is higher since it traverses all subpages.
>
> Actually the most callers of try_to_unmap() don't care about the
> return value at all.  So just need check if page is still mapped by
> page_mapped() when necessary.  And page_mapped() does bail out early
> when it finds mapped subpage.
>
> Suggested-by: Hugh Dickins <hughd@google.com>
> Acked-by: Hugh Dickins <hughd@google.com>
> Signed-off-by: Yang Shi <shy828301@gmail.com>

Reviewed-by: Shakeel Butt <shakeelb@google.com>