[PATCH v3 4/7] mm/hotplug: Allow pageblock alignment via altmap reservation

Aneesh Kumar K V aneesh.kumar at linux.ibm.com
Wed Jul 12 13:16:53 AEST 2023

On 7/11/23 10:49 PM, David Hildenbrand wrote:
> On 11.07.23 06:48, Aneesh Kumar K.V wrote:
>> Add a new kconfig option that can be selected if we want to allow
>> pageblock alignment by reserving pages in the vmemmap altmap area.
>> This implies we will be reserving some pages for every memoryblock
>> This also allows the memmap on memory feature to be widely useful
>> with different memory block size values.
> "reserving pages" is a nice way of saying "wasting memory". :) Let's spell that out.
> I think we have to find a better name for this, and I think we should have a toggle similar to memory_hotplug.memmap_on_memory. This should be an admin decision, not some kernel config option.
> memory_hotplug.force_memmap_on_memory
> "Enable the memmap on memory feature even if it could result in memory waste due to memmap size limitations. For example, if the memmap for a memory block requires 1 MiB, but the pageblock size is 2 MiB, 1 MiB
> of hotplugged memory will be wasted. Note that there are still cases where the feature cannot be enforced: for example, if the memmap is smaller than a single page, or if the architecture does not support the forced mode in all configurations."
> Thoughts?

With module parameter, do we still need the Kconfig option? 


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