memory-leaks.md

Finding Memory Leaks

This is a guide to finding and fixing memory leaks.

Memory leaks are a common bug where a program retains allocated memory after it is no longer needed, and over time this makes the program slow (and even slows down the whole operating system.)

To see if they are happening, you can log and graph the memory consumption of your Activity.

1. Log the memory usage

Start sugar, your Activity, then the Terminal Activity.

In Terminal run htop, look for the pid of your Activity, and quit.

Run a loop that measures the memory consumption of your Activity,

while true; do
  echo $(date +%s.%N) \
    $(awk '/VmSize/ { print $2; }' /proc/$(pgrep -f jarabe)/status)
  sleep 1
done | tee memory.log

Switch to your Activity, and follow some procedure to test it, then stop using it and wait a couple of minutes to let it settle down.

Tip: Use xdotool to script the interaction with your activity, so you can reliably reproduce the testing procedure. For example, xdotool key F6

Switch to Terminal and stop the loop by pressing CTRL-C

2. Graph the log

Create a graph of the data, either quickly with plotutils,

graph -T png data > graph.png;

or with gnuplot, run this script

#!/bin/bash
gnuplot -persist <<EOF
# comment out the following 2 lines to display on screen
set terminal png
set output "memory.png"

set title "XO-1.5 ... \nVmSize leak test\n2015-10-06\nby James Cameron"
set xlabel "Clock time MM:SS"
set ylabel "VmSize kb"
set nokey

set xdata time
set timefmt "%s"

set grid
set style data step

plot "memory.log" using 1:2 title "run #1" lw 2

The memory.png might look like this:

Finally removes the files,

rm data  graph.png memory.log memory.png;

Real World Example

A memory leak was found and discussed in the Sugar Desktop programs (jarabe), sugarlabs/sugar#520, with a fix in sugarlabs/sugar#614. That discussions is the source for this guide.