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Date:   Tue, 8 Mar 2022 09:07:20 -0800
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Subject: Re: [PATCH -V11 2/9] mm/migrate: update node demotion order on
 hotplug events
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To:     Oscar Salvador <osalvador@suse.de>,
        "Huang, Ying" <ying.huang@intel.com>
Cc:     Abhishek Goel <huntbag@linux.vnet.ibm.com>,
        Dave Hansen <dave.hansen@linux.intel.com>, linux-mm@kvack.org,
        linux-kernel@vger.kernel.org, Zi Yan <ziy@nvidia.com>,
        David Hildenbrand <david@redhat.com>,
        Yang Shi <yang.shi@linux.alibaba.com>,
        Andrew Morton <akpm@linux-foundation.org>
References: <20210721063926.3024591-1-ying.huang@intel.com>
 <20210721063926.3024591-2-ying.huang@intel.com>
 <eb438ddd-2919-73d4-bd9f-b7eecdd9577a@linux.vnet.ibm.com>
 <f5edb9dc-8b25-47c2-9905-09e88e41861b@intel.com>
 <4e8067e1-0574-c9d2-9d6c-d676d32071bd@linux.vnet.ibm.com>
 <87pmnb3ccr.fsf@yhuang6-desk2.ccr.corp.intel.com>
 <YicvnkVODh5qbxTC@localhost.localdomain>
From:   Dave Hansen <dave.hansen@intel.com>
In-Reply-To: <YicvnkVODh5qbxTC@localhost.localdomain>
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On 3/8/22 02:27, Oscar Salvador wrote:
> @@ -2043,7 +2044,12 @@ static void __init init_cpu_node_state(void)
>  static int vmstat_cpu_online(unsigned int cpu)
>  {
>  	refresh_zone_stat_thresholds();
> -	node_set_state(cpu_to_node(cpu), N_CPU);
> +
> +	if (!node_state(cpu_to_node(cpu), N_CPU)) {
> +		node_set_state(cpu_to_node(cpu), N_CPU);
> +		set_migration_target_nodes();
> +	}
> +
>  	return 0;
>  }
> 
> @@ -2066,6 +2072,8 @@ static int vmstat_cpu_dead(unsigned int cpu)
>  		return 0;
> 
>  	node_clear_state(node, N_CPU);
> +	set_migration_target_nodes();
> +
>  	return 0;
>  }

Yeah, those callbacks do look like they're reinventing the wheel.  This
is a much more direct way of doing it.