Red Hat Enterprise Linux 5 Administration Unleashed

Managing Memory with NUMA 431If it is enabled, in some cases, you might need to disable it. To disable NUMA, boot withthe numa=off kernel boot parameter. Refer to “Adding Boot Parameters” in Chapter 2,“Post-Installation Configuration” for step-by-step instructions on adding this boot parameterto the boot loader configuration file. Alternatively, use the numa=on kernel bootparameter to explicitly enable NUMA.21To verify that NUMA is enabled on your system, use the numactl --show command fromthe numactl package. If it is not installed on your system, refer to Chapter 3, “OperatingSystem Updates,” for details on installing additional software. If NUMA is available and isenabled on the system, the output should look similar to Listing 21.2. If NUMA is notavailable on the system or it is disabled, the following message is displayed:No NUMA support available on this system.LISTING 21.2NUMA Enabled on Systempolicy: defaultpreferred node: currentphyscpubind: 0 1cpubind: 0nodebind: 0membind: 0To show the size of each memory node and how much memory is free in each node, usethe numactl --hardware command. For example, Listing 21.3 shows four memory nodeson a system with four processors.LISTING 21.3NUMA Nodes and Free Memory on Each Nodeavailable: 4 nodes (0-3)node 0 size: 2047 MBnode 0 free: 1772 MBnode 1 size: 2047 MBnode 1 free: 1712 MBnode 2 size: 2047 MBnode 2 free: 1756 MBnode 3 size: 2047 MBnode 3 free: 1973 MBThe numactl utility also allows the administrator to tweak the NUMA policies such assetting up interleave memory nodes and configuring a preferred node on which to allocatememory if possible. For descriptions of these additional options, refer to the numactlman page with the man numactl command.To display statistics for each NUMA node, execute the numastat command. It reads the/sys/devices/system/node/ subdirectories and displays their data in a more user-friendlyformat as shown in Listing 21.4 for a system with four memory nodes.