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

Michal Hocko
2020-01-20T10:01:12Z

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@linux.intel.com>

Acked-by: Michal Hocko <mhocko@suse.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