My Centos box seems to be using lots of caching, most of the used memory is used for cache, how can I find out what the cache is for?
total used free shared buffers cached
Mem: 16439708 10469864 5969844 0 197936 9534176
-/+ buffers/cache: 737752 15701956
Swap: 16763816 0 16763816
The cache memory in Linux-based machines is often used to cache disk blocks into memory to prevent writing to the harddisk and speed up I/O operations. Also, a lot of free memory is cached and released when it is actually required.
When interpreting the output of free, you should look at the second row for the actual memory usage.
The above numbers can be interpreted as:
For more information, take a look at http://www.faqs.org/docs/linux_admin/buffer-cache.html.
You can look at /proc/slabinfo or use the command slaptop to have a top-like interface to the cache objects.
The cache is for speed up the disk I/O operations.
As Linus Torvalds once said, "free memory is bad memory". Linux kernel uses unused (by system/applications) memory for cache, should a program require more memory, the system gets it from cache.
