Flushing Filesystem Buffers

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

Helpful Hint: This will be much more effective if you run sync first.

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.

This tunable was added in 2.6.16.

Robbed from: LinuxInsight