On Tue 18-02-20 08:43:54, Wei Yang wrote:
> The cpu online notification is used to adjust kswapd cpu affinity when a
> NUMA node gains a new CPU.
>
> Since currently we don't see a real runtime configuration like this,
> let's drop this online notification for now.
This deserves much more explanation IMHO. What would you say about the
following.
"
kswapd kernel thread starts either with a CPU affinity set to the full
cpu mask of its target node or without any affinity at all if the node
is CPUless. There is a cpu hotplug callback (kswapd_cpu_online) that
implements an elaborate way to update this mask when a cpu is onlined.
It is not really clear whether there is any actual benefit from this
scheme. Completely CPU-less NUMA nodes rarely gain a new CPU during
runtime. Drop the code for that reason. If there is a real usecase then
we can resurrect and simplify the code.
"
>
> Suggested-by: Michal Hocko <mhocko@xxxxxxxxxx>
> Signed-off-by: Wei Yang <richardw.yang@xxxxxxxxxxxxxxx>
Acked-by: Michal Hocko <mhocko@xxxxxxxx>
>
> ---
> v3:
> * remove the cpu online notification suggested by Michal
> v2:
> * rephrase the changelog
> ---
> mm/vmscan.c | 27 +--------------------------
> 1 file changed, 1 insertion(+), 26 deletions(-)
>
> diff --git a/mm/vmscan.c b/mm/vmscan.c
> index 665f33258cd7..a4fdf3dc8887 100644
> --- a/mm/vmscan.c
> +++ b/mm/vmscan.c
> @@ -4023,27 +4023,6 @@ unsigned long shrink_all_memory(unsigned long nr_to_reclaim)
> }
> #endif /* CONFIG_HIBERNATION */
>
> -/* It's optimal to keep kswapds on the same CPUs as their memory, but
> - not required for correctness. So if the last cpu in a node goes
> - away, we get changed to run anywhere: as the first one comes back,
> - restore their cpu bindings. */
> -static int kswapd_cpu_online(unsigned int cpu)
> -{
> - int nid;
> -
> - for_each_node_state(nid, N_MEMORY) {
> - pg_data_t *pgdat = NODE_DATA(nid);
> - const struct cpumask *mask;
> -
> - mask = cpumask_of_node(pgdat->node_id);
> -
> - 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;
> -}
> -
> /*
> * This kswapd start function will be called by init and node-hot-add.
> * On node-hot-add, kswapd will moved to proper cpus if cpus are hot-added.
> @@ -4083,15 +4062,11 @@ void kswapd_stop(int nid)
>
> static int __init kswapd_init(void)
> {
> - int nid, ret;
> + int nid;
>
> swap_setup();
> for_each_node_state(nid, N_MEMORY)
> kswapd_run(nid);
> - ret = cpuhp_setup_state_nocalls(CPUHP_AP_ONLINE_DYN,
> - "mm/vmscan:online", kswapd_cpu_online,
> - NULL);
> - WARN_ON(ret < 0);
> return 0;
> }
>
> --
> 2.17.1
--
Michal Hocko
SUSE Labs
