Re: [PATCH 1/8] mm/migrate.c: skip node check if done in last round

Michal Hocko
2020-01-20T09:36:51Z

On Sun 19-01-20 11:06:29, Wei Yang wrote:
> Before move page to target node, we would check if the node id is valid.
> In case we would try to move pages to the same target node, it is not
> necessary to do the check each time.
>
> This patch tries to skip the check if the node has been checked.
>
> Signed-off-by: Wei Yang <richardw.yang@linux.intel.com>
> ---
> mm/migrate.c | 19 +++++++++++--------
> 1 file changed, 11 insertions(+), 8 deletions(-)
>
> diff --git a/mm/migrate.c b/mm/migrate.c
> index 430fdccc733e..ba7cf4fa43a0 100644
> --- a/mm/migrate.c
> +++ b/mm/migrate.c
> @@ -1612,15 +1612,18 @@ static int do_pages_move(struct mm_struct *mm, nodemask_t task_nodes,
> goto out_flush;
> addr = (unsigned long)untagged_addr(p);
>
> - err = -ENODEV;
> - if (node < 0 || node >= MAX_NUMNODES)
> - goto out_flush;
> - if (!node_state(node, N_MEMORY))
> - goto out_flush;
> + /* Check node if it is not checked. */
> + if (current_node == NUMA_NO_NODE || node != current_node) {
> + err = -ENODEV;
> + if (node < 0 || node >= MAX_NUMNODES)
> + goto out_flush;
> + if (!node_state(node, N_MEMORY))
> + goto out_flush;

This makes the code harder to read IMHO. The original code checks the
valid node first and it doesn't conflate that with the node caching
logic which your change does.

>
> - err = -EACCES;
> - if (!node_isset(node, task_nodes))
> - goto out_flush;
> + err = -EACCES;
> + if (!node_isset(node, task_nodes))
> + goto out_flush;
> + }
>
> if (current_node == NUMA_NO_NODE) {
> current_node = node;
> --
> 2.17.1

--
Michal Hocko
SUSE Labs