linux-kernel - Re: [PATCH -V8 02/10] mm/numa: automatically generate node migration order

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Date:   Mon, 21 Jun 2021 12:53:04 -0700
From:   Dave Hansen <dave.hansen@...el.com>
To:     "Huang, Ying" <ying.huang@...el.com>, Zi Yan <ziy@...dia.com>,
        Dave Hansen <dave.hansen@...ux.intel.com>
Cc:     linux-mm@...ck.org, linux-kernel@...r.kernel.org,
        Yang Shi <shy828301@...il.com>, Michal Hocko <mhocko@...e.com>,
        Wei Xu <weixugc@...gle.com>,
        David Rientjes <rientjes@...gle.com>,
        Dan Williams <dan.j.williams@...el.com>,
        David Hildenbrand <david@...hat.com>,
        osalvador <osalvador@...e.de>
Subject: Re: [PATCH -V8 02/10] mm/numa: automatically generate node migration
 order

On 6/19/21 1:18 AM, Huang, Ying wrote:
>>>  int next_demotion_node(int node)
>>>  {
>>> -	return node_demotion[node];
>>> +	/*
>>> +	 * node_demotion[] is updated without excluding
>>> +	 * this function from running.  READ_ONCE() avoids
>>> +	 * reading multiple, inconsistent 'node' values
>>> +	 * during an update.
>>> +	 */
>>> +	return READ_ONCE(node_demotion[node]);
>>>  }
>> Is it necessary to have two separate patches to add node_demotion and
>> next_demotion_node() then modify it immediately? Maybe merge Patch 1 into 2?
>>
>> Hmm, I just checked Patch 3 and it changes node_demotion again and uses RCU.
>> I guess it might be much simpler to just introduce node_demotion with RCU
>> in this patch and Patch 3 only takes care of hotplug events.
> Hi, Dave,
> 
> What do you think about this?
> 

Squashing them seems like a good idea to me.