linux-kernel - Re: [PATCH v2 2/2] mm: memory_hotplug: drop memoryless node from fallback lists

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Date:   Thu, 19 Oct 2023 10:11:19 +0200
From:   David Hildenbrand <david@...hat.com>
To:     Qi Zheng <zhengqi.arch@...edance.com>, akpm@...ux-foundation.org,
        rppt@...nel.org, vbabka@...e.cz, mhocko@...e.com
Cc:     willy@...radead.org, mgorman@...hsingularity.net, mingo@...nel.org,
        aneesh.kumar@...ux.ibm.com, ying.huang@...el.com,
        hannes@...xchg.org, osalvador@...e.de,
        linux-kernel@...r.kernel.org, linux-mm@...ck.org
Subject: Re: [PATCH v2 2/2] mm: memory_hotplug: drop memoryless node from
 fallback lists

On 19.10.23 09:36, Qi Zheng wrote:
> In offline_pages(), if a node becomes memoryless, we
> will clear its N_MEMORY state by calling node_states_clear_node().
> But we do this after rebuilding the zonelists by calling
> build_all_zonelists(), which will cause this memoryless node to
> still be in the fallback list of other nodes. This will incur
> some runtime overhead.
> 
> To drop memoryless node from fallback lists in this case, just
> call node_states_clear_node() before calling build_all_zonelists().
> 
> Signed-off-by: Qi Zheng <zhengqi.arch@...edance.com>
> ---
>   mm/memory_hotplug.c | 2 +-
>   1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/mm/memory_hotplug.c b/mm/memory_hotplug.c
> index d4a364fdaf8f..18af399627f0 100644
> --- a/mm/memory_hotplug.c
> +++ b/mm/memory_hotplug.c
> @@ -2036,12 +2036,12 @@ int __ref offline_pages(unsigned long start_pfn, unsigned long nr_pages,
>   	/* reinitialise watermarks and update pcp limits */
>   	init_per_zone_wmark_min();
>   
> +	node_states_clear_node(node, &arg);
>   	if (!populated_zone(zone)) {
>   		zone_pcp_reset(zone);
>   		build_all_zonelists(NULL);
>   	}
>   
> -	node_states_clear_node(node, &arg);
>   	if (arg.status_change_nid >= 0) {
>   		kcompactd_stop(node);
>   		kswapd_stop(node);

Probably worth a comment.

/*
  * Make sure to mark the node as memory-less before rebuilding the zone
  * list. Otherwise this node would still appear in the fallback lists.
  */

Acked-by: David Hildenbrand <david@...hat.com>

-- 
Cheers,

David / dhildenb