Memory Leak Detection and Resolution

Introduction

A memory leak occurs when an application fails to properly release memory it has used, causing RAM usage to continuously increase over time. Eventually the system runs out of memory, swap space fills up, and the server slows down or crashes. This guide covers how to detect and resolve memory leaks.

Symptoms

Typical signs of a memory leak:

RAM usage continuously increases over time (returns to normal after restart)
Available memory in free -h output gradually decreases
Swap usage increases
Application slows down over time
OOM (Out of Memory) killer activates and kills processes
oom-kill messages appear in dmesg

Step 1: Check Current Memory Status

hljs bash

# General memory status
free -h

# Detailed memory info
cat /proc/meminfo

# Swap usage
swapon --show

# OOM killer logs
dmesg | grep -i 'oom\|killed process\|out of memory'
journalctl -k | grep -i 'oom\|killed'

If the available value in free -h drops below 10% of total RAM, you have memory pressure.

Step 2: Which Process Uses the Most Memory?

hljs bash

# Sort by memory usage with ps
ps aux --sort=-%mem | head -20

# Real-time monitoring with top
top
# Press 'M' to sort by memory

# More detailed memory analysis with smem
sudo apt install smem -y
smem -r -k | head -20

# Monitor a specific process
watch -n 2 'ps aux | grep app_name | grep -v grep'

Step 3: Confirm the Memory Leak

hljs bash

# Find the PID of a specific process
pgrep -f app_name

# Log memory usage every 30 seconds
while true; do
    echo "$(date): $(cat /proc/PID/status | grep VmRSS)"
    sleep 30
done

# Detailed memory map
cat /proc/PID/smaps | grep -E '(Rss|Pss|Shared|Private)' | awk '{sum += $2} END {print sum/1024 " MB"}'

Step 4: Application-Specific Solutions

Node.js Memory Leak

hljs bash

# Set Node.js memory limit
node --max-old-space-size=512 app.js

# PM2 auto-restart on memory limit
pm2 start app.js --max-memory-restart 500M

PHP-FPM Memory Leak

hljs bash

# /etc/php/8.x/fpm/pool.d/www.conf
# pm.max_requests = 500  # Restart worker after 500 requests

# PHP memory limit
# memory_limit = 256M

MySQL/MariaDB Memory Usage

hljs bash

# /etc/mysql/mysql.conf.d/mysqld.cnf
# innodb_buffer_pool_size = 256M  # 25-50% of RAM

Step 5: Emergency Solutions

Clear Memory Cache

hljs bash

# Clear page cache (safe)
sync && echo 1 > /proc/sys/vm/drop_caches

Use drop_caches carefully in production. Disk I/O may temporarily increase after clearing the cache.

Restart the Leaking Service

hljs bash

# Restart service
sudo systemctl restart service_name

# Apply memory limit with systemd
# /etc/systemd/system/service.service
# [Service]
# MemoryMax=512M

Add Swap Space

hljs bash

# Create swap file
sudo fallocate -l 2G /swapfile
sudo chmod 600 /swapfile
sudo mkswap /swapfile
sudo swapon /swapfile

# Make permanent
echo '/swapfile none swap sw 0 0' | sudo tee -a /etc/fstab

Conclusion

To resolve memory leaks, first identify which process is consuming memory with ps aux and smem, then confirm the leak by monitoring growth over time. In the short term, restart the leaking service and apply a memory limit with systemd. For a permanent fix, investigate the application's source code using tools like Valgrind (C/C++), heapdump (Node.js), or jmap (Java). Contact REXE support if the issue persists.

Memory Leak Detection and Resolution

Table of Contents

Introduction

Symptoms

Step 1: Check Current Memory Status

Step 2: Which Process Uses the Most Memory?

Step 3: Confirm the Memory Leak

Step 4: Application-Specific Solutions

Node.js Memory Leak

PHP-FPM Memory Leak

MySQL/MariaDB Memory Usage

Step 5: Emergency Solutions

Clear Memory Cache

Restart the Leaking Service

Add Swap Space

Conclusion

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