Memory Leak Diagnosis — /proc/meminfo · smaps · valgrind

# Overall memory status
free -h
# Mem: total=16G, used=14G, free=500M, buff/cache=2G, available=1G
# available is what matters — actually usable memory

# Detailed information
cat /proc/meminfo | grep -E "MemTotal|MemFree|MemAvailable|Cached|Buffers|SwapTotal|SwapFree"

# Watch memory changes over time
watch -n 5 'free -h'

# Check swap activity with vmstat
vmstat 5 10
# If the si/so columns are not consistently 0, memory is insufficient

# Top 10 by memory
ps aux --sort=-%mem | head -11
ps aux --sort=-rss | awk '{print $2, $4, $6, $11}' | head -11

# Memory of a specific process
ps -p 1234 -o pid,rss,vsz,cmd
# RSS: actual resident memory (KB)
# VSZ: virtual memory size (includes shared libraries)

# Observe memory trend with pidstat
pidstat -r -p 1234 5 12   # 5-second interval, 1 minute

# pmap — memory mapping summary
sudo pmap -x 1234
# RSS total is actual usage
sudo pmap -x 1234 | tail -1

# /proc/PID/smaps — detailed analysis
sudo cat /proc/1234/smaps | awk '
  /^Private_Dirty/ { pd += $2 }
  /^Shared_Dirty/  { sd += $2 }
  END { printf "Private Dirty: %d KB\nShared Dirty: %d KB\n", pd, sd }
'

# smaps_rollup — summary (kernel 4.14+)
sudo cat /proc/1234/smaps_rollup

# Check heap size
sudo cat /proc/1234/status | grep -E "VmRSS|VmHeap|VmPeak"

sudo apt install -y valgrind

# Memory leak check
valgrind --leak-check=full \
         --show-leak-kinds=all \
         --track-origins=yes \
         --verbose \
         ./myprogram 2>&1 | tee valgrind.log

# Key output
# "definitely lost": definite leak
# "indirectly lost": indirect leak
# "possibly lost": possible leak

# Enable at compile time
gcc -fsanitize=address -g -O1 myprogram.c -o myprogram
./myprogram   # Automatically reports on leak

import tracemalloc

tracemalloc.start()

# Code to analyze
do_something()

snapshot = tracemalloc.take_snapshot()
top_stats = snapshot.statistics('lineno')
for stat in top_stats[:10]:
    print(stat)

# Compare snapshots with heapdump
node --expose-gc server.js

# Connect Chrome DevTools
node --inspect server.js
# Memory profile in chrome://inspect

# Check whether a process was killed by OOM
dmesg | grep -i "oom|killed process|out of memory"
sudo journalctl -k | grep -i oom

# Check OOM score (higher = killed first)
cat /proc/1234/oom_score

# Protect an important process from OOM
echo -1000 | sudo tee /proc/1234/oom_score_adj

# Drop page cache
sync; echo 1 | sudo tee /proc/sys/vm/drop_caches

# Drop slab cache as well
sync; echo 3 | sudo tee /proc/sys/vm/drop_caches

# Add swap (temporary)
sudo dd if=/dev/zero of=/swapfile bs=1G count=4
sudo chmod 600 /swapfile
sudo mkswap /swapfile
sudo swapon /swapfile