Configuring deferred writing and ultra-large memory

Transparent Huge Pages (THP) is a Linux® memory management system that reduces the overhead of Translation Lookaside Buffer (TLB) lookups on machines with large amounts of memory by using larger memory pages.

Ultra-large main memory configurations and deferred writing are configured in the user interface in Administration > System Configuration > Deferred Writing. If you are using it on Linux operating systems, you might experience faster restarts and more stable latencies when transparent huge pages are disabled. Transparent huge pages might block the memory for seconds when it is defragmenting the RAM. During defragmentation, it is not possible to make even small memory allocations.

Be careful with this setting. It can also result in slower overall message computation when deferred writing is disabled.

To disable transparent huge pages temporarily, run the following commands:

echo never > /sys/kernel/mm/transparent_hugepage/defrag
echo never > /sys/kernel/mm/transparent_hugepage/enabled

Next, restart IBM® Safer Payments.

To check whether the defragmentation file is disabled, run the following command:

cat /sys/kernel/mm/transparent_hugepage/defrag

The output is:

always defer defer-madvise madvise [never]

To check whether transparent huge pages are disabled, run the following command:

cat /sys/kernel/mm/transparent_hugepage/enabled

The output is:

always madvise [never]

In RHEL, you can disable transparent huge pages with the command tuned.

See https://access.redhat.com/solutions/1320153 for details.

You can query the current active profile with:

# tuned-adm active 
Current active profile: latency-performance

To create a customized profile, create a new directory in the /etc/tuned directory with the wanted profile name.

# mkdir /etc/tuned/myprofile-nothp

Next, create a new tuned.conf file for myprofile-nothp, and insert the new tuning information.

# cat /etc/tuned/myprofile-nothp/tuned.conf
[main]
include= latency-performance
[vm]
transparent_hugepages=never

Next, make the script executable:

# chmod +x /etc/tuned/myprofile-nothp/tuned.conf

Next, enable myprofile:

# tuned-adm profile myprofile-nothp

The change takes effect immediately and persists after the system is rebooted.