Support for Virtual Memory Devices

As Linux continues to support ever larger and weirder hardware, the needs of giant tech companies play an ever greater role in its development. And as each company writes patches for its own purposes, they can sometimes find themselves in conflict with each other.

An example of this happened over the course of the last half of 2025, as representatives of Microsoft, Google, and Intel strove mightily to make sure they could all stay happy. Mike Rapoport of Microsoft kicked things off with a patch to let the user cordon off sections of RAM and make them look like their own memory devices. This was useful, he said, for virtual machines (VMs) that needed to isolate their resources from the main host system.

Mike posted a patch to create a new RAMDAZ driver file in the NVDIMM driver, to allow the "creation of DIMM devices on top of E820_TYPE_PRAM regions and devicetree pmem-region nodes." As he put it, "The DIMMs support label space management on the 'device' and provide a flexible way to access RAM using fsdax and devdax."

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