Manually online memory

If you have disabled automatic memory onlining, newly added memory blocks, such as those from a hot-plugged CXL device, remain offline by default. You can manually online these memory blocks by using the sysfs interface.

Before you begin

  • You have root privileges on your system.

Procedure

  1. Identify the offline memory block identifier using the lsmem command: 
    # lsmem
     
    RANGE                                  SIZE  STATE REMOVABLE BLOCK
0x0000000000000000-0x000000007fffffff    2G online       yes  0-1
0x0000000100000000-0x000000087fffffff   30G online       yes  4-33
0x0000000880000000-0x00000008ffffffff    2G offline           34-41

Memory block size:       256M
Total online memory:      32G
Total offline memory:      2G

    In this example, the offline memory blocks are 34-41.

  2. Online a specific memory block by writing to its state file: 
    
            echo online > /sys/devices/system/memory/memory<_identifier_>/state

    Replace memory<_identifier_> with the identifier of the memory block, for example, memory34.

Results

  • Verify the memory block is online: 
    cat /sys/devices/system/memory/memory<_identifier_>/state
     
    online