How to Clear filesystem memory cache

he linux Kernels 2.6.16 and Newer kernels provide a mechanism to have the kernel drop the page cache and/or inode and dentry caches on command, which can help free up a lot of memory.

You have to first check the memory usage with command

#free -m

To use /proc/sys/vm/drop_caches, Now echo a number to it.

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, run sync first!
sync; echo 3 > /proc/sys/vm/drop_caches

How the command works :

root@sserver # free -m
            total       used       free     shared    buffers     cached
Mem:         12174       7824       4349          0        414       5953
-/+ buffers/cache:       1456      10718
Swap:        24003        241      23761

root@server # sync; echo 3 > /proc/sys/vm/drop_caches

root@server # free -m
            total       used       free     shared    buffers     cached
Mem:         12174       1684      10489          0          9        125
-/+ buffers/cache:       1549      10624
Swap:        24003        241      23761