#!/bin/bash
echo "it requires at least 3GB free in /tmp"
sync
echo 3 > /proc/sys/vm/drop_caches
dd if=/dev/zero of=/tmp/testfile count=1 bs=999M
sysctl -w vm.vfs_cache_pressure=100
echo "Executing find /, that's gonna take a while..."
find / > /dev/null
echo "OK. Copying huge file..."
cp /tmp/testfile /tmp/testfile2
echo "Let's do find / again, checking how much time takes"
time find / > /dev/null
sysctl -w vm.vfs_cache_pressure=50
echo "Executing find /, that's gonna take a while..."
find /  > /dev/null
echo "OK. Copying huge file..."
cp /tmp/testfile2 /tmp/testfile3
echo "Let's do find / again, checking how much time takes (it should be less than before one)"
time find / > /dev/null
rm -f /tmp/testfile /tmp/testfile2 /tmp/testfile3