linux-kernel - Re: [PATCH v2 4/9] mm/vmscan: save a bit of stack space in shrink

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Date:   Tue, 12 Apr 2022 08:57:31 +0800
From:   "ying.huang@...el.com" <ying.huang@...el.com>
To:     Miaohe Lin <linmiaohe@...wei.com>, akpm@...ux-foundation.org
Cc:     songmuchun@...edance.com, hch@...radead.org, willy@...radead.org,
        linux-mm@...ck.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 4/9] mm/vmscan: save a bit of stack space in
 shrink_lruvec

On Sat, 2022-04-09 at 17:34 +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 59b96320f481..0e5818970998 100644
> --- a/mm/vmscan.c
> +++ b/mm/vmscan.c
> @@ -2881,8 +2881,9 @@ 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];
>  	unsigned long nr_to_scan;
>  	enum lru_list lru;
>  	unsigned long nr_reclaimed = 0;

As Christoph pointed out, this is hacky without much benefit.  Please
drop this patch.

Best Regards,
Huang, Ying