linux-kernel - Re: [PATCH v3 2/3] mm,memory_hotplug: Implement numa node notifier

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Message-ID: <aBTkgnYYSN0SMQCU@gourry-fedora-PF4VCD3F>
Date: Fri, 2 May 2025 11:28:02 -0400
From: Gregory Price <gourry@...rry.net>
To: Oscar Salvador <osalvador@...e.de>
Cc: Andrew Morton <akpm@...ux-foundation.org>,
	David Hildenbrand <david@...hat.com>, linux-mm@...ck.org,
	linux-kernel@...r.kernel.org, Vlastimil Babka <vbabka@...e.cz>,
	Hyeonggon Yoo <42.hyeyoo@...il.com>,
	Jonathan Cameron <Jonathan.Cameron@...wei.com>,
	Rakie Kim <rakie.kim@...com>, Harry Yoo <harry.yoo@...cle.com>,
	dan.carpenter@...aro.org, honggyu.kim@...com
Subject: Re: [PATCH v3 2/3] mm,memory_hotplug: Implement numa node notifier

On Fri, May 02, 2025 at 10:36:23AM +0200, Oscar Salvador wrote:
> There are at least six consumers of hotplug_memory_notifier that what they
> really are interested in is whether any numa node changed its state, e.g: going
> from being memory aware to becoming memoryless and vice versa.
> 
> Implement a specific notifier for numa nodes when their state gets changed,
> and have those consumers that only care about numa node state changes use it.
> 
> Signed-off-by: Oscar Salvador <osalvador@...e.de>
> Reviewed-by: Harry Yoo <harry.yoo@...cle.com>
> Reviewed-by: Jonathan Cameron <Jonathan.Cameron@...wei.com>
>  
> diff --git a/mm/mempolicy.c b/mm/mempolicy.c
> index f43951668c41..b3ad63fb3a2b 100644
> --- a/mm/mempolicy.c
> +++ b/mm/mempolicy.c
> @@ -3591,20 +3591,20 @@ static int wi_node_notifier(struct notifier_block *nb,
>  			       unsigned long action, void *data)
>  {
>  	int err;
> -	struct memory_notify *arg = data;
> +	struct node_notify *arg = data;
>  	int nid = arg->status_change_nid;
>  
>  	if (nid < 0)
>  		return NOTIFY_OK;
>  
>  	switch (action) {
> -	case MEM_ONLINE:
> +	case NODE_BECAME_MEM_AWARE:
>  		err = sysfs_wi_node_add(nid);
>  		if (err)
>  			pr_err("failed to add sysfs for node%d during hotplug: %d\n",
>  			       nid, err);
>  		break;

May I suggest rolling this patch in with this change:
https://lore.kernel.org/linux-mm/aAij2oUCP1zmcoPv@stanley.mountain/

seems to fix the underlying problem, and returning an error now makes
sense given the change. 

+cc: Honggyu Kim, Dan Carpenter

> -	case MEM_OFFLINE:
> +	case NODE_BECAME_MEMORYLESS:
>  		sysfs_wi_node_delete(nid);
>  		break;
>  	}
> @@ -3639,7 +3639,7 @@ static int __init add_weighted_interleave_group(struct kobject *mempolicy_kobj)
>  		}
>  	}
>  
> -	hotplug_memory_notifier(wi_node_notifier, DEFAULT_CALLBACK_PRI);
> +	hotplug_node_notifier(wi_node_notifier, DEFAULT_CALLBACK_PRI);
>  	return 0;
>  
>  err_cleanup_kobj: