linux-kernel - Re: [PATCH] mm/workingset.c: avoid unnecessary max_nodes estimation in count_shadow

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Message-ID: <8dea8eff-3100-4f57-5d61-e532803d256f@suse.cz>
Date:   Tue, 26 Jan 2021 17:24:57 +0100
From:   Vlastimil Babka <vbabka@...e.cz>
To:     Miaohe Lin <linmiaohe@...wei.com>, akpm@...ux-foundation.org
Cc:     linux-mm@...ck.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] mm/workingset.c: avoid unnecessary max_nodes estimation
 in count_shadow_nodes()

On 1/23/21 8:38 AM, Miaohe Lin wrote:
> If list_lru_shrink_count is 0, we always return SHRINK_EMPTY regardless of
> the value of max_nodes. So we can return early if nodes == 0 to save some
> cpu cycles of approximating a reasonable limit for the nodes.
> 
> Signed-off-by: Miaohe Lin <linmiaohe@...wei.com>

Acked-by: Vlastimil Babka <vbabka@...e.cz>

> ---
>  mm/workingset.c | 5 ++---
>  1 file changed, 2 insertions(+), 3 deletions(-)
> 
> diff --git a/mm/workingset.c b/mm/workingset.c
> index 10e96de945b3..7db8f3dad13c 100644
> --- a/mm/workingset.c
> +++ b/mm/workingset.c
> @@ -461,6 +461,8 @@ static unsigned long count_shadow_nodes(struct shrinker *shrinker,
>  	unsigned long pages;
>  
>  	nodes = list_lru_shrink_count(&shadow_nodes, sc);
> +	if (!nodes)
> +		return SHRINK_EMPTY;
>  
>  	/*
>  	 * Approximate a reasonable limit for the nodes
> @@ -503,9 +505,6 @@ static unsigned long count_shadow_nodes(struct shrinker *shrinker,
>  
>  	max_nodes = pages >> (XA_CHUNK_SHIFT - 3);
>  
> -	if (!nodes)
> -		return SHRINK_EMPTY;
> -
>  	if (nodes <= max_nodes)
>  		return 0;
>  	return nodes - max_nodes;
>