First of all check how much memory you have left:
$ mehdi@MPourhadi ~/> free -m
total used free shared buffers cached
Mem: 5968 5630 337 64 116 1038
-/+ buffers/cache: 4475 1492
Swap: 6139 56 6083
Issue the the command “sync” to flush the file system buffer then change to root user.
For Debian-base users : “sudo bash”
For RPM packages “su or su -”
When you are root user issue the following command and see the diffrence :
root@MPourhadi:~/# echo 3 > /proc/sys/vm/drop_caches
NOTE :
echo 1 is for free pagecache
echo 2 is for free dentries and inodes
echo 3 is 1+2
root@MPourhadi:~/# free -m
total used free shared buffers cached
Mem: 5968 4399 1568 60 2 318
-/+ buffers/cache: 4078 1889
Swap: 6139 56 6083