Recently I came across an application in my workplace which is still under test phrase thrashing cache on RedHat linux server. If this application would run for an hour, the Server would start slowing down and the only way out was restart the linux server.
Then I came across this:
Writing to this 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” first in order to make sure all cached objects are freed.
This tunable was added in 2.6.16.