Clearing i/o cache on Linux
Running
sync; echo 3 > /proc/sys/vm/drop_caches
under root or
sudo bash -c 'sync; echo 3 > /proc/sys/vm/drop_caches'
when using sudo helps to avoid some i/o caching issues when benchmarking file system operations such as duplicate finding. Meaning of values (from kernel documentation, https://www.kernel.org/doc/Documentation/sysctl/vm.txt):
To free pagecache:
echo 1 > /proc/sys/vm/drop_caches
To free reclaimable slab objects (includes dentries and inodes):
echo 2 > /proc/sys/vm/drop_caches
To free slab objects and pagecache:
echo 3 > /proc/sys/vm/drop_caches