How to free up memory consumed by Linux cache

[[email protected] ~]# free-m
              total       used       free      shared    buffers     Cached
mem:           3792       3663        128        184        148        3003
-/+ buffers/cache:         511       3280
swap:             0          0           0

[Email protected] ~]# cat/proc/sys/vm/drop_caches
0

[[email protected] ~]# sync

[Email protected] ~]# echo 3 >/proc/sys/vm/drop_caches
[Email protected] ~]# cat/proc/sys/vm/drop_caches
3

[Email protected] ~]# free-m
Total used free shared buffers Cached
mem:3792 395 3397 184 2
-/+ buffers/cache:372 3419
swap:0 0 0

How to free up memory consumed by Linux cache