linux-kernel - Re: [PATCH v1] mm/vmscan: simplify the nr assignment logic for pages to scan

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Date:   Thu, 17 Nov 2022 13:07:24 -0500
From:   Johannes Weiner <hannes@...xchg.org>
To:     Chao Xu <amos.xuchao@...il.com>
Cc:     akpm@...ux-foundation.org, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org, Chao Xu <Chao.Xu9@...krlife.com>,
        yu@...xchg.org
Subject: Re: [PATCH v1] mm/vmscan: simplify the nr assignment logic for pages
 to scan

On Thu, Nov 10, 2022 at 07:31:30PM +0800, Chao Xu wrote:
> By default the assignment logic of anonymouns or file inactive
> pages and active pages to scan using the same duplicated code
> snippet. To simplify the logic, merge the same part.
> 
> Signed-off-by: Chao Xu <Chao.Xu9@...krlife.com>
> ---
>  mm/vmscan.c | 13 +++++--------
>  1 file changed, 5 insertions(+), 8 deletions(-)
> 
> diff --git a/mm/vmscan.c b/mm/vmscan.c
> index 04d8b88e5216..69e458e51c81 100644
> --- a/mm/vmscan.c
> +++ b/mm/vmscan.c
> @@ -5932,14 +5932,11 @@ static void shrink_lruvec(struct lruvec *lruvec, struct scan_control *sc)
>  		 * scan target and the percentage scanning already complete
>  		 */
>  		lru = (lru == LRU_FILE) ? LRU_BASE : LRU_FILE;
> -		nr_scanned = targets[lru] - nr[lru];
> -		nr[lru] = targets[lru] * (100 - percentage) / 100;
> -		nr[lru] -= min(nr[lru], nr_scanned);
> -
> -		lru += LRU_ACTIVE;
> -		nr_scanned = targets[lru] - nr[lru];
> -		nr[lru] = targets[lru] * (100 - percentage) / 100;
> -		nr[lru] -= min(nr[lru], nr_scanned);
> +		for ( ; lru <= lru + LRU_ACTIVE; lru += LRU_ACTIVE) {

As Yu points out, this will loop until lru overflows.

NAK.