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 16:22:38 +0800
From:   Qi Zheng <zhengqi.arch@...edance.com>
To:     David Hildenbrand <david@...hat.com>
Cc:     akpm@...ux-foundation.org, rppt@...nel.org, vbabka@...e.cz,
        mhocko@...e.com, 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

Hi David,

On 2023/10/19 16:11, David Hildenbrand wrote:
> 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.
>   */

OK, will add it in the v3.

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

Thanks.

>