Recommendation to disable Linux kernel Transparent HugePages (THP) setting for performance improvement

0 Likes

over 7 years ago

PROBLEM:

Many Linux platforms have a memory management feature known as "Transparent HugePages", or "THP" for short, that's enabled by default. This is meant to transparently provide memory pages that are larger than the default 4k size. But over time, management of this can cause performance problems itself, especially with databases such as PostgreSQL.

SOLUTION:

If you find that AccuRev performance seems to have become slow on your Linux server (this FAQ does not apply to Windows or any non-Linux operating system) and there's no apparent reason, then disabling this system feature may help. If you wish, you can first check performance with the system 'top' command while you're having a slowdown occurrence. If the 'khugepaged' process shows up in the output or if you see a larger than normal percentage of CPU usage spent in "system", then THP could be the cause of the slowdown.

AccuRev recommends disabling THP if it is available on your Linux operating system. Check for the existence of the following directories to determine if you have this feature on your system:

-- Red Hat/CentOS: /sys/kernel/mm/redhat_transparent_hugepage

-- Ubuntu/Debian: /sys/kernel/mm/transparent_hugepage

If so, then running the following commands as root will temporarily disable THP on your system:

% echo "never" > full_pathname_above/enabled

% echo "never" > full_pathname_above/defrag

NOTE: Once you've changed the settings of the 'enabled' and 'defrag' files to "[never]", the system should slowly come back to more normal performance within several minutes.

To permanently disable THP across reboots, add the following to /etc/rc.local:

====================

if test -f /sys/kernel/mm/transparent_hugepage/enabled; then

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

if test -f /sys/kernel/mm/transparent_hugepage/defrag; then

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

if test -f /sys/kernel/mm/redhat_transparent_hugepage/enabled; then

echo never > /sys/kernel/mm/redhat_transparent_hugepage/enabled

if test -f /sys/kernel/mm/redhat_transparent_hugepage/defrag; then

echo never > /sys/kernel/mm/redhat_transparent_hugepage/defrag

====================

To verify that THP has been disabled, a 'cat' of the "enabled" and "defrag" files will display what state is currently active in brackets. For instance:

====================

% cat /sys/kernel/mm/transparent_hugepage/enabled

always madvise [never]

% cat /sys/kernel/mm/transparent_hugepage/defrag

always madvise [never]

====================

In the above output, "[never]" indicates that THP is disabled.

For further questions, contact the Micro Focus SupportLine.

Comment List

Recommended

Menu

AccuRev

Recommendation to disable Linux kernel Transparent HugePages (THP) setting for performance improvement

Resources