Re: [LSF/MM/BPF TOPIC] Restricting or migrating unmovable kernel allocations from slow tier

Gregory Price
2025-02-07T09:27:41Z

On Fri, Feb 07, 2025 at 03:57:45AM -0500, Gregory Price wrote:
> On Fri, Feb 07, 2025 at 04:20:24PM +0900, Byungchul Park wrote:
>
> My thoughts here are that memory tiering is the wrong tool for the
> problem you are trying to solve.
>
> Maybe there's a world in which we propose a ZONE_MEMDESC which is
> exclusively used for `struct page` for a node.
>
> At least then you could design CXL capacities *around* that.
>

Dumb question time

Is this maybe not an entirely horrible idea? Even at 16-byte page
structs we use 4GB-per-1TB of capacity.

Maybe a memory device providing additional capacity SHOULD be made
(given the option?) to service its own struct pages - but maintain
some control over hot-plug-ability?

At least it could tear down all the ZONE_MOVABLE regions and finally
release the MEMDESC region when finished.

Seems too obvious to have not been proposed already. :shrug:

~Gregory