RE: FW: [LSF/MM/BPF TOPIC] SMDK inspired MM changes for CXL

[Dan Williams <dan.j.williams@intel.com>]

Kyungsan Kim wrote:
[..]
> >In addition to CXL memory, we may have other kind of memory in the
> >system, for example, HBM (High Bandwidth Memory), memory in FPGA card,
> >memory in GPU card, etc.  I guess that we need to consider them
> >together.  Do we need to add one zone type for each kind of memory?
> 
> We also don't think a new zone is needed for every single memory
> device.  Our viewpoint is the sole ZONE_NORMAL becomes not enough to
> manage multiple volatile memory devices due to the increased device
> types.  Including CXL DRAM, we think the ZONE_EXMEM can be used to
> represent extended volatile memories that have different HW
> characteristics.

Some advice for the LSF/MM discussion, the rationale will need to be
more than "we think the ZONE_EXMEM can be used to represent extended
volatile memories that have different HW characteristics". It needs to
be along the lines of "yes, to date Linux has been able to describe DDR
with NUMA effects, PMEM with high write overhead, and HBM with improved
bandwidth not necessarily latency, all without adding a new ZONE, but a
new ZONE is absolutely required now to enable use case FOO, or address
unfixable NUMA problem BAR." Without FOO and BAR to discuss the code
maintainability concern of "fewer degress of freedom in the ZONE
dimension" starts to dominate.