linux-kernel - Re: [PATCH 6/8] mm/migrate.c: handle same node and add failure in the same way

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Message-ID: <20200120100108.GQ18451@dhcp22.suse.cz>
Date:   Mon, 20 Jan 2020 11:01:08 +0100
From:   Michal Hocko <mhocko@...nel.org>
To:     Wei Yang <richardw.yang@...ux.intel.com>
Cc:     akpm@...ux-foundation.org, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org, yang.shi@...ux.alibaba.com
Subject: Re: [PATCH 6/8] mm/migrate.c: handle same node and add failure in
 the same way

On Sun 19-01-20 11:06:34, Wei Yang wrote:
> When page is not queued for migration, there are two possible cases:
> 
>   * page already on the target node
>   * failed to add to migration queue
> 
> Current code handle them differently, this leads to a behavior
> inconsistency.
> 
> Usually for each page's status, we just do store for once. While for the
> page already on the target node, we might store the node information for
> twice:
> 
>   * once when we found the page is on the target node
>   * second when moving the pages to target node successfully after above
>     action
> 
> The reason is even we don't add the page to pagelist, but store_status()
> does store in a range which still contains the page.
> 
> This patch handles these two cases in the same way to reduce this
> inconsistency and also make the code a little easier to read.

Yeah, the improvement is really marginal. I do not feel strongly one way
or another.

> Signed-off-by: Wei Yang <richardw.yang@...ux.intel.com>

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

> ---
>  mm/migrate.c | 16 ++++++++--------
>  1 file changed, 8 insertions(+), 8 deletions(-)
> 
> diff --git a/mm/migrate.c b/mm/migrate.c
> index 46a5697b7fc6..aee5aeb082c4 100644
> --- a/mm/migrate.c
> +++ b/mm/migrate.c
> @@ -1657,18 +1657,18 @@ static int do_pages_move(struct mm_struct *mm, nodemask_t task_nodes,
>  		err = add_page_for_migration(mm, addr, current_node,
>  				&pagelist, flags & MPOL_MF_MOVE_ALL);
>  
> -		if (!err) {
> -			/* The page is already on the target node */
> -			err = store_status(status, i, current_node, 1);
> -			if (err)
> -				goto out_flush;
> -			continue;
> -		} else if (err > 0) {
> +		if (err > 0) {
>  			/* The page is successfully queued for migration */
>  			continue;
>  		}
>  
> -		err = store_status(status, i, err, 1);
> +		/*
> +		 * Two possible cases for err here:
> +		 * == 0: page is already on the target node, then store
> +		 *       current_node to status
> +		 * <  0: failed to add page to list, then store err to status
> +		 */
> +		err = store_status(status, i, err ? : current_node, 1);
>  		if (err)
>  			goto out_flush;
>  
> -- 
> 2.17.1
> 

-- 
Michal Hocko
SUSE Labs