linux-kernel - Re: [PATCH 1/2] mm/migrate: optimize hotplug-time demotion order updates

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Date:   Tue, 21 Sep 2021 10:01:35 -0700
From:   Dave Hansen <dave.hansen@...el.com>
To:     "Huang, Ying" <ying.huang@...el.com>
Cc:     Dave Hansen <dave.hansen@...ux.intel.com>,
        linux-kernel@...r.kernel.org, oliver.sang@...el.com,
        mhocko@...e.com, weixugc@...gle.com, osalvador@...e.de,
        rientjes@...gle.com, dan.j.williams@...el.com, david@...hat.com,
        gthelen@...gle.com, yang.shi@...ux.alibaba.com,
        akpm@...ux-foundation.org
Subject: Re: [PATCH 1/2] mm/migrate: optimize hotplug-time demotion order
 updates

On 9/21/21 7:36 AM, Huang, Ying wrote:
>> This removes the need for the demotion code to track *any* state.  I've
>> attached a totally untested patch to do this.
> Yes.  This sounds good.  I will try to test this patch on my side.
> 
>>>From another point of view, we still need to update demotion order upon
> CPU hotplug too, because whether a node has CPU may be changed there.
> And we need a solution for that too.

Just to recap...  The reason I sent this series is that there's a known,
detectable regression in a memory hotplug "benchmark".  This affects the
5.15 series.

While I agree that we should look into the impact on CPU hotplug, I
think we should probably focus on the *known* memory hotplug issue for 5.15.