On Sun, Mar 3, 2024 at 6:47 PM Huang, Ying <ying.huang@intel.com> wrote:
>
> "Ho-Ren (Jack) Chuang" <horenchuang@bytedance.com> 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@PH0PR08MB7955.namprd08.prod.outlook.com/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".

Thank you and I didn't mean anything specific. I simply reused phrases we discussed

earlier in the previous patchset. I will change them to the following in v2: 

"At boot time, current memory tiering assigns all detected memory nodes

to the same DRAM tier. This results in CPUless memory/non-DRAM devices,

such as CXL1.1 type3 memory, being unable to be assigned to the correct memory tier,

leading to the inability to migrate pages between different types of memory."


Please see if this looks more specific.

> > 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

--
Best regards,
Ho-Ren (Jack) Chuang
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