linux-kernel - Re: [v4 PATCH 2/2] mm: rmap: make try_to

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Message-ID: <CALvZod7AXsky5ojvc_4E8=vK3eaBmto0XHcc41fBLFuWHUA4+g@mail.gmail.com>
Date:   Wed, 26 May 2021 16:03:23 -0700
From:   Shakeel Butt <shakeelb@...gle.com>
To:     Yang Shi <shy828301@...il.com>
Cc:     Hugh Dickins <hughd@...gle.com>, Zi Yan <ziy@...dia.com>,
        "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
        Minchan Kim <minchan@...nel.org>, naoya.horiguchi@....com,
        wangyugui@...-tech.com, Andrew Morton <akpm@...ux-foundation.org>,
        Linux MM <linux-mm@...ck.org>,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: [v4 PATCH 2/2] mm: rmap: make try_to_unmap() void function

On Wed, May 26, 2021 at 1:12 PM Yang Shi <shy828301@...il.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@...gle.com>
> Acked-by: Hugh Dickins <hughd@...gle.com>
> Signed-off-by: Yang Shi <shy828301@...il.com>

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