Red Hat Enterprise Linux (RHEL) uses udev rules to automatically online newly added memory devices, including Compute Express Link (CXL) memory. This mechanism ensures that hot-plugged memory blocks are immediately available to the operating system without manual intervention.

The default udev rule for memory hot-plug operations is located at /usr/lib/udev/rules.d/40-redhat-hotplug.rules. This file contains the configuration that triggers automatic memory onlining and, where applicable, assigns memory blocks to ZONE_MOVABLE.

In RHEL bare metal, ZONE_MOVABLE is configured automatically through this default udev rule set. This ensures that when memory is dynamically added to the system, the kernel reserves a portion as ZONE_MOVABLE, which can be safely removed later if needed. No manual configuration is required for hot-plugged memory devices.