Step 3 - Enable large page use in WAS

To allow the WAS process to utilize the available large page size, set the LDR_CNTRL environment variable from within the console.

  • Open the WebSphere integrated solutions console.
  • In the navigation tree, expand Servers, click Application servers, and select the appropriate server.
  • Expand Java and Process Management and click Process Definition.
  • Click Environment Entries, then click New.
  • Set LDR_CNTRL to the value LARGE_PAGE_DATA=Y. Refer to Figure 6-4 to see an example.

    Figure 6-4 Setting LDR_CNTRL in the Process Definition


    Step 4 - Verify actual large page usage

    You can use the vmstat command to see page size usage statistics.

    To see statistics displayed on a per-page basis, enter the vmstat -P all command. See Example 6-8 for sample output that includes 16 MB large pages in use. The actual pages used appear in column avm. In the example, twenty-one 16 MB pages are in use.

    Example 6-8 View page size statistics per page 

    # vmstat -P all

    System configuration: mem=8192MB

    pgsz            memory                           page
    ----- -------------------------- ------------------------------------
               siz      avm      fre    re    pi    po    fr     sr    cy
       4K   561424   382048   130451     0     0     0     0      0     0
      64K    30447     2093    28354     0     0     0     0      0     0
      16M      256       21      233     0     0     0     0      0     0

    An alternative way to view the actual page usage, but on a per-process basis, is to use the -Z option. Example 6-8 shows that a data page size of 16 MB is being used for the server process, which in this case has a PID of 364600.

    Example 6-9 View page size statistics per process 

    # ps -Z -p 364600
        PID    TTY  TIME DPGSZ SPGSZ TPGSZ CMD
     364600  pts/1  0:58   16M    4K    4K java