Device DAX for persistent memory and CXL memory expansion
Device DAX provides direct, byte-addressable userspace access to non-traditional memory regions, originally NVDIMM persistent memory and now increasingly CXL memory expansion modules found in modern datacenter servers. It either exposes the capacity as a /dev/dax character device for applications that map it directly, or hot-plugs it into the system as ordinary RAM through the dax_kmem path.
recommendation
It should stay in the kernel because this is an active core subsystem, not a legacy driver. It exposes persistent memory and CXL Type-3 memory expansion devices to userspace as /dev/dax character devices or hot-plugs them as system RAM via dax_kmem. Upstream work continues into 2026, kernel documentation still describes it as the userspace access path for CXL capacity, and vendors like Micron are still selling new CXL memory modules that depend on it.
repository signals
sources
- lore.kernel.org
Recent 2026 patch touching drivers/dax/cxl.c shows active upstream development rather than removal.
- docs.kernel.org
Kernel documentation says the DAX subsystem is used by CXL memory devices to expose /dev/dax or hotplug memory via dax_kmem.
- kernel.org
Kernel documentation describes DAX devices as the userspace access path for CXL capacity exposed as /dev/dax.
- micron.com
Micron markets current CXL memory expansion modules, indicating relevant DAX-backed CXL hardware remains commercially available.
codex reasoning notes (technical)
Keep: drivers/dax is an active core driver subsystem, not an orphaned legacy leaf. Evidence came from local tree inspection via shell (`drivers/dax/Kconfig` and module descriptions) plus `lore_file_timeline` on `drivers/dax/cxl.c`, which showed multiple 2026 patches and no removal signal. Web search provided current kernel docs for DAX/CXL usage and a current Micron CXL product page showing new hardware is still sold. Deployment is low because DAX hardware is niche datacenter/persistent-memory/CXL infrastructure, but it is still relevant and gaining CXL use rather than fading out.