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Subject: Re: [PATCH] mm: don't rely on system state to detect hot-plug
 operations
To:     Michal Hocko <mhocko@suse.com>
Cc:     akpm@linux-foundation.org, David Hildenbrand <david@redhat.com>,
        Oscar Salvador <osalvador@suse.de>, rafael@kernel.org,
        nathanl@linux.ibm.com, cheloha@linux.ibm.com,
        stable@vger.kernel.org,
        Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        linux-mm@kvack.org, LKML <linux-kernel@vger.kernel.org>
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From:   Laurent Dufour <ldufour@linux.ibm.com>
Message-ID: <31cfdf35-618f-6f56-ef16-0d999682ad02@linux.ibm.com>
Date:   Thu, 10 Sep 2020 09:51:39 +0200
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Le 10/09/2020 à 09:23, Michal Hocko a écrit :
> On Wed 09-09-20 18:07:15, Laurent Dufour wrote:
>> Le 09/09/2020 à 12:59, Michal Hocko a écrit :
>>> On Wed 09-09-20 11:21:58, Laurent Dufour wrote:
> [...]
>>>> For the point a, using the enum allows to know in
>>>> register_mem_sect_under_node() if the link operation is due to a hotplug
>>>> operation or done at boot time.
>>>
>>> Yes, but let me repeat. We have a mess here and different paths check
>>> for the very same condition by different ways. We need to unify those.
>>
>> What are you suggesting to unify these checks (using a MP_* enum as
>> suggested by David, something else)?
> 
> We do have system_state check spread at different places. I would use
> this one and wrap it behind a helper. Or have I missed any reason why
> that wouldn't work for this case?

That would not work in that case because memory can be hot-added at the 
SYSTEM_SCHEDULING system state and the regular memory is also registered at that 
system state too. So system state is not enough to discriminate between the both.

I think I'll go with the option suggested by David, replacing the enum 
memmap_context a new enum memplug_context and pass that context to 
register_mem_sect_under_node() so that function will known when node id should 
be checked or not.

Cheers,
Laurent.