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

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Date:   Wed, 9 Nov 2022 17:19:52 -0800
From:   Andrew Morton <akpm@...ux-foundation.org>
To:     Chao Xu <amos.xuchao@...il.com>
Cc:     linux-mm@...ck.org, linux-kernel@...r.kernel.org,
        Chao Xu <Chao.Xu9@...krlife.com>
Subject: Re: [PATCH] mm/vmscan: simplify the nr assignment logic for pages
 to scan

On Wed,  9 Nov 2022 15:04:16 +0800 Chao Xu <amos.xuchao@...il.com> 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.
> 
> --- 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++) {

The "lru++" implicitly assumes that LRU_ACTIVE=1.  That happens to be
the case, but a more accurate translation of the existing code would
use "lru += LRU_ACTIVE" here, yes?

> +			nr_scanned = targets[lru] - nr[lru];
> +			nr[lru] = targets[lru] * (100 - percentage) / 100;
> +			nr[lru] -= min(nr[lru], nr_scanned);
> +		}
>  
>  		scan_adjusted = true;
>  	}