linux memory buffers vs cached

in the memory commands output such as 'vmstat', the item buffers or cached is sometimes confusing.

let's do some testings to show what is the difference:

what is buffers:

Here is the output after I did the ‘ls –al ’ command. You will see the buffer information increased a little. It is because the ls –al will get the directory content (not the file content) which is the meta data of the file system.

Another example is 

 free                                         //check the current memory usage including buffers and cached

 time find . > /dev/null                //print whole files name and checked the time usage

 free                                         //check the current memory usage again

 time find . > /dev/null                // print whole files name and checked the time usage again

 free                                         //check the current memory usage again

here are the testing results:

1.     In step 2, lots of buffers are used and the find command used about 9 seconds. No cached memory is used.

2.     In step 4, same commands neither buffers nor cached is used as the results is stored in buffers. The find command is much quicker (0.2 seconds).

what is cached:

Then let’s check how the cached is used. Testing scripts are

free                  //check the current memory usage including buffers and cached

man pwd           // check the man page for ps command

free                  //check the current memory usage including buffers and cached again

man pwd           // check the man page for ps command again

free                  //check the current memory usage including buffers and cached again

here are the testing results:

1.     In step 2, a little cached is used no buffers memory is used.

2.     In step 4, same commands neither buffers nor cached is used as the results is stored in cached.

So there is the conclusion:

Buffers are associated with a specific block device, and cover caching of filesystem metadata as well as tracking in-flight pages. The cache only contains parked file data. That is, the buffers remember what's in directories, what file permissions are, and keep track of what memory is being written from or read to for a particular block device. The cache only contains the contents of the files themselves.