linux-kernel - Re: [PATCH] mm/memcg: remove unneeded nr

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Message-ID: <YkGjnAOidFD8bA3a@dhcp22.suse.cz>
Date:   Mon, 28 Mar 2022 14:01:32 +0200
From:   Michal Hocko <mhocko@...e.com>
To:     Miaohe Lin <linmiaohe@...wei.com>
Cc:     hannes@...xchg.org, roman.gushchin@...ux.dev, shakeelb@...gle.com,
        akpm@...ux-foundation.org, cgroups@...r.kernel.org,
        linux-mm@...ck.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] mm/memcg: remove unneeded nr_scanned

On Mon 28-03-22 19:41:44, Miaohe Lin wrote:
> The local variable nr_scanned is unneeded as mem_cgroup_soft_reclaim always
> does *total_scanned += nr_scanned. So we can pass total_scanned directly to
> the mem_cgroup_soft_reclaim to simplify the code and save some cpu cycles
> of adding nr_scanned to total_scanned.

Maybe the compiler could be clever enough to generate a good code.
mem_cgroup_soft_reclaim doesn't have other caller so it could be
inlined. But I do agree that the change makes sense because it makes the
code more consistent as mem_cgroup_soft_limit_reclaim already uses
total_scanned this way.

> Signed-off-by: Miaohe Lin <linmiaohe@...wei.com>

Acked-by: Michal Hocko <mhocko@...e.com>

Thanks

> ---
>  mm/memcontrol.c | 5 +----
>  1 file changed, 1 insertion(+), 4 deletions(-)
> 
> diff --git a/mm/memcontrol.c b/mm/memcontrol.c
> index b686ec4f42c6..79341365ec90 100644
> --- a/mm/memcontrol.c
> +++ b/mm/memcontrol.c
> @@ -3384,7 +3384,6 @@ unsigned long mem_cgroup_soft_limit_reclaim(pg_data_t *pgdat, int order,
>  	int loop = 0;
>  	struct mem_cgroup_tree_per_node *mctz;
>  	unsigned long excess;
> -	unsigned long nr_scanned;
>  
>  	if (order > 0)
>  		return 0;
> @@ -3412,11 +3411,9 @@ unsigned long mem_cgroup_soft_limit_reclaim(pg_data_t *pgdat, int order,
>  		if (!mz)
>  			break;
>  
> -		nr_scanned = 0;
>  		reclaimed = mem_cgroup_soft_reclaim(mz->memcg, pgdat,
> -						    gfp_mask, &nr_scanned);
> +						    gfp_mask, total_scanned);
>  		nr_reclaimed += reclaimed;
> -		*total_scanned += nr_scanned;
>  		spin_lock_irq(&mctz->lock);
>  		__mem_cgroup_remove_exceeded(mz, mctz);
>  
> -- 
> 2.23.0

-- 
Michal Hocko
SUSE Labs