Clear Memory Cache on Linux Server

Flush file system buffers by executing,

# sync

Kernels 2.6.16.x and newer versions of kernel provide a mechanism to have the kernel drop the page cache and/or inode and dentry caches on command, which can be helpful to free up a lot of memory.

To free page cache:

# echo 1 > /proc/sys/vm/drop_caches

To free dentries and inodes:

# echo 2 > /proc/sys/vm/drop_caches

To free page cache, dentries and inodes:

echo 3 > /proc/sys/vm/drop_caches

or

sync; echo 3 > /proc/sys/vm/drop_caches

Sync should be run because this is a non-destructive operation, and dirty objects are not freeable.
So you run sync in order to make sure all cached objects are freed.

To do clearing memory cache on a particular interval, just add the command to cron job

vi cacheclear.sh

#!/bin/sh
sudo sh -c "sync; echo 3 > /proc/sys/vm/drop_caches"

Ref: http://www.unixmen.com/how-to-clear-memory-cache-on-linux-servers/