linux-kernel - Re: [PATCH 0/4] Support dynamic (de)configuration of memory

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Message-ID: <abdd6107-d380-48f5-9a25-22a5f560c78b@redhat.com>
Date: Wed, 8 Oct 2025 11:43:05 +0200
From: David Hildenbrand <david@...hat.com>
To: Heiko Carstens <hca@...ux.ibm.com>
Cc: Sumanth Korikkar <sumanthk@...ux.ibm.com>,
 Andrew Morton <akpm@...ux-foundation.org>, linux-mm <linux-mm@...ck.org>,
 LKML <linux-kernel@...r.kernel.org>, linux-s390
 <linux-s390@...r.kernel.org>, Gerald Schaefer
 <gerald.schaefer@...ux.ibm.com>, Vasily Gorbik <gor@...ux.ibm.com>,
 Alexander Gordeev <agordeev@...ux.ibm.com>
Subject: Re: [PATCH 0/4] Support dynamic (de)configuration of memory

On 08.10.25 11:12, Heiko Carstens wrote:
> On Wed, Oct 08, 2025 at 10:02:26AM +0200, David Hildenbrand wrote:
>> On 08.10.25 08:05, Sumanth Korikkar wrote:
>>>>> chmem changes would look like:
>>>>> chmem -c 128M -m 1 : configure memory with memmap-on-memory enabled
>>>>> chmem -g 128M : deconfigure memory
>>>>
>>>> I wonder if the above two are really required. I would expect most/all users
>>>> to simply keep using -e / -d.
>>>>
>>>> Sure, there might be some corner cases, but I would assume most people to
>>>> not want to care about memmap-on-memory with the new model.
> 
> ...
> 
>>> 2) If the administrator forgets to configure
>>> memory_hotplug.memmap_on_memory=Y, the following steps can be taken:
>>> Rescue from OOM situations: configure with memmap-on-memory enabled, online it.
>>
>> That's my point: I don't consider either very likely to be used by actual
>> admins.
> 
> But does it really hurt to add those options?

Oh, I don't think so.

I was just a bit surprised to see it in the first version of this, 
because it felt to me like this is something to be added later on top 
quite easily/cleanly.

In particular, patch #2 would get a lot lighter also in terms of 
documentation.

So no strong opinion about adding it, but maybe we can just split it 
into a separate patch and focus on patch #2 on the real magic?

-- 
Cheers

David / dhildenb