THP

THP (Transparent Huge Pages) is a Linux kernel feature that automatically promotes 4 KB memory pages to 2 MB in the background, without explicit configuration. Unlike static Huge Pages, they are managed by the khugepaged kernel process.

How it works #

When active (default always), the kernel attempts to compact normal pages into huge pages in the background. The khugepaged process works continuously to find and merge groups of contiguous pages, causing unpredictable micro-freezes during compaction operations.

Why it matters #

For Oracle they are a disaster. Oracle states explicitly in its documentation: disable THP. The “freezes of a few seconds” that users complain about are often caused by khugepaged. They are disabled with echo never > /sys/kernel/mm/transparent_hugepage/enabled and via GRUB for persistence across reboots.

What can go wrong #

The confusion between Huge Pages (good for Oracle, statically configured) and THP (harmful for Oracle, active by default) is one of the most common mistakes. A DBA who sees “Huge Pages” in the documentation and doesn’t disable THP is making things worse instead of better.