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28.4. Configuring Persistent Memory for use in Device DAX mode

Device DAX (devdax) provides a means for applications to directly access storage, without the involvement of a file system. The benefit of device DAX is that it provides a guaranteed fault granularity, which can be configured using the --align option with the ndctl utility:
# ndctl create-namespace --force --reconfig=namespace0.0 --mode=devdax --align=2M
The given command ensures that the operating system would fault in 2MiB pages at a time. For the Intel 64 and AMD64 architecture, the following fault granularities are supported:
  • 4KiB
  • 2MiB
  • 1GiB
Device DAX nodes (/dev/daxN.M) only supports the following system call:
  • open()
  • close()
  • mmap()
  • fallocate()
read() and write() variants are not supported because the use case is tied to persistent memory programming.