daxctl

List DAX devices

$ daxctl list

$ daxctl list -d

$ daxctl reconfigure-device --mode=system-ram [dax0.0]

$ daxctl reconfigure-device --mode=devdax [dax0.0]

$ daxctl online-memory [dax0.0]

$ daxctl offline-memory [dax0.0]

daxctl command [options] [device]

daxctl manages Device DAX (Direct Access) devices, which provide direct memory-mapped access to persistent memory (PMEM) or CXL memory regions. It configures how this memory appears to the system.
In devdax mode, memory is accessed through a character device for applications needing direct access (databases, memory-mapped files). In system-ram mode, the memory appears as regular system RAM and can be used by any application.
The tool works with regions created by ndctl (for NVDIMM) or cxl (for CXL memory). It's essential for managing disaggregated and persistent memory in modern server systems.

list [options]

List DAX devices and regions.

Change device mode.

Bring DAX memory online for system use.

Take DAX memory offline.

Include device details in listing.

Include region details.

Device mode: devdax or system-ram.

Force operation.

Don't automatically online memory.

Verbose output.

devdax: Direct character device access (/dev/daxX.Y)

Used for applications that explicitly mmap the device

Treated as regular RAM, usable by any process

Mode changes may require the device to be unmapped first. System-ram mode memory may have different NUMA characteristics than normal RAM. Requires kernel support for DAX (Device-DAX). Persistent memory in system-ram mode loses persistence benefit.

daxctl is part of the ndctl project led by Dan Williams at Intel. It was developed alongside Linux kernel support for persistent memory (NVDIMM) starting around 2016. As persistent memory technology (Intel Optane, CXL memory) evolved, daxctl became essential for managing how this memory integrates with the operating system.

ndctl(1), cxl(1), numactl(8)