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

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Message-ID: <YK7LykQE0LzysBYU@google.com>
Date:   Wed, 26 May 2021 15:29:30 -0700
From:   Minchan Kim <minchan@...nel.org>
To:     Yang Shi <shy828301@...il.com>
Cc:     hughd@...gle.com, ziy@...dia.com, kirill.shutemov@...ux.intel.com,
        naoya.horiguchi@....com, wangyugui@...-tech.com,
        akpm@...ux-foundation.org, linux-mm@...ck.org,
        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 01:12:39PM -0700, Yang Shi 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>
Acked-by: Minchan Kim <minchan@...nel.org>

Thanks for the update, Yang Shi.