How to disable filesystem cache

#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

#REMEMBER sync
sync

Reference: Linux Questions