Re: MM global locks as core counts quadruple

[Karim Manaouil <kmanaouil.dev@gmail.com>]

On Fri, Jun 21, 2024 at 03:54:31AM +0100, Matthew Wilcox wrote:
> I think a more productive solution to contention on the LRU lock is to
> increase the number of zones.  I don't think it's helpful to have a
> 1TB zone of memory.  Maybe we should limit each zone to 16GB or so.
> That means we'd need to increase the number of zones we support, but
> I think that's doable.

What do you mean by zones? The usual ZONE_{DMA|DMA32|NORMAL|HIGHMEM}?

But that's historically existed to deal with physical addressing
limitations (e.g. DMA for devices that can't deal with addresses
larger than 16MiB, or HIGHMEM on 32-bits to access physical memory
beyond what could be directly mapped by the kernel).

Maybe you mean turning ZONE_NORMAL into an array with each entry
pointing to a smaller ZONE_NORMAL region of, let's say, 64GiB or smthng. 
Or it could be divided by the number of CPUs within the NUMA node and each
CPU will be given one ZONE_NORMAL segment with a fallback list to other CPUs
segments in case it runs out of memory. Does that make sense?

Cheers
Karim
PhD Student
Edinburgh University