linux-kernel - Re: [PATCH 1/8] mm/vmscan: remove redundant folio_test

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Message-ID: <CAMZfGtUPQvgaxG_6A0n6HwD9VjqbQUbnF99Ei9WpMZbTbnz4zg@mail.gmail.com>
Date:   Wed, 30 Mar 2022 16:13:06 +0800
From:   Muchun Song <songmuchun@...edance.com>
To:     Miaohe Lin <linmiaohe@...wei.com>
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        Linux Memory Management List <linux-mm@...ck.org>,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 1/8] mm/vmscan: remove redundant folio_test_swapbacked
 check when folio is file lru

On Tue, Mar 29, 2022 at 9:26 PM Miaohe Lin <linmiaohe@...wei.com> wrote:
>
> When folio is file lru, folio_test_swapbacked is guaranteed to be true. So
> it's unnecessary to check it here again. No functional change intended.
>
> Signed-off-by: Miaohe Lin <linmiaohe@...wei.com>
> ---
>  mm/vmscan.c | 3 +--
>  1 file changed, 1 insertion(+), 2 deletions(-)
>
> diff --git a/mm/vmscan.c b/mm/vmscan.c
> index 1678802e03e7..7c1a9713bfc9 100644
> --- a/mm/vmscan.c
> +++ b/mm/vmscan.c
> @@ -1434,8 +1434,7 @@ static void folio_check_dirty_writeback(struct folio *folio,
>          * Anonymous pages are not handled by flushers and must be written
>          * from reclaim context. Do not stall reclaim based on them
>          */
> -       if (!folio_is_file_lru(folio) ||
> -           (folio_test_anon(folio) && !folio_test_swapbacked(folio))) {
> +       if (!folio_is_file_lru(folio) || folio_test_anon(folio)) {

At least your login is no problem since folio_is_file_lru() is equal to
!folio_test_swapbacked().  But the new code is not clear to me.
The old code is easy to understand, e.g. folio_test_anon(folio) &&
!folio_test_swapbacked(folio) tells us that the anon pages which
do not need to be swapped should be skipped. So I'm neutral on
the patch.