linux-kernel - Re: CXL Boot to Bash - Section 3: Memory (block) Hotplug

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Message-ID: <Z9BmQH5EMpC1noCz@localhost.localdomain>
Date: Tue, 11 Mar 2025 17:35:12 +0100
From: Oscar Salvador <osalvador@...e.de>
To: Zi Yan <ziy@...dia.com>
Cc: Gregory Price <gourry@...rry.net>, David Hildenbrand <david@...hat.com>,
	Yang Shi <shy828301@...il.com>, lsf-pc@...ts.linux-foundation.org,
	linux-mm@...ck.org, linux-cxl@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: CXL Boot to Bash - Section 3: Memory (block) Hotplug

On Tue, Mar 11, 2025 at 12:08:03PM -0400, Zi Yan wrote:
> Or a new option for memmap_on_memory like “use_whole_block”, then hotplug
> code checks altmap is NULL or not when a memory block is plugged.
> If altmap is NULL, the hot plugged memory block is used as memmap,
> otherwise, the memory block is plugged as normal memory. The code also
> needs to maintain which part of the altmap is used to tell whether
> the memmap’d memory block can be offline or not.

One of the first versions of memmap_on_memory did not have the restrictions of
working only per memblock, so one could hot-plug more than a memory-block worth
of memory using memmap_on_memory, meaning that we could end up with memblocks
only containing memmap pages.

Now, we decided to go with only one memblock at a time because of simplicity
and also because we did not have any real-world scenarios that needed that
besides being able to have larger contiguos memory for e.g: hugetlb.

If people think that there is more to it, we could revisit that and see how it
would look nowadays. Maybe it is not too much of a surgery. (or maybe it is :-))

-- 
Oscar Salvador
SUSE Labs