Clearing caches from memory

From version 2.6.16 Linux kernel has a tunable parameter named

If you want to force to clear pagecaches from memory use:

echo 1 > /proc/sys/vm/drop_caches

If you want to clear dentry and inode caches from memory:

echo 2 > /proc/sys/vm/drop_caches

and if you want to clear both of the pagecaches and dentry and inode caches just use:

echo 3 > /proc/sys/vm/drop_caches

In order to make sure all cached objects are freed you must execute the sync command first.