Re: [PATCH] mm/workingset.c: avoid unnecessary max_nodes estimation in count_shadow_nodes()

From: Vlastimil Babka
Date: Tue Jan 26 2021 - 11:26:14 EST


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@xxxxxxxxxx>

Acked-by: Vlastimil Babka <vbabka@xxxxxxx>

> ---
> 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;
>