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SubjectRe: [PATCH] mm/vmscan.c: only adjust related kswapd cpu affinity when online cpu
On Sun, 26 Jan 2020, Wei Yang wrote:

> When onlining a cpu, kswapd_cpu_online() is called to adjust kswapd cpu
> affinity.
>
> Current routine does like this:
>
> * Iterate all the numa node
> * Adjust cpu affinity when node has an online cpu
>
> Actually we could improve this by:
>
> * Just adjust the numa node to which current online cpu belongs
>
> Because we know which numa node the cpu belongs to and this cpu would
> not affect other node.
>

Is there ever a situation where the cpu to be onlined would have appeared
in the cpumask of another node and so a different kswapd's cpumask would
now include an off-node cpu?

> Signed-off-by: Wei Yang <richardw.yang@linux.intel.com>
> ---
> mm/vmscan.c | 19 ++++++++++---------
> 1 file changed, 10 insertions(+), 9 deletions(-)
>
> diff --git a/mm/vmscan.c b/mm/vmscan.c
> index 572fb17c6273..19c92d35045c 100644
> --- a/mm/vmscan.c
> +++ b/mm/vmscan.c
> @@ -4049,18 +4049,19 @@ unsigned long shrink_all_memory(unsigned long nr_to_reclaim)
> restore their cpu bindings. */
> static int kswapd_cpu_online(unsigned int cpu)
> {
> - int nid;
> + int nid = cpu_to_node(cpu);
> + pg_data_t *pgdat;
> + const struct cpumask *mask;
>
> - for_each_node_state(nid, N_MEMORY) {
> - pg_data_t *pgdat = NODE_DATA(nid);
> - const struct cpumask *mask;
> + if (!node_state(nid, N_MEMORY))
> + return 0;
>
> - mask = cpumask_of_node(pgdat->node_id);
> + pgdat = NODE_DATA(nid);
> + mask = cpumask_of_node(nid);
> +
> + /* One of our CPUs online: restore mask */
> + set_cpus_allowed_ptr(pgdat->kswapd, mask);
>
> - if (cpumask_any_and(cpu_online_mask, mask) < nr_cpu_ids)
> - /* One of our CPUs online: restore mask */
> - set_cpus_allowed_ptr(pgdat->kswapd, mask);
> - }
> return 0;
> }
>
> --
> 2.17.1
>
>
>

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