How to purge disk I/O caches on Linux?

Question

I need to do it for more predictable benchmarking.

Answer 1

Disk cache purging: echo 3 | sudo tee /proc/sys/vm/drop_caches

Command documentation: https://www.kernel.org/doc/Documentation/sysctl/vm.txt

Writing to this will cause the kernel to drop clean caches, dentries and inodes from memory, causing that memory to become free.

To free pagecache:

echo 1 > /proc/sys/vm/drop_caches

To free dentries and inodes:

echo 2 > /proc/sys/vm/drop_caches

To free pagecache, dentries and inodes:

echo 3 > /proc/sys/vm/drop_caches

As this is a non-destructive operation, and dirty objects are not freeable, the user should run "sync" first in order to make sure all cached objects are freed.