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From:   "Huang\, Ying" <ying.huang@intel.com>
To:     Dave Hansen <dave.hansen@linux.intel.com>
Cc:     <linux-kernel@vger.kernel.org>, <linux-mm@kvack.org>,
        <yang.shi@linux.alibaba.com>, <rientjes@google.com>,
        <dan.j.williams@intel.com>
Subject: Re: [RFC][PATCH 8/8] mm/numa: new reclaim mode to enable reclaim-based migration
References: <20200629234503.749E5340@viggo.jf.intel.com>
        <20200629234517.A7EC4BD3@viggo.jf.intel.com>
Date:   Fri, 03 Jul 2020 17:30:09 +0800
In-Reply-To: <20200629234517.A7EC4BD3@viggo.jf.intel.com> (Dave Hansen's
        message of "Mon, 29 Jun 2020 16:45:17 -0700")
Message-ID: <87imf5djz2.fsf@yhuang-dev.intel.com>
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Dave Hansen <dave.hansen@linux.intel.com> writes:
> +/*
> + * React to hotplug events that might online or offline
> + * NUMA nodes.
> + *
> + * This leaves migrate-on-reclaim transiently disabled
> + * between the MEM_GOING_OFFLINE and MEM_OFFLINE events.
> + * This runs whether RECLAIM_MIGRATE is enabled or not.
> + * That ensures that the user can turn RECLAIM_MIGRATE
> + * without needing to recalcuate migration targets.
> + */
> +#if defined(CONFIG_MEMORY_HOTPLUG)
> +static int __meminit migrate_on_reclaim_callback(struct notifier_block *self,
> +						 unsigned long action, void *arg)
> +{
> +	switch (action) {
> +	case MEM_GOING_OFFLINE:
> +		/*
> +		 * Make sure there are not transient states where
> +		 * an offline node is a migration target.  This
> +		 * will leave migration disabled until the offline
> +		 * completes and the MEM_OFFLINE case below runs.
> +		 */
> +		disable_all_migrate_targets();
> +		break;
> +	case MEM_OFFLINE:
> +	case MEM_ONLINE:
> +		/*
> +		 * Recalculate the target nodes once the node
> +		 * reaches its final state (online or offline).
> +		 */
> +		set_migration_target_nodes();
> +		break;
> +	case MEM_CANCEL_OFFLINE:
> +		/*
> +		 * MEM_GOING_OFFLINE disabled all the migration
> +		 * targets.  Reenable them.
> +		 */
> +		set_migration_target_nodes();
> +		break;
> +	case MEM_GOING_ONLINE:
> +	case MEM_CANCEL_ONLINE:
> +		break;

I think we need to call
disable_all_migrate_targets()/set_migration_target_nodes() for CPU
online/offline event too.  Because that will influence node_state(nid,
N_CPU).  Which will influence node demotion relationship.

> +	}
> +
> +	return notifier_from_errno(0);
>  }
> +

Best Regards,
Huang, Ying