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numa_fill_memblks() fills in the gaps in numa_meminfo memblks over an physical address range. The ACPI driver will use numa_fill_memblks() to implement a new Linux policy that prescribes extending proximity domains in a portion of a CFMWS window to the entire window. Dan Williams offered this explanation of the policy: A CFWMS is an ACPI data structure that indicates *potential* locations where CXL memory can be placed. It is the playground where the CXL driver has free reign to establish regions. That space can be populated by BIOS created regions, or driver created regions, after hotplug or other reconfiguration. When BIOS creates a region in a CXL Window it additionally describes that subset of the Window range in the other typical ACPI tables SRAT, SLIT, and HMAT. The rationale for BIOS not pre-describing the entire CXL Window in SRAT, SLIT, and HMAT is that it can not predict the future. I.e. there is nothing stopping higher or lower performance devices being placed in the same Window. Compare that to ACPI memory hotplug that just onlines additional capacity in the proximity domain with little freedom for dynamic performance differentiation. That leaves the OS with a choice, should unpopulated window capacity match the proximity domain of an existing region, or should it allocate a new one? This patch takes the simple position of minimizing proximity domain proliferation by reusing any proximity domain intersection for the entire Window. If the Window has no intersections then allocate a new proximity domain. Note that SRAT, SLIT and HMAT information can be enumerated dynamically in a standard way from device provided data. Think of CXL as the end of ACPI needing to describe memory attributes, CXL offers a standard discovery model for performance attributes, but Linux still needs to interoperate with the old regime. Reported-by: Derick Marks <derick.w.marks@intel.com> Suggested-by: Dan Williams <dan.j.williams@intel.com> Signed-off-by: Alison Schofield <alison.schofield@intel.com> Signed-off-by: Dave Hansen <dave.hansen@linux.intel.com> Reviewed-by: Dan Williams <dan.j.williams@intel.com> Tested-by: Derick Marks <derick.w.marks@intel.com> Link: https://lore.kernel.org/all/ef078a6f056ca974e5af85997013c0fda9e3326d.1689018477.git.alison.schofield%40intel.com |
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