linux-kernel - Re: [PATCH 4/8] mm/vmscan: save a bit of stack space in shrink

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Message-ID: <YkMRFaRwS6dadsQ0@infradead.org>
Date:   Tue, 29 Mar 2022 07:00:53 -0700
From:   Christoph Hellwig <hch@...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 4/8] mm/vmscan: save a bit of stack space in shrink_lruvec

On Tue, Mar 29, 2022 at 09:26:15PM +0800, Miaohe Lin wrote:
> LRU_UNEVICTABLE is not taken into account when shrink lruvec. So we can
> save a bit of stack space by shrinking the array size of nr and targets
> to NR_LRU_LISTS - 1. No functional change intended.
> 
> Signed-off-by: Miaohe Lin <linmiaohe@...wei.com>
> ---
>  mm/vmscan.c | 5 +++--
>  1 file changed, 3 insertions(+), 2 deletions(-)
> 
> diff --git a/mm/vmscan.c b/mm/vmscan.c
> index a6e60c78d058..ebd8ffb63673 100644
> --- a/mm/vmscan.c
> +++ b/mm/vmscan.c
> @@ -2862,8 +2862,9 @@ static bool can_age_anon_pages(struct pglist_data *pgdat,
>  
>  static void shrink_lruvec(struct lruvec *lruvec, struct scan_control *sc)
>  {
> -	unsigned long nr[NR_LRU_LISTS];
> -	unsigned long targets[NR_LRU_LISTS];
> +	/* LRU_UNEVICTABLE is not taken into account. */
> +	unsigned long nr[NR_LRU_LISTS - 1];
> +	unsigned long targets[NR_LRU_LISTS - 1];

This looks like a problem waiting to happen..