Linux Cache Clearing

Clearning the Linux Memory cache can be a quick way to regain system resources. 
Writing to the drop_cache process will cause the kernel to drop clean caches, dentries and inodes from memory, causing that memory to become free.


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, the user should run “sync” command first in order to make sure all cached objects are freed.

Example – 
Memory before:

[root@localhost ~]# free -m
             total       used       free     shared    buffers     cached
Mem:          1010        361        648          0         25        271
-/+ buffers/cache:         64        945
Swap:         2047          0       2047

Memory after:

[root@localhost ~]# sync

[root@localhost ~]# echo 3 > /proc/sys/vm/drop_caches

[root@localhost ~]# free -m

             total       used       free     shared    buffers     cached

Mem:          1010         81        929          0          0         20

-/+ buffers/cache:         60        950

Swap:         2047          0       2047