linux-kernel - Re: [PATCH 03/10] mm/migrate: update node demotion order during on hotplug events

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Message-ID: <fb51273c-12e5-f47f-064b-86f5b30b1072@redhat.com>
Date:   Fri, 9 Apr 2021 20:59:21 +0200
From:   David Hildenbrand <david@...hat.com>
To:     Oscar Salvador <osalvador@...e.de>,
        Dave Hansen <dave.hansen@...ux.intel.com>
Cc:     linux-mm@...ck.org, linux-kernel@...r.kernel.org,
        shy828301@...il.com, weixugc@...gle.com, rientjes@...gle.com,
        ying.huang@...el.com, dan.j.williams@...el.com
Subject: Re: [PATCH 03/10] mm/migrate: update node demotion order during on
 hotplug events

On 09.04.21 12:14, Oscar Salvador wrote:
> 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?

The only way to add more System RAM is via add_memory() and friends like 
add_memory_driver_managed(). These all require CONFIG_MEMORY_HOTPLUG.

Memory ballooning is a different case, but there we're only adjusting 
the managed page counters.

-- 
Thanks,

David / dhildenb