With hardware these days from Intel Optane DC Persistent Memory to HBM being stacked on chips for specialized use-cases, the Linux kernel has been preparing support for the new EFI Special/Specific Purpose Memory specification for knowing about such specialized memory use-cases it shouldn't be treating as normal RAM.

EFI Special Memory (EFI_MEM_SP) succeeds the earlier ACPI HMAT (Heterogeneous Memory Attribute Table) for indicating if a memory pool is general purpose memory or intended for application-specific usage. If it is and the kernel obeys this new attribute, the kernel will avoid allocating to that region and reserve it for use by applications specifically looking for this specialized memory. For the most part it's intended for cases like HBM (High Bandwidth Memory) on a chip that may be addressable by the system itself but given its performance heuristics and limited capacity should be reserved for application-specific purposes rather than inadvertently being used by the kernel for mundane memory storage.

Intel developers have been busy in working on this EFI Specific/Special Purpose Memory support and the latest patches were posted on Thursday, which ride off the Linux 5.2's HMAT/HMEM_REPORTING code. More details via this patch series. With more interesting hardware hitting the market soon and likely supporting this EFI specification, hopefully the code will make it into Linux 5.3.