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

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Message-ID: <20251008091226.7407Ba1-hca@linux.ibm.com>
Date: Wed, 8 Oct 2025 11:12:26 +0200
From: Heiko Carstens <hca@...ux.ibm.com>
To: David Hildenbrand <david@...hat.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 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? If really needed then all of
the sudden admins would have to deal with architecture specific sysfs
layout - so the very rare emergency case becomes even more complicated.

Given that these tools exist to help that people don't have to deal with
such details, I'm much in favor of adding those options.