# MongoDB startup: WARNING: /sys/kernel/mm/transparent_hugepage/enabled is 'always'. We suggest setting it to 'never'

**Code:** `WARNING: /sys/kernel/mm/transparent_hugepage/enabled is 'always'` · **Category:** MongoDB · **Seen on:** MongoDB, Linux

Transparent Huge Pages are enabled, which can hurt MongoDB performance (latency spikes).

## Meaning

MongoDB recommends disabling THP for `mongod`: use the official packages (which include a service) or add a systemd unit that sets `never` for `enabled` and `defrag` at boot. Verify with `cat /sys/kernel/mm/transparent_hugepage/enabled`. A startup warning, not a failure.

## Common causes

- OS default THP=always/madvise
- Custom install without tuning
- Cloud images enabling THP
- Container hosts sharing kernel settings
- No boot-time setting persisted

## Quick fix

1. `echo never | sudo tee /sys/kernel/mm/transparent_hugepage/enabled` (temporary)
2. Persist via a systemd unit or `tuned` profile
3. Verify after reboot

## Detailed fix by platform

### Linux

1. `cat /sys/kernel/mm/transparent_hugepage/enabled /sys/kernel/mm/transparent_hugepage/defrag`

## How to diagnose

1. **Setting** — always/never?
2. **Persist** — Reboot-safe?
3. **Impact** — Latency?

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Source: [WhatIsMyError](https://whatismyerror.com/errors/mongodb/transparent-hugepages-warning)