Re: [PATCH -V2] mm/migrate: fix CPUHP state to update node demotion order

[Andrew Morton]

On Mon, 27 Sep 2021 16:11:00 +0800 Huang Ying <ying.huang@xxxxxxxxx> wrote:

> The node demotion order needs to be updated during CPU hotplug.
> Because whether a NUMA node has CPU may influence the demotion order.
> The update function should be called during CPU online/offline after
> the node_states[N_CPU] has been updated.  That is done in
> CPUHP_AP_ONLINE_DYN during CPU online and in CPUHP_MM_VMSTAT_DEAD
> during CPU offline.  But in commit 884a6e5d1f93 ("mm/migrate: update
> node demotion order on hotplug events"), the function to update node
> demotion order is called in CPUHP_AP_ONLINE_DYN during CPU
> online/offline.  This doesn't satisfy the order requirement.

What are the user-visible runtime effects of this error?

>  So in
> this patch, we added CPUHP_AP_MM_DEMOTION_ONLINE and
> CPUHP_MM_DEMOTION_DEAD to be called after CPUHP_AP_ONLINE_DYN and
> CPUHP_MM_VMSTAT_DEAD during CPU online and offline, and register the
> update function on them.
> 
> Fixes: 884a6e5d1f93 ("mm/migrate: update node demotion order on hotplug events")
> Signed-off-by: "Huang, Ying" <ying.huang@xxxxxxxxx>
> Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
> Cc: Dave Hansen <dave.hansen@xxxxxxxxxxxxxxx>
> Cc: Yang Shi <shy828301@xxxxxxxxx>
> Cc: Zi Yan <ziy@xxxxxxxxxx>
> Cc: Michal Hocko <mhocko@xxxxxxxx>
> Cc: Wei Xu <weixugc@xxxxxxxxxx>
> Cc: Oscar Salvador <osalvador@xxxxxxx>
> Cc: David Rientjes <rientjes@xxxxxxxxxx>
> Cc: Dan Williams <dan.j.williams@xxxxxxxxx>
> Cc: David Hildenbrand <david@xxxxxxxxxx>
> Cc: Greg Thelen <gthelen@xxxxxxxxxx>
> Cc: Keith Busch <kbusch@xxxxxxxxxx>
>