linux-kernel - Re: [PATCH 2/8] mm/migrate.c: not necessary to check start and i

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Date:   Sun, 19 Jan 2020 14:14:28 -0800 (PST)
From:   David Rientjes <rientjes@...gle.com>
To:     Wei Yang <richardw.yang@...ux.intel.com>
cc:     akpm@...ux-foundation.org, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org, mhocko@...e.com,
        yang.shi@...ux.alibaba.com
Subject: Re: [PATCH 2/8] mm/migrate.c: not necessary to check start and i

On Sun, 19 Jan 2020, Wei Yang wrote:

> diff --git a/mm/migrate.c b/mm/migrate.c
> index ba7cf4fa43a0..c3ef70de5876 100644
> --- a/mm/migrate.c
> +++ b/mm/migrate.c
> @@ -1664,11 +1664,9 @@ static int do_pages_move(struct mm_struct *mm, nodemask_t task_nodes,
>  		err = do_move_pages_to_node(mm, &pagelist, current_node);
>  		if (err)
>  			goto out;
> -		if (i > start) {
> -			err = store_status(status, start, current_node, i - start);
> -			if (err)
> -				goto out;
> -		}
> +		err = store_status(status, start, current_node, i - start);
> +		if (err)
> +			goto out;
>  		current_node = NUMA_NO_NODE;
>  	}
>  out_flush:

Not sure this is useful, it relies on the implementation of store_status() 
when i == start and the overhead of the function call should actually be 
slower than the simple conditional to avoid it in that case?