Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 23.128.96.18 as permitted sender) client-ip=23.128.96.18;
Subject: Re: [PATCH 03/10] mm/migrate: update node demotion order during on
 hotplug events
To:     Oscar Salvador <osalvador@suse.de>,
        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
References: <20210401183216.443C4443@viggo.jf.intel.com>
 <20210401183221.977831DE@viggo.jf.intel.com>
 <YG7Sc3i54IV6KyPn@localhost.localdomain> <20210409101400.GA32159@linux>
From:   David Hildenbrand <david@redhat.com>
Organization: Red Hat GmbH
Message-ID: <fb51273c-12e5-f47f-064b-86f5b30b1072@redhat.com>
Date:   Fri, 9 Apr 2021 20:59:21 +0200
User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101
 Thunderbird/78.8.1
MIME-Version: 1.0
In-Reply-To: <20210409101400.GA32159@linux>
Content-Type: text/plain; charset=utf-8; format=flowed
Content-Language: en-US
Content-Transfer-Encoding: 7bit
Precedence: bulk

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