Re: [RFC PATCH 1/4] mm/memory_hotplug: Add interface for runtime (de)configuration of memory

David Hildenbrand
2025-05-21T14:25:37Z

On 21.05.25 16:21, Heiko Carstens wrote:
> On Wed, May 21, 2025 at 02:33:42PM +0200, David Hildenbrand wrote:
>> On 21.05.25 12:34, Sumanth Korikkar wrote:
>>> As you pointed out, how about having something similar to
>>> 73954d379efd ("dax: add a sysfs knob to control memmap_on_memory behavior")
>>
>> Right. But here, the use case is usually (a) to add a gigantic amount of
>> memory using add_memory(), not small blocks like on s390x (b) consume the
>> memmap from (slow) special-purpose memory as well.
>>
>> Regarding (a), the memmap could be so big that add_memory() might never
>> really work (not just because of some temporary low-memory situation).
>
> What is "big"? Worst case for s390 with existing machines would be an
> increment size (aka memory block size) of 64GB.
Oh! I was assuming the increment size would always be around 256MiB or so.

In that case, it can make sense to have this, yes!

--
Cheers,

David / dhildenb