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

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Message-ID: <YkMNq0531jBomnkv@casper.infradead.org>
Date:   Tue, 29 Mar 2022 14:46:19 +0100
From:   Matthew Wilcox <willy@...radead.org>
To:     Miaohe Lin <linmiaohe@...wei.com>
Cc:     akpm@...ux-foundation.org, linux-mm@...ck.org,
        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 09:26:12PM +0800, Miaohe Lin 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.

ummm ... is your logic right here?  The condition is:

	if (!a || (b && !c))

I don't see how it follows that a => c means we can do any
simplification at all.

> 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)) {
>  		*dirty = false;
>  		*writeback = false;
>  		return;
> -- 
> 2.23.0
> 
>