Re: [PATCH v1 0/1] Improved Memory Tier Creation for CPUless NUMA Nodes

[Huang, Ying]

"Ho-Ren (Jack) Chuang" <horenchuang@xxxxxxxxxxxxx> writes:

> The memory tiering component in the kernel is functionally useless for
> CPUless memory/non-DRAM devices like CXL1.1 type3 memory because the nodes
> are lumped together in the DRAM tier.
> https://lore.kernel.org/linux-mm/PH0PR08MB7955E9F08CCB64F23963B5C3A860A@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx/T/

I think that it's unfair to call it "useless".  Yes, it doesn't work if
the CXL memory device are not enumerate via drivers/dax/kmem.c.  So,
please be specific about in which cases it doesn't work instead of too
general "useless".

> This patchset automatically resolves the issues. It delays the initialization
> of memory tiers for CPUless NUMA nodes until they obtain HMAT information
> at boot time, eliminating the need for user intervention.
> If no HMAT specified, it falls back to using `default_dram_type`.
>
> Example usecase:
> We have CXL memory on the host, and we create VMs with a new system memory
> device backed by host CXL memory. We inject CXL memory performance attributes
> through QEMU, and the guest now sees memory nodes with performance attributes
> in HMAT. With this change, we enable the guest kernel to construct
> the correct memory tiering for the memory nodes.
>
> Ho-Ren (Jack) Chuang (1):
>   memory tier: acpi/hmat: create CPUless memory tiers after obtaining
>     HMAT info
>
>  drivers/acpi/numa/hmat.c     |  3 ++
>  include/linux/memory-tiers.h |  6 +++
>  mm/memory-tiers.c            | 76 ++++++++++++++++++++++++++++++++----
>  3 files changed, 77 insertions(+), 8 deletions(-)

--
Best Regards,
Huang, Ying