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Date:   Fri, 9 Apr 2021 12:14:04 +0200
From:   Oscar Salvador <osalvador@suse.de>
To:     Dave Hansen <dave.hansen@linux.intel.com>
Cc:     linux-mm@kvack.org, linux-kernel@vger.kernel.org,
        shy828301@gmail.com, weixugc@google.com, rientjes@google.com,
        ying.huang@intel.com, dan.j.williams@intel.com, david@redhat.com
Subject: Re: [PATCH 03/10] mm/migrate: update node demotion order during on
 hotplug events
Message-ID: <20210409101400.GA32159@linux>
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On Thu, Apr 08, 2021 at 11:52:51AM +0200, Oscar Salvador wrote:
> I am not really into PMEM, and I ignore whether we need
> CONFIG_MEMORY_HOTPLUG in order to have such memory on the system.
> If so, the following can be partly ignored.

Ok, I refreshed by memory with [1].
From that, it seems that in order to use PMEM as RAM we need CONFIG_MEMORY_HOTPLUG.
But is that always the case? Can happen that in some scenario PMEM comes ready
to use and we do not need the hotplug trick?

Anyway, I would still like to clarify the state of the HOTPLUG_CPU.
On x86_64, HOTPLUG_CPU and MEMORY_HOTPLUG are tied by SPM means, but on arm64
one can have MEMORY_HOTPLUG while not having picked HOTPLUG_CPU.

My point is that we might want to put the callback functions and the callback
registration for cpu-hotplug guarded by its own HOTPLUG_CPU instead of guarding it
in the same MEMORY_HOTPLUG block to make it more clear?

-- 
Oscar Salvador
SUSE L3